UC Riverside UC Riverside Electronic Theses and Dissertations Title Ecological Impacts of Nitrogen Deposition, Drought and Nonnative Plant Invasion on Coastal Sage Scrub of the Santa Monica Mountains Permalink https://escholarship.org/uc/item/7vp1961j Author Valliere, Justin Michael Publication Date 2016 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA RIVERSIDE Ecological Impacts of Nitrogen Deposition, Drought and Nonnative Plant Invasion on Coastal Sage Scrub of the Santa Monica Mountains A Dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Plant Biology by Justin Michael Valliere June 2016 Dissertation Committee: Dr. Edith B. Allen, Chairperson Dr. Jeffrey M. Diez Dr. Louis S. Santiago Copyright by Justin Michael Valliere 2016 The Dissertation of Justin Michael Valliere is approved: Committee Chairperson University of California, Riverside Acknowledgements Firstly, I would like to thank my principal advisor, Dr. Edith B. Allen, for the past five years of generosity, support, friendship and encouragement. My time as a graduate student would not have been nearly as fun, rewarding or productive without her. I also extend my sincere gratitude to Dr. Irina Irvine of the National Park Service for her constant support and enthusiasm. I would like to thank my dissertation committee members, Dr. Jeffrey Diez and Dr. Louis Santiago for their continued guidance and positivity. Many other faculty and collaborators were extremely generous with their time, resources and ideas: Dr. Michael Allen, Dr. Emma Aronson, Dr. Adrzej Bytnerowicz, Dr. Norman Ellstrand, Dr. Exequiel Ezcurra, Dr. Mark Fenn, Dr. Jodie Holt, Dr. Darrel Jenerette and Robert Johnson. I’ve been fortunate to have the assistance of many past and present UCR graduate students, especially Dr. Mike Bell, Dr. Bridget Hilbig, Jennifer Eberwein, Dr. Alejandra Martinez, Matthew O’Neill, Dr. Alexandria Pivovaroff, Amanda Swanson, and Dr. Shana Welles, and many undergraduate students: Joshua Dansie, Amanda Haraksin, Sharon Orpet, Erin Reilly, Daniel Sanchez, Dwight Williams and Cierra Wikman. I am also indebted to the many staff and interns at the Santa Monica Mountains National Recreation Area and California State Parks. Lindsay Swinger rescued me during a time of need and introduced me to California’s beautiful flora, mountains and deserts, and for that I am eternally grateful. Finally, I would like to thank my friend and mentor Dr. Sandra DeSimone, who is a constant source of inspiration, ecological insight and thoughtful feedback, and who helped me fall in love with the coastal sage scrub of California. iv This research was made possible through funding from the National Park Service Air Resources Division, The Santa Monica Mountains Fund, The Southern California Research Learning Center, California Native Plant Society, Audubon California’s Sea and Sage Chapter and the National Science Foundation. Two chapters have been previously published in peer-reviewed journals: chapter three in Plant and Soil and chapter four in Biological Invasions . v ABSTRACT OF THE DISSERTATION Ecological Impacts of Nitrogen Deposition, Drought and Nonnative Plant Invasion on Coastal Sage Scrub of the Santa Monica Mountains by Justin Michael Valliere Doctor of Philosophy, Graduate Program in Plant Biology University of California, Riverside, June 2016 Dr. Edith B. Allen, Chairperson Multiple drivers of global environmental change increasingly threaten native ecosystems, including atmospheric pollution and resulting changes in climate and nutrient cycling, and the globalization of species. These factors may also have complex and interactive ecological effects. Nitrogen (N) deposition, the input of reactive N from the atmosphere to the earth’s surface, is increasing dramatically worldwide due to anthropogenic air pollution, with the potential to negatively impact terrestrial plant diversity. Elevated N deposition may also interact with other drivers of environmental change, for example by promoting the invasion of nonnative plant species, or increasing plant susceptibility to drought or other secondary stressors. Perhaps nowhere in the U.S. is this of more immediate environmental concern than in southern California, which is a global hotspot of biodiversity and one of the most air-polluted and populous parts of the country. High levels of N deposition have been implicated in the widespread conversion of coastal sage scrub (CSS) to annual grasslands dominated by nonnative grasses and forbs. The Santa vi Monica Mountains National Recreation Area of southern California protects a substantial area of remaining CSS, but due to the park’s proximity to the City of Los Angeles, stands of CSS nearest urban areas are subject to high levels of N deposition. The state of California is also in the midst of a record-breaking drought, beginning in 2011, and this may exacerbate the negative impacts of N deposition and nonnative plant species. The objective of this work is to explore the effects of N deposition, drought and nonnative plant invasion on CSS of the Santa Monica Mountains at multiple ecologically relevant scales. I explored relationships of atmospheric N pollution and N deposition with native plant richness and cover of nonnative species at the landscape level, finding N deposition reduces richness of native herbaceous species and is associated with higher nonnative cover. I also investigated the impact of multiple realistic levels of N addition on CSS in a field fertilization experiment on the low end of the N deposition gradient during a period that coincided with the California drought. Through this experiment, I demonstrated increased N availability may reduce water-use efficiency and drought tolerance of native shrubs, resulting in increased dieback, while concomitantly favoring nonnative annual species. Finally, I explored the role of the soil microbial community in mediating impacts of these factors on native and nonnative plant species, finding that N-impacted soil communities may provide less protection against drought in native shrub seedlings and increase growth of invasive plant species. Collectively, these results illustrate the significant ecological threat of increased N deposition on the severely threated CSS of southern California, and potential interactions with other drivers of global change such as extreme drought and nonnative plant invasion. vii Table of Contents Introduction ........................................................................................................................ 1 Literature cited ....................................................................................................... 6 Chapter 1: Relationships between atmospheric nitrogen deposition, plant diversity and invasion in coastal sage scrub of the Santa Monica Mountains Abstract ................................................................................................................ 10 Introduction .......................................................................................................... 11 Methods ................................................................................................................ 15 Results .................................................................................................................. 22 Discussion ............................................................................................................ 30 Literature cited ..................................................................................................... 43 Tables and Figures ............................................................................................... 52 Chapter 2: Experimental nitrogen deposition promotes shrub dieback and invasion of California coastal sage scrub during extreme drought Abstract ................................................................................................................ 72 Introduction .......................................................................................................... 74 Methods ................................................................................................................ 79 Results .................................................................................................................. 84 Discussion ............................................................................................................ 89 viii Literature cited ..................................................................................................... 97 Tables and Figures ............................................................................................. 106 Chapter 3: Interactive effects of nitrogen deposition and drought-stress on plant-soil feedbacks of Artemisia californica seedlings Abstract .............................................................................................................. 115 Introduction ........................................................................................................ 116 Methods .............................................................................................................. 120 Results ................................................................................................................ 127 Discussion .......................................................................................................... 131 Literature