Sheep Grazing and Wildfire: Disturbance Effects on Dry Grassland Vegetation in the Western Italian Alps

Land abandonment represents a major threat to the conservation of European semi-natural dry grasslands. To ensure biodiversity and habitat conservation, in this study, sheep grazing was reintroduced in abandoned Festuco-Brometea dry grasslands of a western Italian alpine valley. The experimental design included three treatments, along a gradient of increasing disturbance: (i) notgrazed, (ii) grazed, and (iii) penning areas. Unexpectedly, two years after grazing reintroduction, a wildfire hit the study area. To investigate the short-term effects of grazing and wildfire disturbances on vegetation, 62 permanent transects were monitored from 2014 to 2018. Vegetation cover, plant diversity, and richness and abundance of three functional groups of species were analyzed through generalized linear mixed models. Grazing caused little changes in vegetation, with the greatest effects observed in penning areas: the pioneer xerothermic species group, including many rare plant species, benefited from the reduction in the litter layer and the opening of gaps in the sward induced by trampling. The wildfire led to an increase in plant diversity and to changes in plant composition: dry grassland species decreased, while pioneer xerothermic and ruderal species increased their abundance. Short-term results suggest that both disturbances may foster the conservation of alpine dry grasslands.