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Grazing for pasture management in the rangelands

A.C. Grice

NSW Agriculture, Cobar, NSW 2835


Rangelands contain many diverse, interacting species and growth forms. Climate and soil are major factors influencing the biomass, composition and productivity of rangeland pastures but grazing can also be important. This paper will consider four major questions in relation to herbivore induced changes in vegetation.

What changes occur in rangeland vegetation in response to grazing? Grazing by livestock, rabbits, other feral animals and large kangaroos has contributed to change in rangeland vegetation since European settlement. Changes include the proliferation of unpalatable endemic shrubs, a decline of perennial grasses, elimination or reduction of perennial chenopods, an increase in the undesirable grasses such as Aristida spp. and the failure of recruitment in some common palatable trees and shrubs. The introduction of exotic species has led to major shifts in the species composition of pastures. Mediterranean annuals have invaded with some species becoming pasture weeds and others useful sources of forage. In many areas, unpalatable indigenous shrubs and exotic grasses and forbs will continue to proliferate or occupy new areas. There is insufficient information to adequately describe continuing long-term trends in the composition of the herbaceous layer or the implications of these trends.

What are the mechanisms by which changes occur? Mechanisms of change in rangeland vegetation include grazing induced mortality of perennial grasses and chenopods, reduced perennial grass seed production, release from competition for annuals, shorter lived grasses, some chenopods and the seedlings of unpalatable shrubs, and enhanced mortality of the seedlings of a range of palatable trees and shrubs. The interaction of fire and grazing has been important in many communities. Changes in soils and microtopography are important in relation to changes in pastures. In some circumstances, soil changes may mean that a deterioration in pastures is irreversible within a reasonable time frame or likely economic scenario.

What constitutes a desirable pasture? There have been few attempts to measure the benefits and disadvantages of pastures that vary in biomass and composition. The costs incurred by the presence of dense stands of unpalatable shrubs have been quantified for some areas. It is commonly assumed that a prominent perennial grass component is desirable in many of our range types. However, while it has been shown that the presence of these grasses can reduce shrub establishment and have benefits in terms of soil water relations, there is little quantification of their impact upon animal production.

What management practices are available to bring about change? In general, management has emphasised animal condition and productivity rather than the pastures upon which the animals depend. Management must also focus on deliberate manipulation of rangeland vegetation using herbivores. Goals and strategies for using herbivores to manipulate rangeland pastures must be developed and promoted. Continuous stocking of pastures has remained the usual approach in most Australian rangelands but non-continuous grazing may benefit desirable pasture components. Rigid grazing systems are inapplicable. Rather, management must be responsive to crucial episodic climatic events. It should consider both long- and short-term implications of particular strategies and should not attempt to manipulate individual components of the system in isolation.

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