The effects of prescribed burning in the spring on avian communities in the Sierra Nevada of California.

摘要

Prescribed fire is becoming an increasingly important tool in efforts to reduce the risk of severe wildfires, but little is known about its effect on natural communities. I examined short-term changes (0-6 years postfire) in avian communities following the application of low-intensity prescribed fire in the spring in the Sierra Nevada of California. The results are in three parts: avian abundance and community composition, snag populations and cavity-nesting species, and nest success for five open-cup nesting species.; Avian abundance and community composition were recorded using a strip transect. Avian communities as a whole did not change as a result of prescribed burns. Abundances of 25 species were analyzed and, of these, six responded positively to fire, six responded negatively, and the remaining 13 species showed no consistent response. Grouping species into guilds, the only effects I found more than two years after fire were increases in snag-nesting and bark-foraging species and declines in oak-associated and canopy-foraging species. Comparisons with historical data collected by Joseph Grinnell found differences in avian communities that were hypothesized to be the result of the loss of fire since the 1910s.; Snag data was collected by following a population of random snags before and after fire as well as snags used for breeding. Snag population changes were greatest following the first introduction of fire after a long fire-free period. Snags preferred for nesting were generally of ponderosa pine (Pinus ponderosa), of larger diameter, and moderately decayed as compared to available snags. White fir (Abies concolor ) and incense cedar (Calocedrus decurrens) were avoided. There was a small loss (-1.5 ha-1) of snags predicted to be usable for nesting after burning. Nest success for cavity nesters was lower during the first year following fire but was not related to selected snag attributes.; Nests of Spotted Towhee (Pipilo maculates), Dark-eyed Junco (Junco hymelis), Black-headed Grosbeak (Pheucticus melanocephalus), Hutton's Vireo (Vireo huttoni), and Cassin's Vireo (Vireo cassinii) were monitored. I used Principal Components Analysis (PCA) to group variables describing nest location and used the resulting factor loadings in a logistic exposure model to evaluate nest success. Vegetation at the nest site was related to nesting success for all species except Spotted Towhee. Fire altered this relationship for Black-headed Grosbeak and Dark-eyed Junco. Nest success for Hutton's Vireo was consistently positively related to concealment, which was reduced by burning. Both vireos had higher rates of parasitism on burned plots.