Title

Tracking Forest Fire Impacts on Stream Temperatures & Ensuing Shifts in the Salmonid Community

Presenter Information

Christopher Rotar

Presentation Type

Poster

Abstract

Understanding how salmonids respond to habitat changes associated with wildfire is necessary to predict the impacts of future increases in wildfire frequencies and severities on salmonid populations. This is important in headwater streams which serve as cold water refuge for the threatened bull trout (Salvelinus confluentus) during the summer months. Canopy cover losses after wildfire events can result in increased stream temperatures, leading to displacement of coldwater fishes. In the summer of 2018 we evaluated habitat changes one year after the 2017 Meyers Fire of the BeaverheadDeerlodge National Forest. We performed habitat surveys and installed temperature loggers at 28 study sites throughout Montana's upper Rock Creek and Flint Creek drainages, including 20 sites across 7 wildfire-affected streams and 8 sites across 2 control streams. We found decreased canopy cover at sites with higher burn severities. Across all sites 2018 mean August stream temperatures were higher on average than the baseline predicted stream temperatures (Norwest modeled August averages) and there was an increasing trend of higher differences between observed and predicted temperatures at sites with higher burn severity. We also assessed current native and non-native salmonid distributions by sampling the fish communities at 24 of these 28 sites throughout the study basin. Nonnative brown trout (Salmo trutta) were found at novel upstream locations relative to previous sampling events in both burned and unburned (control) watersheds. In 2018, bull trout and brown trout distributions were found to be overlapping in all locations where brown trout were observed. Nearly all sites with mean August stream temperatures above 10°C showed declines in the relative proportions of bull trout present. The relative proportions of community composition of native salmonids were found to have decreased and relative proportions of nonnative salmonids were found to have increased since the previous sampling events, likely irrespective of fire.

Category

Life Sciences

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Apr 17th, 11:00 AM Apr 17th, 12:00 PM

Tracking Forest Fire Impacts on Stream Temperatures & Ensuing Shifts in the Salmonid Community

UC South Ballroom

Understanding how salmonids respond to habitat changes associated with wildfire is necessary to predict the impacts of future increases in wildfire frequencies and severities on salmonid populations. This is important in headwater streams which serve as cold water refuge for the threatened bull trout (Salvelinus confluentus) during the summer months. Canopy cover losses after wildfire events can result in increased stream temperatures, leading to displacement of coldwater fishes. In the summer of 2018 we evaluated habitat changes one year after the 2017 Meyers Fire of the BeaverheadDeerlodge National Forest. We performed habitat surveys and installed temperature loggers at 28 study sites throughout Montana's upper Rock Creek and Flint Creek drainages, including 20 sites across 7 wildfire-affected streams and 8 sites across 2 control streams. We found decreased canopy cover at sites with higher burn severities. Across all sites 2018 mean August stream temperatures were higher on average than the baseline predicted stream temperatures (Norwest modeled August averages) and there was an increasing trend of higher differences between observed and predicted temperatures at sites with higher burn severity. We also assessed current native and non-native salmonid distributions by sampling the fish communities at 24 of these 28 sites throughout the study basin. Nonnative brown trout (Salmo trutta) were found at novel upstream locations relative to previous sampling events in both burned and unburned (control) watersheds. In 2018, bull trout and brown trout distributions were found to be overlapping in all locations where brown trout were observed. Nearly all sites with mean August stream temperatures above 10°C showed declines in the relative proportions of bull trout present. The relative proportions of community composition of native salmonids were found to have decreased and relative proportions of nonnative salmonids were found to have increased since the previous sampling events, likely irrespective of fire.