Date of Award:

1993

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Natural Resources

Department name when degree awarded

Range Science

Advisor/Chair:

David A. Pyke

Abstract

Current revegetation practices in the lntermountain West include the use of Nordan (Agropyron desertorum) and Hycrest (A. cristatum x desertorum) crested wheatgrass on rangeland susceptible to cheatgrass (Bromus tectorum) invasion, although little quantitative data exists that compares their competitive abilities. We evaluated both the competitive ability of Hycrest and Nordan in two-species mixtures with cheatgrass, and evaluated seedling establishment characteristics for all three species in a greenhouse study. Linear and nonlinear models were developed for a range of densities for each species to predict median above-ground biomass and tiller numbers. In both experiments, increasing Hycrest and Nordan densities reduced their own biomass and tiller production while cheatgrass biomass and tiller production was not influenced. However, increasing cheatgrass densities reduced both Hycrest and Nordan biomass and tiller production, as well as its own biomass and tiller production. Examination of trends in competition indices, such as relative resources totals, substitution rates and perceived densities indicated that as seedlings, Hycrest was a better competitor with cheatgrass than Nordan at lower crested wheatgrass densities (130 plants/m2 ). Results from this experiment indicate that Hycrest is a better competitor than Nordan with cheatgrass and suggest that seeding Hycrest at lower densities than currently recommended may optimize its seedling growth when competing with cheatgrass. Future research concerning competition in these species using similar designs should focus on competition in successive years after establishment and on field experiments to verify these results.

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