Speargrass (Heteropogon Contortus) in Australia : Dynamics of Species and Community.

Abstract

The perennial tallgrass Heteropogon contortus is widespread and both ecologically and economically important. It often dominates the understorey of Eucalyptus woodlands in tropical and subtropical Australia. We present an historical overview of management and research in these important grasslands and review currently available information, particularly in relation to change at the community level. The use of H, contortus communities for extensive pastoralism led to its increase at the expense of other grasses. Ecological studies sought to explain how it came to dominate large areas but much research focussed on identifying pasture species, particularly legumes, that could replace or supplement what were seen as unproductive native grasses. Other efforts were directed at improving the generally low levels of animal production that resulted from the extreme seasonality of forage quality, and examining the animal production consequences of various management actions. There is some evidence that H. contortus has declined over large areas since the 1970s, but this process and its mechanisms are not well documented. Generally, research that has taken an empirical approach to improving animal production is poorly placed to provide a comprehensive ecological understanding. This is evident in several attempts to synthesise an ecological .understanding of H. contortus communities, notably in the form of state-and-transition models. These models contain generalities, some of which have little confirmation in experimental results. The geographic range and temporal variability of H. contortus communities make it difficult to generalise on the basis of single site, short term experiments that investigate one or a few factors in isolation. There is an increasing awareness of the need for sustainable management of native and natural pastures, including the H. contortus grasslands. Meeting this need will require the maintenance of the perennial grasses of northern Australian savannas and an ecological knowledge that can predict change in a variety of circumstances and locations.