Intermediate foraging large herbivores maintain semi-open habitats in wilderness landscape simulations

Abstract

In the context of the rewilding Europe debate, the German national strategy on biodiversity aims to dedicate two percent of the German state area to wilderness development until 2020. Many of these potential large wilderness reserves harbor open habitats that require protection according to the Flora-Fauna-Habitat-directive of the European Union. As forests prevail in potential natural vegetation, research is required, to which extent wild large herbivores and natural disturbances may create semi-open landscape patterns in the long-term. We used the spatially explicit process-based model of pasture-woodland ecosystem dynamics WoodPaM, to analyze the long-term interactions between intermediate foraging large wild herbivores and vegetation dynamics in edaphically heterogeneous forest-grassland mosaic landscapes. We newly implemented a routine for intermediate foraging herbivores. We determined herbivore impact on vegetation from the quantitative balance between the demand and supply of herbaceous forage and woody browse. In abstract landscapes that represent the conditions in the established German wilderness area "Döberitzer Heide", we simulated potential future landscape dynamics on open land, in forest and along forest edges with and without intermediate foraging large herbivores and for a climate change scenario.In our simulations the currently open landscape was conserved and even more the opening of current oak and beech forest was promoted. Canopy thinning and patch-mosaics of oak, birch, poplar and pine stands increased the overall nature conservation value in the long-term. To the contrary, open habitats were lost in simulations without herbivores. Moreover, our simulations suggested that intermediate foraging herbivores are especially suitable to maintain semi-open landscapes in wilderness areas, because (i) no additional winter forage was required, the natural availability of browse was sufficient. (ii) Their grazing maintained open land and their browsing thinned tree canopies even on poor sites that were unattractive for foraging. Here, habitat was maintained for threatened species from dry grasslands.