This article is based on a presentation Bob Hamilton made during this spring's annual docent reorientation session in the new Ecological Research Station at the Tallgrass Prairie Preserve. Hamilton is director of science and stewardship for the preserve and has been associated with the project since The Nature Conservancy purchased the Barnard portion of the former Chapman Barnard Ranch in 1989.

Bison resting near the bison loop

Hamilton said, "We want the bison to be as natural a component on the prairie as possible. They provide ecological services to the prairie ? that's why we put them there. They are a big part of the landscape dynamic." He pointed out that bison are not being looked at as a species target because they are not a threatened or endangered species. Once on the brink of extinction, bison are now back as an economical and ecological contributor to our society. The bison population has grown from a little over 500 head in 1889 to somewhere between 300 and 400 thousand head in the U.S. today. The largest proportion of this number is privately owned.

Patch-burning is done in all different seasons in the bison unit. During the first growing season after a burn these patches attract intensive bison grazing due to the lush green regrowth. In fact, the grazing pressure on the grasses is so intense that their vigor declines which allows forbs (broad leaf, flowering plants) to thrive. Once two to three years has passed, however, the native bluestem grasses are once again dominant. The Nature Conservancy, in its effort to promote plant and wildlife diversity on the preserve likes to see the forbs as part of the plant community because it?s these plants that enhance the bulk of diversity on the prairie.

The diet of the bison herd on the preserve is not artificially supplemented so about 40% of their intake during the winter months comes from off-season summer and fall burns. These burns work against the dominant warm season grasses and allow the cool season sedges and grasses to express themselves. The bison really take advantage of these grasses because of their high nutritional quality.

In a system that's thought of as being dominated by warm season grasses by utilizing spring, summer, and fall burns, a little different grazing opportunity is offered. Hamilton says that's one thing preserve managers are trying to build into their patch-burning program. Spring burning programs common to the Flint Hills are managed to kick-start the growth of warm season grasses, but reduces the growth of some of the forb species necessary to promote prairie diversity.

A program where all the acreage is burned every spring allows animals to take advantage of high quality forage early in the growing season - so much so that it promotes double-stocking with steers from mid-April to mid-July before sending them to the feed lot. That type of program has a lot of economic sense behind it, but could explain the 6-7% annual decline in prairie chicken population. Prairie chicken numbers held steady during the 1970s and 1980s, but after double- stocking became popular these prairie chicken numbers started coming down.

Over the years researchers typically identified 70-80 male prairie chickens on the leks (booming areas) on the preserve. Their numbers jumped to about 160 in the spring of 2003 and that level has been maintained since that time. All of the acreage in the bison unit is currently under patch-burn management. As more of the preserve is put under a patch-burning regimen, it will be interesting to see what effect that has on the prairie chicken population.

Hamilton says that with the new patch-burning program under consideration with OSU, a 5-6 month grazing pattern on the cattle pasture may be instituted rather than the current 3-month grazing pattern. He said there are typically no significant differences in weight gains between annual burning and patch-burning with a 90-day grazing season. He feels that by burning in late summer and early fall and keeping the steers on the prairie an additional 90 days will give them an opportunity to graze on that rich, nutritious new growth that should in turn give them a chance to put on more weight.

6-02-05 Bill Rinehart, Conservancy volunteer (918)299-4104