How wind affects growth in treeline Picea abies

Abstract

Globally, treeline position is driven by temperatures during the growing season. Nevertheless, at regional scales, the position of uppermost tree stands also reflects other climatic factors, including wind action. It remains uncertain, however, how much do intense winds depress the treeline below its potential position. Our objective was to quantify the effect of wind speed on the possible depression of upper forest margins below the potential treeline in a windy mountain range with the treeline located close to summit areas. In the Giant Mountains, Czech Republic, growth parameters and symptoms of wind-induced loss of biomass were determined for Norway spruce (Picea abies [L] Karst.) in 70 plots distributed along a gradient of wind speed within the treeline ecotone. Wind speed was modelled for each plot. General linear models were applied to discern the effect of wind on tree growth. Our results show that high wind speeds are reflected in the presence of clonal tree islands and irregular tree crowns. Despite evident wind-induced biomass loss, radial growth was not significantly affected, and the effect of wind on height increment was limited only to parts of the stem from 2 m above ground. Considering that the height growth was substantially reduced by wind in about half of the treeline area, and wind was able to limit only growth of trees taller than 2 m, the overall wind-induced depression of highest treeline positions is probably low, even in windy mountain regions.