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ARS Home » Pacific West Area » Burns, Oregon » Range and Meadow Forage Management Research » Research » Publications at this Location » Publication #150858
Title: EFFECT OF SOIL NITROGEN ON CHEATGRASS, BLUEBUNCH WHEATGRASS, AND CANBY BLUEGRASS

Author
item POKORNY, M - MONTANA STATE UNIV
item SHELEY, ROGER - MONTANA STATE UNIV
item Carpinelli, Michael

Submitted to: Ecological Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/7/2003
Publication Date: 11/3/2003
Citation: POKORNY, M.L., SHELEY, R.L., CARPINELLI, M.F. 2003. EFFECT OF SOIL NITROGEN ON CHEATGRASS, BLUEBUNCH WHEATGRASS, AND CANBY BLUEGRASS. ECOLOGICAL SOCIETY OF AMERICA ANNUAL MEETING. FT. LAUDERDALE, FL, NOV. 3-7.

Interpretive Summary: Much of the rangelands of the West, once dominated by native perennial grasses, has been replaced by the weedy, nonnative cheatgrass. Native perennial grasses provide higher quality forage for wildlife and livestock than cheatgrass does. The objective of this study was to determine if soil nitrogen is affected by long-term dominance by cheatgrass in a way that favors cheatgrass over native perennial grasses. We found that soil from a site dominated by cheatgrass was higher in nitrogen than soil from a site dominated by native perennial grasses. Cheatgrass grew better on both soils, with and without added nitrogen, than the two native perennial grasses tested. We concluded that the ability of cheatgrass to displace and exclude native perennial grasses may be due, in part, to its relatively high growth rate, regardless of soil nitrogen levels. Manipulating soil nitrogen levels does not appear to be a worthwhile strategy for managing cheatgrass.

Technical Abstract: To manage nonindigenous plant invasions, mechanisms of invasion resistance must be identified and modified as a portion of management. One mechanism is that functionally diverse plant assemblages use resources more completely. We investigated the ability of three desirable plant species with different spatial and temporal growth patterns to resist invasion by a nonindigenous species, Centaurea maculosa (spotted knapweed). Niche differentiation between desired species was quantified using their relative competitive coefficients. Centaurea maculosa recruitment was negatively related to desired species richness. In more diverse, native plant communities, we investigated the ability of functional groups to resist invasion by C. maculosa and quantified resource use by indigenous functional groups and the invader. This study suggested that establishing and maintaining a diversity of plant functional groups within the community enhances resistance to invasion. Forbs were particularly important to resisting invasion because the indigenous and nonindigenous forbs are functionally similar. Understanding and identifying which functional groups, combinations of functional groups, or key species resist invasion by nonindigenous species through niche complementarity and resource preemption is critical for management and restoration. Because a generalized objective for invasive plant management is to establish and maintain invasion resistant plant communities that meet other land-use objectives, we have reestablished diverse indigenous communities in various restoration projects. Our restoration research in invasive plant dominated lands included testing seeding methods (drill, broadcast, seed island), seed bed preparation, herbicide treatments, and seed mixtures with varying functional diversities. Establishing and maintaining diverse, weed resistant plant communities must be a major goal of all integrated weed management programs.