The effect of termite biomass and anthropogenic disturbance on the CH 4 budgets of tropical forests in Cameroon and Borneo

Abstract

Summary The exchange of CH 4 between tropical forests and the atmosphere was determined by simultaneously measuring the net CH 4 flux at the soil surface and assessing the flux contribution from soil‐feeding termite biomass, both within the soil profile and in mounds. In Cameroon the flux of CH 4 ranged from a net emission of 40.7 ng m –2 s –1 to a net CH 4 oxidation of –53.0 ng m –2 s –1 . Soil‐inhabiting termite biomass was significantly correlated with CH 4 flux. Termite mounds emitted up to 2000 ng s –1 mound –1 . Termite‐derived CH 4 emission reduced the soil sink strength by up to 28%. Disturbance also had a strong effect on the soil sink strength, with the average rate of CH 4 oxidation, at – 17.5 ng m –2 s –1 , being significantly smaller (≈ 36%) at the secondary forest site than the –27.2 ng m –2 s –1 , observed at the primary forest site. CH 4 budgets calculated for each site indicated that both forests were net sinks for CH 4 at – 6.1 kg ha –1 y –1 in the near‐primary forest and – 3.1 kg ha –1 y –1 in the secondary forest. In Borneo, three forest sites representing a disturbance gradient were examined. CH 4 oxidation rates ranged from 0 to – 32.1 ng m –2 s –1 and a significant correlation between the net flux and termite biomass was observed only in an undisturbed primary forest, although the biomass was insufficient to cause net emission of CH 4 . Rates of CH 4 oxidation were not significantly different across the disturbance gradient but were, however, larger in the primary forest (averaging – 15.4 ng m –2 s –1 ) than in an old‐growth secondary forest (–13.9 ng m –2 s –1 ) and a young secondary re‐growth (– 10.8 ng m –2 s –1 ). CH 4 flux from termite mounds ranged from net oxidation in an abandoned mound to a maximum emission of 468 ng s –1 mound –1 . CH 4 budgets calculated for each site indicated that CH 4 flux from termite mounds had an insignificant effect on the budget of CH 4 at the regional scale at all three forest sites. Annual oxidation rates were – 4.8, – 4.2 and – 3.4 kg ha –1 y –1 in the primary, secondary and young secondary forests, respectively.

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