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RESEARCH ARTICLE
Contents Vol 31(4)

Demography of three perennial grasses in a central Queensland eucalypt woodland

P. Jones A , P. Filet A and D. M. Orr B C
+ Author Affiliations
- Author Affiliations

A Department of Employment, Economic Development and Innovation, Locked Mail Bag 6, Emerald, Qld 4720, Australia.

B Department of Employment, Economic Development and Innovation, PO Box 6014 Rockhampton Mail Centre, Rockhampton, Qld 4702, Australia.

C Corresponding author. Email: david.orr@deedi.qld.gov.au

The Rangeland Journal 31(4) 427-437 https://doi.org/10.1071/RJ09035
Submitted: 16 June 2009  Accepted: 5 November 2009   Published: 27 November 2009

Abstract

The population dynamics of the palatable, perennial grasses Bothriochloa ewartiana (Domin) C.E.Hubb. (desert Mitchell grass), Chrysopogon fallax S.T.Blake (golden beard grass) and Heteropogon contortus (L.) P.Beauv. ex Roem. & Schult. (black speargrass), were studied in an extensive grazing study conducted in a eucalypt woodland within the Aristida–Bothriochloa pasture community in central Queensland between 1994 and 2000. Treatments were three grazing pressures based on light, medium and heavy utilisation of forage available at the end of summer and two timber treatments (trees intact and trees killed). Seasonal rainfall throughout this study was generally favourable for plant growth with no severe drought periods. Grazing pressure had a greater overall impact on plant dynamics than timber treatment, which had minimal impact. Grazing pressure had a large impact on H. contortus dynamics, an intermediate impact on B. ewartiana and no impact on C. fallax. Fluctuations in plant density of both B. ewartiana and C. fallax were small because both species were long lived with low levels of seedling recruitment and plant death, whereas fluctuations in H. contortus density were relatively high because of its relatively short life span and higher levels of both recruitment and death. Heavy grazing pressure increased the recruitment of B. ewartiana and H. contortus in some years but had no impact on that of C. fallax. Heavy grazing pressure reduced the survival of the original plants of both B. ewartiana and H. contortus but not of C. fallax. For H. contortus, the size of the original plants was larger where trees were killed than where trees were left intact and plants of the 1995 seedling cohort were larger in 1998 at heavy compared with those at light and medium grazing pressure. Grazing had a minor negative impact on the soil seed bank of H. contortus. Populations of all three species remained stable throughout this study, although the favourable seasonal rainfall experienced and the short duration of this study relative to the life span of these species may have masked longer term, deleterious impacts of heavy grazing pressure.

Additional keywords: Bothriochloa ewartiana, Chrysopogon fallax, Heteropogon contortus, plant, seedling recruitment.


Acknowledgements

We wish to acknowledge Charlie and Jacqui Hawkins and later Cameron and Jude Hicks, past and present owners of Keilembete for the use of land and for cattle management and for hosting field days throughout this study. David Osten, Melinda Cox, Stephen Ginns and Anne Shepherd provided valuable technical assistance, Christina Playford provided statistical analyses and Madonna Hoffman prepared the figures. Significant funding towards this project was provided by Meat and Livestock Australia.


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