Iowa's oak savannas: Rekindling a Relationship
"Oak Savanna" is arguably the most rare and least understood of Iowa's major ecosystems, though it once comprised an estimated 10% of our vast, native landscape.
Karl DeLong, a retired ecologist at Grinnell College, is restoring 30 acres of his own land to savanna. "Savannas need to be restored and preserved for their own sake," notes DeLong. "They are beautiful and they give us a glimpse of our history. Studying the factors and processes which forge this community will enable us to be better caretakers of the land."
This article appeared in the Summer 2003 issue of the Iowa Natural Heritage magazine.
By Molly McGovern
Definitions of Midwestern oak savanna-also known as oak groves, oak openings and oak barrens-are as numerous as the people interested in the topic. Simply stated, a Midwestern oak savanna is an ecosystem consisting of two key layers: an overstory of primarily open-grown oak trees, and a groundcover composed of grasses, sedges, wildflowers and occasionally brush. Prairie fires, which frequently permeated the savannas, were critical in maintaining this two-tiered structure.
With no sizeable, high-quality remnant savannas in the state, Iowans are left with spotty historical accounts, degraded remnants, pioneering restoration efforts and our imagination to piece together the great complexity of plants, mammals, birds, insects, reptiles, amphibians, fungi and other components that made up our oak savanna communities.
Fire under the oaks
Oaks were the predominant tree species of Iowa savannas. Bur oak was probably the most ubiquitous savanna tree due to its superior ability to tolerate fire and a wide variety of soil and moisture conditions. The bur oak has several adaptations to fire including an extensive root system; thick, corky bark; and rot resistance even when scarred by fire. A thick, woolly cap protects its acorns.
Young bur oaks are able to vigorously re-sprout when "top killed" by fire. Each year these fire-grubbed re-sprouts build a deeper, stronger root system, thicker trunk and bark, and greater energy stores. These bur oak "grubs" bide their time until a wet year or other prolonged interruption in the fire cycle occurs. Using their built-up reserves, they seize the opportunity to shoot up past the "grubbing" stage and-with any luck-survive as mature trees.
Oaks not only tolerate fire, but their flammable leaves promote it. Fire probably reduced the spread of disease in oaks by incinerating unhealthy individuals.
While less tolerant of fire than bur oaks, white oaks were also a major component of oak savannas. Red oaks, swamp-white oaks, black oaks, chinkapin oaks, hickories and walnuts were present on a more limited, site-specific basis.
Savannas in the landscape
Historical accounts and clues in the landscape indicate that the location of oak savanna on the vast prairie landscape varied from the lone bur oak on the clay ridge-top to the swamp-white oak savanna in the river bottoms. Stands of oaks dotted the eastern rims of major river valleys, occupied islands surrounded by lakes or wetlands, and ventured out from the deeper woodlands and forests of eastern Iowa onto the prairie.
However, even with adaptations to fire, oaks generally needed some other form of protection to lessen the severity or frequency of searing prairie fires. This protection came in the form of wetland complexes, major rivers, streams, side-hill seeps, steep topography, bluffs and other local environmental factors such as the movement and habits of bison and elk. On any given site, these ever-changing factors-along with climate-dictated savanna's advance and retreat for centuries.
The human connection
Humans have long supported and been supported by oak savanna. Native Americans fostered the openness of the savanna with annual fall burning. They depended on savannas for many things, including firewood, building materials and campsites that provided shade but remained open, breezy and easily traversable.
Savannas also captivated the hearts and pens of early European explorers and settlers. Numerous written accounts eloquently convey the beauty, sense of security and serenity these mighty groves must have provided to the peoples of Iowa for thousands of years.
"Among the oak openings you find some of the most lovely landscapes of the west, and travel for miles and miles through varied park scenery of natural growth, with all the diversity of gently swelling hill and dale; here the trees are grouped or standing single, and there arranged in long avenues, as though by human hands, with strips of open meadow between." — H.L. Ellswort, Illinois in 1837.
More quotes about early oak savanna
Demise of the savanna
Despite-or perhaps because of-the human attraction to savannas, Midwestern savannas suffered a near complete demise within 50 to 80 years of European settlement.
Many savannas were chosen as ideal sites for homesteads and towns, giving rise to place names like Linn Grove, Eagle Grove and Ida Grove. Others were purchased and logged or railroads. Savannas flat and rich enough to be farmed were cleared and plowed. Areas too poor for row cropping were often grazed, logged
Around the late 1800s, the prairie fire era ended-initiating the last major oak regeneration event in Iowa. Oaks grubbed for years by fire were able to reach for the sky, unimpeded by future burns. Most of the large oaks in our woodlands today derived from this event. Unfortunately, fire cessation also allowed many fire-intolerant species to sprout and grow, converting many oak savannas to dense oak forests in a mere 20 to 40 years.
Rekindling a relationship
In the 1980s, Steven Packard, initially working with prairie remnants along the North Branch of the Chicago River, began mixing fires and oaks once again. His successes, failures, research and observations triggered a Midwestern "rediscovery" of oak savanna by scientists, conservationists and nature enthusiasts.
Inspired by Packard, many Iowans are rediscovering and restoring what remains of our oak savannas. By removing brush and conducting controlled burns, they "liberate" oaks from the choking effects of secondary tree and brush growth-which liberates an astonishing array of other species as well. Suddenly, after more than 100 years of fire suppression and other abuses, sedges flourish and spread, wildflowers bloom as never before seen in our generation, and insects, reptiles and birds respond and return.
Though we may never fully know or understand this degraded ecosystem, seeds of hope are becoming seedlings of hope as the fire renewing process begins and fire-grubbed oaks begin to take root.
Molly McGovern is a botanist and prairie/savanna enthusiast. She and her family live on INHF's Snyder-Heritage Farm, where they witness daily progress on the site's 80-acre savanna restoration.
Map of potential Iowa Savannas before European settlement
Locator map for selected Iowa savannas you can visit today
References for this article
Related article on critical role of fire in natural landscapes