How to help forests fight global warming?

To deal with climate change crises and the loss of biodiversity, planting trees seems like a simple and natural solution. They provide the necessary habitat for flora and fauna and, in addition, capture COtwo of the atmosphere.

It is not surprising, then, that trees are considered the ideal weapon. So why not plant more? It turns out that in every high-profile planting operation, devastating failures have occurred. In Turkey, Sri Lanka and Mexico, massive plantations have killed millions of seedlings or driven farmers to clear intact forests. Trees planted in the wrong places have reduced water resources for farmers, destroyed the highly diverse soils of carbon-absorbing grasslands, or allowed invasive vegetation to proliferate.

“Planting trees is not a simple solution,” says Karen Holl, a restoration ecologist at the University of California, Santa Cruz, who works with Pedro Brancalion. Reforesting the planet cannot replace the decline due to fossil fuels. Tree planting cannot replace old-growth forests either. It took hundreds, if not thousands of years to arrive at these complex biological systems. Saving them is even more important than growing new forests.

The true value of a tree is in its lifespan, which means making sure it doesn’t die. When reviewing planting proposals for the World Economic Forum, Karen Holl realized that even the best projects only track results for twenty-four months. If the objective is carbon storage and biodiversity, “we cannot assess it in two years”, she warns.

What also matters is where – and how – the trees are planted. For example, planting tree species in the snowy far north creates darker landscapes that absorb more sunlight, potentially contributing to global warming. In 2019, nearly half of Bonn Challenge countries planned to plant trees and regularly cut them for wood or pulp, rather than cultivating natural forests – despite these sequestering, on average, much more COtwo.

So what to do?

The answer is obvious to Pedro Brancalion: primary forests must be restored, especially in the tropics, where trees grow quickly and land is cheap. It may then be necessary to plant some. But it can also mean eliminating invasive weeds, rejuvenating the soil, or even improving crop yields for farmers so that less farmland is needed and more forests are returned.

Pedro Brancalion focused on Brazil’s Atlantic Forest, 75% of which disappeared in favor of cities, livestock, paper production or the cultivation of sugarcane and soy. But, often, these exploited lands are not well used. Areas like these – located on steep slopes, close to remnants of forest patches, for example – allow for restoration.

The combination of harvesting eucalyptus with planting native species is a reminder that successful restoration must also benefit local communities. In Niger, for example, since farmers realized they could grow more cereals by planting around forest land – rather than clearing it – 200 million trees have returned.

For Pedro Brancalion, when resources are limited and there is no time to waste, starting natural processes can be useful. Because in many cases, if you let nature do the heavy lifting, he adds, “the forest really grows very well.”


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