Large Trees Drive Carbon Sequestration in Degraded Tropical Forests

by Stephen Johnson

Deforestation is responsible for 15% of human-caused carbon release and hence is a key driver of global climate change. However, less known is the role that degradation plays. Forests become degraded by persistent human use or through selective logging, decreasing biodiversity and potentially hindering ecological dynamics. In the Amazon basin, degradation may account for up to 25% of carbon emissions by land use. Selective logging commonly targets the largest trees, which by definition contain the most biomass and carbon. By removing these, logging often substantially reduces forest carbon stocks. Relatively little is known, however, about how this disturbance affects biomass dynamics among size classes at a tree stand level. Sist et al. (2014) address this deficit by following biomass changes among trees of various size classes through 8 years after selective logging. They surveyed 18 experimental plots every two years, collecting data on biomass changes within individual trunk diameter categories and on mortality or morbidity in each category. They found that while small trees increased in biomass, large trees are the key drivers of ecosystem carbon storage. Large trees account for close to half of total carbon storage and experienced high post-logging mortality, which caused significant carbon losses. In order to compensate for this, the authors conclude that logging intensity may need to be reduced and a maximum diameter cutting limit should be adopted. Continue reading