Stability, resilience and sustainability in pasture-based grazing systems

Two sets of simulations were run to illustrate the use of the pasture envelope concept to explore the economic and biological stability and resilience of the pasture system. The first set was designed to explore the financial and biological stability of the enterprise and involved simulating the impact of different stocking rates and rotation period on pasture production and composition, and cash flow. The second set of simulations was designed more to explore the resilience of the enterprise and involved introducing shocks to the enterprise in the form of `droughts' of varying strengths. This was achieved by, for example, reducing the maximum growth rate for both pasture species by 50% but maintaining the same seasonal pattern in the maximum growth rates of each species. The first simulation showed that at low stocking rates the enterprise was biologically stable, but cash flow was also low. Increasing stocking rates increased the cash flow, but also reduced the biological stability of the pasture until at very high stocking rates the pasture system collapsed. Changing the rotation period also affected the stability of the enterprise. In situations where the rotation period was very long, greater than 120 days (or 20 days/paddock), the biological system became unsustainable due to detrimental changes in pasture composition. The enterprise was somewhat resilient to drought at stocking rates less than 1 steer/ha. At stocking rates of 1 steer/ha, the enterprise was economically and biologically unsustainable in moderate or severe droughts. At a stocking rate of 1.25 steers/ha, the enterprise was unsustainable for droughts of any severity.