Tucked into rocks and cliffs on Lake Superior’s wild and rocky shores live some modest plants that normally only grow in high alpine areas or the Arctic: plants with such unlikely names as black crowberry (Empetrum nigrum), bilberry (Vaccinium uliginosum), arctic fir clubmoss (Huperzia selago), English sundew, (Drosera anglica), elegant groundsel (Packera indecora), and encrusted saxifrage (Saxifraga paniculata). Botanists refer to these species as “disjuncts,” meaning they are separate from the main ranges of their relatives. They have evolved uniquely to adapt to the extreme conditions in which they live, setting them apart from the more common natives of Minnesota. Some are even carnivorous.
These unusual plants have attracted the interest of many botanists over the years. In the 1990s, and again in the early 2000s and mid-2010s, Emmet Judziewicz, now an emeritus professor at the University of Wisconsin Stevens Point, explored the Apostle Islands and Isle Royale to record dozens of rare species: their populations, preferred habitats, and threats. One of the young technicians accompanying him as he trudged the rough shorelines and gazed at sheer cliffs from choppy waters, straining to identify tiny plants growing from the rock faces, was Sarah Johnson. Now a professor at Northland College, Johnson has devoted herself to renewing his research. “He is an amazing botanist,” Johnson said in a recent interview. “His reports are very complete and full of detail, quite remarkable.” Judziewicz’s work established where populations of these rare plants were on Isle Royale and the Apostles. “He covered more square inches of these parks than most people, maybe more than anyone else,” Johnson said. “He made hand-drawn maps, recorded details of populations sizes, and noted other species associated with the rarer ones.”
On Isle Royale, he established permanent plots, so in 2016, botanists with the National Park Service and Johnson worked together to go back to those sites, counting individual plants of 25 rare species and recording how many were flowering and fruiting. Later she did the same on the Apostles, with a list of 33 rare species. The research team digitized Judziewicz’s records and used his methods to count current numbers, to make sure the more recent data would be consistent with his.
That makes almost 30 years of close attention to these rare plants.
Anyone who has visited Gooseberry Falls State Park or other bedrock beaches will recognize the progression of plants from the water’s edge, continually slapped by Lake Superior’s cold waves, to the orange lichen, sometimes called sunburst lichen (Xanthoria elegans) that covers the rock further inland, to the juniper/saxifrage fringe, followed by low shrubs and hardy trees, with special mini-ecosystems in the plentiful pools that pock the bedrock. All these small biomes developed on glacier-scarred terrain.
The most recent glaciers began retreating north about 12,000 years ago. As they shrank, they left scoured land strewn with deposits of rock and sand. Only the hardiest of plants could make a skimpy living in this forbidding landscape. Many of the rare plants on Isle Royale now occupy sparsely-vegetated rocky shoreline habitat that is most recently exposed above Lake Superior as isostatic rebound occurs (the land is still rebounding after being squashed downward by a mile high or more of ice). Long, cold winters, short summers, icy winds, and wild temperature swings did not deter boreal and other cold-loving plants.
What qualities did these plants possess that allowed them to survive? Retired DNR botanist Chel Anderson provides an evocative description in “Living Relicts – The North Shore’s Intriguing Disjunct Flora” in Quetico Superior Wilderness News. She says their adaptations include “small and often compact aerodynamic forms, fibrous roots, insectivory, multiple reproductive and dispersal options.”
Sarah Johnson calls these characteristics “superpowers.” Encrusted saxifrage, for example, sometimes grows on cliffs that can get sun-baked in the summer. Its adaptations to this challenge are many: “It has succulent leaves to retain water in times of drought; it can eat the rock it’s growing in and excrete calcium carbonate through pores in its leaves. It can adjust the angle of its leaves to reduce water loss. It has outer leaves protecting inner leaves, and the leaves are waxy, light in color, reflecting sunlight.” Noting that its flower stalks are hairy, sometimes trapping insects, Johnson wonders if this plant could be carnivorous.
One definite meat-eater is butterwort, which supplements its sparse nutrient intake by capturing and eating insects.
By land and by lake
Johnson’s research assistants must have some of the best experiences an undergraduate student could hope to have. They don’t need to spend hours cutting back invasive species; rather they get to see unusual species in fairly intact ecosystems.
Isle Royale, as many of us know, is a long boat trip on often choppy waters. At its northeastern end cluster hundreds of islands, and during their visits, Johnson and her National Park Service collaborators moved island to island by motorboats. In calmer areas they used a canoe, which allowed them access to parts of islands where the lake is too rocky for a motorboat. Hiking across islands was sometimes harrowing, as some were covered densely in devil’s club (Oplopanax horridus), which is “pretty vicious,” all its parts covered in thorns. It seems ironic that the researchers—so eager to find disjunct plants in this environment—were harassed by a disjunct from the Pacific Northwest.
The Apostles work sounds more adventurous. “It’s like a big treasure hunt, where you have a list of species you’re looking for,” Johnson said. “I trained students on key identifying characteristics, and they’d help me find them and count them. At times we had to look for tiny plants on cliff faces using binoculars while standing on a moving boat. We’d jump off the boat to scramble on the rocky shoreline; we climbed eroding clay bluffs; we hiked around dunes and through forests; we even stayed overnight in a lighthouse. The students were seeing the rarest plants in the rarest habitats in the region.”
Climate change outlook
Johnson and her collaborators found that most of these rare plants are showing welcome signs of resilience. On Isle Royale, among the 25 species studied in 2016, “site occupancy increased for 13, remained steady for six, declining in another six.” And the majority were as abundant or more abundant than before Lake Superior’s water levels dropped for an extended period.
Lake Superior is notoriously warming faster than many other lakes; scientists say the average surface temperature in summer months has risen 2 degrees Celsius in the past 30 years. “As the Lake warms, that could influence the temperature around it, which could impact these cool habitats where we’re seeing these arctic species,” she conceded. But she remains hopeful, as long as cold waves continue to splash the shore. “Being between a rock and a big lake, many of these species don’t have much room to move, and it is possible some may be better adapted than others to keep holding on, she said. “Lake levels can also have a dramatic impact on plant life along the shore. Judziewicz did his initial surveys in the 1990s, when Lake Superior was just slightly higher than average. He returned around the turn of the century, so there is data for the longest period on record of below-average water levels, 1998 to 2013. Johnson’s survey work began at a time when Superior made a quick jump from extreme low to extreme high: 2019 saw record highs. “I wanted to see if populations remained at similar numbers across the extreme water level differences,” she said. Many did survive over the years, “so they’ve been resilient in the dynamics of the lake we’ve experienced in the last 30 years or so.”
Why should we care?
These plants are not rare worldwide, but they are rare in our region, and they are confronting a future climate in which they are likely to become even rarer. Why should we be concerned about them?
Sarah Johnson answers: “Apart from the question, ‘is it ever okay to let any species go extinct in the wild?’ this kind of long-term research can help us recognize ecosystem changes we wouldn’t be aware of otherwise.” She points out that it’s helpful to learn about these outlying populations “because they may have evolved traits that have allowed them to be more resilient, more adaptable to climate change compared to their relatives in the Arctic. Understanding the adaptive capacity of these species might help us better understand what other species might need.” And above all, “They’re intriguing, they’re charismatic, and their life story could point to changes in more common species that we’re not monitoring.”
Next summer Johnson will guide more students at Isle Royale to complete data collection at the same sites she’s visited since 2016.
Other cool spots
Our region is home to other unusual habitats, including the Algific Talus slopes in the driftless area of Minnesota, Wisconsin, and Iowa. “Algific” comes from a Greek word meaning “makes cold,” and “talus” is a cliff or very steep rocky slope, with rock fragments tumbled at the bottom. These formations occur on north- or east-facing slopes of dolomitic limestone bedrock. Water flows into the cracks and pores of the rock, freezes in winter, and slowly melts over the summer, creating cold microclimates where arctic and alpine plants can flourish. Northern monkshood (Aconitum noveboracense) is common here, along with mosses, liverworts, lichens, and ferns. Pleistocene-era snails glide along in the cool, moist landscape.
Johnson cautions that both the Lake Superior shoreline and the Algific Talus slopes are fragile landscapes, easily disturbed by human visitors. If you are exploring and come upon signs posted by the National Park Service or other authorities, please honor the warnings and leave these vulnerable places alone.
Sarah Johnson studies plant communities, plant populations, and ecological monitoring, focusing on dynamics of vegetation change across space and time. She says naturally dynamic habitats pose interesting challenges in discerning among various drivers of ecosystem change. She appreciates the experiential learning that is core to Northland College.