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Soil Organic Carbon Stock in Restored and Natural Forests in Northern Thailand

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Nuttira Kavinchan, Prasit Wangpakapattanawong, Stephen Elliott, Sutthathorn Chairuangsri, and Jitti Pinthong

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In order to increase understanding of the role that tropical forest restoration might

play in mitigating global climate change, soil organic carbon (SOC) was determined in a

chrono-sequence of plots in northern Thailand; from a site undergoing unassisted natural

forest regeneration (control); through 3 sites undergoing forest restoration by the framework

species method, aged 2, 7 and 11 years since tree planting (R2, R7, R11); to a nearby area

of relatively intact forest (NF). Forest restoration greatly increased SOC stocks compared

with pre-restoration data, predicting a return to NF levels in less than 21.5 years after

commencement of restoration activities. However, SOC stocks, measured in soil pits dug

down to 2 m depth, did not increase in sequence with forest development, as expected:

control 205.8 tCha-1; R2, 254.4; R7, 251.1; R11, 161.8 and NF, 244.9. The incongruously

low SOC in the 11 year-old restoration plot might be explained by the persistent, overriding,

effects of land use history reducing SOC in the lower soil layers. Per cent organic carbon

declined with soil depth, following reliable power functions (R2 0.92-0.97): %SOC=k.

DEPTHp (k=7.7 to 22.2; p=-0.41 to -0.80). Comparison with other studies showed that

forest restoration by the framework species method sequestered more soil carbon than

monoculture plantations in the same region.

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Chiang Mai, Climate change, Forest restoration, FORRU, Framework species method