How Jack Pines Came to Indiana Dunes: A Northern Tree Stranded by the Ice Age

The jack pine (Pinus banksiana) is a tree of the northern evergreen forests. Yet at Indiana Dunes, on the southern shore of Lake Michigan, it grows in its southernmost natural stands anywhere.

Jack pines often grow near "pannes," wetlands between the dunes. NPS / Zachary Lindeman

So how did a northern tree end up this far south?

Cowles's answer, for schoolchildren

In 1925, Dr. Henry Chandler Cowles and Bertha Morris Parker, of the University of Chicago's School of Education, published The Book of Plants for middle-school students. In a chapter on jack pines, Cowles told the story.

The jack pine's natural range. Its southern tip is at Indiana Dunes. USGS

The Indiana pines, he pointed out, grow farther south than jack pines grow anywhere else in North America — and North America is the only place they grow at all. His explanation went like this:

1. Before the ice. A few thousand years ago, as he put it, jack pines grew in the northern evergreen forests with spruces and firs, probably nowhere as far south as northern Indiana. They couldn't spread south, because oaks, maples and other hardwoods filled the land.
2. The cold came. Winters lengthened and summers shortened until not all the winter's snow melted. Year after year it piled up, and the mass turned to ice — a glacier many times thicker than a school building is tall, covering hundreds of square miles.
3. The march south. As the ice crept south, the cold killed the northernmost hardwoods and made room. Pines can't walk, but their seeds travel — by wind, perhaps by animals. Seeds blown toward the ice died; seeds carried south grew. The forest moved south a step at a time, spruces and firs with it, keeping ahead of the slowly spreading ice. Eventually ice hundreds of feet thick covered what is now Canada and almost all of Wisconsin, Michigan, Iowa and northern Illinois, and jack pines grew only as far south as southern Indiana and Illinois.
4. The retreat. When the climate warmed, the hardwoods returned and pushed the evergreens north again — at least four times over.
5. Stranded. The last time, some pine seeds fell on barren sand near the southern end of Lake Michigan. The hardwoods crowded the spruces, firs and pines off the good soil — but couldn't grow on the sand themselves. So the jack pines stayed.

A jack pine forest on the lakefront near Gary, Indiana, in 1903. Photograph by Ira Benton Meyers; University of Chicago Photographic Archive, aep-inn179, Hanna Holborn Gray Special Collections Research Center, University of Chicago Library.

Dunes formed, and jack pines grew on the young ones. Even now, Cowles noted, as soon as a dune becomes fit for oaks the pines are crowded out — but there are always new dunes not yet ready for oaks. The trees, he wrote, "should remind you of the time when a large part of North America was a barren dreary waste of ice and snow."

A jack pine branch and cone at Indiana Dunes, early 1900s. Photograph by William Johnston Cribbs; University of Chicago Photographic Archive, aep-ins255, Hanna Holborn Gray Special Collections Research Center, University of Chicago Library.

The same kind of branch today. NPS / Zachary Lindeman

Jack pines at Indiana Dunes today

The park describes jack pines as relics of the Ice Age, from a time when a vast sheet of ice covered northwest Indiana. They survive on poor soils and in harsh conditions where other trees can't. In the dunes' plant succession they usually grow near the lakeshore, after cottonwoods and before oaks. Along with other northern species, they show how varied the park's habitats are, and how it has served as a refuge.

A jack pine in a coastal dune complex. NPS / Zachary Lindeman

Jack pines among the dunes. NPS / Zachary Lindeman

See them on the Dunes Succession Trail at West Beach or the Paul H. Douglas Trail in Miller Woods — and help protect these habitats by staying on official trails.

Sources

Based on "Jack Pines on Lake Michigan's Southern Shore," National Park Service, Indiana Dunes National Park, including an excerpt from Henry Chandler Cowles's chapter in The Book of Plants (1925), which is summarized here and quoted once. An undated illustration from the Westchester Township History Museum and a photograph by Joe Gruzalski are left out; rewritten in hubnx's own words.