Tree growth and disturbance dynamics in old-growth subalpine spruce forests of the Western Carpathians

Abstract

Are the dynamics of natural subalpine spruce ( Picea abies (L.) Karst.) forests of central Europe governed by stand-replacing disturbances caused mostly by winds or by moderate disturbances resulting from bark beetle outbreaks? We analyzed tree-ring series from subalpine spruce forests in two mountain ranges of the Western Carpathians to determine the frequency and severity of disturbances and their effects on tree recruitment. The boundary-line method was employed to identify significant growth releases, interpreted as results of disturbances. In both study areas, major releases were not numerous but were regularly distributed over time. We found no evidence for stand-replacing disturbances. This result contrasts sharply with earlier findings from the Western Carpathians. The age structure of the forests studied indicates that the amount of tree recruitment was greater 150–200 years ago than in the subsequent 150 years. Our results suggest that stand dynamics in the forests analyzed are driven by numerous events of limited spatial extent and that stand-replacing disturbances are not necessary for the development of unimodal age structure.