Deforestation triggers carbon collapse of tropical peatlands

Tropical peatlands, with their high water tables and low decomposition rates, form vast stores of organic carbon tens of metres thick. Most of it is found in Indonesia, where the natural swamp forests (also home to endangered animal species such as orangutans) are increasingly being destroyed by deforestation, drainage and fire, to make way for agriculture, in particular oil palm for biofuels and food. 

Dr Sam Moore, lead author of the study and former Open University PhD student, explained: “We measured carbon losses in channels draining intact and deforested peatlands, and found it is 50 per cent higher from deforested swamps, compared to intact swamps. Dissolved organic carbon released from intact swamps mainly comes from fresh plant material, but carbon from the deforested swamps is much older – centuries to millennia – and comes from deep within the peat column.”

Deforestation of Asian peat swamps is an important source of carbon dioxide emissions globally and its emission may be larger than previously thought. Carbon dating shows that the additional carbon lost from deforested swamps comes from peat which had been securely stored for thousands of years. Carbon lost from the drainage systems of deforested and drained peatlands is often not considered in ecosystem exchange carbon budgets, but the research team found it increased the estimated total carbon loss by 22 per cent.  

Changes in the water cycle seem to be the principal driver of this increase in carbon loss.  Much of the water falling as rain would normally leave the ecosystem through transpiration in vegetation, but deforestation forces it to leave through the peat, where it dissolves fossil carbon on its way.

Dr Vincent Gauci, Senior Lecturer in Earth Systems and Ecosystem Science at The Open University, and corresponding author said: “Essentially, ancient carbon is being dissolved out of Asian peatlands as they are increasingly being turned over to agriculture to meet global demands for food and biofuels. This has led to a large increase in carbon loss from Southeast Asian rivers draining peatland ecosystems - up by 32 per cent over the last 20 years, which is more than half the entire annual carbon loss from all European peatlands.  The destruction of the Asian peat swamps is a globally significant environmental disaster, but unlike deforestation of the Amazon, few people know that it is happening”. 

The authors concluded that their results increase the urgency for protecting these ecosystems from ongoing destruction for oil palm and other uses.