Dunes: A Shifting Landscape
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St. Joseph is located in the beach dune habitat that stretches along the Lake Michigan coast. Beach dunes are typically found along the southern coast, while perched dunes are found farther north and along Lake Superior.
Wind and water shape the dunes through a cyclical process along the Great Lakes. Water moves sand along the shore via waves and current, and both marine and inland winds transport the sand into dunes. Over time, plant growth stabilizes deposited soil and begins the process of ecological succession. High water levels, foot traffic, and severe storms also reduce soil stability, making the dunes more vulnerable to erosion and the loss of endangered flora and fauna found in the delicate ecosystem.
The area of the habitat closest to the water is the beach. Beaches are particularly challenging for plant growth due to sun and wind exposure and the frequency of rough waves. Calm waves deposit sand onshore, and strong waves carry sand offshore. On the beach, you can find plants like sea holly and sea rocket.
The next area of habitat inland is called the foredune. Foredunes are the first depositional area. High waves typically do not reach the foredune, however, as water levels rise, the risk of erosion increases. Pioneer grasses stabilize the sandy soil. Marine wind off of the lake deposits sand in this area. On the foredune, you can find plants like marram grass, harebell, sand reed grass, and riverbank grape.
Next, we have the transitional dune area. Transitional dunes have decreased wind and increased soil stability, which supports a more diverse plant pallate, including sand cherry, creeping juniper, bearberry, blueleaf willow, summer grape, and little bluestem. This area may have slacks. A slack is a boggy hollow within the dunes that often contains wetland species and standing water.
Finally, the backdunes are furthest from the water, experience the least wind, and provide the most soil fertility. Because of these conditions, backdunes contain the most plant diversity. In this area, you can find plants like canada wild rye, beach pea, red osier, serviceberry, yew, ground juniper, and kalm St. John's wort. You can also find trees like the cottonwood, linden, red maple, red oak, black oak, white pine, jack pine, and balsam fir. The cottonwood tree is the most prominent tree because it can survive the harsh conditions and grows quickly. It also reproduces by cloning, meaning that new trunks grow from its large root system.
These different areas stretching from the beach to the backdune are a visible demonstration of ecological succession. Ecological succession is the process of one plant community replacing another over time. Vegetation forms new growth above accumulating sand while stabilizing it with its roots. As organic material is added to the sand, plant diversity increases until the soil eventually supports an oak forest.
