Abstract
Globally, grasslands and the wildlife that inhabit them are widely imperiled. Encroachment by shrubs and trees has widely impacted grasslands in the past 150 years. In North America, most grassland birds avoid nesting near woody vegetation. Because woody vegetation fragments grasslands and potential nest predator diversity and abundance is often greater along wooded edge and grassland transitions, we measured the impacts of removing rows of trees and shrubs that intersected grasslands on potential nest predators and the three most abundant grassland bird species (Henslow’s sparrow [Ammodramus henslowii], Eastern meadowlark [Sturnella magna], and bobolink [Dolichonyx oryzivorus]) at sites in Wisconsin, U.S.A. We monitored 3 control and 3 treatment sites, for 1 yr prior to and 3 yr after tree row removal at the treatment sites. Grassland bird densities increased (2–4 times for bobolink and Henslow’s sparrow) and nesting densities increased (all 3 species) in the removal areas compared to control areas. After removals, Henslow’s sparrows nested within ≤50 m of the treatment area, where they did not occur when tree rows were present. Most dramatically, activity by woodland-associated predators nearly ceased (nine-fold decrease for raccoon [Procyon lotor]) at the removals and grassland predators increased (up to 27 times activity for thirteen-lined ground squirrel [Ictidomys tridecemlineatus]). Nest success did not increase, likely reflecting the increase in grassland predators. However, more nests were attempted by all 3 species (175 versus 116) and the number of successful nests for bobolinks and Henslow’s sparrows increased. Because of gains in habitat, increased use by birds, greater production of young, and the effective removal of woodland-associated predators, tree row removal, where appropriate based on the predator community, can be a beneficial management action for conserving grassland birds and improving fragmented and degraded grassland ecosystems.
Highlights
Grassland habitats and the animals that depend upon them are widely imperiled by the degradation and fragmentation associated with agricultural and energy development, succession, and urbanization [1]
In the past 150 years, woody vegetation has become more widespread in grasslands and savannas of North and South America, Africa, Australia, and southeast Asia [6], [7]
Density Bobolink, Eastern meadowlark, and Henslow’s sparrow were the common grassland species found on all control and tree row removal sites, accounting for 75% of the grassland birds detected
Summary
Grassland habitats and the animals that depend upon them are widely imperiled by the degradation and fragmentation associated with agricultural and energy development, succession, and urbanization [1]. In the past 150 years, woody vegetation has become more widespread in grasslands and savannas of North and South America, Africa, Australia, and southeast Asia [6], [7]. This encroachment can fundamentally change grasslands, jeopardizing biodiversity and threatening the sustainability of pastoral, subsistence, and commercial livestock grazing [8], [9]. Such changes may adversely impact up to 20% of the world’s population [10]
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