Disturbance of the herbaceous layer after invasion of an eutrophic temperate forest by wild boar.
Disturbances of the soil and the tree canopy are crucial factors determining the diversity, composition and biomass of the herbaceous layer in forests. This study presents a detailed account of ground vegetation in permanent plots surveyed before and after invasion of wild boar (Sus scrofa) to a temperate deciduous broadleaf forest. Specifically, we aimed to quantify the effect of wild boar rooting on cover, richness and composition of spring ephemerals, summer green herbs and saplings of woody species in relation to tree canopy cover. Rooting frequency in sample plots increased from 0% in 2010 to 61% in 2013. In heavily rooted plots, the mean cover of spring ephemeral geophytes (mainly Anemone nemorosa, A. ranunculoides and Ranunculus ficaria) decreased from 75% to 39% between 2010 and 2013. Species richness of summer green herbs generally increased between 2010 and 2013 and was additionally positively affected by heavy rooting and low canopy cover. Rooting also caused heterogenization of the herbaceous layer and amplified ongoing compositional changes induced by changing light conditions. Frequency and richness of spring ephemeral and woody species remained unchanged. We conclude that overall species richness of the herbaceous layer may increase in the short-term as a result of increased plant recruitment and seed dispersal. However, wild boar rooting can greatly reduce the ground cover of spring ephemerals in eutrophic broadleaf forests, thereby threatening their important ecological function. To avoid long-term losses of characteristic spring flora elements, local population control of wild boar is necessary to reduce abundance and frequency of soil rooting.