Natural forest regeneration has been seen as an ecologically sound way to restore large areas of tropical forest at lower costs compared to active tree plantings.Natural forest regeneration has been seen as an ecologically sound way to restore large areas of tropical forest at lower costs compared to active tree plantings.

Tropical forests are home to more than 53,000 tree species, accounting for 96% of global tree diversity. These hyperdiverse forests are threatened by high levels of deforestation, mostly driven by agricultural expansion. Once agricultural fields are abandoned, they can be rapidly colonized by naturally regrowing forests, which are called “secondary forests.”

Led by researchers from Wageningen University, the scientists set out to see if these regrowing forests could help reverse species loss and bring back native species. They inventoried trees in 1,800 tropical forest plots located in 56 sites across 10 countries in Latin America. They used plot data from secondary forests of different ages and compared it to neighboring, well-conserved, old-growth forests. They show that species richness of these small forest patches recovers in a few decades, but that it may take centuries before their species composition becomes similar to that of old-growth forests.

“This study underscores the potential for biodiversity conservation in secondary forests. However, it also shows that biodiversity recovery takes time,” Letcher said. “In order for recovery to occur, we have to conserve old growth forests, and is some cases we may also need targeted restoration efforts.”

Professor Susan Letcher uses her passion for plants to teach courses like Forest Ecology and Res...Professor Susan Letcher uses her passion for plants to teach courses like Forest Ecology and Restoration Ecology at College of the Atlantic.

Although the number of species may recover relatively fast, the study also shows that the tree species found in regrowing forests are usually different from those in neighboring old-growth forest. After 20 years of regrowth, only 34% of the original species composition has recovered. Therefore, it may take centuries before these regrowing forests harbor the same tree species as the original forest again, and maybe they never attain the original species composition.

“While young secondary forests contribute importantly to biodiversity conservation in these modified landscapes, they do not contain many of the species found in well-conserved forests,” Professor Lourens Poorter, leader of the 2ndFOR network, says. “Both secondary and old-growth forests must be preserved to guarantee biodiversity conservation in human-modified landscapes.”

This unique study has direct implications for forest restoration policies and practice. Natural forest regeneration has been seen as an ecologically sound way to restore large areas of forest at lower costs compared to active tree plantings. Natural forest regeneration may therefore be the ideal method to meet the goal to restore 350 million hectares of forest in 2030, as set under the Bonn Challenge.

“We were impressed to find that it takes only five decades, on average, to recover the total number of species found in well-conserved old-growth forests, and that within only 20 years already 80% of the number of species is present.” According to her, “This emphasizes the importance of secondary forests for biodiversity conservation in human-modified tropical landscapes,” says Dr. Danaë Rozendaal, lead author of the study.

This research is a product of the 2ndFOR collaborative research network on secondary forests. It involves 85 researchers from 16 different countries. The network focuses on the ecology, dynamics, and biodiversity of secondary forests, and the ecosystem services they provide in human-modified tropical landscapes. The 2ndFOR network is coordinated by Prof. Lourens Poorter, Prof. Frans Bongers and Dr. Rozendaal (Wageningen University, the Netherlands).

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