Meta-analysis Contrasting Freshwater Biodiversity in Forests and Oil Palm Plantations with and without Riparian Buffers.

The expansion of oil palms has led to land-use change and deforestation in the tropics, affecting biodiversity. While the impacts of the crop on terrestrial biodiversity have been extensively reviewed, the effects on freshwater biodiversity remain relatively unexplored. We reviewed the research assessing the impacts of forest-to-oil palm conversion on freshwater biota, and the mitigating effect of riparian buffers on these impacts. First, we search for studies comparing taxon richness, abundance, and community composition of macroinvertebrates, amphibians, and fish in streams in forests (primary and disturbed) and oil palm plantations with and without riparian buffers. Then, we conducted a meta-analysis to quantify the overall effect of the land-use change on the three taxonomic groups. We used 29 studies, as these alone fulfilled the inclusion criteria. On aggregate, across the three taxonomic groups, the plantations lacking buffers hosted 44% and 19% fewer stream taxa than primary and disturbed forests. However, when plantations retained buffers, these differences were reduced to 24% and no difference, respectively. In contrast, stream community composition differed between forests and plantations regardless of the presence of riparian buffers. These differences were attributed to agrochemical use and altered environmental conditions in the plantations including temperature changes, worsened water conditions, microhabitat loss, and food and shelter depletion. On aggregate, abundance did not differ among land uses, as increases in generalist species offset the population decline of vulnerable forest specialists in the plantation. Our study reveals significant impacts of forest-to-oil palm conversion on freshwater biota, particularly concerning taxon richness and composition (not aggregate abundance). While preserving riparian buffers within the plantations can mitigate the loss of various aquatic species, it cannot conserve primary forest communities. Therefore, safeguarding primary forests from the oil-palm expansion is crucial, and further research is needed addressing riparian buffers as a promising mitigation strategy in agricultural areas. This article is protected by copyright. All rights reserved.