An examination of the impacts of invasive woody vegetation on grassland birds and waterfowl

Abstract

Efforts to remove woody vegetation are becoming a management priority in many grassland regions. Encroaching trees are thought to degrade habitat for grassland birds by altering predator communities, increasing competition, altering food webs, or by disrupting habitat selection patterns based on historical landscapes. Once established, trees and shrubs can be difficult and expensive to eradicate from grasslands. In order to best utilize limited conservation resources, grassland managers require information on how detrimental trees are for target species and where tree-removal actions might be the most beneficial. My dissertation research focused on exploring the consequences of woody vegetation encroachment on grassland bird habitat selection and waterfowl nest survival in western Minnesota. I also examine the results of experimental tree-removal on grassland songbird abundance. Most species of grassland birds exhibited strong patterns of tree avoidance. Tree-avoidance may be a more important driver of habitat selection than grass extent or quality in this landscape. Contrary to expectations, waterfowl nest survival was not related to the amount or proximity of woody vegetation. The effects of experimental tree-removal on songbirds were mixed. Grassland birds responded negatively for several years following initial treatment, but eventually the removal led to increases in abundance compared to control sites. The initial negative response was likely due to disturbance on the site, including fire treatments intended to reduce tree re-growth.