Fire and Aquatic Ecosystems in the Context of Climate Change: A Synthesis for Improved Management

Fire will be the proverbial eye-of-the-needle through which many western U.S. mountain, forest, and stream ecosystems will pass as the climate changes. Historic observations show increased dryness and temperatures accompanying more widespread fire and forest die-off. These events may punctuate gradual changes to ecosystems, or may be a mechanism driving stepwise changes in ecosystems. Most western ecosystems are strongly tied to cycles of fire and recovery, and the changing nature of fire will have profound consequences. There is no question that vulnerability assessments of western U.S. ecosystems need to account for fire in their calculus. The biophysical template of the forest, riparian, and stream ecosystems determines much of the response to fire. The degree of forest adaptation to fire, including fuel loading, fuel continuity, and species mixes are clear determinants of fire spread, fire severity, and the forest’s response. For aquatic systems the relative spatial scales of fire and connected fish habitats form another critical factor in long-term population persistence. Terrain, climate, and geology all exert controls on the hydrology of both forests and streams which sets much of the stage. Land and water management alter these contexts, sometimes dramatically, particularly those associated with scales of fuel continuity and aquatic fragmentation. Intertwined are the roles of invasive terrestrial and aquatic species and their roles in changing the scales of events and the connectivity and size of populations. Adaptation to climate change in the combined context of fire and climate change takes on greater dimensionality than management for either alone. Conceptually the detrimental contributions of prior human interventions provide substantial fodder for corrective action in anticipation of future severe events. However, an equally strong conceptual argument notes that restoration to historical conditions is itself an unstable solution at best. Despite clear knowledge that resistance, for example in the form of fire suppression, has built an unsustainable legacy of risk, resistive techniques will necessarily play future roles because the contexts are changing so fast. Sustainable approaches will rely on activities encouraging resilience in forests, riparian habitats, and streams alike, as opposed to those benefiting one ecosystem component at the expense of another. We also need to understand how human activities, even seemingly nurturing ones, can interfere with basic dynamic processes that form the foundation of resilience in fire adapted ecosystems. By understanding the processes reducing vulnerability to both severe disturbance and climate change, we can begin to envision many ways to facilitate more reliable positive outcomes for fire and related ecological dynamics. The future will likely require an increasing number of rapid decisions with a great deal of uncertainty about what will happen in the future, which would suggest that a present focus on reducing uncertainty about current resource conditions and limitations would be a wise investment. Adaptation taken in its most commonly used sense is about evolving, which is to say it is about learning; learning what works best. A principal goal of this GTR is to describe the framework of how we think that fire and climate change work together to affect fish communities. Learning will come from testing, probing, and pushing that framework to understand how it doesn’t work and then proposing new ideas. The western U.S. is a big place, with many diverse landscapes, defying generalizations and much learning must necessarily be local in implication. We present what we hope serves as a scaffold for that learning. This GTR comprises 2 parts: An overview document speaking to the breadth of processes interlinked by forests, fish, fire, and climate change, and a brief series of more specific and scholarly papers describing the biological interactions of fish, fire, and land management in more detail. Any one of these documents could stand on its own. Taken together they serve as a useful reference with varying levels of detail for land managers and resource specialists