Monitoring Recent Vegetation Changes in Nutrient-Rich Beechwoods in Central Germany

Abstract

Recent changes in the vegetation structure and site conditions of nutrient-rich beech woods were studied in a set of permanent plots uninfluenced by silviculture. Within the nine-year observation period, there has been a remarkable temporal variation in vegetation structure reflecting significant changes in soil reaction and nitrogen supply of the top soil. By means of redundancy analysis part of the spatial variation in the data set could be partialled out. A temporary increase of nitratophilous species in the herbaceous layer is accompanied by the development of a shrub layer formed largely by Sambucus sp. and Rubus idaeus. This process is induced obviously by considerable defoliation of the overstorey tree crowns as a consequence of forest decline. The increase in light availability and nitrogen supply as expressed by the increase of nitratophilous species in the ground vegetation and the shrub layer turns out to be more or less reversible. The suppressed trees of the understorey profit by the increased light level as well and show an increase in foliation, whereas the overstorey trees develop adventitious twigs and branches in the lower trunk area. As an outcome the light availability in the shrub and herbaceous layer decreases again from the middle of the observation period onward and the vegetation structure returns back close to the original situation. However, the increase in the pH of the top soil appears to be more permanent.