Graduate Thesis Or Dissertation
 

Songbird communities in burned and logged stands with variable tree retention in the Canadian Rocky Mountains

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  • By emulating natural disturbances such as wildfire, managers hope to maintain biodiversity in managed forests. Leaving residual (live) trees in harvested areas is key to this strategy. However, the effectiveness of this approach is unknown. I surveyed songbirds in 176 stands in the Rocky Mountains of southeastern British Columbia, Canada, that had been logged or burned by wildfire. Stands varied in time-since-disturbance from 5-45 yr. and in residual tree density from 0-2 16 conifer overstory, 0-268 conifer understory, and 0-35 broadleaf trees/ha. In 28 of these stands, artificial and natural nests were used to examine nest predation. Logged and burned stands had similar dominant species, evenness, and diversity (Simpson's index) of birds, but logged stands had higher richness and abundance. Of 26 species analyzed, 20 had similar or greater abundance in logged stands; 6 had greater abundance in burned stands. Differences in songbird communities were likely related to differences in vegetation. As a result of non-intensive logging practices, logged stands had greater shrub cover, shrub richness, broadleaf tree basal area, and more vegetation layers, but fewer regenerating trees, snags, and down wood than burned stands. As time-since-disturbance increased, bird communities in the two disturbance types became more similar at higher elevations, but not at lower elevations. Residual broadleaf and conifer understory tree density positively influenced songbird richness and abundance. Abundance of individual bird species was positively and negatively associated with residual trees. There was no strong or consistent evidence that depredation of nests of ground- and shrub-nesting songbirds increased with residual tree density. Depredation of artificial nests increased with residual tree density in logged stands in one of two years, but not in burned stands. Depredation was higher for artificial than natural nests. Retaining residual trees in managed stands can enhance richness and abundance of songbirds without increasing nest predation. The range of densities in this study provided good habitat for most early seral songbirds, but higher densities of overstory trees and snags are needed to provide good habitat for some species. Logging practices that reduce broadleaf trees, shrub cover, or residual conifer understory trees may reduce songbird richness and abundance.
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file details Stuart-SmithAKari2001.pdf 2017-10-20 公开 下载