Permanently marked tillers of five perennial grasses, native to the mixed-grass prairie of North America, were monitored on a pasture in Texas, to determine patterns of defoliation, architectural attributes influencing probabilities of defoliation, and post-defoliation responses. Frequency of tiller defoliation was greatest for one of the dominant midgrasses (sideoats grama (Bouteloua curtipendula)), intermediate for the remaining midgrass (Texas wintergrass (Stipa leucotricha)), and dominant shortgrasses (buffalograss (Buchloe dactyloides) and common curlymesquite (Hilaria belangeri)), and least for the subdominant midgrass (red threeawn (Aristida longiseta)). The relative intensity of defoliation did not vary among species or grazing periods indicating that intensity of defoliation was primarily a function of pre-defoliation tiller height. Tiller architecture, including height, lamina number and the presence of reproductive culms, did not significantly influence frequency or intensity of defoliation within a species. The lack of evidence supporting tiller architecture as a selection criterion within a species suggests that cattle were selecting on vegetation parameters at higher levels of vegetation organization than individual tillers. The patterns of interspecific tiller defoliation observed in this study parallel the long-term patterns of grazing-induced species replacement observed in this grassland.
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