Newspaper article MinnPost.com

A Disappearing Ecosystem: Minnesota's Oak Savannas

Newspaper article MinnPost.com

A Disappearing Ecosystem: Minnesota's Oak Savannas

Article excerpt

Oak savannas -- open grassland studded by tall, spreading oak trees -- once covered 10 percent of Minnesota, mostly in the southeast quarter of the state. They are an attractive ecosystem for animals such as deer, turkeys, and red-headed woodpeckers. Before European immigration, indigenous people valued the savannas for the good hunting they provided, fostering and maintaining them through the use of regular fire. In 2017, only about one percent of the savannas that existed 200 years ago remain.

The oak savanna is a transitional ecosystem, between prairie and woods. In Minnesota it consists mainly of scattered bur oak trees amid grasslands. Historically, the state's savanna lands existed mostly in a band from south of what became the Twin Cities to the Iowa border. This was the northern extension of savannas that covered most of present-day southern Wisconsin and southern Iowa, northern Missouri and Illinois, and large fractions of Oklahoma and Texas.

Oak savannas can exist and persist only where there is regular fire. Without fire, the transition zones tend to fill with brush, shrubs, and fire-intolerant trees; the savannas turn into woods. Before large-scale Euro-American immigration, prairie fires took place regularly in Minnesota, but natural fires, caused by lightning, did not happen widely enough or often enough to maintain Minnesota's vast savanna land. That oak savanna was a human creation.

Before the arrival of settler-colonists, American Indians made frequent use of fire all across North America, for hunting and to create and maintain open land. Compared to oak savanna, forest was not good hunting country, nor did it produce much food. The great food-producing animals of the Midwest -- bison, deer, and elk -- fed well in the grasslands and savannas, where they were also the easiest to hunt. Indigenous people understood this, and set fires annually to preserve and extend open country. Fire also fertilized the grasslands, to the benefit of the animals and their human hunters.

Minnesota's oak savanna country occupied the territory between the Big Woods of the southeast and the open prairie of the southwest. The then-dominant tree species of southeastern Minnesota -- elm, maple, basswood -- did not tolerate fire well; regular fire keeps them in check. …

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