Patterns and processes in the Townsville stylo-annual grass pasture ecosystem.
Stylosanthes humilis was grown for 5 years on cleared Tippera clay loam and its behaviour in competition with the annual grasses Digitaria ciliaris, Brachiaria ramosa, Pennisetum polystachion, Echinochloa crus-galli and Brachyachne convergens was followed using aerial colour photography and quadrat samples taken along representative transects. Results were assessed using a pasture stability index (PS), a real stability index for each component (RCS) and an apparent component stability index [defined] describing persistence of animal carrying capacity (ACS). In most years pasture stability (assessed by PS) was maintained. A balance developed in the species distribution in which the grasses were characteristic of the depressions in the pasture and the legume characteristic of the slopes (gradient 1:400). In one year, however, following intensive grazing and intense rainfall, water runoff and the consequent transport of seed was so great that PS was substantially decreased. The relationships between the components of the pasture ecosystem are expressed in the form of a diagram which was thought to reflect those principles generally applicable to annual legume/grass pastures in dry monsoonal environments and to give guide lines for future research.