METHANE EMISSION BY TERMITES AND OXIDATION BY SOILS, ACROSS A FOREST DISTURBANCE GRADIENT IN THE MBALMAYO FOREST RESERVE, CAMEROON

Methane fluxes were measured, using static chambers, across a disturba nce gradient in a West African semi-deciduous humid forest. Soil-feedi ng termite biomass was simultaneously determined, in an attempt to exa mine its influence on the net soil-atmosphere exchange of CH4. CH4 emi ssion rates from individual termite species were determined under labo ratory conditions, permitting the gross production of CH4 to be compar ed with net fluxes to the atmosphere. Both net CH4 oxidation(-) and em ission were observed, and CH4 fluxes ranged from -24.6 to 40.7 ng m(-2 ) s(-1). A statistically significant relationship between termite biom ass and CH4 flux was observed across the forested sites such that: CH4 flux (ng m(-2) s(-1)) = 4.95 X termite biomass (gm(-2)) - 10.9 (P < 0 .001). Rates of CH4 oxidation were on average 60% smaller at the clear felled and Terminalia plantation sites than at the near-primary forest site. Two of the disturbed sites were net CH4 sources during one of t he sampling periods. Disturbance of tropical forests, resulting in a d ecrease in the CH4 sink capacity of the soil, may therefore increase t he contribution of termite-derived CH4 to the atmosphere. Measurements from the mounds of the soil-feeding termites Thoracotermes macrothora x and Cubitermes fungifaber from the old plantation site gave a CH4 em ission of 636 and 53.4 ng s(-1) mound-l, respectively. The forest floo r surrounding the mounds was sampled in three concentric bands. Around the mound of T. macrothorax the soil was a net source of CH4 estimate d to contribute a further 148 ng s(-1). Soil surrounding the mound of C. fungifaber was mostly a net sink. The mounds of soil-feeding termit es are point sources of CH4, which at the landscape scale may exceed t he general sink capacity of the soil, to an extent dependent on season al variations in soil moisture and level of disturbance.