When people talk about the carbon stored in forests, they tend to think mostly of the trees. Usually, most of the carbon is in the trees. But in tropical peat swamp forests the carbon stored below the ground can be ten times more than that above the ground. The soils under peat swamp forests are full of organic matter and therefore a lot of carbon.
These soils are usually submerged under a water table that can be a metre or more above the surface of the soil. Whenever any vegetation from the forest falls onto the forest floor, it settles and is preserved in the water. This organic matter doesn’t undergo any decomposition due to the waterlogged conditions and thus the carbon in it is preserved. Over the years more and more debris is accumulated on the forest floor, building up a layer of highly organic, carbon rich peat that can be metres deep.
Due to increasing global demand for palm oil and paper pulp, peat swamp forests in South East Asia are being drained and cleared to make way for oil palm and acacia plantations. The loss of habitat for the forest dwelling biodiversity, most famously orang-utans but also species which we don’t even know about yet, is devastating – as is the loss of hydrological regulation that the forest maintains. And then there’s the soils – drainage of the peat results in immediate oxidation of the previously un-decomposed organic matter. No matter what land use you apply to the land after drainage, the carbon losses resulting from drainage are extensive. Carbon is lost from the soil due to microbial decomposition of the exposed peat, emitting carbon dioxide (CO2). Rates of CO2 emissions from tropical peatland degradation contribute between 1 – 3% of global human induced greenhouse gas emissions.
My research in Indonesia set out to try to quantify some of these loses (check out the project website). I spent hours and days in muddy swampy bogs; in one of the most special, pristine peat swamp forests in Indonesia, in one of the largest commercial oil palm plantations and with a handful of smallholder plantation growers in Eastern Sumatra.
Each of these areas was fascinating to be in and in each of them I felt privileged to have access and to be there. Of course, by far the most special was the peat swamp forest of Berbak National Park. After travelling for two days by boat to reach the area, we then had a 2 km walk through the swamp starting from the river’s edge with very little peat soil, transecting along the peat dome where the peat became increasingly deeper. At times we would be chest deep in black swamp water, our field kit on our heads, as we staggered over submerged logs and masses of roots. The vegetation changed along the transect – from the fringing palms along the river’s edge, mixed forest, bamboo sections and then the core primary forest vegetation. Throughout, the potential face-off with a Sumatran tiger was never far from our minds! Covered in dengue fever riddled mosquitoes, taking gas samples from the soil was a constant battle of swatting the mozzies and taking measurements on time. Taking peat cores was almost impossible, as the auger worked its way through the soil until it hit a solid tree trunk meters below in the peat – perfectly preserved in the submerged conditions. And at the end of the day we faced another 2 hour, 2 km slog back through the swamp to the awaiting base camp.
In the plantation sites we would work from dawn to dusk making the same measurements, usually in the blazing sun where it got so hot the tops of our wellies would burn our legs. Tropical downpours often interrupted an afternoon’s work, as we sheltered under our tarpaulin, focused on keeping the gas analyser dry.
Why do it? Why risk death by tiger, or malaria, or a broken limb two days from the nearest hospital? The answer: because there is so much to learn. The data we were collecting had never been collected in these areas before. The data gaps are huge in this field, in particular in tropical peats as they undergo land use change. So to be able to contribute to the pool of evidence on the effects that the conversion of peat swamp forests has on the soils and the carbon contained within them is a fabulous opportunity. It is exciting be able to contribute to the collection of data on a topic that demands such attention due to the scale of its impact. The results go beyond academic outputs, as they provide the evidence for decision makers to make informed, sustainable, land management choices.
Having finished my research in Indonesia, I am now undertaking research in the peat soils under papyrus wetlands in Uganda, the country I call home. Our research is looking at the links between soil carbon, livelihoods and poverty in these ecosystems. Fieldwork begins in early 2014, so more tropical swamp adventures will follow then…
Sheil, D., Casson, A., Meijaard, E., van Nordwijk, M. Gaskell, J., Sunderland-Groves, J., Wertz, K. and Kanninen, M. 2009. The impacts and opportunities of oil palm in Southeast Asia: What do we know and what do we need to know? Occasional paper no. 51. CIFOR, Bogor, Indonesia.
Murdiyarso, D., K. Hergoualc’h, and L. V. Verchot. 2010. “Opportunities for Reducing Greenhouse Gas Emissions in Tropical Peatlands.” Proceedings of the National Academy of Sciences of the United States of America 107 (46) (November 16): 19655–60. doi:10.1073/pnas.0911966107.
Hergoualc’h, K., and L. V. Verchot. 2011. “Stocks and Fluxes of Carbon Associated with Land Use Change in Southeast Asian Tropical Peatlands: A Review.” Global Biogeochemical Cycles 25 (2) (April 14). doi:10.1029/2009GB003718.
Page, S. E., J. O. Rieley, and C. J. Banks. 2011. “Global and Regional Importance of the Tropical Peatland Carbon Pool.” Global Change Biology 17 (2) (February 4): 798–818. doi:10.1111/j.1365-2486.2010.02279.x