How African restoration projects spill over into surrounding landscapes

Researchers from the University of Sheffield and the University of Cambridge have conducted a comprehensive study on how habitat restoration in sub-Saharan Africa affects tree loss outside project boundaries. Published in Nature Sustainability, the research highlights a phenomenon called leakage, where the impacts of a restoration project extend beyond its immediate area.

Led by Xinran Miao, a Ph.D. student at the University of Cambridge, the study analyzed nearly 130,000 restoration sites across 27 countries, covering an area of about 6.8 million hectares. The team used satellite data to determine whether restoration led to positive leakage (decreased tree loss in surrounding areas) or negative leakage (increased tree loss beyond project boundaries).

The findings show that natural regeneration and active restoration strategies reduce tree loss within projects and surrounding areas by up to 9.1 and 8.9 percentage points, respectively, after 10 years. This positive leakage may be due to projects that involve local communities, improve land tenure, or provide resources like fuelwood and jobs.

Conversely, agroforestry, which integrates trees into croplands, is linked to increased tree loss both within the project and in surrounding landscapes, averaging 7.9 and 7.5 percentage points, respectively. This negative leakage may occur when tree addition on farms competes with crops for resources, leading farmers to clear nearby forests or fallow land.

Dr. Oscar Morton from the University of Sheffield notes that these results provide the first large-scale evidence that different restoration strategies can have contrasting effects on deforestation rates in the wider landscape. The study also reveals that outcomes vary significantly across countries, with Kenya and Tanzania showing positive results across restoration types, while Ethiopia and South Africa occasionally experience negative leakage.

This variation is influenced by factors such as land tenure security, incentive structures, and community participation. The findings emphasize the importance of considering off-site impacts in carbon markets and certification standards, as current frameworks often overlook these effects, potentially undervaluing native forest restoration or overlooking risks associated with certain agricultural and timber production activities.