Defoliation and its effects on Enneapogon avenaceus and Cenchrus ciliaris populations during two summer growth periods in central Australian rangelands.

Abstract

The frequency and intensity of defoliation on Enneapogon avenaceus (oat grass) and Cenchrus ciliaris (buffel grass) populations under various grazing pressures were studied during two summer gowth periods. The effects of defoliation on seed head production and long term productivity were also investigated. The degree to which cattle concentrated on E. avenaceus is directly related to the available E. a~,enacetrs biomass. In contrast, the degree of concentration on C. ciliaris populations is not only a function of the availability of C. ciliaris biomass, but also of the available palatable ephemeral biomass. Highest seed head production for both species came from ungrazed and lightly-defoliated plants. Sufficient seed replenishment for continued persistence of E. avenaceus populations was obtained when more than 60% of the plants in the population were ungrazed or only Lightly-defoliated. In this study continued dry matter production of C. ciliaris populations was not affected by defoliation. Longer term investi- gations are needed to define defoliation thresholds for the management of this species. Perennial C. ciliaris plants in open woodland communities nre important for the persistence of the shortlived E. aal'crracects popu- lations. Cattle concentrated more on C. ciliaris than on E. avenaceus plants during the fu~t two weeks of a growth period, which allowed the latter to grow and even to start producing seed before cattle concentrate on them.