Articles

Ohio has its own prairie patches

Timothy A. Snyder
Ohio Division of Natural Areas and Preserves
Urbana Daily Citizen Sunday, January 12, 2003

"Here are level plains, too wide for the eye to measure; green undulations, like motionless swells of the ocean; abundance of streams followed through all their windings by lines of woods and scattered groves."

The prairie as described by Francis Parkman in his 1849 classic "The Oregon Trail" was a land of broad views and black mud. To the Oregon-bound pioneers with him, it was just the first of many barriers to be crossed.

It would give them many anxious moments searching for wood and water, and take many of their families into its deep soil. It was not a place to settle. Wood for houses and barns was scarce and the sod was too thick to break with a plow.

Prairie was not new to Americans. They had first encountered patches of wildflowers and head-high grass breaking the dark forest canopy in the Ohio Country.

The farther west the pioneers went, the more prairie they saw. The tiny patches grew larger and joined together until beyond the Missouri River they dominated the land and it was the trees that were found in scattered clumps.

To the naturalists of the day, the presence of the western prairies was explained easily enough. They were due to a lack of rain the vegetation types of North America seemed to be arranged in wide north-south bands across the continent.

In the humid east where annual precipitation was high, trees grew. To the west, annual precipitation dropped below the level needed by trees and so only prairie grasses could grow.

From the Mississippi to the hundredth meridian (mid-Nebraska) grew the tall-grass prairie, lush though nearly treeless. From the hundredth meridian to the Rocky Mountains grew the short-grass prairie-scraggly water-efficient plants growing in scattered clumps. Farther still, where water became truly scarce, lay the desert.

A very tidy picture, except for one errant stroke, those Ohio prairie patches. How could plants that supposedly grew only in areas of low rainfall survive under Ohio's thirty-plus inches of annual rain?

It was a problem that occupied some of the finest minds of the last century. Many theories were proposed and much data was gathered, but it was not until 1935 when E. N. Transeau published his paper, "The Prairie Peninsula" in the journal "Ecology" that the answer began coming into focus.

Prairie plants are not dependent on rainfall, Transeau said, but on wide variations in a number of environmental factors. Because they are well adapted to climactic extremes, they can survive both drought and flood, and so can occupy dry hilltops and marshy lowlands where trees struggle. On the best sites, prairie grass grows tall and thick and shades out any tree seeds that might sprout so that, once established, prairies tend to maintain themselves.

So much for the survival of prairies in Ohio. How did they get here in the first place? To answer that, Transeau restated an earlier theory that research has since strengthened. When the eastern boundary of the tall-grass prairie is mapped, a strange thing appears: a thumb of prairie thrusting into Illinois and Indiana with unattached plots in Michigan and Ohio - a "prairie peninsula" surrounded by forest.

To explain this, Transeau suggested a long, dry period sometime after the last Ice Age. This extended drought (called the Xerothermic period from Greek for "dry heat") killed off the forests and allowed the prairie to push eastward, reaching its greatest extent about 4,000 years ago.

Then the dry trend reversed, the drought was broken and trees moved westward again until, by 1700, they dominated Ohio and the prairie was reduced to scattered outliers. Thus was born the landscape on which Ohio was built.