Wild boar (Sus scrofa) increases species diversity of semidry grassland: Field experiment with simulated soil disturbances

BACKGROUND: Foraging activities of wild boar (Sus scrofa) create small‐scale soil disturbances in many different vegetation types. Rooting alters species composition by opening niches for less‐competitive plants and, as a recurrent factor, becomes a part of the community disturbance regime. Vegetation responses to wild boar disturbance have mostly been studied in the boar's non‐native range or in native forest, rather than in open habitats in the native range. We investigate the response of open European semidry grassland vegetation dominated by Brachypodium pinnatum to native wild boar pressure in an abandoned agricultural landscape. METHODS: To describe the disturbance regime, we repeatedly mapped rooted patches during a 5‐year period. Additionally, to study the vegetation response, we performed an artificial disturbance experiment by creating 30 pairs of simulated disturbances and undisturbed plots. The vegetation composition of the paired plots was repeatedly sampled five times in eight years of the study. RESULTS: Based on repeated mapping of disturbances, we predict that if the disturbance regime we observed during the 5‐year period were maintained over the long term, it would yield a stable vegetation ratio consisting of 98.7% of the grassland undisturbed, 0.4% with fresh disturbance, and 0.9% in older successional stages. Vegetation composition in the artificially disturbed plots was continuously converging to that of undisturbed vegetation, but these disturbed plots still differed significantly in composition and had higher species number, even after eight years of succession. SYNTHESIS: Our results thus show that wild boar disturbance regime in its native range increases heterogeneity and species diversity of semidry grassland vegetation.