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In southeastern Utah, Bromus tectorum occurs where Hilaria jamesii is dominant and rarely where Stipa hymenoides/S. comata dominate. To determine whether this distribution is due to soil characteristics or microhabitat, we transplanted H. jamesii soil to a Stipa site and vice versa during a severe drought (2001) and a wetter year (2002). Additionally, we planted B. tectorum under H. jamesii and Stipa canopies, with or without H. jamesii litter, and with or without herbivory. Bromus tectorum emergence and biomass in reciprocal transplants were similar at both sites; there were no site differences for all microhabitat treatments. Being under a plant canopy increased emergence in 2001 and decreased survival during...
The introduction of nonnative plant species may decrease ecosystem stability by altering the availability of nitrogen (N) for plant growth. Invasive species can impact N availability by changing litter quantity and quality, rates of N2-fixation, or rates of N loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N cycling in an arid grassland on the Colorado Plateau (USA). The invasion occurred in 1994 in two community types in an undisturbed grassland. This natural experiment allowed us to measure the immediate responses following invasion without the confounding effects of previous disturbance. Litter biomass and the C:N and lignin:N ratios were measured to determine the effects on...
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The introduction of nonnative plant species may decrease ecosystem stability by altering the availability of nitrogen (N) for plant growth. Invasive species can impact N availability by changing litter quantity and quality, rates of N2-fixation, or rates of N loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N cycling in an arid grassland on the Colorado Plateau (USA). The invasion occurred in 1994 in two community types in an undisturbed grassland. This natural experiment allowed us to measure the immediate responses following invasion without the confounding effects of previous disturbance. Litter biomass and the C:N and lignin:N ratios were measured to determine the effects on...
Soil evaporation, a critical ecohydrological process in drylands, can exhibit substantial spatio-temporal variation. Spatially, ecohydrological controls of soil evaporation may generally depend on a hierarchical structure spanning from the presence or absence of litter, through canopy patches of woody plants and intercanopy patches separating them, up to the overall vegetation mosaic characterized by density of woody plant cover in the landscape, although assessment of these factors in concert is generally lacking. Temporally, ecohydrological controls can be further complicated by not only seasonal climate, but also phenology, particularly in seasonally deciduous drylands. We experimentally assessed the interactive...
The effect of tree canopy, understory, herbivores, and litter depth on seedling establishment, survival, and reproduction of the alien grass, Bromus tectorum (cheatgrass), was examined in a series of experiments in four forest habitat types in western North America. Higher recruitment, survival, and reproduction on clearcuts, which would be expected if the overstory alone is limiting the distribution of cheatgrass in forests, were not observed. Removing the understory in an otherwise undisturbed Pinus ponderosa forest did, however, increase the emergence of B. tectorum, but plants in these experimentally-created openings were more vulnerable to grazing by small mammals. In contrast, removing the sparse understory...
    map background search result map search result map Exotic plant invasion alters nitrogen dynamics in an arid grassland Exotic plant invasion alters nitrogen dynamics in an arid grassland