Reforestation on farmland is surprisingly fast

With rising temperatures due to climate change, it is increasingly important to have a literally greener planet. Masses of trees and plants, like tropical rainforests, remove carbon dioxide from the Earth’s atmosphere. The increasing deforestation of these tropical forests raises the question of how long it will take for old-growth forests to return to previous levels, as these forests are important in the fight against the climate crisis. A network of researchers around the world recently discovered that regrowth may take less time than expected.

Their research, published in the journal Science Thursday, shows that tropical forests cut for agricultural purposes, and their soils, are extremely resilient. In just 20 years, these rainforests on former agricultural lands in Central and South America and West Africa have regained about 80% of the value of ancient forests.

[Related: World leaders promise to end deforestation. Is that even possible?]

A young secondary growth forest in Costa Rica. Robin Chazdon

The team of scientists analyzed 77 rainforest sites across the Americas and West Africa, representing a total of 2,275 varied plots of land. Each plot was originally old-growth rainforest turned into farmland. The plots had each been abandoned for a different number of years, so the researchers could study a full picture of the regrowth.

The sites were analyzed based on 12 tropical forest attributes such as forest density, soil nutrient content, leaf area and tree diameter. After compiling everything into a database and comparing them to ancient forests, the researchers discovered a surprisingly resilient landscape. First author Lourens Poorter, a tropical biologist at Wageningen University in the Netherlands, expected soil nutrient levels to rise after more vegetation began to grow in the area, as the decomposition of the vegetation returns nutrients to the soil. The ground actually recovered quite quickly, however, before major vegetation grew back. In about ten years, the soil had recovered from agricultural use.

[Related: Fossilized plants give us hints about what ice age forests may have looked like.]

“The funny thing is that the people who practice shifting cultivation in these areas, the local people, have already known about it for centuries,” says Poorter. Local people are cutting and burning the land to help return nutrients to the soil after a few years of farming, he says. Then they abandon the land to let it recover. Ten years later, the land is ready to be worked again.

Poorter explains that while this rapid regrowth is good, it’s still important to maintain the old-growth forests that exist, because those rainforests store a lot of carbon. However, saving ancient forests is having results that policy makers around the world may never be able to see. Poorter warns that these results are not a signal that forests need to be continuously destroyed. On the contrary, this finding shows how quickly tropical rainforests growing on abandoned agricultural land, often called secondary forests, recover and rapidly recover the quality of their soil without any human interaction.

“It’s a message of hope,” says Poorter. “It’s not a license to kill.”

Amalia H. Mercado