Alnus cordata was the most productive species and Tilia platyphyllos the least. Five of the six tree species had crude protein values above 140 g kg-1 dry matter, which is higher than most grass-based forage in summer. Salix caprea was the species with the highest palatability and in vitro digestibility and reduced in vitro methane production per g of digested organic matter by up to 27%, when included at 60% in the diet.