Pasture production and composition response after killing Eucalypt trees with herbicides in central Queensland
Trevor J. Hall A E , Paul Jones B , Richard G. Silcock C and Piet G. Filet D
+ Author Affiliations
- Author Affiliations
A Department of Agriculture and Fisheries (DAF), PO Box 102, Toowoomba, Qld 4350, Australia.
B DAF, Emerald, Qld 4720, Australia.
C DAF, Brisbane, Qld 4102, Australia.
D Formerly Queensland Department of Primary Industries, Emerald, Qld 4720, Australia.
E Corresponding author. Email: trevor.hall@daf.qld.gov.au
The Rangeland Journal 38(5) 427-441 https://doi.org/10.1071/RJ16013
Submitted: 9 February 2016 Accepted: 27 June 2016 Published: 4 August 2016
Abstract
Clearing woodlands is practised worldwide to increase crop and livestock production, but can result in unintended consequences including woody regrowth and land degradation. The pasture response of two eucalypt woodlands in the central Queensland rangelands to killing trees with herbicides, in the presence or absence of grazing and regular spring burning, was recorded over 7 or 8 years to determine the long-term sustainability of these common practices. Herbage mass and species composition plus tree dynamics were monitored in two replicated experiments at each site. For 8 years following herbicide application, killing Eucalyptus populnea F. Muell. (poplar box) trees resulted in a doubling of native pasture herbage mass from that of the pre-existing woodland, with a tree basal area of 8.7 m2 ha–1. Conversely, over 7 years with a similar range of seasons, killing E. melanophloia F. Muell. (silver-leaved ironbark) trees of a similar tree basal area had little impact on herbage mass grown or on pasture composition for the first 4 years before production then increased. Few consistent changes in pasture composition were recorded after killing the trees, although there was an increase in the desirable grasses Dichanthium sericeum (R. Br.) A. Camus (Queensland bluegrass) and Themeda triandra Forssk. (kangaroo grass) when grazed conservatively. Excluding grazing allowed more palatable species of the major grasses to enhance their prominence, but seasonal conditions still had a major influence on their production in particular years. Pasture crown basal area was significantly higher where trees had been killed, especially in the poplar box woodland. Removing tree competition did not have a major effect on pasture composition that was independent of other management impositions or seasons, and it did not result in a rapid increase in herbage mass in both eucalypt communities. The slow pasture response to tree removal at one site indicates that regional models and economic projections relating to tree clearing require community-specific inputs.
Additional keywords: basal cover, bio-economic, Dichanthium sericeum, grazing, tree competition, woodland ecology.
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