| Summary: | Removal of deciduous vegetation in managed conifer forests is a major component of most
silviculture programs. Despite controversy over non-target effects, research regarding the impact
of vegetation management on birds is limited. I examined the effect of removing 90-96% of the
deciduous tree volume on breeding bird communities in young conifer plantations during 4
years. Trees were removed by two treatments: manual thinning, and manual thinning plus
application of the herbicide, glyphosate. The control and two treatments were each replicated
three times. During the 3 post-treatment years, the herbicide-treated sites remained depauperate
of deciduous vegetation while the manually thinned sites experienced deciduous regrowth.
Variation in richness of bird species across all sites was solely due to the presence or absence of
rare species. Richness declined, abundance increased, and common species dominated after
herbicide application. Richness, abundance, and evenness increased after manual thinning.
Turnover of bird species was highest in the herbicide-treated areas and lowest in the control
areas. Residents, short-distance migrants, ground gleaners and conifer nesters increased
significantly after herbicide application. Deciduous nesters and foliage gleaners declined in
abundance (nonsignificantly) in areas treated with herbicide. The Warbling Vireo (Vireo gilvus),
a deciduous specialist, declined in areas treated with herbicide. Although treated areas exhibited
similar increases in total abundance, nesting success of open-cup nesting species was
significantly lower in the herbicide-treated than manually thinned areas. Warbling Vireos,
Swainson's Thrushes, and Dusky Flycatchers preferred to nest in untreated or recovered habitat
within larger treated areas. Successful nests were more more likely to be present in areas with
willow. Overall, the composition of bird communities became more homogeneous after
herbicide application, and showed little change after manual thinning.
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