2012-06-20_PERMIT FILE - C2010089 (62)

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Table 5. Average production values in kg ha for the ZSW and SSW. #, *, ** indicate statistical significance at the 0.10, 0.05, and 0.01 levels of probability, respectively. zsw ssw smooth crested russian smooth crested native brome wheatgrass wildrye alfalfa brome wheatgrass mix alfalfa kg ha' kg ha' Toe slope 1510* 1787* 1350 1418 2985 2618t 2720 2750* Mid slope 1748* 2031* 1722 1675 4021 3698t 2819 4361* Shoulder slope 1825* 2289* 1604 1561 3432 3443t 3183 3309* Subsoil A 1504 ** 1821* 1262 ** 1620 SubsoilB 1874 ** 2021* 1778 ** 1620 SubsoilC 1745 ** 2261* 1757 ** 1508 Diversity Results for 2003 Diversity values were only calculated for the ZSW because of a low number of observations (n <20) for the SSW. Alfalfa plots had significantly higher diversity (F <0.01) in toe slope positions (0 -40 cm soil depths) compared to other vegetation species plots and slope locations. Alfalfa is a less aggressive species than smooth brome or crested wheatgrass and also fixes nitrogen in the soil. These characteristics make alfalfa plots more susceptible to native and introduced plant invasion because of low competition compared to other vegetation species and high nitrogen availability in the soil. Species, which invading the alfalfa plots from surrounding experimental plots, consisted of smooth brome and crested wheatgrass. Other native and introduced species found in the alfalfa plots from the surrounding area are listed in Table 6. There were a variety of native and introduced species established on the ZSW which may be a result of invasion by surrounding vegetation or seed distribution through cattle grazing. Again, most of the diversity was found in reduced depths of replaced soil because these areas more conducive to higher diversity and lower production (Bowen, 2003; Schladweiler et al., 2003). In the previous study by Merrill et al. (1998), rabbits also fed on alfalfa stands and caused a weak establishment. This made alfalfa plots more vulnerable to invasion by native and introduced species leading to higher diversity values than other vegetation plots. There were significant differences (F <0.01) in diversity values by subsoil type for crested wheatgrass, Russian wildrye and alfalfa (Table 7). Differences can be attributed to plant soil textural preferences, along with other soil parameters not examined in this study. A significant, but weak relationship (W=0.1168) existed among diversity, soil depth, EC and pH; therefore, diversity may be influenced more b . h e it . arameters not examined in this study. 1240