Reforestation of previously forested areas can bring multiple benefits, but planting trees in places where they do not naturally grow can have serious environmental impacts, including potentially exacerbating the effects of climate change. Savannas are amongst the ecosystems at risk from afforestation programmes. Savannas are grass-dominated, high-diversity ecosystems with endemic species adapted to high-light environments, herbivory and fire . Interactions between climate change, elevated CO2 and the disruption of natural disturbance regimes have led to the widespread encroachment of woody plants , causing a fundamental shift in ecosystem structure and function with loss of grass and reduced fire frequency  and stream flow  . Afforestation exacerbates this degradation . Global-scale analyses aimed at identifying degraded forest areas suitable for reforestation  cannot reliably separate naturally grassy ecosystems with sparse tree cover from degraded forests, so local information is essential to ensure tree planting is targeted where it can benefit most and avoid harm. Figure Box 2.2.1 indicates where these issues are most likely to arise.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report