Study: Deforestation isn’t only threat to Brazilian Amazon

The Amazon is the world’s largest forest carbon repository, with about 86 billion tonnes stored above and below ground. Clear-cutting of the rainforest has led to huge carbon losses, but efforts by the Brazilian government have reduced the annual deforestation rate by 79% from 2005 to 2013.

A new study published in the journal Global Change Biology, however, suggests that curbing deforestation is not enough: Forest degradation due to selective cutting and forest fires is reducing carbon stocks in the Brazilian Amazon by about 540 million tonnes of carbon per year, or about 40% as much as continued clear-cutting.

“The impacts of fire and logging in tropical forests have always been largely overlooked by both the scientific community and policy-makers who are primarily concerned with deforestation,” says Dr. Erika Berenguer, of Lancaster University, lead author of the study. “Yet our results show how these disturbances can severely degrade the forest, with huge amounts of carbon being transferred from plant matter straight into the atmosphere.”

This is the largest study ever to estimate above- and below-ground carbon loss from selective logging and ground-level forest fires in the tropics. A team of European and Brazilian researchers from 11 institutions, including SEI Research Fellow Toby Gardner, sampled 70,000 trees and took thousands of soil, litter and dead wood samples from 225 sites in the eastern Brazilian Amazon.

Soil carbon stocks appeared to be resistant to the effects of logging and fire, and the dead wood and litter carbon pools seemed able to recover rapidly. But live vegetation, the largest carbon pool, was found to be extremely sensitive, storing 18% to 57% less carbon than in undisturbed primary forests.

The authors explain that the forest degradation often starts with logging of prized trees such as mahogany and ipe. The felling and removal of these large trees often damages dozens of neighbouring trees, leaving many gaps in the canopy. This, in turn, creates much drier conditions due to exposure to the wind and sun, increasing the risk of wildfires spreading inside the forest. Over time, the forests become a thick scrub full of smaller trees and vines, reducing carbon storage by an average of 40%.

The study concludes that conservation programs aiming to ensure the long-term permanence of forest carbon stocks, such as REDD+, will remain limited in their success unless they effectively avoid degradation as well as deforestation.

“Our findings also draw attention to the necessity for Brazil, and other nations with tropical forests, to implement more effective policies for reducing the use of fire in agriculture, as fires can both devastate private property, and escape into surrounding forests causing widespread degradation,” says Gardner. “Bringing fire and illegal logging under control is key to reaching our national and international commitment to reducing carbon emissions.”

Gardner, who joined SEI in January as a research fellow funded by Formas, the Swedish Research Council, is a co-founder of the Sustainable Amazon Network, a consortium of scientists, conservation practitioners and local stakeholders to working to develop a deeper understanding of environmental and socio-economic trade-offs in the eastern Brazilian Amazon.

Read the journal article (external link, open access)