Dendroclimatology of Picea glauca at tree line in northern Labrador, Canada

This thesis applies standard dendroclimatological techniques to compare the radial growth response of the dominant species persisting across treeline in northern Labrador, Canada. White spruce (Picea glauca (Moench) Voss) tree-ring width chronologies were constructed from ten sites spanning treeline in northern Labrador from the Labrador Sea to the Quebec border. The effects of climate on radial tree growth were examined at various spatial and temporal scales. -- This is the first study to conduct a regional dendroclimatological analysis of Labrador's treeline with respect to delineating the extent of maritime and continental climatic influences on radial growth. Pearson product moment correlations and response function analyses were used to identify two distinct tree bioclimate zones acting on treeline in northern Labrador. The arctic-maritime zone consists of the northern extension of treeline along Labrador's coast and is primarily characterized by a strong positive correlation to June and July temperatures of the current growing season. Also defined is the subarctic maritime zone encompassing the area immediately below the arctic maritime zone. Trees here also demonstrate a strong positive sensitivity to June and July temperatures, as well as a negative association to current spring temperatures and a positive correlation to previous fall temperatures. These findings indicate that a bioclimatic shifting of the climate-radial growth relationship of white spruce occurs at roughly 56°75'N along treeline in northern Labrador. Furthermore, as white spruce trees at their northern range limit are expected to be susceptible to future changes in climate, radial growth models using only climate variables are produced and future forecasts (2009 - 2100) are also developed. Models were constructed using a stepwise regression analysis, employing monthly compiled variables for all ten sites. Model outputs were cross-referenced and important climate variables to white spruce radial growth were verified and landscape patterns of climatic responses were noted. Radial-growth forecast model outputs illustrate a generally decreasing radial growth rate at extreme northern locales, and moderate radial growth increases for more southern sites by 2100 AD. The radial growth forecasts produced here suggest that southern and intermediate latitude treeline sites may expand inland, while no expansion is expected at extreme northern locales along the coast