Fens are wetlands that occur in springy areas where limestone is at or near the soil surface. As the spring water percolates through the limestone, it dissolves some of the rock and becomes alkaline and mineral rich. This unusual water chemistry poses a challenge to the growth of plants. Many plant species on the preserve are fen specialists that are adapted to these harsh conditions. There are four principal plant communities at Bluff Spring Fen: Wetland, Savanna, Hill Prairie, and Mesic Prairie. Each has a distinct assemblage of plants and animals, and presents distinct set of challenges for management and restoration.