Introducing too many trees to African savannahs may prevent smaller plants from accessing sunlight, which would affect the animals that eat them
Carine Boekee/Alamy
Ambitious tree-planting projects that aim to restore forests in Africa could inadvertently harm grasslands and savannahs by introducing too much shade. This may prevent smaller plants from photosynthesising, which would have knock-on effects for the rest of the ecosystem.
In 2011, The Bonn Challenge was launched by the German government and the International Union for Conservation of Nature to restore 350 million hectares of degraded or deforested land around the world by 2030. As part of this effort, the African Forest Landscape Restoration Initiative (AFR100) was formed, with 34 countries across the continent pledging to reforest 133.6 million hectares of land.
But this has raised concerns about how other key ecosystems in Africa may be affected. To learn more, Kate Parr at the University of Liverpool in the UK and her colleagues compared the size of the areas committed for forest restoration in each AFR100 country to the areas that are naturally forest habitats.
For 18 of the countries, they found that the pledged area exceeds the actual forest area, so non-forest habitats must be included within the pledged regions.
Of the 133.6 million hectares committed for reforestation across Africa, 70.1 million hectares are made up of non-forest ecosystems, mainly grasslands and savannahs. “That’s the size of France, it’s enormous,” says Parr.
The team also found that 52 per cent of the projects that are already underway are taking place on either grasslands or savannahs. Of these, around half are agroforestry projects. These involve planting trees on farmland, which tends to be a non-forest area made up of non-native species with low overall species diversity.
“Individually, trees are great, but when you have a lot of them together, they can really change an ecosystem,” says Parr.
In ecosystems that are open and grassy, trees typically grow in a sparse pattern. When mass planting clumps trees together, they can damage smaller plants by drastically reducing their access to sunlight. This has a knock-on effect on the animals, such as zebras, who feed on these plants.
Many of the involved countries receive funding to carry out reforestation projects, so there is a financial incentive to plant more trees, says Parr. “There’s also a lack of realisation that these ecosystems are being harmed by planting trees,” she says.
Parr hopes those in charge of reforestation initiatives will consider the wider impacts of where they plant trees, while working with local communities to ensure people’s livelihoods aren’t affected.
Jessica Gurevitch at Purdue University in Indiana says: “This is an alarming wake-up call for the NGOs [non-governmental organisations], national and international restoration efforts, and the misguided ‘plant a tree’ feel-good general public that these efforts must be far more controlled and managed, and evidence-based far more rigorously.”
The AFR100 hadn’t provided a comment at the time of publication.
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