All right, all right—the headline is a tad tendentious. However, researchers have long argued that tropical forests are absorbing a good bit of the extra carbon dioxide that humanity is producing by burning fossil fuels. An entire multi-billion dollar United Nations program, Reducing Emissions by Deforestation and Forest Degradation (REDD), is premised on the idea that saving tropical forests from the axe will mitigate climate change. ScienceDaily is reporting a new study in Nature Climate Change which suggests that this process is not as simple as it seems. What's going on? Answer: Rotting leaves.
The researchers used results from a six-year experiment in a rainforest at the Smithsonian Tropical Research Institute in Panama, Central America, to study how increases in litterfall—dead plant material such as leaves, bark and twigs which fall to the ground—might affect carbon storage in the soil. Their results show that extra litterfall triggers an effect called 'priming' where fresh carbon from plant litter provides much-needed energy to micro-organisms, which then stimulates the decomposition of carbon stored in the soil.
Lead author Dr Emma Sayer from the UK's Centre for Ecology & Hydrology said, "Most estimates of the carbon sequestration capacity of tropical forests are based on measurements of tree growth. Our study demonstrates that interactions between plants and soil can have a massive impact on carbon cycling. Models of climate change must take these feedbacks into account to predict future atmospheric carbon dioxide levels."
The study concludes that a large proportion of the carbon sequestered by greater tree growth in tropical forests could be lost from the soil. The researchers estimate that a 30% increase in litterfall could release about 0.6 tonnes of carbon per hectare from lowland tropical forest soils each year. This amount of carbon is greater than estimates of the climate-induced increase in forest biomass carbon in Amazonia over recent decades. Given the vast land surface area covered by tropical forests and the large amount of carbon stored in the soil, this could affect the global carbon balance.
It's always something, isn't it?