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The restoration of forested land at a global scale could help capture atmospheric carbon significantly and mitigate climate change, finds a new study.

The scientists showed for the first time where in the world new trees could grow and how much carbon they would store.

The study report – “The Global Tree Restoration Potential” (Science, 2019; 365 (6448): 76) – by Jean-Francois Bastin, Yelena Finegold, Claude Garcia, Danilo Mollicone, Marcelo Rezende, Devin Routh, Constantin M. Zohner, Thomas W. Crowther identified the areas.

The scientists in their study used direct measurements of forest cover to generate a model of forest restoration potential across the globe.

Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land.

The restoration of trees remains among the most effective strategies for climate change mitigation.

The scientists mapped the global potential tree coverage to show that 4.4 billion hectares of canopy cover could exist under the current climate.

Excluding existing trees and agricultural and urban areas, the researchers found that there is room for an extra 0.9 billion hectares of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally support woodlands and forests. This highlights global tree restoration as the most effective climate change solution to date.

However, climate change will alter this potential tree coverage.

The scientists estimate that if the world cannot deviate from the current trajectory, the global potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority of losses occurring in the tropics.

The study results highlight the opportunity of climate change mitigation through global tree restoration but also the urgent need for action.

Study lead author and postdoc at the Crowther Lab Jean-François Bastin explains: “One aspect was of particular importance to us as we did the calculations: we excluded cities or agricultural areas from the total restoration potential as these areas are needed for human life.”

Reforest an area the size of the USA

The scientists calculated that under the current climate conditions, Earth’s land could support 4.4 billion hectares of continuous tree cover. That is 1.6 billion more than the currently existing 2.8 billion hectares. Of these 1.6 billion hectares, 0.9 billion hectares fulfill the criterion of not being used by humans. This means that there is currently an area of the size of the US available for tree restoration. Once mature, these new forests could store 205 billion tons of carbon: about two thirds of the 300 billion tons of carbon that has been released into the atmosphere as a result of human activity since the Industrial Revolution.

According to Prof. Thomas Crowther, co-author of the study and founder of the Crowther Lab at ETH Zurich: “We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be. Our study shows clearly that forest restoration is the best climate change solution available today. But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage.”

Russia best suited for reforestation

The study also shows which parts of the world are most suited to forest restoration. The greatest potential can be found in just six countries: Russia (151 million hectares); the US (103 million hectares); Canada (78.4 million hectares); Australia (58 million hectares); Brazil (49.7 million hectares); and China (40.2 million hectares).

Many current climate models are wrong in expecting climate change to increase global tree cover, the study warns.

The study finds that there is likely to be an increase in the area of northern boreal forests in regions such as Siberia, but tree cover there averages only 30 to 40 percent. These gains would be out-weighed by the losses suffered in dense tropical forests, which typically have 90 to 100 percent tree cover.


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