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<br />standards for the habitat subclasses is provided in Appendix A, Reference Standards. The <br />purpose for developing the subclassification system was to create a pre-mitigation baseline of <br />wetland habitat information for the MA. The subclassification system was useful for assessing <br />potential mitigation measures in that it identifies several parameters that limit the functional <br />conditions of these habitats. <br /> <br />2.4 Upland Plant Communities <br /> <br />Approximately 899 acres of uplands were delineated within the river valley bottom of the MA <br />(Table 2). In general, upland habitats occur on the low and high terrace surfaces. The presence <br />of upland plant communities on the low terrace surface is evidence that the water table within the <br />zone-of-influence has been diminished by streamflow diversions and further influenced by <br />subsequent channel incision. Upland habitats found on the low terrace include: <br />farmland/pasture; a grass/forb community dominated by wheat grass, cheat grass, and usually <br />non-native forbs such as thistle and leafY spurge; and old cottonwood stands with sagebrush- <br />dominated understories. Upland habitats typically found on the high terrace include: scrub oak; <br />pinyon pine and juniper; a mixed scrub oak and conifer community; sagebrush/grassland <br />complex and farmland/pasture. <br /> <br />The condition of upland habitats has been degraded by the invasion and proliferation of <br />undesirable plant species. In addition, overgrazing has diminished upland habitat structure and <br />has created disturbances that further proliferate the invasion of undesirable weeds. <br /> <br />2.5 Factors Limiting Habitat Functions and Values <br /> <br />There are six main factors that are currently limiting wetland/riparian habitat functions within the <br />MA. First, streamflow diversions for irrigation, municipal and industrial uses reduce the <br />alluvial aquifer and affect the amount ofsurface and groundwater that pre-historically <br />were available to wetland/riparian plants growing in the zone-of-influence. Therefore, it is <br />very important to maintain summer flows and channel maintenance flows2 within the MA to <br />maintain the hydrological conditions that are supporting the wetland/riparians that presently exist <br />within the river's zone-of-influence. <br /> <br />Second, livestock grazing has reduced streambank vegetation, thereby causing accelerated <br />rates of riverbank erosion and loss of wetland/riparian vegetation. The lack of <br />wetland/riparian vegetation also limits the amount of bank storage and moisture available for <br />plants. Grazing also affects habitat structure and limits the amount of cover available for <br />wildlife. The removal of livestock will eliminate the grazing effects that have impacted both <br />bank stability and the functional condition of wetland/riparian plant communities. <br /> <br />2 A channel maintenance flow of 85 cfs for 7 days in the spring was recommended by a <br />hydrogeomorphology study completed in 1995 for Reclamation. Currently channel maintenance <br />flows occur on an average of one out of every four years. <br /> <br />-15- <br />