Limited evidence of biodiversity spillover from forest fragments into oil palm plantations in the Amazon

Oil palm expansion is a major driver of the biodiversity extinction
crisis. Emerging frontiers of oil palm development in the Amazon risk
major biodiversity loss. Spillover of biodiversity from adjacent forest
fragments into plantations may reduce the loss of functional and
phylogenetic diversity, but the extent of this effect remains unclear. We
surveyed bird communities in large forest fragments and oil palm
plantations in the Brazilian Amazon during the dry seasons of 2012 and
2016. We assessed the loss of avian functional and phylogenetic diversity
due to forest conversion, its impact on community structure, and whether
the percentage of forest and proximity to fragments in oil palm points
mitigate losses. Compared to forest fragments, oil palm plantations
exhibited lower phylogenetic and functional diversity. Conversion had a
strong negative effect on functional structure, shifting communities from
overdispersed to clustered, while phylogenetic structure remained largely
unchanged. Trait composition also differed significantly between habitats,
with shifts in the distribution of traits related to foraging behaviour,
movement, and flight efficiency. Surrounding forest cover did not mitigate
the loss of functional and phylogenetic diversity in plantations. Although
bird communities closer to forest edges showed higher mean nearest taxon
distance (MNTD) and its standardized value (sesMNTD), the spillover effect
was weak, as indicated by the low R² in our models. Synthesis and
Applications: Converting primary forest into oil palm plantations results
in substantial biodiversity losses, highlighting the urgent need to
preserve the few remaining large forest fragments in the area. Measures
that enhance matrix permeability are essential to conserving the
evolutionary and functional integrity of Amazonian landscapes and
mitigating the negative effects of oil palm expansion.