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The spatial distribution of Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh within plant communities creates two distinct zones; underneath (subcanopy) and between shrub canopies (interspace). The purpose the study was to determine the influence of subcanopy and interspace zones on microsite characteristics and herbaceous vegetation. Study sites were located at the Northern Great Basin Experimental Range (NGBER) (56 km west of Burns, OR) and Baker Pass (80 km southeast of Burns, OR). At the NGBER, microsite and vegetation differences existed between subcanopy and interspace zones. Compared to the interspace, subcanopy zones were characterized by lower fluctuations in soil temperature, higher...
The primary hypothesis for the astonishing success of many exotics as community invaders relative to their importance in their native communities is that they have escaped the natural enemies that control their population growth ? the `natural enemies hypothesis'. However, the frequent failure of introduced biocontrols, weak consumer effects on the growth and reproduction of some invaders, and the lack of consistent strong top-down regulation in many natural ecological systems indicate that other mechanisms must be involved in the success of some exotic plants. One mechanism may be the release by the invader of chemical compounds that have harmful effects on the members of the recipient plant community (i.e., allelopathy)....
Post-fire changes in desert vegetation patterns are known, but the mechanisms are poorly understood. Theory suggests that pulse dynamics of resource availability confer advantages to invasive annual species, and that pulse timing can influence survival and competition among species. Precipitation patterns in the American Southwest are predicted to shift toward a drier climate, potentially altering post-fire resource availability and consequent vegetation dynamics. We quantified post-fire inorganic N dynamics and determined how annual plants respond to soil inorganic nitrogen variability following experimental fires in a Mojave Desert shrub community. Soil inorganic N, soil net N mineralization, and production of...
Circumstantial evidence suggests that Artemisia tridentata may out?compete Pinus ponderosa and P. jefferyi for water at ecotones between shrub steppe and montane forest vegetation in the Great Basin. Other studies indicate that within the shrub steppe Artemisia may act as a nurse plant for a third species of pine, P. monophylla. We used field experiments to study these contrasting effects of Artemisia on P. ponderosa and P. monophylla within the context of the distributional patterns in western Nevada of all three species on andesite, and on sites where hydrothermal activity has altered the andesite. At intermediate elevations in the Great Basin Artemisia and P. monophylla are restricted to unaltered desert soils,...