Ecological filters to seedling establishment for restoration in a Mediterranean climate Lauren M. Hallett B.Sc. (Biology), Yale University, USA This thesis is presented for the degree of Masters of Science by Research in Natural Resources The University of Western Australia School of Plant Biology 2010 ii Declaration I declare that this thesis is my own account of my research conducted during my period of enrollment at the University of Western Australia. It has not previously been submitted for a degree at this or any other university. As stated in the Acknowledgements, my ideas and research approach have been shaped through interactions with many people. However, any work done jointly with supervisors or co- workers is stated below: Chapter Two: This paper is in preparation for Restoration Ecology by myself with co- authors Justin Jonson, Rachel Standish and Richard Hobbs. It makes use of a restoration site designed and managed by Justin Jonson, and I developed the experimental design and collected the data jointly with him. I developed the questions, conducted the analysis and wrote the manuscript with the guidance of Rachel Standish and Richard Hobbs. Chapter Three: This paper is in preparation for Plant Ecology by myself with co-authors Rachel Standish and Richard Hobbs. I developed the questions, designed the experiment and analyzed the data with their guidance. Lauren M. Hallett iii iv Abstract Ecological filters are abiotic factors, such as limited rainfall, and biotic factors, such as competition, that over time reduce the number of species that can survive at a given site. The filters acting on a restoration site generally differ from those acting on a naturally regenerating community. Summer drought is a primary filter to plant establishment in Mediterranean-climate ecosystems. These two themes were central to my thesis. In the first half of my thesis I explored how local abiotic factors (soil type and nutrient composition) and biotic factors (weed cover) across a restoration site interact with summer drought to influence seedling establishment over time. I found that the effect of soil type differed temporally: spring recruitment was higher in sandy soils, but summer survival was higher in clayey soils. There was no clear relationship between soil type and end-of-summer establishment. Attempts to analyze restoration outcomes that do not consider interactions between local heterogeneity and temporal filters may therefore mask the mechanisms that drive plant establishment. In contrast, documenting these interactions provides a framework for targeted manipulative study and informed restoration decisions. Sandy soils had low water-holding capacities, which likely contributed to the low summer survival in these soils. In the second half of my thesis I explored how a specific plant trait, seed mass, influences a seedling’s ability to survive the summer in sandy soils. I tracked summer survival among four woody genera at a restoration site. Summer survival increased with seed mass within all genera. I hypothesized that the nutrient reserves in large seeds facilitated summer drought avoidance through greater root investment. I investigated this relationship in a glasshouse experiment assessing the growth of Acacia and Eucalyptus species, with a range of seed masses, under mild and severe drought compared with a well-watered control. Root length increased with seed mass consistently across five harvests over 60 days. The benefits of large seed mass for establishment under environmental hazards are often considered temporary, but my findings suggest that seed mass can mediate other traits, including root length, which can influence longer-term survival through the summer drought that is characteristic of Mediterranean-climate ecosystems. Understanding the filters that govern seedling survival in a restoration context allows managers to target interventions to improve seedling survival, either by altering the constraining filters or selecting species with the traits to pass through them. v Acknowledgements Through example and advice my supervisors, Rachel Standish and Richard Hobbs, have defined the type of scientist I would like to be. I admire the creative ways in which they approach questions and experimental design, and the clarity with which they place their research within a wider scientific and environmental framework. I thank them for the attention they devoted toward improving both this thesis and my development as a scientist. This research was possible thanks to financial support from the School of Plant Biology at the University of Western Australia, the Mary Janet Lindsay of Yanchep Memorial Fund, the Ecological Society of Australia, the University of Western Australia Scholarship for International Research Fees and Murdoch University. My time in Australia was supported by a Fulbright Postgraduate Fellowship and the University of Western Australia University Postgraduate Award (International Student). I thank Justin Jonson for his willingness to collaborate at Peniup Farm, and for his help in designing and executing the restoration monitoring scheme. Due to his hard work Peniup is an inspiring example of ecological restoration. I thank Danny Ten Seldam for his effort and care in sowing the site. I am also grateful to Greening Australia, and particularly David Freudenberger and Keith Bradby, for permission to work at Peniup. I thank the West Australian Department of Environment and Conservation for permission to work at Gnangara. I am particularly grateful to Clayton Saunders, Paul Brown and Tracey Sonneman for introducing me to the restoration sites and for their continued support. Many people helped me in the field and glasshouse. Foremost, I thank Tim Morald for teaching me proper techniques for everything from seed germination to soil sterilization, and for all his help both in the glasshouse and at Peniup. I am grateful to Bec Parsons for her help and notable cheer with soil measurements, field work and data entry. Kellie Maher was a friendly and diligent field partner. Luke Barrett also provided field assistance, and Ash Norris, Laura Merwin and Nadia Bazihizina helped me in the glasshouse. Georgie Holbeche demonstrated patience, good humor and skill when teaching me to hand texture soils. I thank Rob Creasy and his staff for running an excellent glasshouse facility and Elizbieta Halladin, Evonne Walker, Gary Cass and Suman George and for sharing equipment and guidance in the soil science labs. vi Conversations with Ann Hamblin, Bob Gilkes, Byron Lamont, Cristina Ramalho, David Merritt, Erik Veneklaas, Hans Lambers, Katinka Ruthrof, Kellie Maher, Mark Tibbett, Peter Gross, Viki Cramer and William Stock provided me with inspiration and helped to shape my thesis proposal and experimental design. Cristina Ramalho, James Hallett, Joe Fontaine, Kevin Murray, Laura Firth, Lori Lach and Mike Perring provided statistical guidance. Comments and review from Kris Hulvey, Mike Perring and Nancy Shackelford improved this thesis considerably. I also thank Heather Gordon for her skilled administrative support, and for attending to the printing of this thesis in my absence. I was fortunate to belong to a large, happy and intellectually exciting lab group and wider research school. I am grateful that its members included: Alison Prior, Ann Hamblin, Barbara Jameson, Bec Parsons, Bryony Retter, Cristina Ramalho, Erik Veneklaas, Heather Gordon, Helen Alison, Joe Fontaine, Juan Garibello, Katinka Ruthrof, Kellie Maher, Kirstin Frost, Kris Hulvey, Laura Merwin, Lori Lach, Mandy Trueman, Michael Renton, Mike Craig, Nancy Shackelford, Pat Kennedy, Peter Gross, Pieter Poot, Rachael Ord, Rory Donnelly, Sue Yates, Sutomo, Tim Morald, Viki Cramer and Wendy Vance. My arrival and the remainder of my time in Australia were much improved through the hospitality of Gillian Henderson. I appreciate and admire her willingness to open her home to waifs and strays. I also thank the Australian Fulbright Commission, and particularly Lyndell Wilson and Mark Darby, for the good care they took of me before my arrival and throughout my time in Australia. Lastly, I am indebted to my parents, Jim Hallett and Peggy O’Connell, whose own scientific background provided me with an early foundation in ecology. I thank them for the love and support they have shared ever since. vii viii Table of Contents Declaration………………………………………………………………...…………... iii Abstract……………………………………………………………………………….... v Acknowledgements……………………………………………………………………. vi Table of Contents………………………………………………...………………….… ix Chapter One: General introduction……………………………………………………... 1 Ecological filters to community assembly……………………………………… 1 Ecological filters and ecological restoration……………………………………. 3 Seedling establishment and restoration………………………………………… 6 Seed mass and establishment…………………………………………………… 6 Study system: Southwestern Australia…………………………………………. 7 Thesis aims and scope………………………………………………………….. 9 Chapter Two: Ecological filters to seedling survival in old-field restoration………… 11 Abstract……………………………………………………………………..… 11 Introduction………………………………………………………………….... 12 Methods……………………………………………………………………….. 14 Results………………………………………………………………………… 19 Discussion…………………………………………………………………….. 24 Chapter Three: Large seed mass increases seedling summer survival…………………28 Abstract……………………………………………………………………….. 28 Introduction…………………………………………………………………… 29 Methods……………………………………………………………………….. 30 Results……………………………………………………………………....… 34 Discussion…………………………………………………………………….. 37 Chapter Four: