Banded vegetation: survival under drought and grazing pressure based on a simple cellular automaton model

In western NSW, Australia, banded vegetation communities in grassland and shrubland remain widespread after up to 150 years of livestock grazing and a number of severe droughts. A simple model based on cellular automata is employed to investigate the robustness of such communities. It is shown that grazing pressure, simulated by the loss of plants at random within the landscape, has little effect on survival of the banded structure, unless pressure is extreme. Drought, associated with the systematic loss of plants in the driest locations, results in more extensive band fragmentation. The model suggests that these seemingly sensitive runoff–runon systems are in fact quite robust, and may well have changed little morphologically since European settlement. Species composition and plant age structure may, however, have been affected.