2010-12-17_REVISION - C1981019 (160)

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In addition to the PCQ data, canopy cover at each sample point was visually estimated by the observer. It is important to note that the aspen canopy at over half the sample points was substantially reduced due to the recent die-off of mature trees (most likely due to the recent drought). 2.7 Sample Adequacy Determination Within each community type (baseline or reference area), sampling for ground cover and production was conducted to a minimum of 20 samples. From these initial samples, a mean and standard deviation for each variable was calculated. Where statistical testing is required (for the establishment of qualified reference areas), collection of an adequate sample (nmin) is typically necessary to insure reliable estimates of the population (e.g., estimates to within 10% of the true mean (p) with 90% confidence). The Cochran formula below was utilized in accordance with directives in Colorado's guidelines (1988). When the inequality (nmin <_ n) is true, sampling can be considered to be adequate, and nmin is determined as follows: nmin = (t2S2) I (0.1x)2 • Where: n = the number of actual samples collected with a minimum of 20 in each unit; t = the value from the t distribution for 90% confidence with n-1 degrees of freedom; s2 - the variance of the estimate as calculated from the initial samples; x = the mean of the estimate as calculated from the initial samples. If the initial minimum number of samples in each area did not provide a suitable estimate of the mean (i.e., the inequality was false), additional samples were collected until the inequality (nmin S n) became true. Only two areas required additional sampling (Juniper Scrub and Bottomland Baseline Areas) where 39 and 17 additional production samples were collected. 2.8 Reference Area Comparability When reference areas are utilized as revegetation standards of success for vegetation cover and production, demonstrations are required prior to permit issuance to document that the selected reference areas are statistically comparable (equal) to the vegetation types for which they represent. The pre- mining demonstration of reference area comparability was made using the two-tailed Students t-test as indicated below. Reference area production and cover are compared at the 95% confidence limit (alpha at 0.05 level) with the respective baseline area production and cover. The sample "P' statistic (t-*) is calculated as follows: CIEDA1R CMMK AM Cll TME, INC. Page 10 2005 Collom Vegetation Survey