Researchers in the Tropical Ecology and Conservation group have conducted the most comprehensive study to date on how habitat restoration in sub-Saharan Africa impacts tree loss beyond project boundaries.
- Largest study to date of how restoration affects tree loss beyond project boundaries in sub-Saharan Africa
- Researchers analysed nearly 130,000 restoration sites across 27 countries, covering 6.8 million hectares
- Natural regeneration and active restoration can reduce surrounding tree loss, while agroforestry may shift pressure into nearby landscapes
- Effects vary over time and between countries, highlighting the need to monitor restoration beyond project boundaries
As global policy targets over 350 million hectares for restoration by 2030, the research, published in Nature Sustainability, highlights a critical phenomenon known as leakage – where the impacts of a project spill over into the broader landscape.
By analysing decades of satellite data, the team assessed whether restoration was associated with ‘positive leakage’ – where tree loss declined in surrounding areas – or ‘negative leakage’ – where tree loss increased beyond project boundaries.
The study, led by Xinran Miao, a PhD student at the Department of Plant Sciences, Cambridge, assembled a geospatial dataset of nearly 130,000 restoration sites across 27 countries, covering approximately 6.8 million hectares.
Contrasting outcomes
The findings reveal marked differences among restoration approaches. Natural regeneration and active restoration were associated with reductions in tree loss of up to 9.1 percentage points within project areas and 8.9 percentage points in the surrounding areas up to 10 kilometres away after 10 years. This positive leakage may reflect projects that engage local communities, strengthen land tenure, or provide resources and livelihood opportunities such as fuelwood and jobs, thereby reducing the pressure on nearby natural forests.
In contrast, agroforestry – the integration of trees into croplands – was associated with negative leakage. On average, tree loss increased by 7.9 percentage points within these projects and 7.5 percentage points in surrounding landscapes. The researchers suggest this may happen when adding trees to active farms reduces agricultural production through competition for light or other resources, prompting farmers to clear nearby forest or fallow land to compensate for lost production.
“These findings provide the first large-scale empirical evidence that different restoration strategies can generate heavily contrasting leakage effects on the wider landscape,” said Dr Oscar Morton from the University of Sheffield, co-author of the study.
The importance of context
The study emphasises that restoration outcomes depend not only on what is planted, but also on where and how restoration is implemented. Results varied considerably among countries. Kenya and Tanzania showed consistently positive outcomes across restoration types, while Ethiopia and South Africa experienced instances of negative leakage, reflecting differences in socio-economic conditions, land-use pressures and institutional contexts.
“These results illustrate how factors such as land tenure security, incentive structures, and community participation can influence whether restoration strengthens or places additional pressure on surrounding landscapes,” said study co-author Dr Chris Bousfield from the University of Sheffield.
Implications for policy and carbon finance
The findings have important implications for carbon markets and certification standards. Current frameworks often neglect off-site impacts, potentially underestimating the value of native forest restoration or overlooking risks associated with some agricultural and timber production interventions.
“It is vital for policymakers to integrate leakage safeguards into landscape planning,” said Xinran Miao. “Accounting for off-site effects is important for recognising the wider benefits of natural habitat restoration, particularly for surrounding high-conservation-value habitats.”
Professor David Edwards, Head of Tropical Ecology and Conservation at Cambridge and Director of the Centre for Global Wood Security, added: “By strengthening land-use planning and ensuring that local communities receive tangible benefits – including secure land rights and sustainable livelihood opportunities – restoration can be scaled up in ways that deliver lasting benefits for climate, biodiversity and people across entire landscapes.”
Reference: Miao, X et al. ‘Restoration-driven positive and negative leakage in sub-Saharan Africa.’ Nature Sustainability, DOI: 10.1038/s41893-026-01936-2.
Image: Agroforestry on the slopes of Mount Meru in the Arusha region of northern Tanzania. Credit: Michele D'Amico supersky77 / Getty Images.