Fire and Floods: The Recovery of Headwater Stream Systems Following High-Severity Wildfire

Jackson M Leonard,Randy K Bangert,Hugo A Magaña,Willson L Montgomery,Daniel G Neary

doi:10.4996/fireecology.130306284

Abstract

This study examined the recovery of both physical and biotic characteristics of small (<0.1 m3 sec−1) headwater stream systems impacted by the Dude Fire, which occurred in central Arizona, USA, in 1990. Data collected prior to the fire from 1986 to1988 was compared to similar data collected at various points after the fire though 2011 in order to assess changes in the geomorphology and macroinvertebrate communities over the 21-year time period. Additionally, several environmental parameters of the impacted streams were compared to neighboring unburned headwater streams in order to determine recovery status. The study hypothesized that the headwater aquatic ecosystems impacted by the Dude Fire have yet to recover to unburned reference conditions. Results show that flooding, which occurred following the fire, resulted in incision in excess of 0.5 m across some stream transects and is continuing to cause shifts in dominant substrate particle size. Macroinvertebrate richness, diversity, and abundance were altered from prefire conditions up to a decade after the fire. Streamside canopy cover across burned streams remained 28 % lower on average. Lower concentrations of key stream nutrients, including nitrate (NO3−) and phosphate (PO43−), within impacted streams are still evident. Increases in summer stream temperatures due to the loss of streamside canopy cover continue to have an adverse affect on salmonid habitat. Thus, the process of recovery is closely tied to streamside vegetation and hydrologic disturbance patterns following the fire event, and will extend beyond the 21-year time period of this study.

Highlights

Decades of fire suppression during the twentieth century across the American West have led to accumulation of forest fuels (Adams 2013), resulting in larger and more destructive wildfires (Westerling et al 2006)
Dude Creek incised an average of −7.9 m2, ranging from 23 m2 to 0 m2; while transects on Ellison Creek were incised an average of −0.5 m2, ranging from −2 m2 to 0.6 m2; and transects on Bonita Creek incised and average of −0.5 m2, ranging from −1.7 m2 to −0.1 m2
The results of this study suggest that burned streams continue to have lower nutrient concentrations, less canopy closure, and, in the case of Dude Creek, higher water temperatures than reference streams after 21 years of recovery

Summary

Introduction

Decades of fire suppression during the twentieth century across the American West have led to accumulation of forest fuels (Adams 2013), resulting in larger and more destructive wildfires (Westerling et al 2006). Severe fire events can have profound impacts on the physical and environmental function of aquatic systems (Dunham et al 2007, Hall and Lombardozzi 2008) These include changes in geomorphology, channel substrate, water temperature, and stream chemistry, among others (Minshall et al 2001a, Isaak et al 2010, Rhoades et al.2011). Stream flow is captured for municipal water supplies or diverted for irrigation purposes, and in other instances, stream flow naturally flows underground due to geologic conditions These fragmented stream habitats often cannot be colonized by species from downstream sources after disturbance events, which may slow or even prevent natural recovery and result in the loss of key habitat functions (Dunham et al 2003, Dunham et al 2007)

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Results

Discussion

Conclusion