High resistance to managed and natural forest fire in a rare rock-outcrop specialist herb (Boechera constancei, Brassicaceae)

Abstract

Fire may increase the abundance of many understory plants in forested ecosystems, such as gap-dependent herbs that respond quickly to increased light availability. Fire may or may not benefit some rarer understory herbs, such as stress-tolerant species specializing on rock outcrops. The latter species may benefit less from post-fire increases in light, and their slow-growing life histories might impair their abilities to survive, recover, and/or increase their rates of growth and reproduction following fires.We examined the impacts of prescribed and natural fire on Boechera constancei (Brassicaceae), a rare herb growing on and around outcrops of infertile serpentine rock in upper montane conifer forests of the northern Sierra Nevada, California. We analyzed demographic transition rates of marked plants in response to experimental burns in winter 2012 and a subsequent lightning-caused fire in summer 2012. We measured leaf litter as a covariate, expecting that fire effects on B. constancei demography might be stronger in sites with more litter.Prescribed fire marginally decreased the fecundity of large individuals, but elasticity analyses found these rates to have no effect on estimated population growth, while the naturally occurring fire had no significant effects on demography. Leaf litter was not significant as a covariate in any analyses. Estimated population growth rates were thus unaffected by either prescribed or natural fire.Our results are consistent with the hypothesis that rock outcrop specialists are relatively insensitive to disturbance, and we suggest that such species may often have little bearing on the ecological costs and benefits of fire in forested systems.