Prescribed fire has slight influence on Roosevelt elk population dynamics

Abstract

Prescribed fires often stimulate short-term productivity of grasslands that influences use by large, grazing herbivores. But studies examining burning effects on large herbivore population dynamics while simultaneously considering other environmental factors that might also influence population dynamics are lacking. We examined the influences of burned area, precipitation during the growing season, and possible distributional shifts from a nearby public hunt on maximum intrinsic rate of population growth (rmax) and environmental carrying capacity (K). We examined the influences of these predictors in a Roosevelt elk (Cervus elaphus roosevelti) population studied across 43 years where abundances ranged from 4 to 322 animals and prescribed fires ranged from 14 to 891 ha of burned area in Redwood National and State Parks, California, USA. The highest count across surveys conducted in a year was our index of elk (females, juveniles, subadult males) abundance. We estimated Ricker type models in a hierarchical, state-space formulation that separated observer error from process variation. We found a slight influence from burned area on both rmax and K but a stronger influence from precipitation during the growing season. The lack of a substantial effect from burned area on elk population parameters might be from a variety of factors such as spatial and temporal variation in intensity of prescribed fires and weak density dependence. Nonetheless, one positive benefit to elk population processes was that the patchwork of burning retarded encroachment of woody plants into forage habitat and, thus, maintained a constant area of forage habitat across 43 years.