Early successional changes in coniferous forest small mammal communities following a high-severity summer wildfire

Abstract

Forest fires in the southern Rocky Mountains are changing due to climate warming and increased fuel loads. Landscape-scale stand-replacement fires create extensive treeless swaths without regenerative seed sources, leading to long-term conversion of coniferous forest to montane meadows and chaparral. Small mammal wildlife responds to these abrupt habitat changes, influencing post-fire succession via trophic interactions (herbivory, granivory, insectivory, and fungivory) and soil disturbance (burrowing, foraging, and seed caching). We examined the effects of the 2011 high-severity Las Conchas wildfire on post-fire small mammal and vegetation successional changes in northern New Mexico's mixed conifer and ponderosa pine (Pinus ponderosa) forests. We sampled forest stand composition and herbaceous vegetation immediately after the fire, then sampled herbaceous vegetation and small mammals each spring and autumn for 3 years (2012–2014) on replicated burned and unburned stands. We recorded 15 small mammal species (11 rodents, one rabbit, and three shrews). Herbaceous vegetation cover increased from 10% to 12% on burned sites in 2011 to 91% in 2014, with no observed conifer regeneration. Small mammals exhibited lower species richness on burned mixed conifer sites than on unburned sites, but species richness was only slightly lower on burned ponderosa pine sites than on unburned sites. Deer mouse (Peromyscus maniculatus) abundances were comparable between burned and unburned sites, but two species of chipmunks (Neotamias minimus, Neotamias quadrivitattus), woodrats (Neotoma spp.), red squirrels (Tamiasciurus hudsonicus), three species of shrews (Sorex spp.), and mountain cottontail rabbits (Sylvilagus nuttallii) were rare or absent in burned forests. Golden-mantled ground squirrels (Callospermophilus lateralis) were more abundant on burned mixed conifer sites than on unburned sites, and voles (Microtus) colonized the burned sites within 3 years (Microtus montanus in 2013, Microtus longicaudus in 2014). Rodent demographic data indicated that mixed sex and age classes were present for the more abundant species, including reproductively active adult females; the exception was M. longicaudus in burned ponderosa pine forests, which had only male adults and subadults. Vole colonization occurred after burned sites attained 80%–90% herbaceous cover. Given the lack of conifer regeneration, we anticipate that the small mammal community will retain its composition of meadow-grassland species for the foreseeable future.