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4.3.3 Woody Plant Density <br />' <br /> Figure 32 compares woody plant densities from 1986, 1988, and 1993 on the Test <br /> Plots, North and South Areas and the Shadscale Shrubland Reference Area. Data for <br />' areas outside the Test Plots was not collected in 1986, while 1988 data from areas <br /> outside the Test Plots was combined (and is represented as N. Area). From these <br />' comparisons, several trends are apparent. Woody plant densities are consistently <br />higher across treatments on Test Plot 2. Test Plot 2 environmental conditions appear <br /> more compatible with the growth requirements of the native shrubs found on the <br /> sampled areas. Test Plot 1 woody densities were consistently lower through the sample <br />' years with the exception of the 48" treatment in 1993. As previously observed, this is <br /> directly attributable to the large influx of Chrysothamnus nauseosus seedlings <br /> colonizing this treatment. Test Plot 3 woody densities showed a consistent decrease <br /> with increasing soil depth for all sample years. This Test Plot was the only area to <br /> exhibit this trend. This trend may also be attributed to the more mesic moisture regime <br />' of this Test Plot, which may provide available moisture above the optimum tolerance <br /> limits for the native shrub species encountered. An alternative explanation may be that <br /> woody species may be out competed early on by the rapidly growing herbaceous <br />' component (graminoids and forts). Woody plant densities were below the densities <br /> sampled on the Reference Area in 1986 and 1988. The determination of woody plant <br />' re-establishment success for this area is based on a numerics] standard (CDMG, 1993). <br />This standard requires that 720 (90% of the 800 numerical standard) live woody <br /> stems/acre be established on the Roadside RDA with 90% statistical confidence. Based <br /> on this standard, only the treatments in Test Plot 2 all satisfy the woody plant density <br />t re-establishment requirement over all sample years. <br />' 4.3.4 Species Diversity <br /> Figures 33-35 illustrate the number of species by lifeform and location for the three <br />' sample years. With the exception of the Reference Area in 1988, total species numbers <br /> have remained between 10 and 20 throughout the life of the study. From the data, no <br /> general trends present themselves with regard to soil depth or aspect related to the Test <br />' Plots. Lifeform representation has remained relatively consistent over time and Test <br /> Plots with the exception of shrubs. The number of shrub species has decreased over <br /> time across the Test Plot treatments. This may be related to the environmental <br />' tolerance levels of the mature plants. Whereas many species seedlings may be present <br /> early in the colonization of an area, few of the species (and individuals of each species) <br /> reach maturity. The decrease in shrub species numbers may reflect the "sorting out" of <br />' the species which find optimal growth conditions on the Test Plots and the RDA in <br /> <br />1 general. <br />70 <br />