Potential of Agricultural Plantations and Orchards to Support Understory Forest Bird Diversity in Southeast Asia

Tropical forests hold two-thirds of the world's biodiversity but have declined due to forest degradation and deforestation, mainly driven by agricultural expansion. Although agricultural lands, such as plantations and orchards, are matrices (i.e., unsuitable habitats) for many forest species in general, their impact on biodiversity could largely differ depending on the type of agricultural land and management practices. Therefore, understanding the impact of different agricultural land types on biodiversity is important for planning matrix management in tropical agricultural landscapes. This study assessed the potential of monoculture oil palm and rubber tree plantations, as well as polyculture orchards, to support understory bird diversity compared to forest reserves in Peninsular Malaysia using mist-netting conducted between 2017-2023. Orchards recorded the highest bird abundance and richness among agricultural lands, but all agricultural lands had less than half the understory bird species found in forest reserves. Bird species composition also differed significantly among all habitats; forest specialists dominated (81.8%) in forest reserves, whereas nonforest specialists were dominant in orchards (76.3%), oil palm (100%), and rubber tree plantations (100%). Among habitat variables, understory vegetation covers positively affected bird species richness. Our results suggest that, despite having much lower diversity than forest reserves, polyculture orchards had some forest-specialist species that possibly spilled over from forest reserves, and thus, are better habitats for understory bird communities than monoculture plantations. Maintaining crop diversity and understory vegetation complexity can improve matrix quality and mitigate the impact on biodiversity in landscapes dominated by monoculture plantations.