This pamphlet provides a summary of a fuller report issued under the title: Classification of mid-seral black spruce ecosystems of northern British Columbia

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Knowledge of optimum concentrations and ratios of major nutrients in tree foliage is required to assess the nutrient status of the boreal forest. This thesis aimed at determining foliar nutritional standards for white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana Mill. B.S.P.) and jack pine (Pinus banksiana Lamb.) and to assess the nutrient status of forest stands across Canada for all major nutrients (N, P, K, Ca, Mg and Mn) using critical values (CVA) and compositional nutrient diagnosis (CND). Trees were sampled at three locations in Ontario and Quebec to cover a gradient of soil fertility levels. A boundary line approach was used in combination with quadratic regression models to assess the relationship between growth and foliar nutrient concentrations or CND scores when free of the effects of interacting environmental factors. (Abstract shortened by UMI.)

A dendrochronological and dendrochemical study was undertaken near the village of Kuujjuaq, northern Quebec. Changes in climate, radial growth and mineral nutrition of trees, as well as the contamination in Mn and Zn of tamarack and black spruce forests of the region during the last forty years were investigated. A growth model based on climatic variables was produced for each species. The regional climate didn't show any steady trend of increase in temperature and precipitation with time. However, the 1953-1964 decade was the warmest one and the 1964-1973 decade received the most precipitation. Radial growth of both species have probably increased during the investigated period. Growth of larch was primarily associated with May and June precipitation (R$ sp2$ = 0.134) when spruce growth was associated with spring temperature and July and August evapotranspiration (R$ sp2$ = 0.352). Wood chemistry (concentration, burden, and elemental ratio) suggests a stable soil fertility in base cations during the last forty years as well as a stable or increased availability of Zn during the last decade. More extensive research, in terms of number of sites and variables studied could confirm the observed trends in growth, soil fertility, and Mn and Zn availability in this part of northern Quebec.

Trembling aspen (Populus tremuloides Michx.) were observed growing along roads far north from the area where it dominates, in sites dominated by black spruce (Picea mariana (Mill.) B.S.P.) forests. This study examined the distribution of aspen at an early development stage and the conditions in which they are growing in a black spruce/feathermoss forest type in northwestern Abitibi, Quebec six years following harvesting. In this region, aspen are appearing in logged and burned areas that had been previously dominated by black spruce. The relationship of aspen growth with Ca availability and mineral soil access is the main focus of the study. Soil and foliar samples from aspen seedlings were collected from roadside, slash and cutover locations during the summer of 2003. Trees were also measured for height and basal diameter. Microsites where aspen was growing and where it was absent were compared to determine whether aspen was associated with specific microsites soil properties. The results suggest that there are differences in the growing conditions for aspen between different locations but that the trees are growing successfully in all of the three location types. In the cutovers, aspen seedlings were consistently found in association with patches of Polytrichum moss. All the sets of data indicate that Ca availability and access to mineral soil are not the main factors influencing the distribution of aspen but that soil pH, or a factor relating to pH, may be important.

Trembling aspen (Populus tremuloides (Michx.)) has become established along a mining road in the lower northern Quebec region (49°39' to 49°45'N and 79°01' to 79°02' W) in areas that have not supported aspen in the past. The primary means of regeneration of aspen is through vegetative root suckers, but it is doubtful that it could progress through this region at such a fast rate solely by asexual reproduction. Aspen are known to produce large amounts of seeds that could account for aspen's rapid progression, but sexual reproduction of aspen is rare; very little is known about Populus tremuloides seed germination and seed survival in natural conditions. The aim of this study was to determine seedbed conditions that facilitate the emergence and survival of Populus tremuloides seedlings, and to identify the key factors involved in these processes. Observations of established saplings and a sowing experiment were conducted on both post harvest and post fire sites. Our data on established saplings showed that there were seed-origin trembling aspen located in both post-harvest and burned areas indicating that Populus tremuloides can and has established from seed in areas where aspen was previously absent. Both our sowing experiment and our greenhouse experiment showed that the emergence of seedlings was relatively low, but that Polytrichum strictum moss and exposed mineral soil depressions were the best seedbeds for seed germination. Extreme temperatures and availability of moisture appeared to be controlling factors on seed germination, but ultimately the physical and biological characteristics of each substrate influenced the substrate's response to these factors in a different way. We conclude that sexual reproduction of trembling aspen may and has occurred in this region, and is promoted by the presence of exposed mineral soil and Polytrichum strictum moss. / Keywords: Bryophytes, Populus tremuloides, Polytrichum, Sphagnum, seedling, seedbed, germination, seed.

Unprecedented rates of climate change have increased forest stress and mortality worldwide. Previous research in the boreal forest has largely documented negative growth responses to climate in forest species and habitats characteristic of drier conditions, emphasizing the sensitivity of drier or warmer landscape positions to climate warming. Tree growth responses to recent climate warming may signal changes in the susceptibility of forest communities to compositional change and consequently impact a wide range of ecosystem processes and services. In this study, I explored relationships between climate and radial growth of black spruce, a dominant tree species typical of cool and moist habitats in the boreal forests of North America. I assessed how growth-climate responses varied with stand characteristics and landscape position across four different regions in Alaska and Yukon Territory and found widespread negative correlations between growth and temperature. Decreased tree growth in association with increasing temperatures is generally accepted as a signal of temperature induced drought stress. However, variations in tree growth alone do not reveal the physiological mechanisms behind recent changes in tree growth. Thus, I used stable carbon isotopes to test if the changes in growth were due to physiological drought stress. My results highlight the prominence of drought stress in the boreal forest, even for trees located in cool and moist landscape positions. As mature trees might be able to survive in stressful environmental conditions that do not permit successful post-fire recruitment and survival of seedling, drought stress could affect the resilience of the boreal forest ecosystem to disturbance from fire. I assessed drought stress in pre-fire trees and used post-fire forest compositional changes as a proxy for ecosystem resilience. My results suggest that forest stands with the lowest resilience to disturbance are those that experienced the compounding effects of climate induced drought stress and high fire severity. These sites were generally located at warmer and drier landscape positions, suggesting they are less resilient to disturbance than sites in cool and moist locations. I conclude that as temperatures continue to warm, the loss of boreal forest resilience to disturbance from fire will vary in association with environmental heterogeneity across the landscape.

The effects of lichen ground cover (predominantly Cladina stellaris) on the growth of Picea mariana at Schefferville, Quebec and Pinus sylvestris at Kevo, Finland, was investigated in situ. Effect on seedling establishment was inferred through examining status quo conditions. While contiguous mat cover precluded establishment, its margins provided ameliorated conditions suitable for establishment. Moss covered areas were the most preferred sites. At Schefferville, ten perturbations involving fertilization, lichen removal, polyethylene overlays, and aqueous lichen extract application were effected on sixteen experimental plots. Branch elongation, needle nitrogen and bole diameter were statistically analyzed as functions of various monitored edaphic conditions. Leader elongation and needle nitrogen was measured at Kevo. Lichen presence over the term of both studies showed net beneficial effect on the trees; lichen extracts had significant detrimental effects. Seed germination was suppressed by lichen presence but enhanced by lichen induced low soil pH when in contact with the soil.

Mémoire (M.Ress.Renouv.)-- Université du Québec à Chicoutimi, 1993. / Bibliogr.: f. 145-153. Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Ress.Renouv.)-- Université du Québec à Chicoutimi, 1993. / Document électronique également accessible en format PDF. CaQCU