Graduate Thesis Or Dissertation

 

Response of avian communities to herbicide-induced vegetation changes, western Oregon Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/gh93h305f

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  • The relationships between avian community structure and herbicide modification of vegetation were analyzed on early-growth clearcuts in western Oregon that had received phenoxy herbicide treatment 1 or 4 years previously. Only minor effects of herbicide treatment were evident 1-year after spraying, except for red adler (Alnus rubra), which still exhibited moderate to severe damage. Most plants showed no obvious signs of the treatment by 4 years post-spray. For both 1 and 4 years post-spray, vegetation development was greater in the second (1.0-3.0 m) and third (>3.0 m) height intervals on untreated (Control) sites; vegetation cover in the lowest (<1.0 m) interval did not vary between treated and untreated sites. All measures of vegetative diversity on untreated sites exceeded those on sprayed sites. Discriminant function analysis identified deciduous tree cover as of primary importance in separation of vegetation of treated and untreated sites. Overall density and diversity of birds were similar between treated and unntreated sites. Several bird species altered patterns of foraging behavior on treated sites. Differences in habitat use were identified for several species; birds using deciduous trees were found to increase use of shrubs on treated sites. Deciduous tree cover usually functioned in ordination of the avifauna on both treated and untreated sites. The primary effect of herbicide application was a reduction in the complexity of vegetation on treated sites, a condition due primarily to the removal of deciduous trees. The substantial shrub cover on treated sites, however, apparently allowed maintenance of an overall avian density similar to that of untreated sites. Small patches of deciduous trees, scattered about on clearcuts treated with phenoxy herbicides can maintain an avian community that is similar to that on untreated sites.
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