Conceptual Framework to Assess the Effects of Wildfire on Aquatic Systems of the Semi-arid and Arid Regions of the Western Gulf Slope Drainages
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In 2011, wildfires burned 1.6 million acres in Texas, an unprecedented wildfire frequency, extent, and intensity attributed to several years of below average annual precipitation. High profile fires, such as the Oasis Ranch Fire (Kimble County, Texas), underscore the lack of knowledge in the effect and mitigation of large-scale wildfires on stream communities in arid and semi-arid regions, which typically support a diverse and endemic fauna limited to one or a few streams and highly susceptible to local perturbations. Purposes of this study were to conduct a literature review of wildfire effects on stream communities from regions where wildfires are common (i.e., Northwest USA, Australia), quantify abiotic and biotic responses within stream communities, and develop a framework to predict community responses relevant to arid and semi-arid regions of western gulf slope drainages of New Mexico and Texas. The framework also provides testable hypotheses, which can be validated with independent replications when wildfires occur within the western gulf slope drainages. Among 63 published and non- published articles, abiotic and biotic responses of aquatic communities following a fire ranged from relatively minor habitat and community changes initially, short term, and long term to relatively major habitat and community changes initially and up to 20 years post-fire. Magnitude of change was associated with precipitation timing and amount that transported sediment, woody debris, and nutrients into the stream, which affected stream morphology, macroinvertebrate communities, and fish communities. Among systems with major habitat changes, biotic effects generally included an increase in tolerant macroinvertebrates and decreases in fish abundances and densities. However, abiotic environments and biological communities were resilient through time and returned to pre-fire conditions. The framework was applied to two fires, one (Canon Ranch Fire, Pecos River drainage) located 5 km from the stream in which no detectable abiotic and biotic responses were detected and another (Oasis Ranch Fire, Colorado River drainage) located adjacent to the stream in which sediments and charred woody debris entered the stream but no biotic responses were detected. Literature review and framework provide natural resource managers with proactive and reactive management options. Management options can be used, when feasible, to mitigate large-scale fire effects on stream communities, especially those that support endemic, threatened, or endangered fauna.