Draft Imnaha Subbasin Summary November 30, 2001 Prepared for the Northwest Power Planning Council Subbasin Team Leader



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Habitat Areas and Quality

Fish

Fish habitat quality in the Imnaha subbasin is considered to be good to excellent, especially in relation to similar subbasins (Wallowa-Whitman National Forest 1998). Habitat condition for anadromous and resident species is generally highest in the upper portions of the subbasin, and decreases with elevation, depending upon season and type of use (most notably through reaches bordered by private ground). Tributaries and mainstem reaches are used by both resident and anadromous species for spawning, rearing, and migratory life history stages.

Anadromous habitat

The total estimated number of stream miles containing anadromous fish habitat is estimated to be 397 (Wallowa-Whitman National Forest 1998; USDA Forest Service 1998a; USDA Forest Service 1998b). Without the Sheep Creek drainage area, the subbasin has 174.5 miles of fish-bearing perennial streams, 147.9 miles of non-fish-bearing perennial streams and 1,094.3 miles of intermittent streams (Wallowa Whitman National Forest 1998). The Imnaha subbasin contains an estimated 263 stream miles of summer steelhead spawning and rearing habitat (USDA Forest Service 1998a), 130.6 stream miles of spring/summer chinook spawning and rearing habitat (USDA Forest Service 1994), and approximately four to six miles of fall chinook habitat (USDA Forest Service 1994).

The National Marine Fisheries Service has designated critical salmon and steelhead habitat for species endemic to the Snake River Basin to include all areas currently accessible to the species within the range of the Evolutionarily Significant Unit (U. S. Federal Register 2000). Critical habitat inherent to this definition includes “all waterways, substrate, and adjacent riparian zones below longstanding, naturally impassable barriers (i.e., natural waterfalls in existence for at least several hundred years)”, which functionally provides “spawning sites, food resources, water quality and quantity and riparian vegetation” (U. S. Federal Register, 2000).


Instream habitat assessment using the NMFS Matrix of Pathways and Indicators (NMFS 1996) has been conducted throughout the Imnaha subbasin. The inventory is used to assess the ESA status of west coast steelhead populations in California, Oregon, Idaho, and Washington by evaluating the condition of their habitat (NMFS 1996). The procedure was designed to comply with Section 7 consultation requirements of the ESA, and was jointly developed by NMFS and Forest Service personnel from Regions 1, 4, and 6 (USDA Forest Service 1998a). Ratings are based upon habitat indicators, which are relative to the various life history pathways of steelhead. Criteria used to evaluate indicators are shown in Appendix E. Table 26 and Table 27 define environmental baseline for habitat indicators in the upper and lower Imnaha (respectively). Table 28 defines environmental baseline conditions for habitat indicators in the Big Sheep Creek watershed.
Table 26. Environmental baseline for habitat indicators in the lower1 Imnaha subbasin (reproduced from USDA Forest Service 1998a)2

Pathways/

Indicators

Environmental Baseline

Properly Functioning

At Risk

Not Properly Functioning











Water Quality


Temperature







3

Sediment/Substrate




4




Chemical Contamination

X



















Habitat Access

Physical Barriers

5



















Habitat Elements

Large Woody Material







6

Pool Frequency and Quality







7

Off Channel Habitat


8







Refugia

9



















Channel Condition

Width:Depth Ratio

10







Streambank Condition

11







Floodplain Connectivity




12
















Flow/Hydrology

Peak/Base Flows

13







Drainage Network

X

















Watershed Conditions

Road Density




14




Disturbance History




15




Riparian Reserves




16
















OVERALL WATERSHED CONDITION

17







CONDITION: USFS SYSTEM LANDS

X







CONDITION: PRIVATE LANDS




X



Notes:


  1. The lower Imnaha River Watershed encompasses the mainstem Imnaha River from RM 0 to approximately RM 24.
  2. Information Source: Stream Surveys. Wallowa County-Nez Perce Salmon Recovery Plan 1994 (revised September 1999).


  3. TEMPERATURE: Stream temperatures are at environmental potential but do not meet PACFISH and NMFS matrix criteria. The Lower Imnaha River flows through low elevation grasslands and basalt rock. At the confluence with the Snake River the elevation is approximately 950 feet. By RM 23, the Imnaha has climbed to an elevation of 1,600 feet. Modification to the floodplain and riparian vegetation has been noted on private land along the mainstem. Here cultivation, farming, and settlement has reduced the occurrence of cottonwood. Personal observation has shown that Perennial Tributaries are Properly Functioning.

Mainstem of the Imnaha River, Reach 1-6, is at environmental potential for most of the length.

  1. SEDIMENT: Perennial Tributaries – appears to be a result of fire and windfall. Stream surveys have little reference to cattle related impacts. Mainstem of the Imnaha River, Reach 1-6; unstable cobble and gravel bars related to the 1997 flood.

  2. PHYSICAL BARRIERS: The only known barrier is a culvert on Rd. 4240-250 at the head of Upper Horse Creek Subwatershed.
  3. LARGE WOODY MATERIAL: Perennial Tributaries – Properly Functioning. Channel modification in Lower Lightning Creek, on private property, has reduced future recruitment. Mainstem of Imnaha River, Reach 1-6 is at natural potential even though it does not have >20 pieces per mile and recruitment potential is limited. Because of the arid grassland environment, channel size, and flow velocities: most large wood is floated in from upstream. LWM collects in jams of smaller pieces having been tumbled and worn during transport. Cultivation of riparian areas has reduced the abundance of cottonwood adjacent to the river.


  4. POOL FREQUENCY: Does not meet PACFISH guidelines and the NMFS Matrix. This is due to the Stream Survey methodology for collecting pool information and inherent channel limitations. Stream Survey methodology does not collect information in pools which are less than full width in size, thus pocket pools and partial width pools are not counted. Stream survey notes indicate that pocket pool habitat may occupy up to 30 percent of the channel. In addition, bedrock outcrops, boulders, and channel morphology features (sinuosity, gradient) are the primary pool forming factors in the mainstem of the Imnaha River. Given the Imnaha Rivers’ width and gradient, most wood is found along the channel margins or in large wood jams. Here it provides slow water habitat and pocket pools. Perennial Tributaries are at natural potential and Properly Functioning. Perennial tributaries are Rosgen A and B type channels with step pool morphology formed by boulders and wood. Mainstem of the Imnaha River, Reach 1-4, pool frequency is at natural potential (Properly Functioning) from the Snake River confluence upstream to Reach 4 (beginning of the cultivated lands and channel modifications). The Mainstem of the Imnaha River, Reach 4-6 is below potential due to cultivation and channel modifications (At Risk). The Imnaha River is a Rosgen B channel with C channel types where the gradient reduces. Pools are primarily plunge and step pools formed at bedrock constrictions, behind boulders, and at sinuosity curves.

  5. OFF-CHANNEL HABITAT: Properly Functioning throughout the watershed except where the channel has been modified (Imnaha River Reach 4-6 and Lower Horse Creek and Lightning Creek).
  6. REFUGIA: Properly functioning throughout the watershed except where the channel has been modified (Imnaha River Reach 4-6 and Lower Horse Creek and Lightning Creek).


  7. WIDTH:DEPTH RATIO: Properly functioning throughout the watershed except where the channel has been modified (Imnaha River Reach 4-6 and Lower Horse Creek and Lightning Creek).

  8. STREAMBANK CONDITION: Perennial Tributaries – Properly Functioning. Stream surveys note bank instability related to fire and windthrow. Mainstem of the Imnaha River, Reach 1-6 – At Risk due to the effects of the 1997 Flood. Minor instability related to roading, trails, cultivation on private land.

  9. FLOODPLAIN CONNECTIVITY: Perennial Tributaries – Properly Functioning. Mainstem of the Imanaha River, Reach 1-6, At Risk due to landuse and ownership patterns within the watershed.

  10. BASEFLOW/PEAKFLOW: Cumulative effects including impacts within the Upper Imnaha River basin. Throughout the upper and lower basins, activities have been/are concentrated along the river corridor.

  11. ROAD DENSITY: Overall road density is low, but most subwatersheds have stream bottom roads.

  12. DISTURBANCE HISTORY: ECA is not a concern within the watershed however disturbance has been/is concentrated along the river corridor.

  13. RIPARIAN RESERVES: Activities have been/are concentrated in the riparian reserves, especially on private lands.

  14. OVERALL WATERSHED CONDITION: BETWEEN PROPERLY FUNCTIONING AND AT RISK.

Table 27. Environmental baseline for habitat indicators in the upper1 Imnaha subbasin (reproduced from USDA Forest Service 1998a)2



Pathways/

Indicators


Environmental Baseline

Properly Functioning

At Risk

Not Properly Functioning













Water Quality

Temperature







3

Sediment/Substrate

4







Chemical Contamination

X



















Habitat Access

Physical Barriers

5



















Habitat Elements

Large Woody Material








6

Pool Frequency and Quality







7

Off Channel Habitat

8







Refugia

9



















Channel Condition

Width:Depth Ratio

10







Streambank Condition

11







Floodplain Connectivity

12



















Flow/Hydrology

Peak/Base Flows

13








Drainage Network

X



















Watershed Conditions

Road Density

14







Disturbance History

15







Riparian Reserves

16



















OVERALL WATERSHED CONDITION

17







CONDITION: USFS SYSTEM LANDS

X







CONDITION: PRIVATE LANDS




X


Notes:


  1. The upper Imnaha River Watershed encompasses the mainstem Imnaha River from RM 24 (approximately 0.7 miles upstream of the town of Imnaha) to RM 77. The river flows eastward from the Eagle Cap Wilderness before turning north to flow to the Snake River. The lower reaches of Subwatershed 09 flow through low elevation grasslands and basalt rock (grassland ecosystems dominate RM 24 to approximately RM 47). Above RM 48, the ecosystem changes to a forested environment with interspersed meadows and grasslands.

  2. INFORMATION SOURCE: Stream Surveys. Wallowa County-Nez Perce Salmon Recovery Plan 1994 (revised September 1999).

  3. TEMPERATURE: Stream temperatures are near or at environmental potential but do not meet PACFISH and NMFS Matrix criteria. Modification to the floodplain and riparian vegetation has been noted on private land along the mainstem. Cultivation, farming, and settlement has reduced the occurrence of cottonwood and conifers. In the upper reaches of the basin, the River flows through wilderness and forested landscapes. Little or no modification of the floodplain and riparian vegetation has been noted. Perennial Tributaries are Properly Functioning. Mainstem of the Imnaha River, Reach 7-16 is near environmental potential, while Reaches 17-23 are Properly Functioning (these reaches are located within the Eagle Cap Wilderness or along portions of the river known for its recreation and scenic values).
  4. SEDIMENT: Perennial Tributaries – The intermittent/upper perennial reaches have reference to cattle related impacts. This concern is being addressed in the Marr Flat Cattle Allotment AMP. The lower reaches of the perennial tributaries are Properly Functioning. Mainstem of the Imnaha River, Reach 7-16 – Unstable cobble and gravel bars related to the 1997 Flood. Mainstem of the Imnaha River, Reaches 17-23 – Properly Functioning. There is an active hillslope erosion on the North Fork of the Imnaha within the Eagle Cap Wilderness. This erosion was triggered by a side channel debris flow during a thunderstorm. The hillslope adjacent to the river contributes sediment into the Imnaha River as the river undercuts the toe of the slope.


  5. PHYSICAL BARRIERS: The existence of physical barriers is unknown for perennial tributaries on private land. There are no known man-made physical barriers on Forest Service System Lands.

  6. LARGE WOODY MATERIAL: Perennial Tributaries – Properly Functioning and At Risk. The 1997 flood scoured the channels of Blackhorse, Beaverdam, Grizzly Creek, Gumboot Creek, Summit Creek, and Nine Points Creek. Some of the headwater reaches have been harvested or roaded reducing large wood recruitment. Mainstem of Imnaha River, Reach 7-16 – at natural potential (Properly Functioning) even though it does not have >20 pieces per mile and recruitment is limited. Because of the grassland environment (in the lower end of the basin), channel size, and flow velocities, most large wood is floated in from upstream. LWM collects in jams of smaller pieces having been tumbled and worn during transport. Cultivation of riparian areas has reduced the abundance of conifers and cottonwood on private land adjacent to the river. Mainstem of the Imnaha River, Reaches 17-23 – Properly Functioning. The headwater area of the Imnaha River consists of high mountain meadows and sub-alpine ecosystems. Wood is transported to the Imnaha River by snow avalanches and debris flows.
  7. POOL FREQUENCY: Does not meet PACFISH guidelines and NMFS Matrix. This is due to the Stream Survey methodology for collecting pool information and inherent channel limitations. Stream Survey methodology does not collect information in pools which are less than full width in size, thus pocket pools and partial width pools are not counted. Stream survey notes indicate that pocket pool habitat may occupy up to 30 percent of the channel. In addition, bedrock outcrops, boulders, and channel morphology features (sinuosity, gradient) are the primary pool forming factors in the mainstem of the Imnaha River. Given the Imnaha Rivers’ width and gradient, most wood is found along the channel margins or in large wood jams. Here it provides slow water habitat and pocket pools. Perennial Tributaries are Properly Functioning or At Risk, depending upon the LWM component. The 1997 Flood scoured the channels of Blackhorse, Beaverdam, Grizzly Creek, Gumboot Creek, Summit Creek, and Nine Point Creek. Perennial tributaries are Rosgen A and B type channels with step pool morphology formed by boulders and wood. Mainstem of the Imnaha River, Reach 7-16 – Pool frequency is At Risk (where channel modification has occurred). Mainstem of the Imnaha River, Reaches 17-23 – Properly Functioning. The Imnaha River is a Rosgen B channel with C channel types where the gradient reduces. Pools are primarily plunge and step pools, formed at bedrock constrictions and at sinuosity curves.


  8. OFF-CHANNEL HABITAT: Properly Functioning throughout the watershed except where the channel has been modified (Mainstem of the Imnaha River, Reaches 7-16), or in the 1997 Flood-scoured tributaries.

  9. REFUGIA: Properly Functioning throughout the watershed except where the channel has been modified.

  10. WIDTH:DEPTH RATIO: Properly Functioning throughout the watershed except where the channel has been modified.

  11. STREAMBANK CONDITION: Perennial Tributaries – Stream surveys note bank instability related to harvest, roads, and grazing in the upper headwaters of the tributaries. Grazing concerns are being addressed during the Marr Flat AMP process. Tributaries, which flow through private land, may have reduced bank stability, depending upon the extent of land management activities. Mainstem of the Imnaha River, Reach 7-16 – On the Line between Properly Functioning and At Risk (At Risk in localized locations). Bank stability has been reduced in localized areas by the 1997 Flood or private land activities. Mainstem of the Imnaha River, Reach 17-23 – Properly Functioning. There is a landslide on the North Fork of the Imnaha River within the Eagle Cap Wilderness. This slide was triggered by a side channel debris flow that formed during a thunderstorm.

  12. FLOODPLAIN CONNECTIVITY: Properly Functioning except where tributaries were scoured during the 1997 Flood, or where land use and ownership patterns have altered the riparian communities.

  13. BASEFLOW/PEAKFLOW: From the Blackhorse Tributary confluence upstream, there are negligible Cumulative Effects. Downstream of Blackhorse confluence, cumulative effects have been identified within the basin. Activities have been/are concentrated along the river corridor.

  14. ROAD DENSITY: Overall road density is low, but most subwatersheds have stream bottom roads.


  15. DISTURBANCE HISTORY: ECA is not a concern within the watershed, however disturbance has been/is concentrated along the river corridor. Within the headwater tributaries, outside of the Eagle Cap Wilderness, land use activities have resulted in cumulative effects.

  16. RIPARIAN RESERVES: Activities have been/are concentrated in the riparian reserves, especially on private lands.

  17. OVERALL WATERSHED CONDITION: PROPERLY FUNCTIONING

Table 28. Environmental baseline for habitat indicators in Big Sheep Creek1, Section 7 Watershed (reproduced from USDA Forest Service 1998b)2.

Pathways/

Indicators

Environmental Baseline

Properly Functioning

At Risk

Not Properly Functioning













Water Quality

Temperature




3




Sediment/Substrate



4





Chemical Contamination

5



















Habitat Access

Physical Barriers

X



















Habitat Elements

Large Woody Material

6







Pool Frequency and Quality




7




Off Channel Habitat

8







Refugia

8

















Channel Condition


Width:Depth Ratio

9







Streambank Condition

10







Floodplain Connectivity

8



















Flow/Hydrology

Peak/Base Flows




11




Drainage Network

12



















Watershed Conditions

Road Density




12




Disturbance History




13


Riparian Reserves





14
















OVERALL WATERSHED CONDITION




X




CONDITION: USFS SYSTEM LANDS

X







CONDITION: PRIVATE LANDS




X



Notes:


  1. Table 28 represents an average condition for the entire Big Sheep Creek Section 7 Watershed.
  2. INFORMATION SOURCE: Big Sheep Creek Watershed Analysis 1995: Stream Survey Reports 1989-1996: Wallowa County-Nez Perce Salmon recovery Plan 1994 (revised 1999). Stream surveys were used to evaluate spot water temperatures, sediment/substrate, physical barriers, large woody material, pool frequency and quality, off-channel habitat, refugia, width:depth ratio, streambank condition, floodplain connectivity and riparian reserves. Data loggers/Ryan Temp. Mentors were used to obtain stream temperature information. Professional judgment and Big Sheep Creek Watershed Analysis were used to interpret water temperatures, sediment/substrate, chemical contamination, pool frequency and quality, off-channel habitat, refugia, streambank condition, floodplain connectivity, flow/hydrology, disturbance history and riparian reserves. Transportation System Plans were used for road density. On Non-Forest Service System Lands the Wallowa County-Nez Perce Salmon Recovery Plan and professional judgment from observations were used.


  3. TEMPERATURE: At Risk throughout the watershed due to irrigation diversions and loss of streamside canopy through land use and fire. Stream temperatures would be expected to increase throughout the basin as one moves from sub-alpine meadows and mountain forests to grassland canyons near the confluence with the Imnaha River.

  4. SEDIMENT: Big Sheep Creek watershed is a geologically young, dynamic system responding to mountain uplift and base level changes in the Snake River as well as the effects of land use, hydroelectric power generation, water diversions, and fire. Tributaries are actively migrating. Headwater streambank material is an unconsolidated mix of glacial till, glacial outwash, colluvium, and alluvium. The upper headwaters provide sediment throughout the watershed. Meadow streambanks are composed of fine-grained sands. These materials are easily eroded where streambank vegetation has been reduced. Fine sediment concerns related to grazing within the Marr Flat Cattle Allotment are being addressed during the Marr Flat AMP Process. Fine sediment concerns related to grazing within the Divide Cattle Allotment are addressed during the annual operating plan for the allotment.

  5. CHEMICAL CONTAMINATION: No portion of the Big Sheep Watershed has been identified as having chemical contamination through the State of Oregon 303 (d) process. Septic tanks and feedlots may be contributing chemical contaminants.
  6. LARGE WOODY MATERIAL: Throughout 70 percent of the watershed, LWM is at environmental potential. Within dry landscapes, LWM input appears to be cyclic in nature. Most of the streamside ponderosa pine was removed years ago by the private landowners. On the upper watershed reaches, current supplies of LWM are high due to the effects of the Canal and Twin Lakes Fires and Spruce-budworm outbreaks. Future LWM recruitment is going to be limited as new forests grow.


  7. POOL FREQUENCY: Pool frequency rates Not Functioning when compared to PACFISH guidelines and the NMFS matrix. However, professional judgment based on onsite observations and stream survey notes, indicates an At Risk rating. This is due to the Stream Survey methodology for collecting pool information and channel constraints. Stream Survey methodology does not collect information in pools which are less than full width in size, thus pocket pools and partial width pools are not counted. Stream survey notes indicate that pocket pool habitat may occupy up to 30 percent of the channel, greatly increasing pool habitat. Most of the channels within the watershed are Rosgen A4/3 and B4/3. These channels are typically cascade and riffle systems, with irregularly spaced plunge pools and step pools. Bedrock outcrops, boulders, LWM and channel morphology features (sinuosity, substrate, gradient) are the primary pool forming factors.

  8. OFF-CHANNEL HABITAT, REFUGIA, FLOODPLAIN CONNECTIVITY: Properly Functioning except in the lower reaches of Big Sheep Creek and Little Sheep Creek where channel and floodplain modification has reduced the occurrence of over bank flow and multi-channel development. The tremendous quantities of blowdown with the Twin Lakes and Canal Fire areas are creating a lot of off-channel habitat.

  9. WIDTH:DEPTH RATIO: Properly Functioning except in the lower reaches of Big Sheep Creek and throughout Little Sheep Creek where channel and floodplain modification have reduced channel stability or resulted in aggradation.

  10. STREAMBANK CONDITION: Properly Functioning except at localized locations where channel and floodplain modification or fire have reduced the bank vegetation.
  11. PEAKFLOW/BASEFLOW: Flow regimes in Big Sheep Creek and Little Sheep Creek have been altered due to aggradation (resulting in subsurface flows), bedload transport (creation of mid-channel bars splitting flows), hydroelectric power generation, and irrigation diversions and withdrawals. The headwaters of Little Sheep Creek, Big Sheep Creek, and Carrol Creek have ECA’s at or approaching 30%, resulting from the Canal and Twin Lakes Fires. These basins have localized locations of bank and channel instability.


  12. ROAD DENSITY AND DRAINAGE NETWORK: Streambottom roads are present in most of the subwatersheds and along Big Sheep and Little Sheep Creeks.

  13. DISTURBANCE HISTORY: In addition to the natural disturbances of geologic uplift, faulting, debris flows and avalanche, and fire (Canal Fire 25,000 acres; Twin Lakes Fire 1,700 acres), the watershed has a rich human history. Settlement along the mainstem of Big Sheep and Little Sheep Creeks and wagon trails up the tributaries attest to a love and use of the land. Most activity has been concentrated along the riparian areas with channel and floodplain modification in the middle and lower reaches of Big and Little Sheep creeks. Tributaries draining the Marr Flat and Harl Butte plateaus have been roaded, harvested and grazed over many years.

  14. RIPARIAN RESERVES: Fire and disturbance concentrated in the riparian areas have reduced the function of the riparian zones throughout the watershed. Vegetation conditions are on an improving trend.

  15. OVERALL SUBWATERSHED CONDITION: At Risk

A more recent application of the NMFS Matrix of Pathways and Indicators was used in an assessment of conditions in Little Sheep Creek, during the planning and investigation phases of a proposed bridge construction project. The assessment identified the following habitat indicators as either at risk or not properly functioning: water temperatures, turbidity/sediment, substrate, large woody debris, pool frequency and quality, off-channel habitat, refugia, streambank condition, floodplain connectivity, peak/base flows, drainage network increase, and disturbance history and regime (NMFS 2001).



Resident Salmonid (bull trout) Habitat Quality

Bull trout habitat in the Imnaha subbasin has been modified largely as a result of legacy effects of land use activities. Timber harvest, road building, mining, grazing, irrigation development, and recreation have contributed to the current amount and condition of available bull trout habitat in the Imnaha (Buchanan et al. 1997). Most of these activities continue to take place, although to different degrees, locations, and manners from what occurred in the past.

Bull trout habitat in the mainstem Imnaha River is generally in good condition with respect to water quality, availability of spawning gravels, and suitability of rearing habitat (Buchanan et al. 1997). Water quality, specifically stream temperatures, may be compromised in some areas due to a lack of riparian vegetation. In the lower Imnaha, stream temperatures exceeding 20C have been recorded on occasion, which is nearing bull trout tolerance levels.

Bull trout habitat quality in the Big Sheep Creek subwatershed is mixed. The condition of riparian vegetation below the Wallowa Valley Improvement Canal, specifically that occurring along the lower 34 miles of Big Sheep and Lick creeks, is considered to be fair to poor (Buchanan et al. 1997). Riparian vegetation between Owl and Lick creeks, however, is unroaded and in excellent condition. Spawning and rearing habitat in Big Sheep Creek above the Wallowa Valley Improvement Canal occurs primarily within a wilderness area. Habitat in this portion of the subwatershed is considered to be pristine, characterized by a relatively steep gradient. Habitat in Little Sheep Creek is marginal. Land use activities, fires, flooding, and landslides have reduced the quality of bull trout habitat in Little Sheep Creek to what is characterized as the most at-risk population of fish in the subbasin (Buchanan et al. 1997).


Wildlife


Wildlife species composition and numbers naturally fluctuate as weather conditions, competition, predation, and parasitism and other environmental processes alter vegetative and wildlife communities. Manipulation of these natural processes by humans has moved some habitat conditions in the Imanha subbasin outside the natural range of variability (USDA Forest Service 1999). Habitats for wildlife have become increasingly fragmented, simplified in structure, and infringed on or dominated by exotic plants (Quigley and Arbelbide 1997).

Forest

Mixed Conifer Forests

At the landscape level, most forested habitats in the subbasin are classified as northeastern Oregon mixed conifer forests (Figure 6). Forested habitats are used by a variety of wildlife species including those from eight of Wisdom et al.’s twelve families (2000). In the Big Sheep Creek watershed alone, 122 wildlife species have been documented or are suspected to occur in mixed conifer forests (Wallowa-Whitman National Forest 1995).

At elevations of 4600-5600 feet, northern slopes contain mostly mid seral stands dominated by grand fir and Engelmann spruce((Wallowa-Whitman National Forest 1998). Fire suppression has led to overstocked stands with one or two story structures and reductions in early seral species such as ponderosa pine and western larch (Larix occidentalis)(Wallowa-Whitman National Forest 1998). Ponderosa pine communities in the subbasin are most common on warm, low elevation sites where they often grade into grassland communities (Wallowa-Whitman National Forest 1995). Historically, small disturbances, particularly low intensity surface fires, favored early seral species dominance (Wallowa-Whitman National Forest 1998). A variety of problems plague current late seral stands: bark beetle attacks, spruce budworm defoliation, and mortality from root rot centers (Wallowa-Whitman National Forest 1998).


Changes in the fire regimes have resulted in changes in plant community composition in forested stands. Mixed conifer forests tend to be densely stocked, providing greater fuel loads than were historically present (Wallowa-Whitman National Forest 1995). Structurally, higher levels of the understory reinitiation and stem exclusion stages exist (Wallowa-Whitman National Forest 1998; Wallowa-Whitman National Forest 1995). Meanwhile, lower levels of mid-seral and the oldest successional stages exist than historically were present (Wallowa-Whitman National Forest 1995). Understory species such as Idaho fescue and bluebunch wheatgrass were favored by the historic fire regime (Wallowa-Whitman National Forest 1998). Today’s less frequent, higher intensity fires burn the herbaceous communities more severely than the low intensity fires of the past (Wallowa-Whitman National Forest 1998). As a result, Idaho fescue and bluebunch wheatgrass are out-competed and replaced by less desirable species such as annual bromes (Bromus spp.) (Wallowa-Whitman National Forest 1998). The communities and structures present today are “very susceptible” to “uncharacteristic stand replacement events” (Wallowa-Whitman National Forest 1998).

Montane Conifer Forests

At higher elevations, the Imnaha River flows through montane coniferous forests intermixed with alpine tundra communities (Rose et al. 1993). Alpine and subalpine forests contain tree species such as subalpine fir, lodgepole pine, Engelmann spruce, western larch, Douglas fir and whitebark pine (Wallowa-Whitman National Forest 1998; Wallowa-Whitman National Forest 1995). In areas where subalpine fir and Engelmann spruce are the climax community dominants, lodgepole pine and western larch are the early successional species (Wallowa-Whitman National Forest 1995). Forested communities of the headwaters area of Lick Creek, a tributary of Big Sheep Creek, contain subalpine fir, Engelmann spruce, and lodgepole pine (Mays 1992). The Imnaha River watershed portion of the subbasin has structural stage patterns in high elevation forests that “compare favorably with historic levels” (Wallowa-Whitman National Forest 1998). The Big Sheep Creek watershed portion of the subbasin differs from historical structural stage ranges (Wallowa-Whitman National Forest 1995). Fire suppression has led to more late successional stands than would have occurred historically (Wallowa-Whitman National Forest 1995). The Big Sheep Creek watershed alpine communities are “relatively healthy” (Wallowa-Whitman National Forest 1995). Subalpine fir forests are used by a variety of wildlife species including at least three amphibian species, 40 bird species, and 30 mammal species (Wallowa-Whitman National Forest 1995).


Grasslands and Shrublands


Grassland and shrubland habitat cover a large portion of the subbasin (refer to Figure 6). Much of this area is currently used or has previously been used for domestic grazing. In the Big Sheep Creek watershed, 4 amphibian, 6 reptile, 28 bird, and 18 mammal species are documented or suspected to inhabit the area’s grassland communities (Wallowa-Whitman National Forest 1995). In the watershed’s shrublands, 5 amphibian, 6 reptile, 51 bird, and 27 mammal species are documented or suspected to exist (Wallowa-Whitman National Forest 1995).

Canyon Grasslands

Grasslands in the subbasin between 6000 and 3000 feet tend to be members of Idaho fescue or bluebunch wheatgrass associations (Wallowa-Whitman National Forest 1998; Wallowa-Whitman National Forest 1995). At elevations below 3000 feet, bluebunch wheatgrass and sandberg bluegrass grow on warm, dry southern slopes (Nez Perce Tribe et al. 1990). Cool, damp northern slopes below 3000 feet contain bluebunch wheatgrass and Idaho fescue (Nez Perce Tribe et al. 1990). Valley bottom grassland communities are usually bluebunch wheatgrass or bluebunch wheatgrass/Idaho fescue associations (Wallowa-Whitman National Forest 1998).

A long-term analysis of allotment areas grazed from Gumboot Creek downstream showed that grassland communities on slopes are in fair to good condition with a trend of stable or improving (Wallowa-Whitman National Forest 1998). Lower canyon bench communities dominated by sand dropseed or red three-awn are in poor to good condition with a trend of stable or improving (Wallowa-Whitman National Forest 1998). Some communities in the subbasin are in disclimax due to dominant annual grasses (Wallowa-Whitman National Forest 1998). Yellow-star thistle, and other noxious weeds are prominent in many communities particularly those in the lower subbasin (Wallowa-Whitman National Forest 1999) .


Shrublands

Three shrub communities located in the subbasin are stiff sagebrush/sandberg’s bluegrass (Artemisia rigida/Poa esperus), mountain big sagebrush/Idaho fescue (Artemisia tridentata vaseyana/Festuca esperus), and bitterbrush/Idaho fescue/bluebunch wheatgrass (Purshia tridentata/Festuca esperus/Agropyron esperus) (Wallowa-Whitman National Forest 1995). When these communities are disturbed, they are susceptible to invasions of gumweed, knotweed, mountain brome, Wyeth’s buckwheat, and yarrow (Wallowa-Whitman National Forest 1995). In heavily grazed areas shrub regeneration has been impaired; this results in a loss to wildlife of both food and cover (Wallowa-Whitman National Forest 1999).
Wetlands

Most wetland habitats in the subbasin are riparian wetlands along streams. The quality and quantity of wetland habitat compared to historical ranges has been altered in parts of the subbasin by grazing, road construction, timber harvest, and changes in plant species present (Wallowa-Whitman National Forest 1998). Wetlands are essential habitat for water-dependent species and provide a water source for other species (Wallowa County and Nez Perce Tribe 1993). The availability of prey makes wetlands an important part of the habitat for eagles, hawks, and coyotes (Wallowa County and Nez Perce Tribe 1993). Species of concern that use wetland habitat in the subbasin include northern bald eagles (Halieetus leucopephalus), harlequin ducks (Histronicus histronicus), Columbia spotted frogs (Rana luteiventris), tailed frogs (Ascaphus truei), western toads (Bufo boreas), and American white pelicans (Pelecanus erythrorhynchos) (Wallowa-Whitman National Forest 1998; Wallowa County and Nez Perce Tribe 1993).

Riparian Communities

Riparian habitatis used by many species throughout their lifespan. In the Big Sheep Creek watershed, riparian and deciduous habitat had more wildlife diversity than any other type of habitat (Wallowa-Whitman National Forest 1995). Over 150 species have been documented or are suspected to occur in the watershed (Wallowa-Whitman National Forest 1995). These species include 7 amphibians, 6 reptiles, 115 birds, and 30 mammals (Wallowa-Whitman National Forest 1995). The riparian communities along the Imnaha River are defined by the geology, drainage, aspect, and elevation of the sites (Wallowa-Whitman National Forest 1998; Wallowa-Whitman National Forest 1995). Throughout the subbasin, primary and secondary riparian zones exist. The primary riparian zone contains water, hydric soils, or hydrophytic plants (Wallowa-Whitman National Forest 1998). The secondary riparian zone shades the stream or provides large woody material to the stream (Wallowa-Whitman National Forest 1998). The canopy coverage of the Imnaha varies per lineal mile from 0% to 20%, although the actual canopy cover often occurs in clumps of up to 80% or more (Mason et al. 1993). Noxious weeds have invaded riparian zones along the Imnaha River. Some of the successful invaders include diffuse knapweed, yellow star thistle, and leafy spurge (Mason et al. 1993).

Near the headwaters of the Imnaha, the primary riparian zone is an alpine community containing grasses, sedges, and forbs with scattered willows (Salix spp.) along the stream bank (Wallowa-Whitman National Forest 1998). The associated secondary riparian zone has only small clusters of small trees (Wallowa-Whitman National Forest 1998). The primary zones of downstream portions of the upper reaches contain red osier dogwood (Cornus stolonifera) and alder with scattered patches of black cottonwood (Wallowa-Whitman National Forest 1998). Some grass and sedge meadows also occur (Wallowa-Whitman National Forest 1998). Below the first half-mile of stream, subalpine fir, lodgepole pine, and whitebark pine dominate the secondary riparian zone in downstream portions of the upper reaches (Wallowa-Whitman National Forest 1998). The lower portions of the upper reaches’ secondary riparian zone include mixed conifer stands with Engelmann spruce, lodgepole pine, grand fir, ponderosa pine, and western larch (Wallowa-Whitman National Forest 1998). In these areas, the Engelmann spruce and true fir individuals are dead or dying (Wallowa-Whitman National Forest 1998).

The primary riparian zone of the middle reaches of the Imnaha River, from Indian Crossing to the town of Imnaha, contains shrub and grass/sedge communities (Wallowa-Whitman National Forest 1998). Common plants within the communities include willows, hawthorne (Crataegus columbiana), alder, Rocky Mountain maple (Acer glabrum), carex, poa, and horsetail (Equisetum spp.) (Wallowa-Whitman National Forest 1998). The secondary riparian zone of the middle reaches has a ponderosa pine and Engelmann spruce overstory. The understory of this zone contains low shrubs (Wallowa-Whitman National Forest 1998). On the Imnaha River downstream from Grouse Creek, the riparian zone is a mix of grassland communities, rock, and pasture areas (Rose et al. 1992). Woody shrubs and small trees occur along the stream banks (Rose et al. 1992).

The Imnaha River’s lower reaches’ primary riparian zone, from the town of Imnaha to the river mouth, contains low shrubs and grasses such as willows, alder, ribes (Ribes spp.), dogwood, brome (Bromus spp.), carex, and fescue (Wallowa-Whitman National Forest 1998). Cottonwood (Populus spp.) and scattered ponderosa pine.

Upper reaches in the Big Sheep Creek watershed have grand fir as the overstory dominant in the primary zone (Wallowa-Whitman National Forest 1995). Engelmann spruce had been an important component of the primary zone, but insect infestations have killed over half of the Engelmann spruce individuals (Wallowa-Whitman National Forest 1995). This has resulted in some areas of the primary zone lacking a tree overstory and instead containing a grass and forb community (Wallowa-Whitman National Forest 1995). Alder and willow are also prevalent in the primary riparian zone within the Big Sheep Creek watershed (Wallowa-Whitman National Forest 1995). The secondary riparian zone contains grand fir, ponderosa pine, lodgepole pine, and western larch (Wallowa-Whitman National Forest 1995). The lower reaches of Big Sheep Creek have primary zones containing shrubs, grasses, forbs, and some trees like grand fir and Engelmann spruce (Wallowa-Whitman National Forest 1995). Big Sheep Creek’s secondary zone contains ponderosa pine, Douglas fir, shrubs, and grasses or forbs (Wallowa-Whitman National Forest 1995). Overall, riparian vegetation in the Big Sheep Creek watershed contains less late seral vegetation than historically was present (Wallowa-Whitman National Forest 1995).


Special Habitat Areas

Caves

Natural caves, are abundant within the subbasin. Cave types vary from rock shelters, solution tubes in limestone formations, and fault-block and talus caves where lithic breakdown has occurred. There are also occasional ‘‘tree-cast’’ and superceded stream caves within and between basalt flows (Wallowa-Whitman National Forest 1999). Caves provide critical habitat particularly for bat species in the subbasin. The number of caves has not changed from historic to current times but recreation related disturbance may be reducing their ability to support bats (Wisdom et al 2000). The HCNRA contains 16 caves on the national significant caves list but not all of these are contained in the subbasin (Wallowa-Whitman National Forest 1999).
Late and Old growth Habitat

Old and mature forested stands are an important habitat requirement for wildlife in the old-forest dependent families and some of the species in the forest mosaic family. These families account for over 25 wildlife species including the American marten, flammulated owl, pileated woodpecker, lynx, and wolverine. For the lynx, the forested mosaic must contain old forest habitat with denning sites and early seral habitat with prey species. A forested mosaic needs to have connectivity between the different habitat types. Connectivity can be detrimentally impacted by human activities such as road building or timber harvest (Wallowa-Whitman National Forest 1995).

Old forests contain large diameter trees and trees with softer wood, both qualities that make trees more suitable for some bird species to use as nesting sites. Old forests also contain more downed wood, an important component of denning sites for forest carnivores like the lynx. In the Big Sheep Creek watershed, mature and old growth seral stages have the greatest animal diversity out of all forest stages (Wallowa-Whitman National Forest 1995). In that part of the subbasin, mixed conifer mature forests have a total of 105 species, of which 64% are birds, approximately 30% mammals and the remainder comprised of either amphibians or reptiles (Wallowa-Whitman National Forest 1995). There is an estimated 73% less old forest habitat available now than was historically present in the Big Sheep Creek watershed (Wallowa-Whitman National Forest 1995).

Recent large stand replacing fires have reduced late and old growth forest habitats in the subbasin. Twenty five percent of the late and old growth habitats on the HCRNA have burned since 1970. A continued high incedence of stand replacing fires can be expected unless the high fuel loads present in dense stands of mid-seral species can be reduced. Despite these losses late and old structure forests are estimated to comprise about 30% of the HCRNA and in most parts of the HCRNA are considered above the natural range of variability (USDA Forest Service 1997). On many of the privately owned lands in the subbasin timber harvest combined with the altered fire regime has reduced the extent of late and old structural forests below that present historically (Quigley and Arbelbide 1997). Late and old growth habitat in the subbasin is most commonly found along cool, moist stream bottoms or on north-facing slopes where infrequent or low intensity fires have allowed late and old-growth characteristics to develop.


Snags

In Wallowa County, over 60 animal species use the habitat provided by snags as a food source, as a nesting site, or as a place for shelter (Wallowa County and Nez Perce Tribe 1993; Wallowa-Whitman National Forest 1995). Very large snags are used by species such as pileated woodpecker, Vaux’s swift, and black bear (Wallowa-Whitman National Forest 1995). Down wood is used by over 170 animal species, including amphibians, reptiles, birds, and mammals, in Wallowa County (Wallowa County and Nez Perce Tribe 1993). The habitat provided by down wood is used as a food source, as a lookout, as a place for thermal or hiding cover, as a nesting site, as a food storage site, as a hibernation site, or as a living site (Wallowa County and Nez Perce Tribe 1993). Previous management for fire suppression and timber harvest reduced the availability of downed wood and snags in the subbasin (Wallowa-Whitman National Forest 1995). Recent fires in sections of the subbasin, such as the Twin Lakes and Canal fires, have increased availability of these habitat components in some areas (Wallowa-Whitman National Forest 1995).




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