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As well as taking into account how these schemes are implemented, experts argue that reforestation efforts might be best targeted at particular areas of the world. Trees grow and take up carbon more quickly near the equator, for example, where it is warm and humid, and land is relatively cheap and available. A study published earlier this year in Science Advances found that more than 3.3 million square miles of lost tropical rainforest across Africa, Southeast Asia, and the Americas could be restored.
Keijzer calls tropical reforestation the “low-hanging fruit” for two reasons: “First, because you do create economic values for countries that need it most, so it’s an opportunity to lift millions of people out of extreme poverty.” Secondly, she points out that “if you wanted to plant a tree in Belgium, for example, you would probably spend more than 10 euros per tree if not 15,” but in tropical regions “you can plant it for half a dollar.”
But tropical reforestation can require significant research so projects need to be realistic about what they can achieve. “There are very few parts of the tropics where there’s enough expertise and knowledge to bring back native forests on a large scale,” says Andrew Marshall, head of the not-for-profit ecological restoration organization Reforest Africa.
He compares the U.K., where there are fewer than 20 tree species native to the whole country, to Tanzania, which has the same amount of diversity in a single acre. “You’re talking hundreds of species that you need to get methods for and/or work out a key few that grow well and the others come back,” he says. “You can’t work with everything.”
How exactly forest land is restored depends on two key factors: what it currently looks like and what the ultimate aim of reforestation is.
The land might already host a degraded forest, with less tree cover, fewer species, and poorer soil. It may have been deforested, where many trees have been cut down and the land is primarily used for another purpose such as farming or infrastructure. It might be dominated by an invasive species such as lianas — the big woody vines that Tarzan swings from which can quickly take over tropical land — or molinia — a grass that spreads across the Welsh uplands after fields stop being grazed.
In the most extreme cases, the land may even have become incapable of hosting life, but Keijzer says she has never come across a place that can’t be restored.
In theory, reforestation in many places could be achieved through natural regeneration, where land is left to return to forest with minimal human intervention. “The safest way to do it is to find places that will recover naturally and areas that are already near other areas of forests, areas that have just very recently been cut down,” says Marshall. “Because you would expect that there would still be some seedstock in the soil and the birds and wildlife will be dispersing seeds.”
This option also has the benefit of being cheap, but letting nature take its course is not always feasible for a mixture of practical, social, and economic reasons, and a helping hand is often needed. Across the Sahel Desert in northern Africa, farmers are successfully using a managed natural regeneration technique in which they carefully nurture the remnants of old tree roots under the ground to bring trees back to life.
Afforestt, a company based in India that operates globally, has developed an artificial soil formula that involves brewing a compost ‘tea’ filled with microorganisms.
And elsewhere more advanced technologies are playing a role. Mangrove trees in Myanmar have been planted using drones designed by the U.K.-based startup Dendra Systems (formerly known as Biocarbon Engineering) to fire seeds directly into fields, for example.
Afforestt founder Shubhendu Sharma sees value in this diversity of approaches: “There are 100 ways to bring back a lost forest,” he says. “Like religion, there is one god and different paths to reach that.”
Experts agree that the ultimate aim should be to make the forest sustainable in the long term, which means weighing global, national, and local interests.
Marshall stresses that reforestation must be done in collaboration with those directly affected; after all, there was usually a human reason why the forest was cut down or degraded in the first place. “If people need to feed their families that’s massively more important than whether a monkey in the tree is not going to have a place to sleep that night,” he says.
At the local level, Keijzer says, simply planting trees is not enough. The forest economy should be designed to benefit residents. This might mean building woodlots for local use, planting exotic species that grow faster and are worth more money alongside native ones, or creating nature reserves with associated tourism jobs. With a sustainable local economy, Keijzer says, people will be less likely to cut down all the trees in order to simply make ends meet.
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