WHAT ARE SAND DUNES?
Most of the NorthShore property is within the boundaries of Michigan’s designated Critical Dunes that are protected under the State of Michigan’s law and regulated by the Michigan Department of Natural Resources. In fact, the Legislature of the State of Michigan has found that Critical Dune areas of the state are a “unique, irreplaceable, and fragile resource that provide significant recreational, economic, scientific, geological, scenic, botanical, educational, agricultural, and ecological benefits to the people of Michigan.” To see a map of Critical Dunes areas in Saugatuck Township, click here.
According to the Michigan Natural Features Inventory, “globally imperiled” interdunal wetlands (or wetpannes) are found throughout the Saugatuck Dunes. Out of “at least 21 distinct interdunal wetpannes” in the Saugatuck Dunes—roughly a dozen occur either in the Saugatuck Harbor Natural Area or the NorthShore property.
These wetpannes are very unique and provide refuge for several endangered plants and animals that can survive nowhere else. For example, the Blanchard’s Cricket Frog and a rare wetland wildflower called the Zigzag Bladderwort both rely on this healthy habitat for their continued existence. Both of these endangered species have been documented on the former Denison property by the Michigan Natural Features Inventory.
Dune Life Zones
According to the State of Michigan Department of Natural Resources and Environment’s website, dune habitat consists in general of several distinct parts, including beaches, foredunes, interdunal wetlands, and back dunes:
“Beaches are zones where water meets land. The constant movement of sand by the wind, pounding storm waves, and winter ice and snow make this a formidable habitat for any living thing. For this reason, few plants or animals live on the beach. Most wildlife seen there are just visitors. Among these visitors are scavengers ranging in size from small flies and beetles to shore birds, herring gulls, and even bald eagles. The remains of fish, birds, and insects washed ashore provide food.
“Mammals that venture down to the beach include the raccoon, skunk and fox, which wait until dark to search the shoreline for food.
“The sea rocket is one of the few plants specially adapted to withstand the pounding of waves and other adverse conditions. It sinks its roots to the water table and stores water in its succulent leaves.
“The foredune is the first ridge behind the beach. Although foredunes are above wave action most of the time, they are regularly subject to storm waves.
“Like the beach, life in the foredune is a daily struggle against shifting sand, scarcity of nutrients, rapid water drainage, high evaporation rates, and storms. Out of the reach of waves, a few hardy plants, such as marram grass and sand reed grass, are able to survive. These grasses are known as pioneer species, because they are one of the first plants to become established, and they create habitat for other plants by stabilizing the soil with their extensive root systems, thus increasing the soil’s capacity to retain water and nutrients. Marram grass spreads quickly by sending stems to the surface to form new plants. As drifting sand accumulates in the marrarn grass, the central stem continues to grow, keeping the plant’s leaves exposed to the sun and air. This keeps the grass from being buried and increases the height of the foredune.
“A foredune stabilized by these grasses can host a wide variety of wildflowers and shrubs. They include beautiful clusters of the yellow hairy puccoon, the common milkweed, beach pea, sand cress, smooth rose, bearberry, poison ivy, wild grape and sand cherry. Foredunes will remain stable as long as the vegetation is undisturbed.
“Unlike plants, animals can escape the extreme temperatures and harsh conditions. Most birds migrate seasonally or retreat daily to the cover of heavy vegetation. Many animals are nocturnal and are most active during the cooler nighttime hours. Like the plants, animals that live on the grass covered foredune have special adaptations that help them survive the extreme temperatures of summer and winter. Surface temperatures on the open dunes can reach 120 degrees Fahrenheit. The sand wolf spider is adapted to extreme temperatures by living in a burrow deep under the sand. Its sandy brown color also helps it blend into its surroundings when leaving its burrow home.
“Interdunal wetlands are shallow ponds or pools located between dunes. They typically are found between low dunes or sand spits created when water levels drop or as shoreline currents change. Ponds may vanish during dry periods. These fluctuations in water table are important for plants such as the threatened Houghton’s goldenrod.
“The animals and plants found in and around interdunal wetlands are similar to those inhabiting most ponds. Insects like water striders may skate across the surface. Whirligig beetles make erratic patterns on the surface. Shorebirds, like the greater yellow legs, feed on the rich insect life. Spikerushes and sedges grow in the shallows.
“Dune forests can be found on stabilized dunes protected from intense wind erosion. The dominant forest type varies as one travels north along the coastline. In southern Michigan dunes, oak hickory forests are common. Northern dune forests are dominated by beech, maple and hemlock.
“The uniqueness of dune forests stems from the fact that they develop on steep, barren sand slopes that are a short distance from open dunes. The contrast between the cool, shaded dune forest and the extreme temperatures and intense sunlight of the open dune can be striking. Though thin and slow to accumulate, the topsoil of dune forests supports a variety of spring wildflowers and woodland plants.
“Studies of dune slopes reveal varying patterns of vegetation, depending on the direction of sunlight and the amount of shade, moisture, and protection from the wind. For example, Eastern hemlocks prefer shady, north facing slopes. Spring wildflowers such as the white trillium bloom in abundance on south facing slopes where they can absorb more sunlight.”