Assessing the effects of oil palm replanting on arthropod biodiversity.
Palm oil is the most traded vegetable oil worldwide. Production is concentrated in Southeast Asia, where established oil palm plantations dominate the landscape in many regions. Although levels of biodiversity are much lower than in forest, mature oil palm plantations can support a wide range of generalist species. However, these species may be threatened, as large areas of plantation have already been, or will soon be, replanted as they near the end of their productive life (20-30 years). Replanting changes vegetation complexity and microclimate, but short- and long-term effects on biodiversity are largely unstudied. We surveyed an oil palm chronosequence (first-generation mature palms, and replanted second-generation palms aged 1, 3 and 8 years) in an industrial plantation in Riau, Indonesia to assess the impacts of replanting over an 8-year period on arthropods in the ground, understorey and canopy microhabitats. Replanting was carried out using current recommended strategies, which included staggering replanting events to promote landscape-level heterogeneity, retaining mature oil palm riparian buffers, planting a cover crop immediately after replanting, and using chopped mature palms as mulch after clearance. We assessed changes in total arthropod abundance and order-level community composition, as well as specific changes in spider communities. We observed no significant declines in total arthropod abundance after replanting, but arthropod order-level community composition varied across the chronosequence in all microhabitats. These findings were replicated, or more pronounced, in spider-specific analyses. Spider abundance and species richness decreased in the understorey in the first year after replanting (although these returned to pre-replanting levels after 3 years), and spider species-level community composition in all microhabitats differed significantly across the chronosequence. Synthesis and applications. Our findings indicate that total arthropod abundance is resilient to replanting of oil palm, but that replanting changes total arthropod and spider community composition and decreases spider abundance and species richness in some microhabitats. While it is somewhat encouraging from a management perspective that recommended replanting strategies maintain overall arthropod abundance, the changes in arthropod composition and spider biodiversity that we observed may impact ecosystem processes, such as pest control, in second-generation oil palm plantations, with potential implications for yield. Additional studies that focus on other taxonomic groups and assess the effects of individual replanting strategies are needed before the long-term ecological impacts of replanting on existing oil palm plantations can be fully determined.