GRAZING IN REMNANT WOODLAND VEGETATION - CHANGES IN SPECIES COMPOSITION AND LIFE FORM GROUPS

Grazing by domestic livestock in native woodlands can have major effec ts on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in flori stics in a large group of remnants of native woodland left after agric ultural clearing in southwestern Australia. Species richness and diver sity were significantly reduced in remnants and the proportion of exot ic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and iden tified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that norma lly influence floristic patterns. Floristic characteristics of sites t hat were influencing the position of plots on the ordination diagram i ncluded proportion of exotic species and proportion of native perennia l shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form g roups such as native perennial grasses and geophytes were not signific antly affected by grazing. Reproductive strategies of perennial specie s showed a significant decrease in numbers of resprouters and a signif icant increase in numbers of facultative seeder/sprouters. Exclosure p lots showed increases in number and cover of perennial shrubs and herb s after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of excl osure plots in grazed sites became closer to that of the ungrazed site s.