Carbon Flux in Drylands: The Forgotten Dimensions?

Abstract:

There has been a significant emphasis recently on the rôle of vegetation change and land degradation in drylands on carbon sequestration and the provision of related ecosystem services. Studies have typically focussed on the storage of carbon in biomass over short timescales. Over intermediate timescales, an important component of carbon-related ecohydrological processes is the way in which carbon is transferred from biomass to soil organic matter. These transfers are also significantly affected by land degradation via erosion processes which result in redistribution and net loss of carbon from the local system. Many drylands are underlain by significant stores of inorganic carbon, some of which is deposited from aeolian material, but vertical transfer from the surface stores is also an important process. Numerous studies suggest that these stores are in place from thousands to millions of years and thus contain carbon that has long been taken out of the global cycle. As progressive land degradation occurs, these stores are increasingly being exposed at the surface, and thus reactivated as part of the global cycle. In the context of climate change where increasingly stormy conditions are likely to accelerate the mobilization of sediment and associated carbon, and where increasingly acidic rainfall exacerbates dissolution of inorganic carbon, there is the potential for a significant addition to atmospheric carbon at regional and global scales. We will evaluate the relative importance of this mechanism compared to sequestration in vegetation and discuss the implications for maximizing ecosystem-service provision in drylands.