Donkey feeding behavior in shrub- and tree-encroached pastures in Gran Paradiso National Park

Since the 1950s, land abandonment has caused widespread encroachment of Alpine grasslands by woody species (shrubs and trees), resulting in a decrease in forage quality and quantity. Silvopastoral systems with livestock hardy species able to consume woody plants, such as donkeys, could represent a suitable option for the management and recovery of encroached grasslands. In this study, the feeding behaviour of a herd of 18 donkeys was analysed by direct observations (15-seconds record, 20-second pause) in a 11 ha pasture in Gran Paradiso National Park during summer 2023. Available and consumed plants were recorded in the feeding station of donkeys, spatially identified as a volume extending 2 m in height from the ground surface, with a radius of 0.5 m around animal mouth. Research questions were: (1) do donkeys feed on a mixture of herbaceous and woody plant species, following a mixed diet? (2) Are some plants preferred and others refused? (3) Is the relative consumption of woody species influenced by their abundance in the environment? A total of 6472 observations were carried out by two to nine observers throughout the grazing season. The available-consumed relationships (modeled with GAMs) were analyzed with cluster analysis and three groups of plants were identified: preferred, indifferently consumed, and rejected. The results showed a preference of donkeys for herbaceous forages (66-96% of the diet), although they were able to browse woody species and ferns (0-22%), making this livestock species effective in contrasting encroaching species. Donkeys preferred Fraxinus excelsior and Rubus idaeus, whereas Hypericum perforatum and Betula pendula were refused. Furthermore, the consumption of many species - particularly, Alnus viridis and Athyrium filix-femina - was influenced by their availability in the environment and increased proportionally to it. These results suggest that the integration of donkeys into the grazing pasture management systems could be a promising strategy for maintaining grassland biodiversity and improve forage quality of Alpine pastoral ecosystems. Research supported by Gran Paradiso National Park.