Large-scale tree planting is often presented as a simple solution to conserving the environment and preventing climate change through carbon capture. But reforestation is more complicated than it looks.
“It's very easy to say, you're going to plant a tree,” says Erin Axelrod, the program director for Jonas Philanthropies' Trees for Climate Health initiative. “It's very, very complex, to actually follow that pledge through to the outcome of having a tree that is not only effective at removing carbon dioxide from the atmosphere, but also effective from the standpoint of doing all the other great things that trees can do.”
In recent years, massive reforestation efforts have included shockingly high numbers of tree-planting goals linked to them as a low-cost, high-impact solution to climate change. In 2019, Ethiopia claimed to have planted 350 million saplings in under 12 hours, breaking the world record for trees planted in a day. China is on course to plant 87 million acres of trees by 2050 to make a “Great Green Wall” the size of Germany. And just last year, the World Economic Forum began its 1t.org project, aiming to conserve, restore or grow one trillion trees by 2030.
Too Much of A Good Thing
Tree-planting campaigns are media-friendly and politically popular (who’s opposed to trees and preventing climate change?). Plus, it’s easy to see a tangible impact happening right in front of you when filling a barren area with saplings. However, a growing number of scientists are challenging the tree-planting narrative, saying that when planting isn’t done carefully, it can lead to lower biodiversity, less carbon capture, dried-up soil and the displacement of indigenous people. Further, researchers say that tree planting shouldn’t distract from greater priorities.
“Tree planting and ecosystem restoration is a good thing,” says environmental scientist Karen Holl at the University of California Santa Cruz, who specializes in restoration ecology. “It needs to be done right, and it shouldn't be thought of as a substitute, but it should be additional to protecting existing ecosystems and reducing greenhouse gas emissions.”
If it isn’t done right and the wrong trees are planted in the wrong place, research shows that non-native trees can crowd out native species and consume significantly more water than native plants would, drying out soil.
In South Africa, many natural habitats, such as grasslands, have been overrun with invasive species like eucalyptus and acacia — they’re common in tree-planting campaigns because they grow quickly in a wide range of habitats. Recently, South Africa faced critical water shortages affecting major cities, a problem exacerbated by these invasive trees.
Moreover, there is a conflict between using land for trees and using it for agriculture to generate income or feed growing populations in some parts of the world. Planting trees on land that could be used to grow crops, for livestock to graze or that has been used by nomadic populations can displace indigenous people and take away livelihoods.
Axelrod says that it’s important to acknowledge that tree-planting can have negative effects, but that it is possible to accomplish the goals of sequestering carbon, rebuilding forests and improving agriculture with the "right tree, right place, and right community” approach.
“The bottom line is that we need to make changes fast, and I'm not saying tree planting is a bad thing,” says Holl. “It's just one tool in the toolbox. It's not going to solve climate change alone.”
Because of this, scientists came up with rules to consider when planning reforestation efforts to determine if the project will provide more benefit than harm.
The review of previous research, published in the Global Change Biology journal, highlights the main environmental risks of large-scale tree planting and presents 10 golden rules based on the most recent ecological research to follow when planning reforestation efforts. The rules are meant to maximize carbon sequestration and biodiversity recovery while improving livelihoods.
The 10 Golden Rules for Reforestation
(1) Protect existing forest first: Before planning reforestation efforts, work to protect existing forests.
(2) Work together: Involve all stakeholders and make local communities central to the project.
(3) Aim to maximize biodiversity recovery to meet multiple goals: Maximizing biodiversity helps to facilitate other goals, including carbon sequestration, socioeconomic benefits and soil and water stability.
(4) Select appropriate areas for restoration: Avoid lands that weren’t forested previously, and instead restore degraded forests or expand existing forests.
(5) Use natural regeneration wherever possible: Leaving forests to naturally regenerate is much cheaper and more effective than tree planting, offering more benefits such as greater carbon capture and biodiversity.
(6) Select species to maximize biodiversity: When planting, use a mix of species while prioritizing native plants that favor mutual interactions, and excluding invasive species.
(7) Use resilient plant material: Use seeds or seedlings that are genetically diverse and consistent with local and regional genetic variability to maximize the forest’s resilience.
(8) Plan ahead for infrastructure, capacity and seed supply: Develop the required infrastructure, capacity and seed or seedling supply system far in advance of the implementation of the project.
(9) Learn by doing: Ideally, large-scale initiatives should follow the successful implementation of small-scale trials. Reforestation initiatives should be based on the best scientific evidence and knowledge from local, indigenous people.
(10) Make it pay: Reforestation efforts are much more likely to succeed in the long-term if the project’s income exceeds the income that could be generated from using the land for other purposes, such as farming. Income must be shared equitably between all stakeholders.
The rules show how much more complex reforestation is than many think. Large-scale reforestation can improve global ecology and help to prevent climate change, but these long-term benefits only happen when relying on sound science and the support of local communities.