A survey of the natural pastures of the Trangie District, New South Wales, with particular reference to the grazing factor.

Abstract

The Trangie district has a rainfall of 1,750 points with a slight summer maximum, a high relative variability of rainfall, and high summer temperatures. Disclimax pasture communities produced by a range of sheep grazing intensities operative during the past 20-30 years are described. On light soils ungrazed pasture comprises a wide range of perennial grasses. Light grazing (1 sheep per 2 acres) gives increased dominance by Stipa fulcata. With successive increases in grazing pressure Chloris acicdaris and Stipa setacea become conspicuous in turn, only to be virtually replaced by Chloris trumata as grazing intensity reaches 1 sheep per 0.5 acre. On heavy soils Stipa aristiglumis is dominant under light grazing. With increased rate of stocking, first Sporobolus caroli and then Stipa setacea gain dominance. At the highest stocking rates all these species are largely replaced by Chloris truncata. Throughout the sere the number of species is far more restricted than on the light soils. The striking feature of these results is that though botanical composition of the perennial grass component on light and heavy soils respectively is vastly different under light grazing, it becomes similar under heavy grazing and almost identical under severe grazing. Degenerative changes common to pastures of both soil groups under increasing grazing pressure are the decline in density and basal area of the perennial grass component, the greater population of winter and summer annuals, and the declining contribution of perennial grasses to green forage production in the spring. The basis of these findings is firstly the measurement of basal area, density and yield of perennial grasses, and density and yield of annual species in pastures of varying stocking history, and secondly, the measurement of pasture composition in relation to increasing distance from watering points.