Tropical Grasslands (2006) Volume 40, 202212
Impact of short-term exclosure from grazing on pasture recovery
from drought in six Queensland pasture communities
D.M. ORR, M.C. YEE AND D.J. MYLES
Department of Primary Industries and Fisheries,
Rockhampton, Queensland, Australia
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.