The role of wildfire in shaping the structure and function of California ‘Mediterranean’ stream-riparian ecosystems in Yosemite National Park DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Breeanne Kathleen Jackson Graduate Program in Environment and Natural Resources The Ohio State University 2015 Dissertation Committee: S. Mažeika P. Sullivan, Advisor Amanda D. Rodewald Desheng Liu Copyrighted by Breeanne Kathleen Jackson 2015 Abstract Although fire severity has been shown to be a key disturbance to stream-riparian ecosystems in temperate zones, the effects of fire severity on stream-riparian structure and function in Mediterranean-type systems remains less well resolved. Mediterranean ecosystems of California are characterized by high interannual variability in precipitation and susceptibility to frequent high-intensity wildfires. From 2011 to 2014, I investigated the influence of wildfire occurring in the last 3-15 years across 70 study reaches on stream-riparian ecosystems in Yosemite National Park (YNP), located in the central Sierra Nevada, California, USA. At 12 stream reaches paired by fire-severity (one high- severity burned, one low-severity burned), I found no significant differences in riparian plant community structure and composition, stream geomorphology, or benthic macroinvertebrate density or community composition. Tree cover was significantly lower at reaches burned with high-severity fire, however this is expected because removal of the conifer canopy partly determined study-reach selection. Further, I found no difference in density, trophic position, mercury (Hg) body loading, or reliance on aquatically- derived energy (i.e., nutritional subsidies derived from benthic algal pathways) of/by riparian spiders of the family Tetragnathidae, a streamside consumer that can rely heavily on emerging aquatic insect prey. In addition, I observed minimal changes in the above responses at a subset of study locations in the first summer following the extensive and severe Rim Fire of 2013, although shrub cover at one location burned with low-severity ii fire was significantly reduced. Furthermore, fire frequency at the catchment scale was significantly correlated with fluvial geomorphic characteristics (embeddedness, D50, entrenchment, and width-to-depth ratio) and model-selection results indicated that variability in benthic macroinvertebrate density, catchment-scale fire frequency, and precipitation were important drivers of tetragnathid spider density and trophic position. Along a gradient of drainage area in two rivers located in the same catchment (also located in YNP), I also measured wildfire as a potential agent of disturbance within a food-chain length (FCL) framework, where I quantified the relative effects of wildfire characteristics (frequency, timing, and magnitude) as well as classic drivers of FCL including hydrologic disturbance, ecosystem size, and productivity on trophic position (here, a proxy for FLC) as well as reliance on aquatically-derived energy of/by aquatic benthic insect predators and riparian tetragnathid spiders. Ecosystem size (i.e., drainage area and channel width) received strong support as an environmental determinant of both trophic measures, with variability in flood magnitude emerging as an important mechanism linking ecosystem size and invertebrate trophic responses. Fire metrics were highly correlated with drainage area (positive relationship) as there was greater historic fire extent lower in the catchment. Fire did not emerge as a significant driver of trophic responses by invertebrate predators, however initial evidence suggests that non-linear effects of fire may shed further insight into these relationships. I also estimated reliance on aquatically-derived energy and trophic position of the American dipper (Cinclus mexicanus) – a species intimately tied to stream systems for energetic and habitat requirements – in 27 mountain streams of the western slope of the iii central Sierra Nevada affected by frequent, recent, or severe wildfire. Aquatic birds are considered landscape integrators and are constrained by different ecological processes than aquatic organisms, therefore assessment of the trophic dynamics of aquatic-obligate birds may illuminate divergent patterns and processes related to both fire and food-web dynamics. Model-selection results indicated that dippers occupying territories that were longer and within larger catchments relied more heavily on aquatically-derived energy. Dipper reliance on aquatically-derived energy was also greater in territories draining catchments with a greater proportion of recent, frequent, or severe wildfire, especially in smaller headwater streams (i.e., < 3rd order) possibily indicating a shift toward greater benthic primary poductivity resulting from removal of the riparian canopy by fire. Precipitation was a strong predictor of dipper reliance on aquatically-derived energy (negative relationship), especially in network streams (i.e., > 3rd order) which may be driven by shifts in water quality (e.g., turbidity) or assemblages of available prey items. For dipper trophic position, these same independent variables received support, but were weaker predictors. Taken together, these results, combined with the long period of time since fire at some study reaches, indicate support for interactions between wildfire and climate across complex spatial and temporal scales as drivers of both structural and functional responses of stream-riparian ecosystems to fire. Generally, stream-riparian organisms are highly adapted to natural disturbance processes, and there is a growing body of literature that suggests that the occurrence of dynamic, mixed-severity fire regimes may be necessary to maintain ecological function and native biodiversity. However, in this study, precipitation iv and flood magnitude generally were more influential drivers of riparian spider density and reliance on aquatically-derived energy and trophic position of dippers and tetragnathid spiders, indicating that climate variability and hydrology could outweigh the influence of fire in stream-riparian ecosystems of California’s Mediterranean-type climate. v Dedicated to cowboys, mermaids, stowaways, and monkeys: you know who you are! vi Acknowledgements I would like to thank my advisor Mažeika Sullivan, who has been my mentor for a decade. I would also like to thank my committee members, Amanda Rodewald and Desheng Liu for their contributions, and Eric Toman for helping me with the proposal and candidacy portion of my program. Thank you to the faculty, staff, and students of The Ohio State University and the School of Environment and Natural Resources. In Yosemite National Park I received invaluable support from Gus Smith, Sarah Stock, and Kent Van Wagtendonk. I would surely never re-emerge from the Yosemite Wilderness without the humor and stamina of Dulcinea Groff and Madeleine Ledford, and I deeply appreciate additional field and laboratory assistance received from Lars Meyer, Katherine Hossler, Melissa Hickson, Danielle Vent, Kai Zhao, Adam Kautza, and Paradzayi Tagwireyi. I give special thanks to teachers who inspired me to be a scientist: Jim Durando, Ron Olowin, Steve Bachofer, Carla Bossard, Steve Takata, Penny Morgan, and Jeff Braatne and thanks to Adam Sowards for teaching me that the humanities contribute essential knowledge and perspectives that inform our world view where science cannot. Thanks to my mom, Kathy Jackson, for always saying I am the best daughter ever even when I am a brat; thanks to my husband, Paul Koubek, for inspiring me to live a life of adventure without compromise or apology; thanks to my friends for always making me vii laugh; and special thanks to my dad, Curtis Jackson, for raising me in a fire truck and being my hero. viii Vita June 2000…………………………………………………………..….Sierra High School May 2004…………………….B.S. Environmental Science: Earth Science Concentration, Saint Mary’s College of California December 2008………………….M.S. Leadership in Physical Education and Recreation, University of Idaho December 2009……………………………………………...M.S. Environmental Science, University of Idaho Publications Jackson, B.K., S.M.P. Sullivan, C. Baxter, and R. Malison (In press) Stream-riparian ecosystems: mixed- and high-severity fire in DeLaSalla, D. and C. Hanson, editors. The Ecological Importance of Mixed-Severity Fires: Nature’s Phoenix. Elsevier Jackson, B.K. and S.M.P. Sullivan (In press) Responses of riparian tetragnathid spiders to wildfire in forested ecosystems of the California Mediterranean climate region, USA. Freshwater Science. Jackson B.K., S.M.P. Sullivan, and R. Malison (2012) Wildfire severity mediates fluxes of plant material and terrestrial invertebrate to mountain streams. Forest Ecology and Management. 278, 27-34. Jackson, B.K. and S.M.P. Sullivan (2009) Influence of fire severity on riparian vegetation heterogeneity in an Idaho, U.S.A. wilderness. Forest Ecology and Management. 259, 24-32. Field of Study Environment and Natural Resources Major field Ecosystem Science ix Table of Contents Abstract ............................................................................................................................... ii Acknowledgements ........................................................................................................... vii Vita ....................................................................................................................................