Correlates of grass-species composition in a savanna woodland in northern Australia
K. A. Scott A B E , S. A. Setterfield A B , A. N. Andersen B C and M. M. Douglas B DA School of Environmental and Life Sciences, Charles Darwin University, Darwin, NT 0909, Australia.
B Bushfire Cooperative Research Centre, East Melbourne, Vic. 3002, Australia.
C CSIRO Sustainable Ecosystems, PMB 44, Winnellie, NT 0821, Australia.
D School for Environmental Research, Charles Darwin University, Darwin, NT 0909, Australia.
E Corresponding author. Email: kenneth.scott@hotmail.com
Australian Journal of Botany 57(1) 10-17 https://doi.org/10.1071/BT08120
Submitted: 7 July 2008 Accepted: 12 January 2009 Published: 23 March 2009
Abstract
Environmental features associated with the distribution of grass species are poorly known in tropical savannas, particularly at smaller spatial scales. The present study aimed to determine the relative influence of 11 environmental characteristics on grass-species composition in a savanna woodland in northern Australia. Environmental characteristics relating to woody-vegetation structure and soil, plus the long-term (14-year) fire frequency, were documented along an environmental gradient and compared with grass-species composition. Differences in grass-species composition, as well as richness and evenness, were related to differences in vegetation structure and edaphic characteristics. In particular, grass-species composition was most strongly related to plant-available moisture, the density of woody plants in the midstorey (2.0–9.99 m height), and canopy and litter cover. Grass-species richness and evenness were extremely low in areas where midstorey density, canopy cover and litter cover were high, and where soil moisture content in the root zone of grasses was low. Differences in fire frequency also influenced grass-species composition, with areas that had experienced lower fire frequency during the previous 14 years having lower density of the annual grass Sorghum intrans (F.Muell. ex Benth.) and the perennial grass Heteropogon triticeus (R.Br.) Stapf, and increased dominance of the perennial Eriachne triseta Nees ex Steud. The results of the present study demonstrate a complex interplay between bottom-up environmental factors and top-down processes such as fire, as determinants of grass-species composition in tropical savannas.
Acknowledgements
Funding for this study, and a PhD scholarship for K Scott, was provided by the Bushfire Cooperative Research Centre, Melbourne. For field assistance, we thank the late Jack Cusack, Gary Fox, Wawan Sastrawan Manullang, Sally Mitchell, Ken Nicholl and Jon Schatz. Ian Cowie and Jenni Low Choy provided much appreciated plant identification. Andrew Edwards kindly compiled the fire history of the site.
Abule E,
Smit GN, Snyman HA
(2005) The influence of woody plants and livestock grazing on grass species composition, yield and soil nutrients in the Middle Awash Valley of Ethiopia. Journal of Arid Environments 60, 343–358.
| Crossref | GoogleScholarGoogle Scholar |
[Verified 28 April 2008].
van Langevelde F,
van de Vijver CADM,
Kumar L,
van de Koppel J,
de Ridder N,
Van Andel J,
Skidmore AK,
Hearne JW,
Stroosnijder L,
Bond WJ,
Prins HHT, Rietkerk M
(2003) Effects of fire and herbivory on the stability of savanna ecosystems. Ecology 84, 337–350.
| Crossref | GoogleScholarGoogle Scholar |
Veenendaal EM,
Ernst WHO, Modise GS
(1996) Effect of seasonal rainfall pattern on seedling emergence and establishment of grasses in a savanna in south-eastern Botswana. Journal of Arid Environments 32, 305–317.
Vetaas OR
(1992) Micro-site effects of trees and shrubs in dry savannas. Journal of Vegetation Science 3, 337–344.
| Crossref | GoogleScholarGoogle Scholar |
Williams PR,
Congdon RA,
Grice AC, Clarke PJ
(2003) Effect of fire regime on plant abundance in a tropical eucalypt savanna of north-eastern Australia. Austral Ecology 28, 327–338.
| Crossref | GoogleScholarGoogle Scholar |
Williams RJ,
Duff GA,
Bowman DMJS, Cook GD
(1996) Variation in the composition and structure of tropical savannas as a function of rainfall and soil texture along a large-scale climatic gradient in the Northern Territory, Australia. Journal of Biogeography 23, 747–756.
| Crossref | GoogleScholarGoogle Scholar |
Wilson BA, Bowman DMJS
(1994) Factors influencing tree growth in tropical savanna: studies of an abrupt Eucalyptus boundary at Yapilika, Melville Island, northern Australia. Journal of Tropical Ecology 10, 103–120.
Woinarski JCZ,
Risler J, Kean L
(2004) Response of vegetation and vertebrate fauna to 23 years of fire exclusion in a tropical Eucalyptus open forest, Northern Territory, Australia. Austral Ecology 29, 156–176.
| Crossref | GoogleScholarGoogle Scholar |
Yeaton RI,
Frost S, Frost PGH
(1986) A direct gradient analysis of grasses in a savanna. South African Journal of Science 82, 482–486.
