Umwelt- und Nutzungswandel im Kalkbuchenwald (Hordelymo-Fagetum lathyretosum) – Ein Vergleich alter und neuer Vegetationsaufnahmen aus dem Göttinger Wald

Abstract

Schmidt, W., HeinrichS, S.: Environmental and land use change in beech forests on limestone (Hordelymo- Fagetum lathyretosum) - A comparison of old and recent vegetation surveys from the Göttinger Wald. - Hercynia N. F. 48 (2015): 21 – 50. Species rich mesophilous beech forests on limestone (Hordelymo-Fagetum lathyretosum) are rare in Central Europe. Although intensively used in the past, they remained close-to-nature and are therefore in the centre of nature conservation concepts that call for a larger area of unmanaged forests in order to promote biodiversity. By comparing old and recent vegetation surveys as well as surveys from managed and unmanaged forests sampled in the Hordelymo-Fagetum lathyretosum, we wanted to evaluate the effectiveness of the proposed management abandonment by simultaneously considering vegetation dynamics of vascular plants caused by environmental changes. In particular we asked: 1) How have structure, diversity and species composition changed? 2) Which factors have caused these changes? 3) What conclusions can be drawn for a future management of these forests? We compared 132 vegetation surveys of the Hordelymo-Fagetum lathyretosum sampled between 1955 and 1967 in managed forests with 155 surveys (including 50 surveys from now unmanaged forests) sampled within the same community between 2000 and 2012 by concentrating on vegetation structure, diversity and species composition. We as well contrasted the now unmanaged with the still managed stands. The shrub layer largely increased in the last 50 years, mainly caused by an intensified hunting. Beside the woody species, in particular shade-tolerant, nutrient demanding species increased in the understorey vegetation, whereas species of more open, nutrient poor forests decreased including many characteristic species of the Hordelymo-Fagetum lathyretosum. These changes could be detected in managed and unmanaged stands, and can be explained by a denser shrub layer changing the forest microclimate, by atmospheric nitrogen depositions and by more soil protecting forest management techniques compared to 50 years ago. An influence of global climate change can only be deduced from an increase of the evergreen, oceanic-distributed ivy (Hedera helix) and of spring geophytes (mainly Allium ursinum). The unmanaged forests were characterized by a denser tree layer, a higher proportion of species typical for closed forests and a lower proportion of disturbance indicators. Furthermore, they contained less species and showed a more homogeneous species composition compared to managed forests. The structure and floristic composition of mesophilous beech forests on limestone changed considerably in the last decades in both managed and unmanaged stands. Main reasons are the reduction in roe deer browsing and atmospheric nitrogen depositions that caused a loss in species and heterogeneity. This loss was in particular noticeable in today unmanaged forests and will further increase with an expansion of the unmanaged forest area in the future, if not natural disturbances will disrupt this succession. Key words: biodiversity, climate change, deer browsing, eutrophication, forest management, homogenization, nature conservation, winner / loser