Dynamics of Hedera helix L. in Central European beech forests on limestone: results from long-term monitoring and experimental studies

Abstract

A spread of Hedera helix L. into beech forests has been observed during the last 20 years in Central Europe. As this species is susceptible to intensive frost, it is believed that climate change with mild winters is the responsible driver. Other factors can, however, be equally important including forest management, eutrophication, and browsing. We compared old (sampled 1955-1967) and recent (sampled 2000-2012) relev,s as well as managed/unmanaged, fenced/unfenced, and fertilized (N, P and a combination of both)/unfertilized plots sampled in two beech forest communities of the Gottinger Wald (Lower Saxony, Germany), and addressed these potential drivers and their effect on H. helix. The H. helix abundance significantly increased in the last 50 years, accompanied by a general temperature increase and a reduction in severe frost events suggesting an influence of climate change. Inter-annual changes in H. helix cover correlated with climate variables reveal an interplay between low minimum temperatures and snow cover. The spread of H. helix, however, also goes along with higher nitrogen availability and a reduction in browsing pressure. A fertilization experiment underlines a positive impact of N and P on the H. helix abundance, whereas fencing and management reduced it by promoting a competing shrub layer. Thus, climate change could not be identified as the main driver of a H. helix spread in the Gottinger Wald. It is rather caused by a complex interaction of changing abiotic (climate change and eutrophication) and biotic (browsing, competition) conditions, that is not fully understood yet.