Forest dynamics in the strict forest reserve Echinger Lohe - findings after four decades of permanent plot research

The Echinger Lohe strict forest reserve in the vicinity of Munich (Germany) is a secondary oak-hornbeam-forest (Galio-Carpinetum), which developed through coppice-with-standards and silvopasture management. Since the 1970s various vegetation surveys have been conducted at permanent monitoring plots. In 2017 the most recent vegetation survey was carried out with the specific aim to test for vegetation changes through time and to interpret potential changes based on vegetation indicators. Indeed changes were noticeable in all vegetation layers (herb-, shrub- and tree-layer). Specifically, a change in tree species composition was found. While ash (Fraxinus excelsior), maple (Acer pseudoplatanus) and hornbeam (Carpinus betulus) increased in timber volume, oak (Quercus robur) timber volume decreased throughout time. Unlike expectations, the Ash dieback has not caused significant decreases in the ash timber volume, although the disease is already widely distributed in the Echinger Lohe strict forest reserve. Indeed, ash is the tree species, which showed the highest increases in timber volume besides hornbeam and maple. However, it can be assumed that this will change in the next years when large proportions of ash will likely die due to the disease and its subsequent damages. Also, changes in the shrub layer were noticeable in terms of a decrease in species diversity. Along with these changes in shrub- and tree-species diversity, a decrease in the coverage was noted for these species groups. Some species, e.g. oak, which is especially important for the species- and structural composition of the Galio-Carpinetum forest, were not longer detected in the shrub layer at the sampling plots. Within the herb layer especially an increase of shade-tolerant species as well as a decrease in light-dependent species was noticeable. Species with positive and species with negative responses can also be differentiated in terms of their nutrient demands. The 'winners' are mainly species which prefer mesotrophic to eutrophic habitat conditions, while species with preference for oligotrophic habitat conditions can be considered 'losers' through time. The main contributing factors for the noted changes are the discontinuation of the management practices of the formerly intensively used forest, anthropogenic nitrogen intake as well as a high browsing pressure by ungulates. In the intermediate and long term, these factors will likely lead to a loss of the characteristic species- and structural diversity of the oak-hornbeam-forest and concurrently, to a decline of the conservation status in the protected Echinger Lohe forest reserve.