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Terrestrial gastropods are important decomposers, herbivores, and prey items in forest systems and constitute a poorly understood element of forest biodiversity in Canada. I studied gastropod assemblages in relation to forest cover type and in response to variable retention harvesting in the mixedwood boreal forest of northwestern Alberta. Gastropods were sampled using two methods: board traps and collection of litter samples. Gastropod assemblages were influenced by canopy composition, with most gastropods of the mixedwood showing a strong affinity for broadleaf dominated forests. Tree species mixture influenced gastropod distribution; basal tree area of either conifer or broadleaf trees was generally associated with gastropod distribution within a stand. Harvesting was clearly associated with increased abundance of many species 9 years post-harvest, however, abundance declined for other species. Harvesting with retention helps to maintain pre-harvest boreal gastropod assemblages and will likely conserve boreal gastropod assemblages if used as a tool for biodiversity management. / Conservation Biology

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Forest tent caterpillar (Malacosoma disstria Hübner; FTC), a major defoliator of aspen trees, occupies both aspen and mixedwood forest stands in Alberta’s boreal forest. Forest stand composition could influence the spatial pattern of FTC outbreaks if mortality from natural enemies differs between stand types. I conducted field experiments to determine whether predator- or parasitoid-caused mortality of FTC differed between aspen and mixedwood forest stands and developed a spatial population model to determine the effects of variation in generalist predation on the spread of an FTC outbreak, including the effects of potential predator-caused Allee effects. Generalist predation on FTC was higher in aspen stands than in mixedwood stands, and the spatial model suggests that these observed differences may be sufficiently large to impact FTC outbreak spread rates. Forest stand composition may contribute to the spatial pattern of FTC outbreaks through variation in the impacts of predators on FTC populations. / Ecology

The main goal of this thesis was to improve our understanding of the long-term effects of establishment treatments and climate change on lodgepole pine and white spruce growth in the western boreal forests. My dissertation also investigated the combined effects of climate and competition on white spruce and trembling aspen growth in boreal mixtures. In the first part of the thesis I evaluated the effects of site preparation treatments on growth of lodgepole pine and white spruce in north-eastern British Columbia. Results indicate that mechanical site preparation can provide yield gains of up-to 10 percent for pine and spruce at 60 and 80 years, respectively. These stands are showing a Type 1 growth response which implies that the treatment effect will eventually cease 90-100 years after planting. In the second part of the thesis I explored pine and spruce growth in relation to past climate and site preparation. Results indicate that up-to 45% and 37% of the respective variation in spruce and pine growth can be explained by selected climatic variables. Future projections indicated that height growth of young pine plantations in the sub-boreal zone could benefit (in the short term) from longer growing seasons by up-to 12% on untreated stands. Untreated young spruce plantations in the boreal zone may suffer height growth decreases of up-to 10% due to increased drought-stress. Vegetation control and mechanical site preparation treatments appear to mitigate effects of climate change to some extent. In the third part of the thesis I explored the combined effects of climate and trembling aspen competition on spruce and aspen growth using data from a long-term study in the boreal zone. Results indicate that climate variables and initial size of the tree can account for significant portions of the annual growth of spruce. Including an estimate of aspen competition in the equations improved the predictive ability of these models. Evidence of the inter-annual variability in aspen competitiveness on spruce and aspen growth indicates that the stress-gradient hypothesis can be applied in boreal mixedwood forests. / Forest Biology and Management

This literature review is a synthesis of recent publications and developments regarding the growing acceptance and potential of Alnus rubra (Bong) commonly called red alder. The project summarized some of the concerns and benefits of including red alder in coastal forest mixedwood management strategies. Some of the concerns include overtopping of conifers and competition for light. Some benefits include increases to site productivity, biodiversity, forest health and diversification of the coastal forest industry. It also examined past and current industry and government policies towards alder in mixedwood management and recent changes in some of these policies including the just released “Hardwood Management in the Coast Forest Region” policy paper. There is now recognition of the importance of alder management and there is a framework in place for patch mixedwood management in coastal BC. But before intimate mixedwood strategies are accepted and used operationally, further research and trials are required. There needs to be a better understanding of both the competetitive and beneficial effects of red alder in mixture with conifers for complex forests to in order to assist forest managers in making sustainable management decisions.

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