RAPID: Food webs of 10 lakes before and after a mega-wildfire

Wildfires have grown in size and intensity across the forested mountains of the western USA in the last two decades. While there is much investigation of their impacts of forests themselves, almost no studies evaluate their impacts on the mountain lakes that are embedded in these ecosystems. After wildfires burn through a watershed, large quantities of organic debris can wash into lakes.

Little is known about the extent to which fires-related effects such as these organic inputs, alter freshwater species and ecosystems, even though freshwater taxa may be notably sensitive to fire impacts. During summer 2021, the Dixie Fire burned ~1 million acres of forest in Northern California. This research project takes advantage of unique pre-wildfire (2020) data collected on the fish and food webs of 10 glacial lakes within the burn scar, and aims to resample these same ecosystems post-fire to understand how severity of fire in watershed impacts lake ecology.

In particular, researchers will investigate whether this large wildfire kills fish populations in lakes and whether this depends on lake size or basin characteristics. Additionally they will evaluate how reductions in fish populations cascade through the food webs to affect the overall health of lake ecosystems. Insights gained through this study will enable better management of lake fisheries and heritage species (e.g., native frogs) following severe wildfire.

Further, data collected from this study will inform decision makers on how to manage these systems into the future, including when and whether to stock lakes, and how fires impact freshwater ecosystems more generally. Researchers will engage in a science communication strategy aimed at calling public attention to this work, and will recruit students from historically-excluded backgrounds to participate in the full life-cycle of this research.

This research will investigate the effects of a mega-wildfire (the Dixie Fire) on 10 lake ecosystems in the Lassen National Forest, Caribou Wilderness, California, USA. Specifically, we will examine 1) whether fishes are eradicated in some or all lakes following mega-wildfires,2) whether fish removal changes a trophic cascade, 3) if trophic cascade strength varies with ecosystem size, and 4) how lake food web structure and function shifts following watershed burning.

This project uses both on the ground measurements of fish, invertebrates and lake chemical features, and uses stable isotopes to evaluate changing food webs. These assessments will be used to test ecological theory, namely the role of disturbance-mediated trophic cascades, and their control over lake food web structure and function. Results from this work will be useful to diverse ecologists interested in effects of climate change mediated disturbances, but especially limnologists and freshwater scientists struggling to manage these taxa in human dominated landscapes. Undergraduate students from diverse backgrounds will be included in the research process.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.