Effects of fuel reduction on bird density and reproductive success in riparian areas of mixed-conifer forest in southwest Oregon

Abstract

Studies in southwest Oregon suggest that riparian areas within mixed-conifer forests historically burned with frequencies and intensities similar to upland areas and that fire played an important role in maintaining both of these ecosystems. Currently, most fuel reduction projects do not include riparian, due to the perception that these riparian areas are negatively affected by anthropogenic disturbance. However, there is very little information on the ecological consequences of including riparian areas in fuel reduction projects. We compared the effects of non-commercial thin and handpile treatments followed by prescribed burns in riparian areas of intermittent and perennial streams that were treated to the streamside (unbuffered), to the typical prescription in which sites were treated only in the adjacent upland (buffered). Unbuffered fuel reduction treatments have the potential to affect bird density and reproductive success differently than buffered treatments by altering (1) available nest habitat, (2) predator and nest parasite abundance, and (3) food availability in riparian areas. This study assessed whether unbuffered fuel reduction treatments yielded similar bird response as buffered treatments by quantifying differences in density and reproductive success of five bird species, vegetation structure, the frequency of occurrence of predators and a nest parasite, and arthropod biomass. Density was greater for the shrub and tree-nesting Pacific-slope Flycatcher in buffered streams post treatment. Reproductive success showed a minimal, near-term effect for the shrub-nesting Black-headed Grosbeak. For potential causal factors, we found differences between buffered and unbuffered streams only for available nest habitat in the upper-ground strata and frequency of occurrence of raptors. Overall, results suggest that fuel reduction in riparian areas as compared with typical upland treatments with buffers had a small effect on bird density and a near-term effect on reproductive success. Additional study of fuel reduction in riparian areas is warranted because of its effectiveness in reducing the risk of unnaturally severe wildfire and, correspondingly, the potential benefit to bird communities over the long-term.