Co-ordinating Editor: Suzanne Prober
Plant species richness responses to grazing protection and degradation history in a low productivity landscape
Article first published online: 9 JUN 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 22, Issue 6, pages 997–1008, December 2011
How to Cite
Fensham, R.J., Silcock, J.L. and Dwyer, J.M. (2011), Plant species richness responses to grazing protection and degradation history in a low productivity landscape. Journal of Vegetation Science, 22: 997–1008. doi: 10.1111/j.1654-1103.2011.01305.x
Fensham, R.J. (corresponding author, firstname.lastname@example.org): Queensland Herbarium, Department of Environment and Resource Management, Mt Coot-tha Road, Toowong, Queensland 4066, Australia; Department of Biological Sciences, The Ecology Centre, University of Queensland, St Lucia, Queensland 4072, Australia Silcock, J.L. (email@example.com) & Dwyer, J.M. (firstname.lastname@example.org): Department of Biological Sciences, The Ecology Centre, University of Queensland, St Lucia, Queensland 4072, Australia.
- Issue published online: 5 OCT 2011
- Article first published online: 9 JUN 2011
- Received 2 July 2010, Accepted 27 April 2011
- Disturbance–diversity models;
- Intermediate disturbance;
- State and transition models
Questions: Does species richness and abundance accumulate with grazing protection in low productivity ecosystems with a short evolutionary history of grazing, as predicted by emerging theory? How do responses to grazing protection inform degradation history?
Location: Mulga (Acacia aneura) dry forest, eastern Australia, generally considered chronically degraded by livestock grazing.
Methods: Three paired exclosures (ungrazed, and macropod-grazed) were compared with open-grazed areas after 25 years using quadrats located on either side of the fences. Additionally, the regional flora for mulga dry forest was assessed to identify species that may have declined and could be threatened by grazing.
Results: Low herbaceous biomass accumulation (<1.3 t ha−1) with full grazing protection confirmed a low productivity environment. For most plant life forms the highest species richness was in macropod-grazed exclosures, an intermediate grazing disturbance that best approximates the evolutionary history of the environment. This was the net outcome of species that both declined and increased in response to grazing. Regeneration and subsequent self-thinning of mulga was promoted with grazing protection, but did not confound interpretation of species richness and abundance responses. At the regional scale only 11 native species out of 407 comprising the mulga dry forest flora were identified as rare and potentially threatened by grazing.
Conclusions: Significant increases in richness or abundance of native plants with grazing protection, persistence of perennial grasses, regeneration of mulga and scant evidence of a major decline in the regional flora are not consistent with established assertions that long-grazed mulga dry forest has crossed functional thresholds that limit recovery. Further, a peak in species richness under intermediate (macropod) grazing is counter to the shape of the response predicted by emerging theory for recovery of species richness in a low productivity environment. The finding prompts a more thorough understanding of the distinction between environments with inherently low productivity and those degraded by grazing.