Mammalian resistance to megafire in western U.S. woodland savannas

Abstract

Increasingly frequent megafires are dramatically altering landscapes and critical habitats around the world. Across the western United States, megafires have become an almost annual occurrence, but the implication of these fires for the conservation of native wildlife remains relatively unknown. Woodland savannas are among the world's most biodiverse ecosystems and provide important food and structural resources to a variety of wildlife, but they are threatened by megafires. Despite this, the great majority of fire impact studies have only been conducted in coniferous forests. Understanding the resistance and resilience of wildlife assemblages following these extreme perturbations can help inform future management interventions that limit biodiversity loss due to megafire. We assessed the resistance of a woodland savanna mammal community to the short‐term impacts of megafire using camera trap data collected before, during, and after the fire. Specifically, we utilized a 5‐year camera trap data set (2016–2020) from the Hopland Research and Extension Center to examine the impacts of the 2018 Mendocino Complex Fire, California's largest recorded wildfire at the time, on the distributions of eight observed mammal species. We used a multispecies occupancy model to quantify the effects of megafire on species' space use, to assess the impact on species size and diet groups, and to create robust estimates of fire's impacts on species diversity across space and time. Megafire had a negative effect on the detection of certain mammal species, but overall, most species showed high resistance to the disturbance and returned to detection and site use levels comparable to unburned sites by the end of the study period. Following megafire, species richness was higher in burned areas that retained higher canopy cover relative to unburned and burned sites with low canopy cover. Fire management that prevents large‐scale canopy loss is critical to providing refugia for vulnerable species immediately following fire in oak woodlands, and likely other mixed‐forest landscapes.

Forest type modulates mammalian responses to megafires

“…Species richness was higher in polyspecific forests for both observed and estimated richness, highlighting their resistance, to some extent, to wildfires 26 , 27 , even during catastrophic events, something observed in other heterogeneous fire-prone ecosystems (e.g., 43 ). Despite differences in assemblage richness and composition, the aggregated relative abundance was similar between forest types, indicating a distinct landscape use by the species.…”

“…More than one-third of the study area was affected by the 2020 megafire 16 , leaving some unburnt forest patches that possibly acted as refugia for the high-mobile mammal species in the reserve and its surroundings. Large unburnt areas and forest canopy preservation are crucial to support vertebrate survival after megafires 20 , 21 , 43 , especially for diet and habitat specialist taxa, such as those recorded in this study.…”

“…Wildfire activity and its impacts on biodiversity are being transformed by anthropogenic drivers, such as climate and land use changes 30 , tending to increase conditions that favor wildfires in the Pantanal in the forthcoming years 49 . Cumulative effects, frequency, and severity of wildfires are responsible for reducing the diversity and abundance of organisms 4 , 5 , 7 , 43 . If such events, analogous to the Pantanal 2020 megafire, become recurrent, they might trigger local and regional extinctions in a short time.…”

Neotropical mammal responses to megafires in the Brazilian Pantanal

“…Only jaguars had the fire covariate of AB in the extinction parameter in their top model, despite negative trends in occupancy for many of the species post-fire and relatively high extinction values. We attribute this to the limited number of post-fire records for many species, and the entire area being affected by the high burn severity (an average of 70% of the AB for the buffer area considered each camera), thus reducing differentiation by site (Calhoun et al, 2023). Additionally, ΔNBR should be individually calibrated in each vegetation type because of the difference in their chlorophyll and density values (Kokaly et al, 2007;Miller & Quayle, 2015;Picotte & Robertson, 2011), but such measures do not exist for Brazil.…”

“…Mammal responses to fire vary depending on their habitat and resource requirements, their dispersal ability, and other trait-based characteristics (Calhoun et al, 2023). Mammal communities in nonfire-adapted regions may lack sensory cues to detect and flee from fires.…”