Fires, floods, and other infrequent, large-scale disturbances can strongly affect the dynamics of species and ecosystems. These disturbances are becoming more frequent and severe as climate change takes effect; forest fires in the western United States, for example, have increased four-fold over the last 30 years. The effects of disturbance events are extremely difficult to study, because the events are often unpredictable in time and scale. As a result, there is great uncertainty about how disturbances such as fires alter communities and ecosystems. Does wildfire, for example, harm or help vulnerable fish populations, and under what conditions? This research investigates how changes triggered by fire spread through time, space, and food webs. It focuses on the August 2009 wildfire that burned much of Scott Creek, a coastal California watershed containing populations of steelhead trout and coho salmon, both ESA-listed salmonids. Fortuitously, the spatial burn pattern created fire treatments of burned, unburned, and downstream reaches. Furthermore, there are extensive pre-fire datasets on the watershed, fish, and their food webs in all of these three fire treatments. This study will utilize a post-fire airborne LiDAR (Light Detection And Ranging) flight to characterize geomorphic change on the watershed scale. Nested within this detailed understanding of how fire changes the landscape, this study will use monitoring and experimental manipulations of food webs within each natural burn treatment to examine the importance of species interactions (including nonnative crayfish) in modulating the community response to fire. This project focuses on the short-term impacts of fire on streams (within 1 year), a critical but poorly understood period that likely determines the trajectories of community and ecosystem recovery.
The goal of the work is to increase understanding of the interconnected responses of landscapes, ecological communities, and populations to major disturbance events. These data will help illuminate basic scientific questions regarding how large and infrequent disturbances drive ecological dynamics. This understanding will additionally provide information critical to effective, integrated management strategies for fire and imperiled fishes, informing questions about, for example, the extent to which wildfire should be prevented (or encouraged) in watersheds with populations of endangered fish. The project provides support for a research assistant who is preparing for graduate school, offering her valuable training and experience in a diverse set of field techniques and applications. Results will be made available to a broad audience via diverse media and communication outlets, ranging from websites to scientific publications.
Wildfires in many parts of North America are becoming more frequent and more severe. Because wildfires are unpredictable and can burn vegetation, change soil erosion, or even directly kill animals, studying how such fires impact ecosystems has proven challenging. We studied the impacts of a wildfire that burned approximately 40% of Scott Creek, a 77 km2 California watershed in August 2009 (Figure 1). This watershed contains ESA-listed salmonids such as steelhead trout and coho salmon. Furthermore, this watershed has been extensively studied by fishery scientists, stream ecologists, and watershed geomorphologists. This project focused on the short-term impacts of fire on streams (first year), a critical period that defines the initial recovery of ecosystems and the majority of post-fire geomorphic change. We combined geomorphology, ecosystem, and food-web studies with monitoring of salmonid populations. Remote sensing (aerial LiDAR) before and after the wildfire allowed us to create detailed maps of the change in tree and shrub cover. The fire burned the vegetation in patches, with a tendency for more decreased vegetation on ridge-tops. Within the stream itself, burned region warmed approximately 0.5 degrees Celsius during the summer following the fire but this increase did not yet exceed tolerances of the salmonids that need cold water. Instead, in the summer after the fire, the burned region supported approximately 1.5X as much salmonids. The rest of the food web of the stream such as algae and benthic invertebrates apparently responded more variably, if at all, to the wildfire. Through linking studies of fish, stream food webs, and watershed geology, we gained insight into the rapid and inter-connected response of a watershed to a major wildfire. While the wildfire removed vegetation in much of the watershed, the stream and its food-web was remarkably resilient to this major disturbance. Management and conservation of imperiled species, such as salmonids in their southern range, needs to consider rare events such as wildfire. The fire even appeared to increase the carrying capacity of the system for salmonids, but did increase the water temperatures which may render burned watersheds more sensitive to climate warming. More generally, our research shows how perspectives from geology and ecology can provide insight into how systems respond to large-scale disturbance.
