Effects of microsite on growth of Pinus cembra in the subalpine zone of the Austrian Alps

Abstract

We examined growth in Pinus cembra L. (28 years old) across the treeline ecotone from 1900 to 2100 m elevation in the Alps. Eighteen plots were chosen at different microsites which are defined as a combination of elevation and steepness (gentle vs. steep slope) on a south-facing slope in the Schmirn Valley, Tyrol/Austria. Over the range of altitudes studied, elevation and steepness had influences on growth depending on tree size: (1) Elevation and steepness had little effect on growth as long as trees were very small (< 0.5 m in height); (2) Both elevation and steepness affected tree growth significantly when the tree height was between 0.5 and 3 m; (3) As trees exceeded 3 m in height, tree canopies fully covered the ground surface and created a forest microclimate causing growth to decline with increasing elevation, irrespective of steepness. We conclude that the microsite related to microclimate, controls growth during the early life stages of trees, but following canopy closure the local climate (mesoclimate) associated with topography begins to determine tree growth.