Species distribution within improved pastures over central N.S.W. in relation to rainfall and altitude

Abstract

Botanical composition has a large influence on pasture productivity, but little information is available about the botanical composition of pastures on farms, the interactions of species or reasons for their distribution. A survey was done, during two successive springs and using a point quadrat method, of the botanical composition of improved pastures in central New South Wales and maps prepared of the proportion of species or groups of species in pastures. The survey area covered a wide range in rainfall (600-1000 mm), altitude (300-1400 m) and the boundary where perennial and annual pasture species overlap. Subterranean clover was the most common legume and occurred in all parts of the region. Above 700 mm rainfall, white clover replaced subterranean clover in a linear relationship, though the proportion of the pasture occupied by both species never exceeded 30%. Annual grasses were found throughout the survey area, and they were also replaced by perennial species at higher rainfall, higher altitude sites, in a linear relationship. The total proportion of the pasture from both perennial and annual grasses did not exceed a mean of 55%. The high proportion of annual species was attributed in part to continuous grazing practices. Perennial species were found down to 600 mm rainfall but only exceeded the proportion of annual species when the rainfall exceeded 800 mm for legumes or 900 mm for grasses or where the altitude was above 900 m (<12¦C mean annual temperature) for both groups. It was concluded that among perennial or annual groups, legumes and grasses occupied slightly different niches in the pasture, and they would not always replace one another exclusively. The legume content of pastures, especially in the higher rainfall areas, was considered to be less than satisfactory for animal production. Pasture recommendations need to consider the climatic limits where species are able to make a major contribution to production as well as the climatic limits for persistence.