Studies in the ecology of the Riverine Plain. IV. Basal area and density changes of Danthonia caespitosa Gaudich, in a natural pasture grazed by sheep

Abstract

The changes in basal area and density of Danthonia caespitosa were measured over the 9-year period 1949-1957 by charting permanent quadrats in plots which were ungrazed, and lightly, moderately, and heavily grazed.

Compared with the control, the grazing treatments had no effect on basal area, and a significant but not substantial effect on the contribution made by the various age groups of the dominant grass.

There were no real differences between the age groups of D. caespitosa on continuously and intermittently grazed treatments, and it is suggested that the design of grazing experiments might be simplified, cognizance being given to the stage of degeneration reached by the pasture, and to the possibility that seasonal deferment procedures might cause substantial changes in botanical composition.

. In the autumn or winter of 1951 the mature population of D. caespitosa was almost wiped out and the build-up of basal area and density over the 1951-1957 period was very slow.

Dry summers and the late arrival of the opening rains in autumn appeared to be responsible for substantial losses in D. caespitosa. Abnormally high rainfall during the preceding growth season appeared to accentuate these losses.

In the gilgai microrelief death rates were greater on the depression than on the shelf. It is suggested that the D. caespitosa grassland was degraded, and reached a "steady state" condition under the influence of cattle, sheep, rabbits, and drought. If grazing treatments are to induce changes in such a plant population, such treatments must be a wide departure from the previous procedures which have given rise to the existing plant community.

The results are discussed in relation to grazing experiments in Queensland, New South Wales, South Australia, and the north-west of Western Australia.