Conservation value of low-elevation forests for birds in agroforestry-dominated landscapes in a biodiversity hotspot

Abstract

ABSTRACTProtected areas (PAs) and multi-use landscapes beyond PAs play important and complementary roles in conserving global biodiversity. Across the tropical forest biome, remnant forests and agroforestry plantations in mixed-use landscapes often have high taxonomic diversity, but their ability to sustain functionally and phylogenetically diverse assemblages and retain conservation-priority species is unclear. Additionally, our understanding of impacts of land-use change across species, function and communities is poor.In India’s Western Ghats (WG) biodiversity hotspot, like in many other tropical regions, PAs cover just 12% of the land and are concentrated in higher elevations. Here, in an approximately 15,000 km2landscape in the northern WG, we compared bird communities across six land-use categories: state-owned high-elevation PAs and low-elevation Reserved Forests beyond PAs, and privately-owned periodically clear-felled low-elevation forests and three types of low-elevation agroforestry plantations (cashew, mango, and rubber).We sampled 184 line transects totalling 137.5 km across habitats, compared taxonomic, functional, and phylogenetic diversity metrics and used joint species distribution models to test for species-trait-habitat associations.Forests in general and lowland forests in particular had higher taxonomic, functional and phylogenetic diversity, and higher occurrence probabilities of evergreen forest-affiliated, conservation-priority, and frugivores than agroforestry plantations. The ranking of land-use types varied across indicators, with rubber ranking higher than cashew and mango for functional and phylogenetic diversity but lower in species occurrence probabilities.Synthesis and Applications: Our findings underscore the irreplaceability of less-disturbed forests for birds in mixed-use landscapes, especially when considering multiple dimensions of biodiversity, habitat specialists, and conservation-priority species. We advocate the simultaneous examination at multiple levels (community, species and traits) to determine the impacts of land-use change as divergent information of conservation importance is gleaned from each level. Reserved and private forests of low elevations of the Northern Western Ghats are critical for avian conservation, given that they harbour significant diversity, and the absence of representative PAs in the region. Given the vulnerability of these low-elevation forests to conversion for non-forestry activities and overexploitation for fuelwood, there is a need to develop viable models of partnership with landowners in these multi-use landscapes for ecological restoration of degraded forests.