Across the globe, tropical forests are disappearing at an alarming rate. Deforestation results in the release of climate-warming carbon dioxide, and biodiversity suffers as a result. Farmland, on the other hand, may quickly return to nature if it is left alone.
Forests can recover by over 80 percent in biodiversity and soil health in just 20 years, according to a study published Dec. 10 in Science.
According to ecologist Lourens Poorter, of Wageningen University in the Netherlands, maintaining existing forests is essential to reducing climate change and halting species loss. But new research suggests that allowing trees to repopulate has “tremendous [climate] mitigation potential.”
Poorter says that after a few years of low-intensity agricultural usage, land cleared of tropical forests is generally abandoned, enabling nature to repopulate the land. Using 77 sites in the Americas and West Africa, he and his colleagues were able to see how such ecosystems recover. Researchers used 51 old-growth sites, those that have not been occupied by humans for at least 100 years, as a baseline and studied 12 forest variables related to soil health, ecosystem functioning, forest structure, and plant richness, assessing how rapidly those things returned.
Just 20 years after abandoning their farmland, tropical forests may restore an average of 80% of their original size. This is much faster than previously thought. Soil (red), diversity (orange) as well as forest structure (blue) all rebound at a different pace. Within 20 years, soil carbon and nitrogen levels had returned to those observed in old-growth forests. It takes roughly 40 years for plant species richness, or the number of species, in regrowing forests to approach old-growth levels, whereas species composition, or the relative abundances of those species, can take well over a century to reach old-growth levels. Similarly, experts estimate that total aboveground biomass will take 120 years to reach old-growth levels.
A decade after a site was abandoned, soils recovered the fastest, with carbon and nitrogen levels approaching those of old-growth forest habitats. It took 38 years for regrowing forests to have approximately the same number of plant species as comparable old-growth forests, but the researchers estimate that it will take 120 years for species abundances to recover to 90% of levels seen in old-growth forests. According to the research, it will take an additional 120 years for the total aboveground biomass to reach near-undisturbed forest levels.
Poorter claims that “recovery was much faster than we expected.” The seeds and stumps that were left behind after clearing aided in the haste. A “cheap, natural solution” to help address the climate and biodiversity problems may be slower to recover on land with more intensive agricultural use, but safeguarding regrowing woods can be a “cheap, natural solution.”
