At the climate talks in Paris, all attention was focused on how humanity can reduce climate change by reducing carbon emissions, or by increasing carbon uptake. Forests are an important carbon sink. While most attention has focused on old-growth tropical forests, it turns out that secondary forests that re-grow after forest clearance or agricultural abandonment can sequester large amounts of carbon. Is this a forgotten sink?

A large international team of forest ecologists including U of M ecologist Jennifer Powers and University of Minnesota graduate student Justin Becknell sought to answer that question by analyzing recovery of aboveground biomass using 1,500 forest plots and 45 sites across Latin America. The researchers found that carbon uptake in these new-growth tropical forests was surprisingly robust. Their findings will appear in the print edition of the journal Nature February 11, 2016.

"Secondary forests are literally the forests of the future," says Powers. "Our study focuses much-needed attention on overlooked tropical secondary forests, which now comprise more than half of all tropical forests."

Lourens Poorter, lead author of the study, notes that after 20 years, these forests have accumulated enough biomass to an uptake 3.05 ton carbon per ha per year - 11 times the uptake rate of old-growth forests.

Second-growth forests differ dramatically in their resilience; in 20 years between 20 and 225 tons of biomass has recovered. Biomass recovery is high in areas with high rainfall and water availability throughout the year, whereas soil fertility or the amount of forest cover in the surrounding landscape were less important.

"We also used these data to produce a potential biomass recovery map for Latin America," says co-author Danae Rozendaal. "Regional and national policy makers can use this information to identify areas that should be conserved, for instance because they have a slow recovery and are more difficult to restore, or to identify areas with fast recovery, where forest regrowth or reforestation has a high chance of success and a high carbon sequestration potential."

"This study firmly establishes the potential role that tropical secondary forests play in the global carbon cycle, and underscores that policies aimed at mitigating climate change should both reduce deforestation and promote forest regrowth," Powers says.

Jennifer Powers is an associate professor in the College of Biological Sciences with a joint appointment in the Department of Ecology, Evolution and Behavior and the Department of Plant Biology.