Breeanne Kathleen Jackson
Published: 2015
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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 utilized a variety of experimental designs to investigate the influence of wildfire 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, I measured riparian community composition and structure, stream geomorphology, density and community composition of benthic macroinvertebrates, and density, trophic position, mercury (Hg) body loading, and reliance on aquatically-derived energy of/by spiders of the family Tetragnathidae, a common riparian spider that relies heavily on emergent aquatic insect prey. In addition, along a gradient of drainage area in two rivers, I measured the relative effects of ecosystem size, flood magnitude, productivity, and wildfire on trophic position and reliance on aquatically-derived energy of/by benthic insect predators and tetragnathid spiders. Aquatic birds like the American dipper (Cinclus mexicanus) are considered landscape integrators and are constrained by different ecological processes than aquatic organisms, therefore assessment of the trophic dynamics of aquatic-obigate birds may illuminate divergent patterns related to both fire and food-web dynamics. I estimated reliance on aquatically-derived energy and trophic position of dippers in 27 mountain streams and estimated the relative explanatory power of ecosystem size, precipitation, and wildfire as predictors of dipper trophic dynamics. Taken together, the results of my study, 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 stream-riparian ecosystem responses to wildfire.