The chemical composition, secondary metabolite concentration, digestibility parameters, and effect of polyethyleneglycol (PEG) on gas and methane production of plant material from four forage liana species: Clematis cirrhosa, Smilax aspera, Rubus ulmifolius and Hedera helix grazed by ruminants of Ain Khiar alder grove during the year were determined to assess their nutritive potential as well as their anti-methanogenic properties. C. cirrhosa and R. ulmifolius show the highest crude protein (CP) content (12.88-20.99%/kg DM), moderate NDF (32.78-45.9%/kg DM) and low ADL (5.11-12.97%/kg DM), making them the most digestible (48.06-65.04%). The incubated substrates of H. helix in autumn and winter had the lowest digestibility values (32.6 and 35.92%, respectively), given their high lignin contents (17.21 and 23.21%, respectively) and the effective nature of their tannins. The addition of PEG improved their gas production with increasing rates of 23.37% and 41.9%, respectively. This was not the case with C. cirrhosa in winter and spring for which PEG had a depressing effect on gas (- 4.42 and - 2.02%) and methane production (Algeria 37.23 and 33.3%), respectively. Based on the obtained results, the studied species confirm the excellent nutritive profiles that could guarantee a feeding resource throughout the year.