Effects of wildfire on stream temperatures in the Bitterroot River Basin, Montana

Abstract

Wildfire is a common natural disturbance that can influence stream ecosystems. Of particular concern are increases in water temperature during and following fires, but studies of these phenomena are uncommon. We examined effects of wildfires in 2000 on maximum water temperature for a suite of second- to fourth-order streams with a range of burn severities in the Bitterroot River basin, Montana. Despite many sites burning at high severity, there were no apparent increases in maximum water temperature during the fires. One month after fire and in the subsequent year, increases in maximum water temperatures at sites within burns were 1.4–2.2°C greater than those at reference sites, with the greatest differences in July and August. Maximum temperature changes at sites >1.7 km downstream from burns did not differ from those at reference sites. Seven years after the fires, there was no evidence that maximum stream temperatures were returning to pre-fire norms. Temperature increases in these relatively large streams are likely to be long-lasting and exacerbated by climate change. These combined effects may alter the distribution of thermally sensitive aquatic species.

Evidence of Climate-Induced Range Contractions in Bull Trout Salvelinus confluentus in a Rocky Mountain Watershed, U.S.A

“…The watershed is a temperate, snowmelt-dominated system with a range of elevations from 1,220 to 2,887 m. In 2000, wildfires burned 52.0% (29.2% at moderate to high severity) of the basin and 3.8% (2.5% at moderate to high severity) in 2007. Maximum summer stream temperatures in reaches where moderate- to high-severity fires burned in riparian stands remain elevated 1.4 to 2.2°C above those from reaches adjacent to unburned stands [22]. Over a comparable interval (1994–2007) maximum summer stream temperatures at some unburned sites also increased 1.9–2.6°C [22], which is higher than the July/August 0.24°C/decade increase described for the Greater Yellowstone area [26] and 0.22°C/decade increase across the U.S. Northwest [15].…”

Aquatic biodiversity in forests: a weak link in ecosystem services resilience

“…3; Minshall et al 1989;Gresswell 1999). The most commonly documented influences of fire on stream habitats include: (1) warming stream temperatures due to loss of shade from ripariantrees burned by wildfires (Dunham et al 2007;Mahlum et al 2011); (2) pulsed delivery of wood and sediment to stream channels, and increased probability of high-magnitude disturbances from debris flows and other erosional processes immediately following fire Wondzell and King 2003); and (3) potential pulses of nutrients immediately post-fire (Minshall 2003;Spencer et al 2003;Malison and Baxter 2010). Subsequent effects of fire on aquatic biota include a host of changes in species composition linked to the trophic status of streams (Minshall 2003;Malison and Baxter 2010), changes in species demography (Rosenberger et al 2015), and in some cases losses of native species (Dunham et al 2003).…”

Atmospheric Conditions, Landscape Characteristics, and Anthropogenic Factors Affecting Stream Water Temperature

“…It must be mentioned that forest harvesting can have adverse effects on stream water temperature because of the thermal insulation effects of logging debris (Jackson et al, 2001). Systematic investigations are needed to elucidate the complex response of stream water temperature to forest harvesting in conjunction with other factors such as the riparian zone, groundwater influences, and stream orientation and location (Pollock et al, 2008;Quinn and Wright-Snow, 2008;Mahlum et al, 2011;Rex et al, 2012;Kibler et al, 2013) .…”

“…Its response to environmental conditions is influenced by regional incidents and anthropogenic activities such as forest harvesting, wild fires, and reservoir and wastewater discharges (Bartholow et al, 2004;Mahlum et al, 2011;Groom et al, 2011;Xin and Kinouchi, 2013). In recent years, climate change has received considerable attention as a controlling factor of long-term and large-scale variations of stream water temperature Langan et al, 2001).…”