DOI: 10.17863/cam.56212
title: Research data supporting "Assessing the effects of oil palm replanting on arthropod biodiversity"

description: Abstract. 1. 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. 2. We surveyed an oil palm chronosequence (first-generation mature palms, and replanted second-generation palms aged one, three, and eight years) in an industrial plantation in Riau, Indonesia to assess the impacts of replanting over an 8-year period on arthropods in the ground, understory, 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. 3. 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 understory 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. 4. 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. Whilst it is somewhat encouraging from a management perspective that recommended replanting strategies maintain overall arthropod abundance, the changes in 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. $$ \ $$ Methods. Study site. Fieldwork was based in industrial oil palm plantations in Riau, Sumatra, Indonesia (N0 55.559, E101 11.619). We established study sites across a chronosequence spanning four age cohorts in a space-for-time design, to investigate the impacts of replanting over an 8-year post-replanting period. Cohorts were: First-generation mature palms (31 - 33 years old; “Age M”); Second-generation one-year-old palms (“Age 1”); Second-generation three-year-old palms (“Age 3”); and second-generation eight-year-old palms (“Age 8”). $$ \ $$ Data collection. We measured vegetation height using a drop disc. We classified the dominant understory vegetation type(s) touching the disc into four categories: fallen oil palm frond, herbaceous plant, bare ground, and fern. We measured canopy openness using a spherical densiometer. We measured soil temperature using iButton dataloggers. We sampled arthropods in three microhabitats: ground, understory, and canopy. We sampled ground arthropods using pitfall traps. We sampled understory arthropods using brown sticky traps hung approximately 1.5 m from the ground. We sampled canopy arthropods using insecticide fogging. We identified all arthropods to the order-level using stereomicroscopes. We conducted focussed analyses on spiders in all microhabitats. We collected ground and canopy spiders during pitfall trapping and canopy fogging, as described above. Understory spiders caught on sticky traps were often partially damaged and difficult to identify. We, therefore, collected understory spiders by walking each transect and collecting all spiders located above the ground and within 1 m of the observer. In the lab, we separated juveniles from adults, and identified adults to family and morphospecies using dissecting microscopes and relevant keys. It was not possible to match males and females for all species, and therefore we counted each unique male and female as its own species.