Global Impact of Termites on the Carbon Cycle and Atmospheric Trace Gases

Termites have high biomass in many tropical ecosystems and emit the greenhouse gases CO2 and CH4. They are also recognized as ecosystem engineers, mediating decomposition and other aspects of soil function. Therefore, termites may be significant contributors to biogeochemical cycles, notably those of carbon and methane. We review methods of assessing carbon fluxes through termite populations and argue that direct measurements of net CO2 and CH4 emissions from termites in natural settings (in their nests or in the soil) are the best data for scaling-up calculations, if accompanied by accurate estimates of biomass and assemblage feeding-group composition. Actual determinations of gas fluxes from termites, and the attendant computation of regional and global budgets made over the past two decades are reviewed. For CO2, it is concluded that termites contribute up to 2% of the natural efflux from terrestrial sources, a large contribution for a single animal taxon, but small in the global context. For CH4, we note that calculations are still hampered by uncertainties over termite biomass distribution and a general failure to consider local and landscape-level oxidation by methylotrophic microorganisms as a factor mitigating net fluxes. Nevertheless the balance of evidence, including new data on local oxidation, suggests that annual contributions by termites are almost certainly less than 20 Tg, and probably less than 10 Tg (ca. 4% and 2% of global totals from all sources, respectively). Climate changes and land use intensification may cause minor modifications of the overall distribution of termites, but a more serious impact on soil stability and function could result from changes in the balance of feeding groups. The response of termites to changes in the quality and quantity of plant litters is uncertain, but direct effects from elevated atmospheric CO2 are unlikely. Global changes will broadly favour wood- and litter-feeding termites over soil-feeders, but with regional differences and complications arising from patterns of landscape fragmentation and historical factors.