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

The Center for Watershed Sciences is excited to share news of a new NSF Grant for Rapid Research Response proposal that was just successfully funded! Congratulations to PIs Andrew Rypel, Christine Parisek, and Steve Sadro on receiving funding for “RAPID: Food webs of 10 lakes before and after a mega-wildfire.”

In 2021, the largest single source wildfire in California’s history burned ~1M acres, 68.8% of Lassen National Park, and 10 lakes this team sampled for stable isotopes in 2020. The Dixie Fire burned 104 days (mid July– October 2021) and is the first known fire to cross the Sierra Nevada crest. The wildfire burned watersheds and riparian zones of the study lakes, which span a gradient in watershed area and lake size. 

The explosion and intensification of climate-driven mega-wildfires over recent years highlights a pressing need to better understand these impacts at all scales. In California, the 7 largest wildfires all occurred within the last 4 years. Yet despite increasing wildfire disturbance, there lacks understanding of the extent to which fire may alter trophic structure in lakes, or the degree to which fire-effects are mediated by ecosystem architecture. What little is known derives primarily from boreal environments, and there have been no pre- versus post-fire food web comparisons (McCullough et al. 2019). 

The team received RAPID support to quantify: 1) whether fishes are eradicated in lakes following mega-wildfires; 2) if post-fire trophic cascade strength varies with ecosystem size; and 3) how lake food web structure and function shifts following burning. Due to the team’s pre-wildfire samples, this is an unprecedented opportunity to better understand lake food web ecology and response to mega-wildfire activity. Stay tuned for exciting new findings!

NSF Abstract

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

Andrew Rypel (PI)¹², Christine Parisek (Co-PI)¹², Steve Sadro (Co-PI)¹³

¹ Center for Watershed Sciences, University of California Davis
² Wildlife, Fish, & Conservation Biology Department, University of California Davis
³ Environmental Science & Policy Department, University of California Davis

There is an emerging imperative to better understand effects of climate-driven wildfires across the Western USA. 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 may 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 data collected on the food webs of 10 glacial lakes in 2020, and aims to resample these same ecosystems post-fire to understand how severity of fire in watershed impacts lake ecology. In particular, we will investigate whether large wildfires kill fish populations in lakes and how reductions in non-native 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. We 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, USA. Specifically, we will examine 1) whether fishes are eradicated in lakes following mega-wildfires, 2) if trophic cascade strength varies with ecosystem size, and 3) how lake food web structure and function shifts following watershed burning. This project tests ecological theory, namely the role of disturbance-mediated trophic cascades, and their control over lake food web structure and function. We anticipate 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.