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Nonequilibrium Dynamics of Sedge Meadows Grazed by Cattle in Southern Wisconsin

Beth Middleton
Plant Ecology
Vol. 161, No. 1 (2002), pp. 89-110
Published by: Springer
Stable URL: http://www.jstor.org/stable/20051258
Page Count: 22
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Nonequilibrium Dynamics of Sedge Meadows Grazed by Cattle in Southern Wisconsin
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Abstract

Equilibrium theory predicts that after disturbance, ecosystems eventually regain the structural and functional properties characteristic of their predisturbance condition. This study tested this idea by examining the effects of cattle grazing and exclusion on the long-term structural characteristics of sedge meadows in southern Wisconsin. To compare structural changes in mean percentage cover and height, repeated measures analysis was conducted on two sedge meadows over a twenty year period from 1977 to 1997. One sedge meadow was recovering from cattle grazing (cattle excluded in 1973) and the other was a reference area (nearly undisturbed). Both of these study sites changed structurally from 1977 to 1997, supporting non-equilibrium theory. Additional observations were made in a heavily and lightly grazed sedge meadow that were surveyed in 1977. As based on the positions of subunits in an ordination graph produced using Non-Metric Multidimensional Scaling (NMS), the recovery sedge meadow became less structurally similar to the grazed and more similar to the reference site over the 20 year study. However, from the perspective of mean maximum height in another NMS analysis, the recovery sedge meadow became less similar to the reference site over time likely because by 1997, a shrub carr of Cornus sericea had developed in the recovery sedge meadow that had been dominated by graminoids and forbs in 1977 (mean maximum height: 1977 vs. 1997; 0 vs. 47 cm). Seedlings of Cornus sericea were invading the grazed sedge meadows and in the recovery sedge meadow (cattle excluded 4 years earlier) in 1977. A shrub carr did not develop in the reference sedge meadow. Changes in the reference site were relatively minor over this time interval; certain species either increased or decreased in dominance, e.g., Carex stricta increased in cover (1977 vs. 1997, 20 and 28 mean percentage (%) cover, respectively). A few short-term species of the recovery sedge meadow followed the tenets of equilibrium theory. These became less common or disappeared 4-9 years after cattle exclusion including Aster lanceolatus, Calamagrostis canadensis, Poa compressa, Solidago altissima and Verbena hastata. Some of these species were eaten and likely spread by the cattle. This study suggests that the progression of sedge meadow to shrub carr may not be an inevitable outcome of succession but instead can be a consequence of past cattle grazing history. Also, because the recovery and the reference sedge both changed structurally over time, the tenets of non-equilibrium theory were supported by this study.

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