Green alder is an encroaching species on mountain pastures, which causes several agro-environmental issues. Targeted grazing could be a useful tool to limit its spread. We evaluated the nutritional value of green alder leaves and their selection by different livestock categories, such as Capra Grigia and Chamois Coloured goats, Highland cattle and heifers of productive breeds. We collected green alder leaves in summer and analysed their chemical composition and in vitro gas production and digestibility. Mean crude protein content was 201 g kg-1 DM, condensed tannins ranged from 3.4 to 40.9 g kg-1 DM. In vitro, a diet containing 20% green alder leaves showed the highest digestibility and lowest CH4 emissions at the beginning of summer, with lower CH4 emissions compared to a 100% hay diet. Feeding observations showed that green alder accounted for 45% of goats’ diet, 12% of Highland cattle diet, and 1.4% of heifers’ diet. Green alder was actively selected by goats, while Highland cattle were indifferent, and heifers avoided it. Our results suggest that green alder can be a valuable forage, especially at the beginning of the summer. Moreover, robust livestock can exploit green alder and its incorporation into animal diets could reduce greenhouse gas emissions.