A study was carried out to ascertain the biogeochemical role of understory vegetation in three representative sites characteristic of the Mountain Hemlock Biogeoclimatic Zone. The three sites were selected to represent a typical topographic sequence of plant associations and were classified as members of the Vaccinio (membranacei) -Tsugetum mertensianae, Abieto (amabilis) - Tsugetum mertensianae and Streptopo (rosei) - Abietetum amabilis plant associations (xeric, mesic, and hygric site types, respectively). The overstory layer was found to be typical of old growth, high elevation forests of southwestern coastal British Columbia. Overstory biomass on the three sites was estimated to be 60.88, 55.68, and 34.05 kg•m⁻² for the hygric, mesic, and xeric site types, respectively. Understory aboveground biomass was found to be less than one percent of the aboveground overstory biomass. Average values for the three sites were: 44.1, 66.1, and 399.3 g•m⁻² for the hygric, mesic, and xeric site types, respectively. Understory aboveground production (UAP) was found to represent a greater proportion of overstory aboveground production, as indicated by the mean annual increment (MAI), than the biomass figures might suggest. UAP values of 25.95, 14.19, and 63.12 g•m⁻²•yr⁻¹ for the hygric, mesic, and xeric site types, respectively, were equivalent to 11.28 percent, 6.06 percent, and 48.55 percent of the estimated aboveground overstory production. Only a small percentage of the total aboveground nutrient standing crop was found in the understory. This is in agreement with comparable published values for old growth forest ecosystems. However, the understory was found to cycle a much greater proportion of its total standing crop annually compared to overstory. Approximately 80 percent of the macronutrients present in the understory standing crop are found in the understory annual production on the Streptopo - Abietetum amabilis site (hygric site type). Estimates of 17.6, 8.3, and 20.6 g•m⁻²•yr⁻¹ of understory aboveground litterfall (exclusive of the moss layer) were obtained for the hygric, mesic, and xeric sites, respectively. These values are substantially less than for overstory litterfall, but the biomass of different litterfall components (e.g. understory or overstory) was shown to be a poor indicator of the proportional contribution of the components to the quantity of nutrients in aboveground litterfall. Understory was shown to return a significant proportion of the litterfall nutrients on a yearly basis, the bulk of which was returned as a single pulse during the first autumn snowfall. Understory vegetation above the moss layer was shown to have a significant effect on the quantity of nutrients present in throughfall precipitation reaching the ground. The effect was seasonal in nature with PO₄-P, N0₃-N, and NH₄-N being removed in the spring and Ca, Mg, and K being added to overstory throughfall in the autumn. It was concluded that modifications of water chemistry previously attributed to the forest floor may in some cases reflect unmeasured influences of understory vegetation. The understory aboveground nutrient cycles follow two basic patterns. The first pattern, a conservative cycle, is exemplified by nitrogen and phosphorus and has the following characteristics: (1) removal of nitrogen and phosphorus from overstory throughfall by the non-bryophyte understory, (2) estimated annual nitrogen and phosphorus uptake up bryophyte production in excess of the remaining throughfall nitrogen and phosphorus content and (3) a large proportion of the annual requirement was accounted for by internal redistribution within the understory plants. The second cycling pattern, an open cycle, is characteristic of calcium and magnesium and displays characteristics opposite to those of the "conservative cycle". The potassium, manganese, zinc, and copper cycles are intermediate between the "conservative" and "open" nutrient cycles. The results are discussed with respect to a proposed model of ecosystem function and it is hypothesized that understory plays a major role in maintaining ecosystem stability by promoting nutrient cycling. / Forestry, Faculty of / Graduate

An ecosystem study, based on the concept and approach of biogeoclimatology (sensu the Krajina school of ecosystem classification), was conducted in the boreal forest of northeastern British Columbia in the Fort Nelson area. The prime purpose of this study was to produce an ecological classification of forested ecosystems of the area. The resulting classification was based on an analysis of as many environmental and vegetational characteristics as feasible. Interpretations of the environmental and vegetational analyses presented attempt to explain the factors which conspicuously contribute to ecosystem processes and development. The vegetation from 95 phytogeocoenotic plots was classified into 6 orders, 10 alliances and 15 associations and the soils were classified into 17 subgroups, some with their gleyed variations. Detailed soil analysis and descriptions are major components of the ecosystem descriptions. The ecosystems are summarized environmentally by their projection on an eda-topic grid of moisture and nutrient regimes. An elemental ash analysis was carried out on surface organic horizons. Ca and Mg content appear to be good indicators of the positions that ecosystems occupy on the edatopic grid. Additionally, mor humus of black spruce ecosystems was compared with moder humus of aspen ecosystems. It is confirmed that moder humus has properties which are more conducive to high biological activity than does mor humus. It is concluded that the cold boreal climate , flatness of the terrain, prevailingly fine textured soil parent material, and fairly frequent forest fires are the dominant environmental factors influencing ecosystem structure and dynamics in the study area. The fine texture of the parent material frequently causes very slow percolation of water through soils which produces semi-stagnant water conditions instead of the rich seepage sites of more easily drained materials in other areas. Sufficient moisture is retained in these fine textured soils to prevent xeric conditions from developing, even in shedding topographic positions. The cold temperatures reduce biological activity, of the area to the point where nutrient poor, mor humus conditions develop. Mor humus promotes degradation of soils. However, this process is greatly inhibited by frequent forest fires. These fires maintain aspen stands as a fire climax which retards the development of strong acidity, so characteristic in mor humus of black spruce stands (the theoretical climatic climax). The general flatness of the terrain results in poor drainage of the area and favours the development of bogs. In high moors, a permafrost layer consistently occurs. / Science, Faculty of / Botany, Department of / Graduate

The distribution of the above-ground biomass and macronutrient content of the trees were studied on two sample plots in south coastal British Columbia, near Vancouver. The plots differed in elevation (4,600 and 2,200 feet; 1,500 and 700 m), in soil type and depth. Tree age was similar in both plots, ranging from 150 to 530 years. The tree cover on the high elevation plot consisted of Tsuga mertensiana (Bong.) Carr. (mountain hemlock) and Abies amabilis (Dougl.) Forbes (Pacific silver fir) while the lower elevation plot was occupied by Tsuga heterophylla (Raf.) Sarg. (western hemlock), Thuja plicata D. Don (western red cedar) and Chamaecy- paris nootkatensis (D. Don) Spach (yellow cedar). Twenty-four trees were sampled to determine the biomass and nutrient content of wood, bark, branches, twigs, foliage and cones. Another nine trees were sampled for the biomass and nutrient content of wood and bark only. Multiple regression analysis was used to establish the relationship between d.b.h., tree length, crown length and biomass of the various tree components. The regression equations obtained were used to estimate the total biomass of wood, bark, branches, twigs and foliage contained in the trees on each of the sample plots. The data thus obtained were combined with data on chemical concentration and used to estimate the distribution of macronutrient elements in different above-ground biomass components of the stands. / Forestry, Faculty of / Graduate

A major contributor to global warming is the increasing amount of carbon dioxide in the atmosphere. Land use management may be a means to countering global warming by increasing the carbon sink potential. Terrestrial carbon budgets were prepared for forested (Douglas-fir), agricultural (hay), and urban sites in Abbotsford, B.C. The results indicate that the greatest amount of carbon is stored in the forested sites, followed by the hay sites, with the lowest amount in the urban sites. To maximize carbon in storage the use of trees either as forests or in pockets within the landscape is the best option. To simulate and to expand the utility of these carbon budgets, the study used the CENTURY model. The results of the simulations indicate that forests are a major carbon sink as was found earlier. Carbon storage under hay is at a relative steady state, except during the cultivation years when it becomes a carbon source. Lawn in an urban setting is a carbon source. The results of the simulations suggest that management can be used to increase the carbon sink. It also indicates that soils are a major carbon pool representing 20% of the forest, 90% of the hay, and 95% of the lawn budgets. For the general public and decision-makers to become more aware of the impact of changing land use on carbon storage, at the lot, local, or regional levels, they require a userfriendly decision-making tool. A derivative of the CENTURY model, CLU (for CENTURY Land Use), was developed. It was designed to be user-friendly and at the same time maintain the integrity of the parent model. It allows the user to input site-specific data and obtain site related output carbon data on a component basis, which can be used to assess how a potential change in land use or management may affect the amount of carbon in storage. The model should be suitable as a research tool and for planning and educational purposes.

An approximately 228 acres large forested area near Hope, B.C., has been investigated in the mahonietosum subassociation of Pseudotsugeto-Gaultherietum mesic association of the Coastal Douglas-fir Zone. Botanical survey and bird census work by the nest (or territory) mapping method were carried out during two summer seasons. Fifteen ecosystem types are described and their bird population, expressed in average densities per area unit as well as by average biomass is tabulated. Physical environmental conditions, especially pertaining to microclimate, were measured at 55 nests of the eight most common passerine species, and nest placing and construction has been considered at 167 nests of the same species. It has been found that the nesting of these species in their habitats is the function of the present vegetation, physical environment and the adaptive range of the species. In certain species the birds apparently chose nest sites with equable microclimate. In others it was found that the insulation of the nest varies according to the needs indicated by the extremes of the microclimate; again in others the nest material chosen provided the best available resistance to mechanical stresses. While other essential environmental requirements were not studied the results point toward an assumption that microclimate strongly influences the site, height, position, and material of the nests, and ultimately, the selection of nesting habitat of the birds studied. / Forestry, Faculty of / Graduate

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

A major contributor to global warming is the increasing amount of carbon dioxide in the atmosphere. Land use management may be a means to countering global warming by increasing the carbon sink potential. Terrestrial carbon budgets were prepared for forested (Douglas-fir), agricultural (hay), and urban sites in Abbotsford, B.C. The results indicate that the greatest amount of carbon is stored in the forested sites, followed by the hay sites, with the lowest amount in the urban sites. To maximize carbon in storage the use of trees either as forests or in pockets within the landscape is the best option. To simulate and to expand the utility of these carbon budgets, the study used the CENTURY model. The results of the simulations indicate that forests are a major carbon sink as was found earlier. Carbon storage under hay is at a relative steady state, except during the cultivation years when it becomes a carbon source. Lawn in an urban setting is a carbon source. The results of the simulations suggest that management can be used to increase the carbon sink. It also indicates that soils are a major carbon pool representing 20% of the forest, 90% of the hay, and 95% of the lawn budgets. For the general public and decision-makers to become more aware of the impact of changing land use on carbon storage, at the lot, local, or regional levels, they require a userfriendly decision-making tool. A derivative of the CENTURY model, CLU (for CENTURY Land Use), was developed. It was designed to be user-friendly and at the same time maintain the integrity of the parent model. It allows the user to input site-specific data and obtain site related output carbon data on a component basis, which can be used to assess how a potential change in land use or management may affect the amount of carbon in storage. The model should be suitable as a research tool and for planning and educational purposes. / Science, Faculty of / Resources, Environment and Sustainability (IRES), Institute for / Graduate

I explored the importance of decaying wood to survival and growth of trees in south coastal British Columbia, and the effect of decaying wood on the intensity of podzolization on mesic sites. A field pot study was carried out in both high light and low light conditions using woody and non-woody forest floor materials. After two growing seasons, Pseudotsuga menziesii, Tsuga heterophylla, and Abies amabilis seedlings growing in clearcuts had greater survival and growth in the non-woody substrate; however, in the understory, the effect was much less. The proliferation of western hemlock roots was used as an indicator of the value of decaying wood to trees. In both greenhouse trials (using seed sown on a series of planting pots with each half filled with either a woody substrate or a non-woody substrate), and in field sampling of woody and non-woody substrates in mature stands, the non-woody substrate had a larger density of fine and very fine roots compared to the woody substrates or mineral soil. Ten litres of concentrated solutions of non-woody humus substrate and woody substrates were leached through soil columns. Both the non-woody and woody solutions had similar mean pH but significantly different chemical properties. The non-woody solution leachate had greater net average output of dissolved organic C, Fe, and Mn. The mineral soil treated with the nonwoody solution had significantly greater concentrations of total N and pyrophosphate-extractable Fe. In the field, forest floor and soil samples were compared between pedons having large accumulation of decaying wood and pedons with non-woody humus forms. Despite large and significant differences in chemical properties between the two substrates, there were generally no significant differences between the chemical properties of the soils directly under these substrates. In most cases, the results of (3-analyses showed that the means were not pedologically different. Additionally, 18 pairs of zero tension plate lysimeters were installed under the two substrates. The lysimeter solutions showed no significant differences. I concluded that coarse woody debris appears not to have either a positive effect of increased productivity of trees or a negative effect of increased intensity of podzolization.

Engelmann spruce-subalpine fir [Picea engelmannii Parry ex Engelm.-Abies lasiocarpa (Hook.) Nutt.] (ESSF) forests occupy large portions of western North America, and of British Columbia (B.C.) in particular. These areas represent a harsh environment for plant growth. The ESSF forests of B.C. have presented serious problems of regeneration following harvesting; several factors stimulated speculation as to whether N supply limitations were involved. This study was intended to highlight the post-harvest N dynamics of an ESSF forest, and the implications of the latter for silvicultural practices. Its general objectives included characterization of the post-harvest assart effect, and investigation of the N status and growth of advance regeneration. These were achieved by means of a comparative study of an age sequence of harvested sites. The assart effect lasted for at least eight years after harvesting, with a peak of change between years three and six. There were no major physical changes in the forest floor. Low C/N ratios between 19 and 32 were believed to have contributed to increased N availability. ESSF forests may have a generally higher level of N availability than previously supposed. The advance regeneration benefited from the assart effect. Nutrient uptake appeared to increase generally from at least three years after harvesting; increases of up to 78% were noted for N. There appeared to be no general macronutrient or micronutrient limitation to growth. However, evidence of S deficiencies was encountered in some trees. Moreover, the critical levels used for N may be in need of revision. A revised critical level of 1.40% for foliar N concentrations is proposed for subalpine fir advance regeneration. If this is accurate, regeneration may have been at least temporarily N-limited from year eight after harvesting. A more rigorous investigation of these possibilities is needed. The cutting method applied to the sites approximated a one-cut shelterwood method. The method as encountered in this study should not be considered a viable silvicultural option for similar ESSF forests. Its successful application would involve some degree of forest floor manipulation to improve seedbed conditions and soil microclimatic regimes. The findings of this study demonstrate that the environmental and biological characteristics of ESSF forests make high levels of planning and care a prerequisite for the success of silvicultural practices. The question of what comprises realistic growth and yield expectations of second-rotation stands in the ESSF zone needs to be addressed urgently. / Forestry, Faculty of / Graduate

I explored the importance of decaying wood to survival and growth of trees in south coastal British Columbia, and the effect of decaying wood on the intensity of podzolization on mesic sites. A field pot study was carried out in both high light and low light conditions using woody and non-woody forest floor materials. After two growing seasons, Pseudotsuga menziesii, Tsuga heterophylla, and Abies amabilis seedlings growing in clearcuts had greater survival and growth in the non-woody substrate; however, in the understory, the effect was much less. The proliferation of western hemlock roots was used as an indicator of the value of decaying wood to trees. In both greenhouse trials (using seed sown on a series of planting pots with each half filled with either a woody substrate or a non-woody substrate), and in field sampling of woody and non-woody substrates in mature stands, the non-woody substrate had a larger density of fine and very fine roots compared to the woody substrates or mineral soil. Ten litres of concentrated solutions of non-woody humus substrate and woody substrates were leached through soil columns. Both the non-woody and woody solutions had similar mean pH but significantly different chemical properties. The non-woody solution leachate had greater net average output of dissolved organic C, Fe, and Mn. The mineral soil treated with the nonwoody solution had significantly greater concentrations of total N and pyrophosphate-extractable Fe. In the field, forest floor and soil samples were compared between pedons having large accumulation of decaying wood and pedons with non-woody humus forms. Despite large and significant differences in chemical properties between the two substrates, there were generally no significant differences between the chemical properties of the soils directly under these substrates. In most cases, the results of (3-analyses showed that the means were not pedologically different. Additionally, 18 pairs of zero tension plate lysimeters were installed under the two substrates. The lysimeter solutions showed no significant differences. I concluded that coarse woody debris appears not to have either a positive effect of increased productivity of trees or a negative effect of increased intensity of podzolization. / Forestry, Faculty of / Graduate