Tom's Blog

Tuesday, January 11, 2011

Restoration of grazed oak savannas

Many remnant oak savannas are grazed or have been grazed in the past. As I have pointed out elsewhere, if the open-grown oaks are still present, these are prime candidates for restoration. If the savanna has been heavily grazed, there is probably little "good" herbaceous understory (grasses or forbs), and the best thing is to kill off the remaining understory with herbicide and start over, such as one does when planting prairies into ag fields. However, many oak savannas are not heavily grazed, and a less drastic approach may be possible.

Recently I discovered a fascinating article by Christopher Bronny, who was a junior high school teacher in Illinois. ("One-two punch: grazing history and the recovery potential of oak savannas." Restoration and Management Notes Vol. 7, no. 2, Winter 1989, pp. 73-76). Bronny had access to a site in Knox County, Illinois which had been grazed, but had outstanding open-grown bur and white oaks. He was able to fence off 3.7 acres. Surprisingly, a number of "good" savanna species came back quickly, including purple milkweed! Later he found lots of savanna and prairie species coming up. By the second year, he knew this site had strong potential for recovery when Turk's-cap lily, pale spiked lobelia, pale Indian plantain, New Jersey tea, red milkwort, white prairie clover, early buttercup, violet bush clover, yellow star grass, short green milkweed, false Solomon's seal, frostweed, showy tick trefoil, woodland sunflower, Short's aster, early and gray goldenrod, heath aster, little bluestem, Canada milkvetch, and hazelnut all cropped up.

"Obviously the vigorous response of these plants once grazing ceased demonstrates the tolerance to prolonged grazing. But how long they will survive grazing, and how survival is related to grazing intensity remains unclear."

Bronny uses the term "cryptic" to refer to these species, because they weren't visible as long as the cows were on the site, but were obviously ticking along in a repressed site. And of course, there are species that are very sensitive to grazing and would be long gone, such as compass plant and lead plant.

In some ways, a grazed site may be preferable to an abandoned site. Once the cows are gone, brush arrives in a major way, and shades out the understory. But grazed sites generally remain fairly open.

The possibilities for oak savanna restoration are endless.


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