|Blank, Robert - Bob|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/19/2008
Publication Date: 9/15/2008
Citation: Mazzola, M.B., Allcock, K., Chambers, J.C., Blank, R.R., Schupp, E.W., Doescher, P.S., Nowak, R.S. 2008. Effects of Nitrogen Availability and Cheatgrass Competition on the Establishment of Vavilov Siberian Wheatgrass. Rangeland Ecology and Management. 61:475-484. Interpretive Summary: To restore degraded Great Basin rangelands, we evaluated the potential of ‘Vavilov’ Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy) to establish and suppress cheatgrass. Treatments included control, sucrose addition to immobilize N, and seeding different levels of cheatgrass. In the first year after seeding, sucrose reduced cheatgrass density by 35%, and decreased both cheatgrass biomass by 67%. These effects were transitory, and by the second year after seeding there was a 7-fold increase in cheatgrass density. ‘Vavilov’ density decreased as cheatgrass seeding density increased. Seedlings of ‘Vavilov’ were less competitive than cheatgrass.
Technical Abstract: Cheatgrass (Bromus tectorum L.) is the most widespread invasive weed in the sagebrush ecosystems of North America. Restoration of perennial vegetation is difficult and land managers have often used introduced bunchgrasses to restore these degraded communities. Our objective was to evaluate the potential of ‘Vavilov’ Siberian wheatgrass (Agropyron fragile [Roth] P.Candargy) to establish on cheatgrass-dominated sites. We examined the effects of soil nitrogen availability by adding sucrose to the soil to promote N immobilization, and of cheatgrass competition by seeding different levels of cheatgrass. We used a blocked split-split design with two sucrose levels (0 and 360 g m-2), two levels of ‘Vavilov’ (0 and 300 seeds m-2) and five levels of cheatgrass (0, 150, 300, 600, and 1200 seeds m-2). Seeding was conducted in fall 2003 and 2004 and measurements were taken in June 2004, 2005 and 2006. Sucrose addition decreased availability of soil nitrate but not orthophosphate. In the first year after seeding, sucrose reduced cheatgrass density by 35%, and decreased both cheatgrass biomass m-2 and seed production m-2 by 67%. However, these effects were transitory, and by the second year after seeding there was a 7-fold increase in cheatgrass density. As a result, the effects of sucrose addition were no longer significant. Sucrose affected ‘Vavilov’ growth but not density during the first year after seeding. ‘Vavilov’ density decreased as cheatgrass seeding density increased. The decline in ‘Vavilov’ density by the second year coincided with the increase in cheatgrass. Short-term reductions in N or seed supply appeared not to have long-term effects on cheatgrass and were not sufficient to enhance ‘Vavilov’ establishment. Further, ‘Vavilov’ seedlings were less competitive than cheatgrass and short-term reductions in N supply during establishment could hinder revegetation success.