Biodiversity and Ecosystem Services Associated with Remnant Native Vegetation in an Agricultural Floodplain Landscape Rhiannon Smith B Nat Res (Hons) University of New England N Meters 0 500 1,000 2,000 3,000 4,000 A thesis submitted for the degree of Doctor of Philosophy of the University of New England June 2010 Certification I certify that the substance of this thesis has not already been submitted for any degree and is not currently being submitted for any other degree or qualification. I certify that any help received in preparing this thesis and all sources used have been acknowledged in this thesis. Rhiannon Smith i Abstract Biodiversity, ecosystem service provision and human well-being are inextricably linked. The current rate of biodiversity loss worldwide is impacting on ecosystem service provision with negative implications for human well-being. Little quantitative information is available about the provision of most ecosystem services by most ecosystems, the effect of management on the ability of vegetation to provide services, or trade-offs in service provision with land use. This information is particularly important in agricultural landscapes where the extent of landscape change is affecting biodiversity and ecosystem service provision substantially and thus agricultural sustainability. This study quantified the provision of carbon storage, erosion mitigation and biodiversity conservation services by five vegetation communities (river red gum Eucalyptus camaldulensis riparian forests, coolibah E. coolabah woodlands and open- woodlands, myall Acacia pendula tall shrublands and tall open-shrublands, black box E. largiflorens woodland and open-woodland, and mixed grassland – low open-chenopod shrubland) common on the lower Namoi floodplain in northern New South Wales, Australia. Sites represented the full range of structural and compositional variants encountered within each vegetation type over the 7100 km2 study region, from heavily grazed derived grasslands to old-growth woodland or forest evidently little affected by anthropogenic disturbance. The environmental conditions dictating the location of each vegetation type in the landscape were investigated. The distribution of vegetation types depended predominantly on soil type, flood patterns and the interaction between the two. Woody ii and non-woody vegetation was mapped across the study region using unsupervised classification of ten single-date SPOT 5 scenes with 85% accuracy. Woody vegetation covered approximately 7% of the lower Namoi floodplain. Carbon storage was measured or estimated for soils, woody vegetation, dead standing vegetation, coarse woody debris, herbaceous vegetation, litter and roots. River red gum sites were the most valuable vegetation type for carbon storage, having up to 4.5% carbon content in the surface 0–5 cm soil depth increment, with total site carbon storage averaging 216 t C ha–1. The most carbon-dense site was east of Narrabri and dominated by river red gum. Grasslands were the least carbon-dense with 40.0 t C ha–1. The greatest proportion of carbon in river red gum sites was in woody biomass, but in all other vegetation types and especially grasslands, the top 0–30 cm of the soil was the most C-rich component of the ecosystem. Woody biomass C was positively correlated with C derived from dead standing wood, coarse woody debris and litter, but not herbaceous biomass C, which was negatively correlated. Herbaceous vegetation cover, litter cover and macroaggregate stability as determined by the topsoil C:N ratio was used to rank sites for erosion mitigation service provision. Erosion mitigation value was assessed in terms of aggregate stability, which was determined by a relationship between mean weight diameter of aggregates and soil C:N ratio, as well as dominant cations on the clays. Soils with higher C:N contained more stable macroaggregates, and tended to be dominated by river red gum. High aggregate stability in river red gum sites was attributed to large inputs of eucalypt litter and coarse iii woody debris. Highest microaggregate stability was also observed in river red gum sites and attributed to the dominance of Ca2+ rather than Na+ on clay exchange sites. Vascular plant and bird conservation value of sites was determined by ranking sites according to the number of rare (i.e. infrequently observed) species present. For birds, species richness was also taken into account. River red gum sites were ranked highest for vascular plant and bird conservation value because they contained the highest abundance of rare species of both vascular plants and birds. However, river red gum sites also contained the greatest number of introduced plant species presumably as a result of flood mediated dispersal of propagules. All vegetation communities were included among the sites of highest conservation value for both vascular plants and birds. However, in the top 30% (16 of 54) of sites ranked according to conservation value, only five sites were valuable for both plant and bird conservation. River red gum sites had the most structurally complex vegetation, which coupled with their proximity to water, encouraged high bird species richness and abundance. Woody plants were the most influential vegetation component determining bird conservation value, but different vegetation types were preferentially used by different bird species, implying that the full spectrum of vegetation types is required to maximise bird and plant conservation at the regional scale. Increasing grazing intensity severely diminished both plant and bird conservation value at river red gum and coolibah sites as a result of the loss of rare species. Grazing also detracted from carbon storage, both directly through biomass consumption and indirectly through associated management (such as ring-barking to increase herbaceous iv biomass production and clearing). The functional richness (i.e. the number of different life-forms of vegetation types) was more influential than species richness in terms of ecosystem service provision. Shannon–Wiener diversity of vegetation communities showed no relationship with ecosystem service provision. No trade-offs were evident between the three ecosystem services measured in this study, but conservation value and carbon services declined under increasingly intense grazing. Increasing woody vegetation biomass and cover resulted in decreased herbaceous biomass production, leading to the trade-off between nature conservation and carbon sequestration on the one hand, and livestock production on the other. There are few ungrazed sites in the study region, hence natural capital may be diminished still further with continued grazing of almost the entire landscape. v Acknowledgements Firstly, I am indebted to my supervisors, Nick Reid, David Tongway, Paul Frazier and Guy Roth for their friendship, patience and encouragement, and for their generous contribution of time and knowledge. Many landholders allowed access to their properties, provided insightful knowledge of the region and helped with equipment housing and repairs during fieldtrips. In particular, the Swansbra family and everyone at ‘Lammermoor’ provided a home away from home during many weeks of fieldwork, and really went above and beyond to help out in every way possible. Their generous hospitality, support and enthusiasm towards the project were gratefully appreciated. John and Robyn Watson at ‘Kilmarnock’ also provided accommodation and looked after us during field trips, and were involved in shaping the direction of the project in the very early days. Numerous people bravely helped out with fieldwork (some on multiple trips). I am extremely thankful for their assistance and hope the experience hasn’t scared them too much. In particular, Nick Reid, Rohan Smith, Stuart Green, Meg Good, Scott Purcell, Peter Berney, Fiona Norrie, Tegan Smith, Mark Dahm, Guy Roth, Evan Cleland, Stacey Spanswick, Hamish Caddy, Sian Smith and Christopher Hardie helped out immensely. The support staff at UNE: Paul Lisle, Stuart Green, Cate MacGregor, Dan Alter, Leanne Lisle, Marion Costigan, Jim O’Neill, Bec Wood, Jo Porter, Chris Cooper and Shirley Fraser kept things ticking, and John Hunter, Dorothy Bell and Wal Whalley assisted with plant identification. David Tongway, Megan Purvis and Rohan Smith helped in the vi lab. Brian Wilson, Dave Carr, Jackie Reid and Rick Young offered helpful advice along the way, as did Alan Ede, Warick Browne, Ian Oliver, Chris Nadolny, Des Lang, Sean Murphy, Tom Lewis, Michael Drielsma, Simon Ferrier, Rob Loch and Will Dorrington. Thanks to the postgrads, postdocs and academics in EcoMan who made my time here enjoyable and memorable, especially those that I shared an office with. Your humour, support and sympathy helped me through some very long days. Matt Tighe and Carlos Muñoz helped me out on so many levels on so many occasions. Matt’s knowledge of all things soil related is amazing and his ability to make things happen in R is almost magical, while Carlos has a real gift with ArcGIS and both have been good for a cup of coffee and at time, a whinge. Special mention must be made of Subhashni Taylor, Melissa Danks, Morag Stewart, Nick Schultz and Megan Good; I am so grateful for their help with sorting out referencing nightmares in the final few weeks. Finally, my family and friends supported me in every sense of the word and I could not have done this without them. Though they were all so far away they regularly made it known that they were around, and encouraged me the