Agricultural Land Fragmentation and Biological Integrity: The Impacts of a Rapidly Changing Landscape on Streams in Southeastern Wisconsin

Since the end of World War II, there has been significant population growth in the United States causing development to radiate outward from the traditional urban core. This has resulted in the metabolization of large areas of rural countryside with sprawling suburbs and exurbs. Due to the primary conversion of agricultural lands to residential development, exurbia is considered to be the fastest transitioning landscape in the United States. Even though there is limited knowledge on the effects of exurbanization, it is presumed that exurbia has the same effects on ecosystems and ultimately human health as other types of urban development. Development affects the natural ecosystems through: fragmenting landscapes, isolating habitat patches, simplifying biodiversity, degrading natural habitats, modifying landforms and drainage networks, introducing exotic species, controlling and modifying disturbances, and disrupting energy flow and nutrient cycling. We present a method for examining this transitioning landscape of exurbia utilizing the theory and practices established within the field of landscape ecology. In this paper, 31 watersheds were used to separate Southeastern Wisconsin into analyzable landscapes. The overall objectives were: (1) to identify a subset of metrics that capture the majority of variation in agriculture land fragmentation in southeastern Wisconsin, and (2) to identify a subset of metrics that capture the relationship between agricultural land fragmentation and a measure of biotic integrity (IBI: an index score based on fish population variables). Seventy-two landscape metrics were calculated and statistically analyzed. In the end, six landscape metrics were identified that explained 84 percent of the variation in aquatic environmental integrity for Southeastern Wisconsin. The parameters that were linked with higher IBI were associated with larger landscape patch area and distance between patches. Parameters contributing to declines in IBI were associated with patch shape complexity and variability. The strength of these relationships indicates that the spatial design of human development in watersheds has a significant impact on aquatic ecological integrity and that principles of landscape design may have direct relevance to efforts at river and stream restoration and protection.