The effect of exotic pasture development on floristic diversity in centralQueensland, Australia

Floristic diversity was compared across boundaries where the trees have bee n cleared in semi-arid brigalow (Acacia harpophylla), gidgee (A. cambagei) and eucalypt (Eucalyptus populnea, E. melanophloia) woodland and forest in central Queensland. The cleared treatments included Exotic pasture (unculti vated, exotic grasses having more than 10% total cover) and Native pasture (uncultivated, not dominated by exotic grasses). An ordination of presence- absence data did not distinguish the floristic composition of the uncleared pasture and native pasture treatments, however, these treatment types were floristically distinct from the exotic pasture treatment in all three land types. Declines in species richness and diversity were substantial between uncleared and exotic pastures for brigalow and eucalypt lands. Differences were far less substantial for the same comparison in gidgee lands, and bet ween uncleared and native pasture for all three land types. These trends re flected differences in most perennial lifeform groups and the species that show significant declines are identified. There was no significant relation ship between native diversity and the age of clearing. This study draws att ention to the negative impacts on plant diversity posed by deliberate and i nadvertent spread of exotic perennial grasses in tropical forests and woodl ands. (C) 2000 Elsevier Science Ltd. All rights reserved.