Toward agroecosystem health: Assessment of biodiversity in contrasting agricultural landscapes
This thesis applies an evaluative concept, ecosystem health, as a framework for comparing biodiversity indicators between two culturally distinct agricultural landscapes of central Southern Ontario. Ecosystem health standards derive from societal values and scientific concerns. Biodiversity is important from both perspectives, and is thus a key biophysical component of ecosystem health. The landscape study areas were self-contained headwater basins within the Grand River Watershed. These were selected in order to contrast impacts originating from Old Order Mennonite and more conventional farming systems. Farm land use management indicators were used to compare farm stressors, while biophysical response indicators focused on bird and fish communities and habitats in order to compare structural and functional aspects of biodiversity between the two study areas. Indicators developed from fanner interview and air photo data identified differences in land use and habitat pattern, farm inputs, and farm intensity. The conventional farm landscape was more 'coarse-grained', i.e., contained larger farms, larger fields, and less fragmented woodlot habitats. Farms in this area featured more specialized crop and livestock systems, and were more dependent on some chemical inputs (e.g., mixed grain fertilizer). The Old Order Mennonite landscape featured greater proportions of land associated with homes and farm buildings (i.e., 'farmstead' habitat), and of pastured riparian land. Farms in this area were more mixed in terms of crop and livestock components, and featured higher cattle densities. Stream habitat indicators representing channel structure and water quality revealed similarities between the two study areas, however, concentrations of total phosphorus, ammonia, and potassium were higher in the Old Order Mennonite farm sites. These farm management and habitat differences contributed to several differences in bird and fish communities between the two areas. Of birds surveyed in the Old Order Mennonite landscape, exotic species were relatively more abundant, while forest interior-using species were less prevalent. Fish communities sampled in this area were less diverse, and functionally, less balanced due to the dominance of a single species (Brook Stickleback). Collectively, these habitat and community differences indicate that, from a biodiversity standpoint, biophysical health is maintained to a greater extent in the conventional agricultural landscape.