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As the glaciers retreated around twelve thousand years ago, tundra plants colonized a still frozen land of bare bedrock, meltwater lakes, and glacially-strewn rocks and sediments. Yet once the land drained and deeper soils formed, trees moved in and as the climate warmed and dried, the cold, damp, open environments preferred by tundra plants largely disappeared from the region. Some tundra plants, however, survived in microhabitats on the Superior shore. Called glacial relicts, they sometimes became separated by hundred of miles from their primary range on the arctic tundra or mountain slopes of western North America (in which case they're also known as arctic-alpine disjuncts).1

The lake’s deep waters are slow to warm in summer and combine with frequent fogs to depress temperatures during the growing season. While wave spray and seepage create cool, damp pockets in dips and crevices, the inability of many other plants to survive the thin soils and harsh exposure of lakeside outcrops keeps competition at bay. Glacial relicts favor the lake’s cooler Minnesota and Ontario shores, along with the tip of Michigan’s Keweenaw Peninsula. Many also seem to prefer volcanic rocks such as basalt, which erode to produce less acidic soils.2

Each summer on the shore, the flowering of bird’s eye primroses, encrusted saxifrages, and other northern plants offers a testament to the ability of life to not only survive but thrive on the lake’s wind-wracked cliffs and ledges. 

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