Laserfiche WebLink
• approximately the same number of individual samples as were used in sampling with aone- <br />stage approach in previous years (in which sample adequacy was not achieved). <br />Noxious Weeds <br />Of plant species observed during 1997 sampling, Canada thistle (Cirsium aroense, aka Breea <br />arvensis), hoary cress (aka whitetop, Cardaria draba), and musk thistle (Carduus nutans) are <br />listed state-wide among the top ten noxious weeds (C.R.S. 1996). Downy brome (aka <br />cheatgrass, Bromus tectorum or Anisantha tectorum), houndstongue (C~oolossum officinale), <br />and bullthistle (Cirsium vulgare) are also listed as noxious in Colorado. All but Canada thistle <br />and houndstongue are confined to the 1990 reclaimed areas. Houndstongue is regretfully <br />widespread in the native vegetation, mainly in heavily grazed areas. For the first time, Canada <br />thistle has appeared in both the reference areas in 1997. <br />Climatic Conditions <br />Precipitation data by month from the Seneca II Mine for 1992, 1993, 1994, 1995, 1996, and <br />1997 as well as the 10-year average for the mine are shown in Figures 6a and 6b. As can be <br />• seen in those graphs, 1993 had been a relatively favorable precipitation year, but beginning in <br />November 1993 and continuing through 1994, only two months (April and November) even <br />reached average precipitation. In 1995, however, January, February, and March were close to <br />average, and April and May were far above normal (with a total of over eight inches in those two <br />months). For 1996, precipitation returned closer to normal with below average amounts in <br />March and August of 1996, and in 1997, spring (and the preceeding fall) moisture was above <br />average. <br />When examined from the standpoint of what climatic indices seemed to have correlated most <br />closely with the extremely favorable growing conditions of 1995, 1996 and 1997, it would <br />appear that the Total Precipitation for the Previous 6 months (Figure 8) or the Total <br />Precipitation for the Previous 4 Months (Figure 9) were better predictors than the Total <br />Precipitation for the Previous 12 Months (Figure 7). Both Figures 8 and 9 showed that 1995 <br />was greatly superior to other years and this corresponds to the extremely high levels of <br />vegetation growth that were observed in 1995. 1996 shows up as somewhat less favorable <br />(previous 6 months, Figure 8) or considerably less favorable (previous 4 months, Figure 9). <br />• 1997 approached 1995 on previous 6 months graph (Figure 8) and is second only to 1995 on <br />the previous 4 months graph (Figure 9). The observed drop in productivity in 1996 and its rise <br />23 <br />