Room to Grow

Global land available for forest restoration

ETH Zurich, Crowther Lab

Photosynthetic carbon capture by trees is touted as one of the most effective ways to reduce atmospheric carbon dioxide. As a result, a number of international organizations have set targets to restore degraded forest habitat in an effort to combat climate change. To assess whether the targets are achievable, a team of scientists have mapped areas available for forest restoration across the globe.

Led by geographer Jean-François Bastin from the Department of Environmental Systems Sciences at ETH Zurich, the team developed a predictive model to calculate and map the Earth’s tree carrying capacity. They found that two-thirds of terrestrial land (8.7 billion hectares) could support forest in the absence of human activities. They then subtracted existing human developments and agricultural lands from the estimate and found that 0.9 billion hectares scattered around the globe are not currently being used by humans and are potentially available for tree restoration. The area is “about the cumulative size of the United States,” says Bastin, which, if forested, corresponds to just over 200 gigatons of carbon storage. “That’s about a quarter of the total amount that we have in the atmosphere today,” he adds. More than half of that area can be found in only six countries: Russia, the United States, Canada, Australia, Brazil, and China.

Bastin suggests the maps be used at the national or regional level as a first step in identifying areas with restoration potential, but he also cautions that local forestry and land-use experts should be consulted to refine the maps. Locals will have “better knowledge of where crops and forests are, and of areas that shouldn’t be touched,” he says. He also notes that restoration initiatives must not lead to the loss of existing natural ecosystems, such as typically treeless native grasslands that are also important for carbon storage and biodiversity. In some areas, restoration does not necessarily mean putting dense forest everywhere, he says. Sometimes it means adding only 5 or 10 percent tree cover. Next steps for Bastin include developing lists of common native species for each region to help restoration efforts get started. (Science)