Effects of grazing, trenching and surface soil disturbance on ground cover in woody encroachment on the Cobar Pediplain, south-eastern Australia

• Excluding grazing and trenching (cutting roots of woody plants at 30 cm depth) increased herbaceous ground cover.
• Low herbaceous ground cover (<10%) even when grazing and competition from roots of woody plants are removed.
• Woody and herbaceous vegetation compete for resources in this semi-arid environment.
• Herbaceous ground cover is limited by competition from woody plants for resources, and possibly by other factors.

This study investigated three possible reasons for low ground cover in an inter-patch in woody encroachment in semi-arid south-eastern Australia: (1) grazing by large herbivores, (2) competition with woody plants for resources, and (3) the smooth, crusted soil surface impeding litter lodgement and germination of seeds. Grazing exclusion, trenching (cutting roots of woody plants to 30 cm depth) and surface soil disturbance treatments were established in October 2008, and herbaceous ground cover and litter cover were measured after three, 16 and 30 months. Perennial grass cover in the ungrazed area was higher in trenched plots than in untrenched plots. Perennial grass cover in the grazed area was very low in trenched and untrenched plots. Herbaceous ground cover increased over time in ungrazed and trenched plots, much more than in grazed or untrenched plots. Soil disturbance did not affect herbaceous ground cover. Herbaceous ground cover was low in all treatments (<10%). Both grazing and cutting roots of woody plants affected herbaceous ground cover in this study. Herbaceous ground cover increased when roots of woody vegetation were severed (in the absence of grazing), indicating that herbaceous ground cover and woody vegetation compete for resources.