Currently, 18% of the world’s forests, equivalent to 700 million hectares, are under legal protection via national parks and forest reserves. The British Columbia Ministry of Forests defines a forest reserve as “an area of forest land that, by law or policy, is not available for harvesting.” Reserves have long been viewed as a foolproof method for ensuring the sustainability of our forests, and continue to be the chosen method for curbing deforestation and preserving biodiversity.
Traditional measures of reserve effectiveness that compare deforestation rates inside a reserve to outside will almost always conclude that reserves are effective, as deforestation rates tend to be lower in restricted areas than in unrestricted ones. Yet, such inside-outside comparisons may distort our understanding of conservation success by omitting crucial spillover processes.
Many forest reserves are prone to the phenomena of reserve leakage, whereby deforestation mitigated in one area leads to increased deforestation nearby. In fact, the creation of a forest concession or protected area can unintentionally signal that areas without conservation status are free for logging or harvesting purposes, thereby providing an incentive for these activities to take place. Furthermore, road networks are often established alongside new forest concessions, providing increased access to previously inaccessible forest areas. Even when forest reserves are well-managed and well-regulated, leakage can undermine broader conservation efforts.
In 2007, researchers measured the concept of reserve leakage for the first time in the surroundings of a newly created forest concession in the Peruvian Amazon. While deforestation rates decreased significantly within the forest concession, deforestation rates in surrounding areas increased between 300% and 470%. Similarly, a 2020 meta-study attempting to measure reserve leakage across 120 protected areas (PAs) in the tropical forests of South America, Africa and Asia found that across 55 PAs, deforestation rates were higher in buffer zones — the zones that surround a protected area — than in non-protected areas. Perhaps most significantly, the authors found that in most instances where leakage had occurred, deforestation mitigated within the PA was not significant enough to counter the increased deforestation that occurred outside it.
Leakage processes can also occur on a larger scale, with reduced deforestation in one area resulting in increased deforestation across a continent, or even across the globe. For example, the Soy Moratorium agreement in Brazil, which restricted the purchase of soy from recently deforested land, significantly reduced deforestation in the Brazilian Amazon, yet increased deforestation in the nearby Cerrado biome. Similarly, in 2009, researchers estimated that nearly 40% of Vietnam’s forest regrowth in the late 1990s and early 2000s had been offset by increased illegal timber imports from foreign markets. While Vietnam’s domestic forest regrowth was certainly a success, much of this success occurred at the expense of accelerated deforestation abroad. Similar patterns emerge in other studies, where logging restrictions in one locale appear to increase deforestation rates in distant areas.
When it comes to quantifying the effectiveness of forest conservation efforts, it is important to recognize and account for spillover processes. In measuring the success of a forest reserve, it is not enough to focus solely on the deforestation prevented within the boundaries of a reserve or protected area. Rather, we must look at whether a reserve helps to reduce deforestation and preserve biodiversity across a wider ecosystem. When possible, it is also important to consider global linkages between forest systems, and to assess whether reductions in deforestation in one area occur at the expense of increased deforestation across the globe.
When planning for new conservation boundaries, preventative measures can be undertaken to minimize the impacts of potential leakage and preserve the biodiversity of the entire landscape. For example, forest reserves can be designed to maximize the amount of biodiversity being conserved within a single protected area, focusing on measures of species richness rather than land area. In doing so, even if leakage does occur, the entire ecosystem may still benefit from retaining the area with the greatest biodiversity. Additionally, when planning for a new reserve, it is equally important to consider the biodiversity present in surrounding areas and buffer zones, as these are the areas most prone to leakage.
While forest reserves are by no means futile, conservation processes are extremely complex, and conservation planning must include holistic understandings of entire ecosystems, rather than microcosms of them. The phenomena of reserve leakage encourages us to reconsider the net-benefits of localized deforestation policies, and to begin thinking about broader linkages between forest biomes across the globe.
Edited by Ines Navarre