2002-07-08_GENERAL DOCUMENTS - M2002004 (3)

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the improved physical, chemical and biological properties of the direct placed topsoil that manifested these benefits in greater soil moisture and greater mycorrhizal inoculum levels. Stahl et al. (1998) followed this study with a greenhouse study using soil from the same mine site and showed that seedlings growing in topsoil with good levels of mycorrhizal inoculum exhibited significantly greater drought stress tolerance than those grown on non - mycorrhizal topsoil and this increased drought stress tolerance became more pronounced as the seedling aged. Therefore, giving the mycorrhizal seedlings a definite advantage during the period of time (limited seedling root elongation) they are most susceptible to wide swings in soil moisture common in semiarid climates. In a separate phase of the field study reported on by Schuman et al. (1998), Schuman and Booth (1998) reported no differences in sagebrush establishment between direct placed and stockpiled topsoil over 4 years. However, one must keep in mind that biological and physical characteristics of the stockpiled topsoil treatment change with time and it is likely that after 12 -18 months, mycorrhizal inoculum was no longer an issue because of the reinoculation of the stockpiled topsoil by wind and other means (Schuman et al. 1998, Loree and Williams 1984). Schuman et al. (1998) also found that even though mycorrhizal spore counts were significantly lower in stockpiled topsoil compared to direct -placed topsoil, sagebrush seedling infection, 1 year after initial seedling emergence, was not different between the two topsoil sources. They also showed no difference between sagebrush seedling density and topsoil source in subsequent years of evaluation because of continued establishment of sagebrush from remaining viable seed. However, eight years after sagebrush seeding, the average seedling density on stockpiled topsoil was 1.96 compared to 3.22 seedlings m_2 on the direct -placed topsoil treatment (G.E. Schuman, unpublished data, 2000). Even though this large difference was not found to be statistically significant, it definitely has great biological importance when assessing the shrub density against the required standard. Schuman and Booth (1998) showed significant increases in sagebrush establishment over a four year period from a single sagebrush seeding date. Schuman and Booth (1998) also reported that use of a "pioneer species" (in this case Atriplex canescens) did not enhance recruitment of Wyoming big sagebrush as postulated by researchers (Booth 1985; Meyer 1990; Wagner et al. 1978) or diminish its recruitment even when over - seeded with Wyoming big sagebrush in subsequent years. Several researchers have reported that one of the major constraints in successfully establishing big 41 sagebrush on mined lands through direct seeding has been the direct competition for soil moisture by the perennial grasses seeded concurrently with the big sagebrush (Schuman et al. 1998; Blaisdell 1949; Jones 1991; Cook and Lewis 1963; Sturges 1977; Eissenstat and Caldwell 1988; Richardson et al. 1986.) Schuman et al. (1998) found significantly higher initial sagebrush seedling density when seeded without grass compared to being seeded concurrently with grasses at 16 or 32 kg PLS ha'' seeding rates. Richardson et al. (1986) also found that grass and forb seeding rates of 13 kg PLS ha' prevented mountain big sagebrush establishment; however, elimination of grasses and forbs provided good seedling establishment. Fortier (2000) evaluated the effects of three Wyoming big sagebrush seeding rates (1, 2, and 4 kg PLS ha') and seven grass seeding rates (0, 2, 4, 6, 8, 10, and 14 kg PLS ha') on sagebrush seedling establishment. After two growing seasons, she found no statistically significant effect of grass seeding rate (competition) on sagebrush establishment; however, at grass seeding rates above 10 kg PLS ha' a 60% reduction in sagebrush seedling density (Figure 1) was observed, although data variance prevented this large difference from being significant. She also believes that soil moisture competition did not begin to express itself until late in the second growing season because of the above normal precipitation in the first year and spring and early summer of the second year. It is interesting to note that second year planted grass biomass did not differ for grass seeding rates of 4 -14 kg PLS ha' and grass seedling density was not different for the 6 -10 kg PLS ha' grass seeding rates. However, sagebrush density was greatly reduced at the grass seeding rate of 14 kg PLS ha' (Figure 1). Because of these trends, Fortier (2000) recommended that grass seeding rates of 6 -8 kg PLS ha' and sagebrush seeding rates of kg PLS ha' be used to reclaim mined lands to the regulatory requirement of 1 shrub m' on 20% of the reclaimed landscape. This assessment takes into consideration the longer -term survival of sagebrush seedlings found by Kriger et al. (1987) and Schuman (G.E. Schuman, unpublished data, 2000). Kriger et al. (1987) found that 33% of the newly established sagebrush seedlings were still alive after 11 years in northwestern Colorado and Schuman (G.E. Schuman, unpublished data, 2000) reported 59% survival of Wyoming big sagebrush seedlings after 8 years at a study site in the Powder River Basin of Wyoming. Fortier (2000) also found significant increases in sagebrush seedling density for all three sagebrush seeding rates for any given sample date during the 2 year study. However, Fortier (2000) did not show a significant increase in sagebrush seedling density the second year for the 1 kg PLS ha' sagebrush seeding rate