Large mammalian herbivores are keystone species affecting the biodiversity and functioning of ecosystems, since herbivory directly influences plant species competitive ability. Thus, when managing habitats for conservation it is crucial to understand the selection patterns of large herbivores and their effect on plant diversity and assemblage. With this aim, we studied a pastoral system placed in central-eastern Alps, comparing late mowing with grazing by red deer.
We found that, with high stocking rates, red deer significantly affects the species and functional composition of alpine productive pastures, mostly by competitive exclusion of subordinate species due to the spread of poorly palatable, competitive, stress-tolerant tall grasses with strong avoidance strategies. We argued that grazing by red deer with high stocking rates is harmful when acts on formerly managed meadows, while it has a positive impact on plant diversity of long-term abandoned grasslands. Our results indicated that grazing by red deer with high stoking rates hinders the spread of successional/ruderal species, but allows the establishment of competitive dominant tall grasses. Our findings also confirmed the hypothesis that the impact of red deer on grassland biodiversity follows the intermediate disturbance hypothesis.
