The benefits of protected areas (PAs) to biodiversity and ecosystem services often extend beyond the boundaries of the protected zone. Writing in Nature, Graeme Cumming reports on the spillover effect on vegetation cover of 3,063 PAs across Australia between 1988 and 2020. To establish whether the spillover effect was a consequence of the existence of the PA, Cumming developed a counterfactual that compared vegetation cover in polygons within each PA, within a potential zone of influence of that PA, and in a zone outside the influence of the PA, yet closer to that PA than any other PA. Independent analysis of 10 woody and herbaceous vegetation types enabled the author to balance positive effect sizes for some vegetation types with negative effects of others, which, for example, allows for succession dynamics of recovering vegetation to be accounted for. Cumming found that 71% of the PAs had a positive spillover effect on at least one of the vegetation classes in the zone up to 5 km around the PA, with meaningful but declining effect sizes at greater distances. The author also found distinct relationships between spillovers and the IUCN (International Union for Conservation of Nature) category of PA, and between spillovers and the type of PA management implemented by Australian authorities. The author discusses how these relationships must be considered in the context of where PAs of different types are placed relative to areas of human impact and other forms of land use, and suggests that further investigation of how management affects spillover may allow for more-intentional optimization of positive spillover effects.
Original reference: Nature https://doi.org/10.1038/s41586-025-09837-8 (2025)
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