Climate change and shrinking biodiversity are two of the biggest environmental problems facing the world. There’s a danger that tackling one could make the other worse.
Today, people are trying to suck greenhouse gases from the air by boosting the amount of carbon-consuming plants covering the planet. Trees are being planted on the remains of old forests or in places now covered in grass. Crops such as switchgrass are being developed to replace fossil fuels as a source of energy.
While animals often rely on green spaces to live, that doesn’t mean more vegetation always benefits wildlife. Depending on what’s planted and where, the effects on animals could be dramatically different, either undermining or giving a boost to the creatures living there, according to new research in Science.
“In their effects on biodiversity, these strategies are not created equal. It’s critical that, in our work to address climate change, we do not inadvertently worsen the biodiversity crisis,” said Jeffrey Smith, a postdoctoral researcher at Princeton University’s High Meadows Environmental Institute.
The insights come at a time when there is growing pressure to find ways to staunch the flood of carbon dioxide we pour into the atmosphere every day. Despite the rise of renewable energy, the world’s continued appetite for fossil fuels has people trying to stash pollution in all kinds of places, including the ocean, swamps, underground, and in plants.
To understand what this could mean for biodiversity, Smith and colleagues took a closer look at how some of the leading plant-growing strategies might affect animals. They took a list of more than 14,000 vertebrates from around the world, complete with information about what kind of habitat they use and maps of where that land is found. Then the researchers overlaid that with estimates of all the places where people might plant trees or grow bioenergy crops by 2050—excluding places that already have forests or is intensively farmed. That left open spaces such as grasslands as well as pastures and other lightly-farmed land that was once forest or meadow.
They also incorporated information about how climate change could cause habitat to expand or shrink, and how each of the pollution-reducing strategies would alter the amount of habitat available by the middle of the century.
Generally, tree planting outranked bioenergy crops for wildlife benefits in places where either strategy could be tried. Scientists found that in 96% of these lands, trees provided more habitat than crops such as switchgrass for the species there. On 78% of the land were bioenergy crops might grow, the best habitat scenario for the animals was just to leave the land alone.
While growing new trees generally fares better, not all tree planting was the same. Overall, the winning strategy was reforestation—when land previously covered by forest is replanted with trees. Because many of the animals in the area were forest dwellers to begin with, the revival of forests was a boon, according to their analysis. A majority of the wildlife saw an expansion of habitat both from the direct planting and from the reduction in global warming.
By contrast, growing trees on savannas and other places that weren’t forests to begin with was more likely to have an overall negative effect. In places around the world where new forests would be bad overall for wildlife habitat, more than 70% was in this naturally open habitat. Any additional climate benefit was swamped by the damage from the new plantings.
The findings make intuitive sense. Creatures are more likely to respond well to creating more of the habitat they already know and are adapted to, rather than creating an unfamiliar landscape.
It also drives home a lesson that humans get again and again from the natural world—even if we don’t always learn from it. Be very careful when tinkering with nature to solve a problem. Because you just might be creating another problem along the way.
“Few ecologists doubt that addressing climate change would be a boon for biodiversity,” said Jonathan Levine, a Princeton University researcher who also worked on the new study. “However, our study finds that it’s not enough to reach net zero. It also matters how we get there.”
Smith, et. al. “Variable impacts of land-based climate mitigation on habitat area for vertebrate diversity.” Science. Jan. 23, 2025.
Image: Michael Schultze / Alamy Stock Photo
