A Global Treasure

Algific talus slope: not easy to say, nor easy to recognize on the landscape without an observant eye. But these uncommon and delicate microecosystems are worth our attention and protection. What sets these apart from any other slope? 

Iowa has the most! 

Considered globally rare, the formation of algific talus slopes is limited to areas with Karst topography, referring to limestone or dolomite bedrock prone to dissolving, which can be found throughout the Driftless Area. And while algific talus slopes are certainly found in the Minnesota, Wisconsin and Illinois portion of the Driftless, Iowa takes the cake. The exact number is unknown, but it’s estimated that there are at least 50 algific talus slopes within the Upper Iowa River watershed alone. But they’re sensitive and can easily be impacted by land use, invasive plants and other disturbances, and it’s likely there used to be many more algific talus slopes on Iowa’s landscape prior to European settlement. Even though Iowa has a relative abundance, they’re so rare that they’re considered a globally threatened and endangered habitat. 

Geologic wonders with their own climate

Algific means “cold producing,” which is why you may have also heard them referred to as cold-air slopes. And “talus” means loose rock. But how do loose rocks produce cold air? 

Over a great expanse of geologic time, large chunks of dissolving-prone limestone or dolomite bedrock break off and accumulate at the base of a hill or cliff. Even more fractured from the fall, the rock has cracks, crevices, voids and associated sinkholes that allow winter’s cold air to venture deep underground. Water or snowmelt also seeps in, freezing into large veins of ice when meeting the super-chilled rock. Mostly insulated from the sun, the rock warms just enough with the summer heat to slowly melt the ice, releasing water vapor in a flow of cold air that can be felt as you pass by. As seasons shift, the voids retain the warmer air they pulled in over summer via those same cracks and sinkholes. Though not enough to completely melt the ice inside, passersby will notice a flow of warm air from these slopes during the colder months. 

These natural vents essentially have their own microclimate —maintaining a narrow temperature window in the immediate area between 15 and 52 degrees Fahrenheit year-round. These temperatures are reminiscent of the Ice Age, which impacts which plant and animal species want to set up shop.

They’re a safe haven

Mosses, ferns and other species you’d associate with a cooler, wetter climate are often found on algific talus slopes, along with multiple federally endangered plant and animal species.

The Pleistocene snail (Discus macclintocki), a mollusk species previously thought to be extinct, was rediscovered hiding out on Iowa’s algific talus slopes in 1980. They’re very susceptible to changes in their environment — even from simple human foot traffic — and require temperatures above 14 but below 52 degrees Fahrenheit, meaning the only place they can survive in Iowa is on these algific talus slopes. Listed as federally endangered, their population is still dwindling as more of these sites fall victim to quarrying, filling, trampling or other disturbances, as well as a warming climate.

Northern monkshood (Aconitum noveboracense) was listed as federally threatened in 1978, with remaining populations found in only three disconnected locations: the Catskill Mountains of New York, northeast Ohio, and in the Driftless area of southwest Wisconsin and northeast Iowa. With similar habitat requirements as the Pleistocene snail, this member of the buttercup family can find refuge in algific talus slopes. 

Other more common species can find respite from Iowa’s scorching summers and frigid winters on these slopes.

Left: INHF interns assist with a scientific study to search northeast Iowa’s algific talus slopes for the Pleistocene snail, a federally endangered species. Right: Moss, ferns and other species, like the Northern monkshood pictured above, thrive near algific talus slope vents due to the cool air that emits from the rock’s crevices. Photos by Brian Fankhauser, INHF  

The takeaway 

Algific talus slopes are a look into Iowa’s past, carrying forward species that would have been lost long ago. Every one of these precious slopes left in our state is worth preserving. They’re a global treasure!

If you think you’ve found one, don’t just tread lightly… don’t tread at all! Give these sensitive sites the space they deserve. Admire from afar with binoculars or a zoom camera lens.

 

Do you think you have an algific talus slope on your property?

Find resources, learn about protecting your land and connect with us at Iowalandoptions.org.