Paper presented at BioEnergy '98: Expanding Bioenergy Partnerships, Madison, Wisconsin, October 4-8, 1998.

ABSTRACT

The Wisconsin Department of Natural Resources has designated 25 grassland bird species as being of management concern based on criteria that include declining populations and lack of suitable habitat. Switchgrass as a bioenergy crop can potentially provide high quality, perennial nesting cover for many of these species while also providing a sustainable crop for farmers using marginal land. As a feedstock for utility companies, switchgrass may reduce sulphur, nitrogen, and carbon emissions from power plants. The goal of this research was to determine the effects of harvesting switchgrass for biofuel on vegetation structure and grassland bird community composition. Five Conservation Reserve Program switchgrass fields in southwest Wisconsin were used to provide feedstock for combustion tests conducted at a Madison, Wisconsin power plant. Each field was divided into a harvested and an unharvested section. Harvests were conducted in August, 1996. Post-harvest vegetation structure was characterized by greater plant species diversity and lower height-density than was observed in unharvested areas. Harvested areas had reduced amounts of both standing and ground layer residual vegetation compared to unharvested areas. Bird surveys conducted during the spring and summer of 1997 in transects located in harvested and unharvested sections of switchgrass fields showed that both species richness and density of grassland bird species of management concern were significantly higher in the harvested areas than in the unharvested ones. A total of six bird species of concern occurred on pre-harvest transects in 1996; nine species were found in 1997. Of the management concern species occurring in 1997, savannah and grasshopper sparrow and eastern meadowlark were significantly more abundant in harvested plots, and bobolinks showed a trend towards higher abundance in harvested fields. In addition, upland sandpipers and western meadowlarks occurred only on harvested plots. Sedge wrens reached significantly higher densities in unharvested areas than in harvested ones, while two other species of concern, Henslow's sparrow and dickcissel, occurred only on unharvested transects. Our results suggest that switchgrass fields harvested for bioenergy production provide suitable habitat for a number of grassland birds of management concern, particularly those that prefer short to medium height vegetation. Birds that prefer the tall vegetation characteristic of unharvested fields should not be a target for management of switchgrass grown for biomass, unless management includes maintaining unharvested areas within the field.

Keywords: grassland birds, bioenergy crops, switchgrass, nesting cover