In Utah, heavy grazing of a grazing-tolerant Eurasian tussock grass, Agropyron desertorum, before internode elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in spring. The presence of ungrazed tillers on partially grazed tussocks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. Olson and Richards conclude that chronic reduction in tiller replacement will reduce a tussock's competitive ability, and increase the probability of its death.
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