Cattle grazing a riparian mountain meadow: effects of low and moderate stocking density on nutrition, behavior, diet selection, and plant growth response.

Twelve ruminally cannulated and six intact crossbred beef steers were used in a randomized complete block design to evaluate the effects of stocking density of a riparian pasture in the Sierra Nevada mountains on grazing behavior, dietary selection, forage intake, digesta kinetics, and growth rates of Carex nebraskensis and Juncus balticus. Nine .5-ha pastures were assigned to one of three treatments: ungrazed (CON) or grazed to leave either 1,500 kg/ha (LOW) or 1,000 kg/ha (MOD). Two collections were conducted during the summer of 1992 (following winter drought) and 1993 (following above-average winter precipitation). Standing crop biomass was greater (P < .05) in grazed pastures than in CON pastures at initiation of grazing in 1992 but not in 1993. After grazing in both 1992 and 1993, a treatment x intrapasture location interaction was noted (P < .05). Tiller growth rates in both 1992 and 1993 were affected (P < .05) by a treatment x growth period interaction. Stocking density did not alter (P > .10) botanical or chemical composition of the diet in 1992, and only minor differences were noted (P < .05) in 1993. Forage intake, passage rate measures, and total time spent loafing did not differ (P > .10) between LOW and MOD steers. Within the mid-meadow area in 1992, loafing time was greater (P< .05) for MOD steers than for LOW steers. In 1993, a treatment x trial interaction was noted for loafing time in all three areas. Total time spent grazing was greater (P < .05) for MOD steers than for LOW steers in 1992 and was affected (P < .05) by a treatment x trial interaction in 1993. In 1992 grazing time along the streamside was greater (P < .05) for LOW steers than for MOD steers, and significant treatment x trial interactions were noted for grazing time spent along the forest edge and mid-meadow areas. In 1993, only streamside grazing time was influenced by treatment being greater (P < .05) for MOD steers than for LOW steers. In general, our data suggest that management decisions to reduce stocking densities may force cattle to congregate along streambanks and to concentrate grazing and loafing activities in those areas.