This study examined the effects of water-table depth, neighborhood species interactions, and herbivory on the survival, tillering, biomass, and seed production of Carex nebrascensis and Poa pratensis, in two central Nevada riparian meadows. Water table had no effect on tillering or biomass of C. nebrascensis, indicating that it is adapted for growth and persistence over the range of water tables examined. In contrast, growth and tillering of P. pratensis was severely restricted at more shallow water tables. P. pratensis had about 50% fewer tillers and lower biomass for neighbor-removed plots on mid-water table plots compared to low-water-table plots. Clipping had no effect on survival, tillering, or growth of either species. Neighborhood removal resulted in a 3- to 10-fold increase in tillering and higher plant mass for C. nebrascensis; P. pratensis showed an even greater response to neighbor removal. Results from studies on P. pratensis reflect its lack of tolerance of saturated soil conditions and status as a facultative upland species. Disturbances resulting from livestock grazing or other animal activities that increase both space and resources within the community allow both species to expand locally. Under environmental conditions that are favorable to both species, P. pratensis has higher rates of growth and expansion and is able to limit the growth and tillering of C. nebrascensis. Grazing may alter the relative competitive ability of the two species, in favor of P. pratensis.
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