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Effects of Grazing Intensity on Growth, Reproduction, and Abundance of Three Palatable Forbs in Kansas Tallgrass Prairie
Karen R. Hickman and David C. Hartnett
Vol. 159, No. 1 (2002), pp. 23-33
Published by: Springer
Stable URL: http://www.jstor.org/stable/20051206
Page Count: 11
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The effects of different intensities of cattle grazing on the aboveground growth, reproduction, and abundances of three palatable forbs were studied in native tallgrass prairie. Populations of Aster ericoides, Ruellia humilis, and Amorpha canescens were sampled at peak flowering during the 1993-1995 growing seasons in four annually-burned sites varying in cattle stocking density [ungrazed, low, moderate, high]. The three forbs exhibited reduced shoot growth and/or reproduction under moderate to heavy grazing, and in no case did grazing increase any measure of plant performance. Ruellia showed reduced shoot height and biomass, percentage of stems flowering, and reproductive biomass in response to grazing. Aster showed decreases in shoot biomass and height with grazing. Amorpha showed no change in shoot or reproductive biomass, but a decrease in percent of flowering stems and in reproductive allocation with grazing. Patterns in the percentage of stems grazed indicated generally high but variable palatability among these species. By contrast, the three species showed inconsistent population response to grazing. Abundance (frequency) of all three species indicated no short-term change between years in response to grazing intensity. Responses of these species differ considerably from those of most other perennial tallgrass prairie forbs that are unpalatable, unconsumed, and increase in performance (e.g. size, abundance) due to release from competition from the dominant grasses under ungulate grazing. The results demonstrate that immediate aboveground growth and reproductive responses of established adults to grazing are not good predictors of grazer effects on population abundances in tallgrass prairie.
Plant Ecology © 2002 Springer