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Reference Area No. 3 <br />Cover trends for Reference Area #3 differ from the other reference areas, in that cover of all vegetation <br />categories increased sharply between 1998 and 1999. This is due to the fact that the beltline flat was <br />topsoiled and seeded in the fall of 1997, and 1998 was the first growing season. The cover increase from <br />1998 to 1999 reflects maturation of plants that were seedlings in 1998. Vegetation stands in the other <br />reference areas had been seeded at least five years prior to the initial sampling. Since 1999, total vegetation <br />cover and non - noxious forb cover have remained relatively stable, while grass cover has increased, and <br />noxious weed cover has significantly declined (Figure 5). <br />Figure 5 - Beltline Reference Area #3 Absolute <br />Cover Trends; 1998 -2001 <br />60.0% <br />50.0% <br />40.0% <br />30.0% <br />20.0% <br />10.0% <br />0.0% <br />1998* 1999 2000 2001 <br />=Absolute <br />Noxious Cover <br />— .Absolute Grass <br />Cover <br />A bsolute Forb <br />Cover <br />-NE- Total Vegetation <br />C over <br />2001 absolute and relative cover by species and category is presented in Table 9. Absolute and relative <br />cover sample means by category and year are presented in Table 10. Because 1998 was the first growing <br />season, effects of spraying are masked by growth and maturation of individual plants, and as such <br />comparison of 1998 absolute cover values with subsequent year absolute cover values is not meaningful. <br />Relative cover, a measure of species composition, does allow for limited, within category comparison <br />between 1998 and later years. Cover summary tables for 1998, 1999, and 2000 are included in the <br />respective DMG Annual Weed Sampling Report. Based on relative cover, the dominant noxious species in <br />1998 were the biennials plumeless thistle (15.4 %), and musk thistle (10.3 %), with oxeye daisy the <br />remaining noxious species sampled (2.6 %). Relative cover of plumeless thistle roughly doubled between <br />1998 and 1999, but declined sharply between 1999 and 2000, and was not encountered by cover sampling <br />in 2001. Musk thistle was not encountered by cover sampling after 1998 (mis- identification of plumeless <br />thistle seedlings as musk thistle in 1998 is a possibility). Canada thistle was first encountered in 2000, and <br />was a minor stand component in both 2000 and 2001. Relative cover of oxeye daisy remained relatively <br />stable over the course of the study. <br />Between 1999 and 2001, absolute cover of noxious species declined from 16.5% to 2.5 °4 while absolute <br />grass cover increased from 14.3% to 29.3 %. The response of plumeless thistle, which declined from 15.0% <br />absolute cover in 1999, to 0.3% cover in 2000 and 0% cover in 2001, is the reason for the over -all decline <br />in noxious species cover. A number of grass species contributed to the increase in absolute cover of <br />grasses over the period. Absolute cover of non - noxious forbs has remained relatively stable since 1999, <br />with no readily apparent effects of spraying on individual species or the category as a whole. <br />Noxious species density declined sharply between 1998 and 2001, and remained low in 2001, due to the <br />response of the noxious thistle species as illustrated in Figure 6. Although thistle species were not <br />separated in the density estimate, it can be inferred based on the cover data that the dramatic decline <br />reflected the response of plumeless thistle and (possibly) musk thistle. Thistle density sample mean <br />declined by approximately 95% from 1998 to 2001, from 10.7 plants per square meter to 0.5 plants per <br />square meter. Oxeye daisy density was sampled only in 1999 and 2001, and density remained stable at the <br />relatively low level of 1.1 plants per square meter in 1999 and 1.3 plants per square meter in 2001. <br />6 <br />