Correlations between environmental factors, the biomass of exotic annual grasses and the frequency of native perennial grasses
Tanja I. Lenz A and José M. Facelli A BA Environmental Biology, School of Earth & Environmental Sciences, University of Adelaide, SA 5005, Australia.
B Corresponding author. Email: jose.facelli@adelaide.edu.au
Australian Journal of Botany 54(7) 655-667 https://doi.org/10.1071/BT05083
Submitted: 9 May 2005 Accepted: 8 May 2006 Published: 19 October 2006
Abstract
The species composition of temperate grasslands in the mid-north of South Australia has been radically altered from a system dominated by native perennial grasses to a system dominated by Mediterranean annual grasses. This study investigated the importance of chemical and physical soil characteristics, topographical features and climatic variables on the abundance of native and exotic grass species in nine ungrazed grasslands. Overall, climatic and other abiotic factors were highly variable. In addition, past management practices and original species composition are generally unknown, leading to further unexplained variation in the data. On a large spatial scale (among sites), the abundance of exotic annual grasses was positively correlated with mean annual rainfall, and on any scale, with finer soil textures and higher soil organic carbon levels. The most abundant annual grass, Avena barbata (Pott ex Link), was generally associated with soil factors denoting higher soil fertility. The abundance of native perennial grass species was not correlated with any environmental variables at any scale. The various native perennial grass species did not show clear associations with soil factors, although they tended to be associated with factors denoting lower soil fertility. However, at small spatial scales (within some sites) and among sites, the abundances of exotic annual and native perennial grasses were strongly negatively correlated. The results suggest that at the present time, rainfall and soil properties are important variables determining the abundance of annual grasses. The driving variables for the abundance of perennial grasses are less clear. They may be controlled by other factors or extreme rainfall events, which were not surveyed. In addition, they are likely to be controlled by competitive interactions with the annual grasses.
Acknowledgments
We thank T. Cammell, S. Gehrig and J. Prider for fieldwork assistance, M. Nicholls for assistance with study site identification, and G. Hastwell, J. Nicol, C. Rivers and A. Renfrey for assistance with laboratory work. The Burra Community School, R. & H. Bruce, F. & M. Nicholls, A. Michael and J. Trengrove; the Goyder Council; M. & B. Dare; the Northern Areas Council, R. Arthur and I. Falkenberg (NPWS) donated time, access to field sites and records. D. S. Whiting and J. Wurst supplied additional rainfall records. T. Cammell provided valuable comments on earlier drafts of this manuscript. The project was partly supported by the Native Vegetation Council and the National Heritage Trust.
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