Introduction

Grassy ecosystems

Treeless grasslands and grassy woodlands once covered vast areas of south-eastern Australia. These grassy ecosystems probably developed as a result of drying and cooling of the Australian climate. The expanded  grassy ecosystems reached their maximum area during the ice ages, the last of which occurred 15 000 years ago. Lightning strikes or burning by Aboriginals may have also influenced the distribution of grassy  ecosystems.

Since early European settlement, areas containing grassy ecosystems have been recognised as prime sites for agricultural production. The flat or gently rolling terrain of grassy areas with their better water-holding capabilities and generally deeper, more fertile soils were more favourable for agricultural production and required little or no tree clearance. Since then many areas containing these grassy ecosystems have been destroyed for the development of cities, towns and their associated network of roads and railways, resulting in severe fragmentation of the remaining areas.

The structure and composition of remaining grassy ecosystems have been changed as a result of different fire regimes, mowing and grazing (especially in combination with periodic droughts, rabbit and weed infestations), cultivation and pasture improvement. Even the least disturbed remnants have been colonised by introduced plant and animal species. Many native plant and animal species have declined, are threatened with extinction or have become extinct regionally. Many grassland and grassy woodland communities are severely reduced in extent, abundance and integrity, or are threatened with extinction.

Some lowland grassland sites rival the alpine herb-fields in their wildflower displays, and areas dominated by native grasses have a subtle beauty, especially as they change from season to season.

The remaining sites that are least disturbed are characterised by a diversity of wildflowers and a range of small animals, including birds, reptiles, mammals and many invertebrates. Many disturbed sites also retain some conservation values. In a very few cases grassy remnants have been deliberately managed over a long period of time to protect their conservation values. In most instances, however, conservation values have remained fortuitously as a by-product of other land uses. These land uses include low input rural production, use as travelling stock reserves, road and rail easements, rural cemeteries and open space within cities and towns.

An ecological community is an assemblage of species (plants, animals and other organisms) that occupy a particular area. They can be identified by the species that characteristically occur within them. The composition of communities occurs as a result of landform, soils and geology, altitude, rainfall, temperature and other natural features, as well as past management and disturbance.

Grassy ecosystems include communities where the vegetation of the ground-layer is dominated by native grasses and forbs. Grassy ecosystems are distinguished by their plant species composition and structure, as well as their level of past disturbance. Table 1 describes different grassy ecosystems, although it is not always easy to differentiate between grassy communities because one often merges with another.

Native grasslands occur where trees are absent or are sparsely scattered (this roughly equates to less than two mature trees per hectare). These grasslands may be naturally treeless, or may have resulted from the clearance of trees and shrubs (derived or secondary grasslands).

Grassy woodlands contain wide spreading trees where the crowns are clearly separated (roughly two to about 30 mature trees per hectare).

Depending on the extent of modification of these grassy communities, the groundlayer can be very diverse, containing many wildflower species as well as grasses, or may contain only native grasses. However, some sites with even high disturbance may contain threatened or uncommon species.