Managing a semi-arid rangeland grazing system for sustainability: Can it be done?

The dynamics of semi-arid rangeland systems, particularly the biological mechanisms of their degradation through overgrazing, have been widely studied both in theory and practice. Less well known is how land owners interact with this production system and whether management strategies can be formulated that avoid the tendency of grazing systems to become overexploited.  Here we explore a model that, in addition to incorporating grazing and rainfall-dependent forage production, also investigates the consequences of feedbacks with human decision making. Central to the model is a basic tradeoff between the accumulation of ecologic and economic reserves. Consistent with Noy-Meir’s pulse-reserve paradigm, ecological reserves (e.g. in meristem banks, soil fertility) buffer against the effects of rainfall variation, allow the system to recover rapidly from drought and maintain high levels of rain use efficiency. Conversely, economic reserves (farm assets, money in the bank) buffer ranch operations against the effect of income fluctuations. Both ecologic and economic reserves are drawn from the same source: primary productivity, thus creating the tradeoff. The model explores how differences in the use of economic reserves affect the long-term maintenance of productivity. Results are discussed in the context of climate change and access to reliable ecologic and meteorologic information.