Effects of simulated grazing on growth and persistence of Artemisia frigida in a semiarid sandy rangeland

To assess the tolerance of fringed sagewort (Artemisia frigida Willd.) to grazing in semiarid sandy rangeland, forty-five fringed sagewort plants of similar size were chosen randomly from sandy rangeland and divided into three cohorts (fifteen plants per cohort) that were subjected to simulated grazing management in 1998. Plants were cut in spring on 24 April and again in summer on 26 July at either 2-3 cm (severe), or at 5-6 cm (moderate), or uncut to serve as the control. Plant responses to intensity of cutting were monitored over two consecutive years differing substantially in the amount and seasonal distribution of rainfall. Cutting in spring (moderate or severe) did not influence plant height, average canopy diameter, the number of branches, and specific branching density measured in July 1998. Moderate cutting in summer reduced plant height compared with the uncut treatment but did not influence other plant growth variables in September 1998. However, severe cutting in summer during the reproductive stage strongly reduced plant height, canopy size, the number of branches, individual shoot weight and specific branching density in September 1998 compared with moderate and no cutting and its negative impacts on the growth of this species were evident in the following year. Severe cutting in spring significantly increased the number of flowering shoots, whereas cutting in summer (at either level) reduced the capacity of fringed sagewort to produce flowering shoots. Also, the negative impact of summer cutting on seed production continued in the following year. The production of plant biomass was similar in the three treatments in 1998, but it was significantly lower in cut than uncut plants in 1999. The reduced biomass was due to a decline in plant height, canopy size, number of branches and specific branching density. Compared with the uncut plants, the cut plants tended to allocate a greater proportion of their biomass to vegetative shoots and leaves than to flowering shoots in 1998; in 1999, although cutting treatments had ceased, the cut plants still allocated a greater proportion of new biomass to vegetative shoots and less to flowering shoots, but a similar proportion to leaves.