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Initial effects of slashburning on the nutrient status of two sub-boreal spruce zone ecosystems Taylor, Stephen William 1987

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INITIAL EFFECTS OF SLASHBURNING ON THE NUTRIENT STATUS OF TWO SUB-BOREAL SPRUCE ZONE ECOSYSTEMS by STEPHEN W. TAYLOR Bachelor of Science (Hons.), University of V i c t o r i a , 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Faculty of Forestry, Department of Forest Science) We accept t h i s t h e s i s as conforming to the recjuired standard THE UNIVERSITY OF BRITISH COLUMBIA November 1987 ®STEPHEN WILLIAM TAYLOR,, 1987 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at The University of B r i t i s h Columbia, I agree that the Ilibrary s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission f o r extensive copying of t h i s thesis f o r scholarly purposes may be granted by the Head of my Department or by h i s or her representatives. I t i s understood that copying or publication of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Faculty of Forestry The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: 0 cJU^~ '5i n s ? . 11 ABSTRACT A study was c a r r i e d out to investigate the e f f e c t s of slashburning on the nutrient status of two Sub-Boreal Spruce zone ecosystems i n the west ce n t r a l i n t e r i o r of B r i t i s h Columbia. The slash, forest f l o o r and mineral s o i l (0-15 cm depth) i n these ecosystems were sampled f o r mass and nutrient content before and a f t e r burning on a recently clearcut s i t e . The forest f l o o r and mineral s o i l were also sampled f o r nutrient concentrations nine months following burning. Average losses of organic matter, N, P, S, K, Ca, and Mg to the atmosphere due to slashburning were 11.1 kg/m2 and 563, 55, 87, 60, 252, and 16 kg/ha, respectively, from the mesic ecosystems and 11.5 kg/m2 and 345, 52, 74, 16, 289, and 177 kg/ha, respectively, from the subhygric/hygric ecosystems. These amounts corresponded to 51, 47, 41, 56, 40, 40 and 20%, respectively, of the t o t a l quantities of these nutrients i n the slash and forest f l o o r i n the mesic ecosystems before burning, and 25, 9, 13, 14, 5, 6 and 17%, respectively, of the cjuantities i n the subhygric/hygric ecosystems. There were substantial losses of organic matter from coarse (>8 cm diam.) and f i n e Q l cm diam.) slash and the forest f l o o r components. However, nutrient losses were l a r g e l y attributed to f i n e slash and forest f l o o r consumption. Nutrient losses from the f i n e slash appeared to be independent of f i r e severity, although losses of most nutrients from the forest f l o o r increased with f i r e severity; l n p l o t s i n the mesic ecosystems which received moderate impact burns, and pl o t s i n the subhygric/hygric ecosystems which received low and moderate impact burns, net gains i n forest f l o o r Mg, K, and K and Ca content, Ill respectively, were found. Nine months following burning there were s i g n i f i c a n t increases i n pH and t o t a l Mg concentrations and decreases i n exchangeable K concentrations i n the forest f l o o r i n the mesic ecosystems and S concentration i n the forest f l o o r i n p l o t s which had received low impact burns i n both ecosystems. E f f e c t s of burning on some nutrient concentrations were confounded by the inherent seasonal v a r i a b i l i t y i n l a b i l e nutrient forms. There were no s i g n i f i c a n t changes i n mineral s o i l nutrient concentrations that could be att r i b u t e d to burning. However, any such changes of small magnitude would have been d i f f i c u l t to detect due to the high s p a t i a l v a r i a t i o n i n s o i l nutrient concentrations. The s u r v i v a l and growth of i n t e r i o r spruce seedlings i n the f i r s t season following outplanting was better i n burned than i n unburned areas i n both ecosystems. However, seedling f o l i a r N and P concentrations were lower i n the burned areas. I t i s concluded that i f slashburning i s c a r r i e d out i n the mesic ecosystems, low to moderate severity f i r e s should be prescribed to preserve the nutrient c a p i t a l present i n the forest f l o o r . Slashburning would not su b s t a n t i a l l y reduce the nutrient c a p i t a l of subhygric/hygric ecosystems even with much higher f i r e s e v e r i t i e s than were observed i n t h i s study. i i i a ERRATA The broadcast b u r n i n g s t a t i s t i c s g i v e n f o r the S B S zone are erroneous. Please note the f o l l o w i n g changes: Page I Mne 25 Replace: " ... burn i n g has been c a r r i e d out on some 385,000 ha" With: " ... burn i n g has been c a r r i e d out on some 196,442 ha " Page 2 Line 1 Replace: " - about 54% of the area i n c l e a r c u t b l o c k s " With: " - about 27% of the area i n c l e a r c u t b l o c k s " Page 3 Figure 1 The a c t u a l broadcast burned areas are shown i n the a t t a c h e d f i g u r e . iv T A B L E OF TONTENTS Page ABSTRACT . . a LIST OF TABLES v i i LIST OF FIGURES i x ACKNOWLEDGEMENTS x 1. INTRODUCTION: SLASHBURNING IN THE CENTRAL INTERIOR OF BRITISH COLUMBIA 1 1.1 HISTORY AND POLICY 1 1.2 ECOLOGICAL CONCERNS 4 2. LITERATURE REVIEW: SLASHBURNING EFFECTS ON NUTRIENTS IN NORTHERN FORESTS 6 2.1 NUTRIENTS IN NORTHERN FORESTS 6 2.1.1 Nutrient D i s t r i b u t i o n and A v a i l a b i l i t y . . . . 6 2.1.2 Nutrient Transformations and Transfers . . . . 8 2.2 THE EFFECTS OF SLASHBURNING ON NUTRIENTS 11 2.2.1 E f f e c t s on Nutrient Quantities and D i s t r i b u t i o n 11 2.2.2 E f f e c t s on Nutrient A v a i l a b i l i t y and pH . . . . 17 2.2.3 E f f e c t s on Nutrient Transfers and Transformations 21 2.2.4 E f f e c t s on Nutrient Uptake and Productivity . . 24 3. OBJECTIVES 26 4. STUDY AREA 27 4.1 Location, Physiography and Climate 27 4.2 Ecosystem Cha r a c t e r i s t i c s 27 5. METHODS 32 5.1 FIELD OPERATIONS 32 5.2 FIRE IMPACT ASSESSMENT PROCEDURES 33 5.2.1 Plot Layout and Treatment Plan 33 5.2.2 Slash Sampling 37 V Page 5.2.3 S o i l Sampling 37 5.2.4 Plantation Establishment and Assessment . . . 40 5.3 LABORATORY PROCEDURES 41 5.3.1 Sample Preparation 41 5.3.2 Chemical Analyses 41 5.3.3 Physical Analyses . . . . . 43 5.4 CALCULATIONS 43 5.4.1 Slash Load and Nutrient Content 43 5.4.2 Forest Floor Mass 44 5.4.3 Forest Floor and Mineral S o i l Nutrient Contents 45 5.4.4 Slashburning-Caused Organic Matter Consumption and Nutrient Loss . 45 5.4.5 Relative Height Growth Rate 46 5.5 DATA SYNTHESIS AND STATISTICAL ANALYSIS 46 5.5.1 Slash Load and Nutrient Content 46 5.5.2 S o i l Nutrient Concentrations 47 5.5.3 S o i l Nutrient Contents 48 5.5.4 Organic Layer Consumption and Nutrient Loss . 49 5.5.5 Plantation Establishment 49 6. RESULTS AND DISCUSSION 52 6.1 SLASH LOAD AND RELATIVE DENSITY 52 6.2 FOREST FLOOR DEPTH AND MASS 59 6.3 SLASH NUTRIENT STATUS 64 6.3.1 Slash Nutrient Concentrations 64 6.3.2 Slash Nutrient Content 66 6.4 FOREST FLOOR pH AND NUTRIENT STATUS 69 6.4.1 Forest Floor pH and Nutrient Concentrations . 69 6.4.2 Forest Floor Nutrient Content 74 v i Page 6.5 MINERAL SOIL NUTRIENT STATUS 79 6.6 ORGANIC MATTER AND NUTRIENT DISTRIBUTION 85 6.6.1 Total Organic Matter Consumption and Nutrient Loss to the Atmosphere 85 6.7 SPRUCE SEEDLING GROWTH AND NUTRIENT STATUS 99 7. CONCLUSIONS AND RECOMMENDATIONS 104 7.2 FOREST MANAGEMENT CONSIDERATIONS 107 7.3 RESEARCH RECOMMENDATIONS 112 LITERATURE CITED 116 Appendix A Study Area Location 125 Appendix B Descriptions of Typical Humus Forms and S o i l P r o f i l e s i n the Mesic and Subhygric/hygric Ecosystem Groups 127 Appendix C L i s t of Plant Species Present i n the Mesic and Subhygric/Hygric Ecosystems on the Study Area . 130 Appendix D Weather Observations and FWI System Codes and Indexes on the Study Area During J u l y - Sept. 1983 133 Appendix E Summary of Burning Conditions, Fuel Loads and Fuel Consumption i n Spruce-Fir Slash Fuels . . . 136 v i i LIST OF T A B L E S Page 1. Slash r e l a t i v e d e n s i t i e s and nutrient concentrations . . 52 2a. Slash load and nutrient content i n the mesic ecosystems 53 2b. Slash load and nutrient content i n the subhygric ecosystems 54 3a. Percentage of t o t a l slash load and nutrient content present i n d i f f e r e n t slash diameter classes 55 3b. Percentage reduction i n slash load and nutrient content . 56 4. Correlations between slash consumption and i n i t i a l s l a sh load, by diameter c l a s s 60 5. Summary of forest f l o o r depth and mass reduction and nutrient losses due to burning 61 6. Correlations between forest f l o o r depth reduction and slash consumption and i n i t i a l forest f l o o r depth . . . . 63 7. Correlations between nutrient l o s s from the slash and slash consumption 68 8. Forest f l o o r pH and nutrient concentrations 70 9. Forest f l o o r nutrient contents 75 10a. Correlations between forest f l o o r nutrient l o s s and forest f l o o r depth reduction 78 10b. Correlations between percent forest f l o o r nutrient l o s s and percent forest f l o o r depth reduction 78 11. Mineral s o i l pH and nutrient concentrations 80 12. Mineral s o i l nutrient contents 83 13. Summary of t o t a l organic matter consumption and nutrient losses to the atmosphere due to slashburning . . 89 14. Correlations between t o t a l organic matter consumption and reduction of components and t o t a l organic matter load 90 15a Correlations between t o t a l nutrient l o s s and slash consumption and forest f l o o r depth reduction 92 15b. Correlations between percent t o t a l nutrient l o s s and percent organic matter consumption 93 v i i i Page 16. Organic matter and nutrient losses r e s u l t i n g from f i r e and c l e a r c u t t i n g i n selected forest types 97 17. Survival and growth of spruce seedlings i n the f i r s t season following planting 100 18. Nutrient concentrations i n the current f o l i a g e of spruce seedlings i n the f i r s t season following planting . . . 102 Ix LIST OF FIGURES Page 1. Areas clearcut, broadcast burned, and planted annually i n the Sub-Boreal Spruce zone during 1965-1985 3 2. Potential nutrient transfers and transformations during and a f t e r burning 12 3. Location of the study area within the Sub-Boreal Spruce zone of B r i t i s h Columbia 28 4. Climate diagram f o r Babine Lake, B. C 29 5. A t y p i c a l mesic ecosystem s o i l p r o f i l e (Aug. 1983) . . . 31 6. A t y p i c a l subhygric ecosystem s o i l p r o f i l e (Aug. 1983) . 31 7. I g n i t i o n began at the centre of the block 34 8. Convection column a f t e r i g n i t i o n 34 9. Plot l o c a t i o n within the study area 36 10. Plot layout diagram 38 11. Ty p i c a l slash load i n the mesic ecosystems 57 12. Ty p i c a l mesic ecosystem condition a f t e r burning 57 13. Ty p i c a l slash load i n the subhygric ecosystems 58 14. Ty p i c a l subhygric ecosystem condition a f t e r burning . . . 58 15a. D i s t r i b u t i o n of N by ecosystem component 86 15b. D i s t r i b u t i o n of P by ecosystem component 86 15c. D i s t r i b u t i o n of S by ecosystem component 87 15d. D i s t r i b u t i o n of K by ecosystem component 87 15e. D i s t r i b u t i o n of Ca by ecosystem component . . . . . . . . 88 15f. D i s t r i b u t i o n of Mg by ecosystem component 88 16. Hypothetical r e l a t i o n s h i p between slash and forest f l o o r consumption and t o t a l organic matter consumption . . . . 95 17. Hypothetical r e l a t i o n s h i p between the l o s s of v o l a t i l e nutrients from the slash and forest f l o o r and t o t a l organic matter consumption 96 X ACKNOWLEDGEMENTS I would l i k e to thank the chairman of my supervising committee, Dr. Michael F e l l e r , f o r h i s guidance throughout a l l phases of my graduate study, and committee members Drs. Hamish Kimmins and Gordon Weetman and Mr. Richard Trowbridge f o r t h e i r advice on t h i s t h e s i s project; the l a t t e r also provided invaluable assistance i n coordinating the f i e l d work. I would also l i k e to thank Messrs. A l Gorley (B.C. Forest Service, Prince Rupert Forest Region) and Dan Metcalf (Northwood Pulp and Timber Co., Houston, B.C.), and the Morice Forest D i s t r i c t Staff (B.C.F.S.) f o r t h e i r cooperation. Mr. Owen Croy provided cheerful f i e l d assistance, despite often t r y i n g conditions. Many other persons i n the B.C. Forest Service and at U.B.C. assisted with f i e l d sampling and laboratory analyses; I am e s p e c i a l l y g r a t e f u l to Ms. Anne Macadam and Messrs. Dave Yole and Bruce Blackwell. The B.C. Forest Service Research Branch provided funding fo r the f i e l d work and f o r laboratory analyses. F i n a n c i a l support was also received from the Science Council of B.C. through a Graduate Research i n Engineering and Technology Award, and from the Canadian Forestry Service through a University Block Grant; the C.F.S. also permitted me use of computing f a c i l i t i e s at the P a c i f i c Forestry Centre. Lastly, my thanks go to family and friends f o r t h e i r encouragement, e s p e c i a l l y my parents B i l l and Jean Taylor, and Nancy Kunzli, who also helped with the figures and tables. 1 1. INTRODUCTION: SLASHBURNING IN T H E C E N T R A L INTERIOR OF BRITISH COLUMBIA 1.1 HISTORY AND POLICY. Slashburning has been practised i n forest management i n B r i t i s h Columbia since the e a r l y 1900's. An increase i n continuous c l e a r c u t t i n g i n coastal B.C. at that time resulted i n several disastrous f i r e s - a need for f i r e hazard abatement was recognized and the B.C. Forest Branch began to encourage slashburning to reduce f u e l accumulations (B.C. Forest Branch 1913). However, up u n t i l 1938, burning of hazardous slash on Crown land was not mandatory (Smith 1974). Between 1938 and 1966, licencees i n the Vancouver Forest D i s t r i c t could be instructed to burn slash that was considered to be hazardous. After 1966 t h i s p o l i c y was extended to the rest of the province. Slashburning was introduced to white spruce - subalpine f i r (Picea glauca, (Moench) Voss - Abies lasiocarpa (Hook.) Nutt.) forest management i n c e n t r a l B.C. during t h i s l a t t e r period. Although the forest industry has been active i n the i n t e r i o r since the 1910's, single-tree s e l e c t i o n and s t r i p - c u t t i n g methods which r e l i e d on natural regeneration were pri m a r i l y used i n the white spruce-subalpine f i r type up u n t i l the 1960's (Glew 1955). A s h i f t to block c l e a r c u t t i n g which began during the 1960's resulted i n increased f i r e hazard. The f i r s t experimental burns were c a r r i e d out f o r hazard abatement at that time (B.C. Forest Service 1963). Since the 1960's the area slashburned each year has increased s t e a d i l y -broadcast burning has been c a r r i e d out on some 196,442 ha i n the Sub-Boreal Spruce zone i n the Prince George, Prince Rupert, and 2 Cariboo Forest Regions between 1965 and 1985 - about 27% of the area i n clearcut blocks ( F i g . l ) . Planting of both white spruce and lodgepole pine (Plnus  contorta Dougl.) has also increased s t e a d i l y during t h i s period. Although white spruce seed w i l l germinate on well-burned organic and mineral s o i l seedbeds (Pogue 1949), planting i s considered necessary to obtain prompt regeneration i n clearcut and burned areas, because seed production i n white spruce i s infrequent and because there i s a high r i s k that non-coniferous vegetation w i l l become established before s a t i s f a c t o r y natural coniferous regeneration can occur. Indeed, c l e a r c u t t i n g followed by slashburning and planting has become a well-established treatment sequence i n the management of white spruce - subalpine f i r forests. Furthermore, i t has been recognized that slashburning may r e s u l t i n s i t e preparation benefits such as reduced planting costs (Vyse and Muraro 1973), elimination of some pathogens, increased s o i l temperatures (Endean and Johnstone 1974) and the reduction of competing vegetation (McMlnn 1982). The costs and r i s k s of slashburning to prepare land f o r planting were i n i t i a l l y thought to be u n j u s t i f i a b l e i n the s p r u c e - f i r type (Smith 1955). However the development of a e r i a l i g n i t i o n systems and the Prescribed F i r e Predictor/Planner (Muraro 1975) has enabled the safe and economic a p p l i c a t i o n of slashburning over extensive areas. As well, increasingly greater emphasis l s being placed on achieving prompt regeneration following c l e a r c u t t i n g . Although hazard abatement i s s t i l l an important benefit of slashburning and llcencees can s t i l l be i nstructed to burn slash, s i l v i c u l t u r a l objectives have l a r g e l y supplanted hazard abatement as the primary goal of slashburning on s p r u c e - f i r s i t e s . (0 C C < TJ © "5 CD I_ (0 o L . to 70000 -Clearcut Blocks Broadcast Burned 60000 - Planted 50000 -40000 - \ 1 ^ \ J \ vx 7 / 30000 " / / / 20000 " / 10000 -0 -i A . / / / \ x A. ,./ / / \ s4 \ / / / ' — / / ^ -7 ' — 1965 1970 1975 1980 1985 Year of Treatment Figure 1. Areas clearcut, broadcast burned, and planted annually i n the Sub-Boreal Spruce zone i n the Prince George, Prince Rupert and Cariboo Forest Regions during 1965-1985 (Data from the B.C. Ministry of Forests and Lands S i l v i c u l t u r a l History Records System, March 1987). Totals: 718,824 ha i n clearcut blocks, 196,442 ha broadcast burned, 284,456 ha planted. 3 (S 3 C C < XJ o « o CO CD cd 1 70000 " Clearcut Blocks Broadcast Burned 60000 " Planted 50000 " 40000 " \ / ^ 30000 " J i i i 20000 " 10000 -/ *—• o -^ —*' 1965 1970 1975 1980 1985 Year of Treatment Figure 1. Areas clearcut, broadcast burned, and planted annually i n the Sub-Boreal Spruce zone i n the Frince George, Prince Rupert and Cariboo Forest Regions during 1965-1985 (Data from the B.C. Ministry of Forests and Lands S i l v i c u l t u r a l History Records System, March 1987). Totals: 718,824 ha i n clearcut blocks, 196,442 ha broadcast burned, 284,456 ha planted. 4 1.2 ECOLOGICAL CONCERNS Despite the recognized benefits of slashburning, there has been recurring concern with the po t e n t i a l e f f e c t s of slashburning on forest productivity f o r many years. E a r l y investigators examined the e f f e c t s of slashburning on s o i l s and organic matter (Fowells and Stephenson 1934; Isaac and Hopkins 1937) and on natural and a r t i f i c i a l regeneration (B.C. Forest Branch 1923; Wright 1941). Wright (1941) examined the e f f e c t s of very severe slashburns on Vancouver Island i n 1938 on regeneration and concluded that "the issue i s not so much whether to burn or not to burn but how burning should be c a r r i e d out". Although slashburning prescriptions have become more sophisticated since that time, and the severe slashburns which sometimes occurred i n former times are no longer common, Wright's observation i s s t i l l pertinent. Unfortunately, there are s t i l l very few quantitative data on slashburning impacts on f u e l s to t e s t prescriptions, and a poor linkage between the pr e d i c t i o n of f i r e impacts on f u e l s and r e s u l t i n g e c o l o g i c a l e f f e c t s (Lawson 1981). In p a r t i c u l a r , the long-term e f f e c t s of slashburning on nutrients and forest productivity are s t i l l not well-known. In the c e n t r a l i n t e r i o r of B.C. the ear l y growth of plantations can be excellent on slashburned s i t e s . Draper (1983) examined operational spruce stock t r i a l s i n the Prince George Forest Region and found that both the best and poorest performing spruce plantations were on slash-burned areas. However the long-term e f f e c t s of slashburning on productivity i n these ecosystems, as i n other forest ecosystems i n B. C., are unknown. An experimental project was i n i t i a t e d by the B.C. Forest Service i n 1982 to investigate the e f f e c t s of slashburning on ecosystems i n the Prince 5 Rupert Forest Region (Macadam 1983). The study reported here i s part of t h i s project. E x i s t i n g information on the e f f e c t s of slashburning on nutrients pertinent to c e n t r a l i n t e r i o r ecosystems was reviewed and a f i e l d i n v e s t i g a t i o n was undertaken to quantify the e f f e c t s of slashburning on the nutrient status of t y p i c a l Sub-Boreal Spruce zone ecosystems i n west ce n t r a l B r i t i s h Columbia. The r e s u l t s and conclusions drawn from t h i s study are presented, and the nature of remaining uncertainties are described. The implications of the conclusions and uncertainties f o r slashburning practice are discussed and suggestions are made where further research i s required. 6 2. L I T E R A T U R E R E V I E W : SLASHBURNING E F F E C T S ON NUTRIENTS IN N O R T H E R N FORESTS This review examines the nutrient status of northern forests and the probable e f f e c t s of slashburning on nutrients from a forest ecosystem perspective. A comprehensive review of the e c o l o g i c a l e f f e c t s of slashburning i s beyond the scope of t h i s study; a review with p a r t i c u l a r reference to B.C. was c a r r i e d out by F e l l e r (1982). The e f f e c t s of f i r e i n northern forests have been recently reviewed by Viereck and Schandelmeier (1980) and various authors i n Vein and MacLean (eds.) (1983). The e f f e c t s of f i r e on s o i l s have also been reviewed by Wells fit a l . (1979), and the e f f e c t s of f i r e on nutrient cycles by Woodmansee and Wallach (1981) and Maclean fit a l . (1983). 2.1 NUTRIENTS IN NORTHERN FORESTS The climate and vegetation i n northern forests has a profound e f f e c t on the rate of nutrient transfer and transformation processes, which i n turn r e s u l t s i n c h a r a c t e r i s t i c patterns of nutrient d i s t r i b u t i o n and a v a i l a b i l i t y . 2.1.1 Nutrient D i s t r i b u t i o n and A v a i l a b i l i t y . Large proportions of nutrients i n northern forest ecosystems are o r g a n i c a l l y bound and unavailable to plants, while the immediately available pool i s r e l a t i v e l y small (Rodin and B a s i l e v i c h 1967; Krause fit a l . 1978). As the forest f l o o r contains large proportions of both available and organically bound nutrients i t i s i n f e r r e d to be the major source of nutrients f o r plant growth. In white spruce stands i n Alaska, Van Cleve fit a l . (1983) found 7.4 kg/m2 organic matter and 572, 65, 347, 921, and 306 kg/ha of N, P, 7 K, Ca and Mg, respectively, i n the forest floor. Furthermore, the fine roots of white spruce , subalpine f i r , and lodgepole pine (which are thought to f a c i l i t a t e most nutrient uptake) are largely distributed i n the forest floor (Bis 1970; Kimmins and Hawkes 1978; Safford and B e l l 1972). Forest floor manipulation studies have provided additional empirical evidence of the importance of the forest f l o o r to the productivity of northern forests. Weber et a l . (1985) investigated a 50 year old jack pine stand i n Ontario eight years following complete removal of the forest floor, removal of the forest floor with subsequent annual l i t t e r removal, and removal of the forest floor with replacement of ash derived from the removed material. They found that periodic diameter growth over t h i s period declined 30% i n a l l treatments, though f o l i a r N concentrations were significantly lower only i n the annual removal treatment. The quantity of nutrients i n the forest floor may change with succession and stand development. Organic matter and nutrient quantities i n the forest floor tend to decrease following forest disturbance (Weetman 1980), but probably increase over the course of stand development (Miller 1984). The distribution of nutrients within vegetation varies between plant components and may also change over the course of succession and stand development. Coniferous stands i n particular accumulate a large proportion of nutrients i n above-ground components during their development. Van Cleve et a l . (1983) found that the largest proportions of above-ground N, P, K, Ca and Mg i n a mature white spruce stand i n Alaska were distributed i n the foliage. Calcium accumulation i s also high i n the wood and bark of boreal conifers (Krause fit a l . 1978). The accumulation of N i n foliage tends to be highest prior to and during canopy closure, while the accumulation 8 of Ca i n woody tissues continues during stand development ( M i l l e r 1984). 2.1.2 Nutrient Transformations and Transfers Nutrients are transferred from the vegetation to the s o i l i n organic matter ( l e a f and root l i t t e r ) , root exudates, stemflow and throughfall. As these nutrients are released during decomposition they may be taken up by plants or t h e i r mycorrhizal associates, completing the b i o l o g i c a l cycle. In northern forests, the combination of low s o i l temperatures and the chemistry of coniferous l i t t e r r e s u l t s i n slow decomposition and nutrient release rates, and the accumulation of nutrients and organic matter i n the forest f l o o r . Van Cleve fit a l . (1983) estimated that the residence times for organic matter, N, P, K, Ca and Mg i n the forest f l o o r of coniferous stands i n the t a i g a of Alaska were 33, 56, 84, 65, 36 and 66 years respectively. Kumi (1984) found that the decomposition rate of jackpine forest f l o o r s increased with repeated N and NPK additions, which she suggested indicated that decomposition was l i m i t e d by nutrient a v a i l a b i l i t y . Competition fo r nutrients by s o i l organisms and other plants i n northern f o r e sts may further l i m i t nutrient a v a i l a b i l i t y to trees. Weber and Van Cleve (1984) reported that mineral N additions to black spruce ecosystems i n Alaska were quickly immobilized by feathermosses and released very slowly to lower layers of the forest f l o o r where vascular plant roots were located. Decomposition and nutrient release rates may increase i n disturbed stands due to increased s o i l temperatures and possibly due to reduced anti-microbial a c t i v i t y by mycorrhizal fungi ( G a d g i l l and G a d g i l l 1978). As a r e s u l t , the amount of forest f l o o r organic 9 matter may decrease and nutrient a v a i l a b i l i t y may increase f o r a short period following disturbance - t h i s has been re f e r r e d to as the "assart e f f e c t " (Krause et. a l . 1978; Weetman 1980); nutrient a v a i l a b i l i t y may also increase following disturbance due to reduced stand uptake. Spruce-fir stands have substantial nutrient requirements. Weetman and Webber (1972) estimated that the average annual uptake of N, P, K, Ca and Mg was 40, 5, 15, 36, and 3 kg/ha, respectively, over a 65 year period f o r a spr u c e - f i r stand i n Quebec. Van Cleve et a l - (1983) estimated that the average annual requirements f o r these same nutrients i n a white spruce stand i n Alaska were 16, 2, 14, 14, and 2 kg/ha, respectively. Nutrient requirements may be even higher i n managed stands - indeed, nutrient d e f i c i e n c i e s are most frequently observed i n managed stands (Morrison 1974). As the demand f o r nitrogen i s greater than f o r other nutrients, i t i s not surprising that nitrogen i s also the nutrient most often d e f i c i e n t i n white spruce plantations i n c e n t r a l i n t e r i o r B.C. ( B a l l a r d 1985). Nutrient requirements also vary over the course of stand development. The requirements f o r nutrient quantities are lowest immediately a f t e r planting and r i s e to a maximum as stands approach canopy closure ( M i l l e r 1981, 1984). Nutrients may be transferred between the b i o l o g i c a l cycle and the geochemical cycle through p r e c i p i t a t i o n , leaching and erosion processes as well as through b i o l o g i c a l f i x a t i o n , d e n i t r i f i c a t i o n , chemical adsorption and v o l a t i l i z a t i o n processes i n the case of nitrogen, and mineral weathering processes i n the case of P, S, K, Ca and Mg. Nutrient inputs i n p r e c i p i t a t i o n vary with the concentration of 10 nutrients i n p r e c i p i t a t i o n and the amount of p r e c i p i t a t i o n ; nutrient inputs i n dry deposition may vary with canopy development ( M i l l e r 1981). Nutrient inputs i n p r e c i p i t a t i o n i n Alaska (Van Cleve s i a l . 1983), Alberta (Baker fit a l . 1977) and B. C. (Scrivener 1977; F e l l e r and Kimmins 1979) reported by Kimmins fit a l . (1985) are i n the order of 2 - 4, <0.5, 0 - 2 , 0 - 3 , 1 - 4 and 0 - 3 kg/ha/year f o r N, P, S, K, Ca, and Mg respectively. Leaching losses of nutrients vary with p r e c i p i t a t i o n inputs and s o i l conditions. However, Van Cleve fit a l . (1983) found that the net change i n s o i l nutrient content due to p r e c i p i t a t i o n , l i t t e r f a l l and throughfall inputs and leaching losses were s l i g h t i n boreal forest types i n Alaska. Nitrogen inputs may occur through nitrogen f i x a t i o n and adsorption, while losses may occur through d e n i t r i f i c a t i o n and v o l a t i l i z a t i o n . Symbiotic nitrogen f i x i n g species such as Alnus. Sheperdia. legumes or some lichens are present i n northern forests and may be important N suppliers i n some ecosystems. Alexander and B i l l i n g t o n (1986) reported inputs of 1.2 kg/ha/yr of N from non-symbiotic nitrogen f i x a t i o n i n feathermosses i n a black spruce stand i n Alaska. Granhall and Lindberg (1980) and Granhall (1981) suggest that non-symbiotic nitrogen f i x a t i o n may account f o r inputs of as much as 1 - 20 kg N/ha/yr i n northern forests. Higher inputs were associated with the presence of Sphagnum mosses with blue-green alga associates. Few quantitative data are available on d e n i t r i f i c a t i o n , adsorption and v o l a t i l i z a t i o n rates rates i n northern coniferous forests. D e n i t r i f i c a t i o n l s not thought to be an important pathway as there i s l i t t l e free NO3. Adsorption of atmospheric N by the s o i l and v o l a t i l i z a t i o n of s o i l N are not thought to be important due to the low pH i n most s o i l s (Krause fit 11 a l . 1978). There are also few data on nutrient input rates from weathering of the parent material. 2.2 THE EFFECTS OF SLASHBURNING ON NUTRIENTS. Though an ephemeral process i n nutrient cycles, f i r e can have profound e f f e c t s on the cjuantity, d i s t r i b u t i o n , and a v a i l a b i l i t y of nutrients, and on the rate of a number of nutrient t r a n s f e r and transformation processes (Fig. 2). 2.2.1 E f f e c t s on Nutrient Quantities and D i s t r i b u t i o n . Nutrients i n vegetation, woody debris and the forest f l o o r may be transferred to the atmosphere i n smoke or to the s o i l surface i n ash during combustion. Nutrient Transfer ytanhapl p n f a Nutrient transfer to the atmosphere i n smoke occurs through v o l a t i l i z a t i o n , through p a r t i c u l a t e (ash) movement or through both of these mechanisms. Raison e i al.(1985a) stated that the r e l a t i v e contribution of v o l a t i l e as compared to p a r t i c u l a t e mechanisms of nutrient transfer to the atmosphere depends on the vaporization temperature of the nutrients under consideration and on f i r e i n t e n s i t y . They believed that temperature (and so v o l a t i l i z a t i o n losses) and convection (and so pa r t i c u l a t e losses) are re l a t e d to f i r e i n t e n s i t y i n vegetation f i r e s . As nitrogen and su i f u r w i l l v o l a t i l i z e at r e l a t i v e l y low temperatures (300 - 400°C), N and S losses from forest f u e l s are thought to occur mainly by v o l a t i l i z a t i o n (Knight 1966; De B e l l and Ralston 1970; Tiedeman and Anderson 1980). V o l a t i l i z a t i o n of N and S increases with increasing temperature and duration of burning. NUTRIENT FORMS /POOLS ATMOSPHERE ORGANICALLY BOUND AVALABLE MINERALIZED VEGETATION SLASH FOREST FLOOR. MINERAL SOL Volotilizotion ond Particulate Tronsfer n i Plant Uptake Ash Deposition I--I Mineralization I I I | Minerolization | UNAVAILABLE GASEOUS AND MINERAL Denitrification. N Volatilization Nitrogen Fixation, Adsorption Precipitation (ASH) Surface Runoff, Wind . J 1 Weathering Leaching F i g u r e 2. P o t e n t i a l n u t r i e n t t r a n s f e r s and t r a n s f o r m a t i o n s d u r i n g and a f t e r b u r n i n g . 13 Knight (1966) found that 25 and 64% of the nitrogen i n forest l i t t e r was released at temperatures of 300 and 700°C, respectively. Evans and A l l e n (1971) reported nitrogen losses of 42 and 57% and s u l f u r losses of 17 and 37% at temperatures of 310 and 750°C, respectively, i n heather burning. King e i a l . (1977) found that about 50% of the S and P present i n forest l i t t e r samples was l o s t during burning i n the laboratory - as Ca l o s s due to burning was minimal, they i n f e r r e d that there was l i t t l e p a r t i c u l a t e transfer, and that S and P losses were due to v o l a t i l i z a t i o n . The temperature at which nutrients v o l a t i l i z e may vary between compounds containing the same nutrient and so between plant species or organic matter f r a c t i o n s with d i f f e r e n t i a l chemical composition. Tiedeman and Anderson (1980) found that v o l a t i l i z a t i o n of S was greater from deciduous f o l i a g e and l i t t e r (63-82%) than from coniferous f o l i a g e (24-69%) and l i t t e r (32-37%) at temperatures of 375 - 575 *C, which they at t r i b u t e d to the presence of d i f f e r e n t s u l f u r compounds i n coniferous versus deciduous f o l i a g e . However they found n e g l i g i b l e differences i n S l o s s between coniferous and deciduous f o l i a g e at higher temperatures (775 - 1175°C), though losses from the l i t t e r were s t i l l somewhat lower than from f o l i a g e . They speculated that a f t e r i n i t i a l S losses at low temperatures, the re s i d u a l S i n the deciduous tissues was resi s t a n t to further v o l a t i l i z a t i o n , although v o l a t i l i z a t i o n of s u l f u r from the coniferous t i s s u e s and forest l i t t e r continued with increasing temperature. V o l a t i l i z a t i o n temperatures of elemental forms of other nutrients range between 774°C f o r P and K to 1170, 1500 and 1900°C fo r Ca, Mg and Mn, respectively (Weast 1980). Thus an increasing proportion of atmospheric transfer of these elements i s a t t r i b u t e d 14 to p a r t i c u l a t e s with increasing v o l a t i l i z a t i o n temperature. However, these elements may v o l a t i l i z e at much lower temperatures as constituents of organic or Inorganic compounds i n vegetation and l i t t e r materials (Raison e i a l . 1985a). Evans and A l l e n (1971) reported losses of 20% K, 13% Ca, 15% Mg, 15% P, 15% Fe, 10% Mn, 17% Cu and 20% Zn from heather i n laboratory burns at temperatures up to 750°C, where entrainment of p a r t i c u l a t e s was l i k e l y minimal. Combustion temperatures i n forest f u e l s vary between about 500°C i n the glowing stage to about 750°C i n the flaming stage (Brown and Davis 1973). However, temperatures may be much higher i n mass f i r e s and may reach l e v e l s s u f f i c i e n t f o r the v o l a t i l i z a t i o n of most macronutrients. Philpott (1965) reported temperatures of up to 2200 °C i n both the flame and f u e l zones within heavy f u e l p i l e s . Temperatures of up to 1500°C have also been recorded i n the f u e l zone i n a moderate severity broadcast burn i n western hemlock -western red cedar slash and up to 800 °C at the forest f l o o r surface i n a low se v e r i t y broadcast burn i n spruce - f i r slash (unpublished data of the Can. For. Serv., Pac. For. Cent.). Temperature i s probably a more important influence on the mechanism of P, K, Ca and Mg l o s s than i t i s f o r N and S, as temperatures above the threshold f o r v o l a t i l i z a t i o n of N and S w i l l be experienced i n most forest f i r e s . P a r t i c u l a t e transfer to the atmosphere i n slashburns i s probably r e l a t e d to the degree of smoldering combustion and to the strength of convection. Ottmar e i a l . (1985) found that smoldering combustion and p a r t i c u l a t e emissions increased with increasing f u e l moisture content i n slashburns i n Washington. They at t r i b u t e d the greatest proportion of p a r t i c u l a t e emissions to smoldering of the forest f l o o r . The strength of convection i n mass f i r e s i s 15 influenced by combustion rate as well as by atmospheric conditions (Countryman 1964). A small proportion of the nutrients transferred to the atmosphere as p a r t i c u l a t e s may subsequently be redeposited on the s i t e or l n adjacent areas (Clayton 1976). However nutrients transferred through v o l a t i l i z a t i o n are probably e n t i r e l y l o s t from the s i t e . Substantial amounts of some nutrients are also transferred to the s o i l surface during burning i n ash. Boyle (1973) estimated that 210 and 404 kg/ha of K and Ca, respectively, were deposited i n ash due to slash burning i n a jackpine cutover. Vitousek (1981) suggested that some N may also be transferred from upper to lower s o i l depths during burning, i n v o l a t i l e products which d i f f u s e downward through the s o i l atmosphere during burning and condense on cooler s o i l p a r t i c l e s . However, the importance of t h i s pathway has not been quantified. Nutrient Transfer and Fuel Consumption. In general, nutrient transfer increases with increasing organic matter ( f u e l ) consumption (Wells g£ a l - 1979; F e l l e r 1982) though the strength of the r e l a t i o n s h i p varies between i n d i v i d u a l nutrients. Raison e i a l . (1985a) found that nutrient transfer from vegetation and l i t t e r as a proportion of pre-burn nutrient quantities decreased i n the order N > P > K > Ca > Mg > Mn > B. They found r a t i o s of percentage nutrient l o s s / percentage f u e l consumption due to burning were 0.63 and 0.97 f o r nitrogen and 0.25 and 0.92 f o r phosphorus i n laboratory and f i e l d conditions, respectively. Greater percentage nutrient losses from f i e l d burns may be an a r t i f a c t r e s u l t i n g from greater sampling error i n f i e l d 16 si t u a t i o n s . However, larger-scale f i e l d burns of higher temperature and with greater convectlve a c t i v i t y than laboratory burns might reasonably be expected to r e s u l t i n greater nutrient losses through both v o l a t i l i z a t i o n and p a r t i c u l a t e emissions. In turn, slash and forest f l o o r consumption i s r e l a t e d to f u e l moisture, load, piece s i z e , arrangement and i g n i t i o n pattern. In the s p r u c e - f i r slash type i n i n t e r i o r B. C., Lawson and Taylor (1987) found consumption of cumulative <22 cm diam. and t o t a l slash f u e l s was strongly correlated with pre-burn slash load i n these classes, though f i n e f u e l (<1 cm diam.) consumption was poorly correlated with pre-burn load i n t h i s c l a s s or with moisture content (represented by the f u e l moisture codes of the Canadian Forest F i r e Weather Index (FWI) System (Can. For. Serv. 1984)). This i s because f i n e f u e l s were almost completely consumed i n a l l of the experimental burns. Forest f l o o r depth reduction was p o s i t i v e l y correlated with the Drought Code of the FWI System as well as with cumulative < 17 cm and <22 cm diam. f u e l consumption. L i t t l e and Klock (1985) found greater N and S losses from harvesting and slashburning combined on blocks where low u t i l i z a t i o n standards were employed than on blocks where higher u t i l i z a t i o n standards were used, though nutrient l o s s due to harvesting alone was greater with higher u t i l i z a t i o n standards. They att r i b u t e d t h i s to greater forest f l o o r consumption and associated nutrient l o s s on blocks with lower timber u t i l i z a t i o n and higher slash loads. Much of the nutrient c a p i t a l i n northern forest ecosystems i s present i n the vegetation and i n the forest f l o o r , and so i s susceptible to atmospheric transfer during burning. However, few quantitative data are available on the magnitude of nutrient losses due to slashburning i n northern forests. Skokelfald (1973) and 17 Braathe (1974) reported losses of 160 kg N/ha and 11 tonnes/ha of organic matter (25% of pre-burn quantities) from the forest f l o o r due to slashburning i n Norway spruce-Scots pine cutovers i n Norway. Viro (1969) estimated losses of 100 kg N/ha from the forest f l o o r and a l o s s of 5 tonnes/ha of F and H material from the forest f l o o r due to slashburning on a thick-moss s i t e type i n Finland. There are apparently no data on nutrient losses due to slashburning from spru c e - f i r forests i n North America, nor are there data from northern forests which include nutrient losses occurring from the slash. 2.2.2 E f f e c t s on Nutrient A v a i l a b i l i t y and pH The concentrations as well as the quantities of ava i l a b l e forms of s o i l nutrients subject to v o l a t i l i z a t i o n may decrease due to burning. However, following burning, s o i l nutrient concentrations ( p a r t i c u l a r l y i n the upper horizons) may increase as nutrients i n the ash and f i n e l y - d i v i d e d charcoal and are leached i n t o the res i d u a l forest f l o o r and mineral s o i l . The degree of change i n i n d i v i d u a l s o i l nutrient concentrations due to ash deposition depends on the amount and composition of the ash. Grier (1975) found that nutrient concentrations i n the ash from a w i l d f i r e i n a coniferous forest decreased i n the order Ca > K > Mg > N. Thus, following burning, increases i n Ca, K, and Mg concentrations are common. As concentrations of these elements increase, H ions are displaced from exchange s i t e s , r e s u l t i n g i n higher s o i l pH. The magnitude of ash deposition, and increases i n s o i l cations and pH, may be re l a t e d to f i r e severity. Adams and Boyle (1980) found greater increases i n s o i l Ca, Mg, K and t o t a l N concentrations following burning on a conventionally-clearcut s i t e than on a 18 whole-tree logged s i t e , which they attributed to larger quantities of f u e l and greater f u e l consumption (and consequently ash) on the conventionally-clearcut s i t e . Nissley fit a l . (1980) found that pH increases where highly correlated with N losses i n burning. Dyrness and Norum (1983) found that pH, and extractable and t o t a l P concentrations In the forest f l o o r , and extractable P concentrations i n the mineral s o i l also increased with f i r e s e verity (and l i k e l y ash deposition), following experimental f i r e s i n black spruce stands i n Alaska. They also found that t o t a l nitrogen concentrations increased i n moderately burned forest f l o o r s but decreased i n severely burned forest f l o o r s . Increases i n t o t a l N were thought to be due to inputs of ash from overhanging trees coupled with lower N v o l a t i l i z a t i o n losses i n the moderately burned areas. The e f f e c t s of ash deposition on cation concentrations are probably also Influenced by differences i n the strength of adsorption of i n d i v i d u a l cations (Ca > Mg > K > Na) on exchange s i t e s . Strongly adsorbed cations such as Ca may displace weakly adsorbed cations from exchange s i t e s . Concentration differences between cations may also influence t h e i r adsorption on exchange s i t e s , as more abundant cations may displace l e s s abundant cations by mass action. Baker (1968) found higher pH and exchangeable Ca and Mg concentrations but lower exchangeable K and Fe concentrations i n the forest f l o o r s of slashburned s i t e s than i n unburned forest f l o o r s . The lower K concentrations might be explained by displacement of K from the forest f l o o r s of slashburned s i t e s by Ca and Mg. In s o i l s with pH-dependent ion exchange capacities, increases i n s o i l pH following burning may r e s u l t i n an increase i n cation exchange capacity (CEC) and a decrease i n anion exchange capacity. Baker (1968) found that CEC was higher i n the forest 19 f l o o r of slashburned than of unturned i n t e r i o r cedar-hemlock s i t e s . However, he attr i b u t e d t h i s to charcoal deposition. Smith (1970) reported an increase i n CEC i n the mineral s o i l following burning of jack pine slash which he attributed to increased leaching of organic c o l l o i d s from the forest f l o o r . Increased pH may also a f f e c t the s o l u b i l i t y and hence a v a i l a b i l i t y of some nutrients. In p a r t i c u l a r , Cu, Mn, and Fe s o l u b i l i t y decreases with increasing pH. However, d i s s o l u t i o n of i r o n and aluminum may be enhanced by the d i s s o l u t i o n of Fe and Al phosphates. Increasing pH may also disperse Fe, Cu and Mn bound i n organic c o l l o i d s . Phosphate s o l u b i l i t y i s also pH dependent. As the formation of HPO^.-2 i s favoured over l e s s soluble forms of phosphate at pH values of 4.5 - 6.5, P a v a i l a b i l i t y may be increased i n a c i d i c s o i l s with increasing pH following burning. However, Beaton e i a l . (1960) suggested that phosphorus a v a i l a b i l i t y may decrease following burning due to adsorption on charcoal. Adams and Boyle (1980) found that the concentration of extractable P i n the forest f l o o r following burning was lower on a conventionally-clearcut s i t e than on a whole-tree logged s i t e , which they attributed to adsorption by a greater quantity of charcoal on the conventionally-clearcut s i t e . Smith and Jones (1978) attributed a decrease i n extractable P concentrations i n the forest f l o o r following burning i n part to f i x a t i o n by Fe and A l . F i r e may also e f f e c t nutrient a v a i l a b i l i t y by influencing soil microbial populations. Perry e i a l . (1984) found lower l e v e l s of hydroxymate siderophores (HS) i n forest s o i l s i n burned logged areas than on unburned logged areas; l e v e l s i n logged areas were much lower than i n adjacent undisturbed stands. HS are high a f f i n i t y i r o n chelators predominantly produced by fungi, including 20 mycorrhizal forms, which may be important to i r o n a v a i l a b i l i t y i n the rhizosphere. Lower HS l e v e l s also suggest that burning may af f e c t mycorrhizal fungi, but t h i s has apparently not been investigated. The persistence of changes i n nutrient a v a i l a b i l i t y v a r i e s with slashburn severity and ecosystem type. In Norway spruce - Scots pine cutovers i n Norway, Skokelefald (1973) and Braathe (1974) reported that t o t a l and exchangeable K, Na, Mg, Ca and Mn a l l increased immediately following burning. However, K and Na concentrations subsequently decreased and were lower than on unburned s i t e s a f t e r 3 years. Exchangeable Mg, Ca and Mn l e v e l s were higher on the burned s i t e s over 8 years, although Mg concentrations decreased during t h i s period. The forest f l o o r pH increased 2.7 units (from 4.0 to 6.7) i n the l i t t e r layer and 0.3 units i n the humus layer i n the f i r s t year following burning but was s i m i l a r to unburned p l o t s a f t e r 8 years. The amounts of t o t a l N and P i n the forest f l o o r were lower following burning and continued to decrease over the 8 year period. On a thick-moss s i t e i n Finland, Vlro (1969) also found increases i n pH, and exchangeable Ca and Mg as well as i n extractable P and NH4 i n the forest f l o o r following burning. There was no change i n the concentration of exchangeable K immediately following burning but i t was 50% lower than on the unburned s i t e a f t e r 10 years. Following a severe prescribed burn on a t h i n humus s i t e i n Sweden, Uggla (1967) found increases i n pH and exchangeable Ca which persisted f o r 21 years. However, following a spring burn under aspen i n Ontario, Smith and Jones (1978) found that increases i n extractable P, and exchangeable K, Mg and Ca concentrations i n the surface organic matter only persisted f o r 3-4 months. 21 2.2 .3 E f f e c t s on Nutrient Transfers and Transformations. The long-term e f f e c t of slashburning on nutrient a v a i l a b i l i t y i s the net r e s u l t of the i n t e r a c t i o n of the nutrient transfers and transformations which occur during and immediately following burning with subsequent mineralization and nutrient input and output processes ( F i g . 2). The rates of processes such as mineralization, N f i x a t i o n , leaching and plant uptake may i n themselves be influenced by burning. Heating of the organic matter during burning may influence the s i z e and species composition of s o i l microbial populations. Ahlgren and Ahlgren (1965) found that the number and a c t i v i t y of micro-organisms decreased immediately following burning, but rose sharply during the f i r s t growing season. Changes i n microbial populations due to burning may a f f e c t decomposition and nutrient mineralization rates i n the re s i d u a l organic matter. Also, changes i n f o rest f l o o r chemistry may a l t e r i t as a substrate f o r microbial a c t i v i t y - although some of the more e a s i l y decomposable l i t t e r and forest f l o o r material i s consumed during burning, higher pH and nutrient concentrations i n the re s i d u a l organic matter may favor microbial a c t i v i t y i n a s i m i l a r manner to the f e r t i l i z e r additions reported by Kumi (1984). Baker (1968) found lower organic carbon concentrations and C/N r a t i o s i n the forest f l o o r s on slashburned s i t e s than on unburned s i t e s - such changes may also favour decomposition. Higher temperatures i n the re s i d u a l organic matter following burning (Endean and Johnstone 1974) are another factor which may favour decomposition. Apparently decomposition and mineralization rates i n the r e s i d u a l organic matter have not been investigated following burning. However, Skokelefald (1973) and Braathe (1974) found a greater reduction i n forest f l o o r organic 22 matter quantities on burned clearcuts than on unburned clearcuts i n Norway over an eight year period, which may be due to increased decomposition rates. Van Cleve and Dyrness (1983) found increases i n pH and Ca concentrations, but no changes i n NH4, NO3, PO4 or K concentrations i n the s o i l s o l ution one year following burning of a black spruce - feathermoss forest f l o o r . They suggested that the lack of change i n N, P, and K concentrations might be due to microbial immobilization of these elements, as a r e s u l t of increased microbial a c t i v i t y following burning. Leaching may involve nutrient l o s s from the s i t e i n groundwater or e f f e c t i v e l o s s i n nutrient movement beyond the rooting zone. The rate of leaching i s r e l a t e d to the s o i l i on exchange capacity, the amount of ash, and the amount and pattern of water movement through the s o i l ( F e l l e r 1982). Leaching of i n d i v i d u a l cations i s probably also Influenced by t h e i r strength of adsorption on the exchange complex (which decreases i n the order K > Na > Mg > Ca). G r i e r and Cole (1971) found that i n the accompanying anion leaching, n i t r a t e , s u l f a t e and phosphate may also be l o s t , though carbonate l o s s predominates. Adams and Boyle (1980) found that leaching from the surface s o i l peaked one month following burning and that a greater quantity of cations was leached (decreasing i n the order Ca > K > Mg) from the forest f l o o r following burning on a conventionally- clearcut than on a whole-tree logged s i t e following burning, which they attributed to greater ash deposition on the conventionally clearcut s i t e . G r ier and Cole (1971) and Grier (1975) reported that over 90% of the Mg, Ca and K that was leached i n t o the upper 19 cm of s o i l during the f i r s t snowmelt following a w i l d f i r e was retained there, although Na losses were s i g n i f i c a n t l y greater; quantities leached decreased i n the order Na > Ca > K > Mg. 23 Grier (1975) also found that leaching increased with the volume of water flowing through the forest f l o o r , and was somewhat greater under heavy ash layers. Severson e i fll. (1975) found that cjuantities of i n d i v i d u a l ions leached from burned s o i l columns decreased i n the order Ca > K > P and that cjuantities v aried between s o i l types. F e l l e r and Kimmins (1984) found higher K, Na and NO3 concentrations and pH i n streamwater following c l e a r c u t t i n g and slashburning of a watershed i n southwest B. C. Chemical concentrations i n the streamwater increased a f t e r the f i r s t r a i n and were higher than pre-burn l e v e l s f o r 2 years. Potassium concentrations showed the most prolonged and s i g n i f i c a n t increases. However, nutrient losses to the atmosphere during slashburning were found to be much greater than losses i n streamwater, e s p e c i a l l y f o r nitrogen. Increases i n chemical concentrations i n streamwater following burning may r e s u l t from overland flow as well as from leaching. Nutrient l o s s through erosion may increase following s l a s h -burning as well, as a r e s u l t of reductions i n vegetation and forest f l o o r cover, exposure of mineral s o i l , reduction of s o i l porosity, induction of hydrophobicity and breakdown i n s o i l structure ( F e l l e r 1982). The s e v e r i t y of the erosion depends on the amount and i n t e n s i t y of r a i n f a l l a f t e r burning, the i n t r i n s i c e r o d i b i l i t y of the s o i l (slope, s o i l texture, structure), f i r e s e v erity and the rate of vegetation re-establishment ( F e l l e r 1982). The e f f e c t of slashburning on erosion i n c e n t r a l i n t e r i o r forests apparently has not been investigated. However, as r a i n f a l l and t e r r a i n i n the c e n t r a l i n t e r i o r of B. C. are generally moderate, erosion may be of minor si g n i f i c a n c e . 24 2.2.4 E f f e c t s on Nutrient Uptake and Productivity. Changes i n nutrient a v a i l a b i l i t y following burning may a f f e c t plant nutrient uptake and productivity. As the e f f e c t s of f i r e on nutrient a v a i l a b i l i t y vary with ecosystem type, f i r e severity, and time, nutrient uptake and growth would be expected to vary i n a s i m i l a r manner. Skoklefald (1973) and Braathe (1974) found that f o l i a r nitrogen concentrations and height growth i n Norway spruce and Scots pine seedlings planted on burned and unburned s i t e s were greater on the burned s i t e s f o r the f i r s t 2 years following burning, but greater on unburned s i t e s a f t e r 5 years. A f t e r 8 years t o t a l height and height growth on unburned M y r t i l l u s and O x a l l i s s i t e types surpassed that on burned s i t e s i n these types, although growth was s t i l l greater on burned than on unburned Calluna s i t e s . Uggla (1974) reported that the height growth of planted spruce seedlings was i n i t i a l l y greater on a severely slashburned s i t e i n Sweden than on an adjacent unburned s i t e , but a f t e r 21 years was only 65% of that on the unburned s i t e . These r e s u l t s suggest that there i s a threshold l e v e l of f i r e impact which r e s u l t s i n impaired productivity i n some ecosystems. This threshold l e v e l would be expected to vary between ecosystems depending on t h e i r o r i g i n a l nutrient status, and be expressed at d i f f e r e n t times following burning depending on nutrient demand. Ba l l a r d (1985,1987) examined the growth and f o l i a r n u t r i t i o n of twenty 2 - 1 0 year old white spruce plantations i n the c e n t r a l i n t e r i o r of B.C. He found that f o l i a r N, Mg, Fe and Cu concentrations were seriously d e f i c i e n t i n young planted white spruce i n general, and that d e f i c i e n c i e s were more frequent where slash burning had been c a r r i e d out, although height growth was often 25 better. On one s i t e , f o l i a r N and "active" Fe and Cu concentrations l n 5 year o l d 2+0 spruce growing i n an area that had been slash burned were 27, 66 and 40% lower, respectively, than i n an adjacent unburned area. However, height growth was 36% greater i n the burned area. These lower f o l i a r nutrient concentrations may be explained i n part by a d i l u t i o n e f f e c t , although d i l u t i o n of other f o l i a r elements was not apparent. On a s i t e where study p l o t s had received a range of burn impacts, height growth was weakly negatively correlated with r e s i d u a l forest f l o o r depth, and s o i l mineralizable N and f o l i a r N and Cu concentrations were p o s i t i v e l y correlated with r e s i d u a l forest f l o o r depth. Better growth on the areas which had received higher burn impacts was t e n t a t i v e l y a t t r i b u t e d to increased s o i l temperatures. Poor correlations between growth and f i r e impact may have been due to the f a i r l y narrow range of burn impacts on the sample plo t s , or due to a lack of s e n s i t i v i t y of f o l i a r nutrient concentrations to differences i n s o i l nutrient a v a i l a b i l i t y . There are apparently no data on the e f f e c t s of burning on the quantity of nutrients taken up by trees, nor on nutrient use e f f i c i e n c y . Such measures may be more sens i t i v e to f i r e impacts than are f o l i a r nutrient concentrations alone. 26 3. OBJECTIVES The e f f e c t s of slashburning on the nutrient status of spruce -f i r ecosystems l n the ce n t r a l i n t e r i o r of B. C. have not previously been investigated. The objectives of t h i s study were: 1. To cjuantify changes i n organic matter load and nutrient concentrations and content caused by burning i n ecosystems commonly planted to i n t e r i o r spruce i n the Sub-Boreal Spruce zone i n the ce n t r a l i n t e r i o r of B. C. 2. To examine relationships between i n i t i a l f u e l load and f u e l consumption, and between f u e l consumption and nutrient l o s s i n these ecosystems. 3. To determine the e f f e c t s of burning on the i n i t i a l growth of planted i n t e r i o r spruce seedlings. \ 27 4. STUDY A R E A 4.1 LOCATION, PHYSIOGRAPHY AND CLIMATE The study s i t e i s located within the Sub-Boreal Spruce biogeoclimatic zone, subalpine f i r subzone (SBSel) (Pojar e i a l . 1984) at 54° 44' North l a t i t u d e and 126° 27' West longitude at an elevation of 950 m on the Nechako Plateau (Holland 1964) (Fig.3). The s i t e i s approximately 100 km East of Smithers, B. C., within the Northwood Pulp and Timber Co. T.S.H.L. A-01475, CP 004, Block 3. A large-scale map of the study area l o c a t i o n l s shown i n Appendix A. The wet continental climate of the area i s c l a s s i f i e d as Dfc a f t e r Koppen (Kendrew and Kerr 1955). At the nearest climate s t a t i o n (Babine Lake), the mean annual p r e c i p i t a t i o n i s 601 mm and the mean annual temperature i s 1.1°C. A climate diagram f o r t h i s s t a t i o n i s shown i n F i g . 4. 4.2 ECOSYSTEM CHARACTERISTICS Two ecosystem groups were distinguished on the study s i t e . Both groups are dominated by " i n t e r i o r " spruce (Plcea glauca x engelmannll) i n mature forests i n the SBS zone and are commonly planted with i n t e r i o r spruce following clearcutting. The s o i l parent material i n both ecosystem groups was g l a c i a l t i l l . The well-drained upland or mesic ecosystem group occurred on mid- to upper-slope topographic positions with north-facing gentle to moderate slopes (3-10%). These ecosystems were c l a s s i f i e d l n the mesic bunchberry moss association (SBSel/01) (Pojar e i a l . 1984). The s o i l s i n the mesic ecosystems Included Podzolic Gray Luvisols, B r u n i s o l i c Gray Luvisols, Orthic D y s t r i c Brunisols, and Orthic Gray Luvisols 28 Figure 3. Location of the study area within the Sub-Boreal Spruce zone of B r i t i s h Columbia. 29 Figure 4. Climate diagram f o r Babine Lake, B. C. (a f t e r Walters and Le i t h 1967). The upper l i n e indicates mean monthly p r e c i p i t a t i o n , the lower l i n e mean monthly temperature, and the shaded area the period with no water d e f i c i t . Data from B. C. Dept. of Agric. (1974). 30 (Canada S o i l Survey Committee 1978) overlain by moderately deep (5-12 cm) forest f l o o r s . The humusforms i n t h i s group were predominantly c l a s s i f i e d as Orthi Hemi Mors (Klinka et. a l . 1981). These ecosystems had supported stands of i n t e r i o r spruce and subalpine f i r (Abies  lasiocarpa). with a small component of lodgepole pine (Pinus  contorta). The most common understory species were Vacclnium  membranaceum (black huckleberry), Cornus canadensis (bunchberry), Rubus pedatus (five-leaved bramble), and the feather mosses Pleurozlum sohreberl, P t l l l i u m c r l s t a - c a s t r e n s i s . and Hylocomlum splendens. The imperfectly drained subhygric/hygric ecosystem group occurred on north-facing, l e v e l to moderately sloping (0-10%) lower slope and receiving positions. These ecosystems were c l a s s i f i e d i n the h o r s e t a i l f l a t (SBSel/09) and Devil's club (SBSel/08) associations. The s o i l s i n t h i s group included Orthic and Rego Humic Gleysols and Gleyed Grey Luvisols (Canada S o i l Survey Committee 1978) with deep (12-30 cm) forest f l o o r s . The humusforms i n t h i s group were c l a s s i f i e d as Orthi Hydromoders and Amphi Mormoders (Klinka et. a l . 1981). The subhygric/hygric ecosystems had supported mature stands of i n t e r i o r spruce with a small component of subalpine f i r . The most common understory species i n these ecosystems were T.oni oe^a. involuorata (twinberry), Rubus p a r v i f l o r u s (thimbleberry), Sangulsorba Sltchensjs ( S i t k a burnet), Cornus canadensis. Equlsetum spp. (h o r s e t a i l s ) , and the feather mosses mentioned previously. Photographs of representative s o i l p r o f i l e s i n both ecosystems are shown i n Figs. 5-6 and are described i n Appendix B. A l i s t of plant species that were present i n the study p l o t s i n the f i r s t summer following logging i s given i n Appendix C. Figure 6. A t y p i c a l subhygrlc/hygric ecosystem s o i l (Plot 14, Aug. 1983). 32 5. METHODS 5.1 FIELD OPERATIONS The study s i t e was logged i n the winter of 1982-83 and was yarded with groundsel ciders. S o i l disturbance was l a r g e l y confined to the skidroads and landings. The stand had been attacked e a r l i e r by the spruce bark beetle (Dendroctonus rufipennis). The s i t e was scheduled to be burned i n the f a l l of 1983 to reduce the amount of slash and the forest f l o o r depth i n preparation f o r planting i n the spring of 1984. An impact rank of 3 from the Prescribed F i r e Predictor/Planner (PFP) (Muraro 1975) was prescribed i n the operational burning plan. This impact rank would r e s u l t i n a forest f l o o r depth reduction of 50% on the mesic ecosystems and 20% i n the subhygric ecosystems. An automatic weather s t a t i o n (Forest Technology Systems) was established i n an adjacent clearcut with the same elevation and aspect e a r l y i n J u l y of 1983 and temperature, r e l a t i v e humidity, windspeed and d i r e c t i o n , and r a i n f a l l ( i n the previous 24 hours) were recorded at 12:00 hours (Local Standard Time). These observations were used to calculate the codes and indexes of the Canadian Forest F i r e Weather Index (FWI) System (Canadian Forestry Service 1984) using the computer program of Van Wagner and Pickett (1985). B. C. Forest Service hazard s t i c k s were placed i n the slash and i n the adjacent stand i n mid-August. The weather s t a t i o n was removed 2 weeks p r i o r to the i g n i t i o n date; weather observations (uncorrected f o r elevation) from the nearest f i r e weather s t a t i o n i n Houston, B.C. were used to ca l c u l a t e the FWI System codes and indexes f o r the remaining 2 week period. Weather observations and FWI System codes and indexes f o r the e n t i r e period are given i n Appendix D. A slash burn was i g n i t e d at 14:00 hours on September 33 29, 1983 using a helicopter d r i p torch. A c e n t r e - f i r e i g n i t i o n pattern was used to develop a convection column. Ig n i t i o n continued p e r i o d i c a l l y u n t i l 16:00 hours. Photographs of the i g n i t i o n process and convection column are shown i n Figs. 7 and 8. Codes and indexes of the FWI System at 12:00 hours Local Standard Time on the burn day (calculated from i n i t i a l on-site observations followed by 2 weeks of observations from Houston) were: FFMC 86, DMC 14, DC 363, ISI 3, BUI 26, and FWI 6; the B. C. Forest Service hazard s t i c k s had a nominal moisture content of 11.7%. The f i r e d i d not spread well at the south, west, and east borders of the block which were shaded by the adjacent stand during some parts of the day at t h i s time of year. The f i n e f u e l s i n these areas probably had a higher moisture content, which l i m i t e d f i r e spread. The weather i n September, 1983 was cool and moist - f r o s t and l i g h t snow were observed. The FWI System codes and indexes (and e s p e c i a l l y the Duff Moisture Code) would suggest that f u e l moisture contents were much higher than would be required to achieve the prescribed impact on the forest f l o o r . 5.2 FIRE IMPACT ASSESSMENT PROCEDURES 5.2.1 Plot Layout and Treatment Plan The e f f e c t s of slashburning were assessed i n 0.04 ha permanent sample p l o t s . I t was o r i g i n a l l y planned to sample p l o t s with 3 l e v e l s of f i r e s e v e r i t y within the one burn. Severity l e v e l s were to be imposed through manipulation of plot l o c a t i o n and f u e l moisture. Plots were located i n each ecosystem type (mesic and subhygric) i n areas within the block where d i f f e r e n t severity l e v e l s (unburned control, low, moderate and high) could be imposed, and so treatments Figure 8. Convection column a f t e r i g n i t i o n . 35 could not be randomly assigned to the plo t s . Three r e p l i c a t e p l o t s were established i n each ecosystem x treatment combination f o r a t o t a l of 24 p l o t s . I t was thought that plots located near the i g n i t i o n centre would receive a high impact while plots located near the perimeter would receive a moderate impact. An attempt was made to impose a low impact treatment by sp r i n k l i n g designated p l o t s with known amounts of water i n a manner simulating r a i n f a l l , i n order to increase the moisture content of the slash and the forest f l o o r . The sprinklings were applied i n e a r l y September and were entered as p r e c i p i t a t i o n events i n a separate c a l c u l a t i o n of the FWI System codes and indexes f o r the sprinkled p l o t s . The sprinklings lowered the values of the codes and indexes, and were expected to r e s u l t i n lower f i r e i n t e n s i t i e s and organic matter consumption. However, 20 mm of p r e c i p i t a t i o n f e l l during the two weeks p r i o r to burning. This, coupled with low temperatures and high r e l a t i v e humidities during t h i s period, overwhelmed the e f f e c t of the sprinklings and equalized the moisture codes over a l l p l o t s . Control plots were established i n an area within the block that was separated from the other p l o t s by a road which provided a guard to the spread of f i r e from the main block (Fig. 9). Due to the poor spread of f i r e near the perimeter of the block, four p l o t s i n the low and moderate impact treatment groups were only p a r t i a l l y burned. These p l o t s were not included i n the subsequent analyses. However the f i r e d i d spread to the con t r o l area, p a r t i a l l y burning four of s i x (2 mesic and 2 subhygric) c o n t r o l p l o t s . These p l o t s were not included i n subsequent sampling. In the spring following burning three add i t i o n a l control p l o t s (1 mesic, 2 subhygric) were established i n the remaining unburned area. .Thus, the 36 • SUBHYGRIC PLOTS SCALE 1:7920 F i g u r e 9 . P l o t l o c a t i o n w i t h i n the study area. P l o t s sampled b e f o r e b u r n i n g but not resampled a f t e r burning are not shown. 37 number of pl o t s sampled during the f i r s t post-treatment year was 7 mesic burned + 7 subhygric burned + 2 mesic control + 3 subhygric control = 19 p l o t s . 5.2.2 Slash Sampling The l i n e i n t e r s e c t technique (Van Wagner 1968) was used to estimate the load of slash pieces > 1.0 cm i n diameter. Nine 10 m long transects forming three contiguous e q u i l a t e r a l t r i a n g l e s were established i n each plot ( Fig. 10) before burning. The diameter of each slash piece > 1.0 cm diam. intersected by the transects was measured both before and a f t e r burning. The transect ends were marked with i r o n bars to f a c i l i t a t e t h e i r r e l o c a t i o n a f t e r burning. The species composition of the slash i n each p l o t was determined p r i o r to burning f o r each of four diameter classes: 1.1-3.0 cm, 3.1-5.0 cm, 5.1-8.0 cm and > 8.0 cm. Representative samples of each species were c o l l e c t e d from each diameter c l a s s before burning f o r analyses of r e l a t i v e density and nutrient concentration. After burning, samples were c o l l e c t e d f o r these analyses by diameter c l a s s only, as species were not r e a d i l y i d e n t i f i a b l e . The load of slash pieces ± 1.0 cm diam. (including needles) was estimated both before and a f t e r burning by destructive gravimetric sampling of twelve randomly located 0.5 m2 subplots. Before burning, a l l samples were weighed a f t e r a i r drying and t h i r t y subsamples were randomly taken f o r moisture content and nutrient concentration determination. After burning, a l l samples taken were oven dr i e d and f i f t e e n samples were taken randomly f o r nutrient analysis. 5.2.3 Soil Sampling S o i l sampling was c a r r i e d out i n both the forest f l o o r and 38 Figure 10. Plot layout diagram. 39 the upper mineral s o i l horizons (0-15 cm depth) as these horizons were considered to be most important to tree n u t r i t i o n and the deeper horizons were considered u n l i k e l y to be affected by slashburning. Forest f l o o r samples (20 x 20 cm x the f u l l depth to mineral s o i l ) were c o l l e c t e d at twenty randomly located sample points i n each plot i n August of 1983, before burning. These i n d i v i d u a l samples were bulked i n t o four composite samples per plot f o r mass and nutrient concentration determination. The average forest f l o o r depth (average of the four depths at the corners of the 20 x 20 cm cjuadrat) was also determined at each sample point. Mineral s o i l samples (0-15 cm depth) were c o l l e c t e d at each of the 20 sample points i n each plot and bulked i n t o composite samples (four per p l o t ) f o r nutrient concentration determination. Samples were c o l l e c t e d f o r bulk density determination at four of the sample points within each plot using the excavation method (Black fit a l . 1965). Forest f l o o r depth reduction caused by burning was measured using forest f l o o r reduction pins (McCrae fit a l . 1979). Eighteen pins were placed systematically along the l i n e transects i n each p l o t before burning (Fig, 10). The s o i l s were sampled i n the week following burning (before any s i g n i f i c a n t p r e c i p i t a t i o n had occurred) i n the burned p l o t s only, as some of the control p l o t s had been inadvertently burned. Depth-of-burn was measured at each p i n and twenty samples each of the forest f l o o r and mineral s o i l were c o l l e c t e d from points located one metre south of the previous sampling points. The i n d i v i d u a l samples were bulked i n t o composite samples by horizon, as was done f o r the pre-burn sampling. In June of 1984, nine months following burning, twenty samples of f o rest f l o o r and mineral s o i l were c o l l e c t e d from random locations 40 within each p l o t , including the new control p l o t s . These samples were bulked as was described previously f o r determination of forest f l o o r mass and forest f l o o r and mineral s o i l nutrient concentrations. The average forest f l o o r depth was also measured at the twenty sampling points i n each p l o t . On a l l sampling occasions, forest f l o o r and mineral s o i l c o l l e c t e d f o r nutrient analysis were subsampled i n the f i e l d before bulking. These subsamples were frozen at the end of each day and were l a t e r used i n extractable N H 4 and N O 3 determinations. 5.2.4 Plantation Establishment and Assessment In the spring following burning ( l a t e May, 1984) 2 + 0 bareroot spruce seedlings grown at the B.C. Ministry of Forests Surrey nursery from seedzone 4076 and l i f t e d i n January, 1984, were planted i n a l l p l o t s . Seedlings were planted at 2.7 m square spacing (1200/ha), with 49 trees i n each 0.04 ha square seedling assessment p l o t superimposed on each 0.04 ha c i r c u l a r s o i l sampling plot (a t o t a l of 931 sample trees) and one row of outside buffer trees. To minimize bias due to planting q u a l i t y , nine planters were used and each planter was randomly assigned a row to plant i n each p l o t . A l l sample p l o t seedlings were planted i n the same day. The rest of the block was planted with a mixture of container-grown and bareroot i n t e r i o r spruce and lodgepole pine stock within a week of the study plot planting. Seedling height was measured a f t e r planting and at the end of the f i r s t growing season following planting. Foliage samples were c o l l e c t e d from trees i n the buffer s t r i p at the end of the f i r s t growing season following planting and bulked i n t o one composite sample fo r each p l o t . 41 5.3 LABORATORY PROCEDURES 5.3.1 Sample Preparation Forest f l o o r and mineral s o i l samples were a i r d r i e d and ground i n a f l a i l m i l l to pass a 2 mm mesh sieve and the f i n e (<2 mm) f r a c t i o n was c o l l e c t e d f o r chemical analysis. Slash and f o l i a g e samples were a i r d r i e d then ground i n a Wiley m i l l to pass a 1 mm sieve. The moisture content of the samples was determined p r i o r to analysis. S o i l subsamples frozen f o r extractable NH4 and NO3 analyses were thawed at room temperature, and then immediately oven d r i e d at 105°C to prevent mineralization. 5.3.2 Chemical Analyses T o t a l N, P, S, K, Ca and Mg concentrations were determined i n the forest f l o o r , slash and f o l i a g e samples. T o t a l N, C and S concentrations were also determined i n the mineral s o i l samples. Mineralizable N, extractable NH4 and NO3, exchangeable K, Ca, and Mg, and available P concentrations, cation exchange capacity (CEC), and pH were determined i n forest f l o o r and mineral s o i l samples. A l l t o t a l N, P, S, K, Ca, Mg and extractable NH4 and NO3 analyses were c a r r i e d out i n the Forest Ecology Laboratory i n the Faculty of Forestry at U.B.C. The s o i l s sampled i n 1983 were analyzed f o r mineralizable N, extractable P, t o t a l C, pH, exchangeable cations and CEC at the B. C. Forest Service (BCFS) North Road Laboratory i n V i c t o r i a . These analyses (with the exception of CEC) were c a r r i e d out at U.B.C. f o r the s o i l samples c o l l e c t e d i n 1984. The following laboratory methods were used: To t a l N and P Kjeldahl digestion (Black e_£ a l . 1965) Total S Leco SC-32 sulphur determinator 42 To t a l cations Dry ashing (3 hours at 475*C) followed by d i s s o l u t i o n of the residue i n d i l u t e HCl Total C BCFS: Walkley-Black wet digestion UBC: Dry combustion (3 hours at 475°C) Mineralizable N Anaerobic incubation at 35°C f o r two and four weeks f o r the mineral s o i l and forest f l o o r , respectively (Waring and Bremner 1964), but without the additional water extraction Extractable NH4, N03 2 M KCl extraction (Black et. a l . 1965) Extractable P Bray #1 a c i d NH4F extraction (Black gt a l - 1965) CEC and exchangeable 1 M NH4.OAC extraction at pH 7 (Black et cations a l - 1965) pH ( i n water) 1:1 r a t i o of mineral s o i l to d i s t i l l e d water and 1:5 r a t i o of forest f l o o r to d i s t i l l e d water Concentrations of a l l cations i n solution were determined by atomic absorption spectrophotometry. Solutions analysed by the BCFS laboratory used an air-acetylene flame and added a La i o n i z a t i o n buffer f o r Mg and Ca determinations; solutions analysed at U.B.C. used an air-acetylene flame f o r K and Mg, and a nitrous oxide-acetylene flame f o r Ca determination. To determine the re l a t i o n s h i p between the two methods used f o r Ca and Mg determination, ten extracts from each of the mineral s o i l and forest f l o o r were analysed at U.B.C. using both methods. Somewhat higher Ca values were obtained with the a i r acetylene flame when La was added but no corrections were made as there d i d not appear to be a simple r e l a t i o n s h i p between the two sets of values. A l l N and P forms i n solutions prepared at U.B.C. and N i n 43 solutions prepared by the BCFS la b were analysed using standard colori m e t r i c methods on a Technicon autoanalyser. P forms i n solutions prepared at the BCFS la b were analysed c o l o r i m e t r i c a l l y using a spectrophotometer. 5.3.3 Physical Analyses The r e l a t i v e densities of slash samples i n the > 1.0 cm diam. classes were determined by displacement and expressed i n grams oven-dry mass (70 6C) per cm3. The oven-dry mass of the forest f l o o r and the i 1.0 cm diam. slash samples was found by f i r s t determining the a i r dry mass, then oven drying a subsample (at 70°C), and applying the r e s u l t i n g correction factor to the a i r dry mass. The coarse fragment-free mineral s o i l bulk density was determined from oven-dry mass (at 105°C) of the f i n e (<2 mm) f r a c t i o n of samples of known volume. The volume of coarse fragments i n each sample was determined by displacement. 5.4 CAJXJDLATIONS 5.4.1 Slash Load and Nutrient Content The slash load i n each diameter c l a s s > 1.0 cm diameter was calculated from the transect-based diameter measurements and the mean r e l a t i v e density f o r each diameter class using a computer program developed by B. Wong at U.B.C. Slash loads were calculated f o r each of the three small t r i a n g l e s i n each plot (Fig. 10) before and a f t e r burning. Average slash loads f o r each diameter c l a s s were obtained f o r each p l o t using these three estimates. In preburn calc u l a t i o n s , a weighted mean r e l a t i v e density f o r each diameter c l a s s was calculated by weighting the average r e l a t i v e density of each species by the 44 proportion of the t o t a l number of slash pieces a t t r i b u t e d to that species i n that diameter class. In post-burn calculations (where species were un i d e n t i f i a b l e ) a simple mean r e l a t i v e density f o r each si z e c l a s s was used f o r a l l plots. Slash consumption i n each diameter class was assumed to be the difference between pre- and post-burn slash loads f o r that diameter c l a s s . The average t o t a l slash load (including the i l . O cm diameter class) was also determined f o r each plot before and a f t e r burning. The nutrient content i n each slash diameter c l a s s > 1.0 cm before burning was calculated f o r each plot as the product of the average slash load and the mean weighted nutrient concentration f o r each diameter c l a s s . The mean weighted nutrient concentrations i n each diameter class i n each plot were calculated i n exactly the same way as were the mean r e l a t i v e densities described above. The nutrient content i n each diameter c l a s s a f t e r burning and i n the ± 1.0 cm diameter s i z e class both before and a f t e r burning was calculated f o r each plot as the product of the average slash load f o r that plot and the simple average nutrient concentration f o r each diameter c l a s s . 5.4.2 Forest Floor Mass The forest f l o o r mass before burning was determined by destructive gravimetric sampling as was described previously. The forest f l o o r mass a f t e r burning i n each plot (W2) was estimated as: ¥ 2 = w i x (D - R) / D [1] where Wi i s the average pre-burn forest f l o o r mass, R i s the average forest f l o o r depth reduction i n each plot, and D i s the average pre-burn forest f l o o r depth. This method was used because destructive sampling following burning yielded widely varying and unreasonable re s u l t s , which was attributed to the high s p a t i a l v a r i a b i l i t y i n 45 forest f l o o r mass. The forest f l o o r mass i n the control p l o t s was assumed to be the same at subsequent sampling times. 5.4.3 Forest Floor and Mineral S o i l Nutrient Contents The forest f l o o r nutrient content i n each plot was calculated as the product of the average forest f l o o r mass and the concentration of each nutrient. The nutrient content i n the 0-15 cm mineral s o i l layer was calculated as the product of the average nutrient concentration and the quantity of f i n e s o i l (<2mm) per hectare i n the 0-15 cm layer. 5.4.4 Slashburning-Caused Organic Layer Consumption and Nutrient Loss The t o t a l mass and nutrient content of the organic layer both pre-burn and post-burn, were determined by summing, f o r each variable separately, the mass or nutrient quantity i n each slash diam. c l a s s and the forest f l o o r . T o t a l organic layer consumption and nutrient losses to the atmosphere were calculated as the difference between the pre-burn and post-burn t o t a l mass and nutrient contents. Due to the d i f f i c u l t y i n d istinguishing the boundary between the forest f l o o r and the underlying Ah horizon i n the subhygric ecosystems, the nutrient content of only the surface 8.9 cm of forest f l o o r (the same depth as the grand mean of the mesic ecosystem forest f l o o r depth) was used i n the nutrient l o s s calculations f o r these ecosystems. Thus, nutrient l o s s from the subhygric forest f l o o r s (NL S) was calculated as: NL S = NiO*! x 8.9 / D) - N 2 (Wx x (8.9 - R) / D) [23 where Wi was the pre-burn forest f l o o r mass, D was the pre-burn forest f l o o r depth (cm), R was the depth-of-burn (cm) and 8.9 (cm) was the grand mean forest f l o o r depth In the mesic forest f l o o r s before burning, and Nj and N 2 were the nutrient concentrations before and 46 a f t e r burning, respectively. 5.4.5 Relative Height Growth Rate The r e l a t i v e height growth rate (RHGR) of the planted tree seedlings was calculated as: RHGR = l n (HT 2) - l n (HT^) [3] where HT^ and HTo, are seedling height at the beginning and end of the growing season, respectively. Relative growth rates are measures of growth e f f i c i e n c y and are more sens i t i v e to treatment e f f e c t s than are absolute growth rates, as they are unaffected by i n i t i a l s i z e differences (Ledig 1974). 5.5 DATA SYNTHESIS AND STATISTICAL ANALYSES Although the planned experimental manipulation of f i r e s e v erity was unsuccessful, there was nevertheless a s i g n i f i c a n t v a r i a t i o n i n impacts among burned p l o t s on both s i t e types which allowed consideration of f i r e severity l e v e l i n the data analysis. Plots were grouped i n t o low and moderate severity classes on the basis of t o t a l organic matter consumption. Plots which exhibited an average l o s s of slash and forest f l o o r materials of ±10 kg/m2 were considered to have been subjected to a low severity burn, whereas p l o t s with a l o s s of >10 kg/m2 were considered to have been subjected to a moderate se v e r i t y burn. 5.5.1 Slash Load and Nutrient Content The average slash load and nutrient content i n each diameter c l a s s was tabulated f o r each f i r e severity c l a s s f o r each ecosystem type both before and a f t e r burning. The standard error of the mean (SEg) nutrient content i n the pre-burn > 1.0 cm diameter classes was 47 simply a multiple of the SE^ of slash load; the average slash r e l a t i v e density and nutrient concentrations i n each plot were considered to be constants i n these calculations, as use of weighted means of these variables i n the mass and nutrient content c a l c u l a t i o n s precluded consideration of t h e i r variance. However, the SEg of the nutrient content of the > 1.0 cm diameter classes post-burn was estimated a f t e r Freese (1962) as: SEx = (mx n) (var^m + v a r ^ ) ) 1 7 2 [4] where m and n are the mean slash mass and nutrient concentration respectively, and v a r ^ and v a r ^ are the variance of the mean slash mass and nutrient concentration, respectively; only r e l a t i v e density was treated as a constant i n these cal c u l a t i o n s . This method of estimating SEg assumes that the variable multiplicands are independent and t h e i r covarlance i s zero. The SE^ of the nutrient content i n the i l . O cm diam. slash was also estimated (both pre-burn and post-burn) i n a s i m i l a r manner, except the v a r i a t i o n i n r e l a t i v e density was inherently included i n the mass determinations f o r t h i s diam. c l a s s . Correlations between mean slash consumption (absolute and percent) i n each diam. class with mean i n i t i a l load i n each diam. cl a s s were determined using the s t a t i s t i c a l f a c i l i t y SAS (SAS I n s t i t u t e 1985). 5.5.2 Soil Nutrient Concentrations Forest f l o o r and mineral s o i l chemical concentration data were subjected to 3-way analysis of variance ( f i r e s e verity x sampling time x s i t e type) using the computer program UBC-GENLIN (Greig and Bjerring 1977). The homogeneity of variance of each variable was tested and transformations were subsequently c a r r i e d out to reduce the heteroscedacity of some variables. S i g n i f i c a n t group means were 48 distinguished using Scheffe's multiple comparison t e s t . These analyses were c a r r i e d out on transformed variables. The n u l l hypotheses tested were: H 01: F i r e severity had no e f f e c t on forest f l o o r or mineral s o i l chemistry. H 02: Sampling time had no e f f e c t on forest f l o o r or mineral s o i l chemistry. H 03: Ecosystem type had no e f f e c t on forest f l o o r or mineral s o i l chemistry. H 04: There were no ecosystem x f i r e s e verity i n t e r a c t i o n s with respect to forest f l o o r or mineral s o i l chemistry. H 05: There were no ecosystem x sampling time in t e r a c t i o n s with respect to forest f l o o r or mineral s o i l chemistry. H 06: There were no f i r e severity x sampling time in t e r a c t i o n s with respect to forest f l o o r or mineral s o i l chemistry. H 07: There were no ecosystem x f i r e s e verity x sampling time interactions with respect to forest f l o o r or mineral s o i l chemistry. Inferences about treatment e f f e c t s and interactions must be made with caution as the sampling approach and c l a s s i f i c a t i o n of f i r e s e v erity l e v e l s resulted i n some pseudo-replication (Hurlbert 1984). 5 . 5 . 3 S o i l Nutrient Contents The average forest f l o o r and mineral s o i l nutrient content was tabulated f o r each f i r e severity c l a s s on each s i t e type at each sampling time. The SEg of the average nutrient content i n the mineral s o i l was estimated i n a s i m i l a r manner to that i n Equation 4. This method was used i n c a l c u l a t i n g the SEg of forest f l o o r nutrient contents before burning as well. However, as the c a l c u l a t i o n of 49 forest floor mass after burning included independent estimates of in i t i a l mass, Initial depth and depth reduction in burning, the calculation of SEg of forest floor nutrient contents included estimates of the mean and varg of these three variables and that of nutrient concentration. Correlations between mean forest floor depth reduction and mean Initial forest floor depth and mean slash consumption, and between mean nutrient loss from the forest floor during burning and mean forest floor depth reduction were determined using SAS. 5.5.4 Biomass Consumption and Nutrient Loss The total biomass, nutrient content, consumption, and nutrient loss due to burning were tabulated for the low and moderate fire severity classes in each ecosystem group. The SEg of total biomass and biomass nutrient content were estimated as the square root of the sum of the varg of the mass and nutrient content in each biomass class. The SE^ of biomass consumption and nutrient losses were estimated as the square root of the sum of the varg- of mass and nutrient contents in each biomass class pre-burn and post-burn. Correlations between mean total biomass consumption and mean in i t i a l load and consumption in each biomass class, and between mean total nutrient losses and consumption and mean nutrient loss in each biomass class were determined using SAS. 5.5.5 Plantation Establishment The absolute height increment and relative height growth rate in the first growing season and the total height and survival at the end of the first growing season, in each fire severity class in each ecosystem group were subjected to 2 way analyses of variance using the 50 computer program UBC-GENLIN. Significant group means were distinguished using Scheffe's multiple comparison test . The nu l l hypotheses tested were: H 01: F ire severity had no effect on the above seedling parameters. H 02: Ecosystem type had no effect on the above seedling parameters. H 03: There were no f i re severity x ecosystem interactions with respect to the above seedling parameters. 51 6. RESULTS AND DISCUSSION 6.1 SLASH LOAD AND RELATIVE DENSITY Slash r e l a t i v e d e n s i t i e s are given i n Table 1. In the unburned condition, r e l a t i v e density i n the > 1.0 cm diam. classes generally decreased with increasing piece diameter f o r white spruce, subalpine f i r , and lodgepole pine, probably i n r e l a t i o n to increasing growth r i n g width; < 5 cm d i a . material was predominantly branchwood. The slash loads present before and a f t e r burning are given i n Tables 2a and 2b. Photographs of t y p i c a l pre- and post-burn s i t e conditions i n mesic and subhygric ecosystems are shown i n Figs. 11-14. The percentage of the t o t a l slash load i n each s i z e c l a s s before and a f t e r burning i s given i n Table 3a and the percentage reduction In each s i z e c l a s s i n Table 3b. The i n i t i a l s l a sh loads and slash consumptions measured i n the present study are within the range of other slash load and consumption estimates f o r s p r u c e - f i r slash reported by K i l l (1969, 1971), Alexander (1984), Zasada and Norum (1986) and Lawson and Taylor (1987) given i n Appendix E. The estimate of coarse slash consumption i s rather high and might have been Influenced by a bark beetle attack p r i o r to logging, as some of these pieces were probably dead when cut, and consequently may have had a longer period of drying p r i o r to burning. Before burning most of the slash mass was i n the coarse (>8.0 cm) and f i n e (±1.0 cm) diameter classes i n both ecosystems; there was more t o t a l , coarse and f i n e slash i n the subhygric ecosystems before burning. Percentage consumption generally decreased with increasing slash diameter (Table 3b); the f i n e slash was almost completely consumed during burning, leaving most of the r e s i d u a l T a b l e 1. S l a s h r e l a t i v e d e n s i t i e s and n u t r i e n t c o n c e n t r a t i o n s . Condition Diam. a 1 Relative Nutrient Concentrations (%) /Species Class Density (cm) (g/cm3) H P S K Ca Hg A l l Species <1 .0 14 - 0. 521(0. 014) 2 0 .078(0 .003) 0 113(0. 003) 0. 094(0. 009) 0. 525(0. 025) 0. 065(0. 013) Subalpine 1 . 1 -3 .0 6 0. 60(0. 02) 0. 173(0 013) 0 .015(0 .002) 0 052(0. 009) 0. 089(0. 017) 0. 349(0. 022) 0. 037(0. 008) Fir 3 . 1 -5 .0 5 0. 55(0. 03) 0. 102(0 014) 0 .006(0 .001) 0 020(0. 008) 0. 097(0. 022) 0. 275(0. 023) 0. 021(0. 001) 5 . 1 -8 .0 4 0. 50(0. 03) 0. 101(0. 010) 0 .009(0 .003) 0 053(0. 024) 0. 081(0. 041) 0. 208(0. 044) 0. 016(0. 002) >8 .0 4 0. 47(0. 06) 0. 065(0. 019) 0 .005(0 .001) 0 014(0. 010) 0. 040(0. 011) 0. 132(0. 014) 0. 012(0. 002) Interior 1 .1 -3 .0 6 0. 57(0. 05) 0. 158(0. 010) 0 .010(0 .001) 0. 030(0. 006) 0. 052(0. Oil) 0. 421(0. 024) 0. 012(0. 002) Spruce 3 . 1 -5 .0 5 0. 61(0. 02) 0. 081(0. 004) 0 .005(0 .000) 0. 030(0. 010) 0. 030(0. 003) 0. 353(0. 019) 0. 010(0. 001) 5 . 1 -8 .0 4 0. 51(0. 01) 0. 047(0. 005) 0 .004(0 000) 0. 015(0. 006) 0. 024(0. 008) 0. 192(0. 020) 0. 007(0. 001) >8 .0 4 0. 48(0. 03) 0. 064(0. 024) 0 .005(0 001) 0. 014(0. 009) 0. 024(0. 010) 0. 130(0. 012) 0. 005(0. 001) Lodgepole 1 . 1 -3 0 6 0. 59(0. 02) 0. 146(0. 009) 0 .012(0 002) 0. 010(0. 004) 0. 076(0. 009) 0. 195(0. 020) 0. 049(0. 009) Pine 3 . 1 -5 0 5 0. 55(0. 03) 0. 095(0. 011) 0 .006(0 001) 0. 020(0. 004) 0. 059(0. 016) 0. 125(0. 020) 0. 048(0. 004) 5 . 1 -8 0 4 0. 53(0. 04) 0. 058(0. 006) 0 .004(0 000) 0. 008(0. 001) 0. 042(0. 002) 0. 093(0. 002) 0. 039(0. 001) >8 .0 4 0. 49(0. 05) 0. 034(0. 001) 0 .003(0 001) 0. 002(0. 001) 0. 030(0. 005) 0. 083(0. 021) 0. 035(0. 004) Unidentified 1 . 1 -3 0 6 0. 64(0. 02) 0. 076(0. 004) 0 .004(0 000) 0. 025(0. 003) 0. 011(0. 002) 0. 073(0. 009) 0. 015(0. 002) 3 . 1 -5 0 5 0. 53(0. 04) 0. 066(0. 005) 0 .004(0 001) 0. 051(0. 008) 0. 052(0. 009) 0. 096(0. 017) 0. 035(0. 007) 5 . 1 -8 .0 4 0. 47(0. 04) 0. 054(0. 004) 0 .004(0 000) 0. 015(0. 001) 0. 059(0. 006) 0. 081(0. 009) 0. 024(0. 007) >8 .0 6 0. 45(0. 02) 0. 034(0. 003) 0 .002(0 000) 0. 010(0. 002) 0. 022(0. 006) 0. 047(0. 005) 0. 017(0. 002) ^111 J1HLL A l l Species <1 .0 12 0. 868(0. 060) 0 .063(0 004) 0. 086(0. 009) 0. 413(0. 054) 0. 991(0. 070) 0. 149(0. 013) 1 . 1 -3 0 12 0. 52(0. 02) 0. 129(0. 013) 0 .009(0 001) 0. 048(0. 005) 0. 072(0. 013) 0. 215(0. 026) 0. 045(0. 004) 3 . 1 -5 0 11 0. 49(0. 03) 0. 068(0. 008) 0 .006(0 002) 0. 021(0. 004) 0. 052(0. 012) 0. 120(0. 018) 0. 035(0. 004) 5 .1 -8 0 12 0. 43(0. 02) 0. 051(0. 004) 0 .004(0 001) 0. 007(0. 002) 0. 059(0. 027) 0. 081(0. 007) 0. 024(0. 002) >8 .0 12 0. 43(0. 01) 0. 038(0. 005) 0 .004(0 000) 0. 015(0. 003) 0. 037(0. 007) 0. 074(0. 014) 0. 022(0. 003) Ko. of composite samples. Hean (standard error). Standard errors of 0.000 are less than or equal to 0.0005. Table 2 a . Slash load and nutrient content in the mesic ecosystems. Diam. Impact D n*5 Load Nutrient Content (kg/ha) Class Class (fcg/m2) (cm) N P S K Ca Mg <1.0 Low D 48 8. 74 (0.S3) 3 148. 8( 18 7) 21.4 (8.0) 31. 0 (8. 7) 86. 0 (2. 2) 143.9( 13.9) 17. 8 (3. 9) B 48 0. 16 (0.04) 14. 1 [3 3) 1.0 (0.8) 1. 4 (0. 3) 6. 7 (1. 5) 16.0 (3.8) 8. 4 (0. 6) Moderate U 36 8. 35 (0.38) 188. 3( 17. 1) 18.3 (8.6) 86. 5 (3. 7) 88. 3 (3. 1) 123.2( 17.9) 15. 3 (3. 7) B 36 0. 13 (0.04) 11. 6 [3. 7) 0.9 (0.8) 1. 8 (0. 4) 5. 5 (1. 7) 13.3 (4.2) 8. 0 (0. 6) 1.1-3.0 Low 0 18 1. 09 (0.18) 14. 8 [1. 6) 1.1 (0.1) 3. 4 (0. 4) 6. 2 (0. 7) 86.5 (2.9) 3. 2 (0. 3) B 18 0. 88 (0.03) 8. 8 Co. 4) 0.8 (0.0) 1. 0 (0. 2) 1. 6 (0. 2) 4.6 (0.8) 1. 0 (0. 2) Moderate V 9 0. 89 (0.08) 11. 8 ; i . 0) 0.8 (0.1) 2. 8 (0. 3) 4. 3 (0. 4) 19.8 (1.9) 8. 3 (0. 8) B 9 0. 15 (0.08) 8. 8 [0. 8) 0.1(0.03) 0. 7 (0. 1) 1. 7 (0. 1) 3.4 (0.5) 0. 7 (0. 1) 3.1-5.0 Low U 18 0. 67 (0.07) 5. 4 [0. 6) 0.3(0.03) 2. 4 (0. 3) 4. 2 (0. 4) 13.8 (1.4) 1. 8 (0. 2) B 18 0. 37 (0.04) 8. 4 Io. 3) 0.8(0.06) 0. 8 (0. 2) 1. 9 (0. 2) 4.4 (0.8) 1. 3 (0. 2) Moderate U 9 0. 48 (0.06) 3. 9 :o. 5) 0.8(0.03) 1. 8 (0. 2) 3. 4 (0. 4) 9.0 (1.0) 1. 3 (0. 3) B 9 0. 33 (0.08) 8. 8 :o. 2) 0.8(0.05) 0. 7 (0. 1) 1. 7 (0. 1) 3.9 (0.6) 1. 1 (0. 1) 5.1-8.0 Low U 18 0. 88 (0.16) 6. 8 [ i . 1) 0.5 (0.1) 2. 5 (0. 4) 5. 7 (1. 0) 11.4 (2.1) 1. 8 (0. 3) B 18 0. 77 (0.13) 3. 9 :o. 7) 0.3 (0.1) 0. 5 (0. 2) 4. 5 Co. 8) 6.8 (1.2) 1. 9 (0. 4) Moderate U 9 1. 13 (0.14) 8. 0 ;o. 9) 0.6 (0.1) 8. 8 (0. 3) 7. 9 (0. 9) 14.0 (1.5) 8. 8 (0. 3) B 9 1. 01 (0.11) 5. 1 ;o. 7) 0.4 (0.1) 0. 7 (0. 3) 6. 0 (0. 7) 8.8 (1.2) 8. 5 (0. 4) >8.0 Low U 18 8. 08 (1.66) 39. 1 [8. 0) 8.9 (0.6) 9. 8 (2. 0) 24. 3 (5. 0) 73. 9 (15.8) 11. 4 (2. 3) B 18 5. 13 (1.18) 19. 5 [4. 9) 8.0 (0.5) 7. 7 (2. 3) 19. 0 (4. 2) 38.0 (10.9) 11. 3 (3. 0) Moderate U 9 11. 48 (1.56) 64. 7 ( [8. 9) 4.9 (0.7) 15. 8 (8. 2) 39. 2 (5. 5) 184.0 (17.0) 16. 9 (1. 9) B 9 5. 08 (0-71) 19. 1 ( [3. 7) 8.0 (0.3) 7. 6 (1. 9) 18. 6 (2. 7) 37.3 (8.7) 11. 1 (a. 3) Total Low U 13. 46 (1.69) 808. 8(] L5. 2) 36.2 (3.0) 49. 0 (2. 8) 66. 4 (6. 1) 868.6 (81.0) 36. 1 (4. 6) Slash. B 6. 65 (1.13) 48. 7 ( [6. 0) 13.8 (0.5) 11. 5 (8. 4) 33. 7( L3. 0) 69.8 (93.8) 17. 9 (4. 1) Moderate tr 16. 86 (1-61) 810. K L9. 3) 24.9 (3.4) 49. 7 (3. 8) 77. 7 (6. 7) 290.0 (70.7) 35. 6 (4. 6) B 6. 70 (0.78) 40. l [5. 3) 3.6 (0.4) 10. 9 (2. 0) 32. 9 (5. 5) 66.1 (12.5) 17. 4 (4. 1) Total Low 6. 81 (8.03) 165. 5(16. 4) 28.4 (3.1) 37. 5 (3. 7) 32. 7 (8. 4) 199.4 (88.6) 18. 8 (5. 6) Consumption Moderate 9. 56 (1.76) 170. 0(80. 0) 21.3 (3.5) 38. 8 (4. 3) 44. 8 (8. 7) 883.9 (71.9) 18. 8 (4. 9) Sampling date: U = before burning (Sept. 1983) B = immediately after burning (Oct. 1983). Sample s i ze . Mean (standard error) . Standard errors of 0.0 are less than or equal to 0.0. Table 2b . Slash load and nutrient content i n the subhygric ecosystems. Diam. Impact D n 2 Load Nutrient Content (&g/ha) Class Class (Icg/m2) (cm) N P S K Ca Mg <1.0 Low 0 48 3.67 (0. 46) 3 191.5(25 .0) 28. 7 (3.0) 41.5 (5. 4) 34. 9 (4. 5) 193. 0 (26. 1) 23. 9 (5. 7) B 48 0.20 (0. 05) 17.5 (4 .3) 1. 3 (0.3) 1.7 (0. 4) 8. 3 (1. 9) 20. 0 (3. 8) 3. 0 (0. 7) Moderate TJ 36 3.71 (0. 64) 193.3(34 .1) 28. 9 (5.2) 41.9 (7. 4) 35. 2 (6. 2) 194. 8 (35. 1) 24. 1 (6. 4) B 36 0.51 (0. 16) 44.1(14 .6) 3. 3 (1.1) 4.4 (1. 5) 21. 0 (6. 8 50. 3 (4. 2) 7. 6 (2. 5) 1.1-3.0 Low 0 12 1.15 (0. 12) 16.4 (1 • 7) 1. 2 (0.1) 4.1 (0- 4) 6. 4 (0. 6) 35. 3 (3. 6) 2. 5 (0. 3) B 12 0.27 (0. 02) 3.4 (0 .5) 0. 2 (0.0) 1.3 (0. 2) 1. 9 (0. 2) 5. 7 (0. 9) 1. 2 (0. 2) Moderate U 9 1.35 (0. 18) 18.0 (2 .4) 1. 2 (0.2) 4.6 (0. 6) 6. 5 (0. 9) 37. 4 (5. 1) 2. 7 B 9 0.35 (0. 06) 4.5 (0 .8) 0. 3 (0.1) 1.7 (0. 3) 2. 5 (0. 4) 7. 5 (1. 5) 1. 6 (0. 3) 3.1-5.0 Low 0 12 0.48 (0. 05) 4.0 (0 .4) 0. 2 (0.0) 1.5 (0. 2) 2. 7 (0. 3) 12. 3 (1. 3) 1. 0 (0. 1) B 12 0.24 (0. 03) 1.8 (0 .2) 0. 1 (0.0) 0.6 (0. 4) 1. 4 (0. 1) 2. 9 (0. 5) 0. 8 (0. 1) Moderate 0 9 0.52 (0. 10) 4.1 (0 8) 0. 2 (0.1) 1.8 (0. 3) 2. 7 CO. 5) 12. 6 (2. 4) 1. 1 (0. 2) B 9 0.29 (0. 04) 2.0 (0 3) 0. 2 (0.1) 0.6 (0. 1) 1. 5 CO. 2) 3. 5 (0. 1) 1. 0 (0. 2) 5.1-8.0 Low 0 12 0.52 (0. 06) 8.0 (0 s) 0. 6 (0.0) 2.8 (0. 2) 7. 9 Co. 4) 6. 9 (0. 9) 2. 8 (0. 1) B 12 0.50 (0. 08) 2.6 (0 4) 0. 2 (0.0) 0.4 (0. 1) 3. 0 Co. 5) 4. 1 (0. 7) 1. 3 (0. 2) Moderate 0 9 0.51 (0. 10) 3.3 (0 7) 0. 3 (0.1) 1.3 (0. 3) 2. 9 Co. 6) 7. 2 (1. 5) 0. 9 (0. 2) B 9 0.39 (0. 03) 2.6 (0 4) 0. 2 (0.1) 0.3 (0. 1) 2. 3 CO. 5) 3. 1 (0. 7) 1. 0 (0. 2) >8.0 Low 0 12 9.48 (1. 76) 45.5 (8 4) 3. 4 (0.8) 11.3 (2. 1) 27. 9 C5. 2) 86. 4 (16. 0) 12. 6 (2. 3) B 12 6.82 (1. 14) 25. 9 (5 5) 2. 7 (0.5) 10.2 (2. 8) 25. 2 C4. 3) 50. 4 (12. 7) 15. 0 (3. 4) Moderate 0 9 15.40 (2. 93) 80.0(14 8) 5. 8 (1.1) 19.1 (3. 6) 43. 6 C8. 3) 149. 8 (28. 4) 18. 5 (3. 5) B 9 8.57 (1. 45) 32.6 (6 9) 3. 4 (0.6) 12.8 (3. 5) 31. 7 C5. 4) 63. 4 (16. 0) 18. 8 (4. 4) Total Low 0 15.30 (1. 82) 265.4(26 4) 34. 1 (4.4) 61.2 (5. 5) 79. 8 C7. 6) 333. 9 (30. 9) 42. 8 (6. 2) Slash B 8.03 (1. 14) 51.2 (7 0) 4. 5 (0.6) 14.2 (2. 8) 39. 8 C6. 9) 83. 1 (18. 2) 21. 3 (3. S) Moderate 0 21.49 (3. 00) 298.7(37 3) 36. 4 (6.4) 68.9 (7. 5) 90. 9( L0. 9) 401. 8 (45. 2) 47. 3 (7. 4) B 10.11 (1. 47) 85.2(16 2) 7. 4 (1.2) 19.8 (3. 8) 59. 0( LI. 0) 127. 8 (16. 6) 30. 0 (5. 0) Total Low 7.28 (2. 15) 214.8(27 3) 29. 6 (4.4) 47.0 (6. 1) 40. 0( L0. 2) 250. 8 (35. 8) 21. 5 (7. 1) Consumption Moderate 11.38 (3. 34) 213.5(40 7) 29. 0 (6.5) 49.1 (8. 4) 31. 9( L5. 4) 274. 0 (48. 2) 17. 3 (8. 9) re-sampling date: 0 = before burning (Sept. 1983), B = Immediately after burning (Oct. 1983). Sample size. Mean (standard error) . Standard errors of 0.0 are less than or equal to 0.05. Table 3a. Percentage of t o t a l s lash load and nutr ient content present in d i f f e r e n t s l a s h diameter o l a s s e s . Diam. D Low Impact Plots Moderate Impact Plots (cm)S Load N P S K Ca Mg Load K P S K Ca Mg Mesic Ecosystems <1.0 U 20 68 82 63 39 54 49 14 68 73 62 29 42 43 B 2 33 31 12 20 23 13 2 29 25 11 17 20 11 1.1 - 3.0 TJ 8 7 4 7 9 10 9 5 7 4 7 6 7 6 B 3 7 6 9 5 7 6 2 5 3 6 5 5 4 3.1 - 5.0. TJ 5 2 1 5 6 5 5 3 2 1 5 4 3 4 B 6 6 6 7 6 6 7 5 5. 6 6 5 5 6 5.1 - 8.0 0 6 3 2 5 9 4 5 7 4 2 5 10 5 8 B 11 9 10 4 13 10 11 15 13 11 6 18 12 14 >8.0 TJ 60 19 11 20 36 28 32 70 31 20 32 79 47 43 B 77 46 54 67 56 55 63 76 48 56 70 57 57 64 Subhygric Ecosystems <1.0 TJ 22 72 84 68 44 58 56 17 65 79 61 39 48 52 B 2 34 29 12 21 24 8 5 52 49 22 35 39 25 1.1 - 3.0 TJ 7 6 3 7 8 10 6 5 6 3 7 7 9 6 B 3 7 4 9 5 7 6 3 5 1 8 4 6 5 3.1 - 5.0 TJ 3 1 1 2 3 4 2 2 1 1 3 3 3 2 B 3 3 2 4 4 3 4 3 2 1 3 2 3 3 5.1 - 8.0 TJ 3 3 2 4 10 2 6 2 1 1 2 3 2 2 B 6 5 4 3 7 5 6 4 3 1 1 4 2 3 >8.0 TJ 62 17 10 18 35 26 29 72 27 16 26 48 37 39 B 85 50 60 72 63 61 70 85 38 46 64 54 50 63 1 Sampling date: U = before burning (Sept. 1983), B = immediately after burning (Oct. 1983). Table 3b. Percentage reduction i n s l a s h load and n u t r i e n t content. Diam. Low Impact Plots Moderate Impact Plots Class (cm) Load H P S K Ca Mg Load N P S X Ca Mg Mesic Ecosystems <1.0 94 90 95 95 74 89 87 94 90 95 95 75 89 87 1.1 - 3.0 80 81 82 70 74 83 69 83 80 88 75 60 83 70 3.1 - 5.0 45 55 33 67 55 67 28 32 43 0 61 50 57 15 5.1 - 8.0 13 37 40 80 21 46 +5 11 36 33 75 19 41 11 >8.0 36 50 31 21 22 48 1 56 70 59 52 52 70 34 Total 51 79 85 76 49 74 50 59 81 86 78 58 77 51 Subhygric Ecosystems < 1.0 94 82 95 . 96 76 90 87 86 77 88 40 74 68 1.1 - 3.0 77 79 83 68 70 84 52 74 75 75 63 61 80 41 3.1 - 5.0 49 55 50 60 48 76 20 43 51 0 67 44 72 9 5.1 - 8.0 3 68 75 86 62 40 54 24 21 33 77 21 57 0 >8.0 28 43 20 10 10 42 +20 44 59 41 33 27 58 0 Total 48 81 86 77 50 75 50 53 71 80 71 35 68 36 O l 57 Figure 11. Typical slash load i n the mesic ecosystems. Figure 12. Typical mesic ecosystem condition a f t e r burning (same view as F i g . 11 - note the stump i n foreground as a reference point). 58 Figure 14. Typical subhygric ecosystem condition a f t e r burning (same view as F i g . 13 - note the p o s i t i o n of the white rod i n the l e f t mid-ground as a reference point). 59 slash, i n the coarse (>8.0 cm) diameter c l a s s (Table 3a). Slash consumption i n each diameter class was highly correlated with i n i t i a l slash load of the respective diameter class, as was t o t a l slash reduction with the i n i t i a l t o t a l slash load (Table 4). However, percentage slash consumption i n a l l except the 3.1-5.0 cm diameter c l a s s was poorly correlated with i n i t i a l load of the respective diameter c l a s s (Table 4). Although Lawson and Taylor (1987) also found poor correlations between percentage slash reduction and i n i t i a l load f o r f i n e slash (±1.0 cm) (probably because f i n e slash was almost completely consumed i n a l l burns) they found good correlations between these variables f o r larger diameter classes. There may have been some error i n the c a l c u l a t i o n of percentage slash consumption by diameter class i n the present study, as slash pieces which were only p a r t i a l l y consumed during burning may have s h i f t e d from larger to smaller diameter classes, p o t e n t i a l l y r e s u l t i n g i n an over-estimate of percentage consumption l n the > 8.0 cm diam. class, an under-estimate In the ± 1.0 cm diam. cla s s , and both types of error i n the intermediate classes. 6.2 FOREST FLOOR DEPTH AND MASS The forest f l o o r depth and mass pre-burn and post-burn are given i n Table 5. The depth and mass of the forest f l o o r i n the mesic ecosystems and forest f l o o r depth reductions due to burning i n the present study are within the range of those reported by Alexander (1984) and Lawson and Taylor (1987) f o r spr u c e - f i r f o r e s t s (Appendix E). Forest f l o o r depth reduction was greater i n the mesic ecosystems than i n the subhygric ecosystems despite greater slash reduction i n the subhygric ecosystems. This i s probably due to a Table 4. Correlations between slash consumption and init ial slash load, by slash diameter class. Correlation Coefficients (r) I n i t i a l Slash Consumption by Diam. Class (cm) Percent Consumption by Diam. Class (cm) Load by Diam. Class (cm) <1.1 1.1-3.0 3.1-5.0 5.1-8.0 >8.0 Total <1.1 1.1-3.0 3.1-5.0 5.1-8.0 >8.0 Total <1.1 0 .99 • • 0. .44 0.36 -0. , 15 -0.33 0.15 -0. 41 -0.22 0. 48 * -0. . 10 -0. 33 0. ,48 • 1.1-3.0 0 .46 * 0. .94 »* 0.63 ** 0. .87 0.11 0.41 -0. 64 ** -0.20 0. 49 * 0. .53 * -0. 85 -0. , 15 3.1-5.0 0 . 14 0. .61 * 0.98 •* 0. .41 -0.01 0.17 -0. 40 0.10 0. 68 0. .47 -0. 08 -0. ,08 5.1-8.0 -0 .43 0. .03 0.06 0. ,66 ** 0.38 0.84 0. 00 0.30 -0. 18 0. 42 0. 57 * 0. 10 >8.0 -0 .35 0. .88 -0.06 0. .46 0.89 0.78 ** -0. 81 -0.10 -0. 83 0. .63 * 0. 87 -0. .44 Total -0 . 10 0. .41 0.10 0. .58 0.86 *• 0.88 ** -0. 36 -0.14 -0. 08 0. .69 0. 88 -0. .38 *• Significant at P < 0. .01 * Significant at p < 0.05; n = 14. Table 5. Summary of forest f l o o r depth and mass reductions and nutrient losses due to burning. Low Impact F l o t s Moderate Impact P l o t s Depth Load Nutrient Loss (kg/ha) Depth Load Nutrient Loss (kg/ha) (cm) (kg/m 2) N P S K Ca Mg (cm) (fcg/ m 2) N P S K Ca Mg Mesic ecosystems Pre-burn 1 7.3 6.5 854 100 102 75 280 43 9.2 8.4 1233 129 120 92 465 55 L o s s 2 2.8 2.4 307 28 48 21 5 8 3.2 2.9 437 35 50 25 67 + 17 3 % Loss 37 37 36 28 47 28 2 19 35 35 39 27 42 27 14 +31 Subhygric ecosystems Pre-burn 1 24.4 25. 9 3255 309 442 192 3805 813 23.5 31.2 3835 424 487 284 4007 1045 L o s s 4 1.5 1.6 93 17 18 +24 + 19 110 2.5 3.2 158 28 36 28 +46 222 % Loss 6 6 3 5 4 + 13 0 13 11 11 4 7 7 10 + 1 21 From Table 9. Difference of pre- and post-burn values i n Table 9. (+) represents an increase i n nutr i e n t content. Ca l c u l a t e d from estimates of nutr i e n t content i n the upper 9 cms. of the for e s t f l o o r before and a f t e r burning (cf p 45). 62 higher moisture content i n the subhygric forest f l o o r s at the time of burning. Very l i t t l e mineral s o i l (< 5%) was exposed by slashburning i n the mesic ecosystems, and no mineral s o i l was exposed by slashburning i n the subhygric ecosystems. In both ecosystems the res i d u a l forest f l o o r was charred only at the surface. Forest f l o o r depth reduction was poorly correlated with slash consumption i n the mesic ecosystems but f a i r l y well correlated with >8.0 cm diam. slash consumption and t o t a l slash consumption i n the subhygric ecosystems (Table 6). Lawson and Taylor (1987) found a p o s i t i v e association between cumulative slash consumption < 17 cm di a . and forest f l o o r depth reduction. The consumption of moist forest f l o o r material due to burning i s thought to be influenced by the duration of radiant heating from above, which i n turn i s influenced by the degree of coarse slash consumption. The poorer c o r r e l a t i o n i n the mesic ecosystem may be due to a narrower range of slash load and consumption i n the mesic ecosystems. Forest f l o o r depth reduction was poorly correlated with I n i t i a l forest f l o o r depth i n both ecosystems, although percentage depth reduction was strongly negatively correlated with i n i t i a l depth i n the mesic ecosystems (Table 6), probably because of the shallower forest f l o o r depths i n the mesic ecosystems. In the c a l c u l a t i o n of forest f l o o r mass consumption i t was assumed that forest f l o o r bulk density was uniform with depth; t h i s seems reasonable because forest f l o o r s i n the study area were quite uniform i n structure with depth. I t was also assumed that burning had no e f f e c t on the bulk density of the forest f l o o r , as the r e s i d u a l forest f l o o r was charred only at the surface f o r the most T a b l e 6. C o r r e l a t i o n s between f o r e s t f l o o r d e p t h r e d u c t i o n and s l a s h r e d u c t i o n and i n i t i a l f o r e s t f l o o r d e p t h . C o r r e l a t i o n C o e f f i c i e n t s ( r ) Slash Consumption hy Diam. Class (cm) I n i t i a l Forest F l o o r Depth <1. 1 1.1-3.0 3.1-5.0 5.1-8.0 >8.0 To t a l Mesic Ecosystems Depth-of-burn -0.02 -0.36 -0.38 -0.62 -0.10 -0.26 0.01 Percent DOB 0.23 -0.11 0.22 -0.39 -0.39 -0.34 -0.81 » Subhygric Ecosystems Depth-of-hurn -0.31 0.30 0.03 0.67 0.95 *» 0.85 « -0.11 Percent DOB -0.17 0.36 0.10 0.67 0.94 »* 0.90 » -0.28 ** S i g n i f i c a n t at p < 0.01 * S i g n i f i c a n t at p < 0.05; n = 7. 64 part. However, where forest floor bulk density increases with depth and f i r e consumes only the upper layers, this method of calculation would result i n over-estimation of forest floor mass consumption -further s t r a t i f i c a t i o n of the forest floor by depth during mass sampling would be necessary i n such cases. Destructive gravimetric sampling of forest floor mass before and after burning did not provide r e a l i s t i c estimates of forest floor mass consumption due to burning i n the present study, as was discussed i n Section 5.4.2. This was probably due to high spatial variation i n forest floor mass within plots both before and after burning and consequently high sampling error. The mean values for forest floor mass from twenty samples i n two plots i n each of the mesic and subhygric ecosystems had coefficients of variation of 45% and 42%, respectively. Destructive sampling of forest floor mass before and after burning would probably provide more meaningful forest floor consumption estimates on sites with uniformly high f i r e impacts, where burning would be expected to reduce the spatial variation i n post-burn forest floor mass. 6.3 SLASH NUTRIENT STATUS 6.3.1 Slash Nutrient Concentrations Slash nutrient concentrations (Table 1) i n the >1.0 cm diameter class i n the unburned condition generally decreased i n relation to increasing diameter, probably due to the proportion of bark and sapwood decreasing with increasing diameter, as nutrient concentrations are higher i n bark than i n stem- and branchwood i n these species (Kimmins 1974). Similar relationships between diameter and nutrient concentrations have been reported for 65 ponderosa pine (Covington and Sackett 1984) and western hemlock and western red cedar slash ( F e l l e r e i a l . 1983) and f o r white spruce subalpine f i r and lodgepole pine branches (Kimmins 1974). Concentrations of N, P, S, K and Mg were highest i n subalpine f i r i n a l l diameter classes; Ca concentrations were also highest i n subalpine f i r i n the large diameter classes (>5 cm). Concentrations of S and Ca were higher i n spruce than i n lodgepole pine slash (spruce had the highest Ca concentrations of a l l three species i n the <5.0 diameter classes), although K and Mg concentrations were higher i n lodgepole pine. There were no consistent differences between these two species with respect to N and P concentrations across a l l s i z e classes. Concentrations of N, P, K, Mg and Ca i n white spruce, subalpine f i r and lodgepole pine i n the 1.1 - 3.0 cm. and 3.1 - 5.0 cm diameter classes were s i m i l a r to those found i n 0.6 - 2.5 cm and >2.5 cm diameter branchwood of the same species reported by Kimmins (1974). Concentrations of these elements i n the ±1.0 cm diameter c l a s s were also s i m i l a r to those f o r twigs reported by Kimmins (1974). However, concentrations of N, P, K and Mg i n the white spruce and lodgepole pine 5.1 - 8.0 cm and >8.0 cm slash diameter classes were lower than those i n spruce and pine wood reported by Rodin and Ba s i l e v i c h (1967); Ca concentrations were si m i l a r i n pine and higher i n spruce i n the present study. No other data f o r S concentrations i n these species have apparently been reported. After burning, nutrient concentrations i n the r e s i d u a l slash (not d i f f e r e n t i a t e d by species) also decreased with increasing diameter c l a s s . Concentrations of N, K, Ca and Mg i n the burned ±1.0 cm diam. slash were higher than i n the unburned slash; trends for other s i z e s classes and nutrients with burning are not cl e a r . 66 Trends i n nutrient concentrations and r e l a t i v e d e n s i t i e s i n the larger slash pieces with burning would have to be evaluated by tagging pieces of known species and diameter before burning. 6.3.2 Slash Nutrient Content Nutrient contents i n the slash and t o t a l losses due to burning are given i n Table 2a and 2b. The percentage of the t o t a l slash nutrient content i n each slash diameter class i s given i n Table 3a and the percentage reduction i n nutrient content i n each c l a s s i s given l n Table 3b. T o t a l nutrient cjuantities i n the slash before burning followed the order Ca > N > K > S > Mg > P i n both ecosystems. The largest proportion of nutrients ( e s p e c i a l l y of N, P, and S) was i n the f i n e slash (±1.0 cm d i a ) , followed by the coarse slash (>8.1 cm d i a ) . Although nutrient concentrations were lowest i n the coarse slash pieces, the large mass i n t h i s s i z e c l a ss resulted i n a modest nutrient content. Nutrient cjuantities l o s t from the slash due to burning followed the order Ca > N > K , S > P > Mg i n both ecosystem groups. However, these losses do not necessarily represent losses to the atmosphere, as ash and fragments of burned slash may drop to the ground during burning and become incorporated i n the forest f l o o r . Losses of i n d i v i d u a l nutrients as a percentage of the pre-burn cjuantities followed the order P > N > S > Ca > K > Mg. The trend i n t o t a l s lash nutrient losses follows the order of absolute nutrient contents before burning, while the trend i n percentage t o t a l nutrient losses i s s i m i l a r to the order of percentage nutrient content i n the f i n e slash, which accounted f o r the highest pre-burn nutrient content and was almost t o t a l l y consumed during burning. 67 Percentage nutrient l o s s from each diameter c l a s s generally decreased with Increasing diameter - t h i s trend follows from the aforementioned relationships between pre-burn slash nutrient concentration and slash reduction with diameter. The major exception to t h i s trend was the high percentage nutrient l o s s from the >8.0 cm diam. c l a s s i n the moderate impact pl o t s . This exception i s possibly an a r t i f a c t r e s u l t i n g from the ingress of slash pieces from larger to smaller diameter classes mentioned previously. T o t a l losses of N, P, S and Ca from the slash as a percentage of pre-burn quantities were much higher than was the percentage t o t a l slash consumption. Raison e t fli. (1985a) found that percentage losses of N and P from vegetation f i r e s approached unity with percentage f u e l consumption, although r e l a t i v e losses of K, Ca and Mg were lower. However, the f u e l s i n the present study were not homogenous with respect to s i z e (nor with respect to surface area / volume - an important factor i n flammabillty) or nutrient concentration. The high percentage nutrient losses from the slash i n the present study were probably due to the high nutrient content i n the f i n e slash and the high percentage f i n e slash consumption. Nutrient losses from the slash during burning were greater i n the subhygric ecosystems than i n the mesic ecosystems. This l s probably because there was more f i n e slash i n the subhygric ecosystems. Af t e r burning, t o t a l nutrient contents i n the r e s i d u a l slash generally followed the order Ca > N > K > Mg > S > P and most of these nutrients were present i n the coarse slash. Nutrient losses from each slash diameter c l a s s were highly correlated with slash consumption from that c l a s s (Table 7) except f o r Mg l o s s from the > 8.0 cm diam. cl a s s . Percentage t o t a l Table 7. Correlations between nutrient loss from the slash and slash consumption. Correlation Coefficients (r) Slash Consumption by Diam. Class vs. Percent Slash Consumption by Diam. Class vs. — Diam. Class Nutrient Loss by Respective Diam. Class Percent Nutrient Loss by Respective Diam. Class (cm) N P S K Mg Ca N P S X Mg Ca <1.1 0. 99 * * 0. 99 • • 0.99 0. ,79 * * 0.98 * * 0. 98 * * 1. ,00 * * 1. 00 * * 1. 00 * * 1. 00 * * 1. 00 * * 1. 00 * • 1.1-3. 0 0. 96 * * 0. 93 * * 0.82 ** 0. ,87 * * 0.62 * 0. 86 * • 0. .96 * * 0. 93 * i* 0. 89 * * 0. 87 • * 0. 88 • * 0. 78 » * 3.1-5. 0 0. 99 * * 0. 99 * * 0.89 «• 0. ,95 * * 0.69 * * 0. 89 * * 0. .99 * * 0. 99 * * 0. 90 * * 0. 95 * * 0. 71 * * 0. 85 » * 5.1-8. 0 0. 96 * * 0. 95 * * 0.90 ** 0. .97 * » 0.64 * 0. 95 » * 0. .96 « « 0. 93 * * 0. 82 * « 0. 94 * * 0. 74 « * 0. 88 • • >8.0 0. 90 * * 0. 88 » * 0.87 0. .88 * * 0.26 0. 87 * * 0. .82 * * 0. 77 * « 0. 62 * 0. 92 * * 0. 85 * « 0. 74 * * Total 0. 38 0. 24 0.38 0. .52 0.10 0. 57 * 0. .66 * * 0. 78 * * 0. 87 * * 0. 77 * 0. 83 * * 0. 73 * * 05 CO ** Significant at p < 0.01 * Significant at p < 0.05; n = 14 . 69 nutrient losses from the slash were well correlated with percentage t o t a l slash consumption. However, t o t a l nutrient losses from the slash were (with the exception of K and Ca), poorly correlated with t o t a l slash consumption. This i s probably because most of the nutrient l o s s occurs from the f i n e slash which i s almost t o t a l l y consumed even i n low severity burns and consequently increased slash consumption i n the larger diameter classes accounts f o r r e l a t i v e l y l i t t l e increase i n nutrient l o s s from the slash. Thus, accurate estimates of f i n e slash load and consumption are c r i t i c a l f o r nutrient l o s s determination. In some instances, t o t a l nutrient losses were lower i n the moderate impact c l a s s though t o t a l s lash consumption increased. This was apparently due to the larger amount of f i n e slash remaining. 6.4 FOREST FLOOR NUTRIENT STATUS 6.4.1 Forest Floor pH and Nutrient Concentrations Forest f l o o r pH and nutrient concentrations are given i n Table 8 . S i g n i f i c a n t increases i n pH and t o t a l Mg were found i n the burned pl o t s i n the mesic ecosystems nine months a f t e r burning. There were also s i g n i f i c a n t increases i n extractable P i n the low impact mesic pl o t s and extractable N O 3 i n the burned mesic p l o t s immediately a f t e r burning, but they d i d not appear to p e r s i s t . S i g n i f i c a n t increases were also found i n exchangeable K immediately a f t e r burning i n the low impact subhygric p l o t s . However, the l e v e l s were not s i g n i f i c a n t l y d i f f e r e n t from pre-burn values nine months l a t e r . 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Ecosystem Contro Impact Class Low Moderate Extractable mesic TJ 169.2 (7.4] [12]cd 168.4 (8.5] ) [5]bcd 186.0 (14.2) [ l l ] c d P (ppm) B - 274.6 (15.4] [16le 223.2 (20.6) [12]de S 88.3 (3.8] [12]ab 170.6 (11.5] [16]cd 130. 9 (18.6) [12]be subhygric TJ 45.3 (3.3] )[12]a 36.9 (3.9; )[15]a 28.5 (6.2) [ I l i a B - 73.3 (7.6] >[16]ab 80.2 (11.2) [12]ab S 31.0 (2.0: [16]a 37.4 (4.3; l[16]a 40.5 (4.2) [12]a Exchangeable mesic 0 4.2 (0.2; [12]cd 3.7 (0.1] [4]cd 3.3 (0.2) [12]bc K (meq/lOOg) B - 4.9 (0.2] tl6]d 4.6 (0.4) [12]cd S 1.4 (0.2: tl3]a 1.0 (0.1] [16)a 0.8 (0.1) C i l i a subhygric TJ 2.0 (0.2] [8]ab 1.6 (0.1] [15]a 1.4 (0.2) [ l l ] a B - 3.5 (0.2] [16]bc 3.2 (0.3) [12]be S 0.5 (0.0] [12]a 0.6 (0.1] [16]a 0.5 (0.0) [13]a Exchangeable mesic TJ 24.2 (4.0] [12]ab 17.6 (1.0] [9]ab 21.1 (1.5) [12]ab Ca (meq/lOOg) B - 32.1 (2.4] [16]ab 36.8 (3.0) [12]b S 9.6 (1.0] [12]a 21.0 (2.4] [16]ab 23.6 (2.2) [12]ab subhygric TJ 93.7 (4.8] [8]c 90.2 (4.8] Cl5]c 70.8 (5.9) [ l l ] c B - 91.6 (3.8] [163c 93.4 (5.2) [12]c S 26.8 (1.3] [12]ab 31.1 (4.4] [16]ab 23.9 (2.9) [13]ab Exchangeable mesic TJ 4.9 (0.4) [12]ab 4.3 (0.3) [9lab 3.9 (0.1) [12]a Mg (meq/lOOg) B - 4.8 (0.4] [16]ab 6.7 (0.7) [12]abc S 4.3 (0.4) [12]ab 3.5 (0.2) [16]a 2.7 (0.2) Cl3]a subhygric TJ 20.3 (1.1) [8]ef 23.3 (1.2) [15]f 19.9 (1-1) [ l l ] e f B - 22.0 (1.2) [16]f 24.0 (0.8) [12]f S 13.5 (0.7) [12]de 10.3 (1.1) [16]cde 12.4 (1.8) [12]cd -3 to Cation mesic TJ 95.5 (2.7) l"12]a 91 5 (2 9] [9]a 90 8 (2 5) [12]a Exchange B - 85 9 (2 2] [16]a 91 3 (4 3) [12]a Capacity (5.7) [8]b (meq/lOOg) subhygric TJ 146.6 157 2 (5 2] [15]b 133 7 (3 4) [ l l ] b B - 145 5 (3 0] tl6]b 139 2 (1 8) [12]b Sampling date: TJ = unburned (Aug. 1983), B - post-burn (Oct. 1983), S = 9 mo. post-burn (May 1984). 1 Mean (se)[no. composite samples]. For each variable, means followed by the same letter are not significantly different at p < 0.05. 73 interactions where there were pre-burn differences between ecosystems i n forest f l o o r nutrient concentrations. There were s i g n i f i c a n t decreases l n exchangeable K i n the mesic burned p l o t s and i n t o t a l S i n the low impact burned p l o t s i n both ecosystems nine months a f t e r burning. Decreases i n exchangeable K may be due to displacement by Mg or Ca from exchange s i t e s ; decreases i n S may be due to leaching. There were s i g n i f i c a n t changes i n extractable P and NO3 with sampling time i n a l l p l o t s i n both ecosystems and i n exchangeable Ca and Mg i n the mesic ecosystems which are confounded with e f f e c t s of slashburning on these variables. Seasonal v a r i a b i l i t y i n l a b i l e nutrient forms such as NO3 i n these ecosystems may be due to seasonal v a r i a b i l i t y i n nutrient transfer and transformation processes such as snowmelt, mineralization, plant uptake and leaching, weaver and F o r c e l l a (1979) examined the seasonal v a r i a b i l i t y i n nutrient a v a i l a b i l i t y i n s i x Rocky Mountain vegetation types and found that v a r i a b i l i t y decreased i n the order NO3 > NH4 > P > K > Ca > Mg. They also found that concentrations of these nutrients were greatest i n e a r l y f a l l . In clearcut situations, the inherent seasonal v a r i a t i o n may be confounded further with changes i n mineralization rates following disturbance and changes i n plant nutrient uptake with vegetation development. Changes i n exchangeable Ca and Mg i n the subhygric pl o t s between the f i r s t and t h i r d sampling time may also have been due to the differences i n a n a l y t i c a l techniques used to assess these forms. There was no s i g n i f i c a n t change i n CEC due to burning. However, the buffered method that was used f o r CEC determination might have obscurred any difference i n pH-dependent cation exchange capacity. The mesic ecosystems had s i g n i f i c a n t l y lower pH values and t o t a l Ca, t o t a l Mg, exchangeable Mg and CEC and higher extractable P 74 than d i d the subhygric ecosystems. 6.4.2 Forest Floor Nutrient Content Forest f l o o r nutrient contents are given i n Table 9; estimated losses to the atmosphere during burning are given i n Table 5. Changes i n forest f l o o r nutrient content r e s u l t from both changes i n forest f l o o r nutrient concentrations and forest f l o o r mass. Where increases i n nutrient concentration follow burning and reduction i n forest f l o o r mass, there may be increases, decreases or no net change i n nutrient content depending on the r e l a t i v e magnitude of the changes i n forest f l o o r nutrient concentration and mass. Where slashburning consumes some of the forest f l o o r but decreases or no changes i n nutrient concentrations are detected, the forest f l o o r nutrient content w i l l be reduced. There were net losses of a l l nutrients from the forest f l o o r during burning, except f o r Mg from the moderate impact mesic plots and K and Ca from the subhygric ecosystems. In general, forest f l o o r nutrient losses increased with f i r e impact class, except f o r Mg i n the mesic ecosystems and Ca i n the subhygric ecosystems, which exhibited larger net gains i n moderate than the low f i r e impact plots. The gain i n t o t a l and exchangeable Mg content i n the moderate impact mesic p l o t s i s reasonable i n r e l a t i o n to the estimate of Mg l o s s from the slash, though increases i n t o t a l and exchangeable K and Ca i n the burned subhygric p l o t s were greater than estimates of K and Ca l o s s from the slash. On average, nutrient quantities l o s t decreased i n the order N > S > Ca > P > K > Mg i n the mesic ecosystems and Mg > N > S > P > K i n the subhygric ecosystems, though the order varied with impact c l a s s i n the mesic ecosystems, because Ca l o s s was much higher i n the moderate impact mesic plots. There were larger net Table 9. Forest f l o o r nutrient contents. Nutrient Contents (leg/Ha) D 1 Mesic Control Ecosystems / Impact Low Class Moderate Subhygric Control Ecoystems Low : / Impact Class Moderate Total N U 494 (40)2 854 (97) 1833 (103) 1899 (800) 3255 (804) 3835 (361) B - 547 (91) 746 (109) - 3429 (619) 4276 (754) S 386 (31) 491 (82) 611 (95) 1614 (153) 8588 (457) 3147 (568) Total P TJ 63 (5) 100 ( U ) 189 (9) 199 (26) 309 (85) 424 (61) B - 78 (12) 94 (14) - 300 (55) 408 (67) S 58 (5) 63 (11) 83 (13) 808 (19) 318 (58) 347 (61) Total S TJ 57 (4) 102 (12) 180 (9) 856 (28) 448 (33) 487 (54) B - 54 (9) 70 (U) - 444 (83) 484 (89) S 49 (5) 39 (V) 10 (S) 194 (25) 856 (49) 285 (53) Total K u 57 (6) 75 (9) 92 (8) 187 (14) 198 (16) 884 (38) B - 54 (11) 67 (12) - 308 (68) 391 (73) S 35 (6) 36 (7) 39 (8) 93 (12) 810 (45) 188 (36) Total Mg TJ 51 (5) 43 (8) 55 (5) 486 (47) 813 (57) 1045 (96) B - 35 (6) 78 (13) - 574 (112) 583 (185) S 50 (4) 52 (9) 75 (13) 898 (29) 918 (170) 640 (186) Total Ca u 242 (34) 880 (32) 465 (44) 8567 (855) 3805 (267) 4007 (388) B - 875 (48) 398 (62) - 3808 (698) 4744 (838) S 163 (20) 385 (60) 354 (54) 1639 (216) 4183 (814) 3173 (687) Anaerobic U 16 (2) 81 (4) 10 (2) 109 (12) 118 (11) 184 (13) Mineralizable B - 10 (2) 18 (3) - 144 (27) 176 (36) N S 24 (2) 20 (5) 27 (5) 118 (11) 159 (30) 163 (34) Extractable TJ 15 (2) 30 (4) 18 (5) 15 (2) 88 (2) 35 (6) NH 4 + B - 10 (2) 15 (3) - 51 (12) 54 (12) S 9 (1) 14 (2) 20 (3) 39 (4) 54 (10) 74 (14) Extractable TJ 0.2 (0.1) 0.4 (0.1) 0.3 (0.1) 0.6 (0.1) 0.7 (0.1) 1.8 (0.2) N0 3- B - 0.6 (0.1) 0.7 (0.1) - 8.6 (0.5) 3.1 (0.6) S 0.4 (0.1) 0.4 (0.1) 0.4 (0.1) 1.7 (0.2) 1.7 (0.3) 2.6 (0.5) Extractable TJ 6 (0.5) 11 (1) 16 (1) 7 (1) 9 (2) 9 (6) P B - 11 (2) 12 (2) - 18 (5) 28 (7) S 3 (0.2) 7 (1) 7 (1) 5 (2) 9 (4) 11 (5) Table 9. oontd. Nutrient Contents (fcg/ha) D1 Mesic Control Ecosystems / Impact Low Class Moderate Subhygric Control Ecoystems Low / Impact Class Moderate Exchangeable U 63 (5) 93 (10) 108 (10) 121 (14) 158 (12) 172 (28) K B 77 (13) 97 (16) - 334 (64) 351 (70) S 21 (4) 15 (3) 18 (3) 29 (4) 59 (15) 53 (11) Exchangeable u 185 (33) 228 (28) 354 (34) 2907 (301) 4686 (369) 4422 (498) Ca B 261 (46) 404 (33) - 4477 (824) 5222 (959) S 73 (9) 171 (34) 259 (44) 832 (85) 1519 (346) 1336 (283) Exchangeable u 22 (2) 33 (4) 38 (3) 377 (40) 727 (57) 743 (69) Mg B 28 (5) 44 (8) - 645 (121) 805 (143) S 20 (2) 17 (3) 18 (3) 251 (26) 303 (64) 416 (88) Sampling date: U = unburned (Aug. 1983), B = post-burn (Oct. 1983), S » 9 mo. post-burn (May 1984). Mean (standard error of estimate). 77 decreases i n nutrient content (except Mg) i n the mesic forest f l o o r s as they were reduced to a greater degree by burning. Percentage losses were also much greater i n the mesic ecosystems, as the subhygric ecosystems have much greater mass and generally higher nutrient concentrations. There were further increases i n t o t a l Mg and decreases i n exchangeable K and t o t a l S contents nine months following burning i n the mesic p l o t s . This i s probably re l a t e d to the s i g n i f i c a n t changes i n the concentrations of these forms over t h i s time. Trends i n extractable NO3, NH4 and extractable P contents r e f l e c t the seasonal v a r i a b i l i t y i n concentrations of these l a b i l e nutrient forms. Trends i n other nutrient quantities were not c l e a r due to the high sampling error associated with s p a t i a l v a r i a t i o n i n nutrient concentrations, and i n forest f l o o r mass. Standard errors of estimates f o r nutrient contents i n the subhygric ecosystems were generally much larger than those f o r the mesic ecosystems because of greater forest f l o o r mass and high concentrations of elements such as Ca and Mg i n the subhygric ecosystems, making changes of s i m i l a r or lesser magnitude more d i f f i c u l t to detect. Losses of N and P from the forest f l o o r i n the mesic ecosystems (calculated i n terms of immediate post-burn nutrient content) were f a i r l y w e ll correlated with forest f l o o r depth-of-burn (DOB); changes i n P, S and K were well correlated with DOB i n the subhygric ecosystems (Table 10a). Changes i n S, K, and Ca were also well correlated with >8.0 slash reduction i n the subhygric ecosystems. Percent N, P and S losses were well correlated with percent DOB i n the mesic ecosystems; percent P, S, and K changes were well correlated with percent DOB i n the subhygric ecosystems (Table 10b). Table 10a. Correlations between forest floor nutrient content changes and forest floor depth reduotion and slash consumption. Correlation Coefficients (r) Change in Forest Floor Nutrient Content N P S X Ca Mg N F S K Ca Mg Mesic Ecosvstems Subhvt?ric Ecosvstems Forest Floor Seduction Depth 0.79 • 0. ,76 * 0. 41 0, .46 -0, .33 0, ,65 0. .63 0. .78 « 0.87 »» 0. ,88 "« 0. .64 0. 71 Slash Consumption Dy Diam. Class (cm) <l.O -0.34 0. ,18 -0 . 40 0, ,35 0. .35 0. ,33 -0, .48 -0. .46. -0.33 -0. .53 -0. .08 . -o-70 1.1-3.0 -0.63 -0. ,34 -0. 68 -0, .30 0, .26 -0. , 12 -0, ,30 -0. . 12 0.17 0, , 19 0. ,07 0. 02 3.1-5.0 -0.56 -0. ,33 -0. 34 -0. .30 -0, .34 -0. .36 -0. .58 -0. .35 0.06 -0. .06 0. . 16 -0 . 31 5.1-8.0 -0.23 -0. ,56 -0 . 07 -0, ,02 -0. ,25 0. ,00 0. ,01 0. ,24 0.51 0. ,59 0. ,31 0. 47 >8.1 0.33 -0. .06 0. 38 0. .05 -0. .44 0. .24 0. .57 0. .70 0.85 • 0. .77 * 0. .80 * 0. 57 Total 0.17 -0. 12 0. 12 0. , 17 -0. ,36 0. 32 0. ,30 0. ,47 0.72 0. ,56 0. ,77 * 0. 26 Table 10b. Correlations between percent changes in forest floor nutrient content with percent forest floor depth reduotion. Correlation Coefficients (r) Percent Change in Forest Floor Nutrient Content N P S K Mg Ca N P S K Ca Mg HeslC Ecosystems Subhygric Ecoflyatpms Percent Forest Floor Depth 0.93 ** 0.94 ** 0.96 0.64 0.36 0.73 0.63 0.77 * 0.88 ** 0.85 • 0.63 0.56 Seduction ** Signif icant at p < 0.01; * Significant and p < 0.05; n = 7. 79 Percent Mg and Ca losses i n the mesic ecosystems and N losses i n the subhygric ecosystems were much lower than percent forest f l o o r DOB which suggests that there were inputs or retention of these elements i n the forest f l o o r as well. 6.5 MINERAL SOIL NUTRIENT STATUS Nutrient concentrations and pH i n the mineral s o i l are given i n Table 11. The corresponding nutrient contents i n the mineral s o i l are given i n Table 12. There were no s i g n i f i c a n t changes i n pH or nutrient concentrations i n the mineral s o i l that could be a t t r i b u t e d to slashburning, up to 9 months following burning. As very l i t t l e mineral s o i l was exposed during burning i t i s u n l i k e l y that f i r e would have any d i r e c t e f f e c t s on t o t a l nutrient concentrations or contents. S o i l s were sampled immediately following burning before there was any s i g n i f i c a n t p r e c i p i t a t i o n and so i t i s u n l i k e l y that there would be any increases i n pH or concentrations of av a i l a b l e nutrients due to leaching of the ash through the forest f l o o r over t h i s period. However, some increases i n available nutrient concentrations were expected to occur over the nine month period following burning through leaching of ash. The trend i n increasing extractable P concentrations and contents nine months a f t e r burning i n the mesic ecosystems might have resulted from leaching, but was not s i g n i f i c a n t . The s i g n i f i c a n t v a r i a t i o n s i n the mean t o t a l N, C and S concentrations and contents and CEC i n the mineral s o i l of the subhygric ecosystems are not plausible and are probably due to v a r i a t i o n i n the organic matter content of samples at d i f f e r e n t sampling dates. The boundary between the lower H layer of the forest f l o o r and the upper Ah horizon of the mineral s o i l s i n the Table 11. Mineral s o i l pH and nutrient concentrations. Ecosystem D 1 _ T w i * \ a + -Control Low Moderate PH mesic U 4.9 (0.1 )[12]a 2 4.5 (0.1) [16]a 4.7 (0.1) [12]a B - 4.7 (0.1) [163a 5.0 (0.2) [12]a S 4.9 (0.1 )[12]a 4.6 (0.1) [16]a 4.8 (0.1) [12]a subhygric TJ 5.7 (0.1 )[12]b 5.8 (0.1) [16]b 5.9 (0.1) [12]b B - 5.9 (0.1) [16]b 5.9 (0.1) [12]b S 6.0 (0.1. )[12]b 6.1 (0.1) [16]b 6.0 (0.1) [12]b Total H mesic u 0.05 (o.oi; )[12]abed 0.05 (0.00) [16]a 0.07 (0.01) [12]a (%) B - 0.09 (0.01) [16]a 0.09 (0.00) [12]a S 0.08 (o.oi: )[12]a 0.07 (0.01) [16]a 0.08 (0.01) [12]a subnygric TJ 0.45 (0.04; [12]abed 0.33 (0.06) [16]abed 0.18 (0.02) [12]abed B - 1.05 (0.08) [16]cd 0.71 (0.11) [12]d S 0.61 (o.o6: [ l l ]ab 0.56 (0.04) [15]ab , 0.41 (0.05) [12]abc Organic mesic U 2.63 (0.25] [12]a 2.54 (0.28) [16]a 2.38 (0.16) [12]a Carbon B - 2.21 (0.14) [16]a 2.17 (0.10) [12]a (%) S 3.48 (0.17] [12]a 3.53 (0.16) [16]a 3.12 (0.30) [12]a subnygric TJ 12.10 (1.46] [12]bc 16.58 (2.17) [16]c 4.99 (0.80) [12]ab B - 28.99 (2.88) [16]c 12.76 (1.75) [12]bc S 18.82 d .68: [12]c 20.66 (1.69) [15]c 13.51 (1.67) [12]bc Total S mesic TJ 0.001 (o.ooo: [12]ab 0.004 (0.002) [16]abc 0 .008 (0.003) [12]abc (%) B - 0.001 (0.002) [16)a 0 .002 (0.001) [12]ab S 0.001 (o.ooo: [12]ab 0.003 (0.001) [16]abed 0 .000 (0.000) [12]a subhygric 0 0.008 (0.003: [12]abcde 0.032 (0.010) [16]de 0 .004 (0.003) [12]abc B - 0.052 (0.008) 16]e 0 .012 (0.004) [12]bcde S 0.025 (0.005: [12]de 0.018 (0.004) [16]cde 0 .009 (0.006) [12]abcde Extractable mesic TJ 16.2 (3.8: [9]abcde 9.8 (0.9) [15]ab 6.8 (0.1) [12]a N H 4 + (ppm) B - 11.1 (0.6) 16]abc 12.0 (1.0) [12]abed S 43.3 (1.9: [8]efg 44.5 (1.7) [ 1 6 ] e £ g 48.3 (2-0) [12]efg subhygric u 18.9 (3.1: [UJef 29.0 (4.2) [16]b-g 21.6 (2.8) [ l l ]a -g B - 47.7 (9.2) [12]efg 40.7 (6.8) [12]d-g S 61.1 (3.8: [ l l l e fg 63.6 (4.3) [16]fg 72.6 (6.7) [12]fg CO o Table 11. oontd. Ecosystem D1 Impact Class Control Low Moderate Extractable NO3 - (ppm) (ppm) mesic TJ B s 3.0 3.5 (0.4) (0.3 [ lUdef )[8]a-f subhygric TJ B S 0.7 (0.1) [Ilia 3.3 (0.3) [lljbc Anaerobic Mineralizable N (ppm) mesic D B S 16.5 77.5 (3.6) (6.5) [12]a [13]ab subhygric TJ B S 63.6 (8.1) [13]ab 331.6 (15.4) 16] cd Extractable P (ppm) mesic u B S 37.8 36.4 (3.5) (3.5) "13]abc 11]abc subhygric u B S 3.1 (0.6) 12] a 3.5 (0.3) 15]a Exchangeable K (meq/lOOg) mesic TJ B S 0.3 0.3 (0.0) (0.1) 12]a 13]a subhygric u B S 0.3 (0.0) 13]a 0.3 (0.0) 16]a Exchangeable Ca (meq/lOOg) mesic TJ B S 6.0 3.9 (1.1) (0.7) 13]a 13]a subhygric TJ B S 43.0 (3.3) 13]bc 5.7 (0.8) 16]c 3.5 (0.1) [15]ef 3. 7 (0. 2) [12]ef 4. 1 (0.2) [15]f 2. 7 (0. 3) 12]def 3.6 (0.1) [16]def 2. 5 (0. 1) [12]cdef 0.7 (0.1) [16]a 1. 2 (0. 2) [11]abc 3. 1 (0.2) Cl6]bc 3. 9 (0. 3) 12]def 1.5 (0.1) [16]abed 1. 6 (0. 10 [12]abed 5.0 (1.2) [13]a 5. 8 (1. 2) 12]a 5.5 (2.2) [12]a 8. 1 (3. 5) 12]a 44.7 (4.4) [16]a 51. 7 (6. 1) [12]ab 138.5 (37.3) [16]abc 33. 6 (10. 1) :i2]a 254.3 (33.6) [16]d 130. 9 (26. 5) 12]abed 186.4 (30.4) [15]cd 193. 3 (22. 3) [12]cd 63.4 (6.1) [16]cde 48. 2 (10. 1) [12]bcd 70.0 (3.0) [16]de 58. 3 (12. 1) 12]cde 93.1 (8.9) [16]e 80. 6 (11. 2) [12]de 3.7 (0.4) [16]a 1. 6 (0. 7) [12]a 9.9 (1.8) [15]ab 4. 7 (1. 1) 12] ab 1.3 (0.3) [15]a 3. 4 (0. 2) [12]a 0.3 (0.0) [16]a 0. 2 (0. 0) [12]a 0.3 (0.0) [16]a 0. 2 (0. 0) 12]a 0.3 (0.0) [12]a 0. 2 (0. 0) [12]a 0.4 (0.3) [16]a 0. 2 (0. 0) [12]a 0.4 (0.0) [16]a 0. 3 (0. 0) [12]a 0.3 (0.0) [16]a 0. 3 (0. 0) [8]a 3.3 (0.5) [16]a 3. 5 (0. 7) [12]a 3.6 (0.5) [16] a 3. 8 (0. 8) :i2]a 5.9 (0.1) [12]a 5. 9 (0. 1) [12]a 53.9 (6.6) [16]c 18. 7 (2. 2) [12]ab 85.1 (8.1) [16]d 41. 5 (5. 7) [12]bc 11.9 (1.9) [19]a 6. 9 (1. 1) [8]a Table 11. contd. Ecosystem D1 Control Impact Low Moderate Exchangeable mesic U 1 .5 (0.1)[12]ab 0. 8 (0.1)[16]a 1 .0 (0.2)[12]ab Mg (meq/lOOg) B - 0. 7 (0.2)[16]a 1 . 1 (0.2)[12]ab S 1 .1 (0.3)[12]ab 0. 5 (0.1)[12]a 0 .6 (0.1)[12]a subhygric u 9 .9 (0.6)[12]cde 15. 2 (1.6)[16]e 6 .6 (0.5)[12]abc B - 23. 1 (2.1)[16]f 13 .7 (1.2)[12]de S 5 .0 (0.7)[16]abc 7. 0 (0.2)[20]bcd 6 .6 (0.5)[8]abcd Cation mesic u 18 .2 (1.3)[12]a 16. 6 (0.5)[16]a 18 .2 (0.7)[12]a Exchange B - 16. 7 (0.5)[16]a 17 .6 (0.4)[12]a Capacity subhygric U 71 .0 (4.5)[12]bc 89. 3 (8.9)[16]b 32 .7 (2.9)[12]a B — 141. 7 (11.6)[16]c 71 .3 (7.2)[12]bc Sampling date: D = unburned (Aug 1983), B = post-burn (Oct. 1983), S = 9 mo. post-burn (May 1984). Mean (standard error) [no. composite samples]. For each variable, means followed by the same letter do not differ significantly at p < 0.05. Standard errors of 0.0 are less than or equal to 0.05. T a b l e 1 2 . M i n e r a l s o i l n u t r i e n t o o n t e n t s ( k g / h a ) . N u t r i e n t D Mes ic Ecosystems / Impact C l a s s Subhygr ic Ecosystems / Impact C l a s s C o n t r o l Low Moderate C o n t r o l Low Moderate T o t a l N U 752 ( 9 6 ) 2 569 (49) 961 (124) 3911 (796) 3566 (590) 1595 (360) B - 1076 (86) 1231 (96) - 7024 (968) 6121 (1518) s 1129 (104) 916 (103) 1109 (98) 5371 (1061) 3733 (500) 3546 (787) T o t a l S 0 8 (7) 43 (27) 50 (34) 70 (29) 212 (68) 33 (28) s - - 28 (18) - 348 (66) 108 (52) s 8 (6) 42 (12) 3 (2) 221 (55) 120 (28) 80 (40) E x t r a c t a b l e u 23 (6) 12 (1) 9 (1) 17 (4) 19 (27) 19 (4) NH4+ B 14 (1) 16 (2) - 32 (7) 35 (9) s 60 (5) 55 (4) 65 (5) 54 (10) 43 (6) 63 (5) E x t r a c t a b l e u 4 (0 .6 ) 4 (0 .3 ) 5 (0 .4 ) 0.6 ( 0 . 2 ) 0.5 ( 0 .1 ) 1 (0 .2 ) K 0 3 - B 5 ( 0 .4 ) 4 (0 .4 ) - 1 ( 0 . 2 ) 2 ( 0 .5 ) S 4 ( 0 .4 ) 3 ( 0 .2 ) 3 (0 .3 ) 2 ( 0 . 4 ) 1 ( 0 .1 ) 1 ( 0 .3 ) Anaerob ic u 23 (2) 18 (1) 8 (1) 55 (10) 86 (9) 28 (5) M i n e r a l i z a b l e B 32 (2) 11 (6) - 170 (17) 113 (21) N S 108 (7) 55 (3) 70 (4) 195 (34) 125 (13) 167 (32) E x t r a c t a b l e u 39 (6) 78 (9) 65 (14) 2 (1) 2 ( 0 .4 ) 1 ( 0 .7 ) P B 87 (11) 79 (17) - 7 (1) 4 (2) S 37 (6) 114 (13) 103 (17) 2 ( 0 . 4 ) 1 ( 0 .1 ) 2 ( 0 .4 ) Exchangeable 0 111 (11) 86 (7) 95 (7) 62 (11) 114 (40) 52 (11) K B 99 (8) 95 (7) - 100 (14) 95 (20) S 153 (34) 123 (9) 122 (11) 70 (13) 74 (8) 95 (20) Exchangeable V 1672 (333) 569 (126) 933 (187) 7374 (1141) 7084 (1149) 3242 (773) Ca B 656 (139) 1014 (234) - 11379 (1591) 7204 (1692) S 808 (196) 1460 (91) 1596 (314) 1002 (243) 1900 (326) 971 (240) Exchangeable u 251 (33) 111 (20) 202 (30) 1037 (190) 1224 (178) 685 (142) Mg B 99 (22) 189 (40) - 1853 (255) 1422 (300) S 181 (23) 79 (13) 108 (17) 527 (127) 568 (62) 642 (127) Sampl ing da te : U = unburned (Aug. 1983), B = pos t -bu rn (Oct . 1983), S = 9 mo. p o s t - b u r n (May 1984). Mean ( s tandard e r r o r of e s t i m a t e ) . 84 subhygric ecosystems was i n d i s t i n c t and so consistent sequential sampling of the upper mineral s o i l was d i f f i c u l t . Decreases i n exchangeable Ca and Mg i n the subhygric ecosystems nine months following burning were possibly due to a difference i n the a n a l y t i c a l methods used with samples taken at t h i s time ( c f p. 41). There was s i g n i f i c a n t v a r i a t i o n i n extractable NH4 and NO3 and mineralizable N concentrations i n both ecosystems between sampling times. This may have been due to seasonal v a r i a t i o n i n l a b i l e N forms as was suggested f o r the forest f l o o r . Mineral s o i l s i n the subhygric ecosystems had s i g n i f i c a n t l y greater pH and organic carbon, and exchangeable Ca and Mg concentrations than d i d the mesic ecosystems before slashburning, though extractable P concentrations were s i g n i f i c a n t l y higher i n the mesic ecosystem mineral s o i l s . The subhygric ecosystem mineral s o i l had lower bulk densities, but s u b s t a n t i a l l y greater t o t a l N and S, mineralizable N and exchangeable Mg and Ca contents than d i d the mesic ecosystem mineral s o i l s . Mineral s o i l extractable NO3 and P contents were much higher i n the l a t t e r ecosystem; extractable NH4 and exchangeable K contents were quite s i m i l a r i n the mineral s o i l s i n both ecosystems. The destructive sampling technique used i n the present study was probably not very sen s i t i v e to changes i n nutrient concentrations which might be expected to occur through leaching or mineralization, due to inherently high s p a t i a l v a r i a b i l i t y i n s o i l nutrient concentrations. Lysimetric or i o n exchange r e s i n techniques may be more sens i t i v e to changes i n dissolved nutrients i n the s o i l solution, but they can not be r e a d i l y used to determine the changes i n t o t a l or extractable forms i n the bulk s o i l which i s considered to be important to long-term nutrient a v a i l a b i l i t y . The 85 destructive sampling technique was even l e s s s e n s i t i v e i n the subhygric ecosystems where nutrient concentrations were higher, and so small changes l e s s e a s i l y detected. Greater v a r i a t i o n i n s o i l morphology i n the subhygric ecosystems may also have contributed to greater v a r i a t i o n i n chemical properties. 6.6 ORGANIC MATTER AND NUTRIENT DISTRIBUTION Total nutrient contents i n the slash, forest f l o o r and mineral s o i l are shown i n Figs. 15 a-f. Before burning, the forest f l o o r contained greater amounts of N, P, S and K than d i d the mineral s o i l (0-15 cm depth), or the slash i n the mesic ecosystems. Following burning, the mineral s o i l contained the greatest amounts of a l l elements. In the subhygric ecosystems, the forest f l o o r contained greater amounts of P, S, K, and Mg, and the mineral s o i l greater amounts of N and S both before and a f t e r burning. However, few f i n e roots were observed i n the mineral s o i l i n the subhygric ecosystems, so nutrients i n these horizons are probably not available to plants. 6.6.1 Organic Matter Consumption and Nutrient Loss t o the Atmosphere To t a l organic matter reduction and nutrient losses to the atmosphere due to slashburning are summarized i n Table 13. Most of the t o t a l organic matter consumption occurred from the coarse slash (>8.0 cm), f i n e slash and the forest f l o o r . In the mesic ecosystems, t o t a l organic matter consumption was well correlated with coarse and t o t a l slash consumption and pre-burn t o t a l organic matter load, while i n the subhygric ecosystems i t was also well correlated with these variables and with forest f l o o r consumption (Table 14). This suggests that there was a uniformly high f i n e slash consumption i n both ecosystems, i r r e s p e c t i v e of t o t a l organic matter consumption, as l t was poorly correlated with t o t a l consumption. 86 Figs. 15 a-f. D i s t r i b u t i o n of nutrient content among the slash, forest f l o o r , and mineral s o i l (0-15 cm) i n the mesic and subhygric ecosystems before (pre) and a f t e r (post) slashburning.* 9000 Pre Post Pre Post Pre Post Pre Poet Low Moderate Low Moderate Mesic Subhygric F i g . 15b. D i s t r i b u t i o n of t o t a l P i n the slash and forest f l o o r and extractable P i n the mineral s o i l . * Slash and forest values were from Table 5; mineral s o i l values were the average of the three sampling times i n Table 12. 87 Pre Post Moderate Mesic Subhygric 15c. D i s t r i b u t i o n of t o t a l S. 500 400 j ? 300 CO o Q. 200 100 -Slash ^ \ Forest Floor Mineral Soil Pre Post Pre Post Pre Post Pre Post Low Moderate Low Moderate Mesic Subhygric 15d. D i s t r i b u t i o n of t o t a l K i n the slash and forest f l o o r and exchangeable K i n the mineral s o i l . 88 9000 8000 7000 J_ 6000 V. _? 5000 J 4000H o rt 3000 o 2000 1000 0 Slosh Forest Floor Minerol Soil Pre Post Pre Post Pre Post Pre Post Low Moderate Low Moderate Mesic Subhvaric 15e. D i s t r i b u t i o n of t o t a l Ca l n the slash and forest f l o o r and exchangeable Ca i n the mineral s o i l . 6000 5000 4000 cn I 3000 'co CD §> 2000 CO 2 1000 Slosh S ^ S Forest Floor /y Mineral Soil Pre Post Low Pre Post Moderate Pre Post Low Pre Post Moderate Mesic Subhygric 15f. D i s t r i b u t i o n of t o t a l Mg i n the slash and forest f l o o r and exchangeable Mg i n the mineral s o i l . Table 13. Summary of organic matter and n u t r i e n t losses to the atmospere due t o slashburning, Component Organic Nutrient Content (kg/ha) Load. (kg/m2) N P S K Low Impact Class Ca Hg Organic Load (kg/m 2) N Nutrient Content (kg/ha) P S K Ca Hg Moderate Impact Class Slash Loss 1 % of Total Loss Forest Floor Loss 2 % of Total Loss Organic Components Total Loss % Loss % Ecosystem Loss 3 Slash Loss % of Total Loss Forest Floor Loss % of Total Loss Organic Components Total Loss % Loss % Ecosystem Loss Mesic Ecosystems 6.8 166 22 38 33 199 18 9.5 170 21 39 45 224 18 74 35 44 44 61 97 69 76 26 38 44 64 77 900 2.4 307 28 48 21 5 8 2.9 487 35 50 25 67 + 17 4 26 65 56 56 39 2 31 23 74 62 56 36 23 -9.2 472 50 86 54 205 26 12.5 657 56 89 70 291 2 46 44 40 56 38 37 34 51 46 36 52 41 38 2 CO - 25 23 44 22 14 15 - 26 24 45 26 15 1 CD Subhygric Eco systems 7.3 214 30 47 40 251 22 11.4 214 29 49 32 274 17 82 70 64 72 250 108 17 78 58 51 58 48 120 7 1.6 93 17 18 +24 + 19 110 3.2 158 28 36 28 +45 222 18 30 36 26 - - 83 22 42 49 42 42 - 93 8.9 307 47 65 16 232 132 14.6 372 57 85 66 229 239 22 9 14 13 6 6 15 32 9 12 16 20 5 27 - 4 14 10 4 2 6 - 5 12 14 16 3 12 mineral so i l 1 X-antities (0--15 cm depth) from Table 12. Mineral £ .o i l P, K, Ca, and Hg 2 From Table 2. From Table 8. quantities were extractable or exchangeable forms. 4 ( + ) represents a net gain in nutrient content. Table 14. Correlations between total organic matter loss and component consumption and total organic matter load. C o r r e l a t i o n C o e f f i c i e n t s ( r ) Forest Floor Slash Consumption by Diam. Class (cm) — T o t a l Organic Consumption Hatter Load <1.1 1.1-3.0 3.1-5.0 7.1-8. .0 >8.0 Total T o t a l Organic -0.08 -0.88 Hesic Ecosystems 0.05 -0.48 0.73 0.94 ** 0.98 0. .78 * Hatter Subhygric Ecosystems Loss 0.90 *• 0.08 0.48 0.88 0.69 0.90 ** 0.99 ** 0. .86 * *» S i g n i f i c a n t at p < 0.01; * S i g n i f i c a n t at p < 0.05; n = 7. 91 Total nutrient losses followed the order N > Ca > S > K > P > Mg i n the mesic ecosystems and N > Ca > Mg > S > P, K i n the subhygric ecosystems. Percentage losses followed the order S > N > P, K > Ca > Mg i n the mesic ecosystems; no consistent trend was evident i n the subhygric ecosystems. The t o t a l and percentage losses of Mg from the subhygric ecosystems were suspiciously high -they were l a r g e l y due to the high forest f l o o r Mg lo s s estimates, which may have been due i n part to the sampling error discussed previously. When the mineral s o i l was included i n the evaluation, percentage losses were generally much lower, with the exception of S i n the mesic ecosystems, as the mesic ecosystem mineral s o i l S content i s low. In the mesic ecosystems, percent t o t a l N, P, K and Ca losses approached unity with percent organic matter lo s s , percent S losses were somewhat higher, and percent Mg losses somewhat lower. The higher percentage losses were probably due to the high nutrient d i s t r i b u t i o n i n the f i n e slash, which was l a r g e l y consumed. Percentage losses of a l l elements were generally lower than unity i n the subhygric ecosystems where coarse slash accounted fo r a greater proportion of t o t a l organic matter l o s s . Nutrient losses from the forest f l o o r and f i n e slash accounted fo r the greatest proportion of t o t a l nutrient losses. However, t o t a l nutrient losses were well correlated with forest f l o o r depth reduction i n the mesic ecosystems and t o t a l mass and large and t o t a l s lash consumption and forest f l o o r depth reduction i n the subhygric ecosystems (Table 15a). Total nutrient losses as a percentage of pre-burn quantities were best correlated with the percentage forest f l o o r reduction and (with the exception of Mg i n the mesic ecosystems and Mg and Ca i n the subhygric ecosystems) percentage organic matter reduction (Table 15b). This suggests Table 15a. Correlations between total nutrient loss and slash consumption and forest floor depth reduction. Correlation Coefficients (r) Consumption Total Nutrient Loss by Component Mesic Ecosystems Subhygric Ecosystems N P S K Mg Ca N P S K Mg Ca Slash Diam. Class (cm) <1.1 0.02 0.61 0. 61 0. 48 0.41 0.58 -0.10 -0.07 0.17 -0. .16 -0.01 -0. .56 1.1-3.0 -0.66 -0.89 -0. 58 -0. 18 0.87 0.04 0.00 0.16 0.53 0. .49 0.11 0. . 19 3.1-5.0 -0.71 -0.61 -0. 55 -0. 35 0.15 -0.43 -0.88 -0.07 0.43 0. .84 0.80 -0. .05 5.1-8.0 -0.84 -0.56 0. 05 0. 81 -0.33 0.88 0.18 0.38 0.66 0. .75 * 0.38 0. .61 >8.1 0.89 -0.84 0. 06 0. 16 -0.48 0.29 0.57 0.67 0.74 0. .69 0.78 * 0. .68 Total 0.83 -0.11 0. 38 0. 38 -0.35 0.54 0.51 0.65 0.89 0. .69 0.78 » 0. .39 Forest Floor Depth 0.76 * Seduction 0.59 0. 04 0. 16 -0.17 0.18 0.66 0.76 * 0.78 • 0. .86 ** 0.63 0. ,77 Total Organic Load 0.41 0.08 0. 36 0. 36 -0.34 0.56 0.56 0.70 0.87 ** 0. .78 0.78 * 0. .47 ** Significant at p < 0.01; * Significant at p < 0.05; n ° 7. T a b l e 15b. C o r r e l a t i o n s between p e r c e n t t o t a l n u t r i e n t l o s s and p e r c e n t o r g a n i c m a t t e r r e d u c t i o n . Correlation Coefficients (r) Percent Percent Total Nutrient Loss Consumption by Component Mesic Ecosystems Subhygric Ecosystems N P S K Mg Ca H P S K Mg Ca Slash Diam. - Class (cm) < 1.1 0. 30 0. 32 0.08 -0. 22 0. .42 1.1-3.0 -0. 38 -0. 69 -0.61 -0. 38 -0. .82 * 3.1-5.0 -0. 17 -0. 25 -0.00 -0. 20 0. . 17 5.1-8.0 -0. 62 -0. 61 -0.47 -0. 37 -0. .38 >8.1 0. 15 0. 05 0.01 0. 36 -0. 52 Total 0. 49 0. 42 0.61 0. 86 * 0. 04 Forest Floor Depth 0. 95 ** 0. 94 ** 0.87 » 0. 54 0. 62 Seduction Total Organic Load 0.81* 0.74* 0.88** 0.90** 0.33 0.09 0.46 0.40 0.11 0.52 -0.58 0.51 0.69 0.64 0.66 0.49 0.67 -0.44 0.46 0.26 -0.16 0.06 0.08 -0.17 0.13 -0.22 0.32 0.19 0.29 0.53 0.61 0.30 0.70 0.27 0.19 0.02 0.38 0.20 0.52 0.10 0.70 0.26 0.30 0.32 -0.06 0.05 -0.46 0.78 * 0.66 0.61 0.83 * 0.79 * 0.61 0.61 0.91 ** 0.73 0.74 * 0.90 ** 0.66 0.58 0.28 ** Significant at p < 0.01; * Significant at p < 0.05; n = 7. 94 that although t o t a l nutrient losses w i l l increase with Increasing f i r e severity, there w i l l probably be substantial nutrient losses from the f i n e slash even i n very low severity burns where l i t t l e of the forest f l o o r i s consumed. As f i r e severity increases, a d d i t i o n a l nutrient losses w i l l occur mainly from the forest f l o o r . Although d i r e c t nutrient losses from coarse woody f u e l s were minimal, increased reduction of coarse woody f u e l s may cause increased forest f l o o r reduction and so nutrient l o s s . This hypothesis l s supported by L i t t l e and Klock's (1985) f i n d i n g that t o t a l N and S losses were lower due to harvest and slashburning i n settings where high timber u t i l i z a t i o n s were used than i n settings where lower u t i l i z a t i o n standards were employed, which they at t r i b u t e d to lower f u e l loads and l e s s forest f l o o r reduction during burning i n the higher u t i l i z a t i o n settings. Hypothetical rel a t i o n s h i p s between slash and forest f l o o r consumption and t o t a l organic matter consumption and between the l o s s of v o l a t i l e nutrients from the slash and forest f l o o r with increasing t o t a l organic matter consumption are shown i n Figs. 16 and 17. Losses of N i n the present study are 4-5 times higher than losses reported from slashburns i n Norway spruce-Scots pine f o r e s t s (Viro 1969; Braathe 1974), though comparable to N l o s s estimates from slash burns i n Douglas-fir ( L i t t l e and Klock 1985) and somewhat lower than N losses reported from slashburns i n western hemlock - western red cedar forests ( F e l l e r g£ aj,. 1983) given i n Table 16; the Scandinavian studies d i d not include the slash i n nutrient l o s s estimates. Losses of N and P from the mesic ecosystems i n t h i s study were greater than losses that might r e s u l t from whole-tree harvesting of spruce-fir stands (Kimmins 1974), though K and Ca losses were lower and Mg losses were s i m i l a r . 95 £ T O T A L O R G A N I C M A T T E R C O N S U M P T I O N O Figure 16. Hypothetical re l a t i o n s h i p between slash and forest f l o o r consumption and t o t a l organic matter consumption. 96 L E G E N D I | S L A S H > 1.0 cm DIAM. U j S L A S H s= 1.0 cm DIAM. 4 H F O R E S T FLOOR h-TOTAL ORGANIC L A Y E R C O N S U M P T I O N - • Figure 17. Hypothetical relationship between the l o s s of v o l a t i l e nutrients from the slash and forest f l o o r and t o t a l organic matter consumption. Table 16. Organic matter and nutrient losses r e s u l t i n g from f i r e and o l e a r o u t t i n g in seleoted fores t types. Disturbance: Forest type Organic Matter Loss (kg/m a ) N Nutr ient Loss (kg/ha) -S K Ca Mg Others Slashburning: White spruce/subalpine f i r ( th i s study) mesic subhygric Norway spruce/scotch pine (Skoklefa ld 1973; Braathe 1974)* (Viro 1969)* Western hemlock/western red cedar ( F e l l e r ejfc. &1. 1983) Doug las - f i r (Isaac and Hopkins 1937)* ( L i t t l e and Klock 1985) 10x120! 15X1801 Douglas- f ir /western larch (Jurgensen e_fc. aj.. 1981)* Radiata pine ( F l i n n e_t aJL. 1969) Mixed euca lyptus /ra infores t (Harwood and Jackson 1975) W i l d f i r e : Doug las - f i r (Gr ier 1975)* Pnderburninff: Ponderosa pine (Klemmedson e_fc. s_L. 1962)* (Niss ley e_t &1. 1980)* (Covington and Sackett 1984)* 11.1 11.3 1.1 15.8 12.5 13.3 10.2 6.7 29.5 1.3 0.6 2.6 563 242 160 100 982 488 490 397 493 106 220 907 139 110 79 55 33 16 8 10 + 1 87 48 8 2 16 60 30 37 17 21 51 308 + 1 252 125 154 37 123 100 75 20 16 136 29 7 13 37 33 698 (Na) + 1 Table 16. contd. Disturbance: Forest type Organio Matter Loss (kg/nr) N Nutrient Loss (kg/ha) -S K Ca Mg Others C l e a r o v i t t i n g : White spruce - subalpine f i r (Kimmins 1974) 10 cm top whole-tree 150 324 16 42 114 150 359 537 21 31 Lodgepole pine (Kimmins 1974) 10 cm top whole-tree 101 155 13 20 97 111 215 247 37 43 Red spruce - balsam f i r (Weetman & Webber 1972) 8 cm top whole-tree 79 387 11 52 47 159 150 413 14 36 CD Co Black spruce (Weetman & Webber 1972) 8 cm top whole-tree 43 167 12 42 25 84 98 277 8 27 Douglas-fir ( L i t t l e and Klock 1985) 10x120! 49.2 15x180! 57.2 443 525 116 102 * Only changes in the forest f l o o r were examined. + Represents a gain i n nutrient content i n the forest f l o o r . ! Dimensions of the largest log (cm) l e f t remaining. 99 6.7 SPRUCE SKKMI.TNG GROWTH AND NDTRIENT STATUS The svirvival and growth of the spruce seedlings i n the f i r s t season following planting i s given i n Table 17. There was a s i g n i f i c a n t i n t e r a c t i o n between the e f f e c t s of f i r e impact l e v e l and ecosystem type with respect to seedling s u r v i v a l . In the subhygric ecosystems, s u r v i v a l was s i g n i f i c a n t l y lower i n the burned p l o t s than i n the control plots, while i n the mesic ecosystems slashburning d i d not s i g n i f i c a n t l y e f f e c t s u r v i v a l . There was also s i g n i f i c a n t l y greater s u r v i v a l i n the burned mesic p l o t s than i n the burned subhygric plots, although there was no s i g n i f i c a n t difference between seedling s u r v i v a l i n the unburned mesic and subhygric p l o t s . Height increment and r e l a t i v e height growth rate were both s i g n i f i c a n t l y greater i n the burned p l o t s than i n the control p l o t s i n both mesic and subhygric ecosystems and increased s i g n i f i c a n t l y with f i r e Impact l e v e l i n the subhygric ecosystems; f i r e impact l e v e l d i d not have a s i g n i f i c a n t e f f e c t on height growth i n the mesic ecosystems. These r e s u l t s are consistent with those of Endean and Johnstone (1974), McMlnn (1982) and B a l l a r d (1985) who also found greater e a r l y height growth of spruce seedlings on slashburned s i t e s than on adjacent unburned s i t e s . Though the increase i n height growth on the burned p l o t s was of l i t t l e p r a c t i c a l s i g n i f i c a n c e i n the f i r s t year, small i n i t i a l differences i n plant s i z e may increase over time. Even i f i n i t i a l differences i n height growth do not p e r s i s t , more rapi d e a r l y height growth may be h e l p f u l i n establishing plantations before competing vegetation becomes well established. Though height growth was better i n the burned areas, i t was Table 17. Survival and growth of spruce seedlings i n the f i r s t year following outplanting. Mesic Ecosystems / Impact Class Subhygric Ecosystems / Impact Class Control Low Moderate Control Low Moderate Survival (%) 94.9(22.1)[98]a198 .5(12.3)[196]a 95.9(19.8)[148]a 95.2(24.4)[147]a 86.2(34.6)[196]b 83.7(37.1)[147]b Height Increment(cm). 0.9 (1.5)[93]a 3 .6 (1.5)[193]e 3.7 (1.6)[142]e 1.6 (2.2 [141]b 2.2 (2.0)[169]c 2.9 (2.3)[123]d Relative Height Growth Bate 0.049(0.083)a 0.219(0.096)6 0.828(0.105)6 0.093(0.128)1) 0.147(0.140)c 0.184(0.149)d Mean (standard error) [no. of sample trees]. Means followed by the same letter do not differ significantly at p<0.05. 101 s t i l l poor i n r e l a t i o n to the p o t e n t i a l of bareroot spruce planting stock, and much below the p o t e n t i a l of container spruce stock found by Burdett fit aJL. 1984. The buds on many trees d i d not f l u s h at a l l a f t e r planting and those which flushed produced small awl-shaped needles with short stem units. These t y p i c a l symptoms of planting check are often seen i n bareroot spruce stock and may be associated with low root growth capacity (Burdett gt a l . 1984). The container-grown spruce seedlings which were operationally-planted outside of the sample p l o t s appeared to be growing much better than adjacent bareroot seedlings, and also appeared to be growing much better than container stock planted i n the control area. This suggests that there may be a p o s i t i v e i n t e r a c t i o n between slashburning and stock type with respect to the e a r l y growth of planted seedlings. Planting stock with good vigour and growth po t e n t i a l may be better able to respond to favourable environmental conditions and more resist a n t to environmental stresses i n burned areas. B a l l and Kolabinski (1986) found comparable s u r v i v a l but better e a r l y height growth i n 2+2 bareroot than i n container-grown white spruce seedlings growing on slashburned s i t e s i n Saskatchewan. This was a t t r i b u t e d to greater i n i t i a l s i z e of the bareroot stock, an important factor In growth po t e n t i a l . Nutrient concentrations i n the current years' f o l i a g e of the spruce seedlings at the end of the f i r s t growing season following planting are given i n Table 18. F o l i a r N, P, and S concentrations were much higher than c r i t i c a l l e v e l s suggested by B a l l a r d and Carter (1986). Seedling f o l i a r N and P concentrations were somewhat lower i n the burned p l o t s i n both ecosystems. Lower N and P concentrations on the burned p l o t s may be due i n part to a d i l u t i o n e f f e c t , as height increment and probably f o l i a g e increment were also Table 18. Nutrient concentrations in the current foliage of spruce seedlings one season following outplanting. Mesic Ecosystems / Impact Class Subhygric Ecosystems / Impact Class Control Low Moderate Control Low Moderate n 1 2 4 3 3 4 3 % N 2.973 (0. 071) 2 2. 781 (0. 084) 2. 947 (0. 107) 2. 961 (0. 111) 2. 842 (0.115) 2. 729 (0.091) % P 0.650 (0. 002) 0. 532 (0. 005) 0. 560 (0. 006) 0. 655 (0. 010) 0. 579 (0.039) 0. 534 (0.008) % S 0.124 (0. 018) 0. 155 (0. 016) 0. 186 (0. 004) 0. 137 (0. 004) 0. 178 (0.016) 0. 144 (0.015) % K 0.146 (0. 030) 0. 305 (0. 104) 0. 186 (0. 020) 0. 153 (0. 051) 0. 181 (0.040) 0. 161 (0.016) % Ca 0.080 (0. 043) 0. 109 (0. 022) 0. 140 (0. 005) 0. 171 (0. 093) 0. 192 (0.030) 0. 116 (0.049) % Mg 0.037 (0. 018) 0. 042 (0. 008) 0. 054 (0. 002) 0. 026 (0. 004) 0. 060 (0.003) 0. 044 (0.014) H:P 4. .6 5.2 5. .3 4.5 4.9 5.1 K:S 24. .0 17.9 15. .8 21.6 16.0 19.0 K/Ca 1. .8 2.8 1. .3 0.9 0.9 1.4 Ca/Mg 2. .2 2.6 2. .6 6.6 3.2 2.6 Ko. of composite samples. Mean (standard error). 103 greater i n the burned pl o t s . However K concentrations i n the subhygric ecosystems suggest moderate to severe d e f i c i e n c i e s while Ca concentrations i n the mesic ecosystems were s l i g h t l y to moderately d e f i c i e n t . F o l i a r Mg concentrations were moderately to severely d e f i c i e n t i n both ecosystems and were lower i n the unburned pl o t s . F o l i a r S, K and Mg concentrations were higher i n seedlings growing i n burned p l o t s i n both ecosystems; f o l i a r Ca was also higher i n the burned p l o t s i n the mesic ecosystems. However i n the subhygric ecosystems, f o l i a r Ca concentrations were higher i n the low impact burn p l o t s than i n the unburned plots, but were lower i n the moderate impact burn p l o t s than i n the unburned p l o t s . The higher f o l i a r S, K, Mg and Ca concentrations i n the burned p l o t s suggest that slashburning may have resulted i n increased a v a i l a b i l i t y and uptake of these elements, e s p e c i a l l y as they are appear to be associated with higher concentrations i n the s o i l following burning and probably greater f o l i a g e increment. The f o l i a r P and K concentrations i n these seedlings were higher and lower, respectively, than i n any of the 20 spruce plantations sampled by B a l l a r d (1984). However, P and K concentrations were s i m i l a r to those found by Swan (1971) i n white spruce seedlings growing i n the greenhouse with a very low K supply and adequate N and P, and so are not p h y s i o l o g i c a l l y impossible. The very low K concentrations i n the present study may be due to poor nutrient uptake or movement i n the stressed seedlings, while high N and P concentrations may be due to a carry-over from the nursery, as nursery-grown seedlings commonly have very high f o l i a r nutrient concentrations. 104 7. CONCLUSIONS AND RECOMMENDATIONS The following conclusions were reached from t h i s study: 1. Nutrient losses from both mesic and subhygric ecosystems i n t h i s low to moderate impact burn were substantial and increased with f i r e severity. 2. Nutrient losses occurred primarily from the f i n e slash and the forest f l o o r . Nutrient losses from the f i n e s l a s h w i l l probably be high even i n low impact f i r e s , as most of the f i n e slash w i l l s t i l l be consumed. Losses of most nutrients from the forest f l o o r w i l l probably increase with f i r e severity. In p l o t s i n the mesic ecosystems which received moderate impact burns, and plo t s i n the subhygric/hygric ecosystems which received low and moderate impact burns, net gains i n forest f l o o r Mg, K , and K and Ca content, respectively, were found. 3. Nutrient losses from the mesic ecosystems were higher than from the subhygric ecosystems on both a t o t a l and percentage basis. In the mesic ecosystems, losses were greatest f o r N, Ca and S on a t o t a l basis, and f o r S, N, and P on a percentage basis. In the subhygric ecosystems, losses were greatest f o r N, Ca, and Mg on a t o t a l basis; no trends were apparent i n percentage nutrient l o s s from the subhygric ecosystems. 4. Forest f l o o r pH and Mg content increased i n the mesic ecosystems nine months following burning, while extractable K and t o t a l S contents decreased i n the low impact burn p l o t s i n both ecosystems. There were few s i g n i f i c a n t changes i n nutrient concentrations or contents i n the mineral s o i l s i n both ecosystems that could be attributed t o slashburning. 105 5. The technique of destructive sampling of bulk s o i l was not se n s i t i v e to changes i n forest f l o o r mass caused by burning, due to the high s p a t i a l v a r i a t i o n i f forest f l o o r mass. The technique acquire was also not very sen s i t i v e to changes i n nutrient concentrations caused by burning i n the subhygric ecosystem forest f l o o r s , and i n the mineral s o i l s i n both ecosystems, due to the high s p a t i a l v a r i a b i l i t y i n s o i l nutrient concentrations. Equations to predict nutrient l o s s were not developed i n t h i s study due to the r e l a t i v e l y few number of sample p l o t s and narrow range of burn impacts that were examined. However, i f i t i s assumed that 100% of v o l a t i l e nutrients such as N, P, and S, are l o s t during combustion, rough estimates of the l o s s of these elements may be made from f u e l consumption predictions and the concentrations reported i n t h i s study. Increases i n pH, and i n the quantities of some cations i n the forest f l o o r , coupled with increases i n s o i l temperature following burning, may provide an increase i n s i t e f e r t i l i t y i n the short-term, though pH increases may reduce the a v a i l a b i l i t y of micro-nutrients such as Fe and Cu. However, the long-term e f f e c t of nutrient losses from the ecosystem on nutrient a v a i l a b i l i t y and forest productivity cannot currently be determined or predicted with any confidence from these data. Nevertheless, the l i t e r a t u r e does suggest that there i s a threshold l e v e l of f i r e impact and associated nutrient l o s s that adversely e f f e c t s long-term nutrient a v a i l a b i l i t y and forest productivity i n some ecosystems ( c f Skoklefald 1973; Braathe 1974; Viro 1969). In other ecosystems i n the Sub-Boreal Spruce zone, B a l l a r d (1985, 1987) has found a higher 106 frequency of f o l i a r nutrient d e f i c i e n c i e s , but better growth on slashburned s i t e s , which he attributed to higher s o i l temperatures following slashburning. I t i s possible that nutrient d e f i c i e n c i e s on some of these ecosystems may l i m i t growth l a t e r i n plantation development. An economic evaluation of the s i g n i f i c a n c e of slashburning e f f e c t s i s precluded by the lacking of empirical growth data. However, uncertainty as t o the long-term e f f e c t of nutrient losses on the growth of plantations implies r i s k . As nutrients losses increase with f i r e severity, i t follow that the r i s k of p r o d u c t i v i t y impairment also increases with f i r e severity. The r i s k of nutrient impairment w i l l be higher i n ecosystems where nutrient s are p r i m a r i l y d i s t r i b u t e d i n the above-ground vegetation or slash, and i n the forest f l o o r , and higher fo r p a r t i c u l a r nutrients which are predominantly d i s t r i b u t e d i n these components. Results of the present study suggest that the r i s k of nutrient impairment i s much greater i n the mesic ecosystems than i n the subhygric ecosystems, and that the r i s k i n the mesic ecosystems i s greatest f o r impairment f o r N, P and S a v a i l a b i l i t y . The l e v e l of r i s k perceived i s influenced by assumptions about the proportion of the ecosystem nutrient c a p i t a l that can be exploited by plants - nutrient losses are l e s s s i g n i f i c a n t i f more of the s o i l p r o f i l e i s considered to be available. However, nutrient losses from some f u e l components which may be part of a more r a p i d l y c y c l i n g pool (such as from the f o l i a g e i n the f i n e slash) may be more s i g n i f i c a n t than t h i s evaluation would indicate. A better understanding of nutrient c y c l i n g processes and t h e i r r e l a t i o n t o the productivity of white spruce/sub-alpine f i r ecosystems w i l l be required i n order to better evaluate the 107 s i g n i f i c a n c e of changes i n ecosystem nutrient status caused by slashburning. Kimmins (1977) summarized several questions that are important to evaluating the significance of nutrient l o s s e s i n whole-tree logging to future forest productivity. Similar questions would be involved i n a more dynamic evaluation of the e f f e c t s of slashburning on nutrients and t h e i r s i g n i f i c a n c e to future forest productivity. 1. What proportion of the s i t e nutrient c a p i t a l i s removed i n slashburning? 2. How r a p i d l y does the remaining s i t e nutrient c a p i t a l cycle? How available i s i t to plants? 3. How r a p i d l y are losses from either the t o t a l or a v a i l a b l e nutrient pools replenished and by what mechanisms? Are these mechanisms affected by slashburning? 4. What w i l l be the nutrient requirements of future stands? How w i l l nutrient demands vary during stand development? 5. What i s the magnitude of other harvest-induced nutrient losses? 6. How frequently w i l l slashburning occur? What i s the r o t a t i o n length? This study has only addressed the f i r s t question. As quantitative data on nutrient c y c l i n g processes from northern forests i s l i m i t e d and the e f f e c t s of burning on such processes i s l a r g e l y unknown, much additional work i s needed. In addition, the e f f e c t s of nutrient changes due to burning on tree growth need to be quantified through further study. 7.1 FOREST MANAGEMENT CONSIDERATIONS The use of slashburning has increased dramatically i n the 108 Sub-Boreal Spruce zone i n the l a s t 20 years (Fig. 1). The amount of slashburning that i s c a r r i e d out with p a r t i c u l a r areas of the zone depends on several factors: l o c a l conditions that necessitate or enable i t s use, the l e v e l of expertise and tolerance of the r i s k of escape amongst pr a c t i t i o n e r s , the a v a i l a b i l i t y and p r a c t i c a l i t y of a l t e r n a t i v e s i t e preparation techniques, custom, and the pattern of forest tenure and l e v e l of forest management r e s p o n s i b i l i t y . Slashburning i s prescribed where i t i s perceived to be necessary to reduce slash and/or vegetation and forest f l o o r depths i n order to e s t a b l i s h a plantation or reduce the f i r e hazard. Some slashburning objectives such as hazard abatement, increased p l a n t a b i l i t y or s a n i t a t i o n can probably be met with low severity burns which w i l l reduce most of the f i n e slash. Other objectives of slashburning such as increased s o i l temperatures and reduced vegetation competition may require burns of greater severity, depending on ecosystem type. Threshold l e v e l s of f i r e impact that are required to achieve management goals have not been quantified f o r ecosystems i n the SBS zone. However, i n the mesic bunchberry-feathermoss ecosystems i n the present study with moderately deep forest f l o o r s (6-12 cm) and moderate vegetation competition potential, low to moderate severity burns w i l l probably increase p l a n t a b i l i t y , reduce f i r e hazard, and may provide small increases i n s o i l temperature and vegetation control. In the subhygric/hygric h o r s e t a i l and Devil's club ecosystems i n the present study, with deep forest f l o o r s and moderate t o high vegetation competition p o t e n t i a l , moderate to high s e v e r i t y burns w i l l probably be required t o control vegetation, and w i l l not s u b s t a n t i a l l y e f f e c t nutrient c a p i t a l s . I t would be d i f f i c u l t to achieve high forest f l o o r depth reduction i n these 109 ecosystems as the s o i l moisture regime probably impairs forest f l o o r drying. Where extreme vegetation competition or c o l d and wet s o i l s may hinder plantation establishment, a l t e r n a t i v e or ad d i t i o n a l s i t e preparation techniques and regeneration practices may be necessary. The effectiveness of burning and of al t e r n a t i v e s i t e preparation practices i n achieving management goals has not been adequately established. Mechanical s i t e preparation methods have the po t e n t i a l to increase s o i l temperatures through exposing mineral s o i l , as r e s u l t s from windrowing and s c a r i f y i n g , or by elevating mineral s o i l i n mounds or furrows through the use of mounders, disc-trenchers, and ploughs. Vegetation competition may I n i t i a l l y be greatly reduced by mechanical methods involving scalping, but these methods may also create excellent mineral s o i l seedbeds f o r competing species. Practices such as inverted humus mounding may increase s o i l temperatures and nutrient a v a i l a b i l i t y t o a greater degree than does burning, though some scalping procedures have the p o t e n t i a l to reduce nutrient c a p i t a l t o a f a r greater degree than does slashburning, through removal of the e n t i r e forest f l o o r . Mechanical treatments also have the po t e n t i a l to create f a r greater physical disturbance than does burning, which on s e n s i t i v e s i t e s may cause erosion or l o s s of productivity. Unlike burning, the op e r a b i l i t y of mechanical s i t e preparation equipment i s l i m i t e d by slope, slash load, and stump height and spacing. In p a r t i c u l a r , the e f f e c t s of burning and of altern a t i v e mechanical treatments on the need f o r subsequent vegetation control i n plantations needs t o be better evaluated. S i t e preparation practices such as slashburning or brushblading may commit s i t e s to p a r t i c u l a r successional pathways, which may influence the need for vegetation management, or the a b i l i t y t o replant areas successfully In plantations f a i l . 110 Forest managers must balance the r i s k of reducing long-term nutrient a v a i l a b i l i t y by slashburning against the benefits of achieving immediate stand establishment goals, and the r i s k of not achieving these goals i f burning i s not c a r r i e d out. This task would be easier i f l e v e l s of f i r e s e v e r i t y that are required to achieve s p e c i f i c management objectives could be better quantified. The r i s k of inducing nutrient d e f i c i e n c i e s through slashburning may be further reduced by: 1) Refining and moderating the use of slashburning. Burn impacts should be prescribed according to s i t e s e n s i t i v i t y . The use of harvesting practises which w i l l reduce slash loads should also be encouraged, reducing the need f o r burning, or r e s u l t i n g i n lower impacts where burning i s c a r r i e d out. F u l l consideration should also be given to the use of a l t e r n a t i v e s i t e preparation methods. Refining the a p p l i c a t i o n of slashburning w i l l require an increased a b i l i t y t o burn to prescriptions, which implies an increased l e v e l of s k i l l amongst p r a c t i t i o n e r s , and an increased a b i l i t y t o predict f i r e impacts. This l a t t e r requirement may necessitate development of more precise predictive aids, more quantitative assessments of f u e l loading, or more extensive and representative f i r e weather data bases. However, burning to p r e s c r i p t i o n i s inherently l i m i t e d by the i n a b i l i t y to control weather conditions, with the r e s u l t that burning may have to be c a r r i e d out under l e s s favourable conditions i n order to meet time constraints, such as having areas prepared for planting of seedlings which are forthcoming. Because slashburning i s u sually a broadcast treatment, i t may not be possible t o adjust prescriptions to meet ecosystem s p e c i f i c goals where very d i f f e r e n t ecosystem types occur within the same opening. 2) Documenting f i r e e f f e c t s and effectiveness. Better documentation I l l of slashburning conditions and e f f e c t s , and plantation performance on burned areas i s required i n order to determine i f s i t e preparation and plantation establishment goals are being met by prescribed burning. This may involve quantitative assessment of the impact of operational burns. Current prescribed burn documentation includes the F i r e Weather Index values on the date of the burn and v i s u a l assessments of burn impact, while the s i l v i c u l t u r e h i s t o r y records system includes only the type and month of s i t e treatment. In addition, monitoring of height/age curves on areas where slashburn impacts are known may be h e l p f u l i n determining i f plantation performance goals are being met. As burning has been shown to r e s u l t i n substantial nutrient l o s s , and as nutrient d e f i c i e n c i e s have been frequently found i n young spruce plantations, further assessment of the nutrient status of older plantations on burned areas may be desirable, as nutrient demand i s probably at a maximum when plantations begin to approach crown closure. Stands could be further p r i o r i z e d f o r assessment according to r i s k l e v e l ; however p r i o r i z a t i o n may be l i m i t e d to ecosystem type only i n e x i s t i n g plantations, due to the lack of information on h i s t o r i c a l burn impacts. The assessment of plantation nutrient status should also be extended to other species such as lodgepole pine and Douglas-fir which are also commonly established on burned areas. B a l l a r d (19850 suggested that f e r t i l i z e r t r i a l s i n v o l v i n g Fe and Cu f o l i a r sprays would be of int e r e s t to determine the extents to which growth can be enhanced by r e l i e v i n g d e f i c i e n c i e s i n these elements induced by slashburning. Nitrogen f e r t i l i z a t i o n of slashburned areas with N d e f i c i e n c i e s might also be of i n t e r e s t to determine to what extent growth can be improved where slashburning 112 has reduced nitrogen availability. It w i l l become increasingly necessary to carry out prescribed burning to achieve defined objectives, and to be able to show that these objectives are being met, as the long-term effects of slashburning on forest productivity, and the effectiveness of burning w i l l be increasingly questioned. The concern of the public and of other resource managers with the effects of slashburning on resources such as a i r quality and wildlife habitat i s l i k e l y to increase, as i s public concern with the wisdom of many other established forest management practices. P o l i t i c a l concerns with the cost-effectiveness of a l l s i l v i c u l t u r a l practices on public land are also l i k e l y to increase. 7.2 RESEARCH RECOfMEtD-ATIGNS Quantification of slashburning impacts on a greater number of sites over a wider range of fuel loads and f i r e impacts than was achieved i n this study would be required to develop meaningful predictive models of changes i n nutrient status caused by burning. Better prediction of effects of slashburning on nutrients or on the vegetation w i l l also require an increased a b i l i t y to predict fuel consumption. In future f i r e impact assessments, more precise ' estimates of percentage slash reduction i n each diameter class could be obtained by permanently marking and preferably tagging individual slash pieces to f a c i l i t a t e their relocation, at least for the larger diameters. Future studies of f i r e effects on the nutrient status of ecosystems with deep forest floors should consider further stratifying forest floor sampling by depth to reduce sampling error. Quantifying ash deposition from the slash by the use of trays, and the amount of leaching by the use of lysimetry 113 or i o n exchange r e s i n traps would be very useful to v e r i f y estimates of nutrient inputs and movement i n the forest f l o o r to v e r i f y estimates of nutrient inputs and movement i n the forest f l o o r based on destructive sampling. I t would be of i n t e r e s t to extend studies of nutrient l o s s to micro-nutrients as well, p a r t i c u l a r l y as B a l l a r d (1985, 1987) has found a higher frequency of Cu and Fe d e f i c i e n c i e s i n spruce plantations on slashburned areas. In view of the very unusual f o l i a r P and K l e v e l s found i n the seedlings i n t h i s study, i t would also be of in t e r e s t to further examine the f o l i a r n u t r i t i o n of seedlings p r i o r to and following planting, i n order to determine the e f f e c t s of nursery practice and planting stress on the n u t r i t i o n of planted seedlings. At present, i n t e r p r e t a t i o n on the sig n i f i c a n c e of changes i n ecosystem nutrient status due to slashburning i s l i m i t e d by the lack of data on basic nutrient c y c l i n g processes i n Sub-Boreal Spruce zone forests and an understanding of how f i r e e f f e c t s them, and by a lack of well-designed experiments to empirically assess the e f f e c t s of slashburning on forest productivity. Studies are required to assess mineralization rates, nutrient input/loss rates and nutrient productivity relationships i n the SBS zone. Well-designed experiments which w i l l allow comparison of tree growth over a wider range of burn impacts are also required i n order to evaluate the long-term e f f e c t s of slashburning on nutrient a v a i l a b i l i t y and to determined i f there are threshold l e v e l s of f i r e impact that may impair forest productivity. Further research i s also required to compare and evaluate the e f f i c a c y of slashburning with other s i t e preparation a l t e r n a t i v e s . In addition to s i t e preparation treatments, studies should also include other appropriate tree species i n addition to i n t e r i o r spruce, and vegetation c o n t r o l 114 l e v e l s . Studies of prescribed f i r e or s i t e preparation treatment e f f e c t s on ecosystem processes and nutrient status, and on tree growth and n u t r i t i o n may be of two basic types (Hicks 1982): 1) Ex post facto. This category includes survey, h i s t o r i c a l an developmental studies. I t i s characterized by the f a c t that independent variables (such as f i r e impact l e v e l or s i t e preparation method) have not been manipulated by the researcher and he only measures and makes inferences from what has occurred. Thus the p r o b a b i l i t y that the observed e f f e c t s are due to uncontrolled factors cannot be quantified. In f i r e e f f e c t s research t h i s category includes studies of ecosystem nutrient status and of the growth and nutrient status of e x i s t i n g plantations, but where i t cannot be established that study areas have had an equal p r o b a b i l i t y of receiving a p a r t i c u l a r f i r e impact. The advantages of t h i s type of study are that ecosystem nutrient status or plantation growth and n u t r i t i o n may be examined over a wide range and number of ecosystem types and burn s e v e r i t i e s and range of time since burning i n a f a i r l y short period. In t h i s type of study the researcher must assume that the areas being compared are s i m i l a r , though many factors may not be known. For example, i n comparisons of growth on areas that were burned or unburned i n the past, there may have been differences i n vegetation cover, slashloading and s o i l moisture which influenced the decision to burn or burn coverage which are not obvious but may also have influenced growth. In t h i s type of study, inferences about the e f f e c t s of f i r e must be made with extreme caution, and such research i s not l i k e l y t o provide meaningful information about the e f f e c t s of f i r e on tree growth or be u s e f u l i n determining threshold l e v e l s of f i r e severity which may impact 115 growth. However, i t may be useful f o r extending studies of nutrient c y c l i n g processes or of tree nutrient status to a wider range of ecosystems, burn s e v e r i t i e s and ages or species of plantation. 2) Experimental. This type of research may also include comparisons of ecosystem nutrient status or plantation growth on burned and unburned areas, or on s i t e s which have received a range of burn impacts, but study areas have had an equal chance of being burned, and so inferences may be made with much greater confidence. Such experiments would provide better t e s t s of whether there are threshold l e v e l s of f i r e impact that Impair tree growth. However, because experimental treatments must be applied, a long time i s required to obtain long-term r e s u l t s . Another disadvantage of experimental studies with f i r e i s that because f i r e i s more d i f f i c u l t to apply i n a co n t r o l l e d manner than are other treatments such as mechanical s i t e preparation, the complexity of experimental designs and the number of treatments alternatives that can be examined must be l i m i t e d . Thus, i t i s also more d i f f i c u l t to r e p l i c a t e experiments which include f i r e over a number of ecosystem types, or i n time. A strategy f o r prescribed f i r e e f f e c t s research should include studies of both ecosystem processes and empirical assessments of tree growth. Of necessity, both ex post facto and experimental approaches w i l l need to be used to provide information i n the short-term, and increasingly more r e l i a b l e information i n the long-term. 116 LITERATURE CITED Adams, P.W. and J.R. Boyle. 1980 E f f e c t s of f i r e on s o i l nutrients i n clearcut and whole-tree harvest s i t e s i n Central Michigan. S o i l S c i . Soc. Am. J . 44: 847-850. Ahlgren, I.F. and C.E. Ahlgren. 1965. E f f e c t s of prescribed burning on s o i l microorganisms i n a Minnesota jack pine forest . Ecology 46: 304-310. Alexander, M.E. 1984. Prescribed f i r e behavior and impact i n an eastern sp r u c e - f i r slash f u e l complex. Can. For. Serv. Res. 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A study of reforestation on Vancouver Island with p a r t i c u l a r reference to the operations of Bloed e l l , Stewart & Welch Ltd. Unpubl. Rep. Zasada, <T. and R. Norum. 1986. Prescribed burning white spruce slash i n i n t e r i o r Alaska. North. J. Appl. For. 3:16-18. 125 APPENDIX A. STUDY AREA LOCATION. 126 Study area l o c a t i o n (*) on NTS map 93G (1:50,000). 127 A P P E N D I X B . D E S C R I P T I O N S OF T Y P I C A L HUMUS FORMS AND S O I L P R O F I L E S I N THE M E S I C AND S U B H Y G R I C / H Y G R I C E C O S Y S T E M G R O U P S . 128 Mesic ecosytem (Plot 8): Orthi Hemimor / Podzolic Gray L u v i s o l (Aug. 1983). Horizon Depth Description (cm) L 9-5 Dry; feather mosses and coniferous needles; non-compact matted; loose; mossy/acerose; no roots; no v i s i b l e biota; clear, smooth boundary Fq 5-0.5 Moist; non-compact matted; f r i a b l e ; fibrous; p l e n t i f u l , f i n e roots; common, yellow mycelia; clear, smooth boundary. FH 0.5-0 Moist; massive; f r i a b l e ; mushy/fibrous; p l e n t i f u l , f i n e and medium roots; common, yellow mycelia; abrupt, smooth boundary. Bf 0-19 Moist; brown (7.5YR 4/4m); loam; weak moderate sub-angular blocky; f r i a b l e ; abundant, medium roots; gradual, smooth boundary. AB 19-43 Moist; dark yellowish brown (10YR 4/4m); s i l t y c l a y loam; weak moderate sub-angular blocky; firm; few, f i n e roots; gradual, smooth boundary. Bt 43-62 Moist; yellowish brown (10YR 5/4m); s i l t y c l a y loam; moderate medium sub-angular block; firm; very few, f i n e roots; gradual, wavy boundary. BC 62+ Moist; yellowish brown (10 YR 5/4m); s i l t y c l a y loam; massive; firm. 129 Subhygric/hygric ecosystem (Plot 14): Orthi Hydromoder / Rego Humic Gleysol (Aug. 1983). Horizon Depth Description (cm) L 12-8 Moist; moss tissues and coniferous needles; non-compact matted; loose; mossy/acerose; no roots; no v i s i b l e biota; c l e a r wavy boundary. Faq 8-1.5 Moist; non-compact matted; f r i a b l e ; fibrous; p l e n t i f u l , f i n e roots; very few, v i s i b l e fauna; few, mycelia; clear, wavy boundary. Hd 1.5-0 Moist; black; massive; f r i a b l e ; greasy; p l e n t i f u l , f i n e roots; no v i s i b l e biota; c l e a r wavy boundary. Ahg 0-15 Wet; very dark grey (10YR 3/lm); s i l t y c l a y loam; weak f i n e subangular blocky; f r i a b l e ; p l e n t i f u l , coarse roots; no v i s i b l e biota; clear, wavy boundary. I C 15-30 Moist; dark yellowish brown (10YR 4/4m); c l a y loam; massive; firm; no roots; clear, wavy boundary. II C 30+ Moist; dark yellowish brown (10YR 4/4m); cla y loam; weak f i n e subangular blocky; firm; no roots. 130 APPENDIX C. LIST OF PLANTS PRESENT IN THE MESIC AND SUBHYGRIC/HYGRIC ECOSYSTEMS ON THE STUDY AREA. 131 S c i e n t i f i c Names Ecosystem Type Mesic Subhygric/Hygric Cover Freq- Cover Freq-uency uency (%) (%) (%) (%) Vascular Plants Abies lasiooarpa (W.S. Hooker)Nutt. Achillea millefolium L. Actea rubra ( A i t . ) Willd. Alnus lncana (L.) Moench spp. tenufolia (Nutt.) Breitung iL. v i r i d l s ssp. sinuata (Reg.) Love fi? Love Arnica c o r d l f o l l a Hook. Aster c l l i o l a t u s L i n d l . A. modestus L i n d l . i n Hook. CalamagrQstls canadensis (Michx.) Beauv. Ch.imaph.ila umbellata (L.) Bart. C l i n t o n l a u n i f l o r a (J.A. Schutes) Kunth Cornus canadensis L. DryopterlS a s s l m l l l s Walker Epilobioum angustifolium L. Equlsetum anvense L. 3L. sylvaticum L. Fragarla vesca L. IL_ v i r g i n l a n a Duchesne Galium boreale L. CL. t r i f l o r u m Michx. Gymnocarpium drvopterls (L.) Newm. Linnaea b o r e a l i s L. Lonicera lnvolucrata (Rich.) Banks Lycopodium annotinum L. Menziesia ferruginea Smith M i t e l l a nuda L. Oplopanax horridus (Smith) Miq. O r t h i l i a secunda (L.) House Parnassla p a l u s t r i s L. Petasltes palmatus ( A i t . ) Gray Pvrola a s a r i f o l i a Michx. Ribes laoustre (Pers.) Poir Rosa a c i c u l a r i s L i n d l . Rubus ideaus L. IL. p a r v l f l o r a Nutt. R_t. pedatus J.E. Smith IL. pubescens Raf. Sanguisorba s l t c h e n s l s CA. Meyer Senecio t r i a n g u l a r i s Hook. Sheperdia canadensis (L.) Nutt. Sorbus scopulina Greene iL. s i t c h e n s i s M.J. Roemer Streptopug amplexifolius (L.) DC iL. roseus Michx. T l a r e l l a t r i f o i i a t a L. 1 100 1 100 + 15 + 30 + 30 + 20 1 50 + 30 + 30 + 85 + 30 + 20 + 50 + 15 + 15 + 30 4 100 2 80 + 20 + 45 + 50 + 85 1 50 + 15 + 25 + 15 + 50 + 70 + 45 + 50 + 100 + 50 1 100 2 100 + 100 + 70 + 15 + 50 + 30 + 100 + 25 + 100 + 20 + 50 + 100 + 80 + 15 + 20 + 70 + 80 + 30 + 25 + 30 4 35 3 100 1 80 + 30 + 80 + 60 5 80 + 15 + 50 + 15 + 50 + 35 + 30 + 50 + 30 + 45 + 70 132 S c i e n t i f i c Names Ecosystem Type Mesic Subhygric/Hygric Cover Freq- Cover Freq-uency uency (%) (%) (%) (%) Vacclnlum caespetosum Michx. Ya. membranaceum Dougl. sx. Hook. Valeriana sitohensls Bong. Veratrum v i r i d e A i t . Vlbernum edule (Michx.) Raf. Bryophytes and T.i f»h.=mg Aulocomium palustre (Hedw.) Schwaeger Hvlooomium splendens (Hedw.) B.S.G. Pleurozium schreberi (Brid.) Mitt. Peltjgra aphthosa (L.) Willd. Ptillum c r l s t a - c a s t r e n s i s (Hedw.) DeNot Rhytidladelphus triquetrus (Hedw.) Warnst. + 30 3 100 + 50 + 80 + 35 + 45 + 100 2 50 4 60 10 100 40 100 15 100 + + 20 25 100 20 100 + 20 + 35 133 APPENDIX D. WEATHER OBSERVATIONS AND FWI SYSTEM CODES AND INDEXES AT THE STUDY AREA DURING JULY -SEPTEMBER, 1983. 134 Date Weather Observations x FWI System Codes and Indexes'5 (m/d) Temp RH Wind Rain FFMC DMC DC ISI BUI FWI DSR ( C) (%) (km/hr) (mm) 7 21 8.4 63 6 11.4 41.6 8.4 179.5 0.1 15.0 0.0 0.0 7 22 7.1 59 7 0.2 60.2 9.2 184.5 0.6 16.3 0.5 0.0 7 23 9.2 47 6 1.0 70.4 10.5 189.8 0.9 18.4 0.7 0.0 7 24 7.7 85 5 5.3 36.7 6.2 185.1 0.0 11.4 0.0 0.0 7 25 0.8 100 2 10.6 6.8 2.6 166.1 0.0 5.1 0.0 0.0 7 26 6.2 73 14 0.7 30.2 3.1 170.9 0.0 5.9 0.0 0.0 7 27 10.1 80 5 0.5 45.2 3.6 176.4 0.1 6.9 0.1 0.0 7 28 13.7 59 11 2.0 60.1 3.9 182.6 0.7 7.4 0.4 0.0 7 29 16.6 42 8 0.0 79.2 6.3 189.3 1.6 11.7 1.2 0.0 7 30 21.4 48 6 1.0 82.7 9.1 196.9 2.1 16.3 2.8 0.1 7 31 16.5 66 3 0.0 83.5 10.5 203.5 2.0 18.6 2.9 0.1 8 1 15.2 49 6 1.7 76.4 11.2 209.3 1.1 19.7 1.1 0.0 8 2 13.6 92 3 4.8 36.3 6.8 205.8 0.0 12.6 0.0 0.0 8 3 13.1 51 12 0.0 65.4 8.3 211.2 1.0 15.0 0.7 0.0 8 4 15.1 47 7 0.2 79.4 10.0 216.9 1.5 18.0 1.9 0.0 8 5 15.7 51 8 0.0 84.2 11.7 222.7 2.8 20.7 4.7 0.4 8 6 12.6 73 7 2.7 62.5 9.5 228.0 0.7 17.2 0.6 0.0 8 7 15.7 52 5 0.0 76.9 11.1 233.8 1.1 19.9 1.1 0.0 8 8 20.8 47 5 0.0 84.9 13.5 240.6 2.7 23.7 4.9 0.4 8 9 23.2 36 4 0.0 89.2 16.7 247.8 4.7 28.6 9.2 1.3 8 10 19.7 64 6 1.2 80.6 18.3 254.3 1.6 31.0 3.5 0.2 8 11 17.3 54 14 0.0 84.8 20.0 260.4 4.1 33.6 9.0 1.3 8 12 13.6 56 9 0.0 85.1 21.4 265.9 3.4 35.6 7.9 1.0 8 13 14.1 54 11 0.0 85.6 22.8 271.4 4.0 37.7 9.3 1.4 8 14 15.0 49 11 0.0 86.4 24.5 277.1 4.5 40.1 10.7 1.8 8 15 12.6 66 9 0.0 85.4 25.5 282.4 3.5 41.6 8.9 1.3 8 16 14.0 78 9 2.5 63.9 21.7 287.9 0.8 36.5 1.3 0.0 8 17 11.6 42 14 0.0 79.4 23.2 293.0 2.2 38.7 5.5 0.5 8 18 13.5 50 9 0.0 84.0 24.7 298.4 2.9 41.0 7.4 0.9 8 19 13.6 53 17 0.0 85.3 26.1 303.9 5.2 43.0 12.5 2.3 8 20 13.1 55 11 0.2 85.4 27.5 309.3 3.9 44.9 10.2 1.6 8 21 18.3 46 9 0.0 87.2 29.6 315.6 4.5 48.0 11.9 2.1 8 22 20.9 40 6 0.0 88.8 32.3 322.3 4.9 51.7 13.3 2.6 8 23 18.6 43 12 0.0 88.9 34.7 328.7 6.7 54.9 17.4 4.2 8 24 15.8 49 10 0.0 88.6 36.4 334.5 5.8 57.3 16.0 3.6 8 25 16.6 49 7 0.0 88.6 38.3 340.5 5.0 59.8 14.6 3.1 8 26 14.8 60 15 0.0 86.9 39.6 346.2 5.9 61.6 16.9 4.0 8 27 17.0 51 6 0.0 87.0 41.5 352.2 3.8 64.1 12.2 2.2 8 28 14.7 71 5 0.0 85.2 42.4 357.9 2.8 65.4 9.6 1.5 8 29 16.2 71 4 11.9 42.5 21.2 324.4 0.1 36.4 0.1 0.0 8 30 20.1 50 6 0.0 71.6 23.3 331.0 0.9 39.7 1.9 0.0 8 31 16.6 50 7 0.0 81.7 25.2 337.0 2.0 42.4 5.3 0.5 135 Date Weather Observations 1 FWI System Codes and Indexes'3 (m/d) Temp RH Wind Rain FFMC DMC DC ISI BUI FWI DSR ( C) (%) (km/hr) (mm) 9 1 13.4 69 4 0.0 82.4 26.0 341.1 1.8 43.6 5.0 0.4 9 2 13.5 72 8 0.0 82.5 26.7 345.2 2.3 44.7 6.3 0.7 9 3 16.0 48 12 0.0 85.8 28.3 349.8 4.3 47.1 11.4 2.0 9 4 11.0 53 17 0.2 85.9 29.3 353.5 5.6 48.5 14.2 3.0 9 5 10.0 52 11 0.2 85.9 30.2 357.0 4.2 49.9 11.5 2.0 9 6 5.8 100 11 7.3 23.9 16.6 337.4 0.0 29.5 0.0 0.0 9 7 7.7 67 2 0.0 41.2 17.1 340.5 0.0 30.4 0.1 0.0 9 8 8.1 60 4 0.2 58.7 17.7 343.6 0.5 31.4 0.6 0.0 9 9 9.1 54 3 0.0 71.1 18.6 347.0 0.8 32.8 0.9 0.0 9 10 10.7 60 10 0.0 78.7 19.4 350.6 1.7 34.1 3.7 0.2 9 11 10.4 72 4 7.0 42.0 11.3 333.3 0.1 20.8 0.1 0.0 9 12 12.8 54 6 0.2 64.9 12.4 337.3 0.7 22.8 0.7 0.0 9 13 15.0 71 5 6.1 45.3 7.7 324.7 0.1 14.5 0.1 0.0 9 14 15.0 50 6 9.1 46.7 5.0 302.2 0.1 9.5 0.1 0.0 9 15 12.0 64 6 0.0 64.5 5.8 306.0 0.7 11.1 0.4 0.0 9 16 9.0 55 5 3.6 53.6 4.1 302.2 0.3 7.9 0.2 0.0 9 17 7.5 75 6 1.0 59.4 4.5 305.2 0.5 8.6 0.3 0.0 9 18 8.0 64 5 0.0 70.0 5.1 308.4 0.8 9.7 0.5 0.0 9 19 10.0 56 11 0.0 78.7 5.9 311.9 1.7 11.3 1.5 0.0 9 20 12.5 64 5 0.0 81.5 6.8 315.8 1.7 12.9 1.7 0.0 9 21 10.0 83 5 0.0 81.2 7.1 319.3 1.7 13.5 1.7 0.0 9 22 17.0 57 0 0.0 83.3 8.5 324.1 1.7 16.0 2.0 0.0 9 23 15.0 46 5 0.0 85.9 10.1 328.5 3.1 18.7 4.8 0.4 9 24 14.5 49 13 0.0 86.5 11.5 332.8 5.0 21.2 8.2 1.1 9 25 15.0 54 11 0.0 86.5 12.8 337.2 4.5 23.4 7.9 1.0 9 26 10.5 51 13 0.0 86.6 13.8 340.8 5.0 25.1 9.1 1.3 9 27 7.0 46 8 0.0 86.6 14.6 343.8 3.9 26.4 7.5 0.9 9 28 7.0 46 6 0.0 86.7 15.4 346.7 3.6 27.7 7.1 0.8 9 29 8.5 43 5 0.0 86.7 16.4 350.0 3.5 29.3 7.1 0.8 9 30 8.5 49 5 0.0 86.8 17.2 353.2 3.5 30.7 7.4 0.9 Dail y observations at 12:00 hrs., PST. Observations f o r Sept. 14 -30th from the permanent s t a t i o n (Dungate) i n Houston, B. C Canadian Forest F i r e Weather Index System (Can. For. Serv. 1984). I n i t i a l Values f o r FFMC: 85, DMC: 16, and DC: 200 136 APPENDIX E. SUMMARY OF BURNING CONDITIONS, FUEL LOAD AND FUEL REDUCTIONS IN SPRUCE - FIR SLASH FUELS. Fuel Type Ignition Burning Conditions1 — Total Slash — Forest Floor r date FFMC DMC DC BUI Load Consumption Load Consumption Depth DOB*3 m/d/y (fcg/ma) (*g/m2) (*) (fcg/m2) ( ig / m s ) (*) Ccm) (cm) (9f>) White spruce- subalplne f i r (This study) (mesic) (subhygric) (Ki l l 1969, 1971 and CFS unpubl.) (Muraro unpubl.) 3 9/30/83 87 35 154 - 14. .87 6. 81 51 7. .45 3. 67 36 8. 3 3. 0 36 18. .40 11. 38 50 28. 59 3. 41 6 34. 0 1. 9 8 8/10/67 88 13 196 23 10. .19 9. 08 50 19. 03 0. 90 6 19. 4 4. 0 26 8/16/68 85 11 180 30 8. .49 4. 03 47 15. 18 0. 43 3 13. 3 0. 8 6 7/03/68 90 14 131 32 10. ,55 6. 56 63 15. 18 1. 57 10 13. 3 2. 6 19 7/08/68 92 33 160 43 9. 79 6. 72 69 15. 31 1. 99 13 14. 0 3. 9 21 7/33/68 87 32 153 33 7. .97 4. 31 53 87. 74 1. 46 2 44. 9 1. 9 4 6/19/67 94 60 123 60 18. .30 3. 44 13 13. 30 4. 60 35 10. 8 3. 7 36 6/20/67 93 65 131 65 14. 61 4. 24 29 15. 92 7. 41 47 12. 9 6. 0 47 6/22/67 92 73 145 72 8. 16 2. 12 26 13. 82 6. 96 47 11. 2 9. 3 47 6/28/67 92 73 145 73 12. 71 5. 45 43 15. 31 4. 58 30 12. 4 3. 7 30 6/33/67 92 76 152 76 11. 89 1. 36 11 16. 79 6. 40 40 12. 8 5. 3 40 6/34/67 90 79 159 79 16. 35 6. 17 66 14. 30 8. 93 63 11. 6 7. 2 62 6/27/67 85 89 180 89 18. 31 7. 78 43 9. 17 7. 68 84 7. 4 6. 2 84 6/39/67 75 63 184 68 10. 78 3. 39 31 13. 78 9. 37 68 11. 2 7. 6 68 6/30/67 84 66 190 70 16. 40 5. 26 33 8. 38 4. 70 57 6. 7 3. 8 67 7/08/67 85 83 341 89 11. 77 3. 54 30 6. 63 5. 05 76 5. 9 4. 1 76 7/10/67 85 86 393 93 14. 73 7. 39 50 13. 08 9. 82 81 9. 8 7. 9 81 7/11/67 88 89 261 96 18. 60 7. 64 41 9. 04 6. 30 70 7. 3 5. 1 70 7/11/67 88 89 261 96 18. 96 6. 48 34 7. 36 4. 46 61 6. 0 3. 6 61 7/13/67 90 93 268 99 13. 38 4. 41 33 10. 90 7. 06 65 8. 8 5. 7 65 7/13/67 90 96 276 103 11. 57 9. 00 43 11. 42 10. 03 88 9. 2 8. 1 88 7/14/67 90 99 283 105 12. 08 5. 73 47 4. 76 3. 80 80 3. 9 3. 1 80 7/31/67 53 37 389 56 14. 39 3. 41 34 8. 30 5. 76 69 6. 7 4. 7 69 7/33/67 75 39 296 59 12. 13 5. 42 45 9. 09 6. 40 70 7. 9 5. 2 70 7/23/67 86 42 303 63 18. 67 7. 37 39 6. 37 9. 46 86 9. 2 4. 4 86 7/17/67 88 105 303 113 11. 61 5. 54 48 6. 32 4. 91 78 5. 1 4. 0 78 7/33/67 86 43 303 63 19. 04 7. 15 38 7. 60 6. 08 80 6. 1 4. 9 80 7/18/67 85 106 309 114 16. 98 6. 97 41 4. 84 3. 51 72 3. 9 3. 8 72 7/34/67 88 49 310 66 11. 98 4. 42 37 9. 78 7. 42 76 7. 9 6. 0 76 7/35/67 89 48 317 69 16. 98 5. 26 31 9. 14 7. 65 84 7. 4 6. 2 84 7/36/67 90 51 335 74 30. 05 5. 83 39 7. 46 5. 94 80 6. 0 4. 8 80 8/01/67 65 27 336 45 10. 66 0. 64 6 13. 44 10. 00 74 10. 9 8. 1 74 8/02/67 84 30 333 49 10. 66 4. 84 49 6. 91 4. 77 69 9. 6 3. 9 69 8/02/67 84 30 333 49 19. 74 7. 37 37 7. 89 6. 00 76 6. 4 4. 9 76 7/28/67 90 57 340 80 16. 64 6. 33 38 10. 98 10. 43 95 8. 9 8. 4 95 8/07/67 86 37 346 45 17. 56 7. 26 41 9. 74 6. 70 69 7. 9 5. 4 69 8/09/67 86 30 399 90 30. 95 8. 02 38 9. 35 6. 49 69 7. 6 9. 2 69 M 05 -3 Fuel Type Ignition Date m/d/y Burning Conditions FFMC DMC DC BUI — Total Slash. Load Consumption (*g/m2) (fcg/m2) (%) Forest Floor Load Consumption Depth DOB Cfcg/m8) (fcg/m2) (%) (cm) (cm) (%) (BCMFL and CFS unpubl.) 8/10/6? 91 34 366 56 16. .23 5. 77 36 4.99 3. 69 75 4. 0 3. 0 75 8/11/67 89 36 373 58 15, .88 5. 30 33 6.07 5. 24 86 4. 9 4. 2 86 8/12/67 85 39 379 62 20. .88 10. 76 53 7.76 5. 41 70 6. 3 4. 4 70 8/12/67 85 39 379 68 13, .73 5. 18 38 7.76 5. 81 75 6. 3 4. 7 75 8/13/67 90 42 386 67 11. .48 4. 84 41 6.48 4. 58 70 5. 2 3. 7 70 8/14/67 92 46 394 71 20, .72 8. 89 43 7.92 7. 08 89 6. 4 5. 7 89 8/15/67 93 50 401 76 13, .77 8. 15 59 7.38 6. 47 88 6. 0 5. 8 88 8/16/67 93 53 409 81 13. .18 6. 53 50 11.89 10. 88 96 9. 1 8. 8 96 8/17/6? 98 57 416 85 20. .38 9. 79 48 6.30 6. 18 98 5. 1 5. 0 98 8/18/67 92 60 423 85 19. ,10 10. 29 54 7.28 6. 40 88 5. 9 5. 2 88 8/21/67 70 45 428 71 14, ,33 8. 54 60 8.17 7. 13 87 6. 6 5. 8 87 8/19/67 90 63 430 98 19. .33 7. 78 40 8.00 7. 50 94 6. 5 6. 1 94 8/28/67 82 47 433 74 10. .30 4. 74 46 7.68 6. 78 88 6. 8 5. 5 88 8/23/67 8? 49 439 76 13. ,35 3. 52 26 7.30 6. 75 98 5. 9 S. 5 98 8/25/67 86 53 450 81 19. .06 8. 05 42 6.54 6. 23 95 5. 3 5. 0 95 9/10/854 8/26/85* 9/17/824 9/25/844 84 8 881 15 13. ,33 10. 38 78 _ _ _ 7. 9 8. 3 29 85 53 337 76 16. ,30 10. 90 67 - - - 18. 6 4. 9 39 86 12 365 88 5. ,98 2. 05 33 - - - 8. 7 8. 4 27 87 10 402 80 12. 87 8. 00 63 - - - 9. 9 1. 5 15 9/22/834 84 10 443 20 6. 90 3. 08 44 - - - 9. 8 1. 4 14 9/08/85° 72 28 476 49 15. 60 12. 33 79 - - - 8. 8 5. 2 59 9/03/824 86 38 526 65 5. 08 2. 46 49 - - - 10. 4 3. 7 36 CO White spruce - red spruce - balsam f i r (Alexander 1984) 6/11/65 White spruce (Zasada and Norum 1986) 7/13/83 7/88/83 87 35 154 5.48 4.3 4.8 3.82 59 8.89 3.89 67 81 8.35 3.8 38 9.8 13.0 13.8 4.6 5.6 6.8 50 43 55 Codes and indexes of the Canadian Forest Fire Weather Index System (Can. For. Serv. 1984). Depth-of-burn. Unpublished data of Can. For. Serv., Fire Res. Group, Pacific Forestry Centre. Unpublished data of B.C. Min. of Forests and Lands, Forest Sciences Section, Prince Rupert Forest Region. Unpublished data of joint CFS/BCMFL Research and Protection Branch, prescribed f i r e monitoring methodology demonstration, i n cooperation with Northwood Pulp and Timber Co., Houston. 

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