Complexity and variation in the effects of low-severity fires on forest biota

The ecological effects of fire are varied and complex, yet the effects of even the most commonly applied fire treatments in the United States have been documented in ways that necessarily mask complexity and hide much of the variation effected by nominally similar burns. Reliance upon information gleaned from case studies of a narrow range of fire effects within a limited focal area to develop fire-management strategies for a wide domain of interest is especially evident in the American Southwest. Despite ardent speculation on both the acute and chronic influences of prescribed burning on populations of southwestern forest biota, including birds and arthropods, actual responses have seldom been quantified, and have never been quantified in ways that convey reliability.; Here, I provide the first estimates of short-term responses of a wide range of arthropods to low-severity, fall burns in southwestern ponderosa pine forests. I characterize these effects functionally, by grouping all insects, arachnids, and myriapods according to their general ecological roles within the forest community, and quasi-experimentally, by capitalizing on three nominally similar prescribed fires set within widely separated stands of comparable forest. I show that arthropods of southwestern ponderosa pine forest are keenly sensitive to even the most outwardly benign fire treatments, and that similar fires can effect disparate responses from a number of taxa.; Birds that depend heavily on the forest understory for food, cover, or both, are commonly assumed to be sensitive to prescribed burns. I show that the reproductive success of a ground-nesting, ground-foraging, insectivorous bird—the Yellow-eyed Junco—can indeed be compromised by low-severity, autumn fire in southwestern ponderosa pine forest. I attribute this effect to changes in availability of preferred nesting microhabitat. If all fires were to affect junco demography in a similar fashion, the chronic influence (i.e., historic recurrence) of disturbance alone could set bounds to populations of these birds. I show, however, that different prescribed burns can affect key resources in different ways, such that fire's influence on junco populations may differ considerably among treatments.