Effects of sucrose addition and seeding density on native species and cheatgrass establishment in sagebrush ecosystems.
Mazzola, Monica*,1, Chambers, Jeanne, 1 University of Nevada-Reno, Reno, NV
ABSTRACT- Cheatgrass (Bromus tectorum) negatively affects native plant communities in the Great Basin. Exotic annuals have high demands for water and nutrients, especially nitrogen, while native species are generally more tolerant of low soil nitrogen. We manipulated soil N by adding sucrose. Our objectives were (1) examine if sucrose addition reduces cheatgrass and increases native species establishment, and (2) quantify the effect of seeding densities and sucrose addition on plant establishment in a sagebrush community invaded by cheatgrass. A blocked design with two sucrose levels (0 and 1500 kg/ha), five cheatgrass seed densities (0, 150, 300, 600 and 1200 seeds/m2), four native seeding densities (0, 150, 300 and 600 seeds/m2), and three replicates were used. Seeding was in fall 2003 and 2004 and density of cheatgrass and natives were recorded in June 2004 and 2005. Native species included Artemisia tridentata, Poa secunda, Elymus multisetus, Pseudoroegneria spicata, Achillea millefollium and Sphaeralcea grossulariifolia. Establishment of natives the first growing season following sucrose application was affected by native and cheatgrass seeding densities (P<0.05). Cheatgrass density decreased due to sugar addition, but the response was affected by seeding year (P<0.001). Native species density increased with increasing seed density, but low survival of native species was observed in the second growing season (P<0.05). In contrast, an increase in cheatgrass density occurred the second growing season after sucrose addition. The sucrose effect on cheatgrass is likely to be stronger the first growing season after addition, and any competitive advantage gained by natives may be short-lived.
Key words: rangeland restoration, plant invasions, sagebrush steppe
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