Tropical Grasslands (2006) Volume 40, 137144
Pasture management in semi-arid tropical woodlands: colonisation by introduced pasture species
JOHN G. McIVOR
CSIRO Sustainable Ecosystems, St Lucia, Queensland, Australia
Colonisation of unsown areas by Stylosanthes hamata, S. scabra, Cenchrus ciliaris and Urochloa mosambicensis was measured over the period 1983–1992 at Hillgrove and Cardigan stations, near Charters Towers, north-east Queensland. Rate of colonisation (years to colonise 50% of quadrats) varied with species, location and management treatment but significant effects of management were few — tree killing affected only S. hamata, fertiliser application affected only Cenchrus ciliaris, and stocking rate had no significant effects on any species. Colonisation by the 4 species was related to characteristics of the pastures. Yield of the colonising species in autumn (as a surrogate for seed production) and total pasture yield at the end of the dry season were useful predictors of colonisation in the following year. For all species, colonisation increased asymptotically as species yield increased, and decreased as dry season pasture yield increased. Adjusting grazing pressure during and after seed set may be a useful way to influence rates of colonisation. To increase colonisation by these species, management should aim to favour the growth of the species (to increase seed input) and to decrease pasture yields at the end of the dry season to aid establishment; to limit colonisation by a species, yield of that species should be decreased and total pasture yields increased.