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Nitrogen availability and soil microclimate after clearcutting lodgepole pine Haskin, Catherine Marie 1985

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NITROGEN AVAILABILITY A N D SOIL MICROCLIMATE AFTER CLZARCUTTING L O D G E P O L E PINE by CATHERINE MARIE HAS KIN B.Sc, Oregon State University, 1980 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF T H E REQUIREMENTS FOR T H E D E G R E E OF MASTER OF SCIENCE in T H E F A C U L T Y OF G R A D U A T E STUDIES Department of Forest Science We accept this thesis as conforming to the required standard T H E UNIVERSITY O F BRITISH COLUMBIA JULY 1985 ® CATHERINE MARIE HASKIN, 1985 -In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the THE UNIVERSITY OF BRITISH COLUMBIA, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of. this thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Forest Science THE UNIVERSITY OF BRITISH COLUMBIA 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: JULY 1985 ABSTRACT Long term management of lodgepole pine depends, in part, on the nutrient capital of the site. Harvesting has been shown to increase the availability of nitrogen and other nutrients for a limited period of time. This increase, or nutrient flush, following cutting has been attributed to several factors including changes in organic matter quantity and quality, soil moisture and temperature regimes, and competition for nutrients. Knowledge of the duration and the magnitude of the nutrient flush would be valuable for management decisions. A chronosequence of lodgepole pine clearcuts was studied for soil nitrogen availability and microclimate. Mineral soil and forest floor samples were anaerobically incubated and analyzed for ammonium-nitrogen (ppm). The mineral soil showed a flush lasting about 12 years, peaking by year 8, while the forest floor material showed no trend. The size of the increase from year 2 to year 8 was about 52%. Temperature (air and soil), soil moisture, solar radiation, and precipitation data were collected, and a soil water budget was calculated using a simple water balance model. The average calculated soil water deficit was 119 mm, but this may have been an over-estimate. Windrowing following cutting may have depleted the site nitrogen reserve which in turn reduced the amount that was mineralized during incubation. The interaction between the soil temperature and moisture may have further limited nitrogen availability to the lodgepole pine trees. It is concluded that the dynamics of nitrogen availability following clearcutting are important for the establishment and growth of lodgepole pine. The summer moisture deficit appears to limit the nitrogen mineralization rate as well as seedling growth. ii TABLE OF CONTENTS ABSTRACT ii LIST OF TABLES v LIST OF FIGURES vi ACKNOWLEDGEMENT vii DEDICATION viii I. INTRODUCTION 1 II. STUDY AREA .. 6 1. LOCATION 6 2. DESCRIPTION 6 III. METHODS AND MATERIALS 12 A. NITROGEN ANALYSIS 12 1. FIELD METHODS 12 2. LABORATORY METHODS 14 3. STATISTICAL METHODS 16 B. METEOROLOGICAL ANALYSIS 16 1. FIELD METHODS 16 2. ANALYSIS METHODS 19 IV. RESULTS 23 A. NITROGEN ANALYSIS 23 B. METEOROLOGICAL ANALYSIS 29 i i i V . DISCUSSION 4 4 VI. CONCLUSIONS 4 8 VII. MANAGEMENT IMPLICATIONS 50 LITERATURE CITED 53 APPENDIX A 57 APPENDIX B 59 APPENDIX C 63 iv LIST OF TABLES Table Page 1. Characteristics of Seven Harvested Sites in the Okanagan Highlands of British Columbia 9 2. Soil Descriptions for Seven Harvested and Three Control (C) Sites in the Okanagan Highlands of British Columbia 10 3. Forest Floor Descriptions for Seven Harvested and Three Control (C) Sites in the Okanagan Highlands of British Columbia 11 4. Comparison of Mean Daily Total Radiation (MJ/mJ) Between the 1972 Site, and Summerland CDA 1984 and Normal Values 22 5. Nitrogen (ppm) Mineralized by a Laboratory Incubation from Mineral Soil and Forest Floor Materials 24 6. Mineralized Nitrogen (ppm) Extracted Before and After Laboratory and in situ Incubation Treatments of Mineral Soil from Four Harvest Sites 27 7. Comparison of Mean Daily Air Temperature and Total Precipitation between the 1972 site, Chute Lake and Summerland CDA 30 v LIST OF FIGURES Figure Page 1. Location of study area: A. within British Columbia and B. by individual site. 7 2. Ammonium-nitrogen mineralized during anaerobic incubation of mineral soil 25 3. Ammonium-nitrogen extracted before and mineralized during incubation treatments. See text for explanation of treatments 28 4. Mean daily maximum and minimum air temperatures for 3 sites from June 7 to September 13, 1984. The means of the seven-day intervals are plotted at the mid-points of the intervals 32 5. Mean daily precipitation (mm/day) for 3 harvest sites from June 7 to September 13, 1984. No value shown means no data was collected 33 6. Volumetric soil moisture content (%), corrected for coarse fragments, for three harvest sites 35 7. Estimated water storage for three harvest sites from June 7 to September 13, 1984. The values are the amounts available at the beginning of each seven-day interval. Reference values were derived from available wateT storage calculations: wilting point, easily available and field capacity (-1.5, -.10, -.01 MPa). "a" is the estimated coefficient from the transpiration model (0.8 for 1971 and 1972) 36 8. Soil gravimetric moisture content (mm) for 3 harvest sites from June 7 to September 13, 1984. Reference values were derived from available water storage calculations: wilting point, easilv available and field capacity (-1.5, -.10 and -.01 MPa) 38 9. Mean daily soil temperature plus seven-day interval range at 3 depths for harvest site 1980 from June 7 to September 13, 1984. The means of the seven-day intervals are plotted at the mid-points of the intervals 40 10. Mean daily soil temperature at 3 depths for harvest site 1972 from June 7 to September 13, 1984. The means of the seven-day intervals are plotted at the mid-points of the intervals 41 11. Mean daily soil temperature at 3 depths for control site 1972C from June 7 to September 13, 1984. The means of the seven-day intervals are plotted at the mid-points of the intervals 43 vi ACKNOWLEDGEMENT I thank the following people for their assistance and encouragement: Clive David, Marise Wickman, Dr. T. Andy Black, and Barry Wong. I have appreciated the constant moral support of the graduate students in Forestry. The field and lab research was supported by a Canadian Forestry Service Program of Research by Universities in Forestry (PRUF) Contract and a Natural Sciences and Engineering Research Council (NSERC) Development • Grant supervised by Dr. G. F. Weetman. Catherine Marie Haskin July 1985 vii DEDICATION TO THE MEMORY OF MY FATHER AND THE PATIENCE OF MY HUSBAND viii I. INTRODUCTION Intensive management of lodgepole pine ( Pinus contorta var. latifolia , Engelm.) is becoming an important part of forest management in the interior of British Columbia. Nitrogen (N) is considered to be growth-limiting for many lodgepole pine stands in British Columbia (Lotan and Perry, 1983). While there may be a large supply of N in the soil and forest floor, only a small portion is usually readily available for use by trees at any one time (Keeney, 1980). Harvesting, especially clearcutting, redistributes the N that is within the affected biomass. Some of the biomass N is completely removed (in stems and bark) from the site and the rest of the site biomass N is either left scattered about as slash or is piled and burned (at least, partially removed). Harvesting and other disturbances have also been shown to increase the availability of N as well as other nutrients for a limited period of time (Bormann and Likens, 1979; Matson and Vitousek, 1981; Vitousek and Melillo, 1979). The increase in nutrient availability or the nutrient flush after disturbance has been attributed to several factors. These factors include changes in quantity and quality of substrate available for decomposition, moisture and temperature regimes, and in the competition for nutrients. The changes, with subsequent mobilization of nutrients, were seen by Romell (1935, 1938) as a part of the 'activation' of a mor humus, the type of humus commonly found in northern coniferous forests. The mineral soil may be affected as well, the activation process having been started by the disturbance of harvesting with the breaking up and mixing of the mor layer, roots and mycelia. The addition of fresh slash as well as severed roots is a 'green manuring' of a site after clearcutting (Romell, 1935, 1938). Because of the high carbon/nitrogen (C/N) ratio in slash and roots, an initial period of net immobilization of N may be expected. Subsequently, 1 2 increased availability of mineralized N will occur (Keeney, 1980). The duration and magnitude of the increase is of practical importance to forest management The ability to predict the timing of the increased availability would enable forest managers to take advantage of it to enhance crop response (Keeney, 1980). Managers would be able to plan silvicultural operations, such as thinning and fertilization, that would be efficient in the use of N, either that already on the site or any added in amendments. Thinning a stand or any operation where vegetation is killed was also considered to be enough of a disturbance to produce, at least, a less intense pulse of available N (Tamm, 1964). Soil climate, the distribution of soil temperature and soil moisture (Black, 1982), greatly influences microbial mineralization of N (Burger and Pritchett, 1984). Because northern forest floors are considered to be colder and more limiting to microbial activity, any disturbance that increases the soil temperature of the humus layer will most likely improve the microbial environment The effect of disturbance on soil moisture availability may also be beneficial to microbial activity. The extent and duration of change after harvesting depends on the particular site conditions and local climate. However, growing season temperatures and water availability may also interact so that rnicrobial activity is adversely affected or that the mineralized N is made unavailable or both (Bormann, et al, 1968). Lodgepole pine is known for a combination of several traits that are exhibited to an unusual degree. The first one is its ability to grow on relatively infertile soils (Lotan and Perry, 1983). The granitic soils of south-central British Columbia are considered to be a poor source of nutrients for tree growth. The forest floor, because of litter inputs from the forest vegetation, has been an important source of N for cycling within the ecosystem. The amount of N available seems to be inadequate, possibly due to immobilization as organic N in the humus, for some response to N 3 fertilization has been recorded (Cochran, 1985). A second important trait of lodgepole pine is its profuse regeneration after fire. Lodgepole pine produces a good seed crop quite frequently, and, due to cone serotiny, many seeds may be stored on a single tree for a number of years. Serotiny varies greatly across the range of lodgepole pine and a single stand may tend towards being serotinous or nonserotinous, but will have individuals that exhibit all degrees of serotiny (Lotan and Perry, 1983). Regeneration of a site after a wildfire is usually fairly rapid because the stored seeds are released on to a suitable seedbed (mineral soil). Eventually, a very densely stocked stand may be produced (Eis, et al, 1982). On the other hand, natural regeneration of a site after clearcutting may not occur as quickly as after a wildfire, depending on the site preparation method. Site preparation methods can eliminate or reduce the amount of seeds left on a site. Broadcast burning destroys most of the seeds while windrowing removes the cone-bearing slash from most of the site, although some cones remain scattered across the area (Clark, 1974). Drag scarification does not reduce the number of seeds available but creates a limited amount of suitable seedbed (compared to burning or windrowing) (Glen, 1979). The advantage to reducing the initial number of seeds available for regeneration is the probable reduction in stocking levels and possible prevention of dense 'stagnated' stands (Clark, 1974; Lotan and Perry, 1983). Lodgepole pine can continue to add to the stocking (by ingress) for quite a long period of time, up to 15 or more years (Clark, 1984). Therefore, it is desirable to minimize the amount of seedbed that is suitable for germination, but it should be evenly distributed over the site. An important side effect of removing slash and forest floor from most of a site is the reduction in N that can be returned to a particular spot (Morris, 1983; Lotan and Perry, 1983). For a site that is already N-poor, such an occurrence cannot 4 but reduce the growth of seedlings (Lotan and Perry, 1983). The availability of N within the soil may be improved with the site preparation, but there could be a delay before the improvement occurs (Vitousek, 1981). The period of increased N availability will vary depending on the site (Vitousek, 1981). It is possible that lodgepole pine may be able to use the increased N in early growth of a few trees to establish dominance and cover on a site, thereby avoiding a period of stagnation. Another trait of lodgepole pine is its stomatal sensitivity. These close at relatively high leaf water potentials (Bassman, 1985; Lotan and Perry, 1983). On droughty sites, transpiration is reduced as the soil dries out. With increasing moisture stress, photosynthesis is reduced (to 0 at -1.5 to -2.24 MPa) (Dykstra, 1974 and Brix, 1979 cited in Bassman, 1985). South-central British Columbia has hot, dry summers during the growing season and one of the assumptions when working on the Okanagan Highlands is that there is a large growing season water deficit (Mitchell and Green, 1981) . Lodgepole pine is able to survive the dry weather with its moderate drought resistence; probably with little to no photosynthesis occurring during the driest periods (Kramer and Kozlowski, 1979). Knowing the basic attributes of lodgepole pine as a species and the general microclimate of a site, a forest manager would be better able to judge the "limitations due to moisture availability during the growing season" (Black, 1982) . Reduced transpiration during dry spells may help a tree to survive, but the reduction or loss in photosynthesis and N uptake will undoubtedly affect growth potential. The dynamics of N availability on lodgepole pine clearcuts has received little attention; little data is available on the growing season moisture deficit for regeneration on recent clearcuts. A chronosequence of lodgepole pine clearcuts was selected near Okanagan Falls, British Columbia for this study: the sites had thin humus layers and thus limited reserves of humus organic N. 5 The specific objectives of this study were: 1. to verify the occurrence of a nitrogen flush after clearcutting lodgepole pine; 2. to tentatively quantify the duration of the flush and, if possible, the magnitude; 3. to examine microclimatic factors that may affect the availability and use of N. The study was divided into two parts to accomplish the objectives. The first dealt with the N availability. N mineralization rates can be used to indicate N availability (Powers, 1980), but care must be exercised when correlating field potential with laboratory results (Keeney, 1980). The second part was concerned with the meteorological regimes (regional and micro) of the study area. The general data were used to characterize the sites and validate certain assumptions in connection with the N availability part of this study. II. STUDY AREA 1. LOCATION The study areas are located in the Okanagan Highlands between 25 and 40 km from Okanagan Falls, British Columbia, inside Weyerhaeuser Canada Ltd. Tree Farm License No. 15 (Figure 1). The Okanagan Highlands are in the Dry Montane Spruce subzone (MSb, variant 2) (Utzig, et al, 1983). The sites are located in three adjacent drainages: Solco, Vaseux, and Mclntyre. Solco and Mclntyre Creeks drain into Vaseux Creek. 2. DESCRIPTION The seven sites were a series of harvests spanning twelve years, 1971 to 1982, inclusive. The clearcuts were chosen to be as similar as possible within the study area except for the year of harvest They were chosen in the summer of 1983 and a pilot soil N mineralization study was conducted to test the variablity of the sites. See Table 1 for a summary of the basic site characteristics. The stands prior to harvest were predominantly of fire-origin, even-aged mature lodgepole pine with some Engelmann spruce ( Picea engelmannii Parry) at the higher elevations. The stands of all the study areas were tree-length harvested and any slash remaining on the sites was windrowed and burned, except for the 1972 and 1976 sites, which were drag scarified. Burning is usually done to reduce the amount of slash as well as to remove any material infected with dwarf mistletoe ( Arceuthobium  armericanum Nutt) (Lotan, et al, 1985). Windrowing is the concentration of slash into long, narrow rows instead of discrete piles. Natural regeneration has been relied upon to restock the clearcuts, most of the regeneration has been lodgepole pine. 6 Cartographic Centre Outline Maps Faculty of Environmental Studies University of Waterloo. 1975 FIGURE 1. Location of study area: A. w i t h i n B r i t i s h Columbia and B. by i n d i v i d u a l s i t e . 7 8 Depending on the site, the soil subgroup was determined to be either an Orthic Humo-Ferric Podzol (O.HFP) or an Eluviated or Orthic Dystric Brunisol (E.DYB or O.DYB) (CSSC, 1978). All of these were derived from parent materials, such as granite, granodiorite, and quartzite, that have low supplies of available nutrients. The soil nutrient regimes were submeso- to mesotrophic (poor to medium nutrient status) and the soil moisture regimes varied from xeric to mesic. Most of the sites had a shallow rooting depth due to an impeding C horizon. Table 2 gives soil descriptions of the upper 20 cm for the sites. Depth of the forest floor or organic matter (excluding large woody pieces) remaining after site preparation averaged 1.5 cm for all seven sites when measured in 1984. The 1971, 1980, and 1982 sites had a charcoal layer beneath the current forest floor. The humus form subgroups were either Orthihemimor or Orthihemihumimor (Klinka, et al, 1981). Three areas of the residual stands were chosen for use as control sites. They were identified as 1972C, 1974C, and 1982C. The 'C designated the site as being a control and the year was the harvest site of which it was a residual area. The characteristics of the control sites were similar to those of the harvested areas, except for the characteristics that were affected by the harvesting operation. The forest floor depth averaged 3 cm for the control three sites in 1984. See Tables 2 and 3 for additional information. TABLE 1. Characteristics of Seven Harvested Sites in the Okanagan Highlands of British Columbia YEAR OF AGE OF CUT ELEVATION (m) HARVEST IN 1984 (YR) 1971 1972 1974 1976 1978 1980 1982 13 12 10 8 6 4 2 1525 1525 1630 1646 1448 1432 1448 SLOPE (%) 10 0 - 1 2 13 0-10 2-6 FLAT 0-11 ASPECT S-SE NW SW NW S DEPTH TO C HORIZON (cm) 25-36 22 18-25 18-25 14 22 22 SITE POSITION UPPER TO MID-SLOPE LOWER SLOPE MIDSLOPE UPPER SLOPE VALLEY FLOOR VALLEY FLOOR LOWER SLOPE SIZE (ha) 40 30 18 15 25 18 TABLE 2. Soil Descriptions for Seven Harvested and Three Control (C) Sites in the Okanagan Highlands of British Columbia YEAR OF HARVEST SOIL SUBGROUP1 SOIL pH BULK DENSITY (g/cm') COARSE FRACTION (%) DRAINAGE TEXTURE ORGANIC MATTER CONTENT (%) 1971 1972 1974 1976 1978 1980 1982 1972C 1974C 1982C O.DYB O.HFP O.HFP O.HFP E.DYB O.DYB O.DYB O.HFP O.HFP O.DYB 4.67 4.39 4.13 4.47 4.51 4.67 4.67 4.36 4.27 4.60 1.19 0.98 0.97 1.01 1.05 1.37 1.34 0.57 0.78 1.45 18.9 5.6 11.4 14.8 4.7 18.7 19.0 2.4 7.1 20.4 RAPID MOD. WELL RAPID RAPID MOD. WELL WELL WELL MOD. WELL RAPID RAPID SANDY TO COARSE LOAM LOAM LOAM: GRAVELLY TO SANDY LOAM: GRAVELLY TO SANDY LOAM TO CLAY LOAM GRAVELLY SANDY LOAM GRAVELLY SANDY LOAM LOAM LOAM: GRAVELLY TO SANDY GRAVELLY SANDY LOAM 7.1 12.7 12.7 8.5 7.8 7.2 5.6 10.5 8.3 6.4 1 O.DYB or E.DYB = Orthic or Eluviated Dystric Bmnisol: O.HFP = Orthic Humo-Ferric Podzol (CSSC, 1978). 11 TABLE 3. Forest Floor Descriptions for Seven Harvested and Three Control (C) Sites in the Okanagan Highlands of British Columbia YEAR OF HARVEST HUMUS FORM SUBGROUP1 AVERAGE DEPTH (cm) BULK DENSITY (g/cm3) WEIGHT (106 kg/ha) 1971 1972 1974 1976 1978 1980 1982 1972C 1974C 1982C OHM OHM OHM OHM OHHM OHHM OHHM OHHM OHHM OHHM 1.2 1-9 2.2 1.4 1.2 1.3 1.3 2.9 3.6 2.8 0.395 0.392 0.331 0.300 0.210 .0.206 0.206 0.159 0.140 0.159 1.01 0.91 1.52 0.63 0.15 0.38 0.45 0.75 0.45 0.33 1 OHM = Orthihemimor; OHHM = Orthihemihumimor; Klinka, et al, 1981. III. METHODS AND MATERIALS A. NITROGEN ANALYSIS 1. FIELD METHODS Mineral soil and forest floor samples were collected from each of the harvest and control sites in June of 1984. Sampling was systematic and a grid pattern for each site was designed so that the desired number of samples was obtained. The actual sampling was done cutting across windrows and drainages, not following them. Windrows and wet or marshy areas were excluded from sampling by moving to the nearest acceptable spot along the same line if a plot landed in such an area. Data from a pilot study in 1983 was used to determine the number of samples for each harvest site (Appendix A). The older sites required more samples than was possible to collect because of time and cost restrictions. The number collected for those sites was about half of the estimate from the pilot study. The number of samples from the control sites was arbitrarily chosen to satisfy the requirements of the statistical analysis. The mineral soil samples of the harvest sites were collected from the 0 to 15 cm depth. The samples were then composited, using a computer-generated random numbers table, into final bulk samples. For statistical purposes, 30 was chosen as the number of final bulk samples, each being a composite of five or seven samples depending on the harvest site. The forest floor samples of the harvest sites were collected at every fifth or seventh mineral soil plot for a total of 30 samples from each site. The 1978 site was the first one to be collected and the forest floor samples' were gathered at every third plot (50 samples), but it was decided that 50 was too many samples to handle so the spacing was changed to the fifth or seventh plot instead. Sites 1980 and 1982 had 12 13 very little forest floor left due to the completeness of the disturbance, therefore, only 20 "random" samples for each site were collected. No compositing took place for any of the forest floor samples. A template (225 cm2) was placed over the sample point and cut around with a knife. The final sample consisted of all the material that was above the mineral soil surface within the cut square. An average depth, based on one measurment on each side of the square, was recorded. The samples from the control sites were collected in the same manner, except that those from the mineral soil were not composited and those from the forest floor were collected at every second mineral soil plot All the samples from all the sites were labeled and placed in plastic bags since they were still wet The bags were stored in styrofoam chests sunk into the bank of a stream to keep them cool until they could be transported to the lab in Vancouver for analysis. Bulk density for both types of soil material was determined. The measured volume and dry weights of the forest floor samples were used to estimate forest floor bulk density, while separate bulk density samples were obtained for the mineral soil; six samples from each harvested site (seven for 1972) and three from each control site. A hole was dug to about 15 cm and the excavated material was stored in a plastic bag. The hole was then lined with plastic and filled with water level with the top of the mineral soil horizon. The volume of the water was measured in a 5000 ml plastic cylinder to the nearest 5 ml. A study of in situ nitrogen mineralization was conducted using ten randomly-chosen final bulk samples from each of sites 1971, 1978, 1980, and 1982. A 150 ml field-moist subsample was weighed and placed in a tagged plastic bag. Another 75 ml subsample was used to determine the moisture content The samples were randomly distributed between the sites with 12 at the 1971 and 1978 sites and 8 at the 1980 and 1982 sites. They were buried 3 to 6 cm below the surface of the 14 forest floor by carefully lifting up the forest floor, removing some soil to make room for each flattened bag, and then replacing the forest floor over the bags. The samples were buried on June 27 and removed on September 13. The place where they were buried was near a soil temperature measuring site (see below). 2. LABORATORY METHODS The mineral, soil samples were air-dried and sieved, through a 2 mm screen with the coarse fraction (greater than 2 mm) discarded. The bulk density samples were also air-dried and sieved but both fractions were retained and weighed. Average organic matter content of the mineral soil was determined by loss-on-ignition using 20 g subsamples of the fine (< 2 mm) fraction of the bulk density samples. Additional 5 g subsamples of the fine fraction in 10 ml of .01M calcium chloride were used to estimate the pH of the mineral soil. Forest floor samples were air-dried, then oven-dried and weighed. The weight of the forest floor per hectare was determined using the measured weight and volume. After that, the material was ground and seived with the greater than 2 mm fraction being discarded. Mineralizable nitrogen was estimated by anaerobic incubation for both mineral soil and forest floor. A subsample, 5 g for mineral soil and 3 g for forest floor, was placed in a test tube with 25.0 ± 0.5 ml of distilled water and then the mouth of the tube was covered with a parafin film. Since this was to be an anaerobic incubation, as much air was eliminated from the tube as possible when it was being covered by making sure it was filled to the top with water. The samples were incubated at 40° C for seven days, a modification of the Waring and Bremner (1964) method. After incubation, the samples were processed immediately. Extraction of the mineralized nitrogen as ammonium and nitrate was done with 2N potassium chloride. 15 The contents of each tube were placed in a plastic vial along with 30 ml of the potassium chloride. The vials were shaken for one hour and then allowed to equilibrate for 18 to 24 hours. After equilibration, the samples were gravity filtered, with an additional 5 ml of potassium chloride used to rinse out the vials. Each sample was analyzed for gross levels (ppm) of ammonium (NHj) and nitrate (NO;) on a Technicon AutoAnalyser. The values were then converted to NH4-nitrogen (N) or NOj-N. Because the incubation was anaerobic, very little to no NO; was detected. Therefore, only the NH4-N values were used for the statistical analysis. The in situ mineralization samples were processed in the same manner as the other samples. For comparison purposes, additional tests were done on these samples, as well as on the original bulk samples from which they were taken. Non-incubated subsamples of each in situ and original bulk sample were also extracted with 2N potassium chloride as described above. This analysis produced the "initial" levels of mineralized N in the soil (Waring and Bremner, 1964). Another subsample of the in situ material was incubated in-the lab and analysed. These values show what could be additionally mineralized from the soil. The treatments were named: 1. Extraction Bulk (EB) - final bulk samples extracted with potassium chloride, but not incubated; also considered to be "initial" levels of mineralized N; 2. Bulk Incubation (B) - lab incubated final bulk samples; 3. Extraction in situ (EI) - samples extracted with potassium chloride after in situ incubation; 4. in situ Incubation (IS) - in situ samples that were subjected to a lab incubation. 16 3. STATISTICAL METHODS Statistical analyses were carried out on the data using the Michigan Interactive Data Analysis System (MIDAS). All values were subjected to a test of homogeneity of variances. The variances of the final bulk samples and of the forest floor samples were not homogenous. Two transformations, the natural log and a power function, were performed on the data, but the heterogeneity was not reduced. Therefore, the untransformed values, in ppm, were used for the analyses (see Appendix B) and caution should be used when interpreting the results. One-way analysis of variance (ANOVA) was used to test for significant difference between the site means, while Duncan's multiple range test established the order of the differences (p<0.05). The in situ data variances were homogenous, so no transformation was necessary. Two-way analysis of variance (ANOVAR) was used to test for significant differences between the sites and treatments. B. METEOROLOGICAL ANALYSIS 1. FIELD METHODS A number of microclimatic conditions were measured on the harvest and control sites. Air and soil temperature, daily solar radiation, precipitation and soil moisture data were gathered at various sites. The sites for placement of equipment were chosen to span the differences in harvest ages and elevations as well as the geographical range of the study sites. Air temperature was measured with maximum-minimum (max-min) thermometers at six sites. They were positioned on the northern side of an object, near a soil temperature measuring site, out of direct all day exposure to the sun but where air circulated freely. The bulb of the thermometer was within 5 cm of the ground. The soil temperature was measured at ten sites using thermistor probes located 17 at three depths (2, 10 and 30 cm) below the top of the forest floor. The 2 cm depth was the approximate forest floor-mineral soil interface, the 10 cm depth was the middle of the rooting zone, and the 30 cm depth was the top of the C horizon. The daily temperature wave is damped out at about the 30 cm depth for these soils. Roots did not penetrate most of the C horizons so temperatures below that depth would not be affecting root growth. Soil moisture was measured gravimetrically for the 0 to 20 cm depth range (rooting zone) at seven sites. Ten samples (310 cm3) at each site were collected about once every seven days after the middle of June. Undisturbed soil cores were collected in brass rings from the harvest areas to determine the moisture retention curves for the soils. Volumetric water contents were determined at -0.01, -0.033, -0.10, -0.20, -0.40, and -1.5 MPa using a pressure plate method (Richards, 1965). The samples were taken from two collection points at each site. Each point had three cores taken at different depths from the A and B horizons within the top 20 cm. The 1972 site, which was at about the mid-points of the elevation and distance ranges, was used as the central meteorological station. This site was also sufficiently far enough away from the local fishing streams so that the station equipment would not attract the attention of any casual passersby. A fence was built around the station to keep the cattle from using the stands as scratching posts. The meteorological station consisted of a Stevenson screen, a rain gauge and a pyranograph. Both the Stevenson screen and the pyranograph were on top of stands 1 meter high while the rim of the rain gauge was 1 meter from the ground. Inside the Stevenson screen was a max-min thermometer and a 31-day drum hygrothermograph (Model H311-A) from WeatherMeasure. The pyranograph, also from WeatherMeasure, had a 7-day drum. 18 Because of late arrival of equipment, the precipitation at the 1972 site was first collected with a small brass rain gauge set on top of a stump. It was replaced with one that was attached to a wooden post that was driven into the ground. The new rain gauges also had a calibrated collection tube that made recording of amounts collected more accurate. Rain gauges were installed on the 1971 and 1974 sites in late June, the 1971 site being in a different drainage and the 1974 site being at a higher elevation. The additional rain gauges were installed so that a pattern of precipitation would be obtained for the general study area. Unfortunately, in mid-August, the gauge at the 1974 site had to be removed because the cattle were knocking it over. It had been installed in the middle of an old landing and was the only object in the area they could rub against The rain gauge at the 1971 site was inside a fenced area. Data were collected in the following manner. In June, when the soil samples were being collected, each site was visited about every other day. The weather station was visited almost every day to check that the equipment was functioning properly. The 1980 site soil temperature measuring site was located just off the main road and was visited every morning and afternoon when possible during June. After the beginning of July, weekly trips from Vancouver were made to the sites to collect the soil gravimetric samples and record the other data. The collection of the soil temperatures presented a sampling problem. To obtain an idea of the daily fluctuations, both the maximums and minimums needed to be recorded. The thermistor probes were not connected to an automatic recording device, so all that could be obtained during a visit was the instantaneous, or current, soil temperature. To overcome this problem, all the sites were visited in the morning or afternoon on alternate days in June and all data were collected at that time. During the weekly visits,-each site was visited in both the morning and afternoon. 19 2. ANALYSTS METHODS The meteorological data were not statistically analyzed. The data were compiled and averaged over seven-day intervals starting on June 7 and ending on September 13 (14 intervals). This period covered most of the snow-free time or growing season for 1984. Except where noted, only the interval means were reported. Data used in Figures 4 through 11 are in Appendix C. Data from the 1971, 1972 and 1974 harvest sites were chosen for display for the same reasons the sites were chosen as rain gauge sites. The 1972 and 1972C data were considered to be 'average' for the study areas. The water deficit (WD) for the growing season was estimated by summing the WD for the seven-day intervals which were calculated using a simple water balance procedure. First, the water storage (WS) was calculated for each seven-day interval on a daily mean basis using: WS- = WS- -, + P- - E- - D-l i-1 I I I where WSj and WSj_j are, respectively, the water storage (mm) for the interval and the previous interval, and Pj, Ej, and Dj are, respectively, the precipitation, the transpiration rate, and the drainage for the interval (mm/day). Ej is equal to E m a x for WSj greater than the WS at the wilting point (WP); Ej is equal to 0 for WSj less than WS at WP; and Dj is equal to 0 for WSj less than WS at field capacity (FC); but Dj is equal to WSj minus WS at FC when WSj is greater than WS at FC. The model assumes no surface runoff during the growing season. The water deficit for the growing season (WD ) was then calculated using: W D i = Emaxi - E i WDgs = L WD-. The FC (-0.01 MPa) values from the soil moisture retention curves (T.A. Black, pers. comm.) were used to estimate the AWSC (available water storage capacity) 20 al the beginning of the growing season. AWSC (mm) is equal to the rooting zone depth (RD) (200 mm) multiplied by the difference between the volumetric water contents at FC and at WP (-1.5 MPa), i.e., RD(FC-WP). The value for the 1972 site (96 mm) was also used for the 1974 site because no soil cores were collected there and the soils were similar. The AWSC. for the 1971 site was equal to 74 mm. AWSC is not the same as available water (AW). AW is the difference between trie measured water content and that at the WP and it is the water that is considered to be available for growth. Precipitation values from the 1972 site were used to replace the missing data of the first three weeks for the 1971 and 1974 sites as well as the last two weeks for the 1974 site in the water storage calculations. If the water available for transpiration was greater than the AWSC, the excess was considered to be lost from the rooting zone as drainage. The actual water storage was determined using the gravimetric moisture content samples and was graphed by collection date, not seven-day interval. When soil water is not limiting, the transpiration rate (mm/day) is calculated by (Priestley and Taylor, 1972): Emax = a Eeq where ' a ' is an estimated coefficient and E.n is the equilibrium evaporation rate. ' a ' = 0.8 was used for all three sites and ' a ' = 1.0 was also used for the 1974 site. The equation used for the equilibrium evaporation rate was (s/(s + 7 ))(Rn - G) where Rfi and G are, respectively, the daily (daylight hours) values of the net radiation flux density (MJ/m2) and the soil heat flux density (same units), and the s and 7 are, respectively, the slope of the saturation vapor curve and the psychrometric constant, both evaluated at the daily mean air temperature. (s/(s + 7 )) is dimensionless and was taken from Table A.3 in Campbell (1977). G was assumed to be 5% of 2 1 Rn. A more complete discussion of evapotranspiration theory is given in Spittlehouse and Black ( 1 9 8 1 ) . ' The daytime values of R^, (MJ/m2), were calculated using: Rn = asSt + ( e A " e s> 0 Ta(°-2 + ° W N where ag is ( 1 - albedo) = 0 . 8 2 , (albedo assumed to be 0 . 1 8 ) , e A is the emissivity of the atmosphere = 0 . 7 2 + 0 . 0 0 5 T A , (Idso-Jackson, see Campbell, 1 9 7 7 ) , e is the emissivity of soil surface, assumed = 0 . 9 6 , o is the Stefan- Boltzmann constant ( 5 . 6 7 x 1 0 " s W/(m2 K"), Tg is the average daytime air temperature = ( 2 T M A X + T M | N ) / 3 , (°K), (Giles, et al, 1 9 8 5 ) , St is the daily incident solar radiation, (MJ/(m: d)), Stc is the expected clear day value of St, (MJ/(m2 d)), and N is the average length of daylight, in seconds. T_ov and T_. were the average values for each seven-day interval. N was I l ia A IIUX1 calculated for each interval using the duration of daylight at 5 0 ° N from List ( 1 9 7 1 ) . St and Slc were determined from the pyranograph charts. The 1 9 7 2 site was expected to receive approximately 10% more short wave radiation than Summerland CDA because it is higher in elevation (Table 4 ) . The radiation received for the clearest days (maximum values, smooth curve on the chart) was compared with the corresponding Summerland CDA values (AES, 1 9 8 4 ) . Accordingly, the chart values were calibrated by increasing them by 1 2 . 5 % . 22 TART ,F 4, Comparison of Mean Daily Total Radiation (MJ/m2) Between the 1972 Site, and Summerland CDA 1984 and Normal Values MONTH 1972 SITE1 SUMMERLAND CDA 19842 SUMMERLAND CDA NORMALS3 JUNE JULY AUGUST SEPTEMBER 21.97 27.54 21.42 15.51 18.01 20.97 18.66 13.80 22.64 23.68 19.55 •14.47 1 Data collected from June 7 to September 13, 1984. Values for September were calculated only for the first half of the month. 2 Data for 1984 from Monthlv Radiation Summary (AES, 1984). 3 From 1951-1980 Radiation Normals (AES, 1982b). IV. RESULTS A. NITROGEN ANALYSIS The term 'mineralized N' was used to denote the incubation values of NFL-N from this study, in the same manner as Powers (1980) (gross levels) and not like Waring and Bremner (1964), where initial (extractable) N was subtracted from the final extraction results to give net levels. The terms 'potentially mineralizable N' and 'mineralizable N' were considered synonymous and refer to the amount of N that may be mineralized over time within a soil or forest floor. The availability and amount of N mineralized depends on the specfic conditions of each site. Use of the Powers (1980) method of calculating mineralizable N eliminated the need for determining the effects of drying and short-term storage (less than one year) on mineralizable N (Powers, 1984). The results of the anaerobic incubation of the mineral soil and forest floor material are presented in Table 5. The means and standard deviations for the mineral soil are shown in Figure 2. The mineralized N for the mineral soil showed an increase with time (years) since harvest from 1982(2) until 1976(8), then it began to oscillate up and down with 1972(12) being higher than 1976, but 1971(13) being lower than 1974(10). The coefficients of variation (CV) (mean/standard deviation) showed no trend and the standard deviations averaged 22% of the mean for the seven sites. The three control site values for the mineral soil had a much greater range of CV with the control average standard deviation being 110% of the mean. Two of the control sites seem to be quite low in mineralizable N. The increase in mineralizable N may be due to an increase in the supply of N available for mineralization from the addition of organic matter (mostly severed roots) to the sites during logging and a reduction in other vegetative competition for N. The values from sites older than 1976 23 TABLE Nitrogen (ppm>) Mineralized by a Laboratory Incubation from Mineral Soil and Forest Floor Materials YEAR OF HARVEST MINERAL SOIL FOREST FLOOR Mean ± SD1 Mean ± SD 1971 13.2a2 2.9 352.1ab 165.9 1972 25.9c " 7.1 336.6ab 275.7 1974 18.1b 4.2 277.4a 212.2 1976 23.5c 5.9 387.4ab 222.9 1978 20.2b 4.0 539.3c 255.8 1980 18.2b 2.6 342.7ab 140.8 1982 15.5a 4.0 475.9bc 252.4 1972C 28.7-3 13.2 219.5- 48.1 1974C 64.5- 62.6 365.2- 144.3 1982C 20.7- 13.2 366.7- 195.7 CONTROL AVERAGE 38.0- 41.7 317.2- 154.9 1 Mean + 1 Standard Deviauon of the mean. 2 Values in a column followed by the same letter are not significantly different at p<0.05 as determined by Duncan's multiple range test 3 (-): Significant differences were not considered for control site data. 25 FIGURE 2. Ammonium-nitrogen mineralized during anaerobic incubation of mineral s o i l . 26 may be due to readjustment of available N within the soil after the readily available N from the organic matter was incorporated. The harvest sites values did not reach the same level as the control sites average, but they were greater than two of the individual control sites. Of course the lack of homogeneity of the variances should be taken into account when considering the significance of the differences between sites of N mineralized from the mineral soil and the forest fl oor. For the mineral soil, a definite trend or flush was indicated. The N values for the forest floor were much greater than for the mineral soil but they did not show a pattern. The variability of the N values, shown by the standard deviations, was also much greater for the forest floor than for the mineral soil. The standard deviations averaged 56% of the means for the harvest sites and 49% for the control sites. There was no trend with the CV. Large variation was expected due to the difficulty of preventing aerobic mineralization from occurring by keeping all the organic material of the forest floor submerged during the anaerobic incubation (Keeney and Bremner, 1966). The control sites values and average were in the same range as the harvest sites. The results of the in situ treatments are shown. in Table 6 and Figure 3. An increase in mineralized N was again shown with increasing age of harvest from 1982(2) to 1978(6) by both the Bulk Incubation and in situ Incubation. The means were significantly different within those two treatments. It had been anticipated that the two lab incubation treatments would have almost identical results. That is, the in situ samples would have produced as much N as the Bulk samples even after undergoing the field in situ incubation. Such was not the case, but the similarity between the mineralization patterns was still surprisingly close. This shows that, for these samples and conditions, there was not a large supply of N to be mineralized in the mineral soil. The CVs for the two treatments were similar, with about a 3% TART F & Mineralized Nitrogen (ppm) Extracted Before and After Laboratory and in situ Incubation Treatments of Mineral Soil from Four Harvest Sites YEAR OF HARVEST 1971 1978 1980 1982 EXTRACTION BULK2 Mean ± SD1 5.5a3 1.3 6.3a 1.3 6.4a 1.7 4.5a' 0.7 BULK INCUBATION Mean ± SD 12.9a 2.3 20.9b 3.3 18.4c 3.3 16.1d 3.5 EXTRACTION in situ Mean ± SD 3.2a 1.1 3.8a 0.7 3.4a 0.5 3.5a 1.2 in situ INCUBATION Mean ± SD 9.9a 2.4 15.9b 2.1 13.8c 3.2 12.4c 3.0 1 Mean of 10 samples ± 1 Standard Deviation of the Mean. 2 Treatments are explained in the text under Methods and Materials. 3 Values in a column followed by the same letter are not significantly different at p<0.05 as determined by Duncan's multiple range test FIGURE 3. Ammonium-nitrogen e x t r a c t e d b e f o r e and m i n e r a l i z e d d u r i n g i n c u b a t i o n t r e a t m e n t s . See t e x t f o r e x p l a n a t i o n of t r e a t m e n t s . 29 difference between the average standard deviations (18.5% and 21% for the Bulk and in situ Incubations, respectively), but no trend was evident The means for each year within each of the extraction treatments were not significantly different. The Extraction in situ means were almost identical and, except for 1982(2), the same was true for the Extraction Bulk results. The difference between the two treatments was negative, with the Extraction Bulk being the 'before' and the Extraction in situ being the 'after'. The Extraction in situ samples had undergone a field in situ incubation only. During that time, immobilization of N occurred, instead of mineralization, leading to the reduced amount of extractable N. The average standard deviations of the two treatments differed by 3% and were somewhat higher (about 4%) than the ones from the incubation treatments. Again, there was no pattern to the CVs. B. METEOROLOGICAL ANALYSIS When this study was begun, some assumptions were made about the general study area and the individual study sites. The first assumption was that the study area was typical of the lodgepole pine habitat in the Okanagan Highlands. To test that assumption, the mean daily air temperature (°C) and the total precipitation (mm) from June to mid-September were compared (Table 7) between the following three sites: 1. 1972 site: 1525 m; about 49° 15' N, 119° 15' W; 2. Chute Lake: 1194 m; 49° 41' N, 119° 37 W; 3. Summerland CDA: 454 m; 49° 3-T N, 119° 39* W. Chute Lake is also on the Okanagan Highlands, but further north and Summerland CDA is in the Okanagan Valley. The 1972 site values presented were from the 1984 growing season while the other values were 30-year normals (AES, 1982c). The same temperature pattern (Table 7A) was shown by Chute Lake and 30 TABLE 2. Comparison of Mean Daily Air Temperature and Total Precipitation between the 1972 site, Chute Lake and Summerland CDA MONTH A. Mean Daily Air Temperature ( C) 19721 CHUTE LAKE2 SUMMERLAND CDA2 JUNE JULY AUGUST SEPTEMBER 9.5 11.6 14.4 6.9 11.7 14.7 13.9 9.7 17.4 20.9 .20.0 15.2 MONTH B. Total Precipitation (mm) 19721 CHUTE LAKE2 SUMMERLAND CDA2 JUNE JULY AUGUST SEPTEMBER 46.6 1.4 53.1 18.6 46.7 27.6 44.9 35.0 30.6 22.2 27.4 18.8 1 Data collected from June 7 to September 13, 1984. Values for September were calculated only for the first half of the month. 2 From 1951-1980 Temperature and Precipitation Normals (AES, 1982c). 31 Summerland CDA (higher July temperature) while the 1972 site was warmer in August The difference may have been due to having missed extreme values by weekly collection of data from July to September for the 1972 site as opposed to daily collection at the other sites. The total precipitation (Table 7B) pattern was the same for all three sites. The difference between the Highland locations and the valley was readily apparent, Summerland CDA was warmer and drier. Taking the differences in latitude and altitude into consideration, the data for the two Highland sites were quite similar. The 1972 site, as the average site of the study areas, should, therefore, be accepted as being typical of the Okanagan Highlands. The next assumption, an extension of the above but on a smaller or local scale, was that the seven harvest sites were similar to each other in climate. A comparision of air temperature (°C) (Figure 4) between the 1971 and 1972 sites showed that the temperature patterns were similar. The 1972 site had slightly lower maxima and slightly higher minima than the 1971 site, but they were in the same range. The other harvest sites had similar patterns of air temperature. The 1972C control site had lower maxima and about the same minima as the 1971 site. The average daily precipitation (mm/day) of the 1971, 1972 and 1974 sites are shown in Figure 5. The 1972 site had the most complete record for the growing season and it received about 125 mm, which is about average for the area within the range of lodgepole pine (Lotan and Perry, 1983). Differences in amounts of precipitation received were expected because of the differences in elevation and the distances between the collection locations. The patterns of storm events for the three were again quite similar. All showed a dry July and then a storm event in early August For that storm, the 1974 site received a larger amount of precipitation, probably due to it being at a higher elevation and nearer the crest of the Highlands. It seems that the variations shown by the air temperature and precipitation patterns 32 (_) _10 1 I i I i I i I i ! i L -10 H 1 1 1 1 1 1 1 ! 1 1 1 : 1 7 21 5 19 2 16 30 13 JUNE JULY AUGUST SEPTEMBER FIGURE 4. Mean d a i l y maximum and minimum a i r t e m p e r a t u r e s f o r 3 s i t e s from J une 7 t o September 13, 1984. The means o f t h e s e v e n - d a y i n t e r v a l s a r e p l o t t e d a t t h e m i d - p o i n t s of t h e i n t e r v a l s . 7 21 5 19 2 16 30 13 JUNE JULY AUGUST . SEPTEMBER FIGURE 5. Mean d a i l y p r e c i p i t a t i o n (mm/day) f o r 3 h a r v e s t s i t e s f r o m June 7 t o Sep-tember 13, 1984. No v a l u e shown means no d a t a was c o l l e c t e d . 34 were minimal and that the differences in effect on the study sites should be considered as negligible for the purposes of this study. The soil properties for both the harvest and control sites are displayed in Table 2. The soil textures were mostly some type of loam with a moderate to high coarse fragment (>2 mm) content. The retention curves for the soils at three sites are shown in Figure 6. There was a marked decrease in volumetric moisture content from saturation to -0.10 MPa. Volumetric moisture content decreased by only 2-3% from -0.10 MPa to -1.5 MPa. The 1972 site soil, which was classified as a loam, retained more moisture at all manic potentials than the other two soils which had larger coarse fragment contents. Overall, these soils (the top 20 cm) retained little water at -0.10 MPa, leaving little water easily available for tree growth. At -0.01 MPa, field capacity, the water storage of the 1972, 1971 and 1980 sites was 96, 74 and 46 mm while at -0.10 MPa, it was 50.5, 35 and 21 mm, respectively. At the wilting point (-1.5 MPa), the water storage was 27, 15 and 16 mm, which means the available water storage capacity (field capacity - wilting point) was 69, 59 and 30 mm for the three soils, respectively. Some trees may be able to extract water at soil moisture potentials below -1.5 MPa but lodgepole pine seems to be more sensitive and reduces transpiration before that point is reached (Lopushinsky and Klock, 1974). The air temperature and available water storage calculations show that the study area most likely does have a summer moisture deficit, but the severity and length of the deficit are unknown. Figure 7 compares the courses of rooting zone water storage estimated by the water balance procedure for three of the harvest sites. From mid-June to mid-July, the water in storage was steadily reduced, starting at field capacity down to the wilting point The 1971 and 1972 sites are shown as having had a deficit for 7 to 8 weeks. The large storm event in early August is clearly seen for 1.6 Volumetric Soil Moisture Content (%) FIGURE 6. V o l u m e t r i c s o i l m o i s t u r e c o n t e n t ( % ) , c o r r e c t e d f o r c o a r s e f r a g m e n t s , f o r t h r e e h a r v e s t s i t e s . o CO v. !00 ' 1 ' 1 ' -6 7 21 5 19 2 16 30 13 JUNE JULY AUGUST SEPTEMBER FIGURE 7. Estimated water storage for three harvest s i t e s from June 7 to September 13, 1984. The values are the amounts available at the beginning of each seven-day i n t e r v a l . Reference values were derived from available water storage c a l c u l a t i o n s : w i l t i n g point, e a s i l y available and f i e l d capacity (-1.5, -.10, -.01 MPa). " a " i s the estimated c o e f f i c i e n t from the transpiration model (0.8 for 1971 and 1972). 37 the 1974 site, but the storage quickly returned to the deficit level. The calculated water deficit for the growing season was 134, 131 and 92 mm for the 1971, 1972 and 1974 sites, respectively. The actual soil moisture contents (Figure 8) of the same three sites show a mid- to late July reduction. The length of deficit was actually shorter than was estimated in Figure 7 for each site. The gravimetric moisture content (Figure 8) showed a good tracking of, or sensitivity to, the precipitation pattern, even with only weekly sample collection. The soil texture and precipitation received at each site probably have more influence on the water storage capacity and content than this model allowed. This simple model gives a good indication of the potential severity of a growing season deficit It should be noted though, that the matric potentials derived from the gravimetric moisture contents for the 1971 and 1972 sites were less than -0.10 MPa for most of the summer. The water storage calculations were completed as if all the water between field capacity and the wilting point was equally available, however, there is actually a gradient of water availability as a soil dries out, as seen in Figure 6. The water remaining below -0.10 MPa in the soil of those two sites may not have been as available as that previously extracted and so the water deficit for the trees may have been greater than the water storage shown in Figure 8 would suggest The soil at the 1974 site showed no water deficit and only a moderate reduction from field capacity for most of the summer. One anomaly that needs explaining is the continued increase in moisture content after August 8. The 1974 sample collection area had many buried rotten logs and these may have contributed to the retention of moisture in the soil of the area. Even though the samples collected were mineral soil, the additional water would have affected the final moisture content A value of 'c' = 0.8 gave a better estimate of the water storage than 'C = 1.0 38 7 21 5 19 2 16 30 13 JUNE JULY AUGUST SEPTEMBER FIGURE 8. S o i l gravimetric moisture content (mm) for 3 harvest s i t e s from June 7 to September 13, 1984. Reference values were derived from available water storage c a l c u l a t i o n s : wi l t i n g point, e a s i l y available and f i e l d capacity (-1.5, -.10 and -.01 MPa). 39 for the 1984 growing season for all three sites. More specific work is needed to define 'a' for this study area. The temperature of the rooting zone can affect soil water and nutrient uptake (Noggle and Fritz, 1976) and very low temperatures (10° C) can decrease transpiration (Running and Reid, 1980, cited in Bassman, 1985). Figure 9 shows the soil temperature for the 1980 harvest site. The differences in mean daily and seasonal fluctuations for the three depths are readily apparent The 2 cm depth had the greatest amount of change overall. Since the forest floor is considered to be the most active part of a soil biologically, the large daily changes may affect microbial activity in relation to N mineralization (Matson and Vitousek, 1981). At the middle of the rooting zone (10 cm), a definite rise and fall in temperature was recorded over the growing season, but with less daily fluctuation. As expected, the 30 cm depth had almost no daily change (relative to the others) and a much lower seasonal fluctuation (Campbell, 1977). The growing season maximum daily mean temperatures for the 2, 10 and 30 cm depths were 21.7, 17.9 and 14.3° C, respectively. All depths experienced a sharp drop in temperature starting in late August The means then dropped to 9.3, 8.5 and 9.5° C, respectively. The storm event in early August was reflected by a drop in soil temperature at 2 and 10 cm but not at 30 cm. The other soil temperature measuring sites experienced similar seasonal trends at all three depths (example, 1972 site in Figure 10). The mean daily fluctuations were also similar to the 1980 site. For the 1972 site, the growing season maximum daily mean temperatures were 20.5, 17.1 and 12.6° C for the 2, 10 and 30 cm depths, respectively. The 1980 site was on a level clearcut, while the 1972 site was on a slight slope with a NW aspect, which explains the difference in maximum temperatures. 40 20-10-<-> 0 Q) CD 20 cn Q) r o 10-Q) i _ _D "5 <D C L E o =^ 20 O 00 10 ¥ ¥ ¥ ¥ ¥ * ¥ 10 cm J I I I L _ _ _ J L. 30 cm 0 i i 1 1 r 7 21 5 JUNE JULY -i r i r j i ' i r 19 2 16 30 13 AUGUST SEPTEMBER FIGURE 9. Mean da i l y s o i l temperature plus seven-day i n t e r v a l range at 3 depths for harvest s i t e 1980 from June 7 to September 13, 1984. The means of the seven-day inter v a l s are plotted at the mid-points of the inter v a l s . 25 20 15-10-5-2 cm 1972 7 JUNE 2 1 19 16 JULY AUGUST 3 0 13 SEPTEMBER FIGURE 10. Mean d a i l y s o i l t e m p e r a t u r e a t 3 d e p t h s f o r h a r v e s t s i t e 1 972 from June 7° t o September 13, 1984. The means o f t h e s e v e n - d a y i n t e r v a l s a r e p l o t t e d a t t h e m i d - p o i n t s of t h e i n t e r v a l s . 42 In contrast, the control sites had greatly reduced seasonal maxima, most likely due to the tree cover (Figure 11). The growing season maximum daily means for the 1972C site were 13.4, 11.4 and 9.2 for the 2, 10 and 30 cm depths, respectively. The 2 cm depth temperatures were below even what was reorded at the 30 cm depth for the harvest sites. The growing season temperatures were mostly between 5 and 12° C for the control sites but between 10 and 18° C for the harvest sites. The implications for the effect on root growth are not well known for lodgepole pine, but the species does exhibit a low air temperature regime tolerance (Lotan and Perry, 1983). The tolerance of lodgepole pine to flooding probably gives a good indication of its ability to adapt to the local soil conditions and survive (Horton, 1958). 43 FIGURE 11. Mean da i l y s o i l temperature at 3 depths for control s i t e 1972C from June 7 to September 13, 1984. The means of the seven-day inter v a l s are plotted at the mid-points of the int e r v a l s . V. DISCUSSION The pattern of N mineralized from the mineral soil indicates that there was an increase in mineralizable N over time after clearcutting on the study sites. The flush seemed to last 8 to 12 years. For these soils, the amounts actually available were quite low (Extraction Bulk treatment), but were similar for all the harvest sites. Powers (1980) studied mineralizable N within the 18 to 22 cm depth in relation to productive potential of ponderosa pine ( Pinus ponderosa Laws.) in northern California. He concluded that mesic soils with mineralizable N values of less than 12 ppm and frigid soils with less than 16 ppm were deficient and likely to respond to fertilization. Since concentration decreases with depth (Powers, 1980), the mineral soils of the current study which were tested in the 0 to 15 cm depth, could, according to this standard, be considered deficient (not just inadequate), even with the occurrence of the N flush. Because the forest floor layers of the study sites (harvest and control) were thin, the organic N reserves were limited. The decrease in mineralized N from 1972 to 1971 may be the trend of the future for these sites once the N input from harvesting and site preparaton is depleted. The three year results of an optimum nutrition experiment on the 1971 site (excluded from sampling) indicate a positive growth response to the addition of N and phosphorus (G.E. Weber, 1985). On the other hand, the forest floor samples mineralized quite high levels of N during the anaerobic incubation. The organic material left after site preparation is the' major storage site for N. The more material left, the larger the reserve. Weber, et al, (1985), in a study of jack pine, examined the effects of different levels of forest floor removal on site productivity. A one-time removal of all forest floor and organic layers depleted available N reserves in the mineral soil and forest floor and reduced tree growth about 30% over 8 years. The windrowing that occured on the harvest sites of 44 45 the current study removed most of the slash and forest floor, reducing the N reserve on these sites, but not necessarily eliminating it (Burger and Pritchett, 1984). In light of the jack pine study, this reduction may have a detrimental effect on the productivity of the lodgepole pine growing there. Although the organic matter layers are thin on these sites, they are an important part of the nutrient cycling. Areas of low soil fertility will be affected more by the reduction of the organic layer than areas with soils of higher fertility. Removal of the forest floor also reduces the amount of mineralized N that may be leached from it to the mineral soil; this may be the reason for the low levels of mineralizable N produced during the anaerobic incubation of the mineral soil. Additional work is required to quantify the impact of type of site preparation on the N reserves and the N flush on lodgepole pine clearcuts. There are other mechanisms that limit the amount of available N even without reducing the N reserve. The interaction of soil moisture and soil temperature on net N mineralization rate was studied using aerobic incubation by Cassman and Munns (1980). Their conclusion, demonstrated with multiple regression, was that the interaction was significant. The low end of both the temperature (15° C) and moisture (18%) ranges they used are almost too high to compare with this study. The N mineralized at the low end of the ranges, as N03-N, was between 0 and 4 ppm. This amount of N is much lower than that produced by this study's anaerobic incubation, even though NH4-N was measured. The harvest site soils are usually aerobic, so the effect of the interacton of soil temperature and moisture on the rate of net N mineralization is still applicable. During the growing season, the time that soil moisture and temperature are both non-limiting is probably short, may be only a few weeks (from the end of snow-melt to early July and from late August to the first freeze in the autumn). The initial 46 excess followed by a lack of moisture was possibly more limiting to mineralization as well as uptake than soil temperature over the entire growing season. Microbial decomposition is retarded in both waterlogged humus and dry humus because of impaired aeration in the former and reduced populations in the latter (Williams and Gray, 1974; Cochran, 1985). Root uptake of water from a soil is impaired by poor aeration (flooding) and by low moisture content (increasing soil potential) (Kramer and Kozlowski, 1979). Viets (1972) cited several studies that have shown decreases in ammonification of organic matter as soil water content was reduced from Field capacity to the wilting point Scattered rain throughout the growing season undoubtedly helped keep a low level of mineralization occurring. The control sites' soil temperatures remained lower than the harvest sites' throughout the season while soil moisture had the same range and trend as the harvest sites. Moisture was removed by the tree roots as opposed to mostly being remo ved by evaporation from the soil surface as on the clearcuts (Childs and Hint 1984). Lodgepole pine may be able to adapt to cooler soil temperatures, but the rate of mineralization at lower soil temperatures is reduced (Powers, 1980). The establishment and growth of seedlings on a clearcut area will most likely benefit from the increased soil temperature at depth even though a growing season water deficit may occur. Seedling survival depends on the rapid expansion of its existing root system to occupy and exploit the surrounding soil moisture and nutrients. Root development in lodgepole pine is slow, making the seedling vulnerable to drought, at least, in the first year (Lotan and Perry, 1983). Warmer soil temperatures have been shown to increase root growth in loblolly pine ( Pinus taeda L.) (Kramer and Kozlowski, 1979); this may also occur for lodgepole pine. If moisture is not limiting, then decomposition of organic material should increase and eventually produce an increase in the rate of N mineralization (Matson and Vitousek, 1981; Vitousek, 1981). 47 Also, if moisture is not limiting, the transport of N to the roots and root extension into the surrounding soil should result in a greater av ailability of N for absorption (Crafts, 1968; Viets, 1972). However, moisture for these sites did not remain near field capacity over the growing season. For much of the time, the measured soil matric potentials were less than -0.10 MPa. As the soil moisture increases, the sensitive stomatal control of lodgepole pine reduces transpiration quickly, to 12% of the maximum rate at only -1.0 MPa (Lopushinsky and KJock, 1974). Stomatal closure also reduces photosynthesis and nutrient uptake (Viets, 1972). The reduction in availability of N, due to decreasing soil moisture, combined with the reduction in uptake must limit the amount of N available for growth, especially if the reductions are maintained for a long time. It may be possible that on sites of lower fertility such a limitation could lead to the stagnation of the stand, a common occurrence in lodgepole pine. Therefore, the flush of N a few years after clearcutting must also be of some benefit to the regeneration. The amount of mineralizable N increases at the same time the regeneration is increasing its demands for N. It is possible that some of the trees may be able to obtain enough N for faster growth and establish dominance, thereby reducing the possibility of a stagnated stand. However, because these sites have had a large portion of their N reserve removed, the actual amount of N available during the flush may be lower than other wise (Burger and Pritchett, 1984). A high density of seedlings or trees will further dilute, for any individual, the N that may become available. Tree growth and productivity may be adversely affected if the site quality is not maintained during management operations (Weber, et al, 1985). VI. CONCLUSIONS Relative to the stated objectives of this study, the following conclusions can be made about lodgepole pine clearcuts studied in south-central British Columbia: 1. A flush of N occurred after clearcutting. The mineralizable N pattern was shown by the anaerobic incubation of the mineral soil. The NFL.-N values are considered to be an index of available N. 2. For these sites, the flush lasted about 12 years, peaking by year 8. The absolute magnitude of the increase in mineralizable N was 8 ppm NFL-N from year 2 to year 8; the relative increase was 52%. 3. The literature suggests that the method of site preparation can change the N balance of a site. Logically then, a reduction in the amount of organic matter may reduce the magnitude of the N flush as well as change its duration. Further study is necessary to determine the effect of method of site preparation on the N flush on lodgepole pine clearcuts. 4. A soil moisture deficit occurred on the harvest sites from early July to mid-August Estimates, using a water balance model, for three sites were 134, 131 and 92 mm with an average deficit of 119 mm. The actual water storage, measured by gravimetric moisture content, was greater than that which was estimated, but the water availability was still limited. 5. The mean daily soil temperature of the harvest sites was increased over that of the control sites by about 5°C down to the 30 cm depth. The upper 2 cm had large daily fluctuations while at 30 cm mainly the seasonal change was recorded. 6. From the literature it is seen that. the interaction of soil moisture and temperature is an important environmental control of the net N mineralization 48 49 rate as well as seedling germination and survival. The interaction was not studied but the separate effects of the two components was qualitatively analyzed. Soil moisture influences photosynthesis and N uptake by affecting plant water potential and transpiration. Soil temperature influences root growth and the microbial decomposition of organic material. VII. MANAGEMENT IMPIJCATIONS The management of lodgepole pine in south-central British Columbia requires an understanding of the effects of harvesting and site peparation on N cycling, the local climatic conditions and the species itself. Harvesting removes N in biomass, but a flush of increased N availability can occur with the decomposition of slash and severed roots. Site preparation can further reduce N availability by removing a major N reservoir: the forest floor. The peak of the increased mineralizable N may not occur for 8 years and the flush of N may run its course in 12 years. Soil conditions can influence net N mineralization rates regardless of the amount of potentially mineralizable N in both the forest floor and mineral soil. Soil moisture over the growing season, as estimated by a water balance model or measured by gravimetric methods, has a greater effect on mineralization and eventual tree growth than soil temperature, even though the two interact significantly. The sensitivity of lodgepole pine to moisture stress, whether soil or atmospheric, causes the tree to reduce transpiration at relatively high (not very negative) soil matric potentials. This also has the effect of reducing photosynthesis and N uptake for short periods of time. Increased soil temperature will increase N mineralization by improving the microbial environment during the growing season. But the reduced availability of moisture may limit tree access to that N. Management operations can easily modify the N reserve as well as the soil temperature and moisture. Site preparation techniques which remove the slash and most of the forest floor are depleting the N reservoir and its replacement will take too many years to be of much value to the current establishing seedlings. _Ejfj)osure of the soil to the sun will improve the soil temperature for microbial activity as well as root growth. But it will also increase evaporation of the soil moisture which is needed by 50 51 the microbes and trees. Site preparation can be used to reduce the amount of slash on a site but not totally remove it Since the soil is still covered but to a lesser extent, the amount of evaporation will be reduced and soil moisture availability will be increased. The temperature of the soil may be increased, not as much as with full exposure, but enough to be of benefit The amount of suitable seedbed is limited and the stocking levels may not reach exceedingly high densities. An increase in N availability can occur after harvesting, but the duration and magnitude vary depending on the site. Management operations can influence the increase by changing the amount of substrate available for decomposition and by changing the soil microclimate. Silvicultural techniques that conserve organic matter nutrients while producing an adequate and well distributed amount of seedbed will allow a site to recover more quickly from the disturbance of harvesting. Individual site characteristics and any extenuating circumstances must be included in an assessment of the operation alternatives. In consideration of the above points, it appears that the most important objective during harvesting and site preparation should be the conservation or maintenance of the organic matter layer. Depending on the accumulation of slash, a low to medium intensity broadcast burn would be better than windrowing for slash reduction and keeping most of the nutrients distributed across the site. The amount of N volatilization will be minimized if the burn is cooler (Feller, 1982; White, et al, 1973) Large accumulations of slash may require scattered piling, but the size of the piles and area they cover should be minimized. A site does not need to be cleaned of slash down to the mineral soil. Of course, the presence of dwarf mistletoe in a stand may require sanitation by some piling and burning. Slash reduction during the actual harvesting operation would be an even better alternative to burning or 52 windrowing. Using the equipment to crush and break up the slash would take care of two problems at once. Besides reducing the height of the slash and breaking it into smaller pieces that will decompose more quickly, by running over the slash along different pathways each time, the soil problems associated with skid trails will be decreased. The same reduction of slash can be accomplished by drag scarification as a method of site preparation. Some mixing of the humus and mineral soil will occur which is beneficial while changes in soil structure may be reduced. LITERATURE CITED Atmospheric Environment Service (AES). 1982a. Canadian Climate Normals Vol. 4, Degree Days 1951-1980. Environment Canada. 280 pp. Atmospheric Environment Service (AES). 1982b. Canadian Climate Normals Vol. 1, Radiation 1951-1980. Environment Canada. 57 pp. Atmospheric Environment Service (AES). 1982c. Canadian Climate Normals, 1951-1980, Temperature and Precipitation, British Columbia. Environment Canada. 268 pp. Atmospheric Environment Service (AES). 1984. Monthly Radiation Summary. Environment Canada. 25(6-8):21. Bassman, J.H. 1985. Selected physiological characteristics of lodgepole pine. Pp. 27-43. IN Baumgartner, DM., R.G. Krebill, J.T. Arnott and G.F. Weetman, eds. Lodgepole pine: the species and its management-symposium proceedings. (May 1984). Cooperative Extension, Washington State University. Black, T.A. 1982. Determining soil climate for soil surveys. Pp. 216-235 IN Soil interpretations for forestry. Land Manag. Rep. No. 10. BC Min. of For. Bormann, F.H. and G.E. Likens. 1979. Pattern and process in a forested ecosystem. Springer-Verlag. New York. 253 pp. Bormann, F.H., G.E. Likens, D.W. Fisher and R.S. Pierce. 1968. Nutrient loss accelerated by clearcutting of a forest ecosystem. Science 159:882-884. Brix, H. 1979. Effects of plant water stress on photosynthesis and survival of four conifers. Can. J. For. Res. 9(2): 160-165. Burger, J.A. and W.L. Pritchett. 1984. Effects of clearfelling and site preparation on nitrogen mineralization in a southern pine stand. Soil Sci. Soc. Am. J. 48(6): 1432-1437. Campbell, G.S. 1977. An introduction to environmental biophysics. Springer-Verlag. New York. 159 pp. Canada Soil Survey Committee (CSSC). 1978. The Canadian System of Soil Classification. Canada Dept of Ag. Pub. No. 1646. Ottawa, Ontario. 164 pp. Cassman, K.G. and D.N. Munns. 1980. Nitrogen minralization as affected by soil moisture, temperature, and depth. Soil Sci. Soc. Am. J. 44(6): 1233-1237. Childs, S. and L Hint 1984. Seedling responses to heat and moisture environments in clearcuts and shelterwoods. FIR Report 6(2): 3-4. Clark, M.B. 1974. Effects of cutting method, slash-disposal treatment, seedbed preparation and cone habit on natural regeneration of lodgepole pine in the south-central interior of British Columbia. BCFS Res. Note No. 67. 16 pp. 53 54 Clark, M.B. 1984. Lodgepole pine cone distribution after logging with feller buncher/grapple skidder. BCFS Res. Note No. 92. 15 pp. Cochran, P.H. 1975. Soil temperatures and natural forest regeneration in south-central Oregon. Pp. 37-52 IN B. Bernier and C.H. Winget, eds. Forest soils and forest land management Proceedings: Fourth N.A. Forest Soils Conference. Laval University, Quebec, Canada. Cochran, P.H. 1985. Soils and productivity of lodgepole pine. Pp. 89-93 IN Baumgartner, D.M., R.G. Krebill, J.T. Arnott and G.F. Weetman, eds. Lodgepole pine: the species and its management-symposium proceedings. (May 1984). Cooperative Extension, Washington State University. Crafts, AS. 1968. Water deficits and physiological processes. Pp. 85-133 IN T.T. Kozlowski, ed. Water deficits and plant growth. VOL. II: plant water consumption and- response. Academic Press, N.Y. Dykstra, G.P. 1974. Photosynthesis and carbon dioxide transfer resistance of lodgepole pine seedlings in relation to irradiance, temperature and water potential. Can. J. For. Res. 4(1):201-206. Eis, S., D. Craigdallie and C. Simmons. 1982. Growth of lodgepole pine and white spruce in the central interior of British Columbia. Can. J. For. Res. 12:567-575. Feller, M.C. 1982. The ecological effects of slashburning with particular references to British Columbia: a literature review. BC Min. of For. 60 pp. Giles, D.G., T.A. Black and D.L. Spittlehouse. 1985. Determination of growing season soil water deficits on a forested slope using water balance analysis. Can J. For. Res. 15:107-114. Glen, L.M. 1979. Drag scarification in British Columbia. BC Min. of For. 60 pp. Horton, K.W. 1958. Rooting habits of lodgepole pine. Dept N. Affairs and Nat Resources. For. Res. Div. Tech. Note 67. 26 pp. Husch, B., C.I., Miller and T.W. Beers. 1982. Forest mensuration, 3rd edition. The Ronald Press Co. NY. 410 pp. Keeney, D.R. 1980. Prediction of soil nitrogen availability in forest ecosystems: a literature review. For. Sci. 26(1): 159-171. Keeney, D.R. and J.M. Bremner. 1966. Comparison and evaluation of laboratory methods of obtaining an index of soil nitrogen availability. Agron J. 58:498-503. Klinka, K., R.N. Green, R.L Trowbridge and L.E. Lowe. 1981. Taxonomic classification of humus forms in ecosystems of British Columbia, first approximation. Land Manag. Report No. 8. BC Min. of For. 54 pp. Kramer, P.J. and T.T. Kozlowski. 1979. Physiology of woody plants. Academic Press, Inc. Orlando, FL. 811 pp. 55 List, R.J. 1971. Table 171: Duration of daylight Pp. 509 IN Smithsonian meteorological tables, 6th rev. ed. Smithsonian Misc. Coll. Vol. 114. Smithsonian Inst Press. Wash, DC. Lopushinsky, W. and G.O. Klock. 1974. Transpiration of conifer seedlings in relation to soil water potential. For. Sci. 20(2): 181-186. Lotan, J.E., J.K. Brown and L.E. Neuenschwander. 1985. Role of fire in lodgepole pine forests. Pp. 133-152 IN Baumgartner, D.M., R.G. Krebill, J.T. Arnott and G.F.Weetman, eds. Lodgepole pine: the species and its management-symposium proceedings. (May 1984). Cooperative Extension, Washington State University. Lotan, J.E. and D.A. Perry. 1983. Ecology and regeneration of lodgepole pine. USDA FS Agric. HB No. 606. 51 pp. Matson, P.A. and P.M. Vitousek. 1981. Nitrogen mineralization and nitrification potentials following clearcutting in the Hoosier National Forest, Indiana. For. Sci. 27(4):781-791. Mitchell, W.R. and R.E. Green. 1981. Identification and interpretation of ecosystems of the western Kamloops forest Region, first approximation. Land Manag. Report No. 2, Vol 1, Very Dry Climatic Region. BC Min. of For. Morris, L.A., W.L. Pritchett and B.F. Swindel. 1983. Displacement of nutrients into windrows during site preparation of a flatwood forest Soil Sci. Soc. Am. J. 47:591-594. Noggle, G.R. and G.J. Fritz. 1976. Introductory plant physiology. Prentice-Hall, Inc. Englewood Cliffs, NJ. 688 pp. Powers, R.F. 1980. Mineralizable soil nitrogen as an index of nitrogen availability to forest trees. Soil Sci. Soc. Am. J. 44:1314-1320. Powers, R.F. 1984. Estimating soil nitrogen availability through soil and foliar analysis. Pp. 353-379 IN EL Stone, ed. Forest soils and treatment impacts. Sixth N.A. Forest Soils Confer. (June 1983). Dept Forestry, Wildlife and Fisheries, U. of Tenn. Knoxville, TN. Priestley, C.H.B. and RJ.Taylor. 1972. On the assessment of surface heat flux and evaporation using large scale parameters. Mon. Weather Rev. 10:81-92. Richards, L.A. 1965. Physical condition of water in soil. Pp. 128-158 IN Black. C.A., ed. Methods of soil analysis, Part 1. Agronomy No. 9. Am. Soc. Agron. Madison, WI. Romell, L-G. 1935. Ecological problems of the humus layer in the forest Cornell Univ. Agric. Exp. Sta. Memoir 170. Ithaca, NY. 28 pp. Romell, L-G. 1938. A trenching experiment in spruce forest and its bearing on problems of mycotrophy. Svensk Botanisk Tidskrift 32(l):89-99. Rurming, S.W. and CP. Reid. 1980. Soil temperature influences on root resistance of 56 Pinus contorta seedlings. Plant Physiol. (Bethseda) 65(4):635-640. Spittlehouse, D.L. and T.A. Black. 1981. A growing season water balance model applied to two Douglas-fir stands. Water Resour. Res. 17(6): 1651-1656. Tamm, CO. 1964. Determination of nutrient requirements of forest stands. Int Rev. For. Res. 1:115-170. Utzig, G., D. Macdonald, G. Still, M. Ketchespn, T. Bramandl and A. Warner. 1983. Ecological Classification of the Nelson Forest Region, Third Approximation. BC Min. of For. Viets, F.G. Jr. 1972. Water deficits anf nutrient availability. Pp. 217-239 IN T.T. Kozlowski, ed. Water deficits and plant growth, Vol. Ill: plant responses and control of water balance. Academic Press, N.Y. Vitousek, P.M. 1981. Clear-cutting and the nitrogen cycle. Pp. 631-642 IN Clark, F.E. and T. Rosswall, eds. Terrestrial nitrogen cycles. Ecol. Bull. (Stockholm) 33. Vitousek, P.M. and J.M. Melillo. 1979. Nitrate losses from disturbed forests: patterns and mechanisms. For. Sci. 25(4):605-619. Waring, S.A. and J.M. Bremner. 1964. Ammonium production in soil under waterlogged conditions as an index of nitrogen availability. Nature 20(4922):951-952. WeatherMeasure. P.O. Box 41039. Sacramento, CA. 95841. Phone: (916) 481-7565. Weber, G.E. 1985. Three year growth and foliage response in a lodgepole pine optimum nutrition experiment Unpublished BSc. Thesis. Faculty of Forestry, University of British Columbia. Weber, M.G., I.R. Methven and C.E. Van Wagner. 1985. The effect of forest floor manipulation on nitrogen status and tree growth in an eastern Ontario jack pine ecosystem. Can. J. For. Res. 15(2):313-318. White, E.M., W.W. Thompson and F.R. Gartner. 1973. Heat effects on nutrient release from soils under ponderosa pine. J. Range Manag. 26(1):22-24. Williams, S.T. and T.R.G. Gray. 1974. Decomposition of litter on the soil surface. Pp. 611-632 IN CH. Dickinson and G.J.F. Pugh, eds. Biology of plant litter decomposition, Vol. 2. Academic Press. New York. APPENDIX A Table A.1 Estimated and Actual Number of Mineral Soil, and Forest Floor Samples Collected for Nitrogen Analysis 57 58 Table A.l Estimated and Actual Number of Mineral Soil, and Forest Floor Samples Collected for Nitrogen Analysis YEAR OF HARVEST ESTIMATED1 MINERAL SOIL SAMPLES NEEDED MINERAL SOIL SAMPLES COLLECTED FOREST FLOOR SAMPLES COLLECTED 1971 123 150 30 1972 348 210 30 1974 346 210 30 1976 168 210 30 1978 72 150 50 1980 45 150 20 1982 77 150 20 1972C 2 20 10 1974C 20 10 1982C 20 10 1 Estimated from pilot study using N = (t2c2)/(E%)2 (Husch, et al, 1982). N = sample size; c = coefficient of variation, (mean/standard deviation); L at c = .05 (two-tailed), = 2.45 : Student's t test for desired probability level; E% = 10% : allowable standard deviation as a % of the mean. 2 No estimate was made for the control sites. APPFNDTX B Table B.l Year, Replication, and Ammonium-nitrogen (ppm) from Mineral Soil for Seven Harvest Sites Table B.2 Year, Replication, and Ammonium-nitrogen (ppm) from Forest Floor Material for Seven Harvest Sites Table B.3 Year, Replication, and Ammonium-nitrogen (ppm) from Mineral Soil for Three Control Sites Table B.4 Year, Replication, and Ammonium-nitrogen (ppm) from Forest Floor Material for Three Control Sites 59 Table B.I Year, Replication, and Amnion lum-n I tr 1 71 01 9 324 54 72 24 23 996 2 71 02 1 1 562 55 72 25 23 525 3 71 03 1 1 282 56 72 26 30 583 4 71 04 17 529 57 72 27 23 525 5 71 05 15 385 58 72 28 47 992 6 7 1 06 1 1 625 59 72 29 29 172 7 71 07 14 452 60 72 30 16 468 8 71 08 1 1 375 61 74 01 17 49 9 71 09 14 918 62 74 02 15 85 10 71 10 16 783 63 74 03 18 65 1 1 71 11 16 970 64 74 04 22 38 12 71 12 1 1 935 65 74 05 15 38 13 7 1 13 9 604 66 74 06 24 7 1 14 71 14 16 317 67 74 07 19 58 15 71 15 13 054 68 74 08 32 17 16 71 16 20 047 69 74 09 14 92 17 71 17 13 054 70 74 10 18 18 18 71 18 9 324 71 74 1 1 16 32 19 71 19 10 256 72 74 12 24 24 20 71 20 18 648 73 74 13 20 98 21 7 1 21 1 1 189 74 74 14 21 91 22 7 1 22 12 587 75 74 15 16 78 23 71 23 9 790 76 74 16 15 85 24 71 24 12 121 77 74 17 15 85 25 7t 25 14 91B 78 74 18 12 12 26 71 26 12 587 79 74 19 18 65 27 71 27 9 790 80 74 20 1 1 19 28 71 28 12 5B7 81 74 21 20 98 29 7 1 29 15 587 82 74 22 15 85 30 71 30 1 1 935 83 74 23 15 85 31 72 01 23 525 84 74 24 13 99 32 72 02 19 761 85 74 25 19 58 33 72 03 19 761 86 74 26 18 18 34 72 04 30 113 87 74 27 20 33 35 72 05 25 407 88 74 28 15 85 36 72 06 18 820 89 74 29 15 85 37 72 07 21 643 90 74 30 13 99 38 72 OB 23 525 91 76 01 36 699 39 72 09 26 348 92 76 02 26 348 40 72 10 34 818 93 76 03 21 173 41 72 11 23 525 94 76 04 23 525 42 72 12 31 995 95 76 05 23 055 43 72 13 26 819 96 76 06 18 350 44 72 14 16 938 97 76 07 16 468 45 72 15 29 642 98 76 08 32 936 46 72 16 20 702 99 76 09 26 348 47 72 17 19 291 100 76 10 20 702 48 72 18 18 350 101 76 1 1 14 586 49 72 19 4 1 875 102 76 12 33 406 50 72 20 23 525 103 76 13 3 1 524 51 72 2 1 33 877 104 76 14 19 761 52 72 22 26 348 105 76 15 IB 820 53 72 23 23 996 106 76 16 28 23 1 ogen (ppm) from Minora) Sol) for Seven Harvest Sites 107 76 17 23 996 160 80 10 17 716 108 76 18 17 879 161 BO 1 1 17 716 109 76 19 14 1 15 162 80 12 17 716 110 76 20 22 584 163 80 13 21 445 1 1 1 76 21 14 1 15 164 80 14 22 378 1 12 76 22 23 525 165 80 15 13 986 1 13 76 23 31 524 166 80 16 21 445 1 14 76 24 22 584 167 BO 17 20 513 115 76 25 24 937 168 80 18 17 716 1 16 76 26 21 173 169 80 19 16 783 1 17 76 27 23 525 170 80 20 21 445 1 18 76 28 26 348 171 BO 21 14 918 1 19 76 29 28 231 172 80 22 17 716 120 76 30 18 820 173 80 23 19 580 121 78 01 14 918 174 80 24 17 716 122 78 02 22 378 175 80 25 17 716 123 78 03 23 590 176 80 26 20 513 124 78 04 20 513 177 80 27 18 648 125 78 05 16 503 178 80 28 16 783 126 78 06 24 242 179 80 29 24 242 127 78 07 21 259 180 80 30 20 513 128 78 08 22 445 181 82 01 17 249 129 78 09 12 308 182 82 02 17 249 130 78 10 14 452 183 82 03 13 053 131 78 1 1 20 047 184 82 04 27 049 132 78 12 15 664 185 82 05 16 317 133 78 13 22 378 186 82 06 15 385 134 78 14 22 378 187 82 07 16 317 135 78 15 27 506 188 82 08 14 732 136 78 16 22 564 189 82 09 1 1 655 137 78 17 24 242 190 82 io 1 1 002 138 78 18 19 1 14 191 82 1 1 13 054 139 78 19 21 259 192 82 12 1 1 375 140 78 20 17 7 16 193 82 13 20 326 14 1 78 2 1 16 317 194 82 14 19 1 14 142 78 22 20 513 195 82 15 12 121 143 78 23 20 4 19 196 82 16 20 046 144 78 24 13 986 197 82 17 18 182 145 78 25 24 242 198 82 18 15 105 146 78 26 17 995 199 82 19 1 1 189 147 78 27 16 690 200 82 20 17 716 148 78 28 26 107 201 82 21 13 054 149 78 29 19 1 14 202 82 22 16 782 150 78 30 26 573 203 B2 23 IO 256 151 80 01 15 57 1 204 82 24 23 310 152 80 02 18 648 205 82 25 1 1 655 153 80 03 20 513 206 82 26 13 054 154 80 04 15 851 207 82 27 1 1 189 155 80 05 15 851 208 82 28 13 986 156 80 06 16 597 209 82 29 19 580 157 80 07 15 198 2 10 82 30 13 054 158 80 OB 13 054 159 SO 09 17 7 16 T a b l e B.2 Yo.ir,- R e p l i c a t i o n , anrl A m m o n i u m - n i t r o g e n (ppm) f r o m F o r e s t f l o o r M . - i t e M a l f o r S e v e n H a r v e s t S i t e s 1 71 01 310 000 54 72 24 345 59 107 76 17 155.40 160 78 40 496 32 2 71 02 232 65 55 72 25 427 14 108 76 18 124.32 161 78 41 465 30 3 71 03 170 61 56 72 26 427 14 109 76 19 279.72 162 78 42 434 28 4 71 04 201 63 57 72 27 565 52 1 10 76 20 590.52 163 78 43 232 65 5 7 1 05 356 73 58 72 28 219 93 1 1 1 76 21 124.32 164 78 44 124 08 6 71 06 372 24 59 72 29 502 69 1 12 76 22 854.70 165 78 45 224 90 7 7 1 07 224 89 60 72 30 644 07 1 13 76 23 186.48 166 78 46 542 B5 8 71 08 4 18 77 61 74 01 329 89 1 14 76 24 34 1.88 167 78 47 317 96 9 71 09 224 89 62 74 02 188 51 1 15 76 25 124.32 168 78 48 651 42 10 71 10 51 1 83 63 74 03 479 12 1 16 76 26 854.70 169 78 49 1085 70 11 7 1 1 1 147 34 64 74 04 424 14 1 17 76 27 435. 12 170 78 50 434 28 12 71 12 310 00 65 74 05 125 67 1 18 76 28 590.52 17 1 80 01 310 80 13 7 1 13 232 65 66 74 06 259 20 1 19 76 29 427.35 172 80 02 279 72 14 71 14 480 81 67 74 07 596 94 120 76 30 466.20 173 80 03 668 22 15 7 1 15 333 46 68 74 08 958 25 121 78 01 728.97 174 80 04 582 75 16 7 1 16 178 37 69 74 09 4 16 29 122 78 02 271.43 175 80 05 186 48 17 7 1 17 884 07 70 74 10 125 67 123 78 03 837.54 176 80 06 559 44 18 7 1 18 620 40 7 1 74 1 1 235 64 124 78 04 465.30 177 80 07 380 73 19 71 19 186 12 72 74 12 801 16 125 78 05 946.11 178 80 08 310 80 20 71 20 511 83 73 74 13 298 47 126 78 06 1008.15 179 80 09 186 48 21 71 21 170 61 74 74 14 188 51 127 78 07 1202.03 180 80 10 279 72 22 71 22 232 65 75 74 15 204 22 128 78 08 682.44 181 80 1 1 435 12 23 71 23 465 30 76 74 16 282 76 129 78 09 511.83 182 80 12 34 1 88 24 7 1 24 558 36 77 74 17 117 82 130 78 10 1023.66 183 80 13 186 48 25 71 25 240 41 78 74 18 361 31 131 78 1 1 51 1.83 184 80 14 256 4 1 26 71 26 325 71 79 74 19 109 96 132 78 12 527.34 185 80 15 372 96 27 71 27 395 51 80 74 20 251 34 133 78 13 604.89 186 80 16 295 26 28 71 28 465 30 81 74 21 392 73 134 78 14 651.42 187 80 17 186 48 29 71 29 310 00 82 74 22 125 67 135 78 15 1070. 19 188 80 18 435 12 30 71 30 488 57 83 74 23 188 51 136 78 16 620.40 189 80 19 186 48 31 72 01 157 09 84 74 24 259 19 137 78 17 387.75 190 80 20 4 1 1 8 1 32 72 02 204 22 85 74 25 70 69 138 78 18 496.32" 191 82 01 590 52 33 72 03 267 05 86 74 26 120 96 139 78 19 604.89 192 82 02 435 12 34 72 04 157 09 87 74 27 62 84 140 78 20 387.75 193 82 03 427 35 35 72 05 549 82 88 74 28 62 84 141 78 2 1 527.34 194 82 04 839 16 36 72 06 204 22 89 74 29 70 69 142 78 22 341.22 195 82 05 357 42 37 72 07 157 09 90 74 30 2 12 07 143 78 23 387.75 196 82 06 295 26 38 72 08 78 55 91 76 01 699 30 144 78 24 434.28 197 82 07 147 63 39 72 09 62 84 92 76 02 365 19 145 78 25 496.32 198 82 08 683 76 40 72 10 133 53 93 76 03 202 02 146 78 26 651.42 199 82 09 1 1 18 88 41 72 1 1 196 36 94 76 04 334 1 1 147 78 27 310.20 200 82 10 419 58 42 72 12 141 38 95 76 05 450 66 148 78 28 232.65 201 82 1 1 217 56 43 72 13 1 17 82 96 76 06 225 33 149 78 29 837.54 202 82 12 326 34 44 72 14 54 98 97 76 07 248 64 150 78 30 713.46 203 82 13 248 64 45 72 15 109 96 98 76 08 559 44 151 78 31 442.04 204 82 14 62 1 60 46 72 16 2 19 93 99 76 09 248 64 152 78 32 170.61 205 82 15 279 72 47 72 17 1076 07 ioo 76 10 155 40 153 78 33 341.22 206 82 16 279 72 48 72 18 6 12 65 101 76 1 1 582 75 154 78 34 294.69 207 82 17 489 51 49 72 19 102 1 1 102 76 12 597 28 155 78 35 325.71 208 82 18 885 78 50 72 20 243 49 103 76 13 357 42 156 78 36 232.65 209 82 19 295 26 51 72 21 353 45 104 76 14 155 40 157 78 37 759.99 2 10 82 20 559 44 52 72 22 659 78 105 76 15 155 40 158 78 38 387.75 53 72 23 1 107 48 106 76 16 730 38 159 78 39 527.34 Table B.3. Year, Replication from Mineral Soil for 1., and Ammonium-nitrogen (ppm) Three Control Sites 1 72 01 25 87B 2 72 02 28 231 3 72 03 9 410 4 72 04 34 818 5 72 05 23 525 6 72 06 20 702 7 72 07 24 937 8 72 08 12 704 9 72 09 23 525 10 72 10 37 170 1 1 72 1 1 53 638 12 72 12 56 461 13 72 13 15 527 14 72 14 32 936 15 72 15 23 525 16 72 16 16 938 17 72 17 38 582 18 72 18 31 995 19 72 19 48 933 20 72 20 15 056 21 74 01 159 97 22 74 02 197 61 23 74 03 51 76 24 74 04 15 99 25 74 05 188 20 26 74 06 75 28 27 74 07 169 38 28 74 08 56 46 29 74 09 87 51 30 74 10 28 23 31 74 1 1 20 70 32 74 12 35 76 33 74 13 18 82 34 74 14 9 88 35 74 15 14 12 36 74 16 44 70 37 74 17 28 23 38 74 18 31 99 39 74 19 6 12 40 74 20 49 03 41 82 01 15 997 42 82 02 33 877 43 82 03 37 170 44 82 04 20 232 45 82 05 29 172 46 82 06 20 232 47 82 07 1 1 763 48 82 08 10 351 49 82 09 1 1 292 50 82 10 30 113 51 82 1 1 21 173 52 82 12 7 058 53 82 13 7 058 54 82 14 54 108 55 82 15 9 410 56 82 16 13 174 57 82 17 7 058 58 82 18 13 174 59 82 19 42 346 60 82 20 20 232 Table B . 4 . Year, Replication, and Ammonium-nitrogen (ppm) from Forest Floor Material for Three Control Sites 1 72 01 186 .48 2 72 02 182 59 3 72 03 155 40 4 72 04 170 94 5 72 05 279 72 6 72 06 252 53 7 72 07 217 56 8 72 08 303 03 9 72 09 233 10 10 72 10 213 68 1 1 74 01 543 90 12 74 02 435 12 13 74 03 466 20 14 74 04 497 2B 15 74 05 194 25 16 74 06 372 96 17 74 07 132 09 18 74 08 186 48 19 74 09 372 96 20 74 10 450 66 21 82 01 761 46 22 82 02 388 50 23 82 03 598 29 24 82 04 435 12 25 82 05 147 63 26 82 06 404 04 27 82 07 217 56 28 82 08 310 80 29 82 09 225 33 30 82 10 178 71 APPENDIX C TABLE CL Mean Daily Maximum and Minimum Air Temperatures (°C) for Three Harvest Sites from June 7 to September 13, 1984. Dates are the mid-points of the seven-day intervals. TABLE C.2. Mean Daily Precipitation (mm/day) for Three Harvest Sites from June 7 to September 13, 1984. Dates are the mid-points of the seven-day intervals. TABLE C3. Volumetric Soil Moisture Contents (%), corrected for coarse fragments, Versus Soil Matric Potential, for Four Harvest Sites. The 1980 site data were not graphed. TABLE C4. Estimated Water Storage for Three Harvest Sites at the beginning of each seven-day interval from June 7 to September 13, 1984. 'c' is the estimated coefficient from the water balance model. TABLE C5. Soil Gravimetric Moisture Contents (mm) for Three Harvest Sites from June 7 to September 13, 1984. TABLE C.6. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures (°C) at Three Depths for Harvest Site 1980 from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. TABLE C7. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures (°C) at Three Depths for Harvest Site 1972 from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. TABLE C8. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures (°C) at Three Depths for Harvest Site 1972C from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. 63 TABLF, C.l. Mean Daily Maximum and Minimum Air Temperatures (°C) for Three Harvest Sites from June 7 to September 13, intervals. 1984. Dates are the mid-points of the seven-day mi-DAY 1972C Site 1972 Site 1971 Site MAX MIN MAX MIN MAX MIN 6-10 16.8 0.8 15.7 2.2 19.5 2.0 6-17 17.0 '3.8 16.6 1.9 17.5 -1.8 6-24 17.0 0.5 17.7 3.6 21.4 1.4 7-01 18.9 3.9 16.4 2.3 17.5 -0.1 7-08 22.0 2.3 23.0 0.8 26.0 -3.8 7-15 28.5 -2.0 26.0 1.0 30.0 -1.5 7-22 26.0 0.5 30.0 -1.5 32.0 -1.5 7-29 22.5 3.5 28.0 6.0 31.0 4.0 8-05 23.3 3.5 24.5 5.5 27.3 4.0 8-15 26.5 1.3 27.5 4.0 29.3 1.3 8-19 25.5 -0.5 24.0 1.3 26.0 -1.0 8-26 23.3 0.0 21.0 4.0 22.5 -3.0 9-02 18.0 -5.0 18.8 -0.3 22.0 -3.0 9-09 15.2 -3.2 13.5 -4.5 16.5 -7.0 TATU.F C..7. Mean Daily Precipitation (mm/day) for Three Harvest Sites from June 7 to September 13, 1984. Dates are the mid-points of the seven-day intervals. M O N T H - D A Y 1971 Site 1972 Site 6-10 4.93 6-17 1.11 6-24 0.87 7-01 3.92 0.44 7-08 0.0 0.0 7-15 0.0 0.0 7-22 0.0 0.0 7-29 0.31 0.2 8-05 1.13 3.57 8-12 1.57 1.93 8-19 0.74 0.4 8-26 0.1 0.0 9-02 2.16 1.69 9-09 2.66 2.66 66 TABLE C.3. Volumetric Soil Moisture Contents (%), corrected for coarse fragments, Versus Soil Matric Potential, for Four Harvest Sites. The 1980 site data were not graphed. SOIL MATRIC 1971 Site 1972 Site 1980 Site 1982 Site POTENTIAL (-MPa) 0.01 36.95 48.0 22.9 22.7 0.033 31.9 45.3 16.0 17.2 0.10 17.35 25.2 10.3 11.8 0.20 12.95 20.2 9.3 9.9 0.40 10.95 18.6 8.25 9.2 1.5 7.5 13.5 8.0 7.7 T A B L E C A Estimated Water Storage for Three Harvest Sites at the beginning of each seven-day interval from June 7 to September 13, 1984. V is the estimated coefficient from the water balance model. M O N T H - D A Y 1971 Site 1972 Site 1974 Site 1974 Site o = 0.8 a =0.8 a =0.8 a =1.0 6-07 74 96 96 96 6-14 74 96 96 96 6-21 61 82 82 77 6-28 48 70 68 58 7-05 53 50 68 51 7-12 24 27 39 27 7-19 15 27 27 27 7-26 15 27 27 27 8-02 15 27 27 27 8-09 15 30 62 56.5 8-16 15 27 47 34.5 8-23 15 27 27 27 8-30 15 27 27 27 9-06 16 27 27 27 9-12 25 36 35 32.5 68 T A B L E C.5. Soil Gravimetric Moisture Contents (mm) for Three Harvest Sites from June 7 to September 13, 1984. M O N T H - D A Y 1971 Site 1972 Site 1974 Site 6-10 48.8 37.3 — 6-28 47.5 63.2 — 7-12 35.5 55.3 73.5 7-19 22.1 45.6 51.9 7-26 14.8 30.1 46.5 8-02 14.1 44.4 61.1 8-09 15.0 41.1 61.2 8-15 19.5 28.8 65.0 8-23 11.6 21.6 69.2 69 TABLE C.6. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures ( ° C ) at Three Depths for Harvest Site 1980 from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. )NTH DAY MEAN 2 cm MAX MIN MEAN 10 cm MAX MIN MEAN 30 cm MAX MIN 6 10 12.9 14.5 10.5 9.7 11.1 8. 8. 8.7 7.2 6 17 11.4 16.6 8. 10.6 13.9 8.5 9.9 10.1 9.6 6 24 13.7 19.8 9.5 11.8 14.8 8.9 10.4 11.3 9.5 7 1 14.5 19.5 8.6 12. 16.1 8.5 10.5 11.5 8.5 7 8 16.4 19.8 13. • 13.9 16. 11.7 11.6 11.7 11.5 7 15 17.6 22.7 12.5 14.7 18. 11.3 12.4 12.7 12. 7 22 19. 22.8 15.1 14. 15.9 12.2 12.9 13. 12.7 7 29 21.7 23.8 19.6 17.9 19.8 16. 14.2 14.3 14. 8 5 . 19.3 23.3 15.2 16.6 19.2 14. 14.3 14.4 14.2 8 12 21.4 24. 16.4 17.3 19.6 14.1 13.8 14.2 13.1 8 19 18. 22.2 13.7 14.4 16.7 12. 13.2 13.4 13. 8 26 16.3 22.2 11.6 13.4 16.7 11.7 12.6 13.4 11.2 9 2 14.9 17.8 12. 11.5 13.2 9.8 11. 11.2 10.8 9 9 9.3 15.7 4. 8.5 10.9 6.2 9.5 10.6 8.8 70 TABLE C.7. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures (°C) at Three Depths for Harvest Site 1972 from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. >NTH DAY MEAN 2 cm MAX MIN MEAN 10 cm MAX MIN MEAN 30 cm MAX MIN 6 10 10.8 13.4 8.2 8.8 10.7 7.1 7.4 8.2 6.7 6 17 11.8 16.1 9.5 10.1 11.9 9. 9.4 9.9 8.7 6 24 12.6 19.5 9.4 10.8 14.6 8.5 9.6 10.4 8.8 7 1 13.1 19.6 10. 10.9 14.5 9. 10.2 .10.9 9.5 7 8 16.6 19.4 13.8 13.2 14.8 11.6 10.8 10.9 10.6 7 15 17. 20.2 13.7 14.1 16.5 11.7 11.5 11.7 11.2 7 22 19.4 22.4 16.6 16. 18.8 13.4 12.2 12.6 11.7 7 29 20.5 22.4 18.5 17.1 18.8 15.3 12.6 12.6 12.5 8 5 16.9 19.5 14.3 14.9 16.7 13. 12.6 12.8 12.4 8 12 19.1 21.7 16.2 15.7 17.8 " 13.6 12.5 13. 11.8 8 19 16.4 18.3 14.5 13.9 15.2 12.6 12.1 12.4 11.8 8 26 15.8 18.3 15. 12.8 15.2 11.3 12. 12.4 11.7 9 2 12. 15.2 8.7 9.9 11.3 8.5 10.9 11.7 10.1 9 9 8.6 12.2 5.4 7.6 10.2 5.2 9. 10.1 8.5 71 TABLE C.8. Mean Daily and Interval Extreme Maximum and Minimum Soil Temperatures ( ° C ) at Three Depths for Harvest Site 1972C from June 7 to September 13, 1984. Dates are the Mid-points of the Intervals. )NTH DAY MEAN 2 cm MAX MIN MEAN 10 cm MAX MIN MEAN 30 cm MAX MI1S 6 10 5.3 6.4 4.2 4.3 4.8 3.6 3.2 3.7 2.9 6 17 6.2 7. 5. 5.6 6.3 5. 4.6 4.9 4.1 6 24 7.4 8.7 5.6 6.5 7.3 5.5 5.4 5.9 5. 7 1 8.2 10.1 6.8 7. 7.6 6. 6.1 6.4 5.9 7 8 9.4 10.3 8.4 8. 8.2 7.7 6.4 6.4 6.4 7 15 9. 9.3 8.6 9.7 11.6 7.7 • 7.1 7.4 6.7 7 22 10.3 12.4 9.1 10.3 11.6 8.3 7.8 8.4 7.4 7 29 13.4 14.4 12.4 11.4 11.8 10.9 8.3 8.4 8.2 8 5 12.1 13.2 10.9 10.9 11. 10.1 9.2 9.3 9. 8 12 12.1 13.9 10.9 10.4 11.2, 9.5 8.9 9.2 8.4 8 19 10.4 11.4 9.4 9.3 9.6 8.9 8.5 8.7 8.2 8 26 10.3 11.4 9.7 8.8 9.6 7.9 7.9 8.3 7.2 9 2 7.9 9.7 6.1 7.1 7.9 6.3 7. 7.2 6.8 9 9 5.2 7.4 3.3 5.7 7.5 4.7 6.7 7.6 6.3 

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