Publication 1091 December 1960 CANADIAN AGRICULTURE LIBRARY emiJOTHEQUE CANADIENNE DE L'AGRICULTURE *- m iiiiii* fcp n hiwm^ii ,im,wmmmmmmtmmmmmmmr 'VaWMMMMWUM Water Relations and Forest Distribution in the Douglas-fir Region on Vancouver Island R. G. McMinn Forest Biology Division CANADA DEPARTMENT OF AGRICULTURE Ottawa, Ontario Publication 1091 December 1960 Water Relations and Forest Distribution in the Douglas-fir Region on Vancouver Island R. G. McMinn Forest Biology Laboratory Victoria B.C. CANADA DEPARTMENT OF AGRICULTURE Copies of this publication may be obtained from Information Division CANADA DEPARTMENT OF AGRICULTURE Ottawa, Ontario ROGER DUHAMEL, F.R.S.C. QUEEN'S PRINTER AND CONTROLLER OF STATIONERY OTTAWA, 1961 Cat. No. A43-1091 2M— 27087— 4:60 CONTENTS Page Introduction 5 Methods Climate 10 Vegetation 11 Microclimate 12 Soils Profile characteristics 12 Moisture regimes 13 Results Climate 15 Vegetation 17 Microclimate 31 Soils Profile characteristics 36 Moisture regimes 46 Discussion 60 Summary 65 Acknowledgments 66 References 67 Appendices 69 87850-4—1 INTRODUCTION Water relations play an important role in the distribution of vegetation in regions with low summer rainfall because the availability of water is commonly a limiting factor. Pearson (32), for example, concluded that the distribution of certain forest types in the south-western United States was largely determined by the presence or absence of soil drought and differences in its time of occur- rence. McMinn (29) reached a similar conclusion for various plant associations in the northern Rocky Mountains. Even when available soil moisture has not been completely exhausted, the productivity of plants is influenced by deficits, that is by the reduction of soil moisture to amounts less than field capacity (35). The present study was undertaken to evaluate the significance of water relations in the differentiation and distribution of forest associations within the Douglas-fir (Pseudotsuga menziesii1) region on Vancouver Island, British Columbia2. The Douglas-fir region of coastal British Columbia may be defined as the region in which Douglas-fir stands can predominate on most sites. This region is approximately coincident with the Southern Pacific Coast and Strait of Georgia Sections of the Coast Forest Region described by Rowe (39). Krajina (20, 21) recognizes within the Douglas-fir region a Coastal Douglas-fir Zone in which Douglas-fir is considered to be the climatic climax dominant. This Zone corresponds to the Strait of Georgia Section of the Coast Forest Region (39). Elsewhere in the Douglas-fir region, and even on some sites within the Coastal Douglas-fir Zone, the prevalence of Douglas-fir stands appears to be related to the periodic occurrence of forest fires, promoted by the hot, dry summers char- acteristic of the rainshadow climate of this region (40). Without such fires, Douglas-fir forests occurring outside the driest sections of the Douglas-fir region might eventually have been replaced by stands of more shade tolerant species, such as Thuja plicata (western red cedar) and Tsuga heterophylla (western hemlock). Various forest associations occurring within the Douglas-fir region of coastal British Columbia have been defined by Krajina (20). The area selected for study was a portion of the Nanaimo River Valley, some eight miles southwest of Nanaimo, British Columbia (Fig. 1). The Nanaimo River is one of a series of easterly flowing streams arising in the central height of land which runs the length of Vancouver Island. The drainage basins of these rivers constitute much of the Douglas-fir region of coastal British Columbia. The study area (Fig. 2) consisted of a section of the valley extending seven miles downstream from Fourth Lake, which lies approximately twelve miles inland from the east coast of Vancouver Island. The Nanaimo River drops gradually from 1,000 ft. above sea level near Fourth Lake to 600 ft. above sea level east of First Lake. West of Second Lake, the valley floor is less than one- half mile wide and its sides rise steeply for more than 2,000 ft. (Fig. 3). Many of the peaks are over 4,000 ft. high. The topography of this western portion of the study area is typical of the terrain of the central mountainous area of Vancouver Island. To the east of Second Lake, the valley widens and its sides rise less steeply. This section is characteristic of the less rugged topography of eastern Vancouver Island. Nomenclature is that of Little (25) for trees, Peck (33) for other vascular plants, Conard (8) for mosses, and Howard (18) or Fink (11) for lichens, except where other authorities are given. 2This report is based on a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the Department of Biology and Botany, University of British Columbia. 87850-4—2 0 JO m.Us 20 Wtother stations .. . Figure 1 — Map of southern Vancouver Island, showing location of study area and various weather stations. The mountainous topography of the west coast and central regions of the Island contrasts with the less rugged terrain of the eastern side. Vertical scale is increased five times. The dominant tree canopy of most stands in the Nanaimo River Valley originated as a more or less even-aged stand following a forest fire. Within the study area, the age of the oldest trees of the dominant canopy varied from 220 to 320 years (Table I), suggesting their establishment following several different fires. Some stands were evidently also affected by subsequent fires, the most recent of which occurred about 65 years prior to the present study (41). These recent fires had little effect on Pseudotsuga menziesii, a relatively fire- resistant tree with a deep root system and a thick bark at maturity. On the other hand, even ground fires may kill Tsuga heterophylla and Thuja plicata, species which have thin bark and shallow root systems. The Tsuga heterophylla and Thuja plicata understoreys of many stands in the Nanaimo River Valley were of a younger age class than their Pseudotsuga menziesii overstoreys. Such understoreys may have originated following fires which occurred after the establishment of the overstorey. These fires presumably also influenced the composition of subordinate plant layers and the depth of litter layers. The following associations were studied: Pseudotsuga menziesii-Pinus contorta-Gaultheria shallon-Peltigera membranacea- Peltigera aphthosa association (Pseudotsuga-Gaultheria-Peltigera associ- ation3) ; aThe designation of associations is according to the classification proposed by Krajina (20). The ab- breviated names shown in parentheses are used in all subsequent reference to the various associations. 6 -t-=> oS C5 OS O -£3 OS >-. 03 >» Z3 « o M PR Figure 3 — A typical hillside in the Nanaimo River Valley, showing the variation in tree heights from upper slopes to valley floor. This change reflected the sequence of forest associations. Pseudotsuga menziesii-Gaultheria shallon association (Pseudotsuga-Gaultheria association) ; Pseudotsuga menziesii-Tsuga heterophylla-Gaultheria shallon association (Pseudotsuga-Gaultheria association) ; Pseudotsuga menziesii-Tsuga heterophylla-Hylocomium splendens-Eurhynchium oreganum association (Pseudotsuga-Tsuga-Hylocomium association), which occurs as a subassociation typicum and a subassociation nudum: Pseudotsuga menziesii-Thuja plicata-Polystichum munitum association (Pseudotsuga-Polystichum association) ; Thuja plicata-Lysichitum americanum association (Thuja-Lysichitum association). In the easterly portion of the study area, ridges at the top of hillsides characteristically supported stands of the Pseudotsuga-Gaultheria-Peltigera association, with Pseudotsuga-Gaultheria stands occuring on upper slopes, Pseudotsuga-Tsuga-Hylocomium stands at mid-slope, Pseudotsuga-Polystichum stands on lower slopes and the valley floor, and Thuja-Lysichitum stands in swamp}' bottomlands (Fig. 4). Local variation from this catenary distribution of stands was, nevertherless, frequent. In the more mountainous western portions of the valley, Pseudotsuga-Tsuga-Gaultheria stands replaced the Pseudotsuga- Gaultheria association and still other associations occurred at high elevations. Even at low elevations, associations other than those studied were present. A Thuja plicata- Abies grandis-Adiantum pedatum association, for example, was found on occasionally-flooded alluvial benches, an Arctostaphylos uva-ursi association occurred on treeless rock outcrops, and Sphagnum spp. characterized stagnant swamps (20). Other Douglas-fir types have also been described from Washington and Oregon (2). The associations covered in this study, nevertheless, represent some of the most prevalent site classes and commercial timber types of the Douglas- fir region on Vancouver Island. 8 fe O >H Q P H m < fc3 wpQ P? 3^ N y >hO S<^ 5 w <^ H OD t-i £« o« ►H ► 5Q 3* o«i OhJ oq tc w m «!tf HW OQ > Wp PhO oo HZ fe ^ o> HZ 1— 1 >o ffl (—1 So On ft. few Qgg - o c o H o H < O o o CD .9 8 Mx to to ^ CD 0> a cd o ^ T3 O a x 2 2 2 '55 o a •*H CD bJD 03 O O OO Tt* t- t^ A iO >A 00 00 00 00 ££££ 03 CD -2 Q.-2 ft1PSr3 o o o © iO "* © © e S a> 3 3 a s -S 3 =o «o © i i i i 3 a 3 c M Cs ©s ©b Cs S s a a 3 hh so so co so ^ "© '© "e "© I— I "e ~>3 "G "X3 M a a a a w <*> i*> CD m>P x^: CD >j CD * lO CN © t^ t^ t^ t^ -is g"S> a 1 1 vs ass co co co OS o s a a -s> 5? ^ ^> ^> s r^ SO eo CO -C X U w 2 £ ?35 a I I I I c a e c Cs Ce Cs cs s 3 a a co co co co "c "c "c "c 3 3 3 3 f: co co co «o > OpHhJ *^ >-* *** a CO c; ^; H Q A Oh e a e * \ a cd e? ^ a, « 1 1 1 1 -c; 3 3 3 3 CD G> Co C» Cs'S 3 a a a 2, co so co co r? z £j o o © © . £r ~3 -3 "-3 "3 a o s 3 3 g-^, 5J CD CD CD CD 3 ^< so so so so -«; fe o, a, ft, ft, e-h >> o c cd o a c o CD CD CD c3 s o c a a (.) PSEUDOTSUGA GAULTHERIA- PEL TIG IRA ASSOCIATION si 4 Mil *» « PSEUDOTSUGA - GAULTHERIA ASSOCIATION PSEUDOTSUGA - TSUGA -HYLOCOMIUM ASSOCIATION THUJA- LYSICHITUM ASSOCIATION PSEUDOTSUGA- POLYSTICHUM ASSOCIATION I n Pseudotsuga menziesii Tsugo Thuja heferophyllo phcato Polystichum munitum Gaultheria shallon Lysichitum amenconum Effective soil depth llllllllllllllli Water table Figure 4 — Sequence of forest associations in the Douglas- fir region on Vancouver Island. METHODS Groups of plots (Fig. 2, Table I) were selected in mature stands at various locations along the valley so that comparisons could be made between both plots representing different associations under similar climatic conditions and plots representing the same association under different climates. Since plots were to be visited at frequent intervals, accessibility was important and re- stricted the study to areas served by logging roads. This limitation meant that some of the plots chosen were situated in atypical positions in the catenary sequence. All plots, however, were considered to be representative of their association. Twenty-four plots, each of one-quarter acre, were analyzed. Climate Precipitation, and maximum and minimum temperatures were recorded at monthly intervals to indicate the climate of the six localities in which plots were situated. Recording stations were located in clear-cut areas at least 50 m. from the standing timber. Measurements were made from June, 1951, through December, 1956. Data for other locations on Vancouver Island were obtained from the published records of the Meteorological Division of the Canada Depart- ment of Transport and records taken at the Nitinat Camp of the British Columbia Forest Products Company Limited. Kaii] gauges with an orifice of 185 sq. cm. (6 in. in diameter) were used for precipitation measurements, since a large orifice size has been shown to minimize inaccuracies due to wall effect (30). Evaporation of the water collected between 10 readings was restricted by the addition of paraffin oil to the reservoirs. In- accuracies resulting from turbulence about the orifice were reduced by placing the rain gauges in small pits with their orifices almost flush with ground line (38). In winter, extra sleeves were added to bring the orifice of the gauges above the anticipated depth of snow. These sleeves prevented snow from drifting into the gauges, although they had the disadvantage of increasing turbulence about the orifice. Any ice or snow accumulated during winter months was melted with a portable gasoline stove before measurements were made. Initially the Six's type maximum and minimum thermometers used for recording temperatures 1.5 m. above ground level were housed in improvised shelters. During 1955 and 1956, temperatures were also recorded in standard Stevenson screens. Comparison of records for these years showed that maximum values from the improvised shelters were higher than those from the Stevenson screens during warm summer months. Summer values consequently are based only on records from the Stevenson screens. Winter values, on the other hand, are based on the entire 1952-56 record because maximum and minimum values from both types of shelter corresponded closely during this season. Vegetation The trees and subordinate plants (shrubs, herbs, mosses, and lichens) in each plot were analyzed by various techniques appropriate to the different layers. Subordinate plant layers were analyzed during July and early August when all plants were fully developed4. The diameter at breast height (4.5 ft.) of all trees over 4 in. in diameter outside the bark was measured, together with the height and age of trees of each species representative of the diameter classes present. Other tree heights were then obtained from the height/diameter curves constructed for each species in each plot. The average height of the dominants and codominants of each species were determined by averaging the height of the tallest 55 per cent of the trees of each species. Site index for Douglas-fir was determined from the curves developed by McArdle, Meyer, and Bruce (28). Volumes per acre were derived from volume tables prepared by the Forest Surveys Division of the British Columbia Forest Service (13). The density of plants in the shrub layer was determined by line interception (5). Ten lines, each 50 ft. long, were run across the plots at approximately 6-ft. intervals. The length of line covered by a vertical projection of leaf surfaces was recorded and expressed as a percentage of interception. The line interception method as employed in this study involved some inaccuracy, since tall shrubs could not be viewed from directly above. However, any error seemed sufficiently small that the use of a plumb line did not appear warranted. Plants of the herb layer were evaluated by the frequency method (4). The size of frequency frame used, 2 by 5 dm., was gauged to allow an appro- priate number of species to fall within each frame. Since this size was too small to describe accurately the frequency of such large herbs as Polystichum munitum and Lysichitum americanum, these plants were also evaluated by the line inter- ception method. In the case of ferns, the length of line covered by a circle described around the clump was recorded as the amount intercepted. Frequency frames were set at 5-ft. intervals along the lines used for line interception. Eighty to one hundred frames were tallied on each plot and results were expressed as the percentage of frames in which a species occurred. 4Thc original specimens determined during vegetation analyses were destroyed by fire. 11 Mosses and lichens growing on the ground were evaluated by the point frequency method (24). A LO-poinl frame was set at 5-ft. intervals along the line interception tape. Bight hundred to one thousand points were examined on each plot and the frequency with which species were contacted was expressed as a percentage. The abundance and coverage of mosses and lichens growing on decaying logs and the holes of trees up to a height of 2 m. above the ground were estimated according to the 11-point total estimate scale of Krajina and Domin (19). Microclimate Precipitation that penetrated the tree canopy was measured by averaging collections from four rain gauges placed on each plot. Percentages of interception were calculated by comparing the amounts collected within plots with those collected in adjacent open areas. Records were maintained from June, 1951, until October, 1953. Since little or no water ran down tree boles during summer months, the only season when such water might be expected to influence soil moisture content, this component of precipitation was not measured. During part of the study, nine additional rain gauges were placed on four plots of different associations to test the adequacy of the four-gauge sample. It was concluded that the four-gauge average was a satisfactory measure of the precipitation reaching subordinate plant layers because the smaller sample rarely varied from the larger by more than 1 or 2 mm., a difference which could have no appreciable influence on soil-moisture regimes. Porous porcelain atmometers (26) were used to compare evaporation rates in plots and at three of the adjacent open stations. Bulbs were placed at 5 cm. and 100 cm. above ground line. Entry of rain water into the reservoirs was restricted by the use of mercury valves (9). Each atmometer was standardized on a rotating table in the customary manner. Readings were taken twice monthly from June through September, 1951 and 1952. For simplicity, results were expressed as relative evaporation by converting each value to a percentage of the highest value recorded. Maximum and minimum air temperature at 1.5 m. above the ground were recorded on the Wolf Mountain and Fourth Lake plots at monthly intervals June to September, 1953. Soil-surface temperatures were measured with Six's type maximum and minimum thermometers buried with their bulbs approximately 5 cm. below the soil surface. In most cases this depth placed the bulbs just below the litter layer. Readings were made in all plots, twice monthly during the summer and at one- or two-month intervals during other seasons. Records were maintained from June, 1951, until November, 1953. The temperature of deeper soil horizons was measured whenever soil moisture was sampled. During direct sampling, measurements were made by inserting a thermometer into the side of the sampling pit at various depths. The thermisters incorporated in the fiberglas soil moisture units allowed simultaneous temperature measurements during indirect moisture sampling (7). Soils Profile Characteristics Five or more soil profiles were examined in each plot. Descriptions were made in accordance with the terminology of the United States Department of Agriculture Soil Survey Manual (44), although some additional terms were used 12 for humus layers and organic soils (17, 45). In addition to field descriptions, ten profiles were treated with vinylite resin to preserve them for laboratory examination (42). Particle size distribution within the 2-mm. soil fraction was determined by the hydrometer method, according to the procedure prescribed by the American Society for Testing Materials (1). Textural classes were interpreted from the chart included in the Soil Survey Manual (44). Sieved, air-dried soils were re- wet to a saturated paste for pH determinations (34). Measurements were made with a Beckman N-2 glass electrode meter. Moisture Regimes Periodic measurements of soil-moisture contents were made using both direct and indirect sampling methods. Samples for direct determinations were obtained by digging pits because the soils of most plots were too stony for the use of samplers. Samples were taken at 1-dm. intervals to a depth of lm., or to the hardpan in shallow soils. Sample pits were refilled after use and new sample pits were dug at least 3 m. distant from earlier pits. The moisture content of samples was determined by oven drying the 5-mm. soil fraction at 105° C. and results were expressed as a percentage of dry weight. Direct sampling was used from July, 1951, until September, 1952. Indirect measurements of soil moisture were continued from October, 1952, until November, 1953. Fiberglas units (7) were inserted into the side of pits at depths of approximately 5, 15, 30, 50, 80, and 120 cm. in deep profiles or down to the hardpan in shallower soils. This method of placement may have resulted in some soil-moisture values being too high because the number of living roots in the soil adjacent to units was doubtless reduced by the severance of some roots when pits were dug. Nevertheless, seasonal changes in moisture values appeared sufficiently marked to suggest that enough roots were left to bring about soil-moisture depletions to characteristic levels. One bank of units was placed in each plot. The rapid measurement of units was facilitated by connecting their leads to a rotary selector switch. Interpretation of field records was made from calibration curves derived from substitute units because the original soil-moisture units were accidentally destroyed before their calibration had been undertaken. However, tests conducted on ten of the new units in a single test soil showed that variability among such fiberglas units was less than 1 per cent at low soil-moisture contents. Each soil-moisture unit was calibrated against the 5-mm. fraction of the soil which surrounded the original soil-moisture unit in the field. The 5-mm. fraction was used for calibration because collection of the undisturbed cores recommended by Hendrix and Colman (16) was impractical in the coarse, gravelly soils of the study area. Moreover, sieved samples were thought to be satisfactory because wilting percentage is more dependent on soil texture and organic content than on structure, and the major emphasis in this study is on available soil-moisture content. The moisture contents of sieved samples are also considered to be more truly comparable with one another than contents derived from unsieved samples because in the latter case considerable variability may be introduced through differences in coarse gravel contents. The cans used for the calibration of soil-moisture units contained approxi- mately 150 gms. of soil. Uniformity of soil-moisture content in these cans was promoted by covering them with a loosely fitting lid during drying cycles. A drying cycle consisted of a series of warm periods at 35° C. to expel moisture, each followed by an equilibration period of one or more days at 15° C. Tests showed that following this procedure moisture contents were essentially uniform 13 87850-4—3 throughout the can. Can weights and the resistance reading of each unit were determined after each equilibration period. Following determination of the oven-dry weight of soil in the can, the moisture percentage corresponding to each resistance was calculated. The calibration curve plotted for each soil was based on at leasl tour drying cycles, each consisting of six or more readings between saturation and wilt ing range. Since the results of moisture samplings were to be expressed as percentages of available moisture, a wilting percentage was established for each of the nearly 2,200 samples collected. The 15-atmosphere percentage, as determined by a pressure membrane apparatus (36), appeared to be the most satisfactory value that could be obtained for such a large number of samples, even though some deviation between the two values has been reported (27). The procedure followed was similar to that outlined by Richards (34), except that the 5-mm. soil fraction was used. A standard sample of known moisture constant was included with each sample lot. When the value obtained for this standard differed from the true value by less than 2 per cent a correction factor was applied to the values obtained for the unknown samples in the lot. A new extraction was made when the difference was greater than 2 per cent. A 15-atmosphere percentage was determined on a subsample of the soil surrounding each fiberglas unit and each of the samples dug for direct measurement. Available-moisture percentages were found by subtracting the appropriate 15-atmosphere percentage from the field-moisture percentage. While no laboratory procedure is entirely satisfactory for the measurement of field capacities, the 1/3-atmosphere percentage appears to be a convenient value to indicate when soils are nearing saturation (37). The procedure followed was similar to that of Richards (34), except that extractions were made on the 5-mm. soil fraction and a Visking membrane was used. It was found that values obtained using this method corresponded closely to field-moisture contents determined after soils had drained to field capacity following heavy rainfall. The 1/3-atmosphere percentage of all very wet samples was determined to confirm whether gravitational water was in fact present. Observation pits on each plot were also inspected at intervals to determine the depth of any water table present. The volume weight and depth of fine soil present in representative profiles were determined so that soil-moisture contents could be expressed as depths of available water. Sample volume for volume-weight determinations was found by measuring the volume of sand required to fill a plastic bag lining the cavity which remained following the removal of each sample. Volume weights wrere then calculated by dividing the oven-dry weight of each sample by its volume. Values from the five pits sampled at decimeter intervals on each plot were averaged. The amount of fine soil in each 2 dm. of a representative profile was found by sifting the 5-mm. fraction from samples of known cross-sectional area (2 by 5 dm.) and measuring the volume of water it displaced. The depth of fine soil in each 2 dm. was calculated by dividing the volume displaced by the cross-sectional area of the sample. The depth of available water present each time soil-moisture contents were sampled was calculated by multiplying the appropriate depth of fine soil in each 2 dm. of the profile by the percentage by volume of available soil moisture present (volume wreight X percentage by weight of available water/ 100). Assum- ing that the amount of water held by coarse soil fractions is negligible, the total depth of available water was found by summing the depths present in each 2 dm. of the profile. Values for the 30-month period during which soil-moisture contents were sampled were averaged to show the seasonal variation in depth of available water present in each plot. 14 RESULTS Climate Summer months in the Nanaimo River Valley and other locations in the Douglas-fir region, for which long-term records are available, were characterized by potential water deficiences during the study period because summer rainfall was light and temperatures were relatively warm (Table II). Such weather seems quite typical, since the 1951-56 averages differed little from the long-term averages (Appendix I). The low summer rainfall and relatively high summer temperatures char- acteristic of stations within the Douglas-fir region contrast with the higher rainfall and lower temperatures recorded at stations in the hemlock zone (21). The climate of Pachena Point, for example, on the west coast of Vancouver Island is typically maritime, while that of central mountain and east coast stations in the Douglas-fir region has a continental "tone". Such differences in precipitation occur because most rain-bearing winds come from the Pacific Ocean, placing areas to the lee of the mountainous west coast of Vancouver Island under the influence of a rainshadow effect (6). The width of this zone and the intensity of the rainshadow effect is, nevertheless, quite variable. During periods of high rainfall, such as in autumn and winter months, stations in the central mountain portion of the Douglas-fir region (for instance Nitinat Camp or Fourth Lake) seemed to be outside the rainshadow zone, for they received almost as much precipitation as Pachena Point in the hemlock zone (Table II). In summer months, on the other hand, rainfall at such stations amounted to little more than half that at Pachena Point. Presumably this westward displace- ment of the rainshadow climate in summer occurs because the relatively small moisture content of clouds passing the coastal mountains is soon depleted, leaving little to fall farther east. During the growing season, therefore, even the westerly plots in the study area were inside the rainshadow zone. That the intensity of the rainshadow effect increases from west to east is exemplified by records from Nitinat Camp, Cowichan Lake, and Duncan. Average rainfall, both in summer and the year round, at the east coast station (Duncan) was only half that measured at the westerly station (Nitinat Camp). A similar trend was demonstrable in the study area. Potential moisture deficiencies are, therefore, likely to be more extreme in the easterly portion of the study area than farther west. Cloudy weather also occurred less frequently in the easterly section of the valley than it did farther west. Winter temperatures in the study area were usually sufficiently low for much of the December-through-March precipitation to fall as snow. However, the depth and duration of the snow pack in different locations varied considerably. During the period 1952 to 1956, the average maximum depth of snow at the Fourth Lake Station was 38 in., at the Valley Station it was 19 in., and at the Deadwood Creek Station it was only 8 in. Such variation reflected temperature as well as precipitation differences. On several occasions during visits to the study area to collect weather data, snow was falling at Fourth Lake, while only rain was encountered at Deadwood Creek. In the springs of both 1952 and 1954, snow remained at the Fourth Lake and Echo Mountain Stations into April, by which time the ground was only partly covered in the Valley area and the Deadwood Creek area was already clear. Similarly, at the end of March, 1956, the snow pack was still near its maximum depth of 5 to 6 ft. at Fourth Lake and 3 to 4 ft. on Echo Mountain. The Valley Station, on the other hand, had little more than 6 in. and the Deadwood Creek area was largely free from snow. 15 87850-4— :U pq < - = H X M CC o M < <— i H « '-~ *2 So OW OH ^ . °3 Wee WH « > <5 o tf O 3h Q <1 o I— I o GC Hob «<«< oo H i— i hJ U w W H ^ e SR 5 u •£-C oo o o — l>- OS CO ^^ ©.S Q° J? gi rf r^ o O) OO 1> US f o> m n 00 3 E gj 02 IS. 55 < — -r ■J < 88 MM 1 O -f 1 UO «5 CM n CO2^ h < £ ©„ Sw i i i i 1 CM ^ o |h I I I i | y-> FH "" ' QQ 13 ■» 2"W 1 1 ! 1 1 ^ e© "*l c ■ II! 1 CM CM CM 1^ fa t oo » to | O CO CO 63 CO IN CO CO 1 CO CO CM « £> H -« u 2 bco 4> S c8"9 +>.H J 1 115 OO ifl (O 1 OO o •"f P4 1 — < CM CM w H w S w K t-i , — - 3 >- ^_-o> 00 O OS OS | tJ< 00 00 H 1 -*1 "!t< CM X GO »H 1-9 t1 e3 -~- n © 2 bco S £ 5"? H 2; 00 f OO N I «5 CO o O £ os s»« 00 OO 00 00 1 OO C3» r^ § 3 rjO-OJ CO c lH (-. , , © Cco O 5 a) £ o3"? OS 00 N N lO -^ Tfi CO O N N CO lO CO o CO ^h &-a & 2 o.S is? I 2 cm S OO N ■* i-l 00 CO lO « O OO t~ "S N OO ■* CM fc '"' rH ^^ ^ 1 c T C W r; 03 55 c 2 O O Ph © O t, o © x o S 3 -£ ^ 5 S O © c3 4 o o J •- o = O o3 g fe w > e o m < 55 P W ^^ — © 2 -o U £ O 3 — « O O < O - i- i- - & £ & 3 bC OC C B I'l T3 T3 H H M bC B B 11 3 3 3 3 O © "3 "3 © © B B .2 .2 '3 '3 © © B B 03 03 o. o. 3 3 00 GO 08 ^ 3 % 'Si » Hi H © o bi ►"5 «? © cc s-3 £ .3 W 16 The growing season in the study area extended from early May until mid- October. At Fourth Lake and on Echo Mountain, however, the growing season appeared to be somewhat shorter than it was farther east, since phenological events in spring, such as the appearance and increase in size of new Polystichum munitum fronds, were generally one or two weeks later in occurrence. Vegetation Vegetation analyses confirmed that the composition and productivity of tree and subordinate plant layers in the plots studied were typical of their respective associations. Differences evident among plots of the same association seemed attributable to the influence of geographic location, topography, and the soil characteristics of the individual plot. Pseudotsuga-Gaultheria-Peltigera association Despite the relatively large number of Pseudotsuga menziesii per acre, their small height and diameter in the Pseudotsuga-Gaultheria-Peltigera plots resulted in stands with rather open canopies and low volumes per acre (Table III, Fig. 5). At Fourth Lake (Plot LI), volume per acre was further decreased by stand openings occupied by rock outcrops. Tree heights in this plot were also lower than those in the other Pseudotsuga-Gaultheria-Peltigera plots. No secondary canopy of intermediate trees occurred in any plot, although occasional suppressed Pseudotsuga menziesii, and, in some plots, Tsuga heterophylla, Pinus contorta, and P. monticola were present. The absence of a secondary canopy may have been at least partially attributable to ground fires subsequent to stand establish- ment. The presence of charred bark on the lower boles of several trees in each plot attested to the occurrence of such fires. Occasional clumps of Tsuga hetero- phylla up to 40 ft. high were present on most plots and individual Pinus contorta reached 60 ft. in Plot L4. All understorey trees, however, were less than 100 years old, some 100 to 200 years younger than most trees of the dominant canopy. Gaultheria shallon, less than 6 dm. high, constituted the principal cover of shrub layers. Other species occurred only as scattered individuals. Clumps of Tsuga heterophylla, 4 to 5 ft. tall, were present in some plots, particularly those toward the western end of the study area. A few Pseudotsuga menziesii were also included within the shrub layer in the Wolf Mountain Plot (L5). Although a fairly large number of species was represented in the herb layer of most plots, only Linnaea borealis, Chimaphila umbellata, Mahonia nervosa, and Goodyera oblongifolia occurred with any considerable frequency. Camptothecium mega- ptilum, Collier gonella schreberi, Polytrichum spp., and Rhacomitrium spp., mosses characteristic of the association, formed extensive patches on some plots. Hylo- comium splendens and Eurhynchium oreganum were common throughout. Various species of Cladonia, Peltigera, and Stereocaulon were also present amongst the ground cover plants, especially on the Fourth Lake Plot. Other lichens, par- ticularly Alectoria sarmentosa, Sphaerophorus globosus, Parmelia physodes, and Cetraria spp. were a conspicuous feature on the bark of trees in all plots. Pseudotsuga-Gaultheria association The greater height and diameter of Pseudotsuga menziesii in the Pseudotsuga- Gaultheria plots resulted in larger basal areas and volumes per acre than those of the Pseudotsuga-Gaultheria-Peltigera plots (Table III). A secondary canopy of suppressed Tsuga heterophylla and Thuja plicata was present in Plot G6, but these species occurred only as scattered clumps or individuals in other plots and they contributed little to stand volume. All trees of these species, however, were of a younger age class than the Pseudotsuga menziesii overstoreys in the plots analyzed. 17 Figure 5 — A stand of the Pseudotsuga-Gaultheria-Peltigera association, showing the small diameters of Pseudotsuga menziesii and sparseness of Gaultheria shallon. The meter stick is marked in decimeters. Figure 6 — A stand of the Pseudotsuga-Gaultheria association. The increased diameters of Pseudotsuga menziesii and height of the Gaultheria shallon layer may be judged from the meter stick. Figure 7 — A stand of the Pseudotsuga-Tsuga-Gaultheria association, showing the small diameters of both Pseudotsuga menziesii and Tsuga heterophylla. Figure 8 — The Fourth Lake Plot of the Pseudotsuga-Tsuga Hylocomium association, showing the com- paratively large size of Tsuga heterophylla (beside meter stick). One of the rain gauges is evident in the right foreground. 18 The Gaultheria shallon of the shrub layer was commonly over 1 m. in height and considerably denser than in the Pseudotsuga-Gaultheria-Peltigera plots (Fig. 6). Other shrubs still had little cover value and herb layers were char- acterized by a poor species representation. The most common plants of herb layers in the Pseudotsuga-Gaultheria-Peltigera plots were also common in the Pseudotsuga-Gaultheria plots, but their frequencies were lower. Hylocomium splendens and Eurhynchium oreganum were the prominent mosses of moss- lichen layers, and they covered the ground to the virtual exclusion of other species. Lichens were absent from the ground layer. TABLE III VEGETATION ANALYSES OF PLOTS REPRESENTATIVE OF FOREST ASSOCIATIONS IN THE NANAIMO RIVER VALLEY, BRITISH COLUMBIA PSE UDOTS UGA-GA UL THERIA-PEL TIGER A ASSOCI ATIO N Location Plot Number Age of Oldest Tree in Dominant Canopy (years) Site Index for Pseudotsuga (feet at 100 years) Tree Layer Pseudotsuga menziesii Av. height, dom. and codom. (ft.)... Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years)... Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Layer (Line interception) Gaultheria shallon Tsuga heterophylla Pseudotsuga menziesii Mahonia nervosa (Pursh) Nutt Pinus monticola Arctostaphylos columbiana Thuja plicata Vaccinium membranaceum Pinus contorta Vaccinium parvifolium Rosa gymnocarpa Herb Layer (Frequency) Gaultheria shallon Linnaea borealis Chimaphila umbellata Goodyera oblongi folia (Raf.) Boschniakia hookeri Mahonia nervosa Pseudotsuga menziesii Arctostaphylos uva-ursi Festuca occidentalis Vaccinium parvifolium Pyrola picta Allotropa virgata Hieracium albiflorum Chimaphila menziesii Apocynum androsaemifolium Mahonia aquifolium (Pursh) Nutt. . . . Viola orbiculata Pteridium aquilinum Trientalis latifolia Achlys triphylla Malus diversifolia Pinus monticola Vaccinium membranaceum Rosa gymnocarpa Symphoricarpos hesperus G. M. Jones Wolf Mt. L5 220 90 106 17 215 140 250 ,750 25 1 2 + 13 29 11 3 11 9 + + 1 + 1 1 13 4 1 11 7 Deadwood L4 285 80 95 18 240 108 210 5,990 35 1 1 1 3 + + + + 97 4 35 17 3 5 19 + + 3 1 2 1 2 4 + 1 1 3 + 1 1 Deadwood L3 285 80 99 16 250 160 260 ,060 33 + * 1 3 1 + + + + 92 40 40 4 7 20 9 14 + 4 2 1 + + + 7 + 1 + Valley L2 285 90 116 19 230 152 360 12,410 38 3 1 + 84 26 10 2 5 21 + + + 1 1 6 + + + Fourth Lk. LI 275 70 87 19 250 92 185 4,790 24 6 + + 1 + + + 74 21 9 1 1 + 1 4 5 + + + + + 30 19 TABLE III— Continued rs/;i ixrrsi QA-QAULTHERIA-PELTIQERA ASSOCIATION— Concluded Location I'l or N i ICBBB 1 1 kick Latbb (Frequency) — Concluded ( 'ampanula scouli ri ola bracteata Vaccinium ovalifolium Ttvga heterophylla Rubus litifoliits Brotnut vulgaris Monotropa latisquamea (Hydb.) Hulten M . -s-Liohen Layer (Point frequency) Eurynchium orcganum II 'ylocomium splcndcns Rhytidiadelphus triquetrus Rhytidiadelphus loreus Dicranum scoparium Camptothecium megaptilum Sull Peltigera membranacea Ach Peltigera aphthosa Calliergonelia schreberi Dicranum fuscescens Polytrichum juniperinum Cladonia sylvatioa Cladonia gracilis Cladonia squamosa Cladonia furcata Cladonia bellidiflora Cladonia macilenta Cladonia fimbriata Rhacomitrium lanuginosum Rhacomitrium canescens Rhacomitrium heterostichum Aulacomnium androgynum Bryum pollens Swartz Stereocaulon tomentosum Stereocaulon paschale Pilophoron cereolus Pseudotsuga menziesii On Decaying Wood (Total estimate) Dicranum fuscescens Hypnum circinale Aulacomnium androgynum Eurhynchium oreganum H ylocomium splendens Peltigera aphthosa Cladonia gracilis Cladonia bellidiflora Cladonia fimbriata Peltigera membranacea Dicranum, strictum Pseudisothecium sloloniferum Calliergonelia schreberi Polytrichum juniperinum On Pseudotsuga Bark (Total estimate) Alectoria sarmentosa Sphaerophorus globosus Parmelia physodes Cetraria lacunosa Cetraria glauca Cetraria scutata Nephromopsis ciliaris Hypnum circinale Cladonia macilenta Alectoria oregana Alectoria jubata Ochrolechia upsaliensis Lobaria oregana Usnea plicata Lelharia vulpina W'oi.k Mr. L5 1 1 + 19 1 2 + 2 1 + + 1 + + + + + + + + + + + 1 + + 1 + 3 2 2 2 1 2 1 + + Deadwood L4 + 1 + 15 3 + 5 1 1 1 + + 1 + + + + + + + + + + + + + + + + + 1 + + + + 1 1 3 1 2 + 3 + 1 + Deadwood L3 + 1 + + + 23 23 2 + 2 1 1 1 9 + + + + + + + + + + + + + + + + + + 1 + + + + + + + Valley L2 + 22 17 + + 4 3 1 + 3 1 + + + + + + + + + + + 3 3 2 3 3 2 2 + + + 1 + Fourth Lk. LI 1 + + 2 9 + + 2 1 1 1 8 + + 3 + + + 1 + + + + 2 + + 1 + + + + + 20 TABLE lll-^Continued PSEUDOTSUGA-GAULTHERIA ASSOCIATION Location Plot Number Age of Oldest Tree in Dominant Canopy (years) Site Index for Pseudotsuga (feet at 100 years) . Tree Layer Pseudotsuga menziesii Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Tree per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Tsuga heterophylla Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Thuja plicata Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Layer (Line interception) Gaultheria shatlon Mahonia nervosa Polystichum munitum Vaccinium parvifolium Rosa gymnocarpa Thuja plicata Tsuga heterophylla Pseudotsuga menziesii Holodiscus discolor Herb Layer (Frequency) Gaultheria shallon Linnaea borealis Chimaphila umbellata Mahonia nervosa Achli/s triphylla Boschniakia hookeri Rubus vitifolius Goody era oblongifolia Rosa gymnocarpa Chimaphila menziesii Symphoricarpos hesperus Pteridium aquilinum Polystichum munitum Vaccinium parvifolium Pyrola picta Pyrola bracteata Moss-Lichen Layer (Point frequency) Hijlocomium splendens Eurhynchium oreganum Rhytidiadelphus loreus h'ln/tidiadelphus triquetrus Camptothecium megaptilum Dicranum scoparium Pseudisothecium stoloniferum Ilypnum circinale On Decaying Wood (Total Estimate) H ylocomium splendens Eurhynchium oreganum Wolf Mt. Dead wood Deadwood Valley G5 G4 G6 G3 220 320 320 275 130 140 120 140 147 175 148 169 22 27 26 28 215 300 300 250 100 108 104 64 300 470 410 280 13,320 23,650 17,880 12,840 _ 66 88 — — 10 11 — — 190 130 — — 40 16 — — 24 12 — — 640 130 _ 74 60 — — 10 11 — — 220 130 — — 28 12 — — 16 7 — — 475 135 59 41 64 31 4 1 + + + + + 5 — + + — + + + + + + + + + + + + + + — — — — — + 89 78 83 71 11 1 9 10 16 10 1 — 47 10 14 7 56 31 14 29 6 1 1 — 11 6 1 6 + — + — 1 4 — 1 2 1 1 — 4 1 + — 2 + + 1 + + + 10 + + + + + + — — + + — — 1 15 15 16 22 + 13 10 2 + — + — + — — — + — — + + — — — 2 — — + 2 2 4 3 4 3 3 4 21 87850-4—4 T IBLE III— Continued I >& / / hOTSUGA-GA UL THERIA ASSOCIATION— Concluded 1 1 ■ \ Plot \ i mbbb On D» l ting Wood — Concluded Scapania bolanderi .■//urn fuscescens oparium Hf/pnum circulate Wnium punctatum Rhytidiadelphus lorcus 1'st udisothecium stolonifervm Tauga heterophylla On Pseudotsuga Bark (Total estimate) THcranum fuscescens Sphat rophorus globosus Hypnum circinale ( ladonia madlenta aria lacunosa Xephromo]>sis ciliaris Parmclia physodes Ochrolechia pallescens Scapania bolanderi Alectoria sarmentosa Wolf Mr. ( ;.-> 2 2 + + + 1 + 2 3 3 3 + + Dkadu OOD G4 + 1 1 2 1 + + Dbadwood G6 2 + + 2 1 3 4 1 2 + + + V \i.i i.v 1 + 3 1 4 + PSEUDOTSUGA-TSUGA-GAULTHERIA ASSOCIATION Location Plot Number Age of Oldest Tree in Dominant Canopy (years) Site Index for Pseudotsuga (feet at 100 years) Tree Layer Pseudotsuga menziesii Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Tsuga heterophylla Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Thuja plicata Av. height, dom. and codom. (ft ) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Layer (Line interception) Gaultheria shallon Tsuga heterophylla Thuja plicata Vaccinium parvifolium Vaccinium membranaceum Herb Layer (Frequency) Gaultheria shallon Linnaea borealis Vaccinium parvifolium Goodyera oblongifolia Fourth Lk. Echo Mt Gl G2 245 285 90 60 110 77 17 14 235 260 172 104 300 130 10,310 2,950 71 70 10 12 160 250 32 120 17 120 490 2,540 74 64 14 9 200 230 36 24 44 12 1,190 325 50 36 + + + + — + — + 76 76 50 5 12 26 6 5 22 TABLE III— Continued PSEUDOTSUGA-TSUGA-GA ULTHER1A ASSOCIATION— Concluded Location Plot Number Herb Layer — Concluded Mahonia nervosa Chimaphila umbellata Achlys triphylla Boschniakia hookeri Chimaphila menziesii Vaccinium membranaceum Vaccinium ovalifolium Vaccinium alaskaense Howell Gaultheria ovatifolia Tsuga heterophylla Moss-Lichen Layer (Point frequency) Hylocomium splendens Rhytitiadelphus loreus Rhytidiopsis robusta Eurhynchium oreganum Camptothecium megaptilum Plagiothecium undulatum On Decaying Wood (Total estimate) Hylocomium splendens Eurhynchium oreganum Scapania bolanderi Dicranum fuscescens Hypnum circinale Rhytidiopsis robusta On Pseudotsuga Bark (Total estimate) Dicranum fuscescens Sphaerophorus globosus Cladow'a macilenta Parmelia physodes Hypnum circinale Cetraria lacunosa Alectoria sarmentosa Fourth Lk. Gl 15 9 2 + 1 + + 16 5 1 4 1 + + + + 1 + Echo Mt. G2 + 6 1 + 5 2 2 1 23 5 12 + 1 2 + 1 + + + + 1 + 1 + + + PSE UDOTS UGA-TS UGA-H YLOCOMI UM ASSOCI ATIO N Location Plot Number Subassociation Age of Oldest Tree in dominant Canopy (years) Site Index for Pseudotsuga (feet at 100 years) Tree Layer Pseudotsuga menziesii Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Tsuga heterophylla Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Thuja plicata Av. height, dom. and codom. (ft.). . . . Deadwood M4 typicum 320 130 158 26 290 96 380 17,140 85 9 190 176 92 3,670 101 Valley M3 typicum 320 130 157 23 300 84 270 12,870 86 10 190 88 50 1,710 78 Fourth Lk Ml typicum 275 120 144 22 260 68 210 9,110 136 18 220 64 140 7,330 85 Wolf Mt, M5 nudum 220 170 199 33 210 80 500 27,960 65 7 80 96 26 750 Echo Mt. M2 nudum 285 170 209 37 250 72 550 31,400 87 10 170 52 28 960 107 87850-4—41 23 I IBLE III -Continued 7D0TSU0A VSUGA-HYLQCOMIUM ASSOCIATION Concluded ; N l MlU.li. Thuja plicata — concluded ,\v. diain., dom. and codom. (in.). \v. age, dom. and codom. (years). r acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Latbb (Line interception) Gaultheria shallon Malion ia nervosa Polystichum mini it inn Tsuga heterophylla Thuja ])licata Herb Layer (Frequency) Chimaphila menziesii. . . . Mahonia nervosa Linnaea borealis Viola orbiculata Pyrola picta Achlys triphylla Gaultheria shallon Goody era oblongifolia Vaccinium parvifolium . . . Chimaphila umbellata Monotropa unijlora Monotropa latisquamea. . . Lister a cor data Corallorhiza maculata. . . . Polystichum munitum Trillium ovatum Moss-Lichen Layer (Point frequency) Eurhynchium oreganum Hylocomium splendens Rhytidiadelphus loreus Rhytidiadelphus triquetrus Rhytidiopsis robusta Pseudisothecium stoloniferum Camptothecium megaptilum. Dicranum fuscescens Mnium spinulosum On Decaying Wood (Total estimate) . Hypnum circinale Cephalozia media Scapania bolanderi Dicranum fuscescens Lepidozia reptans Rhytidiadelphus loreus Eurhynchium oreganum Hylocomium splendens Tsuga heterophylla On Pseudotsuga Bark (Total estimate) Hynum circinale Dicranum, fuscescens Cladonia macilenta Scapania bolanderi Dead wood Ml 13 190 12 13 500 7 11 2 1 1 3 13 1 + + + + + 10 44 + + + 4 2 2 2 1 + 2 2 2 \ •■ui'1 m 13 200 12 11 350 + + + 2 + 11 + 3 1 + 1 2 + + + + 18 35 + + 4 1 1 1 + + 1 + I'm in ii I.i.. Ml 14 220 68 2,200 3 2 + + + 2 9 49 1 1 4 19 + 21 12 + + 17 8 2 2 + 2 + + 1 1 Woi.i Mi. m + + + + i + i + + 2 + + + + + + 3 2 + + 1 + + + 4 2 2 2 1 + 1 1 1 4 1 4 + I ' ii" Mi . .Ml' 14 170 16 20 800 + + + + 12 1 6 1 3 + 1 + + + + + + 2 + + + + + + 21 TABLE III-^Continued PSEUDOTSUGA-POLYSTICHUM ASSOCIATION Location Plot Number Age of Oldest Tree in Dominant Canopy (years) Site Index for Pseudotsuga (feet at 100 years) Tree Layer Pseudotsuga menziesii Av. height, dom. and codom. (ft.) . . . . Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Thuja plicata Av. height, dom. and codom. (ft.) , . . . Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) .... Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Tsuga heterophylla Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.) Av. age, dom. and codom. (years) .... Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Abies grandis Av. height, dom. and codom. (ft.) Av. diam., dom. and codom (in.) Av. age, dom. and codom. (years) Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Layer (Line interception) Pohjstichum munitum Tsuga heterophylla Mahonia nervosa Thuja plicata Athyrium jilix-femina Rosa gymnocarpa Rubus spectabilis Herb Layer (Frequency) Polystichum munitum Tiarella trifoliata Achlys triphylla Tiarella laciniata Hook Trillium ovatum Athyrium filix-femina Melica subidata Adcnocaulon bicolor Dryopteris linnaeana Blechnum spicant (L.) J. E. Smith Viola orbiculata Galium trijlorum Car ex hendersonii Claytonia sibirica L Disporum oreganum Streptopus amplexifolius Mahonia nervosa Linnaea borealis Vaccinium parvifolium Luzula parviflora Trientalis latifolia Bromus vulgaris Dead wood Fourth Lk Echo Mt. Wolf Mt. Valley P4 PI P2 P5 P3 285 270 285 220 220 200 160 200 180 200 248 199 244 218 233 48 36 42 39 37 270 260 250 200 200 44 40 52 56 64 570 280 440 490 500 37,130 14,150 30,000 28,700 32.500 140 137 178 148 34 31 25 29 — 140 200 240 190 — 12 12 12 12 — 78 77 50 56 — 2,700 3,060 2,710 2,500 — 76 106 83 111 96 10 13 10 11 11 70 220 160 100 150 52 76 28 44 24 31 94 15 35 16 1,250 4,400 540 1,600 600 118 77 — — — 13 9 — — — 120 140 — — — 28 8 — — — 35 4 — — — 1,750 60 33 40 21 20 18 + 1 4 — 2 — + + 1 + — + 1 + — 1 — + + + — — + + + — — + — + 29 41 8 20 10 22 12 58 30 91 24 25 48 13 (if, 1 — 39 8 30 + — 1 1 5 2 — 2 4 + + — 1 3 1 + — 5 + 37 27 — + + 1 — — 4 10 — + 1 25 + — 8 + 17 + + 1 — + + 9 + + + 4 — + — + — 2 + — + 1 + — 4 9 17 1!) — 34 54 + + — 4 2 + 1 1 — + 1 4 — + 10 + 2 + — — + 17 25 TABLE III— Continued l'SUDOTSUGA-POLYSTICHUM ASSOCIATION— Concluded now BB Ml— Li i.i ck Latbb (Point Frequency) •hynchium oreganum // ijlocomium splendens RhyHdiacL I pints loreus Mnium inngne Mnium menzieeii Rhytidiopsis robusta On Decws i\<; Wood (Total estimate) /.( pidozia reptans Mnium punctatum Mnium spinulosum Plagiothecium denticulatum Eurhynchium oreganum Hylocomium splendens Rhytidiadelphus loreus Pseudisothecium stoloniferum Cephalozia media Scapania bolanderi Dicranum fuscescens Icmadophila ericetorum Riccardia latifrons Hypnum circinale Tsuga heterophylla On Pseudotsuga Bark (Total estimate) Hypnum circinale Dicranum fuscescens Scapania bolanderi Hylocomium splendens Cladonia macilenta Sphaerophorus globosus On Tsuga Bark (Total estimate) Pseudisothecium stoloniferum Porella navicularis Neckera douglasii Frullania nisquallensis Radula complanata Hypnum circinale Dicranum fuscescens Eurhynchium oreganum Cladonia macilenta Rhytidiadelphus loreus Deadwood l'4 2 10 1 + + 1 3 2 1 2 1 + 2 1 1 Foi b i ii Lk, P2 9 + + + 1 + + 2 + 1 + 1 + 1 2 3 3 3 3 + Echo Mt. P2 3 + l + + 2 1 + + 2 3 1 1 2 1 1 + Wolf Mt. IT) 2 2 + + 3 4 2 + 4 1 2 + 1 3 + Valley P3 9 1 + 3 1 1 + 2 3 1 2 2 1 1 1 + 4 3 2 1 3 + 4 2 1 2 1 + + 1 1 + THUJA-LYSICHITUM ASSOCIATION Location Plot Number Age op Oldest Tree in Dominant Canopy (years) Tree Layer Thuja plicata Av. height, dom. and codom. (ft.)-- . • Av. diam., dom. and codom. (in.).. . . Av. age, dom. and codom. (years).. . . Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Pseudotsuga menziesii Av. height, dom. and codom. (ft.) Av. diam., dom. and codom. (in.).. . . Wolf Mt. Ly3 220 Deadwood Ly2 285 125 196 177 38 30 25 200 270 250 88 68 60 797 366 220 37,000 20,700 12,000 183 230 206 40 46 36 Echo Mt. Lyl 285 26 TABLE III— Continued THUJA-L YSICHITUM ASSOCIATION— Continued Location Plot Number Pseudotsuga menziesii — concluded Av. age, dom. and codom. (years).. . Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Tsuga heterophylla Av. height, dom. and codom. (ft.)... Av. diam., dom. and codom. (in.)... Av. age, dom. and codom. (years).. . Trees per acre Basal area (sq. ft. per acre) Volume (cu. ft. per acre) Shrub Layer (Line interception) Lysichitum americanum Oplopanax horridus Athyrium filix-femina Rubus spectabilis Blechnum spicant Polystichum munitum Adiantum pedatum Gaultheria shallon Thuja plicata Tsuga heterophylla Herb Layer (Frequency) Lysichitum americanum Claytonia sibirica Galium triflorum Mitella ovalis Viola orbiculata Viola glabella Listera cordala Athyrium filix-femina Stachys ciliata Oenanthe sarmentosa Dryopteris linnaeana Epilobium adenocaulon Hook Car ex leptopoda Thuja plicata Cardamine angulata Galium boreale Maianthemum dilatatum (Wood) Abrams Circaea pacifica Veratrum eschscholtzii A. Gray Tiarella trifoliata Tiarella laciniata Streptopus amplexifolius Achlys triphylla Blechnum spicant Vaccinium parvifolium Gaultheria shallon Adenocaulon bicolor Rubus vitifolius Goodyera oblongifolia Luzula parviflora Moss-Lichen Layer (Point frequency) Mnium punctatum Eurhynchium stokesii Brachythecium washingtonianum Eaton Conocephalum conicum Pellia columbiana Krajina and Brayshaw Mnium menziesii Echo Mt. Lyl 260 16 120 6,700 Swamp 49 76 22 13 3 + 3 + + + + + 3 3 3 + 36 16 14 1 1 3 Banks 10 + 9 1 12 + + 12 + + 2 12 5 7 2 14 5 40 5 + 1 + Swamp 46 54 8 + 5 1 42 2 12 25 3 11 3 3 3 + 2 2 2 + + 40 9 2 + 19 12 2 + 3 1 Banks + + + + 16 3 + + + 5 + + + + + 5 + + + 5 5 5 + + + Swamp 73 + 1 54 11 28 35 28 16 + 1 16 11 3 5 50 11 7 3 1 2 Banks 11 + 32 10 + + 7 7 + 7 7 36 14 57 50 + 14 7 7 27 TABLE III Concluded THUJA-LY8ICHITUM ASSOCIATION Concl I .1. in \ I. \i i K < 'oncluded M mi insigne hynchium oreganum Hylocomium splendens iK 1 >kc i yinq Wood (Total estimate) halozia media Calypogeia trichomanis //// punctatum \ania bolanderi Hylocomium splendens hynchium oreganum Dicranum fuscescens Li pidozia reptans Rhytidiadelphus loreus Mnium spinulosum On Thuja Bark (Total estimate) Hypnum circinale Dicranum fuscescens Cladonia madlenta Sea paiiia bolanderi Frullania nisquallensis S\\ \MI' Banks Su wii- I \ \ • S\\ AMI' + _ 2 — + 2 10 + + — 5 + 2 — Banks + 3 2 2 3 4 3 + 2 1 + 1 + 1 1 + 1 1 2 2 1 1 1 + 2 2 1 + + 2 + 2 2 1 1 2 1 1 + 2 3 + + * Less than one percent. ** According to the total estimate scale of Krajina and Domin (19). Interpretation of the scale values as follows: + solitary, with small dominance. 1 seldom, with small dominance. 2 very scattered, with small dominance 3 scattered, with small dominance. 4 often, with 1/20 dominance. 5 often, with 1/5 dominance. 6 any number, with 1/4 to 1/3 dominance. 7 any number, with 1/3 to 1/2 dominance. 8 any number, with 1/2 to 3/4 dominance. 9 any number, with dominance more than 3/4, but less than complete. 10 any number, with complete dominance. Pseudotsuga- Tsuga-Gaultheria association Site index for Pseudotsuga menziesii in the Pseudotsuga-Tsuga-Gaultheria plots was as low as in the Pseudotsuga-Gaultheria-Peltigera plots (Table III). Unlike the Pseudotsuga-Gaultheria-Peltigera and Pseudotsuga-Gaultheria plots, Tsuga heterophylla constituted nearly half the stand volume of the Echo Mountain Pseudostuga-Tsuga-Gaultheria Plot, although little occurred in the Fourth Lake Plot. Tsuga heterophylla heights and diameters were poor, nevertheless (Fig. 7). The presence of Chamaecyparis nootkatensis, Vaccinium membranaceum, V. alaskaense, and Gaultheria ovatifolia showed the affinity of the Pseudotsuga- Tsuga-Gaultheria plots with stands characteristic of relatively high altitudes. Other plants of shrub and herb layers occurred in both the Pseudotsuga-Gaul- theria and Pseudotsuga-Tsuga-Gaultheria plots, although many were smaller and less abundant in the Pseudotsuga-Tsuga-Gaultheria plots than they were in Pseudotsuga-Gaultheria sites at lower elevations. In the moss-lichen layer, Rhytidiadelphus loreus and Rhytidiopsis robusta were other species common in high altitude stands, although the predominant moss, Hylocomium splendens, was equally widespread in lower altitude plots. Both mosses and lichens were common on the bark of trees, with Lobaria oregana being particularly conspicuous on both living and dead branches in the Echo Mountain Plot. 28 Pseudotsuga- T suga-Hylocomium association The average height of 144 to 155 ft. for the dominant and codominant Pseudotsuga menziesii in the subassociation typicum plots was considerably less than the 199 to 209 ft. averaged in the nudum plots (Table III). In most plots Tsuga heterophylla formed a secondary canopy 70 to 130 ft. below the dominant Pseudotsuga menziesii canopy. Although as numerous as Pseudotsuga menziesii, Tsuga heterophylla made up only a minor proportion of stand volume because individual trees were smaller. With the exception of the Fourth Lake Plot, however, all Tsuga heterophylla were younger than the trees of the dominant canopy. In the Fourth Lake Plot, some Tsuga heterophylla were of the same age class as the Pseudotsuga menziesii and both species were represented in the codominant canopy (Fig. 8). The subordinate vegetation of the Pseudotsuga-T suga-Hylocomium plots was characterized by an almost complete lack of shrubs and herbs. Various inconspicuous plants characteristic of the association were present, but their cover value was small (Table III). Stunted Gaultheria shallon, Polystichum munitum, and Achlys triphylla, species characteristic of other associations, also occurred locally, but their frequency was low. The forest floor in the subassociation typicum plots consisted of an almost continuous green carpet of mosses (Fig. 9), Hylocomium splendens and Eur- hynchium oreganum being the predominant species. The forest floor in the sub- association nudum plots was essentially bare (Fig. 10). Epiphytic lichens were absent from the lower boles of trees in all plots, but bryophytes such as Hypnum circinale, Dicranum fuscescens, and Scapania bolanderi were quite common. Pseudotsuga- Polystichum association The largest trees and highest volumes per acre of any stand were recorded in the Pseudotsuga- Polystichum plots (Table III). Tree heights on the Fourth Lake Plot (PI) were somewhat lower than average for the association because this plot was located toward the upper margin of the stand type. A logging setting lower down the same slope, which had been cut prior to the present study, had large stump diameters and a high site index comparable with those of the other plots of this association (22). With the exception of the Valley Plot (P3), Thuja plicata was the tallest tree of the secondary canopy, although its frequency was low. Tsuga heterophylla constituted the bulk of a secondary canopy, some 100 to 150 ft. below the crowns of the dominants. Tsuga heterophylla volumes were low in most plots because trees were small and considerably younger than the Pseudotsuga menziesii of the dominant canopy. Polystichum munitum clumps, commonly 80 cm. high, dominated sub- ordinate plant layers (Fig. 11). Shrubby plants had little cover value. On some plots other ferns, such as Blechnum spicant on Plot P5, Dryopteris linnaeana on Plot P4, and Athyrium felix-femina on Plot P2, were also common. Achlys triphylla, a characteristic herb of the Pseudotsuga- Polystichum association, was particularly common in the Valley Plot (P3). This plot represented a subtype in which Achlys triphylla is even more abundant than Polystichum munitum (20). Other herbs characteristic of moist and fertile soils, such as Tiarella trifoliata, Trillium ovatum, Adenocaulon bicolor, and Galium triflorum, were represented on most plots. Mnium insigne and M. menziesii, mosses characteristic of the Pseudotsuga- Polystichum association, were present in the moss-lichen layer and other characteristic bryophytes occurred on decaying wood. Epiphytic mosses were also quite abundant, another feature typical of Pseudotsuga- Polystichum stands. 29 87850-4—5 Figure 9 — A stand of the Pseudotsuga-T suga-Hylocomium association, showing the mossy carpet present in subassociation typicum stands. Figure 10— A stand of the Pseudotsuga-T suga-Hylocomium association, showing the bare forest floor of subassociation nudum stands. Figure 11 — A stand of the Pseudotsuga-Polystichum association. The large diameters of Pseudotsuga menziesii are evident. Figure 12 — A stand of the Thuja-Lysichitum association. The Lysichitum americanum leaves in the fore- ground cover a swampy portion of the stand. The Thuja plicata behind are growing on a marginal hummock. 30 Thuja-Lysichitum association Although trees were restricted to the hummocks and banks whiclTbordered swampy areas, volumes per acre in the Thuja-Lysichitum plots were quite high because individual Thuja plicata trees were large (Table III). The occasional Pseudotsuga menziesii included in these plots more properly belonged to adjacent sites bordering the stands analyzed. Lysichitum americanum dominated swampy areas in the Thuja-Lysichitum plots during the growing season (Fig. 12). Other species characteristic of the association which grew among and beneath the Lysichitum americanum leaves included Veratrum eschscholtzii, Mitella ovalis, Circaea pacifica, Mnium punctatum} and Conacephalum conicum. Hummocks and the marginal banks of swamps supported a variety of species which also occurred in other associations. Microclimate Precipitation Interception During the summer, average interception by the tree canopy ranged from 30 to 57 per cent (Table IV). Presumably such high values were recorded because summer rainfall occurred mostly as light showers, and a large proportion of each shower was required to wet the tree canopy before penetration took place. Low humidities and high temperatures might then evaporate much of this foliage moisture before it could drop to the ground (15). Interception by the tree canopy undoubtedly substantially reduced the amount of water that sum- mer rainfall could add to soil-moisture reserves. TABLE IV AVERAGE PERCENTAGE OF PRECIPITATION INTERCEPTED BY THE TREE CANOPIES OF PLOTS REPRESENTATIVE OF FOREST ASSOCIATIONS IN THE NANAIMO RIVER VALLEY, BRITISH COLUMBIA, 1951-1953 Association Pseudotsuga-Tsuga-Gaultheria Pseudotsuga-Gaultheria-Peltigera. Pseudotsuga-Gaultheria Pseudotsuga-Tsuga-Hylocomium . Pseudotsuga- Poly stichum* Thuja-Lysichitum Interception (%) Annual Summer 20 30 28 39 31 49 34 51 44 57 33 40 *Excluding Plots PI and P2, which were understocked. During periods of high rainfall, such as in autumn and winter, interception values were as low as 5 per cent. Mean annual interception values were con- sequently lower than those of the summer months. High percentages of inter- ception did occur with light snowfalls and even in late winter snow depth beneath the trees was less than it was in adjacent open areas. However, since the snow pack in clear-cut areas usually melted earlier than it did beneath the tree canopy, moisture was supplied by melting snow later into the growing season than would have been the case had no tree canopy been present. The highest percentages of interception occurred in the Pseudotsuga- Tsuga-Hylocomium and Pseudotsuga- Poly stichum stands. Tree crowns were large and canopies were dense and two-layered in most of these plots. Inter- ception values in Plots PI and P2 of the Pseudotsuga- Poly stichum association, 31 87850-4— 5* however, were below average for the association, apparently because stocking in these plots was low. Low stand density could also accounl for the low inter- ception values of the Thuja-Lysichitum plots. In the Pseudotsuga-Tsuga-Gaul- theria and Pseudotsuga-Gavliheria-PeltigerQ plots, the small size of tree crowns and absence of a dense secondary canopy doubtless contributed to the relatively low interceptioo value.- recorded. However, the influence of such increased penetration was probably Largely negated by more rapid evaporation than would have occurred had less insolation penetrated the tree canopy. Temperature Air and soil-surface temperatures were highest in the open Pseudotsuga- Gaultheria-Peltigera plots (Table V). Soil-surface temperatures reached 124° F. during summer months, even in undisturbed stands. Still higher values (135° F.) were recorded within the blackened soil-surface layer of Plot G4 of the Pseudo- tsuga-Gaultheria association the summer following a ground fire which destroyed the subordinate vegetation. More moderate temperatures were recorded in the denser Pseudotsuga-Tsuga-Hylocomium and Pseudotsiiga-Polysiichum stands and in the moist Thuja-Lysichitum plots. This trend reflected the moderating influence of stand density and moist soils. The soils of the higher altitude and westerly plots Avere cooler and warmed up more slowly in spring than their lower altitude and more easterly counterparts. Air and soil-surface temperatures however, were higher than their association averages during summer and autumn TABLE V AVERAGE QUARTERLY TEMPERATURES IN PLOTS REPRESENTATIVE OF FOREST ASSOCIATIONS IN THE NANAIMO RIVER VALLEY, BRITISH COLUMBIA, 1951-1953 Association Temperature (°F.) Spring1 Summer2 Autumn3 Winter4 PSE UDO TS UGA-GAULT HERIA-PEL TIGER A (easterly plots: L2, L3, L4, L5) Air, at 1 m. (max./min.) 93/37 47 45 45 89/37 42 42 42 88/49 111/48 59 58 55 87/45 108/46 57 56 53 59/33 45 47 48 54/34 43 44 47 Soil surface (max./min . ) 54/31 5 cm. below surface5 36 15 cm. below surface 36 50 cm. below surface 38 (westerly plot: LI) Air, at 1 m. (max./min.) Soil surface (max./min.) 47/29 5 cm. below surface 35 15 cm. below surface 36 50 cm. below surface 38 PSE UDOTS UGA-GA ULTHERIA (easterly plots: G3, G4, G5, G6) Air, at 1 m. (max./min.) 76/39 45 45 44 85/47 86/49 57 56 54 51/35 45 45 49 Soil surface (max./min.) 47/32 5 cm. below surface 35 15 cm. below surface 36 50 cm. below surface 40 PSE UDOTS UGA-TS UGA-GA ULTHERIA (westerly plots: Gl, G2) Air, at 1 m. (max./min.) 68/38 41 41 42 82/40 83/46 54 54 52 49/33 45 45 46 Soil surface (max./min.) 42/32 5 cm. below surface 35 15 cm. below surafce 36 50 cm. below surface 38 32 TABLE V— Concluded Association Temperature (°F.) Spring1 Summer2 Autumn3 Winter4 PSEUDOTSUGA-TSUGA-HYLOCOMIUM (easterly plots: M3, M4, M5) Air, at 1 m. (max./min.) Soil surface (max./min.) 5 cm. below surface 15 cm. below surface 50 cm. below surface (westerly plots: Ml, M2) Air, at 1 m. (max./min.) Soil surface (max./min.) 5 cm. below surface 15 cm. below surface 50 cm. below surface PSEUDOTSUGA-POLYSTICHUM (easterly plots: P3, P4, P5) Air, at 1 m. (max./min.) Soil surface (max./min.) 5 cm. below surface 15 cm. below surface 50 cm. below surface (westerly plots: PI, P2) Air, at 1 m. (max./min.) Soil surface (max./min.) 5 cm. below surface 15 cm. below surface 50 cm. below surface TH UJA-L YSICHITUM* (easterly plots: Ly2, Ly3) Air, at 1 m. (max./min.) Soil surface (max./min.) 5 cm. below surface 15 cm. below surface 50 cm. below surface 64/38 45 43 44 63/38 42 41 41 79/48 77/49 56 55 54 83/46 75/47 54 53 51 50/35 45 46 47 49/34 43 44 44 63/38 45 43 43 60/39 42 42 41 80/47 72/48 57 55 52 84/46 71/48 53 53 50 50/34 45 46 48 50/34 45 45 48 56/40 43 44 44 80/45 65/49 53 56 51 48/35 43 43 46 46/32 36 37 39 43/32 35 35 37 47/32 35 36 39 42/32 35 37 39 44/32 44 45 45 Measurements made early in April, May, and June. Measurements made early in July, August, and September. Measurements made early in October, November, and December. Measurements made early in January, February, and March. BSubsurface measurements were made at the same time as soil moisture was sampled. 6Plot Lyl was logged before sufficient temperature data had been recorded. months in the Fourth Lake Pseudotsuga-Tsuga-Hylocomium and Pseudotsuga- Polystichum Plots, presumably because both stands were adjacent to cut-over areas. Soil-surface layers did not remain frozen long enough to impede infiltration appreciably, even though monthly minima at the soil surface fell below 32° F. Upper soil horizons commonly had monthly minima as low as 34° F. in winter, but temperatures rarely dropped below 38° F. at depths of 50 or more centi- meters beneath the soil surface. While such temperatures have been shown to impede water uptake by plants (23), some water must always have been avail- able since subsurface soils were not frozen. 33 &H - o£ ^- 3 M S HW *^ hQ go O H Pm ^ a go p * Eh GO - ^3 «1P H J C«0 £# ^ £^ o# ^0 GO *H K< ^z SH oa tf Eh £* £~ 0 go ^2 tf H 0^ Ph h ^ >o H«! oh o <3lH o PS o p, > > < 5 cm. above ground <« OS >0 —. s — _ w 0 10 co CI CI o» < u s«^ O > 3 1 O CO CM h- 10 ^H 0 2 ° 0-0 b, 1 10 ~r -r n M co — el bC 2 . 0)T3 £ > 5 -Q P t^ 00 ^h CO 1 O Ci H -* DQ CM 5 5 o 2 40 * & d 0)T3 R > c ° O 3 2 =* & cdT3 O M d oTJ s > a O £ 3 2 * Sb fl > a •^ 2 ^ bC uo . CD"0 £ > S bfi "3 03 o O e3 CO -* »o »o -<*i •<* i 0; 13 f> a 0 3 III'-* 0 CO 7—1 0^) 0 — bJ3 1 1 1 TJH CO 00 CO 0 —1 a 10 •* o p < GO 53 o) m c n e? © c CI CS 0 a a bS CO CO m 0. 0 *8 -^ iJ a 8) 0 0 U u. CO CO O P. ft, t33to e e a a co co I I <3 ^ Cs Cs a a 09 CO a a co co ft, fts ft, .-^ O 1 a •& cu a co -c ft, E^ c o "5 GO c a> o. O a "3 "c 3 O o o W cy A c o bf! a "> c3 T3 a 03 CO c3 13 CD CO 02 . fe CM O-itj §"» .2h 1— 1 +- I C3 1—1 C >> >2 CD -3 _ o 3 CD ■£ a < 2 +3 34 Evaporation Evaporation rates were lowest in the moist Thuja-Lysichitum plots and highest at the Open Stations and in the open-canopied Pseudotsuga-Gaultheria- Peltigera plots (Table VI). That the high humidity associated with the swampy- soils of the Thuja-Lysichitum plots more than counterbalanced the openness of the tree canopy in these plots demonstrated the influence of soil moisture as well as canopy density on evaporation rates. Transpiration loss by the vegetation of subordinate plant layers was presumably similarly influenced, even though evaporation loss from atmometers has been shown to be somewhat disproportionately influenced by wind movement (3). Plots at higher altitudes commonly had lower evaporation rates than equivalent stands at lower elevations. Evaporation losses at the Fourth Lake Pseudotsuga-T 'suga-Hylocomium Plot, for example, were lower than those of the other plots of this association farther east at lower altitudes. Similarly, despite the openness of their tree canopies, evaporation rates in the Pseudotsuga-T suga- Gaultheria plots were among the lowest recorded. The relative frequency of a low cloud ceiling in the westerly portion of the study area in which these stands were located and the reduced insolation characteristic of north slopes, such as the one on which the Fourth Lake Plot was located, doubtless contributed to such conditions. On the other hand, the relatively high Echo Mountain Open Station had the highest rates of any station, apparently because it was located on a shoulder freely exposed to wind movement. Similarly, evaporation rates in the Fourth Lake Pseudotsuga-Polystichum Plot were higher than average for the association. This plot was exposed to abnormal air movement by its proximity to a cut-over area. The influence of a shrub canopy on evaporation was indicated by the rates from the atmometers 5 cm. above the ground. The Gaultheria shallon canopy apparently exerted an appreciable influence in reducing rates near ground line. At 1 m., rates in the Pseudotsuga-Gaidtheria plots were considerably higher than in the more densely canopied Pseudotsuga-T suga-Hylocomium stands. At 5 cm. the reverse was true. The absence of subordinate vegetation in Pseudo- tsuga-T suga-Hylocomium stands allowed unrestricted wind movement, and no shrub canopy was present to reduce insolation or raise humidities by transpiration. The highest evaporation rates occurred in July (Table VII). Rates during the first half of both July and August, 1952, were nearly double those of the TABLE VII AVERAGE MONTHLY EVAPORATION FROM LIVINGSTON ATMOMETERS AT 100 CM. ABOVE THE GROUND IN PLOTS REPRESENTATIVE OF FOREST ASSOCIATIONS IN THE NANAIMO RIVER VALLEY, BRITISH COLUMBIA, JUNE THROUGH SEPTEMBER, 1951-52 Association Pseudotsuga-Gaultheria-Peltigera Pseudotsuga-Gaultheria Pseudotsuga- T suga-Hylocomium Pseudotsuga-Tsuga-Gaultheria. . . Pseudotsuga-Polystichum Thuja-Lysichitum June 52 46 38 34 34 28 Relative Evaporation* July 68 59 53 44 43 39 August 58 47 43 39 36 32 September 45 33 33 30 28 26 *Actual evaporation expressed as a percentage of the largest value recorded (836 ml., from a standard Livingston atmometer at the Echo Mountain Open Station for the period July 1-15, 1952). 35 second half of each month. During these latter periods, rainfall occurred and cloudy days were more common. Such a difference in rates showed that tran- spiration usage during the Warm, dry summers characteristic of the study area would be considerably higher than in moister, cooler climates outside the rainshadow /one Soils Profile Cluiracteristics l's( udotsugar-Gaultheria-Peltigera association 1 1 profiles in the Pscudotsuga-Gaultheria-Peltigera plots were usually -hallow, being terminated by bedrock or an ortstein layer less than 50 to 70 cm. below the surface (Table VIII, Fig. 13 A and C). Most profiles were gravelly •md angular cobbles and small boulders were numerous. Clinker-like and shotty concretions were also common. In many samples, the 2-mm. fraction made up less than 50 per cent of the 25-mm. fraction and the 2-mm. fraction itself was coarse-textured. Such characteristics resulted in profiles with small moisture storage capacities. The infrequency of mottling in any layer showed the soils of these plots to be little affected by seepage moisture. Figure 13 — Typical soil profiles from plots representative of forest associations in the Nanaimo River valley, British Columbia. The scale is marked in decimeters. A. The Pseudotsuga-Gaul- theria-Peltigera association (Plot LI at Fourth Lake). B. The Pseudotsuga-Tsuga-Gaultheria associ- ation (Plot Gl at Fourth Lake). C. The Pseudotsuga-Gaultheria-Peltigera association (Plot L3 at Dead wood Creek). D. The Pseudotsuga-GaiCltheria association (Plot G6 at Deadwood Creek). E. The Pseudotsuga-Tsuga-Hylocomium association (Plot M5 at Wolf Mountain). F. The Pseudotsuga- Polystichum association (Plot PI at Fourth Lake) . G. The Pseudotsuga-Polystichum association (Plot P3 in the Valley area). H. The Pseudotsuga-Polystichum association (Plot P2 at Echo Mountain). I. The Pseudotsuga-Polystichum association (Plot P5 at Wolf Mountain). J. The Thuja-Lysichitum association (Plot Ly3 at Wolf Mountain). The mor-type humus and quite strongly acidic soil pH values of the Pseudo- tsuga-Gaultheria-Peltigera plots indicated the relative infertility of their soils. The weak definition of A2 horizons, nevertheless, suggested that leaching was less intense than on some moister sites. 36 Profiles in the easterly Plots (L2, L3, L4, and L5) resembled the Shawnigan series described by Day, Farstad, and Laird (10). Most profiles in the Fourth Lake Plot (LI), however, corresponded more closely to the Quinsam series (10). In the moister climate of this westerly portion of the study area, soil colors were brighter and A2 horizons deeper than in the more easterly Pseudotsuga-Gaultheria- Peltigera plots. The gravel content of most profiles examined in Plot LI was also lower than that in the other plots of this association. Pseudotsuga-Gaultheria association The greater depth of material above the ortstein layer in the Pseudotsuga- Gaultheria plots resulted in somewhat larger soil-moisture storage capacities than those of the Pseudotsuga-Gaultheria-Peltigera plots (Table VIII, Fig. 14), even though stones and angular cobbles were equally common and the 2-mm. fraction made up scarcely 50 per cent of the 25-mm. fraction. Moreover, some mottling was usually present in deeper horizons. Such mottling, together with the stronger color of the dappled, reddish-yellow coatings on cobble and gravel particles showed that the soils of the Pseudotsuga-Gaultheria plots were some- what more influenced by seepage moisture than those of the Pseudotsuga- Gaultheria-Peltigera plots. TABLE VIII TYPICAL SOIL PROFILES IN PLOTS REPRESENTATIVE OF FOREST ASSOCIATIONS • IN THE NANAIMO RIVER VALLEY, BRITISH COLUMBIA PSEUDOTSUGA-GAULTHERIA-PELTIGERA ASSOCIATION Lower D eadwood Creek A0F 3-2 cm. H 2-0 cm. A2 0-2 cm. B 2-10 cm. B B B Ortstein 10-20 cm. 20-55 cm. 55-70 cm. 70+cm. Fourth Lake (Plot Ll) A0 F 2-1 cm. H 1-0 cm. A2 0-2 cm. B 2-20 cm. (Plot L3) Very dark brown (10 YR 2/2)* partially decomposed litter; pH4.9. Black (10YR 2/1) granular to felty mor, up to 4 cm. thick among surface cobbles; pH 5.0; roots common. Gray (5Y 6/1) sandy loam; weak fine subangular blocky structure; very friable; pH 4.9. Brown (10 YR 5/3) gravelly sandy loam, with angular cobbles in places very numerous; weak fine subangular blocky structure; loose; numerous shotty concretions, with yellowish red (5YR 5/8) coatings; light, dappled, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.7; roots common. Light yellowish brown (10YR 6/4) gravelly sandy loam, with angular cobbles; weak fine subangular blocky structure; very friable; shotty concretions; dappled, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.6; roots common. Pale brown (10YR 6/3) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable; shotty concretions; dappled, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.7; roots moderately common. Pale olive (5YR 6/3) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable, becoming weakly cemented with increasing depth; numerous light olive gray (5Y 6/2) clinker-like concretions, with yellowish red (5YR 5/8) staining; dappled, yellowish red (5YR 5/8) coatings on cobbles and gravel; pH 5.9; roots sparse, although fine roots common above the ortstein layer. Light olive gray (5Y 6/2) gravelly sandy loam; irregular thick platy structure; cemented; reddish yellow (5YR 6/8) staining, particularly in the upper part; pH 6.2; roots absent. Very dark brown (10YR 2/2) partially decomposed litter. Black (10YR 2/1) felty mor; pH 4.9; roots common. Light gray (5Y 7/1) loam, varying from less than 1 cm. to 5 cm. thick among surface cobbles; weak fine subangular blocky structure; pH 4.5; roots common. Red (2.5YR 4/6) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; friable; shotty concretions, with yellowish red (5YR 5/8) coatings; dappled, yellowish red (5YR 5/6) coatings on cobbles and gravel; pH 5.1; roots common. 37 TABLE \ III— Continued PSEl DOTSl <, AC AULTHERI A-PELTIGERA ASSOCIATION— Concluded Foubth Laki (Plot LI)— Concluded B 20 •".") cm. Yellowish red (SYR 5/0) gravelly sandy loam, with scattered angular cobbles; weak line Bubangular blocky structure; friable; shotty con- cretions; dappled, yellowish red (5YR 5/8) coatings on cobbles and gravel; pll 5.2; roots moderately common. H 35-55 cm. Reddish yellow (5YR 6/8) gravelly sandy loam, weak fine to medium subangular blocky structure; friable; dappled, reddish yellow (5YR 6/8) coatings on cobbles and gravel; scattered, faint blue (7.5BG 7/2) mottling; pH 5.3; roots sparse, although numerous on rock surface, commonly forming a mat; fine dead roots present. D 55+ cni. Rock, seepage water occasionally present. PSEUDOTSUGA-G AULTHERI A ASSOCIATION Upper Dead wood Creek (Plot G6) Ao F 4-2 cm. Very dark brown (10YR 2/2) partially decomposed litter. H 2-0 cm. Very dark brown (10YR 2/2) felty mor; pH 5.2; roots common. A2 0-1 cm. Dark gray (10 YR 4/1) sandy loam; thicker among surface cobbles; weak fine subangular blocky structure; very friable; pH 4.8; roots common. B 1-10 cm. Brown (10YR 5/3) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable; numerous shotty concretions, with reddish yellow (7.5YR 6/6) coatings; dappled, red- dish yellow (7.5YR 6/6) coatings on cobbles and gravel;' pH 5.7; roots common. B 10-25 cm. Pale brown (10YR 6/3) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable; shotty concretions very numerous; dappled, reddish yellow (7.5 YR 6/6) coatings on cobbles and gravel; pH 5.7; roots common. B 25-50 cm. Light yellowish brown (2.5Y 6/4) gravelly loam, with angular cobbles; weak fine subangular blocky structure; very friable; numerous shotty 1 concretions; light yellowish brown (2.5Y 6/4) clinker-like concretions, with reddish yellow (7.5YR 6/8) staining; dappled, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.9; roots moderately common. B 50-80 cm. Pale olive (5Y 6/3) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; firm to weakly cemented with increasing depth; clinker-like concretions common, becoming numerous towards the ortstein layer; dappled, reddish yellow (5YR 6/8) coatings on cobbles and gravel; reddish yellow (5YR 6/8) staining common above the ortstein; pH 6.2; roots sparse, but fine roots common just above the ortstein. Ortstein 80+cm. Olive gray (5Y 5/2) gravelly sandy loam; irregular thick platy structure; cemented; yellowish red (5YR 5/8) staining, prominent in the upper portion; pH 6.5; roots absent. PSEUDOTSUGA-TSUGA-GA ULTHERIA ASSOCIATION Echo Mountain (Plot G2) Ao F 5-3 cm. Very dark brown (10YR 2/2) partially decomposed litter. H 3-0 cm. Very dark brown (10YR 2/2) to black (10YR 2/1) felty mor; pH 4.6; roots forming dense network. A2 0-4 cm. Light gray (10YR 7/1) gravelly sandy loam, in places up to 10 cm. thick among surface cobbles; upper parts often including bleached humus; weak fine subangular blocky structure; very friable; shotty concretions; pH 4.6; roots numerous. B 4-35 cm. Strong brown (7.5YR 5/8) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable; shotty concretions common, sometimes with heavy, red (2.5YR 4/8) coatings; dappled, yellowish red (5YR 5/8) coatings on cobbles and gravel; scattered, faint, yellowish red (5YR 5/8) mottling; pH 5.5; roots com- mon. J3 35-55 cm. Yellowish brown (10YR 5/6) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; very friable; shotty concretions common; dappled, faint, reddish yellow (7.5YR 6/8) coat- ings on cobbles and gravel; pH 5.7; roots moderately common. 38 TABLE VIII— Continued PSEUDOTSUGA-TSUGA-GA ULTHERIA ASSOCIATION— Concluded Echo Mountain (Plot G2) — Concluded B 55-75 cm. Light yellowish brown (10YR 6/4) gravelly sandy loam, with numerous angular cobbles; weak fine to medium subangular blocky structure; friable; dappled, reddish yellow (7.5YR 6/8) coatings on cobbles; pH 5.4; roots sparse, although more numerous on rock surface, commonly forming a mat. D 75+cm. Rock; seepage water occasionally present. (In some profiles the B horizon merged into the D horizon; in others the root zone was terminated by an ortstein layer). PSE UDOTS UGA-TS UGA-H YLOCOMI UM ASSOCIATION Valley (Plot M3) F H 3-2 2-0 cm. cm. Ortstein 0-2 cm. 2-20 cm. 20-45 cm. 45-75 cm. 75-100 cm. 100+cm. Fourth Lake (Plot Ml) Ao F 7-5 cm. H 5-0 cm. A, 0-6 cm. B 6-6.5 cm. B 6.5-20 cm. B 20-40 cm. B 40-65 cm. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.3, Very dark brown (10 YR 2/2) to black (10YR 2/1) felty mor; pH 5.2; roots moderately common. Gray (10 YR 2/1) sandy loam, up to 10 cm. thick among surface stones; weak fine subangular blocky structure; very friable; pH 5.0; roots common. Brown (10YR 5/3) gravelly sandy loam, with numerous angular cobbles and stones; weak fine subangular blocky structure; very friable; shotty concretions common; faint, strong brown (7.5YR 5/8) coatings on cob- bles, gravel and shot; pH 5.5; roots common. Yellowish brown (10YR 5/6) gravelly sandy loam, with angular cobbles weak fine subangular blocky structure; very friable; shotty concretions occasional pale olive (5YR 6/3) clinker-like concretions, with yellowish red (5YR 5/6) staining; dappled, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.3; roots moderately common. Yellowish brown (10YR 5/6) gravelly loamy sand, with angular cobbles; weak fine subangular blocky structure; friable; shotty concretions; clinker-like concretions more common; strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 5.8; roots sparse. Yellowish brown (10YR 5/8) gravelly loamy sand, with scattered angular cobbles; weak fine subangular blocky structure; becoming weakly cemented; shotty concretions; clinker-like concretions nearly continuous; strong brown (7.5YR 5/8) coatings and mottling; faint bluish (7.5BG 7/2) mottling; pH 5.4; roots sparse. Olive gray (5Y 5/2) gravelly sandy loam; irregular thick platy structure; cemented; yellowish red (5YR 4/8) staining; no roots. Very dark brown (10YR 2/2) partially decomposed litter; pH 4.7. Very dark brown (10 YR 2/2) to black (10 YR 2/1) felty mor; pH 4.2; roots numerous. In places the surface horizon consisted of up to 15 cm. of decayed wood. Light brownish gray (2.5Y 6/2) sandy loam; up to 15 cm. thick under decayed wood; weak fine subangular blocky structure; very friable; pH 4.3; roots common. Dark reddish brown (5YR 3/4) loam; discontinuous. Reddish brown (5YR 5/4) gravelly sandy loam, with angular cobbles and stones; weak fine subangular blocky structure; very friable; shotty concretions with yellowish red (5YR 5/8) coatings; dappled, yellowish red (5YR 5/8) coatings on cobbles and gravel; pH 5.3; roots common. Reddish brown (5YR 5/4) gravelly sandy loam, with angular cobbles; weak fine subangular blocky structure; friable; shotty concretions common; occasional light yellowish brown (2.5Y 6/4) clinker-like con- cretions, with heavy, yellowish red (5YR 4/8) staining; heavy, dappled reddish yellow (5YR 6/8) staining on cobbles and gravel; pH 5.3; roots common. Brown (7.5YR 5/4) gravelly sandy loam, with angular cobbles and stones; weak fine subangular blocky structure; friable; shotty concretions; clinker-like concretions more common; heavy dappled, yellowish red (5YR 5/8) staining on cobbles and gravel; faint bluish (7.5BG 7/2) mottling; pH 5.3; roots moderately common. 39 TABLE XIII Continued 1st (, l TSl i, \ -IIYLOCOMIUM ASSOCIATION— Concluded rth 1.\kk PIo1 M l ( 'oncluded It ( ktstein 0 nu. 904-cm. Lower Deadwood (Plot M4) 1' H 3-2 2-0 0-1 cni. cm. B B B B B 1-10 cm. 10-20 cm. 20-40 cm. 40-70 cm. 70-100 cm. Echo Mountain (Plot M2) A0F 2-1 cm, H 1-0 cm A2 0-1 cm, B B B(G) 1-20 cm. 20-40 cm. 40-75 cm. 75-100 cm. Wolf Mountain (Plot M5) AoF 2-1 cm H 1-0 cm, A2 0-1 cm, B 1-10 cm Yellowish brown (10YR 5/6) gravelly Bandy loam, with angular cobbles and stones; weak line t<> medium subangular blocky structure; [liable; shotty concretions; clinker-like concretions numerous; heavy, dappled _\ ellowish led (."> Y I! ."> S i coat iii^s on cobbles and gravel; scat teied bluish (7.5BG 7/2) mottling; pll 5.7; roots Bparse, although One roots common above ortstein layer. Olive gray (5Y 5/2) gravelly sandy loam; irregular thick platy structure; cemented; yellowish red (5YR4/8) staining; no roots. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.3. Black (10 YR 2/1) felty mor; pll 5.5; roots common. Gray (10YR 5/1) sandy loam, often thin but well defined; weak fine subangular blocky structure; very friable; pH 5.6. Brown (7.5YR 5/4) gravelly loamy sand, with angular cobbles; weak subangular blocky structure; very friable; numerous shotty concretions; faint, strong brown (7.5 YR 5/8) coatings on cobbles, gravel, and shot; pH 6.0; roots common. Yellowish brown (10 YR 5/4) gravelly loamy sand, with scattered cobbles; weak fine subangular blocky structure; very friable; numerous shotty concretions; faint, strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; pH 6.0; roots common. Yellowish brown (10YR 5/6) gravelly sandy loam, with scattered cobbles and stones; weak fine subangular blocky structure; very friable; shotty concretions common; light yellowish brown (2.5Y 6/4) clinker-like concretions, with faint, strong brown (7. SYR 5/8) staining; faint, strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; very slight bluish (7.5BG 7/2) mottling; pH 6.0; roots moderately common. Yellowish brown (10 YR 5/8) gravelly loamy sand, with scattered cobbles; weak fine subangular blocky structure; very friable; shotty and clinker- like concretions common; faint, strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; pH 6.7; roots sparse. Light yellowish brown (2.5Y 6/4) gravelly loamy sand, with cobbles; very weak granular structure; loose; cobbles and gravel largely unstained pH 6.2; roots sparse. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.2. Very dark brown (10YR 2/2) felty mor; roots moderately common. Dark gray (10 YR 4/1) sandy loam, in places poorly defined; weak fine subangular blocky structure; very friable; pH 5.7. Yellowish red (5YR 5/8) gravelly sandy loam, with angular cobbles; weak fine subangular blocky structure; friable; shotty concretions com- mon; dappled, strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; pH 5.6; roots common. Yellowish red (5YR 5/8) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; friable; shotty concre- tions; strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; pH 5.9; roots common. Strong brown (7.5YR 5/6) gravelly sandy loam, with scattered angular cobbles; weak fine subangular blocky structure; friable; shotty con- cretions; strong brown (7.5YR 5/8) coatings on cobbles, gravel, and shot; pH 5.9; roots sparse. Yellowish brown (10YR 5/6) gravelly sandy clay loam, with stones and angular cobbles; medium subangular blocky structure; firm; strong brown (7.5YR 5/8) coatings on cobbles and gravel; faint bluish (7.5BG 7/2) mottling; pH 5.7; roots sparse. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.5. Black (10 YR 2/1) duff mull; pH 5.5; roots moderately common. Very dark brown (10YR 2/2) loam; weak crumb structure; friable; pH 5.7; roots moderately common. Red (2.5YR 4/6) loam; weak medium subangular blocky structure; friable; shotty concretions, with yellowish red (5YR 5/6) coatings; diffuse, yellowish red coatings on gravel; pH 6.4; roots common. 40 TABLE VIII— Continued PSE UDOTS UGA-TS UGA-H YLOCOMI UM ASSOCIATION— Concluded Wolf Mountain (Plot M5) — Concluded B B B D 10-20 cm. Yellowish red (5YR 4/6) sandy loam; weak fine subangular blocky struc- ture; friable; numerous shotty concretions; yellowish red (5YR 5/6) coatings on gravel and shot; pH 6.5; roots common. 20-45 cm. Yellowish red (5YR 5/6) sandy loam; weak fine subangular blocky struc- ture; friable; numerous shotty concretions; yellowish red (5YR 5/6) coatings on gravel and shot; pH 6.4; roots moderately common, 45-70 cm. Yellowish brown (10YR 5/8) sandy loam; weak fine subangular blocky structure; friable; shotty concretions; scattered, red (2.5YR 5/8)coatings on gravel; pH 6.1; roots moderately common. 70-100 cm. Light olive brown (2.5Y 5/4) sandy loam; weak fine subangular blocky structure; friable to firm; red (2.5 YR 5/7) coatings on gravel and scat- tered red staining above compact horizon below; faint, bluish (7.5BG 7/2) cast and weak, red mottling; pH 6.3; roots sparse, although some fine roots present just above the compact horizon. 100-130 cm. Pale olive (5Y 6/4) sandy loam; weak medium subangular blocky struc- ture; firm to weakly cemented; compact; diffuse, red (2.5YR 5/8) coatings on gravel; red staining and mottling; pH 6.1; roots absent. PSE UDO TS UGA-POL YSTICH UM ASSOCI ATIO N Upper Deadwood Creek (Plot P4) Very dark brown (10YR 2/2) partially decomposed litter; pH 5.5. Black (10YR 2/1) duff mull to granular mor; pH 5.2; roots common. Black (10 YR 2/1) sandy loam, somewhat discontinuous; crumb structure; friable; roots numerous. Dark reddish brown (SYR 3/3) gravelly sandy loam, with occasional rounded cobbles; weak fine subangular blocky structure; friable; scat- tered shotty concretions; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles; pH 6.3; roots common. Yellowish brown (10 YR 5/6) sandy loam, with occasional rounded gravel and cobbles; weak fine subangular blocky structure; friable; scattered shotty concretions; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles; pH 6.3; roots common. Yellowish brown (10YR 5/8) sandy loam, with occasional rounded gravel and cobbles; very weak fine subangular blocky structure; very friable; scattered shotty concretions; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 6.1; roots common. Gray and brown sand, rounded gravel and cobbles; single grain structure; loose; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles and gravel; roots sparse. Strong brown (7.5YR 5/6) gravelly sandy loam, with scattered rounded coarse gravel and cobbles; weak fine subangular blocky structure; very friable; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 6.4; roots moderately common. Yellowish brown (10 YR 5/7) gravelly loamy sand, with scattered rounded coarse gravel and cobbles; very weak fine subangular blocky structure; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 6.3; roots sparse. Light yellowish brown (2.5Y 6/4) gravelly loamy sand, with scattered rounded coarse gravel and cobbles; very weak fine subangular blocky structure; very friable; scattered, faint, strong brown (7.5YR 5/8) coatings on cobbles and gravel; pH 6.2; roots very sparse. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.0. Very dark brown (10YR 2/2) felty mor; pH 4.5; roots common. Reddish brown (5YR 5/3) sandy loam; weak fine subangular blocky structure; friable; shotty concretions; roots common; this horizon merges into the next. B 1-4 cm. Yellowish red (5YR 5/6) gravelly sandy loam, often discontinuous; weak fine subangular blocky structure; friable; numerous shotty concretions, with heavy, yellowish red (5YR 5/8) coatings; roots common. B 4-20 cm. Yellowish red (5YR 4/6) gravelly sandy loam, with scattered angular cobbles; weak fine to medium subangular blocky .structure; friable; numerous shotty concretions; scattered, reddish yellow (SYR 6/8) coatings on gravel and shot; pH 5.3; roots common. A0F 3-2 cm. H 2-0 cm. Ai 0-1 cm. B 1-10 cm. B 10-20 cm. B 20^0 cm. B 40-50 cm. B 50-75 cm. B 75-100 cm. B 100-130 cm. Fourth Lake (Plot PI) A0F 4-3 cm. H 3-0 cm. A2 0-1 cm. 41 T \BIJ". \ III Continued h()TSUGA-POL YSTICHUM ASSOCIATION— Continued i\\ L\ki Plot PI)— B cm B B B i."> 75 cm. 75-100 cm. 100-120 cm. Echo Mountain (Plot P2) Ao F 8-6 cm. H 6-0 cm. B B B B B 0-1 cm. 1-3 cm. 3-10 cm. 10-20 cm. 20-50 cm. 50-75 cm. Ortstein 75 4- cm. Wolf Mountain (Plot P5) AoF 3-2 cm. Hx 2-1 cm. H2 1-0 cm. A2 0-1 cm. B 1-2 cm. B 2-10 cm. B 10-25 cm. B 25-40 cm. B 40-70 cm. Concludt (I Strong brown (7.5YR 5/6) gravelly Loam, with scattered angular cobbles; weak medium Bubangular blocky structure; friable; shotty concretions; Bcattered, reddish yellow (SYR (i/8) coatings on gravel and shot; pH 5.6; roots moderately common. Yellowish brown (10YR 5/6) gravelly loam, with scattered angular cob- bles; weak medium subangular blocky structure; friable; diffuse, red- dish yellow (5YR 6/8) coatings on cobbles and gravel; pH 5.8; roots common. Yellowish brown (10YR 5/8) gravelly loam, with scattered stones and angular cobbles; weak medium to coarse subangular blocky structure; firm; faint, dappled, yellowish red (5YR 5/8) coatings on gravel and cobbles; pH 5.9; roots sparse. Light yellowish brown (2.5Y 6/4) gravelly loam, with stones and angular cobbles; weak coarse subangular blocky structure; slightly plastic when moist; very firm when dry; dappled, yellowish red (5YR 5/8) coatings on cobbles and gravel; pH 5.6; roots sparse. Very dark brown (10YR 2/2) partially decomposed litter; pH 5.4. Very dark brown (10YR 2/2) duff mull to felty mor; often includes dark reddish brown (2.5YR 3/4) woody peat from decayed wood; where peat absent humus about 2 cm. deep; pH 5.4; roots common. Dark reddish gray (5YR 4/2) loam; under peaty decayed wood, this horizon may be up to 10 cm. thick; weak fine subangular blocky struc- ture; friable; roots common. Dark red (2.5YR 3/6) sandy loam; weak fine subangular blocky structure; friable; shotty concretions with heavy, red (2.5YR 5/8) coatings; dappled, yellowish red (5YR 5/8) coatings on gravel; pH 5.6; roots numerous. Red (2.5YR 4/8) sandy loam; weak fine to medium subangular blocky structure; numerous shotty concretions; yellowish red (5YR 5/8) coat- ings on gravel and shot; pH 5.9; roots common. Yellowish red (5YR 4/8) sandy loam; weak fine to medium subangular blocky structure; friable; numerous shotty concretions; yellowish red (5YR 5/8) coatings on gravel and shot; pH 6.1; roots common. Yellowish red (5YR 4/8) sandy loam; weak fine to medium subangular blocky structure; friable; shotty concretions; yellowish red (5YR 5/8) coatings on gravel and shot; pH 6.0; roots moderately common. Red (2.5YR 4/6) sandy loam; weak fine to medium subangular blocky structure; friable; shotty concretions; diffuse, yellowish red (5YR 5/8) coatings on gravel; roots sparse. This horizon is commonly below the water table; pH 6.1. Olive gray (5Y 5/2) sandy loam; irregular thick platy structure; cemented; prominently mottled with yellowish red (5YR 5/8) on exposure to air; roots absent. Very dark brown (10YR 2/2) partially decomposed litter. Very dark brown (10YR 2/2) felty mor; roots common. Black (10YR 2/1) granular duff mull; roots common. Dark gray brown (10 YR 4/2) loam, often discontinuous and poorly denned; weak fine subangular blocky structure; friable; roots common. Dark reddish brown (5YR 3/2) loam, often discontinuous; weak fine subangular blocky structure; friable; roots common. Dark red (2.5YR 3/6) sandy loam; weak fine to medium subangular blocky structure; friable; numerous shotty concretions with yellowish red (5YR 5/8) coatings; pH 6.0; roots numerous. Red (2.5YR 4/8) sandy loam; weak fine to medium subangular blocky structure; friable; numerous shotty concretions, with yellowish red coatings; pH 6.2; roots common. Yellowish red (5YR 5/6) sandy loam; weak fine subangular blocky struc- ture; friable; shotty concretions common; pH 6.1; roots common. Yellowish brown (10 YR 5/7) gravelly sandy loam; weak fine subangular blocky structure; friable; occasional shotty concretions with bright, yellowish red (5YR 5/8) coatings; scattered, faint, yellowish red (5YR 5/8) coatings on gravel; scattered, distinct, yellowish red (5YR 5/8) mottling; pH 6.1; roots sparse. 42 TABLE VIII— Concluded PSEUDOTSUGA-POL Y STIC HUM ASSOCIATION— Concluded Wolf Mountain (Plot P5) G 70-100 cm. Valley (Plot P3) AoF 1.5-0.5 cm. H 0.5-0 cm. Aj 0-2 cm. B B B B 2-3 cm. 3-8 cm. 8-20 cm. 20-50 cm. 50-70 cm. 70-100 cm. -Concluded Light olive gray (5Y 6/2) gravelly sandy loam, with occasional rounded cobbles; fine to medium subangular blocky structure; firm; compact; gleyed; scattered, faint, yellowish red (5 YE, 5/8) coatings on gravel; occasional yellowish red (5YR 5/8) mottling; pH 6.5; roots very sparse. Very dark brown (10YR 2/2) partially decomposed litter. Very dark brown (10YR 2/2) duff mull; pH 5.1; roots common. Black (10 YR 2/1) loam; weak fine to medium crumb structure; friable; pH 5.2; roots common. Very dark brown (10YR 2/2) loam; fine subangular blocky structure; friable; occasional shotty concretions; roots common. Dark brown (10YR 3/3) loam; weak fine subangular blocky structure; friable; occasional shotty concretions; pH 5.6; roots common. Dark yellowish brown (10 YR 4/4) sandy loam; very weak fine subangular blocky structure; very friable; pH 5.4; roots common. Yellowish brown (10 YR 5/6) sandy loam; very weak fine subangular blocky structure; very friable, with bands of loose sand; pH 6.2; roots moderately common. Dark yellowish brown (10YR 4/4) loam; weak fine subangular blocky structure; very friable; pH 6.0; roots common. This horizon may be the upper part of a buried profile. Light gray and brown, raw, river gravel and sand; single grain structure; loose; occasional, light, dappled, strong brown (7.5YR 5/8) coatings on gravel; pH 6.2; roots very sparse. THUJA-LYSICHITUM ASSOCIATION Wolf Mountain (Plot Ly3) A: Swamp 0-1 cm. 1-20 cm. 20-23 cm. 23-35 cm. B: Banks . \nd Hummocks 0-1 cm. 1-2 cm. 2-20 cm. 20-40 cm 40 + cm. Moss and debris (needles, twigs, wood fragments). Black muck; water level varying from 0 to 10 cm. below the moss layer; pH 5.6. Olive gray (5Y 4/2) mucky sandy loam; firm; compact; roots sparse (mostly Lysichitum). Olive gray (5Y 5/2) gleyed sandy loam; plastic; slightly sticky when wet; firm; compact; hard when dry; brown and yellowish red mottling (faint before exposure to air); pH 6.8; roots absent. Partially decomposed litter. Very dark brown (10YR 2/2) felty mor; pH 4.7. Dark red (2.5YR 3/6) fibrous peat; contains twig and wood fragments; roots forming a dense network. Very dark brown (10YR 2/2) to black muck; pH 4.2: roots sparse. Olive gray (5Y 5/2) gleyed gravelly sandy loam; upper portion heavily infiltrated with muck; slightly plastic; slightly sticky; firm; compact; hard when dry; water commonly running over the surface; pH 6.8; roots absent. *Color descriptions are according to the Munsell Soil Color Chart (Munsell Color Company, Inc., Baltimore, Maryland, U.S.A.) and refer to soils in the moist state. The greater depth of litter layers in the Pseudotsuga-Gaultheria plots seemed partly attributable to the forest floor being cooler and moister than in the P seudotsuga-Gaultheria-P eltigera plots. Although somewhat more productive than P seudotsuga-Gaultheria-P eltigera sites, the mor-type humus and acidic soil pH values of the Pseudotsuga-Gaultheria plots suggested that their soils were not particularly fertile. The deeper A2 horizons of the Pseudotsuga-Gaultheria plots indicated that leaching was more intense than in the Pseudotsuga-Gaultheria.^ Peltigera plots. 43 - ,1 profiles in the Wolf Mountain and Deadwood ("reck Plots (G4, G5, and were comparable with the Shawnigan Beries (10). On the other hand, most, profiles in the Valley Plol (G3) resembled the Sproal series (10), because their colors were brighter and their A., horizons more distincl than those of the more easterly plots. Ps< udotsuga-Tsuga-Gaulthi Ha associal ion Soil tlt^i>t li in most of the profiles examined in the Pseudotsuga-Tsuga- Gaultheria plots was limited by bedrock less than 80 cm. below the surface. Soil-moisture Btorage capacity was further limited by the frequency of small boulders, angular cobbles, and shotty and clinker-like concretions (Table VIII, Fig. 13 B). The occurrence of mottling nevertheless showed that the soils of these plots were affected by seepage moisture. The deep litter layers characteristic of the Pseudotsuga-Tsuga-Gaultheria plots were indicative of the cool and moist condition of the forest floor during much of the year. The mor character of these litter layers, the deep A2 horizons, and si rongly acidic soil pH values of these plots indicated the intensity of leaching and relative infertility of their soils. Soil profiles in the Pseudotsuga-Tsuga-Gaultheria plots corresponded to the Quisam series of Day, Farstad, and Laird (10). P seudotsuga-T suga-Hylocomium association Soil profiles in the typicum plots were characterized by their coarse texture and the clear differentiation of A2 horizons. In the Fourth Lake and Valley Plots (Ml and M3) up to 40 per cent of soil volume was occupied by small boulders, angular cobbles, and clinker-like concretions over 25 mm. in diameter. The last were particularly common toward the base of profiles. Mottling, indicative of the periodic occurrence of seepage moisture, was present in the lower profile of all soil pits examined on Plots Ml and M3 (Table VIII). However, seepage moisture in such coarse-textured profiles was probably less influential than in finer-textured soil because surface layers remained essentially unaffected and rapid internal drainage limited the duration of supplements to soil-moisture reserves. The deep A2 horizon and bright color of profiles in the Fourth Lake Plot (Ml) were characteristics that these profiles had in common with the Stamp series of Day, Farstad, and Laird (10). Such characteristics are typical of profile development in a wet climate. Soil profiles in Plot M3 were similar to the Sproat series (10), another soil developed under quite wet climatic conditions. The soils of Plot M4, being derived from coarse outwash material, resembled the Qualicum series (10). The shallow A2 horizon of such profiles is typical of soil development under relatively dry climatic conditions. In contrast to the typicum plots, soil profiles in the nudum plots were char- acterized by relatively fine soil textures and little or no development of A2 horizons. In the Wolf Mountain Plot (M5), the upper 90 to 100 cm. of the profile consisted of fine outwash material, nearly 90 per cent of which was included within the 5-mm. soil fraction (Fig. 13 E). While the soils of the Echo Mountain Plot (M2) contained angular cobbles and small boulders, clay contents were higher than those of soils in the typicum plots. Both plots consequently had quite high soil-moisture storage capacities. Downward percolation of water was restricted by a compact layer in the lower profile of both plots. The mottling present above this layer indicated the occurrence of high moisture contents during part of the year. Wilde (46) designates such profiles as gamma-gley soils. The occurrence of an Ax horizon with a crumb structure on Plot M5 was indicative of a relatively fertile soil. Even in Plot M2, litter layers were shallow 44 and the A2 horizon weakly defined. Both characteristics suggest that seepage moisture was relatively effective in ameliorating the leaching influence of the wet climate in this section of the study area (20). Most of the profiles examined on Plot M2 were comparable with the Alberni series, although those developed from relatively coarse material resembled the Stamp series more closely (10). Profiles in Plot M5 were similar to the Royston series (10). Pseudotsaga-Polystichum association While the soil parent-material and topographic position of the Pseudotsuga- Polystichum plots were diverse, profile development was such that the soils of all plots supported a similar vegetation type. Salient profile characteristics were the duff-mull character of litter layers, the weak differentiation of A2 horizons, and the moderate acidity of pH values, all features denoting relatively fertile soils. Furthermore, the fairly high proportion of fine material included in all profiles resulted in quite high soil-moisture storage capacities. The mottling evident in most profiles indicated that moisture reserves were also supplemented by seepage moisture. Soil profiles in Plot PI seemed typical of Pseudotsuga-Polystichnm sites developed under fairly wet climatic conditions. Despite the relatively high rainfall of this section of the valley, A2 horizons consisted of merely one or two centimeters of reddish-brown sandy loam (Table VIII, Fig. 13 F). The occur- rence of mottling in all horizons indicated that seepage moisture was influential even in surface layers, a characteristic of beta-gley soils (46). In addition to augmenting soil-moisture supply, this seepage presumably ameliorated the leaching action of the regional climate and limited the development of an A2 horizon. The clay-loam layer at the base of profiles limited the downward perco- lation of seepage moisture. Profiles in this plot were comparable to the Stamp series of Day, Farstad, and Laird (10). The Deadwood Creek Plot (P4), on stratified outwash material in the bottom of a wide U-shaped valley, represented Pseudotsuga-Polystichum stands growing on fertile soils under fairly dry climatic conditions. The presence of a black, loamy, Ai horizon with a crumb structure, indicated the relatively high fertility of the soil in this plot. Although some bleaching was present beneath piles of decayed wood, no A2 horizon had developed. Profiles in this plot were similar to the Qualicum series, although their predominantly yellowish-brown coloration showed that they also had an affinity with the Somas series (10). Soil profiles in Plots P2 and P5 were characteristic of soil development under the influence of a high water table. Profiles in Plot P5 (Table VIII, Fig. 13 I) resembled the Puntledge series of Day, Farstad, and Laird (10) in being comprised of a shallow loamy deposit overlaying an impervious gleyed layer which caused a high water table. In Plot P2 (Table VIII, Fig. 13 H), the presence of fine gravel and shotty concretions seemed to render the profile above the ortstein quite porous. No evidence of the gray coloration usually associated with gleization was apparent. This lack of gray color was attributed to the ease with which ground water moved through the profile, a feature these soils had in common with the Bowser series (10). Soil profiles in Plot P3 (Table VIII, Fig. 13 G) were typical of soil develop- ment on fertile alluvial benches. Most profiles included an Ai horizon, and A2 horizons occurred only beneath piles of decayed wood. The B horizon, which intergraded from a very dark-brown loam to a yellowish-brown sandy loam, contained almost no material larger than 2 mm. in diameter. The soils of this plot corresponded to the Chemainus series (10). 45 Thuja-Lysichitum association The ThujOrLysichUum plots occurred where seepage water came to the surface and the resulting streamlets spread out to form swamps. That such swamps were no1 stagnant and infertile wras shown by their circumneutral pll values (Table VIII) and the slowly moving water which trickled through them. Profiles within the swampy areas consisted of varying depth of black muck, underlain by an olive gray, gleyed, sandy-loam layer (Fig. 13 J). Before exposure to the air, bluish mottling was predominant, indicating that this layer was continuously submerged. Tree roots were not encountered in the swampy parts of these plots. Swampy areas were bordered by hummocks and banks of partially de- composed litter and wood, underlain by layers of very dark-brown, felty mor and reddish-brown, fibrous peat. These layers were densely interwoven by Thuja plicata roots. Tree roots, however, rarely extended into the gleyed, gravelly material below the peaty layers. Moisture Regimes Weather patterns during the soil-moisture sampling period were generally in accord with average values, although some variation did occur (Appendix II). In 1951, for example, below-average rainfall from April until the end of August accentuated the normal summer drought. At Cassidy, 12 miles to the east of Deadwood Creek, rainfall during this period was only 2.88 in. compared with an average of 10.75 in. Even Nitinat Camp in the central mountainous region recorded only 6.60 in., compared writh the 16.44 in. normally received. In 1952, the summer drought period extended into autumn longer than usual. Rainfall at Deadwood Creek during September and October was only 1.3 in. as compared with the 7.5 in. average, and only 5.0 in. were recorded at Fourth Lake, consider- ably less than the average of 16.4 in. for this period. During the winter of 1952-53 temperatures were more moderate than usual and most precipitation fell as rain. Precipitation during December and January was unusually heavy. Deadwood Creek received 31.9 in. during this period compared with an average of 20.6 in. and the Echo Mountain value of 47.8 in. was 18 in. more than usual. Precipitation was also somewhat greater than normal during June and July, 1953, and temperatures were below average. Pseudotsuga-Gaultheria-Peltigera association Depletion of soil-moisture reserves in the Pseudotsuga-Gaultheria-Peltigera plots began in May and continued throughout the growing season (Table IX, Fig. 14). In 1951 and 1952, available soil moisture in the Wolf Mountain, Deadwood Creek, and Valley Plots was reduced to very small amounts at all depths by early July. Although the summer of 1953 was somewhat wetter than usual, low percentages were still recorded by August. Soil-moisture deficits in the Fourth Lake Plot (LI) were less marked than they were in the easterly plots, even during the dry summers of 1951 and 1952. Appreciable reduction in soil-moisture content had not occurred below the surface layers of the relatively fine-textured profile sampled in Plot LI during early September, 1952, although values were quite low in the coarse-textured profile sampled during August. Even litter layers in the westerly plots had shorter periods of desiccation than in the stands farther east. It was noted, for example, that early September rainfall in 1951 was sufficient to re-wet litter layers in the Fourth Lake and Valley Plots, although these layers in the Deadwood Creek and Wolf Mountain Plots remained below wilting percentage until the end of the month. 46 Pseudotsuga-Gaultheria association Available soil moisture was not depleted as early in the growing season in the Pseudotsuga-Gaultheria plots as it was in the Pseudotsuga-Gaultheria- Peltigera stands. Marked reductions were nevertheless evident by July and amounts of available moisture remained small until replenished by the autum- nal rains. As in the P seudotsuga-Gauliheria-P eltigera association, litter layers remained below wilting percentage during much of the growing season. Such desiccation presumably decreased the effectiveness of summer rainfall, since litter layers might absorb nearly 1 cm. of water before horizons containing appreciable numbers of plant roots were re-wet. The importance of vegetation in moisture depletion was evident from the data for Plots G4 and G6 (Table IX). During the autumn of 1952 these plots were swept by ground fires which removed all the subordinate vegetation and, on Plot G6, killed some trees. In 1953, moisture deficits in these disturbed plots were small, even though soil-moisture depletion had been as great as it was in other plots of the Pseudotsuga-Gaultheria association (Plots G3 and G5) during the previous growing season. After periods of heavy rainfall in late autumn, temporary water tables were common above hardpan layers and high moisture percentages were recorded at all depths. When Plot G6 was sampled in early December, 1951, this perched water table above the ortstein layer was 10 cm. deep. On resampling in early January, 1952, some two weeks after a heavy snowfall had covered the ground, there was no gravitational water above the hardpan and the moisture per- centage of all layers was lower. Presumably, such a reduction in moisture content occurred because internal drainage in these gravelly, shotty soils was rapid, and excess moisture quickly drained away once further addition of water was prevented by the snow blanket. During the winter of 1952-53, perched water tables were present more or less continuously since there was little snow or frozen soil to restrict infiltration of the abnormally heavy rainfall of December and January. Pseudotsuga- Tsuga-Gaultheria association Soil-moisture values in the Pseudotsuga-Tsuga-Gaultheria plots were high in the available range during the early part of the growing season. Even litter layers contained available moisture at most samplings. Low values, particularly in the upper 20 cm., were recorded in July, 1951, and August, 1952, although periods with small amounts of available soil moisture were of shorter duration than in the droughty Pseudotsuga-Gaultheria plots. Pseudotsuga- T suga-Hylocomium association Available soil moisture was virtually exhausted from the surface layers of the easterly subassociation typicum plots of the P seudotsuga-T suga-Hylocomium association during the late summer of 1951 and 1952. The moisture content of deeper layers was also reduced to small amounts by the latter part of these growing seasons. This depletion was particularly marked in Plot M4 (Table IX). On the other hand, deficiencies were of shorter duration in Plot Ml at Fourth Lake, where even litter layers contained available moisture at most samplings. Litter layers in the easterly plots remained below wilting percentage much of the growing season. Soil-moisture deficits were smaller in all plots during the wet summer of 1953 than they were during 1951 and 1952. Soil-moisture deficits in the subassociation nudum plots of the Pseudotsuga- T suga-Hylocomium association were smaller than in the typicum plots. 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S e last lectr 5 9 X!^ w T3 O -(-> 03 - ^g>^« ^'E S a rs 3 73 O^ 03 jg 5-mm. iampled 1953, we -i 13 s 13 -i 3b 0 "J . v-^ 93 tc +> fe 5? a 03 o 0 i) C3 *-' a weight, er, 1951, h Novel 4 :c C3 a c3 -i-> 3 to C3 »-. 1 a MO '-4-' tage, Dec 2, th tatic wilt c I rcen and , 195 i9 aa *Pe ober ober 5UJ - + r> oo 57 Pseudotsuga - Gouttheno ■ Peltigera ottoootion EASTERLY PLOTS 124* 07'W ■ Pseudotsuga - Pclysltchum ottociation Pseudotsuga - Tsuga - Hylocomtum ottoootion \ / Pseudotsuga - OoutihenQ onociot ion m%J Pseudotsuga - Gaulthena • Pelligera ottociolion WESTERLY PLOTS 124° 24' W Pseudotsuga - Tsuga - Gaulthena association Pseudotsjga - Tsuga - Hylocon'^m association Pseudotsuga - Potyst/chum association Thuja - LysiChitu association 20-11 Available soil water 2 Upper foot Lower profile PLOT Lyl MONTHS Figure 14 — Average monthly precipitation and average depth of available soil water in plots repre- sentative of forest associations in the Nanaimo River Valley, British Columbia, 1951-1953. The moisture storage capacities of profiles may be judged by comparing the depths of available water present when soils are close to field capacity during winter months prolonged summer drought of 1952. In the Echo Mountain Plot, gravitational water was present above the clay-loam layer during spring and autumn, although none occurred during the summer. Similarly, when this plot was sampled in early January, 1952, two weeks after heavy snowfalls had restricted further infiltration, no gravitational water was found above the clay-loam layer. Ac- cumulations of water did occur in an open observation pit on Plot M5 after the prolonged autumnal rains of 1951, but normally the soil of this plot was well drained to a depth of 1 m. or more. Pseudotsuga-Polystichum association Considerable depths of available moisture were present in most of the Pseudotsuga-Polystichum plots at all seasons and low moisture percentages were infrequent (Table IX). Seepage promoted such moist conditions in several plots. In the Echo Mountain Plot (P2), a high water table was sustained by moisture seeping into the concave portion of the slope on which the plot was located. During spring and early summer, this seepage originated from the melting snow on a slope which reached nearly 3,000 ft. above sea level. The water table in an observation pit showed only moderate fluctuations in level. During much of the year, this level remained within 40 cm. of the soil surface, although in the late summer of 1952 it dropped to 50 cm. and during the winter it sometimes rose to within 20 cm. of the ground line. While such levels repre- sented conditions in a moist part of the stand, since the observation pit was near 58 the margin of a slight depression, soil-moisture samples taken from other loca- tions showed that values remained high in the available range throughout the growing season. Even litter layers were above wilting percentage at most samplings. Fluctuations in the height of the water table in the observation pit on the Wolf Mountain Plot (P5) were greater than in the Echo Mountain Plot. The dry summer climate of the easterly portion of the valley in which Plot P5 was located and the short duration of the snow pack on the adjacent 1,600-ft. slope may account for this difference. During the latter part of the summer the water level in the observation pit was commonly 100 cm. below the soil surface. Although available moisture in upper soil horizons was not exhausted at such times, percentages were usually lower than in the Echo Mountain Plot. At other seasons the water table remained about 40 cm. below ground line. During a prolonged rainy spell in December, 1952, the level in the pit rose to within 10 cm. of the soil surface. Except in late summer and early autumn, some water was present in an observation pit in the Fourth Lake Plot (PI) the year round. Normally this seepage moisture flowed over the compact soil layer toward the base of the profile, some 80 cm. beneath the surface. In late spring and early summer, water from melted snow usually raised the water level and during prolonged wet spells, such as that of December, 1952, water even overflowed from the pit, despite this plot being on a 20° slope. Moisture values in mineral soil layers remained well within the available range throughout the growing season. Ground water was encountered within the upper 100 cm. of the profile in the Deadwood Creek Plot (P4) only once, in early December, 1951, following the heavy rainfall of November. On this occasion, water flowed into the sampling pit 60 cm. below the soil surface. When the same pit was resampled in early January, about two weeks after snowfall prevented further infiltration, no water was encountered within 100 cm. of the soil surface. The high soil-moisture unit readings of early February, April, and May, 1953, however, indicate that seepage moisture may have been present in the lower profile on these occasions as well. The absence of high values later in the season shows that no further supplements to soil-moisture reserves occurred within the upper 100 cm. Never- theless, since this stand was adjacent to the Deadwood Creek Thuja-Lysichitum Plot, it is possible that seepage moisture, which came to the surface in the latter stand, also affected deeper layers than those sampled in the Pseudotsuga- Polystichum Plot. The upper profile, however, appeared little affected by seepage moisture at any time of the year. Although moisture values were high in the available range at most samplings, reserves were reduced to quite low levels during the prolonged drought of 1952, and some deficits occurred in the latter part of each season. During the early months of each growing season, soil-moisture contents were found to be high in the available range in the deep, stone-free profile of the Valley Plot (P3). In dry years, nevertheless, marked deficits were evident later in the season. Values above field capacity were recorded at 125 cm. during October and November, 1953, and each winter, temporary sloughs were present in hollows adjacent to the plot. However, the location of this stand on an old river terrace precluded additions to soil-moisture reserves by ground water during the growing season. This plot was less influenced by seepage1 moisture than any of the other Pseudotsuga-Polystichum stands sampled and it had the driest soil-moisture regime. 59 'Unijti-Lijsiciiitum association Water remained close to the surface of the swampy areas in the Thuja- Lysichitum plots al all times. This water table was perched above the gley layer beneath the muck. Late in summer water levels dropped 10 or 15 cm., but the muck layer remained close to saturation at all times (Table IX). Litter layers on the marginal hummocks of the Deadwood Creek and Wolf Mountain Thuja-Lysichitum Plots (Ly2 and Ly3) dried out by the latter pari of each summer. Farther west in the Echo Mountain Plot, however, even this layer contained available moisture throughout the growing season. The upper portion of the peaty layers beneath the litter layer showed some moisture deficits during summer months, but values did not drop below wilting percentage. Lower layers remained moist even by late summer and they were saturated during winter months. DISCUSSION Water Relations and the Differentiation of Associations The considerable differences in moisture regime between plots representing different associations indicate the importance of water relations in site differ- entiation. Thus, the small size and low volume per acre of Pseudotsuga menziesii in the Pseudotsuga-Gaultheria-Peltigera plots were correlated with a dearth of available soil moisture during much of the growing season. Moisture deficits were likewise sufficient to account for the low height and density of Gaultheria shallon. The high soil-surface temperatures and rapid evaporation rates which resulted from this openness in tree and shrub canopies doubtless accentuated the droughtiness of superficial soil horizons. Such droughtiness could well be a limiting factor in the survival of ground cover species characteristic of more humid locations. The greater height and volume of Pseudotsuga menziesii and increased density of Gaultheria shallon in the Pseudotsuga-Gaultheria plots were associated with a somewhat less droughty soil-moisture regime. However, this greater density of the tree and shrub layers appeared to limit the abundance of the lichens and mosses characteristic of the ground cover and lower boles of trees in Pseudotsuga-Gaultheria-Peltigera stands. The large volume per acre of Pseudo- tsuga menziesii in the Pseudotsuga-Polystichum plots was correlated with soils having relatively small moisture deficits during the growing season. On the other hand, infrequency of Pseudotsuga menziesii in the Thuja-Lysichitum plots was coincident with the occurrence of a very high water table at all seasons. Such swampy areas supported an herbaceous flora characteristically restricted to wet locations with a cool, humid atmosphere. While differences in the floristic composition and productivity of the sites studied were found to be correlated with different soil-moisture regimes, sig- nificant differences in soil-nutrient regimes were also evident. The duff-mull character of litter layers, the limited development of A2 horizons, and the moderate acidity of soil pH values in the Pseudotsuga-Polystichum plots indicate that soil- fertility levels were relatively high. On the other hand, the mor-type humus, clear differentiation of A2 horizons, and acid soil pH values in the Pseudotsuga- Gaultheria plots, for example, suggest that their soils were relatively infertile. The lower site index for Pseudotsuga menziesii of Pseudotsuga-Gaultheria sites seems consequently to result from soil-fertility levels lower than those of Pseudotsuga-Polystichum sites, as well as less favorable soil-moisture regimes. The seepage moisture which augments soil-moisture supplies in Pseudotsuga- Polystichum sites may also ameliorate the leaching action of the regional climate evident in Pseudotsuga-Gaultheria sites (20). 60 Likewise, the composition of subordinate plant layers seemed to be influenced by soil-fertility levels. The absence of Gaultheria shallon, for example, from the mineral soil of the Pseudotsuga-Polystichum plots indicates that other factors than adequate moisture supply limited its distribution. Its presence on decaying wood, but scarcity in stand openings and on clear-cut Pseudotsuga-Polystichum sites suggest that intolerance to the shade conditions prevailing in the dense, two- storied stands characteristic of these sites is not the main obstacle to the spread of this species to Pseudotsuga-Polystichum sites. Evidently such species as Gaultheria shallon, Hylocomium splendens, and Eurhynchium oreganum are sufficiently obligate oxylophytes that their distribution is restricted to less fertile soils than those characteristic of Pseudotsuga-Polystichum sites. Such plants as Polystichum munitum, Achlys triphylla, Tiarella trifoliata, and Mnium insigne, on the other hand, being confined to moist, relatively fertile soils, characterize the Pseudotsuga-Polystichum association. However, their abundance also appears to be somewhat dependent on the humid, shady conditions of the forest floor of Pseudotsuga-Polystichum stands, since most of these species are less numerous in clear-cut areas than they are beneath standing timber (31). As in the Pseudotsuga-Polystichum plots, the large size of the Pseudotsuga menziesii in the subassociation nudum plots of the P seudotsug a- Tsug a- Hylo- comium association was correlated with relatively favorable soil-moisture conditions. The lack of well-defined A2 horizons and the low frequency of Gaul- theria shallon, Hylocomium splendens, and other oxylophytes on the forest floor of these stands suggest that their soils were also quite fertile. However, the paucity of ground-cover plants characteristic of the Pseudotsuga-Polystichum association and the somewhat lower site index for Pseudotsuga menziesii of these plots seem to reflect the occurrence of both slightly larger soil-moisture deficits during the growing season and somewhat less favorable soil-fertility levels than those typical of Pseudotsuga-Polystichum sites. Site index for Pseudotsuga menziesii in the subassociation typicum plots of the Pseudotusga-Tsuga-Hylocomium association was no higher than it was in the P seudotsug a-Gaultheria plots. In the easterly typicum plots, this poor growth would appear at least partially attributable to soil drought, since soil-moisture deficits were comparable with those of P seudotsug a-Gaultheria sites. However, the absence of Gaultheria shallon would imply that other factors were different. Such differences might be related to soil fertility and the fairly dense tree canopy characteristic of P seudotsug a-Tsuga-Hylocomium stands. On the other hand, the low site index for Pseudotsuga menziesii in the Fourth Lake P seudotsug a-Tsuga-Hylocomium Plot (Ml) was probably more closely related to poor soil fertility than soil drought, since soil-moisture deficits in this plot were less pronounced than those of the more easterly Deadwood Creek Plot (M4). Despite its relatively droughty soil-moisture regime, the Deadwood Creek Plot had a higher site index for Pseudotsuga menziesii than the Fourth Lake Plot. The deeper A2 horizon and lower pH values of the westerly plot (Ml) indicate that its soils were more strongly leached than those of the easterly plot (M4). Apparently the more favorable soil-moisture regimes of the Fourth Lake Plot did not offset a less favorable soil-fertility regime. The similarity of site index for Pseudotsuga menziesii in Plots Ml and M4 of the P seudotsug a-Tsuga-Hylocomium association, despite dissimilarities in soil-moisture regime, illustrates the compensatory roles played by soil-nutrient and soil moisture regimes under different climatic conditions. The more favorable soil-moisture regimes of the westerly plots were evidently counterbalanced by more highly leached soils than those of similar vegetation types farther east. 61 The improved Boil-moisture regimes of the westerly plots probably resulted from both rainfall being higher and the snow pack Lasting Longer than farther east. Although summer rainfall at Fourth Lake was li. Vin>DLBTON, W . E. I). L943. Meteorological instruments. Univ. Toronto Press, Toronto, Ont. 31. Muellbb-Dombois, I ). L959. Douglas-fir forest associations on Vancouver Island in their initial stages of secondary succession. Qniv. British Columbia, Ph.D. Thesis. 32 PeabSi \. 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