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properly be known as the Pascopyrum smithii/Critesion jubatum/Elymus <br />tra~ycaulus/Poa jyncifolia plant association. Although it is not present in either the • <br />classification of Baker (1982) or Baker (1984), the true commonness of the type is not <br />known since any assessment of rarity as done by literature reviews such as Baker's is based <br />on documented occurrences of the vegetation type that happen to have been published in the <br />literature. The fact that it does not occur in Baker's classification may be an artifact of the <br />fact that researchers have not had any interest in sampling alkaline swales in landscapes <br />long dominated by agricultutral disturbance. <br />The Alkali Sagebrush/ Greasewood vegetation type corresponds to the rather generalized <br />unit in Tiedeman and Terwilliger (1978) labeled Desert Shrub/Swelling Clays and to the <br />SCS Alkaline Slopes range site description (No. 295) for the Southern Rocky Mountains <br />Land Resource Area (LRA 48). It would also seem to be cbse to the Artemisia longjloba <br />(Seriphydium longilobuml/Agropyron smithii (Pascopyrum smithii) plant association of <br />Baker (1984). <br />Species Density Comparison <br />One of the basic biological characteristics of plant communities is their lifeform makeup, <br />the number of species included, and the cover provided by each. Tables A21 and B28 list the • <br />species density (number of species per 100 sq. m.) by lifeform in each vegetation type. <br />Tables A23 and 830 present a listing of species found in each lifeform in each vegetation <br />type. The number of species in a lifeform in a particular vegetation type is below referred <br />to as species occurrence. The abundance and persistence of a growth form in a plant <br />community is a function of its ability to dominate available resources over time. The <br />stability of the species composition of a community, et least in the short term, may be <br />reflected in the ratio of perennial vs. annual plants (to the extent that annual components <br />are subject to more rapid change in abundance than are perennial components). With some <br />notable exceptions, ecological theory has generally held that greater species diversity <br />relates directly to greater community stability. In the discussion below, vegetation types <br />that were sampled in both 1990 and 1992 are presented on either side of a solidus, <br />respectively (ie. X/Y). <br />It should be noted in general, that introduced species occured in all native vegetation types, <br />largely, if not completely due the the effects of grazing animals creating openings in the <br />native vegetation cover, and, more importantly, the transport of the seeds of introduced <br />species into the native areas via feces and seeds attached to the hair of the grazing animals. • <br />26 <br />