South Asia’s forests help fight climate change but more needs to be done
For the first time, a carbon budget has been calculated for South Asia, showing that forests contribute to reducing carbon dioxide in the atmosphere but rice and livestock add to it, say a team of scientists that includes the Centre’s Rodel Lasco
South Asia is home to 1.6 billion people: almost a quarter of the global population. Most of these people reside in India, which is also one of the fastest growing economies in the world. But until recently, little was known about the region’s contribution to the global carbon budget (the gains and losses of carbon).
To find out, our team estimated the sources and sinks of carbon dioxide and methane from anthropogenic and natural biospheric activities in Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka.
We found that, based on atmospheric carbon dioxide inversions, the net biospheric carbon dioxide flux (the transfer of carbon from one carbon sink to another) in South Asia was a sink, that is, the region soaked up more greenhouse gases than it emitted, thanks in no small measure to an increase in forest cover from 2000 to 2009.
During the last two decades, land use and land cover in South Asia have undergone massive changes. India alone has increased the extent of forest plantations by 4.5 million hectares from 1990 to 2010, which lead to a 26% increase in carbon stock in living forest biomass. As you might expect, this has had a major effect on carbon flux in the region.
We estimated that the annual net carbon flux from land-use change in the region was about −14 ± 50 megatonnes of carbon per year, which resulted from a small sink of −16 megatonnes per year owing to the establishment of tree plantations (−13 megatonnes per year in the most recent decade) and wood harvest (−3 megatonnes per year) and a source of carbon emissions in the order of 2 megatonnes per year owing to the expansion of cropland.
In the last decade, tree plantations—mainly eucalyptus, acacia, rubber, teak and pine—grew by about 300 000 hectares per year, which resulted in increased carbon storage. Surprisingly, harvesting wood resulted in a net sink of carbon. This was because both industrial wood and fuel wood harvesting declined recently, while the recovery of forests that had been harvested in previous years created a net sink in forests. However, the sink generated by expanding plantations and growth of logged forests was offset partially by carbon emissions from the expansion of cropland.
One important issue in India (which has the largest forest area in the region) is the relationship of tree plantations and native forests. A 2009 survey showed that there was a 5% increase in India’s forest area over the previous decade. However, the loss of native forests (0.8–3.5 % per year) was masked by the large increase in tree plantations.
There are, therefore, fears that there is a general lowering of biodiversity levels in India owing to the disappearance of complex native forests in favour of monocultural plantation forests. Another concern is the uncertain nature of estimates of the forest cover in India, which could affect our regional carbon stocks estimate.
The region is also very likely to be a strong source of methane, the second-most significant greenhouse gas after carbon dioxide, owing to rice cultivation (by an amount that still remains controversial), the introduction of high-yielding crop species, increased use of nitrogenous and phosphorus fertilizers, and expansion of cropland to meet the demand for food.
Rice cultivation and livestock are the two major sources of methane emissions from the agricultural sector. India has the world’s largest total livestock population—485 million in 2003—which accounts for approximately 57% and 16% of the world’s buffalo and cattle populations, respectively. Methane emissions from livestock have two components: enteric fermentation and manure management. The total methane emissions from Indian livestock was 11.8 megatonnes in 2003. The total mean emissions from the rice land of India was estimated at 2.5 megatonnes per year. The wet season contributed about 2.3 megatonnes, amounting to 88 % of the emissions.
It’s clear from these results that there is great potential for reducing methane emissions in order to stabilize overall greenhouse gas emissions from the region. This is an area that needs more research, along with the soil carbon pool and fluxes and the contribution of nitrous oxide to total greenhouse gas emissions, which have not been included in our analysis.
Edited by Robert Finlayson
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Patra PK, Canadell JG, Houghton RA, Piao SL, Oh N-H, Ciais P, Manjunath KR, Chhabra A, Wang T, Bhattacharya T, Bousquet P, Hartman J, Ito A, Mayorga E, Niwa Y, Raymond PA, Sarma VVSS, Lasco R. 2013. The carbon budget of South Asia. Biogeosciences 10:513–527. doi:10.5194/bg-10-513-2013.
This work is related to the CGIAR Research Program on Forests, Trees and Agroforestry