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Sapwood water content of lodgepole pine Rothwell, Richard L. 1974

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S A P W O O D W A T E R C O N T E N T O F . L O D G S P O L E P I N E by R I C H A R D L E E R O T H W E L L . • B . S. , U n i v e r s i t y of C a l i f o r n i a , 1962 M . F . , U n i v e r s i t y of C a l i f o r n i a , 1966 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y i n the D e p a r t m e n t of of F O R E S T R Y .We a c c e p t t h i s t h e s i s as c o n f o r m i n g to the r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A • . A p r i l 1974 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y of B r i t i s h C olumbia, I agree t h a t the L i b r a r y 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 r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f f~~of?£^7~/Z y  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada i i ABSTRACT Breast height sapwood water content fluctuations of lodgepole pine (Pinus contorta var. l a t i f o l i a Engelm) were studied with the objective of relating them to conducting xylem area, and to environ-mental and plant variables. Also gamma radiation attenuation was tested as a method for in situ sapwood water content measurement. Sapwood water content fluctuations and upward sap velocity indicated a conducting xylem area 3.25 cm wide from the cambium. For the trees studied, such an area would occupy between 60-80% of total cross-sectional stem area. Multiple regression analyses indicated significant correlation coefficients of 0.36-0.85 between sapwood water content and environmental and plant variables. The most important group of variables included s o i l water content, heat pulse velocity, and precipitation, and these gave a multiple correlation coefficient of 0.85, and a standard error of estimate of 4% o.d.w. with a sample size of 27. Laboratory tests indicated that gamma radiation attenuation is a feasible method for wood water content measurement. In the labor-atory no significant differences were observed between gamma and gravi-metric measurements of wood water content for prepared samples. In the f i e l d , in situ measurements showed similar monthly and diurnal fluctu-ations for gamma and gravimetric estimates. However, gamma water contents were significantly higher than gravimetric, with a mean difference of 17% o.d.w. The higher gamma values were attributed to the inclusion of bark moisture content and measurement of a larger volume of wood. i i i TABLE OF CONTENTS Page INTRODUCTION . 1 LITERATURE REVIEW 2 Sapwood Water Content — 2 Water Movement and Distribution 5 Water Content Measurement 9 OBJECTIVES 1 2 DESCRIPTION OF STUDY AREA 13 ' Climate 13 Geology and Soils 1 3 Vegetation 15 CONDUCTING XYLEM AREA 22 Objective r- 22 Methods 22 Results and Discussion 23 GAMMA RADIATION ATTENUATION FOR WOOD WATER CONTENT MEASUREMENT 32 Objective 32 Theory 32 Application-Wood Water Content 33 Methods 35 Results and Discussion •• 45 SAPWOOD WATER CONTENT-ENVIRONMENTAL AND PLANT VARIABLES 56 Introduction 56 Annual Sapwood Water Content Variation 56 iv TABLE OF CONTENTS CONT'D Page Monthly Sapwood Water Content Variation 61 Diurnal Sapwood Water Content Variation 69 Isolated Tree 82 Environmental-Plant Variables vs Sapwood Water Content -• 93 SUMMARY AND CONCLUSIONS 100 LITERATURE CITED 105 LIST O F T A B L E S T A B L E Page I Sapwood water content for different coniferous species 3 II Soil profile description at Study Area No. 2, Kananaskis Experimental Forest, Alberta (Hillman, 1970)- 16 III Results of mechanical analysis and particle size classification (Hillman, 1970) 18 IV Analysis of variance: Sapwood water content by time July 16-October 15, 1969: 0-6 cm depths from the cambium 0-6 crn and diameter n classes 4. 0-7. 0 inches 24 V Results of Duncan's New Multiple Range Tests for water content means at depths of 0-8 cm from cambium on sample dates July 16, 30; August 18, 26; September 16, 30; and October 15, 1969 26 VI Test of slopes and levels for two regression lines of gamma count ratios obtained in tangential and radial planes of lodgepole pine wood samples on absorption thickness (S) 46 VII Analyses of variance: Sapwood water contents at breast height in lodgepole pine obtained by gamma radiation attenuation and increment boring on June 2-3, 1971 and July 12-13, 1971, Study Area No. 2 53 VIII Analysis of variance: Annual sapwood water s content variation of lodgepole pine at 0-1 cm depth from cambium, at breast height, for July 1970-August 1971, Study Area No. 2 59''• IX Results of Duncan's New Multiple Range Test for annual sapwood water content variation of " lodgepole pine at 0 -1 cm depth from the cambium, at breast height for July 1970-August 1971, Study Area No. 2 .'60': v i T A B L E X XI XII XIII XIV XV XVI XVII Analysis of variance: Sapwood water content at 0-1 cm depth from cambium by time, July 16-October 15, 1969; and diameter classes 4. 0-7. 0 inches, Study Area No. 1 Results of Duncan's New Multiple Range Test for mean sapwood water contents at 0-1 cm depth from cambium for sample dates July 16, 30; August 18, 26; September 16, 30; October 15, 1969, Study Area No. 1 Analysis of variance: Gamma radiation attenuation and bored water contents of lodgepole pine at 0-1 cm depth from cambium, breast height, June-September 1971, Study Area No. 2, lower study plot Analyses of variance: Diurnal sapwood water content at 0-1 cm depth from the cambium by time for sample dates May 7-8, 1969, June 3-4, 1969, July 8-9, 1969 and August 5-6, 1969, Study Area No. 1 Results of Duncan's New Multiple Range Test for mean sapwood water contents 0-1 cm depth from cambium for diurnal samples on May 7-8, 1969, July 8-9, 1969 and August 5-6, 1969, Study Area No. 1 . Analyses of variance: Diurnal sapwood water content variation of lodgepole pine at breast height by gamma radiation attenuation and increment boring on June 2-3, 1971 and July 12-13, 1971, Study Area No. 2, lower study plot. Analyses of variance: Sapwood water content of isolated tree, 1-2 cm depth from tree exterior, at breast height, by gamma radiation attenuation on July 17, August 12, August 18. and September 17, 1971, Study Area No. 2 Analyses of variance: Volumetric soil water content at depths of 6, 12, 24, 36, 48 inches for soils of upper study plot, Study Area No. 2 ____ Page 66. • (ft 71 76/ 77;-. .81': 8-5*, 87-Analysis of variance: Soil water contents in isolated and outside soils of upper study plot for period July 15-September 17, 1971, Study Area No. 2 Analysis of variance: Heat pulse velocities of isolated and control trees, upper study plot, Study Area No. 2 Simple correlation coefficients of gamma and bored water contents on environmental and plant variables used in multiple regression analyses Results of a series of step-wise multiple regression analyses of gamma water content on specific environmental and plant variables -Ranking of variables in importance to sapwood water content by their simple correlation coefficients Results of a series of step-wise multiple regression analyses, gamma sapwood water content on specific environmental and plant variables v i i i LIST OF FIGURES FIGURES Page 1 Radial distribution of water in Douglas-fir 7 2 Radial distribution of water in lodgepole pine 7 3 Radial distribution of water in lodgepole pine 8 4 Radial distribution of water in Engelmann spruce 8 5 Map of Alberta and inset showing location of Kananaskis Forest Experiment Station and Study Areas Nos. 1 and 2 14 6 Soil water de sorption curves for Eutric Brunisol soil at Study Area No. 2, Kananaskis Forest Experiment Station 19 7 Study Area No. 1 Vegetation lodgepole pine with understory of immature Engelmann spruce 20 8 Study Area No. 2 Vegetation lodgepole pine with understory of immature Engelmann spruce 20 9 Sapwood water content variation of lodgepole pine at breast height for 0-6 cm depths from the cambium for the period July 16-October 15, 1969 27 10 Variation of radial sapwood water content distribution of lodgepole pine for annual, monthly and diurnal time bases, for 0-6 cm depths from cambium at breast height 27 11 Per cent frequency of sapwood water contents for 0-8 cm depths from cambium for lodgepole pine at breast height : 28 12 Radial sapwood water content distribution of lodgepole pine at breast height by mean and mode curves 30 13 Per cent frequency of "conducting xylem" in lodgepole pine at breast height in the radial plane. "Conducting xylem" defined as wood of water content greater than 60% o. d. w. in the 0-3 cm depths from the cambium 30 ix FIGURES Page 14 Schematic diagram showing operation of gamma radiation attenuation equipment. Gamma radiation emitted by the cesium 137 source is transmitted in a narrow beam through the trans-verse plane of a tree stem. Gamma photons passing through the tree in a straight line are absorbed by the Nal (Tl) crystal, which produces a light pulse that is converted into an electrical pulse and routed to the pulse height analyzer. The pulse height analyzer electronically discrimi-nates against all photons of energy less than 0. 661 M E V , allowing only those of greater energy (this determined by window setting) to be counted by the scaler - ratemeter 37 15 Portable stand to support gamma radiation equip-ment around trees 16 Permanent stand to support gamma radiation equipment around trees 17 Diagram of trolley system: la-b. Aluminium tubes for holding source and detector; 2. Graduated rod for locating air-tree interface; 3a-b. Metal spacing jigs for source and detector; 4. Trolley constructed from angle iron; 5a-b. Lead collimating blocks for source and detector; 6. Wheels for trolley; 7. Rolling surface of plywood with electrical conduit for tracks 38 38 40 18 Relative count ratios adjusted to a common water content regressed on absorption thickness S. r = 0. 8598, r 2 x 100 = 73. 9%, S E e = 0. 040 15, n = 36. Linear attenuation coefficient equal to slope 0. 0330 g"*. Mass attenuation coefficient for wood equal to slope divided by average density of wood samples (0.4535), 0.072769 cm^g" 1 42 19 Relative count ratios, regressed on absorption thickness S. r = 0. 9920, r 2 x 100 = 99. 8%; S E e = 0. 0280, n = 20. Linear attenuation coefficient equal to slope, 0.0808201 g"-*-. Mass attenuation coefficient of water equal to slope divided by density of water, 0. 0808201 c m 2 g" 1 42 X FIGURES Page 20 Incident counts Ni regressed on ambient air temperature °F at time of observation for temperature correction coefficient. r= 0.8391, or r 2 x 100 = 70.4$, SE e = 4210 ct/min, n=44. Correction coefficient = -.58% change in N^ per 1 degree F rise in air temperature 44 21 Relative count ratios tangentially and radially obtained inwwood samples regressed on absorption thickness S. Tangential: r= 0.9730, r 2 x 100 = 94.8$, SEe= 0.01802, n= 18. Radial: r=0.992, r 2 x 100 = 98.5$ SEe= 0.0154, n = 18 44 22 Pattern of gamma radiation attenuation in a single lodgepole pine at breast height in the transverse plane 47 23 Comparison of gamma radiation attenuation,in woedndensitygand'iwater content in lodgepole pine at breast height in the transverse plane — 47 24 Comparison of gamma radiation attenuation curves obtained in a single lodgepole pine tree et breast height, transverse plane in July, August and September 1970 49 25 Laboratory test. Regression of water contents obtained by gamma radiation attenuation on gravimetric water contents, r = 0.96, r 2 x 100 = 92.6$, SE e = 7.7$ o.d.w., n = 47 51 26 Field test. Regression of water contents obtained by gamma radiation attenuation on bored water contents, r = 0.7736, r 2 x 100 = 59.8$, SE e = 8.7$, n = 33 51 27 Annual variation of sapwood water content of lodgepole pine at the 0-1 cm depth from the cambium at breast height; daily maximum air temperature; and daily precipitation for the period July 1970-August 1971, Study Area No. 2 58 28 Monthly variation of sapwood water content in <» lodgepole pine for the 0-1 cm depth from the cambium at breast height; daily maximum air temperature; daily precipitation and tree water pressure potential for the period July 16-October 15,1969, Study Area No. 1 65 x i FIGURES Page 29 Monthly observation of sapwood water content variation by gamma radiation and increment boring in lodgepole pine at breast height; and monthly variation of daily maximum air temperature; daily precipitation; and volumetric s o i l water content for the period June-September 1971, Study Area No. 2, lower study plot 68 30 Monthly observation of volumetric s o i l water content for period May-September 1971, Study Area No. 2, lower study plot — 70 31 Diurnal variation of sapwood water content at breast height for 0-1 cm depth from the cambium; tree water pressure potential; heat pulse velocity; and air temperature for July 8-9, 1969, Study Area No. 1 74 32 Diurnal variation of sapwood water content of lodgepole pine at breast height, 0-1 cm from the cambium; tree water pressure potential; heat pulse velocity; and air temperature for June 2-3, 1969, Study Area No. 1 75 33 Diurnal variation of sapwood water contents of lodgepole pine at breast height obtained by gamma radiation attenuation and increment boring; and tree water pressure potential; and air temperature for July 12-13, 1971, Study Area No. 2, lower study plot 79 34 Diurnal variation of sapwood water contents of lodgepole pine at breast height obtained by gamma radiation attenuation and increment boring; and tree water pressure potential; and air temperature for June 2-3,1971, Study Area No. 2, lower study plot 80 35 Sapwood water content variation of isolated lodgepole pine, at 1-2 cm depth from tree exterior at breast height and tree water pressure potential; s o i l water contents of isolated and outside soils at 12 inches depth; daily maximum air temperature; daily precipitation for July 16-September 15,1971, Study Area No. 2, upper study plot 84 36 Volumetric s o i l water content variation for i ^ ..• .• isolated s o i l for period'July 15-September 15,1971, Study Area No. 2, upper study plot 86 x i i FIGURES Page 37 Volumetric s o i l water content variation for outside s o i l for period July 15-September 15, 1971, Study Area No. 2, upper study plot 86 38 Heat pulse velocities for isolated and control trees for period July-September 1971, Study Area No. 2, upper study plot 91 39 Double mass curves of heat pulse velocity of isolated tree (K) on control trees (L.M) for period July-September 1971, Study Area No. 2, upper study plot 92 -x i i i ACKNO WLEDGEMENTS Grateful thanks to the Canadian Forestry Service,. Environment Canada for providing time and resources that made this thesis possible; and to colleagues R. H. Swanson and Dr. D. L . Golding at the Northern Forest Research Centre for their helpful suggestions and assistance. Thanks to technical support staff for assistance in data,collection, and to Mrs. R. Warke for her fast and accurate typing of the thesis. Thanks is also made to the members of my thesis committee for their reviews and comments. In particular the late Dr. W. W. Jeffrey is remembered for his encouragement and assistance in my studies. Most of all I thank my wife and family for their support and patience during my studies and the preparation of this thesis. 1 I N T R O D U C T I O N The subject of this thesis is the sapwood water content of lodgepole pine (Pinus contorta var. l a t i f o l i a Engelm. ) with r e s p e c t to t r a n s p i r a t i o n . The upward movement of water l o s t i n t r a n s p i r a t i o n o c c u r s i n the sapwood. To quantify this flux, knowledge of the flow s y s t e m is nece s s a r y . The purpose of this thesis is to define the l e v e l s , fluctuations and d i s t r i b u t i o n of water i n the sapwood of lodgepole pine, with r e s p e c t to t r a n s p i r a t i o n . 2 LITERATURE REVIEW Sapwood Water Content A mature tree stem is composed primarily of sapwood and heart- • wood, which are very different in water content in the great majority of species. Heartwood water content for most conifers is at or slightly above fiber saturation point, and averages between 32-40% oven dry weight (o.d.w.). The levels of heartwood water content are similar throughout a tree, and vary l i t t l e within or between species, and show l i t t l e change with time. Sapwood water content, however, is much higher and more variable, with average water contents for conifers ranging from 60-200% o.d.w. It also varies with tree height or dominance, site, age and species. Furthermore seasonal and diurnal fluctuations of sapwood water content occur in most tree species. Seasonal patterns show maximum water contents i n the winter or early spring,,followed by a steady decrease to a minimum late in the growing season, after which trees start to rehydrate (Gibbs, 1935; Field-ing, 1952; Parker, 1954; Chalk and Bigg, 1956; Gibbs, 1958; Swanson, 1966; Markstrom and Harm, 1972). The general pattern is the same for angio-sperms and gymnosperms; however in evergreens the fluctuations are smaller and this has been attributed to more uniform transpiration caused by their evergreen habit (Clark and Gibbs, 1957). The magnitude of fluctu-ations can be large or small. Seasonal fluctuations of 17-82% o.d.w. are reported in the literature (Table l ) . Information on diurnal fluctuations i s not as abundant, but i t appears that the pattern is similar in form to seasonal fluctuations. 3 Table I Sapwood water contents for different coniferous species. Specie s Depth from Cambium Range Water Contents O. D. W. Per Cent Source Pinus bankisana outer middle inner 139-164" 124-164 103-164 Gibbs, 1935 Pinus radiata annual rings 1- 3 4- 6 7- 9 10-12 13-15 o- -A. vi-126''' 112 111 110 103 Fielding, 1952 Pinus ponderosa sapwood 120 ' ' ' Parker, 1954 Pinus c ontorta sapwood 120-150** Swans on, 1966 Pinus contorta outer inner 122-173"* 126-164 Markstron and Hann, 1972 Picea glauca outer middle inner 146-198" 122-178 112-148 Gibbs, 1935 Picea sitchensis 0 - 2 cm 2 - 4 cm 4- 6 cm 160*** 115 65 Chalk and Bigg, 1956 Picea glauca sapwood 132-162" Clark and Gibbs, 1957 Picea rubens sapwood 95-140* Clark and Gibbs, 1957 variation within growing season annual variation between seasons single observation 4 Table I continued Species Depth from Cambium Range Water Contents O. D. W. Per Cent Source Pinus bankisana oute r middle inner 139-164''' 124-164 103-164 Gibbs, 1935 Pinus radiata annual rings 1- 3 4- 6 7- 9 10-12 13-15 126*** 112 111 110 103 Fielding, 1952 Pinus ponderosa sapwood 120*** Parker, 1954 Pinus contorta sapwood 120-150** Swans on, 1966 Pinus contorta outer inner 122-173** 126-164 Markstron and Hann, 1972 Pice a glauca outer middle inner 146-198* 122-178 112-148 Gibbs, 1935 Picea sitchensis 0 - 2 cm 2 - 4 cm 4- 6 cm 160*** 115 65 Chalk and Bigg, 1956 Pice a glauca sapwood 132-162* Clark and Gibbs, 1957 Picea rubens sapwood 95-140* Clark and Gibbs, 1957 variation within growing season annual variation between seasons single observation 5 Maximum water contents occur during the night or just before sunrise, followed by a decrease during the morning and early afternoon, with rehydration in the late afternoon and evening (Gibbs, 1935; Kramer 1956; Reid, 1961). The magnitude of diurnal fluctuations are less than seasonal values ranging from 12-21% o.d.w. (Gibbs, 1935; Reid, 1961). Both seasonal and diurnal fluctuations appear to be related to transpiration. Maximum and minimum sapwood water contents coincide with conditions favorable to low and high rates of transpiration respectively. Gibbs (1935) associated decreasing water content in birch (Betula alba var. papyrifera (Marsh) Spach) i n the spring with leaf opening and renewed transpiration; and increasing water content in the autumn with leaf f a l l and reduced transpiration. Work by Swanson (1966) with Engelmann spruce (Picea engelmannii Parry) and lodgepole pine indicates periods of maximum and minimum sap flow to be associated with minimum and maximum sapwood water contents. The cause of seasonal and diurnal lowering, is reported to be the lag of water absorption behind transpiration. This has been demonstrated in studies u t i l i z i n g seedlings, cut branches and cut roots (Kramer 1937; Kramer and Kozlowski, I960). However, there is l i t t l e evidence directly linking sapwood water content fluctuations to trans-piration or environmental variables influencing transpiration. Water Movement and Distribution The upward movement of water in the sapwood is customarily described as occurring in a thin layer of sapwood 2-A growth rings wide from the vascular cambium (Chalk and Bigg,1956; Kramer and Kozlowski, 6 I960; Kozlowski, 1961). This appears to be so for ring-porous angio-sperms, but in diffuse-porous angiosperms and gymnosperms a greater area of the xylem may be involved in conduction (Kramer and Kozlowski, 1960; Kozlowski -and Winget, 1963; Zimmermann and Brown, 1971). Dye injection into six coniferous species indicated sap movement in the f i r s t to seventh growth rings, with dye streaks 0.2-13.3 cm wide radially (Kozlowski and Hughes and Leyton, 1967). Swanson (1966) measured sap movement in lodgepole pine and Engelmann spruce at depths of 3.0-3.5 cm from the vascular cambium. Injection of isotope P32 in lodgepole pine and red f i r (Abies Magnifica A. Murr.) indicated movement at depths of 4 cm from the cambium, and maximum concentration of the isotope between the 1-2 cm depths from the cambium (Owston and Smith and Halverson, 1969). A greater flow area is also suggested by the distribution of water in the sapwood, which shows areas of maximum water content coinciding with areas of maximum dye and tracer transport. The dis-tribution shows a characteristic pattern for most conifers (Fielding, 1952; Chalk and Bigg, 1956; Reid, 1961, Swanson, 1966; Markstrom and Hann, 1972; Figures 1-4). The outer and inner sapwood have high water contents ranging from 90-200$ o.d.w. Inward from this area, water contents decrease very rapidly; in some species to 50-60$ o.d.w. at the sapwood-heartwood transition zone, and to near fiber saturation point in the heartwood. The sapwood-heartwood transition zone is defined here as the inflection point, or break in water content between wet and dry wood areas. The transition zone can be abrupt, occurring . within 1-2 growth rings or be very gradual (Dadswell and H i l l i s , 1962; Sandermann, 1967). In some trees a slight increase in water 200-180-160-140-Figure 1 Radial distribution of water in Douglas fir. DOUGLAS FIR 60-40-20-OUTER INNER SAPWOOD OUTER INNER HEARTWOOD MARKSTROM AND HANN 1972 • O 200-180-L O D G E P O L E PINE OUTER INNER SAPWOOD OUTER INNER HEARTWOOD Figure 2 Radial distribution of water in lodgepole pine. MARKSTROM AND HANN 1972 a Figure 3 Radial distribution . of water in lodgepole pine. REID. 1961 MARKSTROM AND HANN 1972 content in the transition zone occurs, and is associated with metabolic processes in the sapwood to heartwood change (Reid, 1961; Sandermann, 1967). If areas of conducting xylem and maximum water content do coincide, temporal changes in the levels or forms of radial wate^ r content distributions may be useful in identifying the location and extent of conducting xylem. Observations by Swanson (1966) show changes in the levels but not the forms of radial water content distributions between winter and fall for Engelmann spruce and lodgepole pine. However, no conclusions were possible because of the small sample size used. More work on this subject is required. Water Content Measurement One of the major problems in studying wood water content of living trees is measurement. The closed nature of the xylem makes accurate determination of wood water content difficult. Most current sampling methods require either small samples cut from a tree, like increment cores, or the complete cutting and sectioning of a tree (Fielding, 1952; Parker, 1954; Chalk and Bigg, 1956; Clark and Gibbs, 1957; Swanson, 1966; Johnstone, 1970; Markstrom and Hann, 1972). Some other methods include the insertion of wooden dowels into tree trunks as moisture sensors. (Etheridge, 1959), and insertion of Colman soil moisture units into tree stems (Bloomberg and Farrel-1 ^ 1965). Electric moisture meters are not suitable for measurements in wood or living trees where water contents exceed fiber saturation point. Above fiber saturation point the relationship between resistivity of wood and water content is nonlinear and of low sensitivity. The disturbance caused by cutting samples or inserting sensors into a tree biases water content measurements. Water in the xylem is in columns under tension, and when these are cut, it rapidly retreats from the cut surface (McDermott, 1941). When this occurs some water is lost from a sample. The effect should be greatest in angiosperms where vessels are long and wide, and smaller in gymnosperms where tracheids are short and narrow. In samples such as increment cores, errors could be serious because of the small sample size relative to water lost. Errors also may vary with sap tension in the xylem, which is less during the night than the day. Different tensions should remove different amounts of water. Another problem with cut samples is that different methods give different results. Personal observations of the author have shown that water contents obtained by an increment hammer are significantly higher by 20-30% o. d. w. than those obtained by a standard increment borer. These differences may be related to sap tension release on cutting the xylem. Water contents obtained by insertion of sensors into a tree stem are also questionable, because scar tissue can develop around the sensor and isolate it from the conducting xylem. To overcome these problems, sampling methods which minimize physical contact and disturbance to a tree stem are required. Gamma radiation attenuation has been proposed for this purpose (Youngs, 1965). This technique has been successfully used to measure density and water content of soils (Van Bavel, 1959; Gurr, 1962), snow .(Smith et al. , 1967), and reservoir sediments (McHenry and Dendy, 1964). Iizuka and Sakamato (196 1) used gamma radiation attenuation to measure relative water content 11 d i s t r i b u t i o n i n green d i s c s of A b i e s mayriaha. It has a l s o been used to detect i n t e r n a l wood defects i n logs ( P a r i s h , 1961). L o o s (1961) concluded that if s p e c i f i c g r a v i t y or m o i s t u r e content of a given thickness of wood is known, the other can be deter m i n e d nondestructive ly, r a p i d l y and a c c u r a t e l y by gamma r a d i a t i o n attenuation. These advantages, plus that of equipment suitable f o r f i e l d use, may make the technique u s e f u l for in situ sapwood water content measurement. In b r i e f s u m m a r y the m a i n points of this d i s c u s s i o n have been: (1) seasonal and d i u r n a l sapwood water content fluctuations in t r e e s are assu m e d to be r e l a t e d to t r a n s p i r a t i o n , but l i t t l e d i r e c t evidence f o r such r e l a t i o n s h i p s has been reported; (2) the a r e a of conducting x y l e m i n the sapwood may be gr e a t e r than p r e v i o u s l y supposed; (3) the study of t e m p o r a l changes i n the d i s t r i b u t i o n of water in the sapwood may be useful i n identify-ing the l o c a t i o n and extent of conducting xylem; (4) c u r r e n t methods of wood water content m e a s u r e m e n t are not s a t i s f a c t o r y f or the study of water i n l i v i n g t rees because of th e i r disturbance or destructive nature; and (5) gamma r a d i a t i o n attenuation m a y be a suitable method f o r i n s i t u sapwood water content measurements. 12 OBJECTIVES The general hypothesis of this thesis is that the conducting xylem of lodgepole pine at breast height occurs within a band of wet wood 3-6 cm wide from the vascular cambium. The conducting xylem is not constant, but varies in area and/or water content in response to transpiration and corresponding increases in plant water stress. The objectives of the thesis are: (1) To determine if temporal fluctuations of water content in the radial plane of lodgepole pine sapwood are indexes of the location and extent of conducting xylem; (2) To test gamma radiation attenuation as a method for in situ sapwood water content measurement; and (3) To relate sapwood water content fluctuations to environmental and plant variables which influence transpiration. Environmental and plant variables selected for study with sapwood water content are: soil water content, plant water stress, sap movement, precipitation, air temperature and relative humidity. The work and results of this thesis are organized and reported in three parts. Each part corresponds to one of the stated objectives: (1) Conducting Xylem Area; (2) Gamma Radiation Attenuation for Wood Water Content Measurement; and (3) Sapwood Water Content and Environmental and Plant Variables. 13 DESCRIPTION OF STUDY A R E A A l l field studies were conducted at the Kananaskis Forest Experiment Station, which is approximately 50 miles west of Calgary, Alberta, on the east side of the Kananaskis River, 5 miles south of its confluence with the Bow River. The area is approximately 51° N latitude and 115° W logitude and is in the east Slopes Rockies Section (SA. 1) of the Subalpine Forest Region (Rowe, 1959) which is a mountain counterpart of the Boreal Forest. Elevation of the area ranges from 4, 600-8, 000 feet M . S. L . . Field studies were conducted in two areas. Study Area No. 1 is located 3. 5 miles south of the station headquarters and 1/4 mile east of the Forestry Trunk Road. Study Area No. 2 is located 1 mile north of the station headquarters, near a secondary road (Figure 5). Climate The climate of the area is humid, cool and temperate. The mean annual temperature is 38° F , the mean frost-free period is 59 days, and mean precipitation is 27 inches of which 17 inches is rain, the latter falling from April through October. The mean monthly temperature for the latter period is 4 8 ° F . Geology and Soils The area is located in the main range of the Rocky Mountains. The present relief and topography were obtained during and subsequent to the Laramide Revolution. Underlying bedrock consists of intermixed calcareous rocks of the Upper Cretaceous of the Upper Alberta Group _N O R T H PROVINCE - B E R CANADA Figure 5 Map of Alberta and inset showing location of Kananaskis Forest Experiment Station, and Study Areas Nos. 1 and 2. 15 (Crossley, 1951). Study Area No. 1 is located on an alluvial fan consisting of coarse alluvium overlying glacial t i l l . The topography is gently sloping, ranging from 10-12%. Study Area No. 2 is located on an alluvial terrace consisting of fine to medium alluvium, 8-9 feet thick overlying coarse gravels. The topography is gentle to moderate, slope steepness ranging from 0-20%. The soil of Study Area No. 2, under the Canadian Soil Classification System (1968) is a Degraded Eutric Brunisol (Hillman, 1970). A detailed description of particle size classes and water retention curves for the soil are shown in Tables 2-3 and Figure 6. The soil is well drained, but has a clay content sufficient to retain water for plant growth. The solum extends to a depth of approximately 1 foot, below which alluvial parent material extends 7-8 feet. A detail description of the soil in Study Area No. 1 was not obtained. The soil is a sandy loam with a high gravel content and is rapidly drained. Crossley (1951) described, the soil as a Calcareous Brown Podzol. Vegetation The forest vegetation of both study areas (Figures 7, 8) is lodgepole pine, with an immature understory of Engelmann spruce. Mean age, height and diameter breast height of lodgepole pine in Study Area No. 1 are: 91 years, 54. 2 feet and 6. 9 inches. Stocking and basal area are 549 trees/ acre and 144 ft. /acre. Mean age, height and diameter breast height of lodgepole pine in Study A r e a No. 2 are: 70 years, 46. 2 feet and 7. 4 inches. 2 Stocking and basal area are 288 trees/acre and 84 ft. /acre. 16 Table II Soil profile description at study site, Kananaskis Experimental Forest, Alberta (after Hillman, 1970). Location: Physiography: Elevation: Parent material: Drainage: Vegetation: Climate: Collector: Date: Soil type: One hundred feet north of lower study plot Alluvial terrace 4, 600 feet Alluvium from Kanasaskis River Well drained Lodgepole pine, spruce understory, grasses, ground juniper, prairie rose, kinnikinnick, strawberry, fire-weed, Indian paintbrush, harebell, buffalo-berry, Populus sp. , aspen, aster, willow, bunchberry Humid, cool temperate. Mean annual temperature: 37 F Mean annual precipitation: 27 inches G. R. Hillman August 31, 1969 Canadian Classification System: 1968--Degraded Eutric Brunisol 1965--Degraded Brown Wooded US Classification System--(Seventh Approximation): Eutric Cryochrept Depth Horizon (in. ) Description L - H 1-0 Roots, undecomposed organic matter, black in color. Layer of pine needles on top A . 0-2 Light grey (10YR 7/1) fine sand; greyish-brown (10YR 5/2) J moist. Fine granular structure (powdery when dry), easily broken, not sticky, few fine roots, fine pores. No reaction with cold H C L . ; pH: 6. 9. Clear, smooth boundary 17 Table II continued Depth Horizon (in. ) De scription B 2-10 Light yellowish brown (10YR 6/4) sandy loam, yellowish brown (10YR 5/6) moist, slight platy structure, hard, firm, slightly sticky when moist; some large (1 inch diameter) and medium roots, many small roots, many fine pores. No reaction with cold HCL. ; pH: 6. 5. Boundary wavy and irregular B . 10-13 Dark yellowish brown (10YR 4/4) sandy clay loam. Dark J brown (10YR 3/3) moist, fine granular structure, sticky when wet, few roots, few fine pores. Reacts quite strongly with H C L . , calcareous. pH: 7. 6; abrupt, irregular boundary C 13-96 Light brownish grey (2. 5Y 6/2) sand. Dark greyish brown (2. 5Y 4/2) moist; fine granular structure, not sticky when moist; few fine roots, few fine pores, few medium pores. Reacts strongly with HCL. , (more so than any other horizon). pH: 8. 2 96+ Gravel (3/4 inch diameter) 18 Table III Results of mechanical analysis and particle size classification (Hillman, 1970). USDA Classification Bulk Natural Soil Sand Silt Clay density class horizon % % % g/cm' Sandy loam A . e3 67. 6 24. 0 8. 4 -Loam/sandy loam B m 49. 6 33. 0 17. 4 1. 29 Clay loam B y 45. 6 30. 0 24. 4 1. 48 Sandy loam C 72. 6 15. 0 12. 4 1. 44 ISSS Classification Bulk Natural Soil Sand Silt Clay density class horizon % % g/cmr Sand A . ej 83. 6 8. 0 8. 4 -Sandy loam B m 75. 6 7. 0 17. 4 1. 29 Sandy clay loam B y 70. 6 5. 0 24. 4 1. 48 Sana' C 87. 6 0. 0 12. 4 1. 44 19, VOLUMETRIC SOIL WATER CONTENT CM WATER CM 3 SOIL 030 O40 050 SAND SANDY LOAM SANDY CLAY LOAM SAND Figure 6 Soil water desorption curves for Eutric Brunisol soil at Study Area No. 2, Kananaskis Forest Experiment Station. 20 F i g u r e 7 Study A r e a N o . 1 ^ ± V e g e t a t i o n l o d g e p o l e p ine w i t h u n d e r s t o r y of i m m a t u r e \ * E n g e l m a n n s p r u c e . F i g u r e 8 Study A r e a N o . 2 V e g e t a t i o n l odgepo le p ine w i t h u n d e r s t o r y of i m m a t u r e E n g e l m a n n s p r u c e . 21 Lower and herbaceous vegetation for both study areas consists of aspen (Populus tremuloides Michx.), alder (Alnus crispa (Ait.) Pursh.), willow (Salix spp.), buffalo berry (Shepherdia canadensis (L.) Nutt.), wild rose (Rosa aciculosis Lindl.), bunchberry (Cornus canadensis L.), kinnikinnick (Arctostaphylos uva-ursi(L.) Spreng.), and a variety of grasses (Agroypyron spp., Agrostis spp., Bromus spp., Calamagrostis spp., and Elymus spp.). 22 CONDUCTING X Y L E M A R E A Objective The objective of this part of the thesis is to determine if temporal fluctuations of sapwood water content in the radial plane of lodgepole pine at diameter breast height can be used as indexes of the locations and extent of conducting xylem. Methods A population of 500 trees was established in Study Area No. 1. Fifty trees were randomly sampled for sapwood water content every two weeks from July 16-October 15, 1969. Samples were obtained with an increment borer at the same time of day for each sample date to avoid diurnal water content fluctuations. Radial water content distributions were obtained by plotting the oven dry weight water contents of 1 cm seg-ments of increment cores on distance from the vascular cambium. Cores were 4 mm in diameter and taken to a depth of 8 cm from the cambium or to heartwood. After extraction, each sample was transported in airtight containers to the laboratory, where the bark was removed and each core sectioned into 1 cm segments, whose water contents were determined. Standard procedures (A. S. T. M. , 1968) and an analytical balance with a precision of -0. 1 mg were used. Concurrent observations of sap flow were obtained by heat pulse methods (Marshall, 1958; Swanson, 1962) to test their correlation with sap-wood water content fluctuations. Trees were instrumented to measure heat 23 pulse velocities at depths of 1 and 2 cm from the vascular cambium. Ten trees were measured per sample date. Results and Discussion The uneven distribution of water in the sapwood and expression of water contents as percentages, suggested frequency distributions other than Normal. A series of Chi-square tests revealed that wood water content per centimeter depth from the cambium is best described by a Poisson distribu-tion. However, plots of Normal and Poisson distributions were so similar, that no data transformations were used in statistical analyses performed. Radial Water Content Distribution. Sapwood water content of lodgepole pine in the radial plane at breast height was highly variable. Water contents for the 0-8 cm depths from the vascular cambium varied from 23-158% o. d. w. , with a mean of 58% o. d. w. and a standard deviation of 21% o. d. w. The outer 0-2 cm had water contents of 100-158% o. d. w. , which decreased with depth to near fiber saturation point in the heartwood. The transition zone from wet to dry wood (i. e. sapwood to heartwood) consistently occurred between the 3-4 cm depths. Analysis of the biweekly observations showed significant differences in the radial distribution of water in the sapwood (Table IV). Average water contents for the 0-6 cm depths from the cambium ranged from 35-96% o. d. w. A Dunctm's New Multiple Range Test for each sample date showed water contents for the 0-3 cm and 5-8 cm depths to act as two statistically different groups. The 3-4 cm depths were independent or transitional in water content between the inner and outer depths. These groupings were 24 Table IV Analysis of variance: Sapwood water content by time July 16-October 15, 1969; 0-6 cm depths and diameter classes 4. 0-7. 0 . . . . . . . . . inches. , , Source of Degrees of Freedom Sum of Square s Mean Square Variance Ratio Time (T) 6 27032. 0 4505. 4 15. 68** Depth (D) 5 183900.0 36799.0 127. 98** Diameter (Da) 3 5453. 1 1817. 7 6. 32*" T x D 30 15693. 0 523. 1 1. 82* T x Da 18 16303. 0 905. 7 3. 15** D x Da 15 4648. 4 309. 9 1. 08 T x D x Da 90 18976. 0 210. 8 0. 73 E r r o r 168 48281. 0 287.39 Total 335 320280.0 ..level of significance 0.01 level of significance 0. 05 Sample date (July 16, July 30, August 18, August 26, September 16, September 30, October 15) Depths from cambium (0-1, 1-2, 2-3, 3-4, 4-5, 5-6 cm) Diameter classes (4.0-4.9, 5.0-5.9, 6.0-6.9, 7. 0-7. 9 inches) 25 consistent for each sample date (Table V). The i n t e r a c t i o n between time and depth in the a n a l y s i s (Table IV) indicates s i g n i f i c a n t d i f f e r e n c e s i n the water contents of the r a d i a l d i s t r i b u -tions between sample dates. Water contents of the 0-6 c m depths f r o m the c a m b i u m had d i f f e r e n t r e s p o n s e s with time ( F i g u r e 9). The outer 0-3 c m had s i m i l a r r e sponses and the greatest fluctuations i n water content, which ranged f r o m 6-44% o. d. w. with a m e a n of 14% o. d. w. The inner 4-6 c m e x p e r i e n c e d s i m i l a r but s m a l l e r fluctuations in water content ranging f r o m 0. 4-22% o. d. w. , with a mean of 6% o. d. w. The g e n e r a l f o r m of the r a d i a l d i s t r i b u t i o n s , i n t e r m s of slope and i n f l e c t i o n points between wet and d r y wood, r e m a i n e d the same between sample dates. S i m i l a r r esponses o c c u r r e d i n d i u r n a l and annual observations of sapwood water content ( F i g u r e 10). A m o r e quantitative d e s c r i p t i o n of r a d i a l water content d i s t r i b u t i o n s was attempted by f i t t i n g different l i n e a r m odels to the data by r e g r e s s i o n analyses. Of the models tested a second degree parabola best d e s c r i b e d the r a d i a l d i s t r i b u t i o n . However, these models and a r i t h m e t i c m e a n c u r v e s were not c o n s i d e r e d r e p r e s e n t a t i v e on an i n d i v i d u a l tree b a s i s , because they smoothed out the a s y m m e t r i c a l d i s t r i b u t i o n of water and o b s c u r e d the sharp boundary between wet and d r y wood areas. To obtain a m o r e r e p r e -sentative d e s c r i p t i o n , water content frequency c l a s s e s and mode water content per centimeter depth were determined. Water content frequency c u r v e s ( F i g u r e 11) show the 0-2 c m depths to have s i m i l a r b e l l - s h a p e d d i s t r i b u t i o n s and mode values of 80% o. d. w. The 2-3 c m depth also has a mode water content of 80% o. d. w. , but its d i s t r i b u t i o n is flat, with values evenly d i s t r i b u t e d between the 30-80% o. d. w. 26 Table V Results of Duncan's New Multiple Range Tests for water content means at depths of 0-8 cm from cambium on sample dates July 16, : 30; August 18, 26; September 16, 30 and October 15, 1969. Sample date Depths from cambium July 16 1 2 3 4 5 6 7 8 July 30 1 2 3 4 5 6 7 8 August 18 1 2 3 4 5 6 7 8 August 26 1 2 3 4 5 6 7 8 September 16 1 2 3 4 5 6 7 8 September 30 1 2 3 4 5 6 7 8 October 15 1 2 3 4 5 6 7 8 No significant differences between depths underlined by the same line at 0. 05 level of signifiance. } •' Figure 9 Sapwood water content variation of lodge-pole pine at breast height for 0-6 cm depths from the ! cambium for the period | July 16-October 15, 1969. t; 100| DECEMBER 1970 2200 MAY 7 ANNUAL OBSERVATIONS JULY 1970 - AUGUST 1971 SAMPLE S I Z E / POINT » 10 DIURNAL OBSERVATIONS MAY 7 - 8 . 1949 SAMPLE SIZE/POINT = 10 MONTHLY OBSERVATIONS JULY-OCTOBER 1969 ^SAMPLE S IZE /POINT = 50 Figure 10 Variation of radial sapwood water content distri-bution of lodgepole pine for annual, monthly, and diurnal time bases, for 0-6 cm depths from the cambium at breast height. DISTANCE FROM CAMBIUM - C M J 28 WATER C O N T E N T CLASSES - P E R C E N T WATER C O N T E N T Q D W F i g u r e 11 P e r c e n t frequency of sapwood water contents for 0-8 c m depths f r o m c a m b i u m for lodgepole pine at b r e a s t height. 29 c l a s s e s . T h i s indicates the 2-3 c m depth to be a t r a n s i t i o n a r e a between wet and d r y wood. Water content d i s t r i b u t i o n s i n the 4-8 c m depths are s i m i l a r and w e l l defined with modes of 30% o. d. w. The plot of mode water contents on distance f r o m the c a m b i u m ( F i g u r e 12) c l e a r l y shows the a s y m m e t r i c a l d i s t r i b u t i o n of water, and the sharp break between wet and dry wood as it o c c u r r e d i n m o s t t r e e s . Conducting X y l e m A r e a . The independence of the outer 2-3 c m f r o m the inner depths of the sapwood in t e r m s of water content l e v e l s and fluctuations is i n t e r p r e t e d as indicative of conducting and nonconducting xylem. T o define the conducting x y l e m it was a s s u m e d that areas of conducting x y l e m and m a x i m u m water content fluctuations coincide, and the outer and inner boundaries of the flow a r e a are r e s p e c t i v e l y the v a s c u l a r c a m b ium and inf l e c t i o n point between wet and dry wood. The in f l e c t i o n point was used, because it o c c u r s i n an a r e a c h a r a c t e r i z e d by s m a l l water content changes. F u r t h e r m o r e , the water contents a s s o c i a t e d with the i n f l e c t i o n point, 50-70% o. d. w. , indicate a low pr o b a b i l i t y of sap flow. When e x p r e s s e d as free water i n t e r m s of percentage of wood pore space, they range f r o m 16-32%. The conducting x y l e m of lodgepole pine at diameter b r e a s t height defined i n these t e r m s and d e r i v e d f r o m F i g u r e 12 is an a r e a 3. 25 c m wide f r o m the c a m b ium with a m i n i m u m water content of 55% o. d. w. and occupies 60-80% of the total c r o s s - s e c t i o n a l stem area. Using a water content of 60% o. d. w. as a c r i t e r i o n to d i s t i n g u i s h between "conducting" and "nonconducting" xylem, a frequ e n c y c u r v e was c o n s t r u c t e d ( F i g u r e 13). The curv e indicates that in 80-90% of the t r e e s sampled, "conducting x y l e m " o c c u r r e d i n the 0-2 30 -MODE CURVE - MEAN CURVE DISTANCE FROM CAMBIUM - C M Figure 12 Radial sapwood water content distribution of lodgepole pine at breast height by mean and mode curve s. 100r 8f+ 2 3 4 5 6 7 8 DISTANCE FROM C A M B I U M - C M 10 Figure 13 Per cent frequency of "conducting xylem" in ,lodgepole pine at breast height in the radial plane. "Conducting xylem" defined las wood of water content greater than 60% o. d. w. in :the 0-3 cm depths from the cambium. 31 c m depths, and beyond the t h i r d c e n t i m e t e r depth the frequency of "conducting x y l e m " r a p i d l y approached zero. Heat pulse observations of sap flow i n some of these trees support these estimates. Heat pulse v e l o c i t i e s of 9-10 cm/hour and 4-5 cm/hour were observed at depths of 1. 0 and 2. 0 c m f r o m the cambium r e s p e c t i v e l y . F u r t h e r m o r e , a conducting x y l e m a r e a of 3. 69 c m wide f r o m the cambium was es t i m a t e d for these t r e e s by fit t i n g heat pulse v e l o c i t i e s obtained at depths of 0. 5, 1. 0, 1. 25, 1. 50 and 2. 0 c m f r o m the cambium to a p a r a b o l i c curve (Swanson, 1971). It is concluded f r o m these r e s u l t s that the d i s t r i b u t i o n and te m p o r a l fluctuations of sapwood water content at b r e a s t height c an be used as indexes of the l o c a t i o n and extent of conducting xylem. The concentration of water in the outer 0-3 c m of xylem, the independence of its r e l a t i v e l y l a r g e , t e m p o r a l fluctuations f r o m the inner xylem, and heat pulse v e l o c i t y p r o f i l e s indicate a conducting a r e a 3. 25 c m wide f r o m the cambium. Such an a r e a accounts f o r 60-80% of the total c r o s s -s e c t i o n a l s t e m a r e a of the t r e e s studied and has water contents of 60-158% o.d.w. However, these values are only approximate, m o r e substantive evidence of sap move beyond 2 c m f r o m the c a m b i u m is required. F u r t h e r work with heat pulse v e l o c i t y techniques, r a d i o -isotopes and e l e c t r o n m i c r o s c o p y should be able to c o n f i r m sap move-ment beyond 2 c m and boundary conditions between conducting and nonconducting xylem. 32 GAMMA RADIATION ATTENUATION FOR WOOD W A T E R CONTENT M E A S U R E M E N T Objective The objective of this part of the thesis is to test gamma radiation attenuation as a nondestructive method for wood water content measurement in living and in dead wood. Theory Gamma radiation attenuation refers to the reduction in intensity of a beam of photons passing through a material as a result of Compton scattering, photoelectric effect, or pair production. The attenuation of a monoenergetic beam of gamma radiation (dN) passing through an absorber (dS) in thickness is given by: -dN = Nj pfx as . : (eq. 1. 1) where N. is the number of incident gamma photons, p is the density of the _3 absorber (units, g cm ), and Jl is the total mass attenuation coefficient of 2 - 1 the absorber (units, cm g ) (Spinks and Woods, 1964; Gardner and Calissendorf f ,1967). The total mass attenuation coefficient describes the reduction in intensity of a beam of gamma photons transmitted through a unit thickness of absorber divided by the density of the absorber. Mass attenuation coefficients are constant for a given material and radiation of a given energy, but vary directly with absorber density. Equation 1. 1 only applies where (dN) and (dS) are small, but integration removes this restriction: 33 N = Nj exp|- P Ms} (eq. 1. 2) or (eq. 1. 3) where N is the number of gamma photons transmitted through an absorber of S thickness (units, cm). The total mass attenuation coefficient for a compound or mixture of elements is additive, being equal to the sum of the individual coefficients for each element or compound on a weight fraction basis. Radiation attenuation in a compound of two absorbers would be: where subscripts 1 and 2 refer to each absorber. Application-- Wood Water Content For the application of gamma radiation attenuation for sapwood water content measurement it is assumed: 1. A tree is composed only of wood and water. 2. The minimum water content of a living tree stem is fiber saturation point. 3. Wood density of a living stem is constant in time. 4. Attenuation coefficients of wood and water are constant and can be approximated with mean values without serious error. 5. The attenuation coefficient of water can be used for sap. In -fjT - ~ S { M I P , + M2P2} (eq. 1.4) 34 Under these conditions, any changes in gamma radiation attenua-tion through a tree stem would be due to variation in water content. Gamma radiation and wood water content are expressed as: °7j:-= S 1 / W P w o + / t v « P w a e w f ( e ci- 5> SPwa/*wat + S / W w o | (eq. 1.6) N = number of emergent photons, counts /minute Nj = number of incident photons, c ounts/minute S = thickness of measured sections, cm 2 -1 u = mass attenuation coefficient wood, cm g •wo ° 2 -1 a = mass attenuation coefficient water, cm g -3 P W O = density of wood green g cm -3 Pw= density of water, g cm 3 -3 0 = wood water content, cm c m wood The tree stem is described in terms of wood and water because they occupy 65-75% of stem volume and account for most radiation attenuation. Furthermore it would be difficult to determine attenuation coefficients for each substance or tissue in a tree stem. Wood is defined as including the bark, cambium, xylem and organic deposits (i.e. all solid materials). Water includes the sap, resins, sugars and carbohydrates in a tree stem (i. e. all dissolved materials). In living trees zero water content was set at the fiber saturation point (28% o. d. w. ), because below this value wood shrinkage and swelling would affect wood density and radiation 35 attenuation (Loos, 1962). Water and its mass attenuation coefficient were used as a substitute for sap because it would be difficult to obtain volumes of xylem sap required to determine its attenuation coefficient. Further-more sap is a very dilute solution. No serious radiation effects which might affect xylem water content or cause permanent cytogenetic or morphogenetic changes in study trees were expected. Total maximum exposure per tree at breast height was 1 rad, obtained from a number of short exposures totalling 4. 5 hours. These levels are low compared to exposures of 1,400-6, 000 rads which resulted in abnormal cell development, growth reduction and mortality at the higher values (Miksche et.al. , 1961; Hamilton, 1963). Loos (1962) 4 reports a threshold level of 3. 4 to 6. 4 x 10 rads is generally required to affect cellulose, and that wood is more resistant because of the presence of lignin and extractives in its lattice structure. Methods Gamma radiation attenuation was tested in the laboratory and field. In the laboratory attenuation coefficients and the effects of wood grain orientation on attenuation were determined, and a test for wood water content was made. In the field, equipment operation was tested, patterns of radiation attenuation in trees were determined and a test for wood water content in living trees was made. Equipment. The equipment used was a two probe gamma radiation density gauge manufactured by Troxler Electronic Laboratories, Raleigh, North Carolina, U. S. A. Counting equipment consisted of a scintillation detector (model no. 310) with a Nal(Tl) crystal 1. 27 cm thick and 3. 81 cm in diameter, coupled to a photomultiplier tube, a battery powered pulse height analyzer (model no. E-200) and a scaler-ratemeter (model no. 1651). The source used was 5 millicuries (mc) of cesium-137 with a half-life of 27 years and a primary energy peak of 0. 661 M E V . The general operation of the equipment is outlined in Figure 14. The resolution of measurements for the equipment without collimation is described by the manufacturer as equal to the thickness of the scintillation crystal, 1. 27 cm. However, this is not completely true because a propor-tion of incident 0. 661 M E V gamma photons are subject to low angle scatter-ing. When a count is made, these scattered photons contribute to the count because their energy is still within the range of the window setting (DeVries, 1969). This was evident at the tree-air interface where counts started to decrease 2-3 cm before the beam was into the tree. To correct this two lead collimating blocks 8 . 4 x 4 . 9 x 6.8 cm with slits of 1 x 3 cm were installed on the source and detector. Because of the length of the collimating blocks the spacing of source and detector was increased from 30 to 48 cm to allow a greater range of tree diameters to be measured. Collimating gave a better definition of the position of the volume of influence within a tree. Resolu-tion was increased to 5-10 mm. The approximate volume of influence of the collimated gamma beam, if fully occupied, is a pyramid 40 x 3 x 1 cm 3 with a volume of 183 cm . To support the source and detector on trees, two stands were tested. The first was a portable stand constructed of aluminum angle and plywood, and could be placed at different heights on a tree stem, and was held in place by its own weight (Figure 15). This stand was satisfactory for determining patterns of gamma radiation attenuation in trees, but was later replaced with permanent stands to insure a constant measuring plane in each 37 D E T E C T O R : N a l ( T l ) CRYSTAL PHOTOMULTIPLIER TUBE IN LEAD COLLIMATING BLOCK TREE STEM TRANSVERSE PLANE I 1 CESIUM 137 SOURCE IN LEAD COLLIMATING BLOCK Poise Height Ana lyzer Sea le r - Ratemete r GAMMA RADIATION BEAM PASSING THROUGH S A P W O O D Figure 14 Schematic diagram showing operation of gamma radiation attenuation equipment. Gamma radiation emitted by the ces'ium 137 source is transmitted in a.narrow beam through the transverse plane of a tree stem. Gamma photons passing through the tree in a straight line are absorbed by the Nal (Tl) crystal, which produces a light pulse that is converted into an electrical pulse and routed to the pulse height analyzer. The pulse height analyzer electronically discriminates against all photons, the energy of which falls outside of the energy range covered by the window, allowing only those photons whose energies fall within the window range to be counted. 38 F i g u r e 15 P o r t a b l e s t and to s u p p o r t g a m m a r a d i a t i o n e q u i p m e n t a r o u n d t r ee s. 39 study tree. Permanent stands were constructed of 1-1/4 inch perforated angle iron, with legs hammered into the ground and guy wired (Figure 16). On each stand a portable U-shaped trolley was used to move the gamma beam through the transverse plane of a tree. The trolley was constructed of 1-1/4 inch perforated angle iron and four 2-1/2 inch diameter hard rubber wheels (Figure 17). The rolling surface for the trolley was a 3/4 inch piece of plywood, with four 3/4 inch electrical conduit pipes as tracks for the trolley. In use, the trolley and rolling surface was placed on a stand and leveled by four screws. Attenuation Coefficients. Mass attenuation coefficients for wood and water were determined in the laboratory by rational and empirical methods. An attenuation coefficient for wood was determined from samples obtained in Study Area No. 2. Wood samples 3-9 cm long and 5 cm wide were cut from heartwood to obtain material at or near fiber saturation point, to establish a common water content among samples. Four 1 minute counts (N) were taken in each sample, 2 in the tangential plane and 2 in the radial plane. In association with each count (N), a count of incident radiation (N )^ and a count through a plastic standard (Ng) were obtained. Following this the density (green volume) and oven dry weight water content of each sample was determined. The empirical and rational mass attenuation coefficients obtained for 2 - 1 2 - 1 wood are respectively 0. 07276 cm g and 0. 07295 cm g . The empirical estimate was obtained by adjusting gamma counts (-In N/N.) to a common water content equal to fiber saturation point. These adjusted values were regressed on sample thickness S to obtain a linear attenuation coefficient, 40 Figure 17 Diagram of trolley system: la-b. Aluminium tubes for holding source and detector: 2. Graduated rod for locating air-tree interface; 3a-b. Metal spacing jigs for source and detector; 4. Trolley constructed from angle iron; 5a-b. Lead collimating blocks for source and detector; 6. Wheels for trolley; 7. Rolling surface of ply-wood with electrical conduit for tracks. 41 which was divided by mean wood density of the samples for a mass attenua-tion coefficient (Figure 18). The rational estimate was a mean value of the coefficients calculated for each wood sample. Coefficients were determined using equation 1. 7: S » w o l Nl/N s + M " a v f The parameters S, 6V , N, N . N were measured for each sample. The J., s 2 - 1 value of Mwa was 0. 0808201 cm g . The mass attenuation coefficient for water was obtained by methods described by Gardner (1965) and Davidson e t aL (1963). An acrylic plastic container 6. 5 cm x 7. 0 cm x 30 cm with four equal compartments was placed in a collimated gamma beam, and a series of 1 minute counts were taken to obtain a base count (N c) for the empty container. Each compartment was then successively filled with distilled water and a series of counts taken for the container and water together + w ). The empirical and rational mass attenuation coefficients obtained for 2 - 1 2 - 1 water are respectively 0.08082 cm g and 0.07961 cm g respectively. The empirical estimate was determined by regressing gamma counts (-In N/1SL) on absorption thickness to obtain a linear attenuation coefficient, which was divided by the density of water for a mass attenuation coefficient (Figure 19). The rational estimate was obtained by using equation 1. 8: „ _ InNc/jcj-wa (eq. 1.8) w a e v s P w a ~ -where the container is full and is unity and S is measured. 4Z 1 2 3 4 5 6 7 8 9 K> 11 12 ABSORPTION THICKNESS S cm. Figure 18 Relative count ratios adjusted to a common water content, regressed on absorption thickness S. r = 0. 8598 r 2 xlOO = 73. 9% SE = 0. 04015 e n = 36 Linear attenuation coefficient equal to slope 0. 0330 g--*-. Mass attenuation coefficient equal to slope divided by-average density of wood samples (0. 4535), 0. 07276 cm2 g-1. ! Figure 19 Relative count ratios, regressed on absorption thickness S. r ' = 0. 992 r 2 xlOO = 99. 8% SE n = 0.0280 = 20 Linear attenuation coefficient equal to the slope, 0. 0808201 g _ 1 . Mass attenuation coefficient equal to slope divided by density of water, 0. 08082 cm2 g-1. 10 15 20 ABSORPTION THICKNESS S cm. 43 Temperature Effects. Field operation of the gamma equipment indicated it was temperature sensitive. Reginato and Jackson (1971) report temperature variation affects the detector, causing changes in the gain of the photo-multiplier tube and in the light output and resolution of the scintillation crystal. These changes cause a shift of the cesium-137 energy spectrum along the baseline and a change in peak pulse height (i. e. incident count Nj). To minimize temperature effects,, the end of the aluminum tube holding the detector was insulated with a 1. 5 inch layer of polystyrene foam. The foam and length of the tube were also covered with aluminum foil to reflect incident solar radiation. Where possible, gamma counts were taken at the same time of day (early morning hours) to obtain similar temperature regimes for each set of observations. To further minimize baseline shifts in the energy spectrum, incident counts (]NL) were checked and referenced to a standard, prior to each count (N) in a tree stem. This approach assumes detector temperature does not significantly change during the counting time in a tree. However, where large temperature changes o c c u r r e d ( 2 0 - 3 0 ° F ) a temperature correction coefficient for the detector was used to adjust incident and sample counts (N., N) to a common temperature. The temperature correction coefficient was obtained by regressing field counts of (N )^ on ambient air temperature at time of observation (Figure 20). These measures were effective, -because incident counts (JNL) were within a counting precision of - three times their standard deviation of 300 counts per minute. 44 /Figure 20 Incident counts N. regressed on ambient air temperature F at time of observation for temperature correction coefficient. = 0. 8391 = 70. 4% = 4210 ct/min. e n =44 Correction coefficient = - . 58% change in N. per 1 degree F rise in air temperature. so So -AIR TEMPERATURE TANGENTIAL PLANE RADIAL PLANE "l 2 3 4 5* t 7~ » ifi n—12 ABSORPTION THICKNESS S cm. Figure 21 Relative count ratios tangentially and radially obtained in wood samples regressed on absorption thick-ness S. Tangential: r r 2 x 100 SE e n Radial: r r 2 x 100 SE e n 0. 9730 94. 8% 0. 01802 18 0. 9924 98. 5% 0. 0154 18 45 Results and Discussion Wood Grain Orientation. The effects of different wood grain orientations in a gamma beam were studied to see if differences existed. If such were the case, more than one attenuation coefficient for wood and special sampling methods would be required. The test was done by regressing gamma counts obtained in the radial and tangential planes of wood sample, on sample thick-ness S separately, and testing the two regressions for significant differences in slopes and levels. Results of the test show no significant differences to * exist between gamma radiation attenuation in the tangential and radial planes of the wood samples tested (Figure 21, Table VI). Radiation Attenuation in Lodgepole Pine. The objectives here were to identify the magnitude, patterns and variation of gamma radiation attenuation in lodge-pole pine. To do this 1 minute gamma counts were taken in the transverse plane of 5 trees at breast height, in successive 1 cm increments across each tree. Attenuation was expressed as counts per minute or as a ratio of emergent to incident radiation, and plotted on tree thickness. The general pattern of attenuation for most trees showed maximum attenuation to occur in the outer 2-3 cm and minimum attenuation at or near tree center (Figure 22). This pattern was attributed to the variation of water content and wood density in a tree stem. To check this, gamma radiation in another single tree was compared to the distribution of water and wood density in the transverse plane. Water contents and wood densities were determined from increment cores. The attenuation was different from the general pattern (Figure 23) but showed maximum and minimum attenua-tion to coincide with areas of maximum and minimum water content and wood density. A regression analysis of attenuation (-In N/N.) on water Table VI Test of slopes and levels for two regression lines of gamma count ratios obtained in tangential and radial planes of lodgepole pine wood samples on absorption thickness (S). Degrees of Sum of Sum of Sum of Degrees of Sum of Mean Variance Group Freedom Squares Y Squares X Products XY Freedom Squares Residual Square Ratio Tangential 17 0. 009 1 56. 20 2. 2981 16 0. 0052 Radial 17 0. 1597 SSY 78. 97 SSX 3. 5236 SPXY 16 32 1 0. 0022 S S R E S 0. 0074 S S S L O P E °- 0 0 0 4 MSjO. 000231 MS 2 0. 0004 1.7316 NS 0. 2588 134. 99 5. 8217 33 1 S S R E S °" 0 0 7 8  S S L E V E L °- 0 0 0 5 MS 3 0. 000236 MS 4 0. 0005 2.1180 NS Total TSSX TSSX TSPXY 35 0.2704 139.7289 6. 0523 34 S S R E S °* 0 0 8 3 NS not significant at 0. 01,, 0. 05 levels of significance. Y = gamma count ratios (In N/Ni) X = absorption thickness (S), C M 47 ATMOSPHERE -TREE INTERFACE F i g u r e 22 P a t t e r n of gamma ra d i a t i o n attenuation i n a single lodgepole pine at bre a s t height in the t r a n s v e r s e plane. 10 15 20 DISTANCE - CM O O 0.6 OS §3 o.i F i g u r e 23 C o m p a r i s o n of gamma ra d i a t i o n attenuation, wood density and water content i n lodgepole pine at breast height i n the t r a n s v e r s e plane. 1 3 4 5 6 7 S 9 K> 11 V2 i3 14 S 16 17 18 iv D I S T A N C E - C M 48 content and wood density gave a multiple correlation coefficient of 0. 87, and simple correlation coefficients of 0. 70 and 0. 05 for wood density and water content, respectively. The high correlation coefficient of wood density indicates its importance to attenuation. The lack of correlation for water content was unexpected and may be caused by bored water contents not being representative of the area measured, by gamma radiation. The importance of wood density is further indicated by replicate observations of attenuation in trees at the same height above ground, which produced characteristic attenuations curves for different directions. These curves were interpreted to reflect wood density variation more than water content in a tree stem. Because of this the same location and orientation of the gamma beam in a study tree was used for all measurements to insure a constant measuring plane and to minimize measurement error. Observations of gamma radiation attenuation in another tree were obtained monthly for July, August and September 1970. The patterns of attenuation for each sample date remained relatively constant, with maximum attenuation at tree edge and minimum attenuation slightly off tree center (Figure 24). The curves, however, show substantial differences in the levels of attenuation. These differences are interpreted to be caused by a combi-nation of water content fluctuations and instrument error caused by temperature variation. ' These patterns of attenuation differ from those of Parrish (1961) who observed a symmetrical U-shaped curve with maximum attenuation occurring through tree center. However, Parrish worked with cut, dry logs of black oak (Quereus velutina Lam. ) and under such conditions radiation attenuation 49 5 6 7 - 8 DISTANCE - CM 10 11 12 13 14 15 16 17 Figure 24 Comparison of gamma radiation attenuation curves obtained in a single lodgepole'pine tree at breast height, transverse plane in July, August, and September 1970. 50 would be primarily a function of sample thickness and wood density. It is concluded that greater attenuation in lodgepole pine at tree edge results from the combined effects of higher wood densities and water contents, which male the total density of the outer edges greater than through tree center. Laboratory Test for Wood Water Content. Gamma radiation attenuation was tested by comparison of gravimetric water contents ( 9 ) and gamma water contents ( 0V) of 16 wood samples. The samples were tangential segments including bark, sectioned from fresh cut discs of lodgepole pine, and^ranged in thickness and water content from 2-11 cm and 28-105% o. d. w. (0. 127-3 -3 0. 467 cm cm wood). For each sample, four 1 minute counts (N), and associated incident (N.) and standard (N ) counts were taken. Water v 1 s contents obtained were absolute and calculated by equation 1. 9: 9 V = - - L ( h * J f ( 1 J (eq. 1. 9) where M w a = 0. 0808 cO • c m 2 g " 1 , M w o = 0. 7288 c m 2 g ' 1 , P W Q= 0. 4535 g cm" 3 , and N, N., N , and S were measured directly. The equation expresses the i s amount of free water in a sample because the attenuation coefficient for wood was determined at fiber saturation point. To obtain total water content, the amount of adsorbed water must be added to 9 . v Gamma and gravimetric water contents were compared by regression analysis, which gave a correlation coefficient of 0. 96 and a coefficient of 2 determination (r x 100) of 92. 6% (Figure 25). The standard error of estimate and sample size were 7. 7 and 47 respectively. Mean gamma and gravimetric water contents were 77. 5% o. d. w. and 71. 0% o. d. w. 51 Figure 25 Laboratory test. Regression of water contents obtained by gamma radiation attenuation on gravimetric water contents. z liffl--jfc—5b—ab <i)—5b—sb—7b—sb—*—rto—ito—ife—i4o 9g - GRAVIMETER WATER CONTENTS O.D.W. / Figure 26 Field test. Regression of water contents obtained by gamma radiation attenuation on bored water contents. r x 100 SE n = 0. 7736 = 59. 8% = 8. 70% = 33 40 60 80 100 120 0g GRAVIMETRIC WATER CONTENT O.D.W. "L 52 respectively. A Student's t-test indicated no significant difference between the two means. Field Test for Wood "Water Content Measurements. Gamma radiation attenuation was tested by comparing the water contents of living trees by gamma radiation and increment borings. Measurements for each method were restricted to separate groups of trees, to minimize disturbance to the trees and to prevent interaction between the methods. Both groups were closely intermixed on Study Area No. 2, and each contained 5 trees of similar height, diameter and crown development. Monthly and diurnal observations of sapwood water content were obtained between June and September 1971. Water contents at the 0-1 cm depth from the vascular cambium for bored samples and 1-2 cm depth from tree exterior for gamma radiation attenuation were compared by analysis of variance and regression. The 0-1 and 1-2 cm depths for both methods are approximately of equal location in the trees. The analysis of variance indicates significant differences between the sampling methods (Table VII). Mean water contents for gamma radiation and increment borings were 130% o. d. w. and 84% o. d. w. respectively. The gamma water contents may be higher because of the inclusion of bark moisture content and the measurement of a larger volume of wood. The volumes of wood sampled by gamma radiation and increment borings are 53 Table VII Analyses of variance: Sapwood water contents at breast height in lodgepole pine obtained by gamma radiation attenuation and incre-ment boring on June 2-3, 1971 and July 12-13, 1971, Study Area No. 2. Date Source of Variation Degrees of Freedom Sum of Square s Mean Square Variance Ratio June 2- 3 Methods 1 1, 188. 64 1, 188. 64 4. 982* Error 30 7, 156. 85 238. 56 Total 31 8, 345. 50 July 12-13 Methods 1 2, 326. 7 2, 326. 7 7.304* Error 33 10, 510. 9 318.5 Total 34 12, 837.6 'Level of significance 0.01 Level of significance 0.05 Methods = water content measurement by gamma radiation attenuation at 1 - 2 cm depth from tree exterior and increment boring at 0 - 1 cm depth from vascular cambium. 54 3 3 19. 0 cm and 0. 158 cm . Furthermore a plot of gamma water contents on depth into the tree stem shows a different pattern of variation than bored water contents. The regression analysis shows significant correlation between gamma and bored water contents. A simple correlation coefficient of 0. 77, with a standard error of estimate and sample size of 8. 7 and 33 was obtained (Figure 26). The degree of association of the two water contents is further illustrated by the plots of monthly and diurnal observations of each method in Figures 29, 33, 34. In both cases the two methods show similar fluctua-tions with time. From these results it is concluded that both methods provide a measure of the same physical phenomenon. However, further study and quantification of differences are required before an exact comparison of water content levels can be made. Precision of Water Content Measurements. The variance of gamma water content measurements is equal to the sum of variances for photon emission, thickness S, wood density o , and attenuation coefficients u u • The J wo wai 'wo precision of measurements, however, is largely determined by the random emission of gamma photons from the source material. The other terms are not random and it was assumed that they were measured with sufficient precision to make their contributions to the total variance negligible. The variance of water content measurements for variation from random gamma photon emission is (Gardner and Calissendorfff 1967): 55 where V = variance, n - attenuation coefficient water, S = thickness of absorber, N gamma count in study material 1NL = incident count and n = ratio of counting times for N/N. . The element (1 + N/nN^) is a correction factor to adjust for differences in counting times between N and N... The standard deviations for in situ sapwood water contents obtained during summer 1971 were calculated by equation 1. 10. They ranged from 0. 0086-. 0045 c m 3 H^O cm" 3 wood for depths 0-1, 1-2, 2-3, 3-4 cm from tree exterior. The standard deviations are variable because S changes with depth into a tree stem. The precision of measurements, defined as -3 times their standard deviations in o. d. w. terms for depths 0-1, 1-2, 2-3, 3-4, are ts. 7%, -3.9%, -3.3%, -3. 0% respectively. 56 SAPWOOD WATER CONTENT-ENVIRONMENTAL AND PLANT VARIABLES Introduction The objective of t h i s section i s to i d e n t i f y sapwood water con-tent f l u c t u a t i o n s , and to r e l a t e them to environmental and plant variables which influence t r a n s p i r a t i o n . Environmental and plant v a r i a b l e s selected for study are: s o i l water content, p r e c i p i t a t i o n , a i r temperature, r e l a -t i v e humidity, sap movement, and plant water s t r e s s . To determine these r e l a t i o n s h i p s study p l o t s were established i n Study Areas No. 1 and 2. The plo t i n Study Area No. 1 was on a f l a t area and contained a population of 500 lodgepole pine trees. The pl o t s established 1 i n Study Area No. 2 were approximately 1,000 feet apart and had an elevation d i f f e r e n c e of 100 feet. The lower p l o t i s 30 X 60 feet i n s i z e and located on a f l a t area. The upper p l o t i s 30 X 50 feet i n s i z e , and located on a k n o l l with the ground sloping downhill (10-25% slope steepness) i n a l l d i r e c t i o n s from p l o t center. On these p l o t s , environmental and plant v a r i a b l e s and sapwood water content v a r i a t i o n s were studied on annual, monthly, and diu r n a l time bases. The sapwood water content of a single tree whose root system was i s o l a t e d from s o i l water recharge was also studied. The r e l a t i o n -ships between environmental and plant v a r i a b l e s , and sapwood water con-tent were evaluated by multiple regression analyses. Annual Sapwood Water Content V a r i a t i o n Methods. Annual v a r i a t i o n was studied on the lower p l o t i n Study Area No. 2 for the period July 1970 - August 1971. Sapwood water contents of 57 the 0-1 cm depth from the cambium were obtained by increment boring as previously described on page 22, and ten trees were randomly sampled once per month from the plo t and adjacent area. D a i l y maximum and min-imum a i r temperatures and d a i l y p r e c i p i t a t i o n for the plo t were obtained from weather records kept at the Kananaskis Forest Research Station headquarters. Results and Discussion. The pattern of annual sapwood water content v a r i a t i o n i n lodgepole pine was found to be s i m i l a r to that shown for other coniferous species (Chalk and Bigg, 1956; Swanson, 1966; Markstrom and Hann, 1972). Maximum water contents occurred i n the months of November - March and averaged 126% o.d.w. (Figure 27). Minimum water contents occurred i n the months June - August and averaged 80% o.d.w. During both of these periods, mean water contents remained r e l a t i v e l y constant, and showed very l i t t l e v a r i a t i o n . The greatest f l u c t u a t i o n s i n sapwood water content occurred i n the spring and f a l l , and ranged i n magnitude from 27-43% o.d.w. These f l u c t u a t i o n s are interpreted as responses to t r a n s p i r a -t i o n , based on t h e i r time of occurrence and v a r i a t i o n with weather con-d i t i o n s . An analysis of variance and multiple range tests indicated that the most s i g n i f i c a n t f l u c t u a t i o n s i n water content occurred during the spring and f a l l (Tables VIII, IX), which coincides with the s t a r t and end of the growing season, when the biggest changes i n t r a n s p i r a t i o n rates and water movement i n trees can be expected. D a i l y maximum a i r temperatures and d a i l y p r e c i p i t a t i o n were used as indexes of t r a n s p i r a t i o n p o t e n t i a l i n the study. A comparison of sapwood water content to these v a r i a b l e s , shows that maximum water F i g u r e 27 Annual v a r i a t i o n of sapwood water content of lodgepole pine a t the 0-1 cm depth from the cambium a t bre a s t h e i g h t ; d a i l y maximum a i r temperature; and d a i l y p r e c i p i t a t i o n f o r the p e r i o d J u l y 1^70-August I97I, S t u d f y Area No. 2. -; 59 Table VIII Analysis of variance: annual sapwood water content variation of lodgepole pine at 0 - 1 cm depth from the cambium, at breast height, for July 1970 - August 197 1, Study Area. No. 2. Source of Degrees of Sum of Mean Variance Variation Freedom Squares Square Ratio Time 14 96, 341. 9 6, 881. 5 20. 9** Error 215 70, 723. 3 328. 9 Total 229 167, 065. 2 level of significance 0.01 level of significance 0. 05 Time = sample dates (July 10, 1970; July 16, 1970; August 14, 1970; September 15, 1970; October 19, 1970; November 19, 1970; December 29, 1970; January 29, 1971; February 1 9 , 1971; March 25, 1971; April 21, 1971; May 17, 1971; June 27, 1971; July 15, 1971; August 18, 1971). Table IX Results of Duncan's New Multiple Range Test for annual sapwood water content variation of lodgepole pine at 0-1 cm depth from the cambium, at breast height for July 1970-August 1971, Study Area No. 2. Sample D a t e s ~ • Arranged in order magnitude Dec 70 Feb 71 Nov 70 Mar 70 Jan 71 May 71 Sept 70 Apr 71 Aug 71 Jun 71 Jul 71 Aug 70 Oct 70 Jul 10 70 Jul 16 70 Arranged in chronological order Jul 10 70 Jul 16 70 Aug 70 Sept 70 Oct 70 Nov 70 Dec 70 Jan 71 Feb 71 Mar 71 Apr 7 1 May 71 . Jun 7 1 Jul 71 Aug 71 No significant differences in water content between sample dates underlined by the same line at 0. 05 level of significance. . O N .. o 6 1 contents coincided with weather conditions unfavorable to high rates of tr a n s p i r a t i o n ; or with s i t u a t i o n s where weather conditions had amelio-rated such that reductions i n t r a n s p i r a t i o n or plant water stress could be expected. An example of the f i r s t case i s the November - March period where water contents were high and temperatures below fr e e z i n g . The only exception was i n January, where an abrupt decrease i n sapwood water content was observed. This probably resulted from water l o s s caused by a combination of cold frozen s o i l s and the occurrence of "chinook" or foehn winds p r i o r to the sample date. Weather records show chinook conditions existed for the periods, January 18-20, and 26-29 with d a i l y maximum a i r temperatures of 44-50°F and maximum wind speeds of 16-30 m.p.h. (Meteorological Branch, 1971; Environment Canada, 1971). An example of the second case i s the August - October period, where sapwood water content increased as temperatures became cooler and p r e c i p i t a t i o n increased i n September; and then decreased i n October with the return of higher temperatures and reduced p r e c i p i t a t i o n . An examination of minimum sapwood water contents show them to be associated with periods favorable to high t r a n s p i r a t i o n . Examples of such are the July - August periods where d a i l y maximum temperatures were 80-90° F, and minimum day time r e l a t i v e humidities 20-30%. Monthly Sapwood Water Content V a r i a t i o n Methods. Monthly observations of sapwood water content were obtained i n Study Area No. 1 and 2. In Study Ar.ea No. 1 sapwood water content of the 0-1 cm depth from the cambium was obtained by increment boring, and f i f t y trees were randomly sampled at breast height every two weeks for the period July 16 - October 15, 1969. Da i l y a i r temperatures and 62 d a i l y p r e c i p i t a t i o n were obtained from a Fuess hygrothermograph on the plot and weather records at the Kananaskis Forest Research Station head-quarters. Plant water stress on each sample date was estimated by the pressure bomb technique (Scholander, Hammel, Bradstreet and Hemmingsen, 1965; Waring and Cleary, 1967; Kaufmann, 1968). In Study Area No. 2 monthly observations of sapwood water content were obtained from May to September 1971, by gamma r a d i a t i o n attenuation and increment boring. To prevent disturbance and i n t e r -action between the two methods, two separate groups of trees were sam-pled. Both groups were thoroughly intermixed on the pl o t and contained 5 trees of s i m i l a r height, diameter breast height and crown development. Water content was measured to a depth of 5 cm from the cambium by both methods. Gamma water contents for the 1-2 cm depth from the tree e x t e r i o r were used for analyses, as they are equal i n l o c a t i o n to the 0-1 cm depth of bored water contents. Gamma water contents were obtained for 1 cm wide sections through tree stems by taking 2-3, one minute counts (N), and associated incident and standard counts (N.,N ) at each centimeter depth. Permanent 1 s stands were used to insure a constant measuring plane i n each tree. The shape of the measured sections i s trapez o i d a l , and the midpoint thickness was used for S. Absolute water contents were calculated for each c e n t i -meter depth by equation 1.6, and converted into equivalent o.d.w. water contents for comparison to bored water values. Bored water contents were analyzed as described on page 22. Wherever possible both gamma and bored water contents were taken i n early morning hours to avoid the e f f e c t s of diurnal f l u c t u a t i o n s and to obtain comparable temperature regimes for each sample date. 63 The environmental and plant variables measured were: plant water stress, s o i l water content, temperature, relative humidity and precipitation. To evaluate plant water stress, two to three tree water pressure potential readings were taken per gamma water content observa-tion. Trees sampled were on and adjacent to the plot. Samples were cut from the lower parts of tree crowns, the upper areas were inacces-sible because of tree height. Soil water content was measured by the neturon scattering method, using a Troxler model S5A-104A depth moisture gauge, with 100 mc of Americium-Beryllium and a Troxler model 1651 scaler-ratemeter. Procedures followed were those outlined by Gardner (1965). and the U.S.D..A. Forest Service (1962). Volumetric s o i l water contents were determined from a f i e l d calibration curve derived for the s o i l and equipment (Hillman, 1970). So i l water contents were determined at depths of 6, 12, 24, 36, and 4<3 inches in the s o i l profile. One min-ute counts, replicated twice, were taken monthly in conjunction with sapwood water content. To sample s o i l water content, a 10 x 10 feet grid of s o i l access tubes (24 tubes total) was established on the plot. Ambient air temperature and relative humidity were measured by a Fuess hygrothermograph located in an opening 100 feet from the plot. Precipitation was measured weekly with Meteorological Service of Canada standard rain gauges (Bruce and Clark, 1966). Precipitation under the forest canopy was measured by 10 roving rain gauges, which were randomly relocated each week on a 5 x 5 feet grid on the lower study plot. Two additional gauges were permanently located in the opening with the hygrothermograph. 64 Results and Discussion. The data of Figure 28 in d i c a t e that monthly observations of sapwood water content i n Study Area No. 1 during the summer of 1969 showed a pattern of decreasing water content from mid-July to l a t e August, followed by an increasing trend i n September and October. Mean water contents for the period varied from 100% o.d.w. on July 16, to '7/9% o.d.w. on August 26, to 123% o.d.w. on October 15. 1 These f l u c t u a t i o n s of sapwood water content are interpreted as responses to t r a n s p i r a t i o n based on the occurrence of minimum and maximum water contents with weather conditions favorable to low and high t r a n s p i r a t i o n r e s p e c t i v e l y . Minimum water contents occurred i n l a t e August under hot and dry conditions, where d a i l y maximum a i r temp-eratures were 75-90° F, and daytime r e l a t i v e humidities 20-40%. Pre-c i p i t a t i o n i n August was a low 0.63 inches compared to 3.10, 1.17 and 2.17 inches i n Ju l y , September and October r e s p e c t i v e l y . Increasing, and maximum sapwood water contents were observed i n September and October i n response to a cooling trend, where p r e c i p i t a t i o n increased and d a i l y maximum a i r temperatures varied from 40-60° F. Observations of tree water pressure p o t e n t i a l f o r the July - October period showed an inverse r e l a t i o n s h i p , with maximum and minimum water contents respec-t i v e l y coinciding with periods of minimum and maximum plant water st r e s s . Further support f or t h i s explanation i s an analysis of variance and multiple range test of the data, which show highly s i g n i f i c a n t changes i n sapwood water content between sample dates i n the August - October period (Tables X, XI). Monthly sapwood water contents i n Study Area No. 2 i n the summer of 1971 displayed a small, but steady decrease from June to September (Figure 29). Measurements by gamma r a d i a t i o n and increment 65 H 1 1 1 r JULY AUG SEPT OCT Figure 28 Monthly v a r i a t i o n of sapwood water content i n lodgepole pine for the 0-1 cm depth from the cambium at breast height; d a i l y maximum a i r temperature; d a i l y p r e c i p i t a t i o n and tree water pressure potential for the period July 16-October 15, I969, Study Area No. 1. 66 Table X Analysis of variance: sapwood water content at 0 - 1 cm depth from cambium by time, July 16-October 15, 1969; and diameter classes, 4. 0-7. 0 inches, Study Area No. 1. Source of Variation Degrees of Freedom Sum of Squares Mean Square Variance Ratio Time (T) 6 - 27, 800. 0 4, 633. 3 10/72**. Diameter (Da) 3 7, 602. 4 2, 534. 1 5. 86** T x D 18 7,321.9 406. 7 0. 94 Error 140 60, 499. 0 432. 1 Total 167 103, 220. 0 level of significance 0. 0 1 level of significance 0. 05 Sample dates (July 16, July 30, August 18, August 26, September 16, September 30, October 15) Diameter classes (4. 0 - 4. 9, 5. 0 - 5. 9, 6. 0 - 6. 9, 7. 0 - 7. 9 inches) 67 Table XI Results of Duncan's New Multiple Range Test for mean sapwood water contents at 0 - 1 cm depth from the cambium for sample dates July 16, August 18, 26; September 16, 30 and October 15, 1969, Study Area No. 1. Sample Oct Sept Sept July July Aug Aug Dates 15 16 30 16 30 26 18 Sample Dates Jul Jul Aug Aug Sept Sept Oct Chronological 16 30_ 18 26 16 30 15 Order Mean Water 99.0 9 1. 2 79.5 87.7 100.4 99. 0 123. 6 Content % o. d. w. Chronological Order - . No significant differences in water content between dates underlined by the same line at 0. 05 level of significance. 6 8 1 I 1 MAY JUNE JULY A U G SEPT F i g u r e 29 Monthly o b s e r v a t i o n s of sapwood water content v a r i a t i o n by gamma r a d i a t i o n and increment b o r i n g i n lodgepole pine a t b r e a s t h e i g h t ; and monthly v a r i a t i o n o f d a i l y maximum a i r temperature; d a i l y p r e c i p i t a t i o n ; and v o l u m e t r i c s o i l water contnet f o r the p e r i o d June-September 19?1, Study Area No. 2, lower study p l o t . 69 boring showed absolute changes of 10% and 23% o.d.w. re s p e c t i v e l y f o r the summer. Larger f l u c t u a t i o n s were anticipated however, because weather and s o i l conditions of the s i t e indicated a p o t e n t i a l for high t r a n s p i r a t i o n and low s o i l water storage. D a i l y maximum a i r tempera-tures and minimum daytime r e l a t i v e humidities i n July - August were 80-90° F and 20-40%. The s o i l on the s i t e i s a sandy loam, and showed a steady decrease i n s o i l water content from May to September (Figures 29,30). Maximum s o i l water depletion i n the root zone (B horizon) and s o i l water matric p o t e n t i a l varied from 21.5-8.5% and -0.3 to -0.5 bars (estimated from Figure 6). Furthermore, observations on the same s i t e i n 1970 had shown large and s i g n i f i c a n t changes i n sapwood water content i n spring and f a l l . An analysis of variance of the 1971 data however, showed no s i g n i f i c a n t d ifferences between sample dates (Table XII). Without further information on either s o i l water a v a i l a b i l i t y or tran-s p i r a t i o n rates, no v a l i d explanation can be offered for these r e s u l t s . Diurnal Sapwood Water Content V a r i a t i o n Methods. Diurnal sapwood water content observations i n Study Area No. 1 were obtained by increment boring, and compared to concurrent observations of sap v e l o c i t y , plant water s t r e s s , and a i r temperature. Ten trees were sampled for water content every four hours over a 24 hour period. Bored water contents were determined as described on page 22. Diurnal observations were obtained once per month i n May, June,a3ulyuahd August 1969. Sap v e l o c i t y and plant water stress were estimated by heat pulse v e l o c i t y methods (Marshall, 1958; Swanson, 1962, 1967) and the pressure bomb technique. Trees were instrumented to measure sap v e l o c i t y 70 io 15 20 25 30 VOLUMETRIC SOIL WATER CONTENT PERCENT Figure 30 Monthly observations of volumetric soil water content on lower study plot for period May-September 1971, Study Area No. 2, lower study plot. 71 Table XII Analysis of variance: Gamma radiation attenuation and bored water contents of lodgepole pine at 0 - 1 cm depth from the cambium, at breast height, June - September 1971, Study Area No. 2, lower study plot. Source of Degrees of Sum of Mean Variance Variation F reedom Squares Square Ratio Method (M) 1 6, 028. 1 6, 028. 1 16. 61""' Time (T) * 3 2, 659.4 886. 5 2. 45 T x M 3 2, 311. 7 770. 5 2. 12 E r r o r 72 26, 128. 0 362.9 Total 79 37, 128..0 level of significance 0. 01 level of significance 0. 05 Method = water content by gamma radiation attenuation and increment borers. Time = sample dates (June 1, July 9, August 12 and September 14, 1971). Replication = 2 replications per tree, 5 trees per sample date for each method. 72 at depths of 1, 2, 3, and 4 cm from the cambium. However, sensors at the 3 and 4 cm depths were improperly i n s t a l l e d and could not be used. Two pressure bomb or tree water pressure p o t e n t i a l readings were taken on each tree sampled for water content. A i r temperature was obtained from a Fuess hygrothermograph located on the p l o t . Diurnal sapwood water content observations on the lower p l o t i n Study Area No. 2 were obtained by gamma r a d i a t i o n and increment boring as described on page 63. Diurnal observations ran for 24 hours and were obtained June 2-3, 1971 and Jul y 12-14, 1971. For each observation sapwood water content was measured every four hours, s t a r t i n g and ending at 1000 a.m. mountain standard time. Gamma measurements were l i m i t e d to a sing l e tree because the time required for measurements made i t impractical to sample more trees. Bored water contents were obtained from trees growing close to the ones sampled by gamma r a d i a t i o n . Five trees, with two r e p l i c a t i o n s per tree were sampled every four hours. Concurrent environmental and plant v a r i a b l e s measured on the plot were: a i r temperature, r e l a t i v e humidity,plant water stress and sap v e l o c i t y . Two to three tree water pressure p o t e n t i a l readings per gamma measurement were used to evaluate plant water s t r e s s . Trees sampled were on and adjacent to the pl o t . Samples were cut from the lower parts of tree crowns, because the upper areas were i n a c c e s s i b l e due to tree heights. A i r temperature and r e l a t i v e humidity were obtained from a hygrothermograph located on the p l o t . For sap v e l o c i t y , ten lodgepole pine trees, exclusive of those measured for water content, were instrumented to measure heat pulse v e l o c i t i e s at depths of 0.75, 1.0, 1.25, 1.50 and 2.0 cm from the vascular cambium at breast height. Measurements were taken i n conjunction with sapwood water content, and 73 at other times to establish the rates and patterns of sap movement. Resuits and Discussion. Figure 31 shows that the patterns of diurnal sapwood water content obtained in 1969 on Study Area No. 1 are similar to previous reports (Gibbs, 1935; Reid, 1961). Maximum water contents occurred in the early morning (0300-0500 hours) prior to sunrise and minimum water contents in the late morning or early after-noon (1100-1500). The only exception to these observations was the June sample which showed l i t t l e water content variation throughout the day (Figure 232). An analysis of variance of these data showed no significant differences in water content between sample times (Table XIII). The lack of significant variation is attributed to low water stress in the trees, caused by moderately low air temperatures, overcast cloud cover and high s o i l water content on the sample date. This i s further supported by tree water pressure potentials which showed l i t t l e change between night and day observations. Analyses of data for the other sample dates indicated highly significant differences i n sapwood water content (Table XIII). Water contents ranged in magnitude from 72-120% o.d.w. and differences between maximums and minimums varied from 24-40% o.d.w. Range tests of these data showed that the most significant fluctuations in water content occurred 2-4 hours prior to and after the time of maximum water content (Table XIV). Outside of this 4-8 hour period (0200-1000), sapwood water contents, remained relatively' constant and showed no significant changes.. Comparison of sapwood water contents to weather conditions and plant variables indicates their fluctuations are responses to transpira-tion. Diurnal observations of air temperature, ..tree water pressure and 74 i JULY 8 - 9 , 1969 11 13 15 17 19 21 2'3 o'l 03 .05 07 55 Ti \3 £121 E H 13 15 lV 19 21 2*3 01 03 05 07 09 H \3 TIME HOURS ["Figure 3 1 D i u r n a l v a r i a t i o n of sapwood water content a t b r e a s t h e i g h t f o r 0 - 1 cm depth from the cambium; t r e e water pressure p o t e n t i a l ; heat pulse v e l o c i t y ; and a i r temperature f o r J u l y 8 - 9 , 1 9 6 9 , S t u d y Area No. 75 TIME HOURS i I ! L___--— : • • • • ' p F i g u r e 3 2 D i u r n a l v a r i a t i o n of sapwood water content ! o f lodgepole pine a t b r e a s t h e i g h t , 0 - 1 cm from the cambium; t r e e water pressure p o t e n t i a l ; heat pulse v e l o c i t y ; and a i r temperature f o r the p e r i o d June 2 - 3 , 1 9 6 9» Study Area No. 1 . 76 Table XIII Analyses of variance: Diurnal sapwood water content at 0 - 1 cm depth from the cambium by time for sample dates May 7 -8, 1969, June 3 - 4, 1969, July 8 - 9, 1969 and August 5 - 6 , . . 1969, Study Area No. 1 . ; Sample Source of Degrees of Sum of Mean Variance Date Variation Freedom Squares Square Ratio May 7 - 8 Time 9 9, 013. 6 1, 001. 5 6. 55** Error 90 13, 750. 3 152. 8 Total 99 22, 764. 2 June 3 - 4 Time 11 3,012.4 273. 8 1. 53 NS Error 108 19, 245. 3 178. 2 Total 119 22, 257. 8 July 8 - 9 Time 11 15, 180.4 1, 380. 0 ** 2. 83 Error 108 52, 653. 9 487. 5 Total 119 67, 834.4 August 5 - 6 Time 11 6, 655. 3 605. 0 3. 74** Error 108 17, 434. 9 161. 43 Total 119 24, 090. 22 level of significance 0. 01 level of significance 0. 05 Time (diurnal samples obtained every four hours by increment boring). 77 Table XIV Results of Duncan's New Multiple Range Test for mean sap-wood water contents 0 - 1 cm depth from cambium for diurnal samples on May 7 - 8, 1969, July 8 - 9, 1969 and August 5 - 6 , 1969, Study Area No. 1. Observation Time - Hours May 7 - 8 2200 0200 0600 0900 1900 1300 1700Q 1100 1500 1700. Order by Magnitude 1700„ 1900 2200 0200 0600 0900 1100 1300 1500 1700 8 Order Chronological 74 86 104 98 9 1 87 79 79 76 79 Mean Water Content % o. d. w. Chronological Order. July 8 - 9 0700 1300n 0900 0500 0100 1900 1700 1500 1100o 2100 1300o 1100n 9 b o y Order by Magnitude 1100o 1300o 1500 1700 1900 2100 0100 0500 0700 0900 1100n 1300 o .. o o , p V Order Chronological 84 79 85 86 87 80 89 95 120 99 78 103 Mean Water Content % o. d. w. Chronological Order August 5 - 6 1100, 1300, 0500 0700 2100 0100 1500 0900 1300c 1900 1100,. 1700 6 6 5 5 Order Magnitude 1100r 1300r 1500 1700 1900 2100 0100 0500 0700 0900 1100, 1300 5 5 b Order Chronological 73 76 84 71 75 85 85 89 86 83 95 91 Mean Water Content % o.d.w. Order Chronological No significant differences in water content between hours underlined by the same line at 0. 05 level of significance. 78 heat pulse v e l o c i t i e s show maximum and minimum water contents to corre-spond to periods of minimum and maximum plant water stress and sap move-ment re s p e c t i v e l y . Tree water pressure p o t e n t i a l s showed minimum stress ( i . e . l e a s t negative) i n the early morning hours (0300-0500 hours) and maximum stress ( i . e . most negative) i n the afternoon (Figures 31,32). Dai l y v a r i a t i o n of pressure p o t e n t i a l s f or May, June, J u l y and August ranged from -(7.4-11.2) , -(8.5-13.6), -(9.6-13.5), -(8.7-14.8) atmo-spheres r e s p e c t i v e l y . Heat pulse v e l o c i t i e s showed no flow at night, and maximum v e l o c i t i e s of 6-8 cm/hour at midday. The timing of sapwood water content f l u c t u a t i o n s i s also important, because they occurred before and a f t e r sunrise with the s t a r t of t r a n s p i r a t i o n and water move-ment i n a plant. Figures 33 and 34 ind i c a t e that d i u r n a l sapwood water contents obtained i n Study Area No. 2 are s i m i l a r i n pattern to those of Study Area No. 1. Both gamma r a d i a t i o n and increment boring samples showed maximum water contents to occur during the nighttime hours and minimum water contents during daytime hours. Water contents ranged i n magnitude from 76-120% o.d.w. and differences between maximums and minimums var i e d from 16-26% o.d.w. for the two sample dates. A i r temperature, tree water pressure p o t e n t i a l and heat pulse v e l o c i t y also showed s i m i l a r patterns of v a r i a t i o n with sapwood water content to those observed i n Study Area No. 1. However, analyses of variance of data showed no s i g n i f i c a n t differences i n sapwood water content with time for both sample dates (Tables XV). The f l u c t u a t i o n s are s t i l l interpreted as responses to t r a n s p i r a t i o n , because i t i s considered that the prevalence of r e l a -t i v e l y cool a i r temperatures (50-60° F) and high s o i l water contents (16-19%) may have minimized s o i l water d e f i c i t s and sapwood water content f l u c t u a t i o n s . 79 120H 100 IsoH o O 6 0 £ 4 0 + -20+ -4 +-12 - 2 JUNE 2-3,1971 ravimetric •90 •80 -70 -60 -50 -40 12 14 16 18 20 22 24 02 04 06 08 10' TIME HOURS F i g u r e 33 D i u r n a l v a r i a t i o n of sapwood water contents of lodgepole pine a t b r e a s t h e i g h t obtained by gamma radiation a t t e n u a t i o n and increment b o r i n g ; and t r e e water pressure p o t e n t i a l ; and a i r temperature f o r June 2-31 1971» Study Area No. 2, lower study p l o t . 80 JULY 12-13,1971 -i 1 1 1 1 1 1 • • 1 l • l 10 12 14 16 18 20 22 24 02 04 06 08 10 TIME HOURS 'Figure 3 4 D i u r n a l v a r i a t i o n of sapwood water contents of lodgepole pine by ; b r e a s t h e i g h t obtained by gamma r a d i a t i o n a t t e n u a t i o n and increment b o r i n g ; and t r e e water pressure p o t e n t i a l ; and a i r temperature f o r J u l y 1 2 - 1 3 , 1 9 7 1 , Study Area No. 2 , lower study p l o t . Table XV Analysis of variance: Diurnal sapwood water content variation of lodgepole pine at breast height by gamma radiation attenuation and increment boring on June 2-3, 1971 and July 12-13, 1971, Study Area No. 2, lower study plot. Sample Source of Degrees of Sum of Mean Variance Method Date Variation Freedom Square s Square Ratio Gamma June 2-3 Time 6,' 974. 85 162.47 3. 56 NS Radiation Error 7 319.50 45. 64 Attenuation Total 13 1, 294. 35 July 12-1-3 Time 6 315. 80 52. 6 1. 12 NS Error 7 328.50 46. 9 Total 13 644.30 Increment June 2-3 Time 6 1, 405. 60 234. 26 0. 623 NS Borings Error 12 4,510.50 375. 87 Total 18 5, 916. 10 July 12-13 Time 6 4, 937. 90 822. 90 2. 34 NS Error 14 4, 928. 60 352.00 Total 20 9,866.50 NS not significant at 0. 01, 0. 05 levels of significance. Time = sample hours (1000, 1400, 1800, 2200, 0200, 0600, 1000) Water content - gamma radiation attenuation at 1-2 cm depth from tree exterior and increment boring at 0-1 cm depth from vascular cambrium. 82 Isolated Tree Methods. On the upper pl o t i n Study Area No. 2, the re l a t i o n s h i p s between sapwood water content of a sing l e tree, whose root system was , i s o l a t e d and environmental and plant v a r i a b l e s were studied. The hypothesis was that water stress i n the i s o l a t e d tree, induced by prevent-ing s o i l water recharge, would cause s i g n i f i c a n t f l u c t u a t i o n s i n sapwood water content. To prevent s o i l water recharge, the tree's root system was i s o l a t e d by removal of a l l trees w i t h i n a s i x feet radius, and excavation of a c i r c u l a r trench 6 feet i n radius, 2 feet wide and 4 feet deep. The inner wall of the trench was l i n e d with p l a s t i c sheeting and the ground covered with a wooden shelter to prevent recharge by p r e c i p i t a t i o n . I t was assumed the slope conditions and the trench would prevent l a t e r a l water flow and root graf t s with surrounding trees. Sapwood water content was obtained by the gamma r a d i a t i o n attenuation method already described on page 63. Concurrent observa-tions of heat pulse v e l o c i t y , tree water pressure p o t e n t i a l , a i r temp-erature, p r e c i p i t a t i o n and s o i l water content were obtained for the iso l a t e d tree and s o i l , and outside trees and s o i l . It was hypothesized that with time differences would occur between the i s o l a t e d and outside measurements. Heat pulse v e l o c i t i e s were obtained f rom the i s o l a t e d tree (K), and two outside trees (L and M). V e l o c i t i e s i n a l l three were measured at a depth of 1 cm from the vascular cambium. Two to three tree water pressure p o t e n t i a l readings were taken from the i s o l a t e d tree and two outside trees for each gamma water content measurement. A i r temperature and p r e c i p i t a t i o n were obtained from the hygrothermograph and r a i n gauges on the lower p l o t . S o i l waterrcontent was measured by the 83 neutron scattering method with four s o i l access tubes in the isolated s o i l and two in the outside s o i l . Water contents were determined at depths of 6, 12, 24, 36, and 48 inches. Results and Discussion. The data of Figure 35 indicate that sapwood water content of the isolated tree remained relatively constant in July, but abruptly decreased in mid-August from 134% o.d.w. to 115% o.d.w. In the following period of August-September, sapwood water content increased to 127% o.d.w. Stat i s t i c a l analysis of the data (Table XVI) shows the decrease in August to be highly significant, and to have occured during the hottest and driest months of the summer. Daily maximum air temperatures and minimum daytime relative humidities of July-August varied between 70-90° F and 20-30%. Precipitation for July and August were 0.81 and 0.59 inches respectively. In September-October sapwood water content increased and weather conditions ranged from 50-70° F and precipitation for each month was 2.17 and 1.20 inches respectively. Soil water contents of the isolated and outside soils both showed a steady decrease for the study (Figures 36, 37). Signs of s o i l water recharge were evident at the 6 inch depth in the outside s o i l on the September observation. Analyses of the data for both soils showed s i g n i f i -cant differences in water content between sample dates (Table XVII). A comparison of the soils showed no significant differences in mean water contents, however an interaction between the soils and water content at depth indicates significant differences in the distribution of water in the soils (Table XVIII). The isolated s o i l had higher water contents and a slower rate of depletion than the outside s o i l . A probable cause for this is that only one tree ut i l i z e d the water available in the isolated s o i l . 84 F i g u r e 35 Sapwood water content v a r i a t i o n of i s o l a t e d lodgepole pine, a t 1-2 cm from t r e e e x t e r i o r a t b r e a s t h e i g h t and t r e e water pressure p o t e n t i a l ; s o i l water contents of i s o l a t e d and o u t s i d e s o i l s a t 12 inches depth; d a i l y maximum a i r temperature; d a i l y p r e c i p i t a t i o n f o r the p e r i o d Julyl6-September 15, 1971, Study Area No. 2, upper study p l o t . 85 Table XVI Analyses of variance: sapwood water content of isolated tree, 1 - 2 cm depth from tree exterior, breast height, by gamma radiation attenuation on July 16, August 12, August 18 and September 17, 1971, Study. Area No. 2, upper study plot. Source of Degrees of Sum of Me an Variance Variation Freedom Squares Square Ratio Time 3 1, 335. 76 451. 92 •A. si-11. 24""" Error 24 964. 60 40. 19 Total 27 2,320.43 level of significance 0. 01 level of significance 0. 05 86 VOLUMETRIC SOIL WATER CONTENT PERCENT Figure 36 Volumetric soil water content variation for isolated soil on upper study plot for period July 15-September 15, 1971. 60. 10 20 30 40 50 VOLUMETRIC SOIL WATER CONTENT PER CENT F'igure 37 Volumetric soil water content variation for outside soil on upper study plot for period July 15-September 15, 1971. 87 Table XVIII Analysis of variance: soil water contents in isolated and out-side soils of upper study plot for period July 15 - September 17, 1971, Study Area No. 2, upper study plot. Source of Degrees of Sum of Mean Variance Variation Freedom Squares Square Ratio Soil (S) 1 77. 98 77. 98 2. 60 NS Depth (Dp) 4 2, 619.63 654. 9 1 - 21. 85** S x Dp 4 294. 07 147. 04 4. 91""" Error 110 3, 296. 35 29. 97 Total 119 6,288.03 level of significance 0. 01 level of significance 0. 05 NS not significant at 0. 01, 0. 05 levels. Soil - isolated soil, outside soil Depth - soil water content measured at 6", 12", 24", 36", 48" deep. 88 Table XVII Analyses of variance: volumetric soil water content at depths of 6, 12, 24, 36 and 48 inches deep for soils of upper study plot, Study Area No. 2. ^ - ^ ^ v .. Source of Location Depth Variation Degrees of Freedom Sum of Square s Me an Square Variance Ratio Isolated Soil 12 24 36 48 Time Error Total Time Error Total Time Error Total Time Error Total Time E r r o r Total 2 19 21 2 19 21 2 19 21 2 19 21 2 19 21 11. 20 108. 4 119. 6 74. 8 105. 9 180. 7 43. 76. 120. 54. 4 55. 9 110. 3 26. 5 301. 4 327. 9 5. 6 5. 7 37. 4 5. 5 21. 7 4. 0 27. 2 2. 9 13. 2 15. 8 0. 98 6. 71 5. 39 9. 23 0. 84 Outside Soil 12 24 36 48 Time Error . Total Time Error Total Time Error Total Time Error Total Time Error Total 2 9 11 2 9 11 2 9 11 2 9 11 2 9 11 56. 8 55. 0 111. 8 90. 7 121. 2 211. 9 131. 6 35. 2 166. 9 27. 0 18. 69 v9.'7 46. 6 56. 3 28. 4 6. 1 45. 3 13. 4 65. 8 3. 9 13. 5 2. 1 4. 8 4. 65 3. 36 16. 83** 6. 53 0. 9 3 level of significance 0. 01 level of significance 0. 05 Time - sample dates 89 Soil water depletion for the isolated s o i l was greatest at the 12 and 36 inches depths, maximum changes being 4.6% and 3.8% respectively. Maximum s o i l water content changes in the outside s o i l occurred at depths of 12 and 24 inches, and were 7.5% and 8.5% respectively. The isolated and outside trees displayed similar patterns of sap movement. Heat pulse velocities in general decreased from July to September except for mid-August where maximum velocities of 7-12 cm/hour for the season occurred. The heat pulse velocities of the outside trees were 25-90% faster than the isolated tree. However, comparisons of heat pulse velocities by analysis of variance and double mass curves showed no significant differences in levels or relationships between the trees. (Table XIX Figures 38, 39). Observations of tree water pressure potential of the isolated tree show maximum plant water stress i n late August, followed by a decrease in September. An examination of the data indicates the isolated tree was under more stress or negative pressure than the outside trees. Mean midday pressure potentials for the isolated and outside trees were -16.0 and -14.0 atmospheres respectively, and a Student's t-test showed them to be significantly different. This result i s surprising, considering the isolated s o i l profile had an average water content of 34% and an average s o i l water matric potential of -0.5 bars (estimated from Figure 6). Average matric potentials however, are not the best measure of water availability as they are determined by potentials in the bulk of the s o i l and in the immediate vi c i n i t y of the water-absorbing root surfaces. Under conditions of high transpiration, s o i l water matric potentials at the root surfaces could be less (i.e. more negative) than those indicated by an average value. 90 Table XIX Analysis of variance: Heat pulse velocities of isolated and control trees... Study Area No. 2, upper study plot. Source of Degrees of Sum of Mean Variance Variation Freedom Squares Square Ratio Heat pulse belocity 2 • 0. 578 0. 289 0. 08 Error 62 218. 965 3. 531 Total 64 219. 544 level of significance 0. 01 level of significance 0. 05 NS not significant at 0. 01, 0. 05. \0 - I 1 1 1 I 1 1 1 I 50 100 150 200 250 300 350 400 450 CUMULATIVE HEAT PULSE VELOCITY cm/hr Figure 39 Double mass curves of heat pulse velocity of isolated tree (K) on control trees (L, M) for period July-September 1971, Study Area No. 2, upper study plot. 93 I t i s d i f f i c u l t t o c o n c l u d e f r o m t h e s e r e s u l t s t h a t t h e changes i n sapwood w a t e r c o n t e n t o f t h e i s o l a t e d t r e e were caused e x c l u s i v e l y by th e t r e a t m e n t . The changes i n w a t e r c o n t e n t may have r e s u l t e d more f r o m w e a t h e r c o n d i t i o n s , t h a n f r o m t r e n c h i n g t o p r e v e n t s o i l w a t e r r e c h a r g e . Measurements o f sapwood w a t e r c o n t e n t i n o u t s i d e t r e e s , and s o i l w a t e r m a t r i c p o t e n t i a l s i n o u t s i d e and i s o l a t e d s o i l s m i g ht have p r o v i d e d b e t t e r d a t a by w h i c h t h e e f f e c t i v e n e s s o f t h e t r e a t m e n t c o u l d have been b e t t e r e v a l u a t e d . The a b r u p t d e c r e a s e i n sapwood w a t e r c o n t e n t o f t h e i s o l a t e d t r e e i s i n t e r p r e t e d as a r e s p o n s e t o h i g h t r a n s p i r a t i o n . The ca u s e s f o r su c h a r e a c o m b i n a t i o n o f h i g h a i r t e m p e r a t u r e s (90° F ) , low r e l a t i v e h u m i d i t i e s ( 3 0 % ) , and no p r e c i p i t a t i o n f o r a p e r i o d o f 12 days p r i o r t o measurement. Even w i t h t h e r e l a t i v e l y h i g h s o i l w a t e r c o n t e n t s , i t i s c o n s i d e r e d t h a t t r a n s p i r a t i o n exceeded t h e r a t e o f a b s o r p t i o n , t h e r e b y , c a u s i n g d e c r e a s e d sapwood w a t e r c o n t e n t . I m m e d i a t e l y f o l l o w i n g t h i s p e r i o d , w e a t h e r c o n d i t i o n s moderated s u c h t h a t t h e i s o l a t e d t r e e r e h y d r a t e d . Maximum sap movement and p l a n t w a t e r s t r e s s f o r t h e same p e r i o d , as i n d i c a t e d by h e a t p u l s e v e l o c i t i e s and t r e e w a t e r p r e s s u r e p o t e n t i a l s , f u r t h e r s u p p o r t t h i s e x p l a n a t i o n . E n v i r o n m e n t a l - P l a n t V a r i a b l e s v s Sapwood Water C o n t e n t Methods. R e l a t i o n s h i p s between e n v i r o n m e n t a l and p l a n t v a r i a b l e s w h i c h i n f l u e n c e t r a n s p i r a t i o n , and sapwood w a t e r c o n t e n t were q u a n t i t a t i v e l y e v a l u a t e d by m u l t i p l e r e g r e s s i o n a n a l y s e s . O b s e r v a t i o n s f r o m t h e upper and l o w e r s t u d y p l o t s were s e p a r a t e l y a n a l y z e d . A n a l y s e s were p e r f o r m e d on an IBM model 370 computer, u s i n g t h e UBC m u l t i p l e r e g r e s s i o n program 94 (Kozak and Smith, 1965). The objectives of the analyses were to obtain a ranking of importance of the different variables to sapwood water content. Results and Discussion. Monthly and diurnal observations on the lower plot were pooled to obtain*a sample size as large as possible. Gamma and bored water contents were regressed on 13 independent variables by a step-wise multiple regression program (Draper and Smith, 1966). Results of the regression show a high degree of correlation between gamma and bored water contents (Table XX). Soil water content was the independent variable with the highest correlation to sapwood water content. Gamma water contents had the higher simple correlations coefficients with s o i l water content, which were 0.52 and 0.42 for the 6 and 12 inch depths. The step-wise regression indicated the most important variables 2 to gamma water content were (bored water content) , (soi l water content 6"), (1/atmospheric vapor pressure d e f i c i t ) , (relative humidity) and (bored water content), Table XXI. This combination of variables gave a multiple correlation coefficient of 0.88, with a standard error of estimate of 6.8 and a sample- size of 34. With the exclusion of bored water content as an independent variable, the regression analysis indicated (soil water 2 content 12") , ( s o i l water content 6") , and '.(soil water content 12") as the most important variables. The multiple correlation coefficient for this group is 0.62. The analysis for the isolated tree on the upper study plot gave slightly better results. Gamma water content was regressed on 19 indepen-dent variables (Table XXII). A ranking of the variables based on their simple correlation coefficients indicates the most important variables are: (atmospheric vapor pressure d e f i c i t ) , (relative humidity), s o i l water content 95 Table XX Simple correlation coefficients of gamma bored water contents on environmental and plant variables used in multiple regression ... analyses. ; : : ; , ; . v . , .  v;:.,„ .;.:,.....,!„:,;.^,:„::..,:::.;:..;:-:!.,:,..v.:.;..::s:.::..::..,:. - . : ... Variable r Gamma 2 r x 100 2 r Bored r 2 x 100 Gamma water content 1. 00 100. 0 0. 77 59. 2 Bored water content 0. 77 39. 2 1. 00 100. 0 1/atmospheric vapor pressure deficit -0. 06 _ -0. 03 Relative humidity - -0. 04 -Precipitation 0. 19 3. 6 0. 13 1. 6 Sample thickness (S) -0. 13 - -0. 04 -Ambient air temperature ° F -0. 21 4. 4 -0. 16 2. 5 Soil water content % vol. 6" deep 0. 52 27. 0 0. 35 12. 2 Soil water content % vol. 12" deep 0. 41 16. 8 0. 23 5. 3 2 (Bored water content) 0. 80 64. 0 0. 99 98. 0 (Soil water content % vol. 6" deep)2 0. 54 29. 2 0. 37 13. 6 (Soil water content % vol. 12" deep)2 o; 42 17. 6 0. 24 5. 7 2 (Sample thickness (S)) -0. 13 1. 7 -0. 04 -1/sample thickness (S) 0. 12 1. 4 -0. 04 . - . Table XXI Results of a series of step-wise multiple regression analyses of gamma water content on specific environmental and plant variables. : : ,; ; , : : : ; , ,. VARIABLES STATISTICS (Swat 6") (RH) (i/VP) (Bored WC) (Swat.6")2 (Bored WC) 2 R . R 2 x 100 SE e d. f. X X X X X X 0. 89 79. 8 6.71 6, 27 X X X X X 0. 88 78. 5 6. 79 5, 28 X X X X 0. 88 77. 4 6. 85 4, 29 X X X 0. 87 75. 3 7. 05 3, 30 X X 0. 84 70. 1 7. 53 2, 31 X 0. 80 64. 0- 8. 23 1, 32 Regression coefficients of all variables significant at 0. 01 level significance. Swat 6" = soil water content at 6 inches R = multiple correlation coefficient 2 RH = relative humidity R x 100 = multiple coefficient determination 1/VP = 1/vaoor pressure defeat of SE Bored W. C. = 1/vapor pressure defeat of atmosphere = bored water content d. f. = standard error of estimate = degrees of freedom 97 Table XXII Ranking of variables in importance to sapwood water content by their simple correlation coefficients. .,.....r;.;:.;:.: . , , Correlation Var iab le „ , coefficient Atmospheric vapor pressure deficit -0. 693 Relative humidity -0. 648 Soil water content - 24" depth isolated soil 0. 624 Maximum air temperature on sample date 0. 502 Soil water content - 24" depth outside soil 0. 495 Time - No. days from June 1 -0.414" Heat pulse velocity of treated tree K 0. 386 Mean maximum air temperature 3 days prior to sample date 0. 361 Heat pulse velocity of control tree L -0. 222 Precipitation prior to sample date -0. 154 Minimum air temperature on sample date -0. 022 Variable transformations Difference between maximum and minimum air temperatures on sample date 0. 638 (Soil water content - 24" depth isolated soil) 0. 629 (Heat pulse velocity K) (outside soil water 24") 0. 579 (Heat pulse velocity K) (isolated soil water 24") 0. 522 2 ** (Soil water content - 24" depth outside) 0. 485 (Time) 2 -0.381** (Heat pulse velocity of control tree L) (outside soil water 24") 0. 088 ' significant at 1% level ' significant at 5% level 98 24", isolated s o i l ) , (maximum air temperature), and (so i l water content 24", outside s o i l ) . Coefficients ranges from 0.36 to 0.69 in magnitude. The ranking from the step-wise regression was slightly different (Table XXIII). The most important variables are: (atmospheric vapor pressure d e f i c i t ) , (soil water content 24", isolated s o i l ) , (heat pulse velocity-isolated tree), (soil water content 24", outside s o i l ) , (pre-cipitation) and (time). The best equation obtained had a multiple correlation coefficient of 0.85 and included the variables: (precipitation), (soil water content 24" isolated s o i l ) , and (time). The rankings indicated by these analyses should be considered as conditional because of the low degree and similarity of correlations obtained. Better or more reliable results might have been obtained with larger sample sizes and data covering a wider range of conditions. The poor results from the lower plot were expected because sapwood water ^ content did not display significant fluctuations or strong trends with other var-iables during the study. If s o i l 'water and plant water deficits had developed on the site, stronger relationships between sapwood water con-tent and other variables might have been evident. The results from the upper study plot are better in that significant fluctuations of sapwood water content occurred and higher levels of correlation were obtained. From these results i t is concluded that sapwood water content is affected by s o i l water content and the evaporative potential of the atmosphere. These variables expressed in terms of atmospheric vapor pressure deficit or relative humidity, heat pulse velocity and s o i l water content singly or in combination explained from 1,8% to 73% of sapwood water content variation about the regression surface. 99 Table XXIII Results of a series of step-wise multiple regression analyses of sapwood water content on specific environmental and plant V a r i -ables. ....... ' - : - : v ^ : v . . : • : Variables R. R 2 x 100 SE d.f. e Inside Inside Outside (Time) (Soil), (Soil)2, (Soil)2 0.85 72.7% 4.54 4,23 Water Water Water Inside 2 Outside _ (Precip), (HPVK- ), ( ) 0. 85 72.7% 4.44 3,24 soil water soil water Outside (HPVL), (Soi l ) 0.81 65.8% 4.88 2,25 Water (Atmospheric Vapor Pressure Deficit) 0.69 48.1% 5.90 1,26 100 SUMMARY AND CONCLUSIONS The purpose of this thesis was to study sapwood water content distribution and fluctuations of lodgepole pine at breast height with respect to transpiration. The objectives of study were to determine if temporal fluctua-tions of sapwood water content can be used as indexes of the location and extent of conducting xylem; to test gamma radiation attenuation as a method for in situ sapwood water content measurement; and to relate sapwood water content fluctuations to specific environmental and plant variables. The radial distribution of water in the sapwood of lodgepole pine at breast height follows a pattern characteristic of other coniferous species. The distribution of water is asymmetrical with water contents decreasing from 100-158% o. d. w. in the outer 0-2 cm from the cambium, to near fiber saturation point in the heartwood. In most trees the boundary between wet and dry wood was abrupt and well defined. Significant differences were observed in the distribution, with the outer 0-1, 1-2, 2-3 cm depths displaying statistically similar water content levels and patterns of temporal variation. The outer depths had the greatest fluctuations in water content, while the inner depths were more or less constant with time. Heat pulse velocity observations in the same trees showed relative rapid sap movement in the 0-2 cm depths from the cambium. It is concluded from these data that sapwood water content fluctua-tions observed in the radial plane of lodgepole pine are indicative of the location of conducting xylem. To estimate the conducting xylem area, the 101 inflection point in water content between wet and dry wood areas was used as a boundary between conducting and nonconducting xylem. By this criterion the conducting xylem area was 3. 25 cm wide from the cambium at breast height, and would occupy 60-80% of the cross-sectional stem area. Such an estimate, however, is only approximate and more substantive evidence of sap movement beyond 2 cm from the cambium is required. Further work with heat pulse velocity techniques, radio-isotopes and electron micro-scopy should be able to confirm these conclusions. Gamma radiation attenuation was tested in the laboratory and field as a method for wood water content measurement. In the laboratory the water contents of prepared wood samples were determined by gravimetric and gamma radiation attenuation methods and compared by regression analyses. Results of the regression analysis yielded a correlation coefficient of 0. 96 and had a sample size and standard error of estimate of 47 and 7. 7. Gamma water contents averaged 6% higher, but were not significantly different from gravimetric water contents. Laboratory tests also indicate that radiation attenuation was not affected by different orientations of wood grain relative to the gamma beam. Observations of gamma radiation attenuation in lodgepole pine trees at breast height showed the cesium 137 source of 0. 661 M E V peak energy to be satisfactory for purposes of the study. The pattern of gamma radia-tion attenuation in the transverse plane of lodgepole pine displayed maximum attenuation at tree edge and minimum attenuation through tree center. Greater attenuation at tree edge results from the combined effects of higher wood densities and water contents, which make the total density of the outer 102 edges greater than thatuthrough tree center. A field test for in situ sapwood water content determination was done by comparing bored and gamma water contents of living trees by regression analyses. Separate groups of trees were measured by each method to prevent disturbance and possible inter-actions. The regression analysis gave a significant correlation coefficient of 0. 77, with a standard error of estimate of 31 and sample size of 32. The gamma water contents were significantly higher, with a mean difference of 17% o. d. w. Gamma water contents should be higher because they include bark moisture content and measure a larger volume of wood than bored samples. It is concluded from these results that gamma radiation attenuation can be used for water content measurement of dead and living wood. To do this an independent measure of wood density is required. In this study, reason-able results were obtained using a mean wood density for a group of similar trees growing close together. This may not work for measurements between fast and slow growing trees and trees growing on different sites. For practical application, further study of the effects of wood density variation and errors involved is required. Furthermore, for field use, equipment should be electronically stable and redesigned to make it more portable. Relationships between sapwood water content, environmental and plant variables were studied by comparison of concurrent observations obtained from a number of plot studies. Temporal variations were studied on annual, monthly and diurnal time bases. On all sites but one, significant fluctuations of sapwood water content with time were observed. In all cases the patterns of variation appeared to be in response to transpiration. 103 Maximum and minimum sapwood water contents coincided with environmental conditions favorable to low and high transpiration. Sapwood water content fluctuations are greatly influenced by the factors of site and environment. It is hypothesized that the absence of significant fluctuations on the lower study plot were affected by high levels of soil water. - - v' Sapwood water contents displayed varying degrees of covariation with: soil water content, tree water pressure potential, heat pulse velocity, precipitation, air temperature and relative humidity. These relationships were quantitatively evaluated by multiple regression analyses. Separate analyses were performed for the lower and upper study plots. The variables were ranked in importance to sapwood water content by a step-wise multiple regression program. Results from the lower study plot showed a low degree of correlation between sapwood water content and the independent variables. The highest correlation coefficient obtained was 0. 62, for a combination of soil water contents at 6 and 12 inch depths. Results from the upper study plot were better in that higher correla-tions were obtained. The step-wise regression program indicated the most important group of variables included soil water content of the isolated and outside soils, precipitation and heat pulse velocity of the isolated tree. The equation for this group of variables had a multiple correlation coefficient of 0. 85. The three most important single variables based on simple correla-tion coefficients were atmospheric vapor pressure deficit or relative humidity, soil water content at 24" in the isolated soil and maximum air temperature on the sample date. • These results indicate that sapwood water content because of its 104 temporal variations and correlation with atmospheric vapor pressure deficit, and soil water content is related to transpiration. However, the results are not definite, because of the low correlations obtained. More substantive evidence is required to directly link sapwood water content fluctuations and transpiration. The use of variables more directly related to transpiration (i. e. net radiation) and larger samples covering a wide range of conditions may be more successful. 105 LITERATURE CITED American Society for Testing and Materials, 1968. 1968 Book of ASTM Standards. A.S.T.M. Philadelphia, Pa., 889pp. Bloomberg, W.J. and 0. Far r e l l . 1965. Measurement of Wood Moisture Content Using the Colman Electrode. For. Chron. 41:352-363. Bruce, J.P. and R.H. Clark. 1966. Introduction to Hydrometeorology, Pergamon Press Ltd. Toronto. 319 pp. Canada Dept. Agriculture. 1970. The System of Soil Classification for Canada. Queens Printer, Ottawa. 249 pp. Chalk, L. and J.M. Bigg. 1956. The Distribution of Moisture in the Living Stem in Sitka Spruce and Douglas-fir. Forestry 29:5-21. Ckafkrejltceand RiDlogibbs.Edl957s, Studies in Tree Physiology IV. Further Investigations on Seasonal Changes in Moisture Contents of Certain Canadian Forest Trees. Can. J. Bot. 35:219-253. Conference of Biological Editors, Committee on Form and Style. 1964. Style Manual for Biological Journals. Second Edition. American Institute of Biological Sciences, Washington, D.C. 117 pp. Crossley, D.I. 1951. The Soils on the Kananaskis Forest Experiment Station in the Sub-Alpine Forest Region in Alberta. Canada Department of Resources and Development, Forestry Branch, Forest Research Note No. 100. 32 pp. Dadswell, H.E. and W.E. H i l l i s . 1962. Wood. P. 3-49. In: H.E. Dadswell (Editor) Wood Extractives. Academic Press. • New York. 513 PP. Davidson, J.M. and J.W. Biggar and D.R. Nielsen. 1963. Gamma-Radiation Attenuation for Measuring Bulk Density and Transi-ent Water Flow in Porus Materials. J. Geophys. Res. 68 (16): 4777-4783. DeVries, J. 1969. In Situ Determination of Physical Properties of the Surface Layer of Field Soils. S o i l S c i . Soc. Amer. Proc. 33(3):344-353. Draper, N.R. and H. Smith. 1966. Applied Regression Analysis. John Wiley & Sons Inc., New York. 407 pp. 106 Environment Canada. 1971. Monthly Record, Meteorological Obser-vations in Canada, January 1971. Environment Canada. UDC:551.506.1(71) 551.521.12(71). Etheridge, D.E. 1959. A Non-Destructive Method for Estimating Moisture in Wood. Can. J. Bot. 37:491-492. Fielding, J.M. 1952. The Moisture Content of the Trunks of Monterey Pine Trees. Austral. Forestry. 16:3-21. Gardner, W.H. 1965. Water Content. P. 82-127. In: C.A. Black (Editor) Methods of Soi l Analysis. Part 1. Amer. Soc. Agronomy. Inc. Madison Wisconsin, 770 pp. Gardner, W.H. and C. Calissendorff. 1967. Gamma_Ray and Neutron Attenuation in Measurement of Soil Bulk Density and Water Content. In: Isotope and Radiation Techniques in Soil Physics and Irrigation Studies. Symposium Proc. Istanbul Turkey, IAEA, Vienna, Austria. Gibbs, R.D. 1935. Studies of Wood II. On the Water-Content of Certain Canadian Trees and on Changes in Water-Gas System during Seasoning and Floatation. Can. J. Res. 12:727-760. G*bbs,CRGD. 15D958. UPatterns in the Seasonal Water Content of Trees. P. 43-69. In: K.V. Thimann (Editor). The Physiology of Forest Trees. Ronald Press Co., New York. 678 pp. Gurr, C.G. 1962. Use of Gamma Rays i n Measuring Water Content and Permeability in Unsaturated Columns of S o i l . S o i l Sc. 94:224-229. Hamilton, J.R. 1963. Characteristics of Tracheids Produced in a Gamma and Gamma-Neutron Environment. Forest Prod. J. 13 (2):62-67. Hillman, G.R. 1970. So i l Moisture Distribution About an Isolated Tree Using Potential Flow Theory. Utah State University. M.S. Thesis (Unpub.). 105 pp. Iizuka, N. and S. Sakamato. 1957. A. Method of Measuring the Relative Water Distribution in Green Disks of Todo Fir By Gamma Rays. In: Forestry Abst. 1958: J. Japan Wood Res. 3(l):14-19. Johnstone, W.D. 1970a. Some Variations in Specific Gravity and Moisture Content of 100-Year-01d Lodgepole pine Trees. Can. Forest Serv. Dept. Fish, and 'Forestry. Forest Research Lab., Calgary Alta. Infor. Dept. A-X-29. Kaufmann, M.R. 1968. Evaluation of the Pressure Chamber Technique for Estimating Plant Water Potential of Forest Trees. Forest Sci. 14:369-374. 107 Kozak, A. and J.H.G. Smith. 1965. A Comprehensive and Flexible Multiple Regression Program for Electronic Computing. For. Chron. 41:438-44.3. Kozlowski, T.T. 1961. The Movement of Water in Trees. Forest Sci . 5:177-191. Kozlowski, T.T. and C.H. Winget. 1963. Patterns of Movement in Forest Trees. . Bot. Gaz. 124(4):301-311. Kozlowski, T.T. and J .F . Hughes and L. Leyton. 1967. Movement of Injected Dyes in Gymnosperm Stems in Relation to Tracheid Alignment. Forestry 40:207-219. Kramer, P.J . 193V. The relation between rate of transpiration and rate of absorption of water in plants. Am. J.dBot. 24:10-15 Kramer, P.J . 1956. Physical and physiological aspects of water absorption. In: Encyclopedia of Plant Physiology Vol. I l l , Ed. W. Rudland, Springer-verlag. Berlin-Goltingen Heidelber I. Kramer, P.J . and T.T. Kozlowski. 1960. Physiology of Trees. McGraw H i l l Book Co., Toronto. 642 pp. Loos, W.E. 1962. Effect of Gamma Radiation on the Toughness of Wood. Forest Prod. J . 12(6):261-264. Markstrom, D.C. and R.A. Harm. 1972. Seasonal Variation •in Wood Permeability and Stem Moisture Content of Three Rocky Mountain Softwoods. U.S. Forest Serv. Rocky Mountain Forest and Range Exp. Sta. Res. Note RM-212. 7 pp. Marshall, D.C. 1958. Measurement of Sap Flow in Conifers by Heat Transport. Plant Physiol. 33:385-396. McDermott, J . J . 1941. The Effect of the Method of Cutting on the Moisture Content of Samples from Tree Branches. Am. J . Bot. 28:506-508. . McHenry, J.R. and F.E. Dendy. 1964. Measurement of Sediment Density by Attenuation of Transmitted Gamma Rays. Soil Sci . Soc. Amer. Proc. 28:817-822. Meteorological Branch. 1971. Monthly Meteorological Summary: For Month of January 1971, Calgary Weather Office, Calgary, Alberta. Dept. of Transport. UDC 551.506.1. Miksche, J.P. and A.H. Sparrow and A.P. Rogers. 1961. Effects of Chronic Gamma Radiation on the Apical Meristems of Pinus  strobus and Taxus media. Am. J . Bot. 48:529. 108 Moss, E.H. 1959. Flora of Alberta. . Univ. of Toronto Press, Toronto. 546 pp. Owston, P.W. and J.L. Smith and H.G. Halverson. 1969. Development of Some Radioisotope Procedures for Measuring Water Move-ment in Trees. U.S. Atomic Energy Comm., Div. of Isotope Develop. TID - 25136. 55 pp. Parker, J. 1954. Available Water in Stems of Some Rocky Mountain Conifers. Bot. Gaz. 115:380-385. Parrish, W.B. 1961. Detecting Defects in Wood by the Attenuation of Gamma Rays. Forest Sci. 7(2):136-143. Reginato, R.J. and R.D. Jackson. 1971. Field Measurement of S o i l -Water Content by Gamma-Ray Transmission Compensated for Temperature Fluctuations. Soil Sci. Soc. Amer. Proc. 35:529-533. Reid, R.W. 1961. Moisture Changes in Lodgepole Pine Before and After Attack by the Mountain Pine Beetle. For. Chron. 37:368-375. Rowe, J.S'.' 1959. Forest Regions of Canada. Canada, Dept. of Northern Affairs and Natural Resources, Forestry Branch. Bulletin 123. Sandermann, W. and B. Hausen and M. Simatupang. 1967. Orienterende Versuche Zur Differenzierung Von Splint Und Kern Sowie Zum Sichtbarmachen Der Ubergangszone Von Fichte Und'V Anderen Nadelholzern. Das Papier Vol 21:No. 7: 349-354. Translation: I n i t i a l experiments to differentiate sapwood and heartwood as well as the transition zone of spruce and other coniferous woods. Translation No. 267, Canada Dept. Forestry, Ottawa, 1968. 15 pp. Scholander,. P.F. and H.T. Hammel and E.D. Bradstreet and E.A. Hemmingsen. 1965. Sap Pressure in Vascular Plants. Sci. 148:339-344. Smith, J.L. and D.W. Willen and M.S. Owens. 1967. Isotope Snow Gauges for Determining Hydrologic Characteristics of Snow-packs. Amer. Union. Geophys. Monograph No. 11:11-21. Spinks, J.W.T. and R.J. Woods. 1964. An Introduction to Radiation Chemistry. John Wiley Sons. New York. 447 pp. Swanson, R.H. 1962. An Instrument for Detecting Sap Movement in Woody Plants. U.S. Forest Ser., Rocky Mountain Forest and Range Exp. Sta. Sta. Pap. 68. 16 pp. 109 Swanson, R.H. 1966a. Seasonal Course of Transpiration of Lodgepole Pine and Engelmann Spruce. P. 419-434. In: W.E. Sopper and H.W. Lul l (Editors). International Symposium on Forest Hydrology. Dergamon Press Ltd., Toronto. 813 pp. Swanson, R.H. 1971. Velocity Distribution Patterns in Ascending Xylem Sap During Transpiration. Paper #4-2-171: Presented at Symposium on Flow—Its Measurement and Control in Science and Industry, Pittsburgh, f a . May 10-14, 1971. U.S. Dept. Agriculture. 1962. Handbook on Measurement of Soil Moisture by the. Neutron Scattering Method. A compilation of Available Information for Use Within the U.S. Forest Service. U.S. Dept. Agric. Forest Serv. Washington, D.C. N - 4084. Van Bavel, C.H.M. 1959. Soi l Densitometry by Gamma Transmission. Soil Sci. 87:50-58. Waring, R.H., B.D. Cleary. 1967. Plant Moisture Stress: Evalu-ation by Pressure Bomb. Science 155:1248, 1253-1254. Youngs, R.L. 1965. Influences of Modern Physics on the Properties of Wood and their Evaluation. Amer. Soc. for Testing Materials Special Tech. Pub. No. 373:90-101. Zimmermann, M.H. and C.L. Brown. 1971. Trees: Structure and Function. Springer - Verlag, New York. 336 pp. 

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