Species extinction is a poorly understood process, particularly at local scales, because there are few ecological data sets that span long enough time periods to reveal patterns of extinction. There is perhaps no single place on Earth where changes in the local assemblage of species have been carefully observed and documented continuously at a decadal time scale over several centuries. As a consequence, many basic questions about patterns and rates of species extinction following environmental change are difficult to answer. For example, how many species have been lost from local areas? Do extinctions follow immediately after a disturbance, or are post-disturbance extinctions delayed, resulting in an 'extinction debt' to be paid in the future? Data collected by this project will begin to fill a deficit that has limited scientists' ability to answer these basic questions. Paleontological techniques that have traditionally been used to study changes in plant communities over many thousands of years will be used to examine changes in plant communities in the past few hundred years. Seeds, leaf fragments, and pollen will be analyzed in sediment cores from disturbed wetlands in the Indiana Dunes to create a long-term ecological data set with approximately ten-year intervals from the present day to about 300 years ago. Analysis of these long-term data will advance ecological theory and aid conservation practice by supplying information critically needed to gauge what current patterns of ecosystem change mean for the future.
This project will provide training and mentorship for several undergraduate students, a high school student, a high school teacher, a technician, and a postdoctoral researcher. The project will also support the development of educational and outreach material for K-12 programs.
When natural habitats are severely disturbed, incumbent species may decline or even go locally extinct and other species may expand or invade into the disturbd habitat. These processes are important in ecological restoration and conservation biology, but they are not well understood. A disturbance may set a species population on the road to extinction, but the extinction process may take years, decades, or even longer. Similarly, invasion and expansion of new species may take a long time, and the dynamics of expansion and decline of different species may be related. Needed are studies capable of examining ecological processes for several decades following a severe disturbance. The Miller Woods section of the Indiana Dunes National Lakeshore is a remnant of what was once a vast complex of dunes and marshes. Most were destroyed in the early 20th Century with the construction of the US Steel mill and the city of Gary, Indiana. The remaining wetlands, preserved in the Miller Woods tract, were severely disturbed by the hydrological changes and habitat fragmentation. The sediments in the marshes record the changes in marsh vegetation by preserving seeds and other plant fossils. We collected cores of these sediments from 100 different locations in the marsh complex. Each core is a column of sediment, with oldest at the bottom and youngest at the top. By examining the seeds and other plant fossils at different levels in the core, and by dating the cores (a dramatic increase in metal content is a very good marker for the opening of the steel mill), we can find out what the marshes looked like before the disturbance, and monitor, retrospectively, the changes that have happened in the marsh since the disturbance. Our results so far show that the marshes were stable for several hundred years, that the disturbances led to immediate declines in some plant species, and set in motion more gradual declines in other species. Several species, including some native to the region and others not native, invaded the marshes. Some of these invasions (cattails, reed grass) are still proceeding. Perhaps the most important finding so far is that the disturbances of the early 20th century set into motion ecological changes that are still unfinished more than a century later. We are currently analyzing our data to determine whether the rates and patterns of change can be predicted from marsh size and severity of local disturbance. Our work will be of value in conservation planning, impact analysis, and restoration programs for coastal marshes of the Great Lakes region, and more generally will help ecologists, conservationists, and resource managers understand the slow dynamics of ecological systems, capable of persisting long after the original disturbances.
