Ecotonal dynamics of the altitudinal forest limit are affected by terrain and vegetation structure variables: an example from the Sudetes Mountains in Central Europe

摘要

At the landscape scale, the response of alpine treelines to increasing temperatures often varies due to second-order factors such as terrain properties, vegetation structure, and land use. In this study, we examined the influence of topographic and vegetation-structure variables on spatial patterns of treeline ecotone shifts in the Sudetes Mountains (Czech Republic). The changing positions of the alpine timberline and alpine treeline were determined from orthogonal aerial images allowing comparisons between 1936 and 2005. Our results showed that the alpine timberline advanced upward at an overall rate between 0.30 m yr-1 in the Hruby Jesenik Mountains (eastern part of the Sudetes) and 0.43 m yr(-1) in the Giant Mountains (western part of the Sudetes). Forest infilling was substantially greater than advances above original alpine treeline positions. Forest upward shifts occurred mostly on sites with already established, well-dispersed trees and low levels of prostrate dwarf pine cover. Topographic variables such as altitude and heat load affected forest advance if initial tree cover was low. The occurrence of competitive prostrate shrubs and the presence of climatically extreme convex parts of slopes appear to be important secondorder factors affecting treeline ecotone shifts, particularly at wind-affected treelines.