Coakley Hollow Fen

Points of Interest:

• Walk a boardwalk over a unique Ozark natural community – a fen.
• See plants that are relicts of the last ice age.
• Learn about karst features of the Ozarks.

Natural History:

This natural area features a unique wetland known as a fen. Fens are wetlands created when calcareous groundwater seeps out to the soil surface. Ozark fens such as these are typically dominated by herbaceous plants and are kept open by both saturated soils and historically occasional wildfires. Coakley Hollow fen is created by groundwater moving down through the Gasconade dolomite formation and hitting a resistant layer, likely sandstone, along which the water then runs horizontally and seeps out onto the lower slopes along the valley. Nearby to the fen is the Ozark Caverns cave system which also is formed in Gasconade dolomite and like the fen is a karst feature. Coakley Hollow Creek is an Outstanding State Resource Waters.

Although small, fens are botanically rich and often support plant and insect species that are restricted to these unique wetlands. Within the 0.75 acre fen proper over 50 native plant species occur. These include plant species considered “glacial relicts.” That is, they are species that were common in Missouri 10,000 years ago when glaciers covered the upper midwest. In the intervening thousands of years Missouri’s climate has gotten warmer and drier. The glacial relict species were able to persist in fens and along spring branches where cool groundwater provides appropriate habitat conditions. Other glacial relict species in Missouri persist on cool, moist north facing bluffs. At Coakley Hollow fen, glacial relicts include interior sedge, prairie straw sedge, and Riddell’s goldenrod. Visitors to the fen may also observe the grey petaltail and the swamp metalmark, a dragonfly and butterfly species respectively, that are highly associated with fens. Although small, fens are hot spots of botanical and insect diversity.

The natural area is located in Lake of the Ozarks State Park, the largest state park in Missouri, which owes its existence to the Great Depression of the 1930s. One of the programs created by the F.D. Roosevelt administration was to buy up tracts of land that were submarginal for agriculture and turn these lands into parks and recreation areas that were then transferred to the states. This happened here at Lake of the Ozarks State Park.

In addition to the fen, this natural area has been expanded to include a larger area of high-quality Ozark woodland natural communities and the Ozark Caverns cave system.