For the high-elevation Engelmann spruce - subalpine fir (ESSF) biogeoclimatic zone of southwestern British Columbia, there is little empirical data on the long-term dynamics of subalpine spruce-fir stands. A lack of a long-term perspective on the growth and development of stands in the ESSF zone hinders both ecological research and silvicultural planning in the ESSF forest. A broadly-focussed pilot study on long-term Engelmann spruce-subalpine fir stand dynamics in the ESSF zone was designed to begin to address this deficiency. This study used two methodological approaches to gain insights into long-term stand dynamics: 1) a retrospective approach to examine historical patterns of: i) postfire conifer regeneration, ii) post-establishment stand structure development, and; iii) basal area production and accumulation in ESSF spruce-fir forests, and; 2) A chronosequence approach to examine overall stand basal area development over a 575-year chronosequence, which is not amenable to detailed retrospective examination. In order to reconstruct the patterns of postfire regeneration and subsequent stand development, measurements of tree age, diameter, radial increment, and height were collected in 8 mesic, 45- to 110-year-old fire-origin stands of Engelmann spruce (Picea engelmannii Parry. ex Engel.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in the ESSFwm and ESSFdc2 biogeoclimatic subzones of the North Cascades mountains. The results of the stand reconstruction were also used to aid in the interpretation of the chronosequence, which was based on basal area and age data from both the retrospective study sites, and the published literature. Based on the graphical analysis and discussion of the data collected in this pilot study, the following features of long-term stand development were noted in subalpine Engelmann spruce-subalpine fir stands: 1) Postfire conifer re-establishment on these burned ESSF sites was slow and erratic; the re-establishment period was 30 to 50 or more years in duration; 2) There appeared to be no consistent or predictable postfire patterns of conifer establishment on the various sites, either over time, or on a site-to site basis; 3) During postfire regeneration and immature stand development, there appeared to be no consistent differences between Engelmann spruce and subalpine fir, either in terms of i) postfire regeneration establishment, or ii) height development; 4) Fire-origin spruce-fir stands in the ESSF zone rapidly develop a complex stand structure, possibly due to the gradual and prolonged patterns of regeneration ingress on these sites; 5) Trees which have initial advantages in height or other competitive advantages over other trees on the site during the establishment phase tend to retain dominant crown positions in the stand at much later stages of development; 6) The relationship of periodic basal area increment (b.a.i.) to initial basal area stocking in immature spruce-fir stands suggests that stand increment is optimized above a critical stand density; 7) The initial basal area level necessary to optimize b.a.i. appears to increase with stand age; and 8) Apparent trends from a 575-year chronosequence of Engelmann spruce-subalpine fir stand development suggests that stand basal area tends to peak, on average, between the ages of 70 and 150 years of age. Subsequently, basal area tends to gradually decline and eventually stabilize between the ages of 300 to 400 years of age. Based on these results, preliminary recommendations were proposed for the long-term silvicultural management of ESSF spruce-fir forest types. Also, the research priorities necessary for building on the results of this pilot study were identified. / Forestry, Faculty of / Graduate

Old-growth stands are important for management, conservation, wildlife, recreation, and maintaining biological diversity in forested landscapes. However, we are lacking the information needed to adequately identify and characterize old-growth stands. This is especially true for high elevation, interior forests. The characterization of stand structure and regeneration pattern will help in the development of site-specific guidelines for identifying old growth stands and restoring some of the old-growth characteristics in managed stands. This pamphlet presents a synopsis of a study investigating stand structure and regeneration of old-growth stands in the Moist Cold Engelmann Spruce - Subalpine Fir (ESSFmc) Subzone near Smithers, B.C. The three stands selected for the study were located on zonal sites, each in different watersheds, and the stands were established after fire. The criteria used for selection were: i) absence of lodgepole pine, ii) presence of advanced regeneration, and iii) abundant snags and coarse woody debris. These stands were presumed to represent the old-growth stage of stand development or the final (climax) stage of secondary succession.

Thesis (M.S.)--Wake Forest University. Dept. of Biology, 2003. / Vita. Includes bibliographical references (leaves 51-57).

The primary objective of this study was to determine the degree of correlation between internal water potential of Engelmann spruce trees and selected environmental factors. The secondary objective of the study was to determine the effect of summer precipitation, both in meadow and forested sites, on the soil drying cycle. Four study plots (each roughly 154 square meters) under spruce cover and two study plots (100 square meters) in a small meadow were established. At each spruce plot, a thermocouple psychrometer was installed at one meter above the ground on the north side of three selected, mature Engelmann spruce trees. Thermocouple psychrometers were installed at 5, 15, and 30 cm depths in the soil at the meadow plots and at 15, 30, 45, and 90 cm depths at the spruce plots. A tensiometer and two soil temperature thermocouples were installed near the thermocouple psychrometers at each of the plots but at 15, 30, 45, and 90 cm soil depths. Throughfall gages were placed at each plot to obtain an estimate of rainfall which was not intercepted by the canopy but which fell to the forest floor. Gross precipitation was measured by a 20.3 cm diameter recording gage located at the meadow. Global radiation and wind were recorded at the meadow area also. Air temperature and relative humidity were recorded in wooden shelters. One shelter was located at the meadow area and one was located in the vicinity of the four spruce plots. Except for wind, weather parameters were recorded continuously. Wind movement was totalized on a digital counter and recorded on data sheets when needed. Psychrometric, pressure chamber, and soil data were obtained according to two schedules. Diurnal measurements of trunk water potential in six trees and independent variables were made during seven days in the summer months of 1971. Seasonal measurements of trunk water potential in twelve trees and independent variables were done at periodic intervals during the summer averaging every three to four days. Data to evaluate the effect of summer precipitation on the soil drying cycle was obtained periodically the summer of 1970 and concurrently (for the most part) with tree water potential measurements during 1971. Significant findings of this study included the following: as shown by analyses of variation of the data, within-season variations of tree water potential (by psychrometer and pressure chamber measurements) were statistically significant. In other words, fluctuations in water potential with time were large enough that they could not have been due to chance alone. On an hourly basis for seven cycles of diurnal measurements, daily peaks in wind movement corresponded roughly with trunk water potential minima, peak radiation occurred about two hours before water potential minima, and maximum vapor pressure deficits corresponded closely to water potential minima. Diurnal fluctuations in water potential of small understory branches, as determined by the pressure chamber, did not correlate well with weather factors. Seasonally, trunk water potential appeared to be highly correlated with fluctuations in vapor pressure deficit and less correlated with global radiation and wind. Soil factors such as matric potential and temperature were not correlated with trunk water potential. Correlations between water potential determined by the pressure chamber and environmental factors were not consistent. Pressure chamber values of water potential, however, did correlate roughly with trunk water potential during the latter half of the summer of 1971. By multiple regression analysis, a predictive equation was devised to predict trunk water potential on a daily and on a seasonal basis. With diurnal input data, radiation, vapor pressure deficit, and a transformation of vapor pressure deficit were significant variables. The model explained 81 percent of the diurnal variation in trunk water potential. Evaluation of the model with seasonal data input showed only one variable, vapor pressure deficit, highly significant. With seasonal data, 72 percent of the variation in trunk water potential was explained. Analysis of 18 rainstorms which occurred during two summers of study showed that roughly 0.25 cm of rain must fall before interception storage of a spruce canopy is satisfied and measurable amounts of rain can fall to the forest floor. Variability among sample catches of a given storm was great, apparently reflecting the irregular nature of the overmature spruce canopy. On the average, 96 percent of rainfall from storms between 0.0 0 and 0.13 cm, 70 percent between 0.13 and 1.3 cm, and 38 percent between 1.3 and 2.5 cm was intercepted. The influence of rain on soil matric potential was restricted to the first 45 cm of soil at the spruce plots with no substantial increase of matric potential before the onset of fall rains. The effect of rain on matric potential of soil in the meadow was more pronounced. The matric potential of the 5, 15, and 30 cm depths fluctuated greatly. A temporary increase in matric potential of these depths following summer storms was noted while more marked increases in matric potential were measured after heavier fall rains. The major conclusions made as a result of this study are (1) relative vapor pressure in the trunks of Engelmann spruce changes markedly from hour-to-hour and from day-to-day during the summer months, (2) trunk water potential as measured by thermocouple psychrometers is functionally related to atmospheric factors of radiation, wind, and vapor pressure deficit, (3) fluctuations in trunk water potential with weather factors imply a causal relation with transpiration, (4) precipitation during the summer months modifies soil matric potential-but only in the shallow profiles, (5) matric potential fluctuations in the meadow areas are extreme (from saturation to low as - 40 bars) and would impose a serious threat to the water economy of young Engelmann spruce seedlings established in such meadows, and (6) Peltier type thermocouple psychrometers are useful instruments for investigation of the soil-plant-atmosphere continuum in field situations.

This document reports the results of 4 studies of subalpine ecosystem ecology, describing ways that spatial heterogeneity in soils and plant communities mediate ecosystem responses to environmental change. Ecosystem responses to environmental change are also mediated by regional climate patterns and interannual variability in weather. In the first chapter we report the results of an experiment to test for the mediating effects of associational resistance in a forest community that experienced wide-spread beetle kill. We found that Engelmann spruce were more likely to survive a beetle outbreak when growing in low densities (host dilution) and not through other types of associational resistance that relate to higher tree-species richness or greater phylogenetic diversity of the forest community. In the second chapter we report the effects of early snowmelt on soil moisture in subalpine meadow and aspen communities. We found that soil organic matter, soil texture, and forest cover mediated the effects of early snowmelt and were more important drivers of growing-season soil moisture than was snow-free date. In the third chapter we report the effect of early snowmelt on growth and seed production of early-season and midsummer herbaceous species. We found that the primary effect that snowmelt timing had on plant growth was through its effect on species distribution. Changes in the timing of snowmelt had limited effect on the growth, flowering, and seed count of species after they were established. In the final chapter, we report the effect of early snowmelt on soil respiration, microbial biomass, dissolved organic carbon and soil organic carbon. We found that early snowmelt resulted in warmer soil temperatures compared to neighboring snow-cover plots, and that microbial biomass and soil respiration showed no signs of a snowmelt legacy effect during the growing season. Soil organic carbon in rapid and slow-turnover pools was affected more by plant community than by snowmelt timing, and the primary drivers of soil respiration during the snow-free period were first soil organic matter and second soil temperature. Taken together, this dissertation reports our findings that subalpine ecosystems are resilient to environmental change in part because organisms in these systems are adapted to environmental conditions that are highly variable between sites, seasons, and years.

Ecosystem-specific forest management requires comprehension of tree species productivity in managed settings, and how this productivity varies with the ecological determinants of site quality, i.e., the environmental factors that directly affect the growth of plants: light, heat, soil moisture, soil nutrients, and soil aeration. A good understanding of this variation is necessary for making species- and site-specific silvicultural decisions to maximize productivity. Productivity of a given species is usually measured by site index (tree height at 50 years at breast height age). Quantitative relationships between site index and these measures of site quality provide predictive models for estimating site index. Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) is an important timber crop species in the coastal forests of British Columbia. In relation to climate, its range in southwestern British Columbia extends from sea level to almost timberline, and from the hypermaritime region on western Vancouver Island to the subcontinental region on the leeward side of the Coast Mountains. In relation to soils, its range extends from slightly dry to wet sites and from very poor to very rich sites. In view of this relatively wide climatic amplitude, a large variability in productivity can be expected. It is particularly important to consider the growth performance of Pacific silver fir when decisions are made regarding whether or not to cut stands on high-elevation sites. In the study summarized here, relationships between Pacific silver fir site index and selected ecological measures of site quality were examined, and site index models using these measures as predictors were developed.

This study examines the influence of climate on tree-ring properties of several major tree species: Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes), subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and lodgepole pine (Pinus contorta var. latifolia Dougl. ex Loud.). Our three objectives were to determine how (1) tree-ring properties change along an elevation gradient, (2) short-term climatic influences are correlated with tree-ring properties, and (3) long-term climatic influence on tree-ring properties.

Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) is an important timber crop species in coastal forests of B.C. Its range extends from sea-level to almost timberline, and from the hypermaritime region on the west coast of Vancouver Island to the subcontinental region on the leeward side of the Coast Mountains. With this relatively wide climatic amplitude, a large variability in the height growth pattern of Pacific silver fir can be expected, since climate is considered to be the most influential determinant of the trajectory of height over age of forest trees. This variability, however, is not reflected in the height growth curves and site index tables used to estimate Pacific silver fir site index, since the curves and tables were developed from low-elevation stands on Vancouver Island. Consequently, when these curves and tables are applied to high-elevation or submaritime stands, we get biased estimates of site index. Accurate estimates of site index are necessary for accurate yield predictions. Furthermore, they are essential for making rational decisions about whether to cut the forest in situations where potential tree growth is marginal, such as in high-elevation forests.

The three major components in the site classification of the biogeoclimatic ecosystem classification system are: climatic regimes, soil moisture regimes (SMRs) and soil nutrient regimes (SNRs). Both SMRs and SNRs can be identified in the field using soil characteristics and indicator plants. In the case of SMRs a quantitative classification was also developed that allow comparison of SMRs in different subzones. However, similar quantitative classification has not yet been developed for SNRs. This pamphlet summarizes and compares the results of several regional studies conducted in different biogeclimatic zones. Each of theses studies aimes to develop a quantitative SNR classification (Table 1). The comparison will examine: (1) how well the field-based classification matches quantitative classification, and (2) which direct measures distinguish best between field-identified SNRs.