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

1. 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. 2. 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. 3. 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
~3% across all dispersal abilities. However, if HCVAs were fully
reforested, then overall landscape connectivity could improve by ~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. 4.Synthesis and applications. The RSPO requires that 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 (P&C) should also ensure
that large (i.e., with a core area >2 km2) HCVAs are reconnected to
continuous tracts of forest to maximise their connectivity benefits.