Native grasslands on non-arable slopes of the Garrawillie Creek sub-catchment, Western Liverpool Plains, New South Wales

Abstract

NSW Government vegetation legislation over the past five years has highlighted the need for a deeper understanding of native grasslands in NSW. The present study looked at such native grasslands on non-arable slopes in the Garrawillie Creek sub-catchment at the western margin of the Liverpool Plains. Sixteen sampling sites were selected on two contrasting rock types and aspects. Species composition and frequency scores were determined at each site using eight concentric nested subquadrats. Cluster analysis revealed seven grassland associations, each designated by a distinctive native grass species. Associated prominent grass species and forbs with 100% fidelity were listed for each grassland association. Within any one association there was a range in condition of the grassland, measured according to the number of perennials + natives relative to the number of annuals + exotics at any individual site. The seven grassland associations were interpreted as states in a state and transition model, in which rock type, aspect and possibly microtopography were important factors determining the states. With some but not all states, management overrode the underlying factors such that transitions occurred across rock type and aspect boundaries. The Sporobulus creber and Eriochloa pseudoacrotricha grasslands were restricted to lighter textured soils on scree slopes of the phonolite lava domes. On the heavy textured soils of the basaltic rocks of the Garrawilla Volcanics, the Bothriochloa spp. grassland maintained a characteristic high level of perennials, even where located within a few metres of land cultivated for at least 30 years. In contrast the Austrostipa aristiglumis grassland, found at lower altitudes on heavy textured soils, displayed low inertia and stability with natives:exotics and perennials:annuals ratios, at the site sampled, close to 1:1. The Eriochloa pseudoacrotricha and Aristida ramosa grasslands were limited to NW slopes.