Land-use type shapes taxonomic, functional and phylogenetic structure of birds in multifunctional Himalayan traditional agroecosystems

Biodiversity conservation is challenging in the current pace of globalization, and requires an optimum model which maintains balance between development and conservation. Traditional agricultural landscapes are increasingly recognized as critical components of conservation, yet their capacity to sustain multiple dimensions of biodiversity remains poorly quantified, particularly in complex mountain systems. We assessed taxonomic (TD), functional (FD), and phylogenetic diversity (PD) of bird communities across five traditional agricultural systems: terrace rice cultivation (TRC), tea cultivation system (TCS), large cardamom-based agroforestry system (LCAS), farm-based agroforestry system (FAS), and agropastoral system (AP) along with corresponding adjacent natural forests in the Eastern Himalaya, an agrobiodiversity hotspot. Using standardized, multi-season bird samplings across 42 transects spanning a broad elevational gradient (772–3948 m), we recorded 9622 individuals representing 239 species and quantified ecological traits and evolutionary relationships to capture multidimensional diversity patterns. FAS and LCAS maintained high taxonomic and several components of functional diversity, in some cases comparable to or exceeding corresponding adjacent natural forests, whereas TRC and TCS showed reductions in taxonomic and/or multiple functional diversity metrics. Phylogenetic responses were more system-specific: TRC and TCS showed broadly comparable phylogenetic structure to the adjacent natural forests, whereas FAS exhibited significant phylogenetic clustering and lower ses MPD than its corresponding natural forest. AP also showed phylogenetic clustering relative to null expectations. Integrating these dimensions, the composite diversity index provided a comparative synthesis of multidimensional bird diversity, with FAS and LCAS exhibiting the highest mean values while revealing distinct biodiversity patterns among systems. Our findings demonstrate that traditional agricultural systems can make important and complementary contributions to maintaining multiple dimensions of bird diversity, although their conservation significance varies among systems and biodiversity dimensions. These findings emphasize the importance of system-specific conservation and land-use strategies that maintain traditional agricultural landscapes alongside natural forests in environmentally heterogeneous mountain regions.