Resilience of terrestrial and aquatic fauna to historical and future wildfire regimes in western North America

Abstract

Wildfires in many western North American forests are becoming more frequent, larger, and severe, with changed seasonal patterns. In response, coniferous forest ecosystems will transition toward dominance by fire‐adapted hardwoods, shrubs, meadows, and grasslands, which may benefit some faunal communities, but not others. We describe factors that limit and promote faunal resilience to shifting wildfire regimes for terrestrial and aquatic ecosystems. We highlight the potential value of interspersed nonforest patches to terrestrial wildlife. Similarly, we review watershed thresholds and factors that control the resilience of aquatic ecosystems to wildfire, mediated by thermal changes and chemical, debris, and sediment loadings. We present a 2‐dimensional life history framework to describe temporal and spatial life history traits that species use to resist wildfire effects or to recover after wildfire disturbance at a metapopulation scale. The role of fire refuge is explored for metapopulations of species. In aquatic systems, recovery of assemblages postfire may be faster for smaller fires where unburned tributary basins or instream structures provide refuge from debris and sediment flows. We envision that more‐frequent, lower‐severity fires will favor opportunistic species and that less‐frequent high‐severity fires will favor better competitors. Along the spatial dimension, we hypothesize that fire regimes that are predictable and generate burned patches in close proximity to refuge will favor species that move to refuges and later recolonize, whereas fire regimes that tend to generate less‐severely burned patches may favor species that shelter in place. Looking beyond the trees to forest fauna, we consider mitigation options to enhance resilience and buy time for species facing a no‐analog future.

Comparing headwater stream thermal sensitivity across two distinct regions in Northern California

“…When stream temperature warms, it can negatively impact sensitive cold water aquatic species, such as salmonid fishes and amphibians, by reducing habitat suitability for spawning and rearing life stages, and influencing individual metabolism and behaviour (Dallas & Ross‐Gillespie, 2015; Eaton & Scheller, 1996; Hester & Doyle, 2011; McCullough et al, 2009; Sloat & Osterback, 2013; Welsh, Hodgson, Harvey, & Roche, 2001). Recent studies have illustrated that climate change and shifts in forest disturbance regimes have the potential to intensify thermal pollution and increase the risks to anadromous fish and other aquatic vertebrate populations (Benjamin, Connolly, Romine, & Perry, 2013; Jager et al, 2021; Thomas et al, 2004; Wagner et al, 2014) In Mediterranean climates, the threat to aquatic species is particularly important during the summer low flow period, when precipitation inputs are low and both thermal inputs from solar radiation and convective heat exchange between the warm air and cooler streams are at their maximum (Arismendi et al, 2013; Larsen & Woelfle‐Erskine, 2018; Xu et al, 2010).…”

Wildfire influences individual growth and breeding dispersal, but not survival and recruitment in a montane amphibian

“…Historical wildfire regimes in our study area were characterized by infrequent (>200‐year return interval), high‐severity fires, whereby subalpine and boreal forests would recover long before another burn (Jager et al, 2021; Turner & Romme, 1994). In the near term, however, wildfire frequency, severity, and area burned are predicted to increase (Hagmann et al, 2021), which could affect overwintering sites in upland habitat and critical riparian corridors, which were strongly preferred by boreal toads during the summer foraging season (July–September; Barrile, Chalfoun, & Walters, 2021b).…”

A possible role for river restoration enhancing biodiversity through interaction with wildfire

“…Trophic cascade effects, such as a longer‐term reduction in leaf litter inputs post‐wildfire (Bixby et al, 2015), are also likely to differ between reconnected river corridors and unrestored river corridors. However, the current literature on the interplay between aquatic ecosystems, wildfires and trophic cascades indicates context‐specific and complex processes that require more research to be understood for a management context (Jager et al, 2021; Minshall, 2003; Verkaik et al, 2015). For instance, aquatic–riparian ecosystems are influenced by the timing of climatic variables, such as precipitation, in concurrence with wildfire events (Jackson & Sullivan, 2015), or reduction of riparian shading, which promotes algal growth, producing shorter‐term flood–wildfire productivity pulse events (Malison & Baxter, 2010).…”