Fahnestock and Knapp assessed the indirect effects of selective grass herbivory by bison on the xylem pressure potentials and primary production of ungrazed tallgrass prairie forbs, during the 1990 growing season in Kansas. Overall, selective herbivory of the grasses had an inconsistent effect on leaf xylem pressure potentials in the remaining forbs.When xylem pressure potentials were relatively high during the growing season, no significant differences in water status were detected between Andropogon gerardii and the forbs. However, when xylem pressure potentials were low, predawn and midday potentials were higher in Vernonia baldwinii, and midday xylem pressure potentials were higher in Ambrosia psilostachya compared with A. gerardii. In contrast, xylem pressure potentials were not very different between Aster ericoides and A. gerardii. Compared with ungrazed areas, end-of-season aboveground biomass in grazed patches was 40% greater for individuals of A. psilostachya and 33% and 26% greater for reproductive biomass and floret numbers, respectively, in V. baldwinii. Selective grazing of the grasses by bison did not significantly alter seasonal plant water relations in the neighboring ungrazed forb species, but some biomass and fitness measures in forbs were increased.
Citations and enhanced abstracts for journals articles and documents focused on rangeland ecology and management. RSIS is a collaboration between Montana State University, University of Idaho, and University of Wyoming.