What drives plant biodiversity in the clay floodplain grasslands of NSW?
Tom Lewis A B D , Peter J. Clarke C , Ralph D. B. Whalley C and Nick Reid BA Department of Primary Industries and Fisheries, Locked Bag 16, Fraser Rd, Gympie, Qld 4570, Australia.
B Ecosystem Management, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
C Botany, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
D Corresponding author. Email: tom.lewis@deedi.qld.gov.au
The Rangeland Journal 31(3) 329-351 https://doi.org/10.1071/RJ08056
Submitted: 14 October 2008 Accepted: 24 December 2008 Published: 28 August 2009
Abstract
An assessment of the relative influences of management and environment on the composition of floodplain grasslands of north-western New South Wales was made using a regional vegetation survey sampling a range of land tenures (e.g. private property, travelling stock routes and nature reserves). A total of 364 taxa belonging to 55 different plant families was recorded. Partitioning of variance with redundancy analysis determined that environmental variables accounted for a greater proportion (61.3%) of the explained variance in species composition than disturbance-related variables (37.6%). Soil type (and fertility), sampling time and rainfall had a strong influence on species composition and there were also east–west variations in composition across the region. Of the disturbance-related variables, cultivation, stocking rate and flooding frequency were all influential. Total, native, forb, shrub and subshrub richness were positively correlated with increasing time since cultivation. Flood frequency was positively correlated with graminoid species richness and was negatively correlated with total and forb species richness. Site species richness was also influenced by environmental variables (e.g. soil type and rainfall). Despite the resilience of these grasslands, some forms of severe disturbance (e.g. several years of cultivation) can result in removal of some dominant perennial grasses (e.g. Astrebla spp.) and an increase in disturbance specialists. A simple heuristic transitional model is proposed that has conceptual thresholds for plant biodiversity status. This knowledge representation may be used to assist in the management of these grasslands by defining four broad levels of community richness and the drivers that change this status.
Additional keywords: cultivation, flooding, grassland composition, grazing, Mitchell grasslands, species richness.
Acknowledgements
This work was undertaken for a PhD degree for T. Lewis who was supported by an Australian Postgraduate Award. Financial support was received from The Grassy Ecosystems Grant Program (a joint initiative of the World Wide Fund for Nature Australia and the National Heritage Trust); the NSW National Parks and Wildlife Service; and the University of New England. We are grateful to all the landholders that let us onto their properties. Staff at the Moree RLPB office were helpful in providing access to permit records and with management information regarding stock routes and reserves.
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