2012-06-20_PERMIT FILE - C2010089 (61)

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Plant Community Diversity Stand ratings of 1978 were found to linearly increase up to a depth of 30 cm then decline (Table 11). The 1979 and 1981, diversity values appeared to increase up to 20 cm and then level off. in 1985, it appeared optimum stand diversity corresponded to the 10 cm soil depth, but differences among means were not significant. The coefficient of correlation values between diversity and topsoil depth were calculated as r = 0.42 (P< 0.48) for 1978; r = 0.64 (P< 0.25) for 1979; r = 0.87 (P< 0.05) for 1981 and r 0.27 (P< 0.66) for 1985. Species richness in 1978, 1979 and 1981 appeared to increase with increasing soil depth (Table 12). However, in 1985, greatest species richness values were correlated with 0 and 10 cm depths. The coefficient of correlation between species richness and topsoil depth yielded the following values: 1978 r = 0.89 (P< 0.04); 1979 r = 0.76 (P< 0.14); 1981 r = 0.91 (P< 0.03) and for 1985 r = -0.85 (P< 0.07). DISCUSSION AND CONCLUSIONS The effect of horizon segregation upon perennial production was evaluated by Power et. al. (1981). Average alfalfa yields were reported to be 1.49 and 1.92 metric tons /ha for mixed topsoil and topsoil over subsoil, respectively. Average perennial forb production for 1985 in our study yielded values of 2.51 and 2.67 metric tons /ha for mixed topsoil and tojoil, dyer subsoil, respectively .) _ %`"Perennial` grass yield - s - obtained by 1985 al — this study were determined to equal 1.54 and 1.63 netric tons /ha for mixed topsoil and subsoil and topsoil over subsoil, respectively. Crested wheatgrass yields were reported by Power et. al. (1981) to equal 2.38 and 2.42 metric tons /ha respectively. We therefore conclude, as did e`! -`"� Power et. al. (1981), to maximize alfalfa c production and perennial grass production, topsoil 1 r° horizons do not need to be segregated. Forage production in this study indicated combined, but the combined composition of the during the earlier years of reclamation thicker two continued to decline as well across all topsoil depths were most productive. However, treatments. Work in Montana has suggested low by 1985. maximum production was associated with species diversity of reclaimed lands could the 20 cm depth. Barth (1984), Doll et al. partially be explained by the dominance of crested (1984), Schunan et al. (1985) and Halverson wheatgrass and smooth brome (Sindelar 1980). et. ai. (1987) all documented in their studies Due to the apparent negative efforts of these that optimum production over time shifted in , species on plant community diversity, the favor of shallower soils. Based upon ourl) 1 composition of these two species was correlated findings, we would suggest topsoil per se, isl " A to species diversity values. The coefficient not necessary to achieve successful reclam.ationjsl of correlation between composition and species for similar sites in northwest Colorado. The 0' diversity produced no evidence that either species findings herein are identical to those reported reduced species diversity. Crested wheatgrass by Parkin et. al. (1980) for nearby nontopsoiled sites. If one assures the spoil used in this experiment is suitable as a plant growth medium (in fact, plant performance on this medium documents it is a suitable plant growth medium) then our findings are very similar to those reported by Power et. al, (1931). In their study, they reported alfalfa yields increased up to 20 cm of respread topsoil then declined. Perennial forb production in our study for 1985 was found to equal 3,639, 3,922, 4,312, 3,939 and 3,405 for the 0, 10, 20, 30 and 46 cm soil depths, respectively. We consider the similarity between our findings and those of Power et. al. (1981) to he meaningful, Both studies suggest the optimum thickness of respread topsoil to max a de +th of '1) cam;, Redente and Hargis (1985) reported on da a collected from a similar site in northwest Colorado. The data indicate significantly higher forb and shrub biomass was associated with the 15 cm depth of respread topsoil than deeper depths. Yields of crested wheatgrass were reported by Power et. al. (1981) to increase linearly with increasing depth of respread topsoil. Redente and Hargis (1985) reported a sinilar finding for seeded perennial grasses. In this study, perennial grass yields progressively increased with topsoil depth. Since there is considerable concern regarding the over- establishment of perennial grasses on reclaimed lands with the resultant exclusion of desirable forbs and shrubs, we suggest, based on the results of this study, more life forms and hence greater community diversity might be obtained by reapplying less topsoil. the responses of individual species on both the horizon segregation and topsoil depth studies were somewhat unexpected. Pronounced declines in cover and composition of intermediate wheatgrass, crested wheatgrass, smooth brome and volunteer species with the exception of mountain brome, were observed over time (Tables 4 and 9), Intermediate wheatgrass dropped fron nearly 10% of the stand to 2% of the stand. Crested wheatgrass essentially disappeared from the seeded stand. Composition of smooth brone declined on all treatments over time. In 1985, smooth brome and meadow brome were accidentally was found to positively influence overall species diversity (r = 0.77 P< 0.0001). Smooth brome grass also was found to positively influence species diversity (r = 0.68 P< 0.0008). The coefficient of correlation calculated from data of Parkin et. al. (1980) for crested wheatgrass