The influence of cattle grazing on tree mortality after drought in savanna woodland in north Queensland

Live and dead trees were measured in macropod-grazed and cattle-grazed Eucalyptus woodland in north Queensland following a severe drought between 1992 and 1994. ANCOVA revealed no effect of grazing treatment on the proportion of drought death. Twenty-seven per cent of all tree species were killed by the drought and the value ranged from about 4% for Corymbia dallachiana (Benth.), K.D.Hill & L.A.S.Johnson to 29% for the dominant species Eucalyptus xanthoclada Brooker and A.R.Bean, although differences were non-significant. There was also no significant difference in mortality between poles (<10 cm d.b.h.) and trees (>10 cm d.b.h.). The study highlights a natural (as in pre-European), catastrophic structural collapse of tropical eucalypt woodland. Presumably the dramatic declines in basal area as a result of drought are recovered during successive relatively wet years by thickening events, although clearly this severe drought and its after-effects warrant further study.