Fall 1998

Rare "hanging fens" and the state's smallest dragonfly, the tiny bluebell.

McHenry County, Illinois

Twelve thousand years ago, the southeast corner of McHenry County was covered by an ice sheet roughly 5,000 feet thick. Some tonnage! The rich and varied soils and unique topography left by the retreating glaciers made the area ripe for the evolution of tremendous biodiversity. One jewel of the realm is Lake-in-the-Hills Fen, 240 acres of rare wild nature, home to seeps, hanging fens, and 404 species of plants. Purchased by a consortium of organizations and government agencies and managed by the McHenry County Conservation District, the land was dedicated as a state nature preserve in 1990. Recently, the Conservation District purchased 131 adjoining acres which will serve as an important buffer and habitat extension.

Come here to learn about fens and seeps. Large gravel deposits left by the glaciers allow rain water to percolate down until it reaches a less permeable layer, usually clay. Choosing the path of least resistance, the water travels horizontally, absorbing minerals and alkalinity from the gravel. Within the preserve are several places where the clay layer is exposed and the water is able to "seep" out. Unlike single-source springs, seep water exits the ground all along the line of the exposed clay. When the exposed clay layer lies up a hillside or near the top of a hill, the emerging water from the seep runs downhill. These geological features are called "hanging fens," designating a wetland on a slope. Lake-in-the-Hills has nine seep locations and eight of them include hanging fens. There are only 26 acres of hanging fens in the nation and Lake-in-the-Hills has approximately four of them. Among the rare biological communities found at this site are graminoid fen, calcareous floating mat, low shrub fen, calcareous seep, dry gravel prairie, and sedge marsh.

Fen water is alkaline (unlike a bog, which has acidic water) and is heavily laden with minerals. The water stays a constant 50°F, having traveled through the ground, so it continues to flow year-round. Not surprisingly, this rare geological ecosystem harbors many of the site's 16 threatened and endangered plant species such as the false asphodel. The fen is also home to the state's smallest dragonfly, the tiny bluebell, found at only one other site in Illinois.

Lake-in-the-Hills also harbors prairies and gravel hills. On the south side of the preserve, you'll see a berm-like hill known as an "esker." Its north and south exposures harbor many special plants such as Hills' thistle, prairie smoke, prairie gentian, and leadplant.

Groups of volunteers have been working for many years to clear brush and inventory the plant and animal species here.

Lake-in-the-Hills Fen is open year-round during daylight hours. There are 1.25 miles of mown trails, and guided nature walks are conducted at 2 p.m. the second Sunday of the month (May — October). Don't miss the observation deck on an adjacent hillside, outfitted with a descriptive plaque and telescope by local benefactor, Joan Larsen.

To arrange a guided walk for private groups, including for hearing- or visually-impaired, call stewards Alan and Barbara Wilson at (847) 658-0024 or the McHenry County Conservation District (815) 678-4431.

— Alan and Barbara Wilson