Ecological response of step-pool streams to wildfire in the Front Range of Colorado (USA)

Abstract

Wildfire affects ecosystems via the disruption of landforms and biota. Step and pool formations in mountainous streams have important hydraulic and ecological functions, but there is little information on wildfire impacts on step‐pool ecosystems. This chapter describes a study examining the biophysical responses of headwater mountain streams for 2 years following the 2012 Waldo Canyon Fire in Pike National Forest (Front Range of Colorado, USA). We focused on the impacts of this wildfire on stream invertebrate communities, including richness, composition, and traits related to disturbance tolerance and habit types, as well as functional feeding groups. We tested the hypothesis that the postfire responses of invertebrate communities will depend on vegetation burn severity (unburned, low severity, and moderate/ high severity), with responses being greater in moderate/high-severity than unburned or low-severity basins. Our results indicated that the relative abundances of sensitive invertebrates decreased and tolerant taxa increased after fire at sites draining catchments burned at moderate/high severity, and few postfire impacts were found on invertebrates at sites draining catchments that burned at low severity, relative to unburned sites. Regarding the relative abundances of trait groups, shredder abundance was higher at low-severity burned sites compared to sites burned at moderate/high severity and unburned sites throughout the study, and sprawler abundance was higher at low-severity burn sites compared to moderate/high-severity burn sites and unburned basins in 2013. However, values of all invertebrate variables in moderately/highly burned reaches generally returned to unburned levels by 2 years postfire. Stream geomorphological variables, specifically changes in the vertical profile of the stream channel over time, were negatively correlated with taxa richness, family biotic index, and percentage of shredders. Fire management strategies that prevent or reduce the severity of catastrophic wildfire, such as forest thinning or prescribed fire, as well as efforts to reestablish natural channel morphology, can ameliorate the impacts of wildfire on stream communities and help to establish stable, healthy, and diverse ecosystems in steep environments in the Front Range and elsewhere.