Impact of short-term exclosure from grazing on pasture recovery from drought in six Queensland pasture communities

Abstract

A study conducted during 2003 and 2004 examined the impact of either 0-, 3-, 6- or 12-month exclosure from grazing on pasture recovery following drought in 6 pasture communities, selected to include a range of pasture conditions on a range of soil types at Injune, Theodore, Charters Towers, Rockhampton, Nebo and Charleville, Queensland, Australia. Unreplicated plots of 25 x 25 m were established at each location in autumn 2003 and sampled at approximately 3-monthly intervals until autumn 2004. Drought prevented sampling at 2 locations until spring 2003.
Rainfall was generally below average to average (deciles 2 to 5) except at the Rockhampton site, which received twice the mean monthly rainfall in 2 consecutive months. There were no major changes in total perennial grass basal area between 2003 and 2004 except at Rockhampton. At that location, basal area of Heteropogon contortus increased substantially with the 12-month exclosure but not in the other 3 treatments. Perennial grass basal area at 4 other locations was moderate, despite prolonged drought and consequent heavy grazing pressure. However, a feature of the pasture at these 4 locations was the high contribution of undesirable species.
Total pasture yields in autumn 2004 were generally highest in the 12-month exclosure treatments. Apart from one treatment at Rockhampton, there were few major changes in perennial grass species composition. At 2 of the 4 locations with relatively high basal area of undesirable grasses, these undesirable species showed the greatest increase in yield. Nitrogen yield increased with increased exclosure from grazing at all locations reflecting dry matter yields.
We concluded that further research is required to improve the understanding of vegetation dynamics in relation to seasonal rainfall and that this research be conducted over a longer period, with spelling during the period of pasture growth.