Tropical peatlands are some of the most efficient carbon sinks worldwide. However, when they are damaged – for instance by changes in land use, degradation, or wildfires – they can become massive emitters of carbon. A research team led by the University of Göttingen has analyzed how peatland in the coastal areas of Borneo and Sumatra in Indonesia has developed over thousands of years in order to shed more light on the relationship between tropical peatlands and climate-related changes such as sea level rise.
The researchers analyzed two peat cores, each over eight meters long, searching for traces of pollen, spores, and charcoal, and conducting carbon dating and a series of biogeochemical investigations. They found that these peatlands contained much higher concentrations of charcoal during the mid-Holocene (9,000 to 4,000 years ago), when sea levels were higher than they are now. The presence of charcoal signifies that there were much larger forest fires during that period.
Later, about 3,000 years ago, the irregular periodic variations in winds and sea surface temperatures known as “El Niño” most probably caused prolonged droughts, making the forests susceptible to fires caused by lightning. Surprisingly though, even during that time, the fires seemed to be fewer than in the earlier, mid-Holocene period.
According to the scientists, the presence of mangrove forests growing along the coast in salty waters may explain this phenomenon. Mangrove forests are a good indicator of rising sea levels and increases of salt in the otherwise freshwater peatland ecosystem. Since salt is harmful to freshwater vegetation, its widespread presence probably resulted in more dry leaves and dead trees, as well as in the reduction of forest canopy cover and air humidity, which are important factors in protecting peatland forests from fires.
“We were surprised to find that rising sea levels could potentially exacerbate fires in coastal areas in Indonesia,” said study lead author Dr. Anggi Hapsari, an expert in vegetation dynamics at the University of Göttingen. “Our findings underline how the interaction between rising sea levels and dry climate may contribute to massive forest fires even in relatively fire-proof ecosystems, such as pristine peatlands. This reveals the potential hidden impact of sea level rise exacerbating climate warming.”
According to Dr. Hapsari and his colleagues, these findings suggest that, if we continue activities such as the destruction of peat swamp forests, peatland drainage, and intentional burning, at a time when climate change is steadily increasing sea levels and is exacerbating patterns such as El Niño, the probability of catastrophic and widespread forest fires and uncontrollable carbon release significantly rises.
“Our unexpected finding adds an as yet unknown threat to the survival of these valuable ecosystems,” explained study co-author Tim Jennerjahn, a researcher at the Leibniz Center for Tropical Marine Research in Bremen. “It demonstrates how the reconstruction of past environmental change can help improve present-day management of coastal ecosystems. It is clear that fire risk assessment in tropical peatlands deserves more attention.”
The study is published in the journal Global Change Biology.