Demography and Survival under Grazing of Three Australian Semi-Desert Shrubs

Longevity, recruitment, survivorship and change in population size of three dominant shrubs were investigated at Koonamore, South Australia. Particular attention was paid to the effects of grazing by sheep and rabbits. Atriplex vesicaria Heward ex Benth. has negative exponential survivorship with a half-life of ca 11 yr. Its populations decline under heavy grazing but increase at the expense of Maireana sedifolia (F. Muell.) P. G. Wilson under intermittent grazing. They also increase after release from grazing. M. sedifolia has negative exponential survivorship with a half-life of ?150 yr. Its populations decline under grazing, and even after 50 yr release from grazing continue to decline. Acacia aneura F. Muell. ex Benth. lives to ca 250 yr. Grazing prevents recruitment, causing its populations to decline. Recruitment resumes after release from grazing, but requires exceptional climatic sequences. These trends if continued will cause drastic change in the dominance of the important low (chenopod) shrubland and low woodland communities of inland Australia.