Unravelling the effects of climate, composition and disturbance on forest productivity in the eastern boreal forest

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Changing climate, disturbance regimes and their interactions are modifying ecosystem dynamics especially in high latitude forests; my long-term objective is to evaluate changes in decades of growth, population and community dynamics of the dominant tree species across a large region of the eastern boreal. Specifically, I will combine growth patterns derived from a province wide collection of tree ring cores to study climate sensitivity of the growth of boreal trees across large environmental gradients. We will investigate both species and site-level within species responses. Another short-term objective is to evaluate long-term changes in population (mortality vs recruitment) and community (changes in composition) dynamics of these same species along east-west (precipitation) and north-south (temperature) gradients. As insects are ectotherms they should also react strongly to warming and may interact with moisture stresses that predispose trees to increased mortality. With range expansion of the spruce budworm, an outbreaking insect, mixes of species that are rare in its traditional range will be increasing under attack. The effects of associational relationships (increased resistance vs susceptibility) in different mixes of boreal tree species will be used as a proxy for resilience to abiotic (climate) and biotic (insects) stresses in boreal forest systems at different spatial scales. To answer these questions, my graduate students and I will combine a large data base of more than 365 000 tree cores collected from across the province with a temporal series of aerial photos taken systematically every decade since 1945. We will also use defoliation and species mixing data from permanent sample plots established at the beginning of the current spruce budworm outbreak. Coupled with geomorphological data bases and climatic data for the last 70 years we will evaluate the effect of climate by site type on the growth and population dynamics of each species Combining temporal and spatial analyses of tree changes will allow us to better explain the influence of recent changes in climate on forest composition and productivity and to then predict future change. By exploring species responses over large temporal and scale scales with multiple tree species this work will also allow me to further our understanding of between species vs within species site-level variability in tree responses to climate change. Most current approaches evaluate one response variable at a time (i.e. growth, or mortality). A multi-pronged approach applied to the boreal forest will permit us to more fully evaluate the real effects of climate change on the productivity of an ecosystem that has undergone some of the largest climatic changes.