COPYRIGHT AND USE OF THIS THESIS This thesis must be used in accordance with the provisions of the Copyright Act 1968. Reproduction of material protected by copyright may be an infringement of copyright and copyright owners may be entitled to take legal action against persons who infringe their copyright. Section 51 (2) of the Copyright Act permits an authorized officer of a university library or archives to provide a copy (by communication or otherwise) of an unpublished thesis kept in the library or archives, to a person who satisfies the authorized officer that he or she requires the reproduction for the purposes of research or study. The Copyright Act grants the creator of a work a number of moral rights, specifically the right of attribution, the right against false attribution and the right of integrity. You may infringe the author’s moral rights if you: - fail to acknowledge the author of this thesis if you quote sections from the work - attribute this thesis to another author - subject this thesis to derogatory treatment which may prejudice the author’s reputation For further information contact the University’s Director of Copyright Services sydney.edu.au/copyright QUANTIFICATION OF THE RISK OF PHYTOPHTHORA DIEBACK IN THE GREATER BLUE MOUNTAINS WORLD HERITAGE AREA Zoe-Joy Newby A dissertation submitted for the degree of Doctor of Philosophy in the Faculty of Agriculture and Environment, The University of Sydney February, 2014 1 Declaration of Originality This dissertation presents the results of research conducted at the Royal Botanic Gardens, Sydney, of the Botanic Gardens and Domain Trust and the Faulty of Agriculture and Environment, The University of Sydney. The content is, to the best of my knowledge, original and contains no work formally published or written by another person except where dully acknowledged. This thesis does not include any material that has been submitted or accepted to any institution for a degree of diploma. Signed, Zoe-Joy Newby ii Abstract Biological invasions exert great pressure on natural ecosystems and conservation areas, the latter of which have been established to conserve biodiversity. The presence of invasive species in natural ecosystems disrupts evolutionary processes, alters species abundance and can potentially lead to extinction (Mack et al., 2000; Crowl et al., 2008). When an invasive species is the cause of plant disease, the potential for that pathogen to survive in a new environment and the expectation of the impacts it may cause, can be estimated from locations where it already occurs. Understanding the dynamics of disease is important for management and research alike, and will hopefully make way for a proactive rather than reactive response. Disease in natural Australian ecosystems caused by the invasive species Phytophthora cinnamomi has been recognised for nearly 100 years (Newhook and Podger, 1972); its devastating impacts have lead to the disease syndrome, Phytophthora dieback, being classified as a Key Threatening Process by the Australian Federal Government (Commonwealth of Australia, 2005). Yet, the assessment of potential disease establishment, that is, disease risk, is limited. This remains true for the globally significant Greater Blue Mountains World Heritage Area (GBMWHA) in New South Wales, a centre of plant and animal conservation. Not only is the understanding of the pathogen distribution limited, so too is knowledge of the potential impacts on flora and the influence climate change may have on disease expression. Management of Phytophthora dieback in the GBMWHA is made increasingly complex by the rugged and remote nature of much of the World Heritage Area, as well as competing demands from tourism, recreation and the impacts of fire and other introduced species. This study aims to address some of these complexities by establishing the suitability of the GBMWHA to P. cinnamomi, its current distribution and the potential for disease. Additionally, with the difficulty of accessing much of the GBMWHA and the risk of disease transmission in mind, an alternate approach to disease identification is trialed. The first task of this project, was concerned with understanding the potential distribution of P. cinnamomi within the GBMWHA using mechanistic modelling and information on the pathogen’s ecology. Most of the GBMHWA was found to be suitable, leading to the acceptance of the first hypothesis that the climatic and topographic conditions of the GBMWHA are conducive to P. cinnamomi establishment. The most conducive areas were characterised by high soil wetness, high rainfall and moderate temperatures, while the areas least conducive were conversely hotter and drier. Although iii the model appeared to overpredict into areas the pathogen was not found, increasing distribution risk was associated with increasing isolations, possibly indicating that the pathogen is yet to reach its potential niche. The modelled distribution of P. cinnamomi was then used to inform a field investigation to determine the actual distribution in the GBMWHA and assess the impact of the pathogen on vegetation communities and individuals. As an invasive species, the distribution of P. cinnamomi was hypothesised to be primarily found in locations with high anthropogenic activity; however it was isolated extensively from remote areas, leading to the rejection of this hypothesis. Disease was never the less expected, albeit sporadic, as per disease expression in other vegetation communities in New South Wales (Arentz, 1974; Walsh et al., 2006; Howard, 2008). Heathland communities that often have a higher incidence of disease (McDougall and Summerell, 2003), had a high rate of pathogen isolation, as well as clear indications of disease in the GBMWHA. Additionally, freshwater wetlands, many of which are endangered ecological communities under Commonwealth and State legislation, had a high rate of pathogen isolation also. The results collected during the field work were then utilised to assess the risk of Phytophthora dieback occurring in the GBMWHA within the context of the disease triangle. The distribution of P. cinnamomi was combined with models of over 130 individual host species to produce a spatially explicit model, quantifying the risk of disease. That a large portion of the GBMWHA is at risk of Phytophthora dieback was not the case, and as such this hypothesis was rejected. Although much of the World Heritage Area had a least some level of risk, greatest risk was associated with a few small areas that occurred at higher elevations with suitable rainfall and temperature conditions. Unfortunately, many of these locations were associated with high levels of tourism and recreation, highlighting the potential for anthropogenic dispersal of P. cinnamomi into, around and out of the GBMWHA. Disease itself has a temporal element which cannot be quantified in one set of field results and as disease spreads the results become outdated quickly (O'Gara et al., 2005). Field-based assessments of disease are expensive and time consuming, and in area as vast and rugged as the GBMWHA, difficult and potentially dangerous. Real-time information on the impacts of disease are therefore needed by land managers to efficiently deploy management strategies (O'Gara et al., 2005). Remote sensing offers an alternative means of assessment not requiring site entry. Vegetation condition can be assessed remotely in all manner of plant systems including the detection and quantification of disease. As such, it was hypothesised here that infection caused by P. cinnamomi could be detected from iv remotely-sensed reflectance and distinguished from spectral changes caused by water stress. To test this theory, five commonly occurring species within the GBMWHA were infected with P. cinnamomi and their foliar responses were monitored over several months. Phytophthora cinnamomi infection was detected by assessing water content and vegetation indices, and when data dimensionality was reduced using principal component analysis. The response of individual species to P. cinnamomi was, however, variable and difficult to identify once water stress had become severe. Phytophthora cinnamomi infection did not appear to invoke a unique spectral response, and this hypothesis was rejected. However, infection was detectible in some species outside the visible range suggesting the potential for remote sensing to identify presymptomatic disease or disease in asymptomatic plants infected with P. cinnamomi. The results of this research will improve the management of P. cinnamomi in the GBMWHA. Prioritisation of management strategies will be supplemented with the understanding of which areas are at greatest risk of disease, which areas can potentially be protected from infection and what activities are associated with disease. Such information is useful to not only land managers, but other park users including locals, tourists and recreationalists. v Acknowledgments This project would not have been possible without the enduring support of numerous organisations and individuals to whom I am truly gratefully. I would firstly like to acknowledge my principal financial support, the Thomas Lawrence Pawlett Scholarship provided by the Challis Bequest Society and bestowed by the Faculty of Agriculture and Environment, whom also gave me the opportunity to take on this PhD. Additional financial support has also been provided from the former chair or the Blue Mountains World Heritage Institute, Donald Stammers. My thanks to the The Royal Botanic Gardens