In Algeria, as in other Mediterranean regions, forage resources, particularly woody forage shrubs, play a crucial role as an alternative and supplementary feed source for ruminants. Their resilience to extreme climatic conditions, their evergreen foliage, and their ability to regrow after grazing make them strategic species in the forage calendar for ruminants in extensive farming systems. It is in this context that we investigated the effect of season on the digestibility of leaves from two forage species in northeastern Algeria: Phylleria media and Rubus fruticosus. Leaves from these species were collected in spring and autumn. Thus, the fermentation kinetics, methane production, and effect of polyethylene glycol on the fermentation of these leaves were investigated. After 72 h of incubation, the average gas production from Phylleria media was higher in autumn than in spring (68.87 vs 61.47 ml/0.2 g DM). In contrast, for Rubus fruticosus, the final gas production remained relatively stable between the two seasons (47.04 ml in spring compared to 46.29 ml in autumn). With regard to methane, production was higher in spring for both substrates. The addition of PEG reduced methane production in both R. fruticosus and P. media during spring. PEG had no significant effect in the autumn. Seasonality modulates fermentation pathways differently: autumn favors CO₂ production, while spring optimizes CH₄ production. These results highlight the importance of seasonal management of woody resources and reinforce the value of woody shrubs in extensive livestock systems, particularly during periods of herbaceous forage scarcity. Their contribution can thus improve food security.