The effect of termite biomass and anthropogenic disturbance on the CH₄ budgets of tropical forests in Cameroon and Borneo

The exchange of CH₄ between tropical forests and the atmosphere was determined by simultaneously measuring the net CH₄ 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 CH₄ ranged from a net emission of 40.7 ng m^-2 s^-1 to a net CH₄ oxidation of -53.0 ng m^-2 s^-1. Soil-inhabiting termite biomass was significantly correlated with CH₄ flux. Termite mounds emitted up to 2000 ng s^-1 mound^-1. Termite-derived CH₄ 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 CH₄ 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. CH₄ budgets calculated for each site indicated that both forests were net sinks for CH₄ at -6.1 kg ha^-1y^-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. CH₄ 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 CH₄. Rates of CH₄ 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). CH₄ flux from termite mounds ranged from net oxidation in an abandoned mound to a maximum emission of 468 ng s^-1 mound^-1. CH₄ budgets calculated for each site indicated that CH₄ flux from termite mounds had an insignificant effect on the budget of CH₄ 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.