What prevails in climatic response of Pinus sylvestris in-between its range limits in mountains: slope aspect or elevation?

Abstract

The roles of slope orientation and elevational temperature gradient were investigated for Scots pine (Pinus sylvestris L.) growth in the middle of its growth range, where these factors can significantly modulate microclimate and thus plant growth. We assumed that slope orientation causes more complex and severe effects than elevation because it influences all three main factors of plant growth: light, heat, and moisture. In addition to the total ring width, the earlywood and latewood width and latewood ratio were considered variables that contain information about tree ring growth during the season and wood structure over all tree life span on three sampling sites at different elevations and opposite slopes. Despite the observed dependence of pine growth rate on temperature and solar radiation, the mean latewood ratio is stable and similar between all sampling sites, being presumably defined by the genotype of individual trees. The seasonality of the climatic response of tree growth is bound to spatiotemporal variation of the vegetative season timing due to the elevational temperature lapse and local warming. However, its direction is primarily defined by slope orientation, where southern slope is moisture-limited, even at adjacent sites, and divergent climatic reactions of earlywood (weak moisture-limited in the last decades) and latewood growth (temperature-limited) were revealed on the northern slope.