Thèse (M.Ress.Renouv..) -- Université du Québec à Chicoutimi, 2006. / Bibliogr.: f. 40-52. Document électronique également accessible en format PDF. CaQCU

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In many natural forests, forest managers fell and debark spruces (Picea abies) colonised by theEuropean spruce bark beetle (Ips typographus) to prevent the beetle from spreading to other tree stands. The aim of this study was to examine how this method affects the biodiversity of other saproxylic beetle species. Eclector traps were installed on debarked and non-debarked dead spruces of four different ages in four nature reserves to compare the richness and composition of saproxylic beetles. The results indicated that a significantly higher number of species and individuals emerged from standing dead trees with bark compared to debarked logs. The highest emergence of species and individuals occurred in one-year-old standing trees with bark. There was a significant interaction between the type and the age of wood, suggesting thatthe richness declined with the aging of wood with bark, while it remained constantly low in debarked logs. The species composition varied greatly between standing trees with bark and debarked logs, as well as between standing trees with bark of different ages. This study demonstrated that debarking spruces as a pest control method reduces the diversity of nontarget saproxylic beetle species. Potential reasons behind that could be the hardening and drying of consumable parts of the wood, rendering it inhabitable for many saproxylic organisms, as well as the presence of the European spruce bark beetle itself, which is associated with many other species.

Trembling aspen (Populus tremuloides Michx.) is one of the most common tree species in the boreal and temperate forests of North America. It grows on many different sites and associates with a variety of tree species. In BC, aspen is frequent throughout all submontane and montane continental forested zones. Relationships between environmental factors and forest productivity have been the subjects of many studies. Most of these studies, using various topographic, soil, physical and chemical properties as independent variables, had limited success in accounting for the variation in SI over a large geographic area. The objectives of this study were (1) to quantify relationships between aspen SI and environmental factors at two spatial scales, and (2) to develop predictive SI models from easily measurable environmental factors.

Accurate and reliable predictions of site index (height of dominant trees at a reference age, usually 50 years at breast-height) for timber crop species is essential for silvicultural site-specific decision making. Site index can be predicted from site quality once the relationship between site index and site quality has been quantified. Site quality is defined as the sum of all environmental factors affecting the biotic community, such as the factors directly influencing the growth of vascular plants (light, heat, soil moisture, soil nutrients, and soil aeration). Since these factors vary greatly in time, indirect estimates of site quality have widely been used as predictors for site index in various multiple regression models. Trembling aspen (Populus tremuloides Michx.) is the most widely distributed broadleaf species in British Columbia, especially in the Boreal White and Black Spruce (BWBS) biogeoclimatic zone. Growing this species for sustainable timber production requires a good understanding of its productivity attributes and accurate predictions of its growth. This extension note presents (1) relationships between trembling aspen site index and some indirect measures of site quality, and (2) site index prediction models using the indirect measures of site quality as predictors.

The boreal forest is confined to the Northern Hemisphere and is the most continuous and extensive forest in the world. In North America boreal forest extends from the Pacific to Atlantic coast spanning over 10° latitude. White spruce (Picea glauca (Moench) Voss), black spruce (P. mariana (Mill.) B.S.P.), and trembling aspen (Populus tremuloides Michx.) are among the dominant tree species. Black spruce and trembling aspen may form pure stands and occupy similar sites as their edaphic amplitudes overlap; however, spruce is rare on water-deficient sites and aspen does not tolerate excess water. Despite many studies conducted in the North American boreal forest, little is known about relationships between the boreal understory vegetation and softwood or hardwood canopy species in different climate regions. Furthermore, the variation in species diversity and succession between the stands dominated by coniferous trees and those dominated by broadleaved trees within the same region is unknown. The objectives of this study are to determine (1) the difference in the species diversity and floristic composition of understory vegetation between black spruce and trembling aspen stands within the same climatic region, and (2) how the species diversity and floristic composition of understory vegetation in each stand type vary with climate, and soil moisture and soil nutrient conditions.

Forest disturbances and the spatial patterns they create affect ecosystem processes through their influence on forest vegetation from individual trees to landscapes. In the boreal and mixed-wood forests of eastern Canada the main agents of disturbance are logging, fire, and defoliation by the spruce budworm (SBW, Choristoneura fumiferana). These disturbances are similar in that they remove forest biomass and influence forest succession but also distinct in that logging creates patterns that are different than those created by natural disturbances. All disturbances are indirectly linked to each other through their mutual effects on forest spatial structure and succession. Through such feedbacks, spatial disturbance legacies can facilitate or constrain further disturbances, including forest management. Surprisingly, the long term spatial consequences of interactions among multiple natural and anthropogenic disturbances remain largely unexplored. This thesis investigates how, and at what spatial scale, legacies in forest composition and age structure influence natural disturbance dynamics, and how natural disturbances constrain forest management. I address four specific questions: (i) For how long do spatial legacies of different forest management strategies persist on the landscape? (ii) How do interactions among logging, fire, SBW, and succession affect timber availability and long term forest patterns in age and composition? (iii) How do these patterns differ from those created by each disturbance individually? And, (iv) How can management be used to reduce the extent and severity of fires and SBW defoliation through the manipulation of forest structure? The key scientific innovations of this thesis are: (i) Characterization of the duration and influence of spatial legacies on forest disturbances and sustainability; (ii) Development of a dynamic spatial forest simulation model that includes distinct successional rules that respond to different types of disturbance and shifts in disturbance regimes; and, (iii) Development and application of a wavelet-based significance testing framework to identify key scales of expression in forest spatial patterns. These innovations provide a scientific basis for landscape level forest management strategies designed to reduce the long term impacts of defoliating insects and to meet multiple objectives.

Population genetic analyses can provide information about both neutral and selective evolutionary processes shaping genetic variation. In this thesis, extensive population genetic methods were used to make inferences about genetic drift and selection in spruce species. In paper I we studied four species from the Qinghai-Tibetan Plateau (QTP): Picea likiangensis, P. purpurea, P. wilsonii and P. schrenkiana. Big differences in estimates of genetic diversity and Ne were observed in the more restricted species, P. schrenkiana, and the other more widely distributed species. Furthermore, P. purpurea appears to be a hybrid between P. likiangensis and P. wilsonii. In paper II we used Approximate Bayesian Computation (ABC) to find that the data support a drastic reduction of Ne in Taiwan spruce around 300-500 kya, in line with evidence from the pollen records. The split from P. wilsonii was dated to between 4-8 mya, around the time that Taiwan was formed. These analyses relied on a small sample size, and so in Paper III we investigated the impact of small datasets on the power to distinguish between models in ABC. We found that when genetic diversity is low there is little power to distinguish between simple coalescent models and this can determine the number of samples and loci required. In paper IV we studied the relative importance of genetic drift and selection in four spruce species with differing Ne: P. abies, P. glauca, P. jezoensis and P. breweriana. P. breweriana, which has a low Ne, exhibits a low fraction of adaptive substitutions, while P. abies has high Ne and a high fraction of adaptive substitutions. The other two spruce, however, do not support this suggesting other factors a more important. In paper V we find that several SNPs correlate with both a key adaptive trait (budset) and latitude. The expression of one in particular (PoFTL2) correlates with budset and was previously indentified in P. abies. These studies have helped characterise the importance of different population genetic processes in shaping genetic variation in spruce species and has laid some solid groundwork for future studies of spruce.

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