Accounting for carbon in grass and forests

4 Sep 2012

Unit: Earth System Science Group

In a new analysis of vegetation and soil carbon, Ishak Yassir shows that to estimate carbon stocks, researchers must better understand the soil properties in different ecosystems such as forests and grasslands. Yassir, originally from Indonesia, recently received his PhD for this research, which he conducted under IIASA Director & CEO Prof. Dr. Pavel Kabat.

In East Kalimantan, Indonesia, spear grass grows rampantly over fields once cleared for agriculture and then abandoned. Left to themselves, the grassy fields would grow into new forests in a year or two, reaching maturity in as little as 15 years. But the grass is incredibly flammable and regular brushfires – caused by human interference - ensure that young forests rarely get a chance to take hold.

Climate researchers use carbon storage estimates to determine how much greenhouse gas gets removed from the atmosphere and stored in vegetation. These estimates are also important for programs that sell carbon credits or reward people for reforestation to reduce climate change. When researchers compare forests to grasslands, they usually assume that forests store more carbon than grass, taking up carbon dioxide from the air and converting it to woody vegetation.

Yassir’s work looked at soil carbon storage during different stages of forest regeneration, from the initial grasslands that grow soon after clearing or fire, to primary forest, which forms in 1 to 2 years following a disturbance, and secondary forest, which replaces primary forest over subsequent years. He showed that even though grasslands have much less carbon content than a forest, fields covered by spear grass acted as a carbon sink, taking up more carbon dioxide than they release to the atmosphere. That’s because the soil under spear grass stores a large amount of plant matter that decomposes only very slowly. Older forests, as expected, also acted as a carbon sink, converting the atmospheric carbon to wood and vegetation and storing it in the vegetation and soil. When primary forests start to form, however, they take up less carbon than either the grasslands or older forests. The old grass starts to decompose in the new forest, emitting carbon dioxide into the atmosphere.

The new work emphasizes the need for better understanding of forest dynamics and carbon cycling.

Publications:

    Van der Kamp, J., Yassir, I., Buurman, P., 2009. Soil Carbon changes upon secondary succession in Imperata grasslands (East Kalimantan, Indonesia). Geoderma, 149: 76-83.

    Yassir, I. and Omon, M., 2006. Hubungan potensi cendawan mikoriza arbuskula (CMA) dengan sifat-sifat tanah pada lahan kritis di Samboja, Kalimantan Timur (The relationship between potency arbuscular mycorrhizal fungi (AMF) and soil properties in marginal land Samboja, East Kalimantan). Jurnal Penelitian Hutan Tanaman. Pusat Penelitian dan Pengembangan Hutan Tanaman, 3:107-115.

    Yassir, I., Van der Kamp, J., Buurman, P., 2010. Secondary succession after fire in Imperata grasslands of East Kalimantan, Indonesia. Agriculture, Ecosystems and Environment, 137: 172-182.