Grassland birds demonstrate delayed response to large-scale tree removal in central North America

Maintenance of early successional and open habitats often requires active removal of encroaching vegetation. In many cases, fire or other historically applied methods can no longer maintain or create open or early-successional habitat. In these situations, managers must employ mechanical or chemical treatments to control vegetation and improve habitat quality for wildlife that depend on open habitats. We conducted a large-scale study of tree removal from 2005 to 2011 on 14 grassland sites in central North America. Beginning in the autumn of 2005, shrubs, scattered trees, shelterbelts and woodlots were removed from six of fourteen study sites with cutting and burning treatments. Trees and shrubs accounted for 7-21% of pre-treatment ground cover. We conducted vegetation and bird surveys on each site for one year before and six years after initiating tree removal treatments. Treatments effectively removed larger woody vegetation (>6 m in height), but effects of shrub removal were less consistent due to rapid regrowth. Tree removal sites also experienced reductions in grassy litter as a result of prescribed fires that were used to discourage shrub and tree regrowth. On untreated sites, abundance of all grassland birds declined throughout the study, on average declining by 62%. On tree removal sites, we estimated that grassland bird abundance dropped from 2·04 (birds per count) before treatment to a low of 0·90 in the second year after initiating treatments, but recovered in the final three years of study with a weak, but significant positive response six years after initiating treatment, with an estimated 1·42 birds per count. Waterfowl and wetland birds increased following tree removal, whereas woodland birds, particularly those that nest in cavities, declined on treated sites. Synthesis and applications. Tree removal did appear to improve habitat suitability for grassland birds, but a positive response was weak and delayed, and treatments caused short-term habitat disturbances that significantly reduced abundance of target species. When planning large-scale tree removal, it may be beneficial to allow undisturbed habitat in the surrounding landscape to ameliorate potential short-term displacement of wildlife in early phases of treatment. In addition, managers should expect site recovery to require repeated treatments over multiple years.