Abstract

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Quamen, F.R. 2007. A landscape approach to grassland bird conservation in the prairie pothole region of the northern Great Plains. Ph.D. Dissertation, University of Montana, Missoula. 150 pp. 

Abstract:

Prairie is one of the most imperiled ecosystems, and grassland birds have experienced steeper and more consistent declines than any other group of birds in North America.  Habitat-based planning tools are a cornerstone of conservation in forested ecosystems, but remain a novel approach in grasslands. In Chapter 2, I developed spatially-explicit habitat models as decision support tools for conservation. I surveyed birds, measured local vegetation and quantified landscape features at 952 sites in western Minnesota and northwest Iowa. Findings indicated that cropland provided little habitat for grassland songbirds and that hayland did not compensate for loss of grasslands. Multiscale models showed that conservation actions that integrate management at local and landscape scales have the greatest chance of success. At landscape scales, conserving and creating grasslands, removing trees from the landscape, or both will increase songbird density.  Density of many species was positively related to amount of grassland at the smallest scale evaluated (0.5km2), but large grasslands were vital for others whose density was related to grassland abundance at large scales (32km2). At local scales, managing for a mosaic of vegetation that varies in structure and composition will increase bird diversity.  Model validation showed that planning maps can be used reliably (r2 ≥ 0.90) to establish a regional conservation strategy. I used spatially-explicit maps to identify five landscapes capable of attracting the highest densities of the greatest number of songbirds, and showed that most of this habitat is unprotected from risk of conversion to other land uses.  Models in Chapter 2 confirmed that woody edges exacerbated effects of habitat loss, so in Chapter 3 I tested whether birds used otherwise suitable habitats by experimentally removing trees in a before-after/control-impact design. This is the first study to experimentally show that songbirds avoid woody edges in otherwise suitable habitat. Avoidance of trees was apparent as far away from woody edges as surveys were conducted (240 m). The spring following tree removal, the four most common species redistributed themselves ubiquitously in grasslands where trees were removed. I recommend that managers remove trees from grasslands and avoid planting trees in grasslands where conservation of songbirds is the management goal.

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