Contributors (in alphabetical order)
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Habitat Areas and QualityFishReservoirs (Corps 1999)The Snake River reservoirs conform to a typical longitudinal impoundment gradient composed of three macrohabitat types, or reaches (Hjort et al. 1981). The tailwater is the section immediately below a dam and is the most riverine in nature. The uppermost portion of Lower Granite Reservoir is also more riverine, but is not a tailwater since there is no impoundment immediately upstream. Impoundment of Lower Granite Reservoir is considered to end near Asotin in the Snake River arm and near the Potlatch Corporation in the Clearwater River arm. A mid-reservoir reach represents the largest section of each impoundment and is a transition area from the lotic (riverine) character of the tailwater to the more lake-like (lentic or lacustrine) conditions nearer the dam. The reach immediately above a dam is the forebay. A sampling protocol described by Zimmerman and Parker (1995) assigned reach lengths of 6 kilometers (3.73 miles) each to a tailwater or forebay, but the length was likely a result of sampling considerations as opposed to defined differences in habitat. So designated, lower Snake River tailwaters and the upper reach of Lower Granite Reservoir comprised 5-15% of total reservoir area. Forebays formed a more uniform 13-18% of total reservoir area, and the remaining 67-72% is mid-reservoir (Zimmerman and Parker 1995). Each macrohabitat reach can contain up to several habitat types. The sampling scheme developed by Bennett et al. (1983) recognized six individual habitat classifications, or mesohabitats, that are described below. Six limnological characteristics of each mesohabitat in Little Goose Reservoir were summarized by Bennett et al. (1983) and are shown in Table 42. These attributes would be generally applicable for the respective habitats in all of the Lower Snake River. Tailwater-The highest water velocities in a reservoir up to 23 ft/sec were always found in the tailwater immediately below the dam. The uppermost area of a tailwater adjacent to the dam is the boat restricted zone (BRZ), which is variable in size but typically less than 0.6 miles long (Ward et al. 1995). Also included in a tailwater are protected areas with little or no current behind the lock chamber walls (most prominently below Lower Granite Dam) or adjacent to the earthen portion of a dam (e.g., below Little Goose Dam). Water current is typically negligible in these areas unless induced by spill. For example, under certain spill conditions, reverse eddy flows can occur below the earthen portion of Little Goose Dam. The bottom slope in a tailwater is moderate with relatively little littoral area and no macrophyte growth. Upper shoal-Moderately sloped areas in the upper portion of a reservoir, but located below a tailwater. Upper shoal habitats have slower velocities and a greater littoral area than in a tailwater due to slightly shallower bottom slopes. As a result of slower velocities, these areas generally accumulate sediment by deposition. In Little Goose Reservoir, water velocities in spring were lower than 3.3 ft/second, but higher than 1.0 ft/second, and intermediate between tailwater velocities and those of more downstream habitats (Bennett et al. 1983). Lower shoal-Moderately sloped areas up to 33 feet deep at 200 feet offshore, with water velocity less than 1.0 ft/second. Macrophyte growth was sparse, averaging about 3.3% of sampled areas. Lower Embayment-Relatively large, shallow (up to 13 feet deep) areas off the main river channel, and typically separated from the main reservoir by a road or railroad berm. No measurable water current occurs, and macrophyte growth can be extensive. In Little Goose Reservoir, the embayment sampled averaged 3.7% macrophyte coverage. Increased siltation from small tributaries and reservoir maturity likely has led to more substantial macrophyte growth in recent years. Examples of embayments include Deadman Bay in Little Goose Reservoir and Dalton and Emma lakes in Ice Harbor Reservoir. Gulch-Small to medium-sized, shallow (up to13 feet deep), off-channel areas with no measurable current. These areas may also be thought of as coves, as they are not cut off from the main reservoir body by a berm. Macrophytes are typically present, and the littoral areas of gulch habitats are typically extensive due to shallow bottom slopes. Deepwater-Steep sloped areas with little or no littoral zone, intermediate to no current (less than 1.0 ft/second) and up to 98 feet deep (as measured in Little Goose Reservoir by Bennett et al. 1983). Macrophytes are absent due to a negligible littoral zone. Comprehensive fisheries sampling conducted by the ODFW in 1991 and 1994 to 1996 in the lower Snake River reservoirs throughout the three macrohabitat reaches identified habitats only as "nearshore" and "offshore" (Zimmerman and Parker 1995; Parker et al. 1995). Nearshore habitats were defined as those less than 40 feet deep within 150 feet of shore. Table 42. Limnological characteristics at major sampling stations on Little Goose Reservoir, Washington (Corps 1999).
Bennett et al. (1983) listed all habitats other than deepwater as having mean depths less than or equal to 33 feet within 200 feet of shore. Thus, the range of mesohabitats less than 33 feet deep sampled by Bennett et al. (1983) is represented within the nearshore habitats sampled more recently by ODFW. Within the nearshore reservoir habitats, Bennett et al. (1983) defined the littoral area as 6.6 feet deep. Subsequent research in Lower Granite Reservoir redefined the littoral depth as 16 to 20 feet, approximately the maximum depth of light penetration (David H. Bennett, UI, personal communication). Snake River embayments between river kilometers RM 59-90 in Lower Monumental and Little Goose reservoirs were surveyed by Corps biologists in 1988 and 1989 (Kenney et al. 1989). Most of the 37 embayments surveyed were canyons and gulches cut off by railroad relocation when Little Goose Reservoir was filled. Most of these embayments remained connected to the main reservoirs by culverts. Others maintained a direct channel opening to the reservoir. The embayments ranged in area from less than 0.1 acre to 11.6 acres, and were generally steep-sided. More than half of the embayments surveyed were greater than 20 feet deep, and 11 were 30 feet or deeper. Aquatic vegetation was generally sparse due to the steep slopes. Shallower embayments with more moderate slopes supported pondweed, cattails, and rushes. Although this survey documented these habitats for a 31-mile portion of the reservoirs, similar embayments occur throughout the impounded reach. The proportion of shoreline distance represented by the six mesohabitats in Little Goose Reservoir, as listed in Bennett et al. (1983), was as follows: deepwater equals 47.8%; upper shoal = 14.8%; lower shoal = 11.9%; embayment = 9.4%; tailwater = 8.6%; gulch = 7.4%. Based on surface area estimates for the various macrohabitat reaches in Zimmerman and Parker (1995), proportionately more tailwater or upper reservoir (in Lower Granite Reservoir) habitat exists in each Snake River reservoir other than Little Goose. Similarly, Lower Monumental Reservoir had proportionately more deepwater habitat than Little Goose Reservoir, whereas Lower Granite and Ice Harbor reservoirs had proportionately less deepwater habitat. Relative to Little Goose Reservoir, both Ice Harbor and Lower Monumental reservoirs likely have more shallow water embayment and/or gulch habitat, whereas Lower Granite Reservoir has less. Reservoir SubstratesSeveral studies have described the substrata in the lower Snake River reservoirs. Bennett and Shrier (1986) conducted the first known substrate analyses in Lower Granite Reservoir. They used a Ponar dredge to characterize the substrate at six stations. Substrate sizes were significantly different between shallow and deep waters, although silt was the predominant substrate class at each of the six study locations. Clay content of the substrate generally increased with distance downstream. Organic content was less than 5%. In 1987, Bennett et al. (1988) surveyed the substrata in five shallow water areas of Lower Granite Reservoir by both systematic diving and Ponar dredge. Larger substrata were found near Wawawai (RM 109) in the lower portion of the reservoir than at other up-reservoir locations. A high degree of embeddedness was found for substrates less than 6 inches in diameter. Organic content ranged from 5.2% to 8.8% and overlapping confidence intervals suggested little difference in organic content among shallow water stations throughout Lower Granite Reservoir. Dredge samples taken from various depths within the littoral zones of Lower Granite and Little Goose reservoirs were analyzed and summarized in Bennett et al. (1998). Although the samples were taken from "largely shallow shoreline areas," they were not keyed to specific mesohabitats as identified above. Due to their shallow nature, however, sampled areas likely were shoal or embayment/gulch type habitats that had moderate to shallow bottom slopes. Littoral substrata in Lower Granite Reservoir were classified as sand, sand-cobble, sand-talus, or rip-rap (Curet 1994). Sampled areas on the north shoreline tended to be comprised of bottom particles greater than 1 inch in diameter. Most of the larger substrates were likely associated with rip-rap placed during parallel road and public access construction. South shore habitats tended to be comprised more of finer sands and silts. The south shore habitats are in reservoir areas less disturbed by anthropogenic activity. Shallow habitats in Little Goose Reservoir were classified as sand, cobble, talus, or rip-rap (Bennett et al. 1998). The north shoreline is largely rip-rap due to placement along the relocated parallel railroad. Finer grained sand and gravel habitats tended to occur more often along the south shore. Dauble and Geist (1992) described substrata within the Snake River arm of Lower Granite Reservoir (upper reservoir) and the tailwater below Lower Granite Dam in Little Goose Reservoir during the 1992 experimental drawdown. Cobble substrate was highly embedded with sand and fines based on visual observations of exposed shoreline areas in upper Lower Granite Reservoir. Measured substrate composition at 16 shoreline transects in the upper 3 miles of Little Goose Reservoir was estimated at boulder-13.5%; cobble-40.3%; gravel-24.5%; sand-15.9%; and silt-5.9%. Cobble substrates were highly embedded except for the upper 0.5 miles of the tailwater in the BRZ immediately below Lower Granite Dam. A trend toward greater deposition of sand and fines was noted with distance below Lower Granite Dam. Gravel/cobble substrates on mid-channel islands 2.5 and 3.0 miles below Lower Granite Dam were also highly embedded. Additional investigations by Dauble et al. (1996) reported large substrata in the cobble to boulder size in the tailwaters of Lower Granite and Little Goose dams on the Lower Snake River. Gravel was generally free of sediments in the tailwaters, which the authors attributed to hydraulic events (e.g., spills and power releases). Bennett et al. (1998) recently completed the most comprehensive survey of substrata in three of the lower Snake River reservoirs. Eighty-one Van Veen dredge samples were collected in total, three each at shallow, mid-depth, and deep locations in each of three sites in Lower Granite, Little Goose, and Lower Monumental reservoirs. Generally, the percentages of fine sediments (silts, clay, and organic material) increased from upstream to downstream in each of the reservoirs. Upstream sample locations were generally higher in sands, although coarse and fine gravels were collected from a shallow water site at RM 117 in Lower Granite Reservoir. Substrata from the three depths were generally similar throughout the three reservoirs. Silt and sand accounted for most of the substrate composition. Substrates were not otherwise classified in Lower Monumental or Ice Harbor reservoirs. Tailwater substrata, including the degree of embeddedness, are likely similar in composition to the more upstream tailwaters. Greater occurrence of fines, especially in down-reservoir areas such as gulch and embayment habitat, would be expected due to greater age and depositional history of these impoundments. TributariesMany of the small tributaries to the Snake River with adequate water are used by steelhead for spawning and rearing. Habitat conditions in these small streams are affected by roads, livestock grazing, farming and other land use activities. Sediment deposition, low water flows and marginal water temperatures are common habitat limiting factors in these tributaries. Riparian vegetation is often absent or degraded along portions or the full length of these streams (G. Mendel, WDFW, personal communication, Jan. 2001). Alpowa CreekA survey in 1980 divided the creek length into three reaches: lower, middle, and upper. Five to six sampling segments were used to characterize riparian and channel conditions. There was evidence during the 1980 survey of high peak flows and channelization along some stretches of this lower reach. Grazing was described as “heavy” within the riparian zone on 83% of the streambanks, resulting in poor herbaceous vegetation quality and quantity on 83% of the banks, poor shrubby vegetation on 67% of the banks and missing on 33%, and poor to fair condition of trees. The trees were described as “relicts” and of little reproductive value. Active erosion was noted on 8% of the banks. Substrate was characterized as a mix of boulder, rubble, and gravel; however, 46% of this substrate was considered embedded with fine particles. This sediment was thought to be the result of gullies draining adjacent upland cropland, and secondarily from bank erosion. Poor riparian conditions, high stream temperatures, and low flows were noted as limiting the value of this portion of Alpowa Creek to salmonids from late spring through the Fall (Soil Conservation Service 1981). Livestock grazing and some cultivation bounded the middle reach. Similar to the downstream reach, a few stretches appeared channelized. Again grazing was described as “heavy” on 83% of the streambanks and “moderate” on just 17% of the banks. Herbaceous, shrubby, and tree vegetation was characterized as either “poor” or “lacking” throughout this portion. One exception occurred along stream segment eight where trees were described in “good” condition despite evidence of heavy grazing in the past. It was suggested that this segment could serve as a model of the potential for riparian condition recovery provided the removal of disturbance (Soil Conservation Service 1981). This is near a site described in the 1998 survey as containing a “good riparian buffer with large trees and no grazing” (Mendel 1999). Grazing is heavy and riparian vegetation is missing just upstream of this site (upstream of Robinson Gulch). An estimated 22% of the streambanks were actively eroding along the middle reach of Alpowa Creek. The channel along this portion was characterized as combined boulder, rubble, and gravel suitable for spawning and rearing of salmonids except that an estimated 50% of the course substrate was embedded with fine particles. Similar to the lower portion, gully contribution from adjacent cropland as well as bank erosion accounted for this sedimentation of fines (Soil Conservation Service 1981). The Washington Department of Game estimated 70% of the stream was in poor condition and considered high stream temperatures, low flows, lack of streamside vegetative cover (primarily caused by overgrazing), lack of instream cover and bank instability (Mendel 1981) and sedimentation (Mendel and Taylor 1981). The majority of Alpowa Creek streamflow originates from springs in the headwaters. Upstream of the final sampling segment, the stream flows only during the spring. Livestock grazing is the primary land use here and was evident during the 1980 and 1998 surveys. Consequently, riparian vegetation is minimal and stream habitat lacks complexity along this reach (Mendel 1999). Herbaceous and shrubby streambank vegetation was either in poor condition or completely lacking in 1981. Trees were in fair condition on 60%, and poor on 40% of the streambanks. This reach contained streambanks that were significantly more vegetated and stable (76%) than the middle reach, with 7percent of the streambanks actively eroding. Channel substrate was boulder, rubble, and gravel, and less embedded in the lower and middle reaches. Because of this relatively low embeddedness, the upper reach is considered as suitable for spawning and rearing salmonids in areas that sustain enough streamflow to maintain cool water temperatures through the summer. Given the minimal or complete lack of shade provided by riparian vegetative cover, it may be the influence of the headwater springs that allows salmonids to use the upper reaches of Alpowa Creek (Soil Conservation Service 1981). The 1980 survey identified a major sediment source between segments 13 and 14 where a cropland terrace system flowed into a failed sediment retaining dam. The failed dam created a 10 to 20 foot deep gully, which apparently transported a large amount of rock and sediment delivering the material to the channel and creating a temporary dam in the stream. Although the retaining dam failure prior to the survey, considerable debris was still present found in the channel and for a distance downstream. In summary, nine percent of the streambanks were identified as having erosion problems, which contribute an estimated 2,988 tons of soil annually to Alpowa Creek. Areas that lack vegetation and bends in the stream harbored the most severe stream channel erosion. The poor condition of the riparian vegetation is attributed to livestock grazing along the banks and either mechanical or chemical removal of vegetation (Soil Conservation Service 1981). The reach from the confluence with the Snake River to the Highway 12 bridge is characterized by limited overhead riparian vegetation cover with grass as the predominant bank and riparian cover type. The channel contains some cobbles and small boulders embedded with a thick silt layer and covered in many places by thick attached algae. Some woody debris appears along this reach though it is mainly strewn outside of the channel, probably remnants of an extreme flood event. Glides and riffles dominate the instream habitat. Dry side channel(s) appear to be old channels as evidenced by adjacent riparian trees and shrubs. The valley broadens in the reach above the Highway 12 bridge crossing with cattle grazing and orchards as the primary land uses (location of Wilson Banner Ranch). The riparian vegetative buffer is thin and the channel straightened in sections along this reach. There appear to be dikes formed along much of this reach by heaping dredged dirt upon the stream banks. Also located in this reach are concrete blocks placed in the channel during the irrigation season (probably sometime in May through the summer) forming the only potential obstruction to fish migration in Alpowa Creek. The effectiveness in blocking the ascent of adult steelhead into the upper watershed is unknown, though it is thought to be minimal (G. Mendel, WDFW, personal communication 1999). Presently there is an effort to completely remove this barrier by pumping in-channel water for irrigation purposes to an off-channel location (D. Bartels, PCD, personal communication 1999). Details of this barrier are described in the Migration Barriers section. A relatively intact riparian vegetative zone occurs where Pow Wah Kee Gulch joins Alpowa Creek. However, there is evidence of grazing within this riparian area. Approximately one mile upstream from the Pow Wah Kee Gulch confluence the streambanks appear more severely degraded from grazing. At 2.8 miles upstream of Pow Wah Kee Gulch a vast grass field supports cattle and vegetation is non-existent along the creek. Just upstream of this section riparian vegetation reappears though grazing still occurs at lower densities. The next reach is defined roughly where Stember Creek joins Alpowa Creek (Alpowa Creek Road and Highway. 12). The lower section of Stember Creek exemplifies poor grazing practices that leave no vegetation whatsoever along the banks and riparian zone. The banks of Stember Creek are exposed and appear highly erosive, and the channel is very shallow, with cobble bars embedded with silt causing a braiding pattern in places. Approximately one mile above the confluence of Stember and Alpowa Creeks, large cottonwoods and other tree and shrub species provide some structure to the channel and substantial solar cover. However, there is little to no recruitment of LWD to the channel along this section. Larger boulders may provide some instream cover in some places in this reach. At 1.65 miles upstream of the Stember Creek confluence the channel splits and there is considerable evidence of livestock grazing along the streambanks and cattle were observed standing in the stream. Although some large cottonwoods exist, the riparian buffer is thin and degraded along this section. A persistent riffle-glide dominates the channel habitat and adequate pools are infrequent as is characteristic of most of the mainstem Alpowa. Any side channels that exist along Alpowa Creek may be important pool or slow water sources for salmonids, especially during high flow events. Two miles upstream of the Stember Creek confluence a small stockyard exists in the middle of the channel. No riparian woody vegetation exists in this location. At 2.5 miles upstream, the riparian vegetation consists of low grazed grasses. Large woody debris exists only out of the channel, possibly as remnants of abandoned channels. Robinson Gulch joins into Alpowa at 3.5 miles upstream of the confluence with Stember Creek. Cattle grazing are evident in this area and cattle were observed nearby. Virtually no riparian woody vegetation exists and streambanks are heavily eroded. Five miles from the Stember Creek confluence, grazing impacts the riparian zone and streambanks, and woody vegetation is sparse. The presence of LWD lodged in trees indicates the occurrence of a significant flood event. The channel is approximately 15 feet wide in this section, shallow with a cobble substrate, and dominated by riffle and glide habitat types. A sizeable remnant channel is evidence of a laterally mobile and dynamic channel through the floodplain. Trichoptera, ephemeroptera, and Simulid larvae were found attached to cobbles removed from the stream. A revisit to Alpowa Creek later in April found an abundance of pebble-cased caddis larvae Trichoptera. Based on accounts of residents and evidence of the riparian and channel characteristics, Alpowa Creek appears to be a highly responsive stream to storm events. Snowpack melt is probably not a major contributor to stream flow thus, stream flow mainly reflects rainfall patterns within the watershed. High stream flow events probably have greater potential for negative impacts to juvenile fish than adults. The lack of side channel pocket habitats and pool areas where small fish can take refuge within the channel leaves young fish especially vulnerable to flood events. Incubating embryos and newly emerged fry are at least as vulnerable as larger juveniles. Larger resident fish and adult salmonids are probably less susceptible to flood events mainly due to their size and ability to hold. However, a powerful enough event can also displace these fish when the lack of protective side channel habitats provides little refuge during floods. Adult salmonids are probably most affected by the shifting of sediments and bed material in the channel, which potentially removes spawning areas. The lack of side channels and large pools in Alpowa Creek is key to the survival of fish during high flows. Re-establishment of a meandering flood plain in areas that have been channelized and woody vegetation in the riparian zone may help develop these refuge habitats. Concrete slabs are temporarily placed in the channel to divert water from the lower reach of Alpowa Creek just upstream of the Highway 12 overpass (Wilson-Banner Ranch). This is thought to normally occur after any adult steelhead have already passed into the upper reaches to spawn (probably at least May), and the structures remain through the irrigation season (September). The previously mentioned problem was corrected in 2000 by Wilson Banner Ranch in cooperation with the Pomeroy Conservation District by cost share funding received from the Salmon Recovery Funding Board. The barriers were removed and an irrigation intake and distribution system for irrigation of orchards and bottomland was installed. The previous barriers at this location are now non existent. High water temperatures in the lower reaches (below Highway 12) of Alpowa Creek are thought to limit the movement of salmonids and any other cold water native species into the upper watershed during the summer months. Streamflow at times during the summer may also become low enough to limit movement into the watershed from the Snake River, although springs in the upper Alpowa usually maintain adequate flow even during this season. In 1998, salmonids were observed in Alpowa Creek downstream to the mouth during the late summer (Mendel 1999). Deadman CreekLivestock grazing and some cultivation bound the full length of the watershed. Herbaceous, shrubby, and tree vegetation was characterized as either “poor” or “lacking” throughout this portion. The majority of Deadman Creek streamflow originates from headwater springs. The presence of low embeddedness, the upper reach was thought to be suitable for spawning and rearing salmonids at least in areas that sustain enough streamflow to maintain cool water temperatures through the summer. Given the minimal or complete lack of shade provided by riparian vegetative cover, it may be the influence of the headwater springs that allows salmonids to use the upper reaches of Deadman Creek. Areas that lack vegetation and bends in the stream harbored the most severe stream channel erosion. The poor condition of the riparian vegetation is attributed to livestock grazing along the banks and either mechanical or chemical removal of vegetation (Soil Conservation Service 1981). The Washington Department of Game identified low summer flows, high temperatures, lack of streamside vegetation, lack of instream cover and eroding banks as limiting factors for most of Deadman Creek and low flows, high temperatures, lack of streamside vegetation and eroding bank for Meadow Creek (Mendel 1981). Based on accounts of residents and evidence of the riparian and channel characteristics, Deadman Creek appears to be a highly responsive stream to storm events. Snowpack melt is probably not a major contributor to stream flow, and therefore stream flow mainly reflects rainfall patterns within the watershed. High stream flow events probably have greater potential for negative impacts to juvenile fish than adults. The lack of side channel pocket habitats and pool areas where small fish can take refuge within the channel leaves young fish especially vulnerable to flood events. Incubating embryos and newly emerged fry are at least as vulnerable as larger juveniles. Larger resident fish and adult salmonids are probably less susceptible to flood events mainly due to their size and ability to hold. However, a powerful enough event can also displace these fish when the lack of protective side channel habitats provides little refuge during floods. Adult salmonids are probably most affected by the shifting of sediments and bed material in the channel, which potentially removes spawning areas. WildlifeWildlife habitats within the subbasin consist of two types: riparian/floodplain, and shrub steppe/agricultural. The riparian/flood plain habitat lies along the Snake River and its tributaries. The shrub steppe/agricultural encompasses the sub-basin uplands and consists mostly of agricultural croplands, rangeland, Conservation Reserve Program lands (CRP), and some shrub steppe habitat. Vegetative associations are described by Daubenmire and Daubenmire (1968), Daubenmire (1970), and Franklyn and Dryness (1973). Native habitats within the subbasin have been altered by human development (e.g., agriculture, livestock grazing, and the invasion of noxious weeds). Riparian/Flood PlainSince the arrival of settlers in the early 1800’s, 50%-90% of riparian habitat in Washington has been lost or modified. Riparian habitat is limited along the Snake River and was inundated when dams were established. The Corps of Engineers has created 3,197 acres of managed habitat units along the river in an effort to improve conditions after inundation; Ice Harbor pool – 1241 ac., Lower Monumental pool – 1035 ac., Little Goose pool – 1890 ac., - Lower Granite pool – 66 acres. Most of these sites were irrigated alfalfa-grass-forbe meadows and planted with a variety of trees and shrubs to provide a mosaic of habitats. In addition, an estimated 4,017 acres of dry land habitat plots exist, which have been enhanced with the addition of guzzlers, goose tubs, and bird boxes, the grassland habitat itself remains unchanged. Shrub Steppe/AgricultureHistorically, shrub steppe habitat consisting of sagebrush, rabbitbrush, and various bunch grasses covered nearly all non-forested lands east of the Cascade Range in Washington, of which only 50% remains (Daubenmire 1970). Due to development, the lowland shrub steppe habitat component within the subbasin has suffered the same fate. Agricultural development results in rapid and extensive loss of vegetation, while livestock grazing results in a slower impact to the composition and structure of native vegetative communities (Dobler and Eby 1990). Species dependent on shrub steppe habitat have been extirpated or populations are severely depressed. In recent years, many acres have been removed from agricultural production in Whitman, Walla Walla, Columbia and Garfield counties (T. Johnson, personal communication 2000) and placed in the Conservation Reserve Program (CRP), which has benefited numerous species of wildlife within the subbasin by re-establishing grassland habitat. TributariesAlpowa CreekThe Alpowa Creek watershed never supported large populations of grazing animals. Although white-tailed deer, mule deer, elk, and pronghorn antelope did occur, their numbers were small in comparison to those found on similar rich grasslands. The low rate of summer precipitation and hunting pressure probably kept grazing populations minimal. Many of the reports by early explorers comment on the scarcity of game in the area (Tisdale 1961). Later, the introduction of cheatgrass further complicated matters for native animals like the sharp-tailed grouse. This change in habitat favored introduced species such as the black-tailed rabbit that out-competed and have now replaced the indigenous white-tailed jackrabbit. | ||||||||||||||||||||||||||||