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• SAMPLE ADEQUACY Tabulated in Table 4-13 are all the sample adequacy numbers for the cover, woody plant density, and herbaceous production data collected in 1982 from the Old Field affected area. The formula used for sample adequacy calculation was: t=s= nmin - d3z where nmin = the minimum required sample size t = a two-tailed t value at 80% confidence# s = sample standard deviation d = desired detectable reduction (10%, d = 0.1) x = sample mean As shown in Table 4-13, minimum sample size for cover was 4; 20 samples were #aken. For herbaceous production, minimum sample size was 47; 50 samples were taken. Thus, for both cover and herbaceous production sample adequacy was achieved. For woody plant density, minimum sample size was 153; sample size was 50. Broom snakeweed IGutierrezia sarothrael and rubber rabbitbrush • (Chrysothamnus nauseosusl are the most abundant shrub species and both are weedy in character. They have been, and perhaps still are, actively colonizing the old field habitats. As is typical in colonization, some areas are better suited than others to the establishment of the invading species. The result is a highly variable presence of the invading species. Ultimately, an equili- brium will probably begin to develop in which the most dense shrub occurrences thin as competition with other perennial species increases. Using the Old Field affected area woody plant density data, a 10% reduction could be detected with about 54 percent confidence, or with 80 percent confi- dence, a 17.5 percent reduction could be detected. The Old Field data do not form the basis for any proposed revegetation standard at the Carbon Junction mine. The woody plant density data function only in characterizing pre-disturbance conditions. it is believed that the data from the fifty samples taken satisfactorily make this description. Even if the data from the Old Field were used for establishing a reclamation standard, a woody plant density standard substantially below the existing density would be requested. #Cover data reveal that woody plants comprised 20.2 of the vegetation cover; qualifying this vegetation as a woody type for which 80% confidence can be • used as sample adequacy calculations [2 CCR 407-2, 4.15.8(311b1, 1411b1].