Global change strategy options in the extensive agriculture regions of the world

The extensive agricultural regions contain relatively little of the world's carbon and their main influence on atmospheric composition is via biomass burning in the more humid regions of the tropics, and methane from cattle production. In terms of direct feedback influence on climate their effects are via opaqueness of the atmosphere (dust and aerosols) and the albedo of the surface. Change in these regions is brought about by the separate and (especially) interactive effects of climate, fire and herbivory. Likely changes in productivity, vegetation structure and soil erosion will lead to some changes in stored carbon and feedback effects. Possible increased cultivation of marginal areas is an important unknown.Management options include livestock numbers, type and distribution, fire regimes, woody vegetation clearing, subsistence cropping and rehabilitation measures. Response strategies in line with IPCC goals include reducing stocking rates, halting clearing of woody plants, reducing fire frequencies and (where cropping is practised) use of zero-tillage. A modelling approach is suggested as a basis for examining which responses are appropriate, given that most managers in these regions have very few options and the regions contribute relatively little to the control of the world's climate.