Unfortunately, even intact wetlands remain vulnerable to invasion by pollutants, sediments, and exotic species, and artificial wetlands to date have duplicated neither the biological diversity nor the hydrological complexity of natural wetlands. Introductions of non-native species either deliberately or accidentally are a growing threat to native populations. These species have rendered the ecology of Lake Michigan unstable, and native mussels are threatened by accidentally introduced zebra mussels. Invasions of Illinois forests by exotic insect and plant pest species are increasing in severity and scope. Habitat fragmentation and other physical changes have surpassed conventional pollution as threats to ecosystem functioning.
Farms are increasingly more specialized.
Illinoisans are arraying themselves on the land in suburban densities. The trend has had effects on air quality, petroleum consumption, and land use that are disproportionate to the population. One estimate found that 17 of Illinois' top 20 farming counties are located in or adjacent to urbanized areas as defined by the U.S. Census Bureau. Illinois still boasts an impressive range of habitat types. But habitat fragmentation and competition from exotic species have combined to render once- stable ecosystems less so.