Natural forest at landscape scale is most important for bird conservation in rubber plantation

Rubber is one of the most rapidly expanding monocultures in the tropics, and has precipitated biodiversity and ecosystem function loss. Identifying measures to improve biodiversity outcomes in rubber-forest mosaics is critical for tropical fauna. We evaluated how avian diversity responded to plantation- and landscape-level environmental variables. The most parsimonious model at the plot scale contained inter-tree planting distance for rubber, plantation age, and inverse distance weight of forest as predictors. The most supported model at the landscape scale contained both distance to forest patches larger than 100 ha and natural forest area as predictors. Model predictions indicated that natural forest area had the largest contribution to bird richness at landscape levels; avian diversity was projected to more than double when natural forest area increased from 25% to 75%. Frugivores and insectivores exhibited the strongest response to gains in natural forest area. Our results indicated that plantation smallholders could achieve biodiversity gains by retaining older trees and planting rubber trees with larger gaps, but that the most critical intervention is retaining large natural forest patches.