Peri-urban forests are increasingly threatened by urbanization, fragmented governance, and limited land-use regulation, especially in Lebanon, where these landscapes play crucial ecological and cultural roles. Reliable sustainability assessment tools are needed to capture their multidimensional value and guide conservation strategies. This study applies the Landscape Sustainability Assessment (LSA) tool to Baabda Forest, a peri-urban green space of high ecological and cultural importance on the edge of Beirut, and compares the outcomes both with the LandScale framework and with results previously obtained from the Tannourine Cedar Forest Nature Reserve, a protected site in North Lebanon. Through a mixed-methods approach integrating spatial analysis, ecological fieldwork, socio-perceptual surveys, and institutional review, the research assessed ecological integrity, social functions, economic potential, and perceptual values. Findings show that Baabda Forest demonstrates significant ecological richness, cultural symbolism, and community engagement, but suffers from weak governance, lack of economic mechanisms, and absence of formal legal protection. In contrast, Tannourine benefits from structured management and national recognition, which strengthen its sustainability profile. The comparison between LSA and LandScale further reveals how international tools highlight governance and production issues but overlook cultural and perceptual dimensions that are critical in peri-urban contexts. This study demonstrates the added value of LSA as a holistic framework and emphasizes the need for participatory governance, sustainable economic activation, and legal designation to ensure Baabda Forest’s long-term sustainability, while providing insights transferable to similar landscapes globally.