By Tina Patterson and Dave Wendling
September 25: Twin Waterfalls has so many reasons to be on the Odyssey list of Showcase Sanctuaries that it is hard to know where to begin. It was the MNA’s 100th acquisition, and although it is only 15 acres, it contains two waterfalls. The Rudy Olson Falls, previously called Tannery Falls, was renamed in honor of member Rudy Olson, and Memorial Falls is named to honor more than one hundred past MNA members who had contributed to the association by the time of this acquisition. Adrienne Bozic, our very energetic and knowledgeable Regional Stewardship Organizer, led the field trip and explained how this is one of the most visited of the MNA sanctuaries, and that is one of the dilemmas of this natural wonder. Located next to a Munising neighborhood, the falls have for many years been used as a neighborhood park, and evidence of its use is everywhere, and it can be difficult to maintain the sense of isolation that is often valued in a sanctuary. While we hiked, we often came upon other hikers, photographers, and dog walkers. While used as a location for many wedding photographs and family portraits, the falls are also unique in that one can actually walk behind the spray for a unique perspective of looking out from behind a waterfall.
The geology here also makes for an interesting experience and in a large part determines some of the special plants that can be found here. The majestic vertical walls of both of the waterfall canyons are part of the Munising Formation, which consists of ancient sandstone that is about 550 million years old. The buff, rose-colored sandstone is soft rock easily eroded by ice and water, due to its composition of small quartz partials that resemble beach sand. The upper rock capping the Munising Formation is made of harder dolomite sandstone, known at the Au Train Formation. This cap erodes at slower rate than the surrounding rock, which results in the shelf over which the water drops. One special fern that requires this type of habitat to survive is the slender cliff brake fern. It grows in the large horizontal crevices in the sandstone where seepage through the rocks supplies constant moisture. Unfortunately for us, this year was especially dry, and the fern was not at its best. Many other ferns and interesting plants can be found on the sandstone and throughout this sanctuary.
As Adrienne led us into a grove of American beech trees, she showed us white streaks that were covering the smooth bark of all the beech trees. She explained that this is the characteristic sign of beech bark disease, which will, sadly, kill all of them within the next five years. She explained that the entire Lake Superior shoreline beech population is being disseminated as a result of this disease. Beech bark disease is caused by an alien beech scale insect Cryptococcus fagisuga, which feeds on the sap of the trees and allows at least two species of Nectria fungus (one of which is alien) to enter the inner bark and kill the tree. The white streaks are produced by the scale insect which secretes a wax-like substance that covers their bodies. This waxy material will actually rub off on your fingers. Adrienne worried about what will happen to the bears and other woodland animals that are dependent upon the beechnuts for their survival. She warned that beech bark disease is likely to spread south and affect all of Michigan’s beech trees. There is some hope because some trees may be resistant to the disease, but the majority of our beech trees are not.
Sharing the same sandstone rock formations as the Pictured Rock shoreline, the Twin Waterfalls Memorial Plant Preserve is a somewhat challenging hike due to the changes in elevation and narrow trails. At many points, however, it is truly spectacular and an especially interesting sanctuary to introduce children to the wonder of the natural world.