Tropical nature reserves are losing their buffer zones, but leakage is not to blame

Tropical forests provide important ecosystem services to humanity, yet are threatened by habitat loss resulting from deforestation and land-use change. Although reserves are considered the cornerstones of conservation efforts in the tropics, their efficacy remains equivocal. One question that remains unresolved is whether leakage - the unanticipated displacement of deforestation from inside reserves into the unrestricted zones just beyond a reserve's administrative boundary - is common around tropical forest reserves, or whether the zones are acting as buffers between the protected area and the outside world. To resolve this question, we used the Landsat-derived Global Forest Change dataset to estimate deforestation rates between 2000 and 2012 inside and outside of 60 nature reserves spread across the tropics. Deforestation rates inside reserves (within 5km of the administrative boundary) were generally lower than those immediately outside the reserves (i.e. in buffer zones 0-10km from the boundary), suggesting that reserves are effective at protecting forests. We hypothesised that leakage would result in greater deforestation rates in reserve buffer zones than in the broader reserve landscapes, but such a pattern was observed in only five African sites, suggesting that leakage does not often occur on the edge of established reserves. However, roughly 80% of reserves experienced deforestation rates that increased gradually from their interiors to the outer periphery of their buffer zones. Thus, while leakage may not be a pervasive phenomenon around tropical reserves worldwide, tropical reserves are often losing their buffer zones, resulting in increased isolation that could have ramifications for ecosystem services provisioning and tropical conservation strategies.