Spiders in canopy and ground microhabitats are robust to changes in understory vegetation management practices in mature oil palm plantations (Riau, Indonesia)

Conversion of natural habitats to oil palm agriculture has caused declines in biodiversity and changes in ecosystem functions. To preserve biodiversity we must protect natural habitats, but once oil palm plantations are established, developing more -environmentally friendly management strategies could support higher levels of within-plantation biodiversity and boost the delivery of ecosystem services, possibly increasing oil palm productivity. In this study, we use a before-after control-impact (BACI) experiment to test whether three understory vegetation management strategies affect spider abundance, species rich-ness, and species-level community composition in canopy and ground microhabitats in mature oil palm plantations. Our treatments encompassed the range of current management practices and included heavy applications of herbicides to eliminate all understory vegetation, maintaining some understory vegetation using business-as-usual herbicide applications, and enhancing understory vegetation by not applying any herbicides. We focussed on spiders, as they are both biologically and economically important in oil palm plantations, owing to their important pest control services. We identified more than 1000 spiders, representing 20 families and 83 morphospecies. The treatments did not affect any aspects of spider biodiversity, although the abundance and species richness of canopy-dwelling spiders changed between pre-and post-treatment sample periods, independent of treatment. Our findings indicate that differences in understory vegetation management practices do not affect spiders, or the pest management services that they provide, in mature oil palm plantations. As such, more extreme changes in management would probably be required to enhance spider biodiversity in oil palm plantations in the long-term. Further studies are needed to determine the practicalities of such approaches, to assess how changes in vegetation management practices affect spiders in additional microhabitats, and how the impacts of such approaches vary across the 20-30 year oil palm commercial life cycle.(C) 2022 The Author(s). Published by Elsevier GmbH on behalf of Gesellschaft fur Okologie.

Automated summary

Conversion of natural habitats to oil palm agriculture has negative impacts on biodiversity and ecosystem functions. Protecting natural habitats and implementing environmentally friendly management strategies can help enhance biodiversity and ecosystem services in oil palm plantations. However, the study found that different understory vegetation management practices did not significantly affect spider biodiversity and pest management services in mature oil palm plantations. More extreme changes in management may be required to promote spider biodiversity in the long term.