Long-term changes in the vegetation after the cessation of livestock grazing in Eucalyptus marginata (jarrah) woodland remnants

This paper documents changes in the floristic composition of Eucalyptus mar ginata Donn (jarrah) woodlands over 7 years of recovery from continual, int ensive livestock grazing. In remnants of native woodland left after agricul tural clearing, which have been subjected to livestock grazing, comparisons were made between the floristics of fenced exclosure plots and open plots that continued to be grazed. The vegetation in nearby remnants, which had n ot been subjected to livestock grazing, was also surveyed. An initial incre ase in annual exotic pasture species after grazing relief was only temporar y and highly influenced by fluctuations in annual climatic patterns, partic ularly rainfall distribution and abundance. Subsequent years saw a decrease in exotic annuals in exclosure plots and an increase in native perennials, in a trend towards becoming more floristically similar to the ungrazed sit es. Germination of overstorey species was observed in the exclosure plots, however, development of seedlings and saplings was sparse. Results indicate that for jarrah woodland in southwestern Australia, natural regeneration i s possible after the removal of livestock, with the return (within 6 years) of native species richness to levels similar to those found in ungrazed ve getation. Re-establishment of cover, however, appears to take longer. The f loristic dynamics are described in terms of a nonequilibrium model. Two veg etation states exist, degraded remnants with an understorey dominated by an nual species, and ungrazed vegetation with an understorey dominated by pere nnial shrubs and herbs. The former state is maintained by continual heavy g razing by livestock. Upon relief from grazing, the vegetation undergoes a t ransition towards floristic similarity to ungrazed vegetation. After 6 year s, vegetation change in the exclosure plots appears to be continuing and th erefore it is still in transition.