Tree planting is one of the most widely proposed solutions to climate change, and for a good reason. Just one mature tree can absorb 25 kilograms of CO2 in a year. Another study found that forests act as a “carbon sink” capable of absorbing 7.6 billion metric tonnes of CO2 per year, more than they release when degraded or cleared.

Given those staggering statistics, world leaders have pledged to restore 350 million hectares of forests by 2030. On paper, it might be tempting to plant trees everywhere there’s empty space. Indeed, savannahs and grasslands have hectares of land covered mostly by a grassy layer and sporadically growing trees. They total 20% of the Earth’s land surface and are home to a rich biodiversity of flora and fauna and a billion humans. Yet in places like this, climate change and habitat loss aren’t the only threat — tree planting is, too!

Where we shouldn’t plant more trees (and why)

Unlike forests, grass-dominated ecosystems in the tropics can be degraded not just by losing trees, but also by increasing them. Studies conducted in South Africa, Brazil, and Australia show that tree planting can actually increase biodiversity loss in grasslands and savannahs. Why is that the case?

More trees can upset the food chain

Trees can reduce the chances of wildfires, given that the grass in these regions is often dry and arid. However, those fires actually serve a purpose: they remove vegetation covering the ground-layer plants that zebra and antelope feed on. More trees also provide extra cover to predators, which means herbivores are more likely to be eaten. That, again, can upset the food chain and the larger ecosystem.

Trees can reduce water supply

In grassy ecosystems, streams and rivers are critical for both animals and humans (who might also depend on these for their livelihood and transport). Increasing tree cover can actually reduce the amount of water in these watering holes, as seen in Brazil, where humans suppressing wildfires led to a decrease in rainwater reaching the ground. According to another study, creating forests in grasslands and shrublands can cause 13% of streams to dry up completely.

Grasslands are often naturally unforested, not degraded

Grasslands and savannas have trees, but they’re either sporadically present or clumped together. The WRI Atlas considered all areas with over 10% tree cover as a form of forest. This means that clumped trees in grasslands are often misclassified as forests, which categorizes the surrounding areas as degraded by default. The plants and shrubs that grow in these regions need both sunlight and fire, which trees can reduce access to. Therefore, empty land isn’t always meant to be forested — it’s important to look into the existing ecosystem before making changes.

Not all trees grow everywhere

Once again, on paper, it’s easy to imagine planting a single species of trees all over the world to increase forest cover. However, this is considered bad science and can do more harm than good.

When we talk about reforestation, we tend to envision a particular kind of forest, often involving thick trunks and green leaves like we’d see in the Amazon. Planting non-native species, for example, can upset an ecosystem. Planting any tree with dense foliage can, as we’ve mentioned, prevent rain and sunlight from reaching ground-level plants that are essential to the ecosystem, however small and stick-like they may look. 

Even the location of the tree matters. A row of trees along the edge or middle of a prairie can damage the ecosystem considering flora and fauna in these regions are attuned to wide-open habitats and ancient routes. Just like a sudden building in the middle of a highway can cause massive damage, so too can one tree wrongly placed affect the ecosystem of a traditionally non-forested area.

The road to planting trees wisely

All of these points indicate that there’s something fundamentally wrong with how we’re approaching reforestation and tree planting. What can we do to more deeply understand how, where, and when to plant trees?

Redefine forests and ecosystems

There’s a prevailing assumption that forests are more important than grasslands, shrublands, and prairies, simply because they have more trees and look more “lush.” As we mentioned before, any area with more than 10% trees is considered a forest, which pushes all other land types into the “empty land” area — but they aren’t empty land. We need to redefine “ecosystems” to include not just forests, but also grasslands and savannas, which are essential in their own right. 

We also need to understand what “degradation” means. It is defined as occurring “when ecosystems lose their capacity to provide important goods and services to people and nature.” In the case of savannas and grasslands, a lack of trees doesn’t equal degradation — the ecosystem is probably thriving because of a lack of trees. Instead, it is often caused by encroachment, logging, overgrazing, and the introduction of invasive plant species (like trees, in this case).

Demand transparency from tree-planting organizations

You’ve probably come across quite a few mass tree-planting projects before. While these look impactful and send a message to an audience, more often than not, they’re poorly executed and not well-thought-out. Plant for the Planet, for example, got into hot soup for their Trillion Tree Campaign: it was revealed that their website was littered with untruths and exaggerations, the most notable one being that one Valf F. from France reportedly planted 682 million trees single-handedly. In other cases, organizations may not reveal what species they plant, may be planting invasive species, or may plant monocultures that are more vulnerable than regular trees. These are plantations, and plantations are not forests. 

This is troublesome because tree planting organizations actually have the farthest reach and the highest potential to make a difference. There are some parts of the world—mostly those affected by land abuse and predatory logging—that can benefit from their large-scale involvement. This can be done by investing in research not just about tree species, but ecosystems and off-limits areas. Partnering with on-the-ground organizations (like EcoMatcher does) can help prioritize native species, provide a livelihood for the locals, and tap into their inherent knowledge about the ecosystem they live in. 

Do your research

When you come across any seemingly climate-friendly initiative, we’d urge you to dig deeper. What seems like a good idea may actually do more harm than good. Take, for example, the biodegradable, reusable coffee mugs that were recently the craze. If planted in one’s balcony pots, they may not make much of a difference. However, if thrown and littered, they could encourage the wrong species to grow in the wrong area. If you’re planning to invest in a tree-planting initiative, ask for every single detail — from what tree is being planted, to where it will be located, to if that region was naturally deforested or previously forested then degraded. 

The final word

Any call for fighting against climate change—especially with trees—needs to look carefully into how they will affect all of Earth’s ecosystems. We might be far removed from most, but there’s no denying that all ecosystems are linked. Domino effects go both ways, so let’s do things wisely!