Floristic composition and diversity changes over 60 years in eastern mulga communities of south central Queensland, Australia

Abstract

Botanical surveys from prior to 1949 documented the plant species composition of the mulga (Acacia aneura) communities in the eastern Mulga Lands Bioregion of Queensland, Australia. These surveys recorded 282 vascular plant species including 268 natives and 14 exotics. Since 1949, mulga communities have experienced considerable modification through continuous grazing by domestic sheep and cattle even during drought periods and extensive vegetation clearance. To increase our knowledge on floristic composition and diversity change over this time, floristic data were recollected from mulga communities in the same region between 2007 and 2010 using a more systematic procedure. These surveys recorded 292 vascular plant species including 269 natives and 23 exotics. Species richness and composition within five life forms: tree, shrub, vine, forb and graminoid were compared between the recent survey data and the historical survey data. The majority of native plant species were either in the forb (45.4% of total native species) or graminoid (25.7% of total native species) life forms over the 60-year period. There was no significant difference in species richness between the historical and recent surveys within tree or shrub life forms, but there were differences in species richness in vine, forb and graminoid life forms over time. Similarities in native species between the historical and recent surveys were high. Sorensen Similarity Indices (ISS) were: 0.77 at species level, 0.84 at genus level and 0.87 at family level. In contrast, the similarity indices for exotic species was low (0.59) for species and genera (0.61), but high for families (0.86). More exotic species were recorded recently than historically. Among these, buffel grass (Pennisetum ciliare) and colocynth (Citrullus colocynthis) were more commonly encountered than other exotic species in the eastern mulga communities of south central Queensland, Australia.