Consecutive wildfires affect stream biota in cold- and warmwater dryland river networks

Abstract

Climate change and fire suppression have altered fire regimes globally, leading to larger, more frequent, and more severe wildfires. Responses of coldwater stream biota to single wildfires are well studied, but measured responses to consecutive wildfires in warmwater systems that often include mixed assemblages of native and nonnative taxa are lacking. We quantified changes in physical habitat, resource availability, and biomass of cold-and warmwater oligochaetes, insects, crayfish, fishes, and tadpoles following consecutive megafires (covering >100 km 2 ) in the upper Gila River, New Mexico, USA. We were particularly interested in comparing responses of native and nonnative fishes that might have evolved under different disturbance regimes. Changes in habitat and resource availability were related to cumulative fire effects, fire size, and postfire precipitation. The 2 nd of 2 consecutive wildfires in the basin was larger and, coupled with moderate postfire discharge, resulted in increased siltation and decreased algal biomass. Several insect taxa responded to these fires with reduced biomass, whereas oligochaete biomass was unaffected. Biomass of 6 of 7 native fish species decreased after the fires, and decreases were associated with site proximity to fire. Nonnative fish decreases after fire were most pronounced for coldwater salmonids, and warmwater nonnative fishes exhibited limited responses. All crayfish and tadpoles collected were nonnative and were unresponsive to fire disturbance. More pronounced responses of native insects and fishes to fires indicate that increasing fire size and frequency threatens the persistence of native fauna and suggests that management activities promoting ecosystem resilience might help ameliorate wildfire effects.

Direct and indirect impacts of wildfire on faunal communities of Mediterranean temporary ponds

“…Therefore, communities of temporary Mediterranean aquatic systems appear resilient to wildfire, recovering faster than perennial habitats (Robson et al, 2018;Verkaik et al, 2013). Thus, if as predicted, there is an increase in the intensity and recurrence of wildfire impacts, communities from dry areas may be substantially affected (Whitney et al, 2015) both directly and indirectly. Thus, if as predicted, there is an increase in the intensity and recurrence of wildfire impacts, communities from dry areas may be substantially affected (Whitney et al, 2015) both directly and indirectly.…”

“…However, a short-term pulse does not always occur (Batzer, 2013;Britton, 1991); if post-fire rains are particularly strong (100-year flood), they can compromise community recovery (Vieira, Barnes, & Mitchell, 2011). Furthermore, low post-fire rainfall and high fire recurrence can also decrease primary production and invertebrate biomass in lotic systems (Whitney et al, 2015). Therefore, depending on wildfire intensity and on immediate post-fire conditions (e.g.…”

Pockets of resistance: Response of arid‐land fish communities to climate, hydrology, and wildfire

“…Consecutive years of drought and wildfire between 2011 and 2013 also resulted in a reduction in the percent of sites occupied and lower densities of fish for a few years following those events. These results are not surprising given the changes wrought by post‐fire precipitation that transported ash and sediment into the stream channel, causing extensive mortality of stream organisms (Gresswell, ; Propst et al., ; Whitney et al., ).…”

“…Increasing ambient temperatures and earlier snowmelt associated with climate change coupled with elevated fuel loads from fire suppression have increased the probability of large wildfires in the American Southwest (>100 km 2 ; Hurteau, Bradford, Fulé, Taylor, & Martin, ; Westerling, Hidalgo, Cayan, & Swetnam, ). In some instances, ash flows following wildfires can have devastating impacts on fish communities (Gresswell, ; Propst, Stefferud, & Turner, ; Whitney, Gido, Pilger, Propst, & Turner, ). Because of the broad extent and high severity of these fires, there is concern that they will surpass the thresholds of native organisms’ resilience.…”

“…Mainstem habitats are also predicted to be more resilient due to increased colonisation opportunities by animals moving downstream from upstream sources (Brown & Swan, ). We also expected that native species might be more resistant than non‐native fishes because of their evolutionary experience with regional disturbance regimes; however, traits of successful invaders, such as reproductive potential or dispersal ability, might favour resilience (Dunham, Young, Gresswell, & Rieman, ; García‐Berthou, ; Whitney et al., ). Additionally, we propose alternative hypotheses for species that vary in body size.…”