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Tropical forests regrow naturally on abandoned farmlands

Tropical forests have been cleared at an alarming rate in recent decades, with the land being converted for agricultural use and pastures. However, deforested areas also have the potential to regrow and recover rapidly if the lands are subsequently abandoned and farming activity ceases. This is the conclusion of a study, published today by AAAS, that finds tropical forests and their soils are very resilient to low-intensity land use.

An international team of scientists set out to gain a holistic understanding of tropical forest regrowth on abandoned lands. Led by Lourens Poorter of Wageningen University and Research, the experts analyzed patterns of forest recovery at 77 secondary forest sites in the Americas and West Africa. 

Since the species of trees found at the sites differed substantially, the researchers decided that comparisons were not a useful way of quantifying forest regrowth or patterns of succession. Instead, they evaluated forest recovery in terms of 12 environmental attributes related to soil, plant functioning, ecosystem structure and biodiversity. 

The experts found that it takes only 20 years for all the forest attributes to regain 78 percent of their original, old-growth values. Recovery is fastest for soil characteristics, where values return to within 90 percent of their old-growth levels within 10 years. Plant functioning returns within 25 years while plant community structure and species diversity recover within 60 years. Recovery is slowest for biomass and species composition, which take roughly 120 years to reach 90 percent of their original, old-growth values.

Further analysis showed that the various forest attributes were clustered in three independent groups, one related to structure, another to species diversity and the third to composition. The attributes within each group were interrelated, as were their patterns of recovery. 

The authors state that secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration. In cases where land clearance has left residual indigenous vegetation, secondary forests will develop naturally as succession takes place. This represents the cheapest option for restoring forest ecosystems. Where bare ground is left after farming use ceases, indigenous trees will have to be planted in order to encourage the process of forest recovery. 

In addition to showing that forest recovery can take place relatively rapidly, the findings also indicate that these secondary forests may play an increasingly important role in climate change mitigation and biodiversity and ecosystem restoration. 

The study is published in the journal Science

By Alison Bosman, Staff Writer

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