Carbon metabolism of the terrestrial biosphere: A multitechnique approach for improved understanding

Understanding terrestrial carbon metabolism is critical because terrestrial ecosystems play a major role in the global carbon cycle. Furthermore, huma ns have severely disrupted the carbon cycle in ways that will alter the cli mate system and directly affect terrestrial metabolism. Changes in terrestr ial metabolism may well be as important an indicator of global change as th e changing temperature signal. Improving our understanding of the carbon cy cle at various spatial and temporal scales will require the integration of multiple, complementary and independent methods that are used by different research communities. Tools such as air sampling networks, inverse numerica l methods, and satellite data (top-down approaches) allow us to study the s trength and location of the global- and continental-scale carbon sources an d sinks. Bottom-up studies provide estimates of carbon fluxes at finer spat ial scales and examine the mechanisms that control fluxes at the ecosystem, landscape, and regional scales. Bottom-up approaches include comparative a nd process studies (for example, ecosystem manipulative experiments) that p rovide the necessary mechanistic information to develop and validate terres trial biospheric models. An iteration and reiteration of top-down and botto m-up approaches will be necessary to help constrain measurements at various scales. We propose a major international effort to coordinate and lead res earch programs of global scope of the carbon cycle.