The contrasting effects of local environmental conditions on tree growth between populations at different latitudes

Abstract

To forecast future forest productivity and function it is critical to account for forests’ responses to current environmental conditions. Current widely used climate envelope approaches, i.e., correlations between climatic variables and the presence of a species, simulate responses for the whole species and predict future range based solely on climatic suitability. However, most tree species will not be able to migrate to environmentally suitable locations fast enough to cope with climate change. Furthermore, short-term tree responses to climate change will take place within current populations, and these populations, acclimated to their local environments, are not likely to respond similarly to climate change. Thus, to develop reliable forecasts of forest responses to climate change, we need to consider this variability among populations. In this study, we tested the effect of environmental conditions on the growth of two common maples species (Acer rubrum L. and Acer saccharum Marshall) at two different latitudes within their northern distributional range. We collected tree growth data, i.e., increment cores, and analyzed year to year variability in tree growth as a function of temperature and precipitation. We identified the times of the year with a stronger association with tree growth, indicating phenological differences between the two latitudes, and quantified growth as a function of those variables. Results showed divergent responses between species and between populations of the same species. Acer rubrum had a positive response to increasing summer temperature and precipitation in the north, but a negative association to increasing summer temperature in the south. Acer saccharum only showed significant responses in the south, negative to summer temperature increases and positive to higher precipitation. Predicted growth under difference climate scenarios predicted for the region, showed that northern populations and southern populations

did not significantly differ from current range of growth variability but, still, reflected future trends of decreased growth under a forecasted climate, i.e., higher temperatures and lower precipitation. These results document population level responses to environmental conditions of these two species providing latitude-specific guidance for future forest management.