Genes or Environment? White spruce and the divergence effect at Alaska's northern treeline

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The basis of tree-ring based climate reconstruction is the assumption of a stable response of tree growth to climate factors. Since the mid-1970s, an increased off-set between tree-ring based temperature reconstructions and measured temperatures was observed at high latitudes, called “divergence effect”. One reason for the divergence effect might be that some trees of a given population react with enhanced growth, others show decreasing growth. The proposed project addresses this problem for white spruce (Picea glauca) at the treeline in Alaska. It will elucidate whether the different behavior of trees is caused by genetic and/or environmental factors, comparing pairwise relatedness of tree microsatellite genotypes with growth response. If a genetic component is identified, cp markers will be used to test whether the differences in climate response 1) are caused by genetic introgression by hybridization with black spruce, 2) origin from different glacial refugia, or 3) from natural genetic variation that acts as preselective adaptation and allows the species to respond to changing environmental conditions in different ways. The findings will bear relevance to the practice of dendroclimatology as well as our understanding of how ecosystems react to global climate change.