Plant Succession

What is Succession?

The Indiana Dunes is a diverse landscape built over thousands of years. The park reflects how the forces of Lake Michigan and the natural process of changing plant communities transform bare sand at the beach to an oak-covered dune.

That process, called ecological succession, describes how a natural group of plants gradually alter their environment so much that they are replaced or “succeeded” over time by different species. Succession was a new concept in the late 1800s when University of Chicago professor Henry Chandler Cowles first brought his students here to study it. Using the area as a natural laboratory, he showed that plant communities succeed each other in a predictable pattern. He achieved worldwide recognition not only for himself but also for this sand dune country along Lake Michigan’s coast. Because of his work, the dunes became known as the Birthplace of American Ecology.

Today, the National Park Service continues to study succession and works to protect and maintain these unique places. Please remain on officially desginated trails and leave no trace of your visit for the benefit of this and future generations.

The story of succession plays out along the lakeshore. One great place to experience the changing habitats is along the Dune Succession Trail at West Beach.

Learn more about the history of plant succession with this video.

 

Beach pea (Lathyrus japonicus) is a state-endangered plant in Indiana.

Zachary Lindeman

Beach Habitat

The bare sand at the beach seems an unlikely beginning for an oak-covered dune. Yet only a few thousand years ago, the shoreline was a mile inland, south of Route 12. As sand was deposited and the lake receded, plants advanced to join the wind and lake in changing the shape and texture of the land.

Opportunistic scavengers like raccoons and herring gulls patrol the shore for animal or plant debris, while scattered annual plants like sea rocket and beach pea survive the harsh conditions of the lakefront. Lake Michigan’s currents and waves wash in grains of sand to the shore. Water and wind roll the sand inland to the first line of plants, which catch and pile it up. This process formed the long, narrow foredune parallel to the beach.

Learn about a beach pea reintroduction project at Indiana Dunes.

Learn more about foredunes and the geology of Indiana Dunes.

 

Marram grass begins the first foredune away from Lake Michigan.

Joe Gruzalski

Dune-Builders

Marram grass is the first widespread plant away from the beach and most important of the dune-builders. It can be seen on dunes all around the Great Lakes and along both the Atlantic and Pacific coasts. Marram grass not only survives the barrage of sand that the lake and wind bring, but it thrives on the rapid sand burial. While green blades of grass form the visible part of the plant, most of its growth takes place in specialized underground stems called rhizomes. At least a dozen internodes, the sections between each joint of these stems, develop each year. If sand piles up fast, the internodes will be long. But if summer breezes are gentle and the sand piles up slowly, the internodes will be short. In sheltered places where there is no wind or sand buildup, the underground roots poke above ground where they may die from exposure. The rhizomes and roots of a single marram grass plant may spread up to 20 feet in all directions. A typical dune is held together beneath the surface with a dense network of these underground threads.

The Eastern cottonwood tree—with its glossy, spade-shaped leaves, is another important dune-builder. Unlike the grass, it needs a low, sheltered spot to sprout; but by the time it is a few feet tall, it can also survive sand buildup. As the tree’s stems are buried, they begin to function as roots; and new stems appear above ground.

 

Little bluestem and marram grasses swirl around an open sandy area; grape vines cover the ridge.

Joe Gruzalski

Open Dune Habitat

Nonliving conditions or abiotic factors such as light, wind, and soil moisture affect the path of succession. Because of the more sheltered conditions behind the foredune, you will find new plant communities developing among these older dunes. Little bluestem grass can be found here where the sands are more protected from the lake’s winds. Look for a subtle change in color between the leaves of little bluestem and marram grass. Although little bluestem cannot build dunes, it grows in thick sturdy clumps and can help hold sand in place.

Endemic to the western Great Lakes, dune thistle or Pitcher's thistle is federally endangered species specialized to live in the open dune habitat. Dr. Noel Pavlovic of the United States Geological Survey has studied Pitcher's thistle for decades.

Other typical dune plants that grow here beyond the reach of the wind’s main force are sand cherries, distinctive three-leaved hop trees, and an increasingly varied collection of wildflowers. A common dune plant is sand cress. Its tiny white blossoms bloom alongside yellow-flowered puccoon throughout most of the summer months. Shrubby species begin to shade more sand and reduce the soil temperature. As plants die and decay, their remains enrich the soil. Changes in these abiotic factors produce conditions suitable for an even greater variety of trees, grasses, shrubs, and wildflowers.

 

Jack pine trees along the Dunes Succession Trail at West Beach.

Joe Gruzalski

Jack Pine Barrens

Naturally, jack pine trees do not grow south of Indiana Dunes. The majority of the jack pine's range occurs in Canada. The first jack pines flourished here soon after glaciers melted back north around 14,000 years ago, when the region’s climate was much cooler. The ground-hugging arctic bearberries and common juniper bushes that thrive beneath the pines are other northern or boreal relicts from this time.

Today– nutrient-poor, sandy soils and Lake Michigan’s microclimate provide the conditions necessary for the pine's survival. Where pine barrens occur on pitted outwash and rolling topography, cold air collects in the depressions and forms frost pockets. Red squirrels chatter on the their branches while brown creepers search for insects along their trunks. These barrens form a typical upland plant community that is adjacent to coastal panne wetlands.

Explore jack pines and other boreal relicts along the Dunes Succession Trail at West Beach.

 

A "panne" wetland viewable from the eastern overlook at the West Beach Bathhouse.

Joe Gruzalski

Panne / Intradunal Wetland

A panne is a unique coastal wetland whose water levels are influenced by rainfall at the surface and Lake Michigan underground. While pannes often have standing water in the spring, they may not even resemble a wetland by summer’s end. They demonstrate how the process of ecological succession is not always an orderly one. These pannes differ in origin, age and plant species composition from numerous interdunal ponds found farther inland in older dune systems. The saturated sand and pond water of interdunal wetlands along the lower Great Lakes is neutral to moderately alkaline because of traces of calcareous minerals in the lake-edge sands. In part because of the unique soil and water chemistry, pannes now provide habitat for plant species found nowhere else in Indiana

Pannes are created as wind carves a channel through a low spot between the dune and lake and blows the sand out down to the water table. Many of the plants and animals in and around this wetland are different from those on the dune slopes, and even from other wetlands in the park. Rosepink, Kalm’s lobelia, and Kalm’s St. John’s wort grow along pannes’ edges, while the Fowler’s toad lays its eggs and passes its tadpole stage in the deeper portions.

Learn about the restoration of a panne at Indiana Dunes.

 

Wind-carved hollow known as a "blowout."

Joe Gruzalski

Blowout

This steep-sided valley is called a blowout. Like pannes, blowouts form when wind whistles in through a low spot in the dunes and carves out a depression. But unlike pannes, these depressions do not reach the water table.

Blowouts may be viewed along the Dunes Succession Trail and West Beach and trails 9 and 10 within Indiana Dunes State Park. The Kemil Beach parking lot is located within a blowout, and the beginning of the Dune Ridge Trail there takes you through this habitat.

Off-trail footsteps have worn away more of the protective vegetation in recent years. Thus, many of the plants you see here are the same you saw beyond the foredune along the beach. Please stay on official trails to prevent unnatural disturbances that disrupt the process of succession.

 

Tucked between beach ridges and dune-capped beach ridges; these long, linear wetlands in Miller Woods are known as interdunal or interridge wetlands.

Joe Gruzalski

Swale / Interdunal Wetland / Interridge Wetland

The water-level fluctuations of the adjacent Great Lakes are important for the dynamics of the interdunal wetlands. Interdunal wetlands are formed when water levels of the Great Lakes drop, creating a swale or linear depression between the inland foredune and the newly formed foredune along the water’s edge. When Great Lakes water levels rise or during storm events, the interdunal wetland closest to the shoreline can be partially or completely buried by sand. Summer heating and evaporation can result in warm, shallow water or even complete drying within the swale.

The Great Marsh is an enormous interdunal wetland that stretches 10 miles from Mount Baldy to the Port of Indiana. It represents a dramatic drop in lake levels. The far western edge of the Great Marsh is known as Cowles Bog, a unique assemblage of a variety of unusual wetland types.

Lake Michigan created a pattern of alternating sand ridges and swales at it's southernmost point near Gary, Indiana. The topography lended well to development, where ridges could be spread into the swales to level the ground. Today, ridge and swale topography is globally rare and can be best experineced on the Paul H. Douglas Trail through Miller Woods. Other portions of ridge and swale are protected in the region by Indiana Department of Natural Resources, Shirley Heinze Land Trust, and The Nature Conservancy.

 

Boardwalk along the Dunes Succession Trail at West Beach.

Joe Gruzalski

Oak Woodland

In summer, the temperature in this woodland is often as much as 10ºF lower than the open slope on which you just walked. Most of the tallest or canopy trees here are black oaks, red oaks, and basswoods. Beneath the tall oaks are slimmer sassafras, dogwoods, and witch hazel shrubs. This variety of trees indicates that this dune is far enough from the lake to be protected from harsh winds and old enough that the soil has been enriched by previous plant communities. But succession’s path can also be changed here. Wind can blow loose sand from the open dune down into these woods, altering the soil and the plants that use it.

The density of the woodland is dependent on how often fire occurs on the landscape. If fires happen regularly on the landscape, an oak savanna habitat may develop– characterized by scattered oak trees with prairie grasses and flowers beneath. Oak savannas are critically imperiled globally. The Paul H. Douglas Trail through Miller Woods showcases some of the highest quality remaining black oak savanna habitat.

 

Hikers descend the stairs along the Dunes Succession Trail at West Beach.

Joe Gruzalski

Sand-mined Landscape

The flat expanse of West Beach's parking lot and the surrounding area once contained rolling, wooded dunes like those surrounding it. In the early 1900s, sand-miners leveled and hauled away the dunes to use the sand for construction purposes. Today, over a hundred years after this disturbance, what was once loose sand has again succeeded into a mix of plant communities not unlike the open dune habitat closer to the beach. Small mounds of sand are stabilized by little bluestem and tall sand reed grass, as well as by sand cherry and hop tree shrubs. If succession is allowed to continue uninterrupted, someday there may be an oak woodland here once again.

Another part of the park that experienced sand mining is Tolleston Dunes. The parking area and land expanse to the east of the trail for the first half mile is flattened because of this exploitative activity. Thankfully these disturbaces happened so long ago that the mined area filled in with mostly native species.

Many areas of the Indiana Dunes region have experience sand mining. Check out this report on the history of sand mining within the Indiana Dunes.