Testing the benefits of conservation set-asides for improved habitat connectivity in tropical agricultural landscapes

Habitat connectivity is important for tropical biodiversity conservation. Expansion of commodity crops, such as oil palm, fragments natural habitat areas, and strategies are needed to improve habitat connectivity in agricultural landscapes. The Roundtable on Sustainable Palm Oil (RSPO) voluntary certification system requires that growers identify and conserve forest patches identified as High Conservation Value Areas (HCVAs) before oil palm plantations can be certified as sustainable. We assessed the potential benefits of these conservation set-asides for forest connectivity. We mapped HCVAs and quantified their forest cover in 2015. To assess their contribution to forest connectivity, we modelled range expansion of forest-dependent populations with five dispersal abilities spanning those representative of poor dispersers (e.g. flightless insects) to more mobile species (e.g. large birds or bats) across 70 plantation landscapes in Borneo. Because only 21% of HCVA area was forested in 2015, these conservation set-asides currently provide few connectivity benefits. Compared to a scenario where HCVAs contain no forest (i.e. a no-RSPO scenario), current HCVAs improved connectivity by similar to 3% across all dispersal abilities. However, if HCVAs were fully reforested, then overall landscape connectivity could improve by similar to 16%. Reforestation of HCVAs had the greatest benefit for poor to intermediate dispersers (0.5-3 km per generation), generating landscapes that were up to 2.7 times better connected than landscapes without HCVAs. By contrast, connectivity benefits of HCVAs were low for highly mobile populations under current and reforestation scenarios, because range expansion of these populations was generally successful regardless of the amount of forest cover. Synthesis and applications. The Roundtable on Sustainable Palm Oil (RSPO) requires that High Conservation Value Areas (HCVAs) be set aside to conserve biodiversity, but HCVAs currently provide few connectivity benefits because they contain relatively little forest. However, reforested HCVAs have the potential to improve landscape connectivity for some forest species (e.g. winged insects), and we recommend active management by plantation companies to improve forest quality of degraded HCVAs (e.g. by enrichment planting). Future revisions to the RSPO's Principles and Criteria should also ensure that large (i.e. with a core area >2 km(2)) HCVAs are reconnected to continuous tracts of forest to maximize their connectivity benefits.