Management Recommendations
for
Cold Water Corydalis (Corydalis aquae-gelidae Peck & Wilson)

v. 2.0

by

M. Stein

December 1998

TABLE OF CONTENTS

EXECUTIVE SUMMARY

Species: Corydalis aquae-gelidae Peck & Wilson (Cold Water Corydalis)

Taxonomic Group: Vascular Plants

ROD Components: 1, 2

Other Management Status: R6 Regional Forester's Sensitive Species List, Draft Bureau of Land Management Bureau Sensitive Species, Washington Natural Heritage Program Threatened Species, Oregon Natural Heritage Program List 1; species threatened or endangered throughout their range, Oregon State Candidate for Threatened or Endangered status.

Range: Corydalis aquae-gelidae is known from 93 sites within Clackamas, Multnomah, Linn, and Marion Counties, Oregon; and Skamania and Clark Counties, Washington. All sites, except 4, occur on federal lands managed by the Gifford Pinchot National Forest, Mt. Hood National Forest, or Bureau of Land Management, Salem District.

Specific Habitat: Habitat requirements include a close proximity to seeps, springs, or streams with relatively cold water, a substrate of gravelly-sand, upper level canopy closure of 70 to 90 percent, and little herbaceous competition. Known sites are between 370 meters (1200 feet) and 1310 meters (4260 feet) in elevation.

Threats: Activities that change hydrologic function, reduce inputs of gravel substrate, increase stream temperature, result in changes in canopy closure, or result in soil disturbance or mechanical damage may impact Corydalis aquae-gelidae populations or individual plants.

Management Recommendations:

1. Evaluate known sites and assess whether habitat conditions are within described parameters.
2. Maintain or restore habitat conditions at sites to meet parameters for hydrologic function, canopy closure of the overstory, stream temperature, and substrate.
3. Activities, such as thinning of the tree and shrub component, may be useful in cases where excessive shading is resulting in reduced population vigor. Planting of fast-growing conifer or deciduous species appropriate to the site may be used to provide shade where deficient.
4. Where stream temperatures are greater than acceptable levels (5.9^oC. (43^oF.) to 14^oC. (57^oF)), maintain existing cover and augment shading by planting trees and shrubs appropriate to the site.
5. Sites that appear to be outside of prescribed hydrologic parameters will need further investigation to determine the exact cause. Changes in hydrology are most often the result of culvert placement and can be remedied by either removing or replacing the culvert. Changes may also occur as the result of road placement or water diversion.
6. Projects designed to trap gravels and sand to enhance fish spawning habitat may also serve to provide required substrates for Corydalis establishment. Efforts should be made to incorporate the needs of Corydalis aquae-gelidae into project design.
7. Avoid trampling, digging, or any other activity that will result in mechanical damage to plants, including habitat restoration projects.

Information Needs:

• Inventories in watersheds that have not been extensively surveyed for Corydalis aquae-gelidae including administrative units adjacent to those which currently have known sites.
• The response of Corydalis aquae-gelidae to habitat manipulation such as thinning and planting.
• Genetic relationships within and between Corydalis aquae-gelidae populations.
• Rate at which newly created habitat is colonized.

I. NATURAL HISTORY

A. Taxonomic/Nomenclature History

Corydalis aquae-gelidae was first noted by Warren C. Wilson in 1942 along the Tanner Creek Trail in Multnomah County, Oregon. The species was described by Morton Peck and Wilson in 1956, based on collections made from a population at the confluence of the Clackamas and Collawash Rivers in Clackamas County, Oregon (Hitchcock et al. 1964). There are no synonyms.

B. Species Description (Hitchcock et al. 1964)

1. Morphology

Corydalis aquae-gelidae is a herbaceous perennial with hollow stems arising from deep-seated, fleshy, tuberous roots. Plants are typically from 0.3-1.1 meters (1.0-3.5 feet) tall. The leaves are 4 to 6 times divided with numerous elliptic terminal leaflets 5-12 mm (0.2-0.5 inches) long and 2-5 mm (0.1-0.2 inches) broad. The showy rose-lavender flowers are 12-20 mm (0.5-0.8 inches) long, bilabiate, with a prominent spur. Arrangement is in a 30-60 flowered , simple to compound raceme (Figure 1). Flowering occurs from May through August. The fruit is an elliptic capsule 10-15 mm (0.4-0.6 inches) long with 2 mm (0.1 inch) long seeds.

Corydalis aquae-gelidae is most similar in morphology to Corydalis caseana (Case's corydalis), which ranges from northeast Oregon and Idaho to California. Within the range of Corydalis aquae-gelidae, Corydalis scouleri (Scouler's corydalis) is relatively common but differs by having less dissected leaves with larger leaflets and flowers.

Figure 1. Corydalis aquae-gelidae line drawing (Hitchcock et al. 1964).
Reprinted by permission of the University of Washington Press

2. Reproductive Biology

A number of the tuberous rooted species of the genus Corydalis are known to reproduce vegetatively from offsets, although it appears that Corydalis aquae-gelidae reproduces by seed only (Goldenberg 1990).

Corydalis aquae-gelidae typically produces 100 to 1500 seeds per plant with occasional plants producing up to an estimated 3000 seeds per plant (Goldenberg 1992). When the seed capsules are mature they dehisce explosively, dispersing the seed up to several meters. Dispersion may also be facilitated by a fleshy food body (elaiosome) attached to the seed, which may be attractive to ants (Goldenberg 1992). Goldenberg (1992) determined that germination occurs when seed is stratified at 3^o C. (37^o F.) for a 6 to 7 month period. Germination also occurred at temperatures of 17^o to 27^o C. (63^o F.- 81^o F.), much greater than those expected under natural conditions, if substrates are kept saturated. Conversely, poor germination results when seed is allowed to dry (Goldenberg 1992; Guerrant 1995). Seedlings appear to establish readily if a moist substrate of gravelly-sand is available but establishment and recruitment are poor in organic substrates or substrates that are not well watered. Demographic studies in Oregon (Goldenberg 1990) found Corydalis aquae-gelidae populations to be comprised of 38 percent seedlings, 48 percent juveniles, 3 percent nonreproductive adults and 11 percent reproductive adults. From these data and observation on seedling growth rates, it appears that juveniles are 2 to 5 years old, adult plants remain in a nonreproductive stage for a relatively short period, reaching reproductive maturity in 6 to 9 years, and adult plants are long-lived, perhaps 25 years or more (Goldenberg and Zobel 1997).

No information could be found on pollinators, although bumblebees have been observed on Corydalis aquae-gelidae flowers.

3. Ecology

Corydalis aquae-gelidae has a relatively high percentage of its biomass stored in the below-ground portion of the plant as starch in the tuberous root (root/shoot ratio of 2.4-3.8) and a low percentage (8%) allocated to reproductive structures. In addition, the species is long-lived (Goldenberg and Zobel 1997). These qualities are characteristic of "stress tolerators", slow-growing plants of relatively unproductive environments that allocate a large proportion of their resources to storage and long-term survival.

Figure 2. Distribution of Corydalis aquae-gelidae

C. Range, Known Sites

Corydalis aquae-gelidae is a regional endemic known from 93 known sites in Clackamas, Multnomah, Linn, and Marion Counties, Oregon, and Skamania and Clark Counties, Washington (Figure 2), a range of approximately 90 air miles north-south and 35 miles east-west (USDA-USDI Appendix J2 1994, Washington Natural Heritage 1994, Oregon Natural Heritage 1995). Oregon sites are concentrated along the Upper Clackamas River, Oak Grove Fork Clackamas River, and South Fork Eagle Creek. The distribution in Washington is more sporadic with most sites occurring in the headwaters and tributaries (stream order 0-2) of Canyon Creek, Wind River, and East Fork Lewis River). All known sites, with the exception of 4, are located on federal lands. This may be due, in part, to a lack of survey work on nonfederal lands, but it is also a likely reflection of the distribution of suitable habitat.

D. Habitat Characteristics and Species Abundance

All known sites of Corydalis aquae-gelidae are located within the Western Hemlock Zone (Halverson et al. 1986; Topik et al. 1986) and Pacific Silver Fir Zone (Hemstrom et al. 1982; Brockway et al. 1983).

Corydalis aquae-gelidae is associated with perennial streams, seeps, and springs with relatively cold water and a substrate of gravelly-sand. Goldenberg (1990) found the horizontal distance of individual plants to the edge of the water line during the growing season ranged from 20 centimeters into the stream (a negative value where 0 equals the edge of the stream) to 290 centimeters away from the water's edge (-0.7-9.6 feet), with a mean of 37 centimeters (1.2 feet) for Oregon populations. Vertical distance to water ranged from 12 centimeters (-0.3 feet) below the water table to 95 centimeters (3.1 feet) above, with a mean of 7 centimeters (0.2 feet) above the waterline. The mean water temperature at these sites was 9.6^oC. (49^oF.) during the growing season with a range from 5.9^oC. (43^oF.) to 14^oC. (57^oF.). Plants are absent from organic substrates such as marshes and bogs.

Light levels appear to be an important determinant of suitable habitat. Gamon (1983) reports that, where canopy level approaches 100 percent closure, the number of individual plants decrease as does the incidence of flowering. Goldenberg (1992) observed plants growing within clear-cuts to have yellowed foliage, poor growth, and no seedling recruitment. This may not only be a factor of intense solar radiation but also an inability to compete with aggressive pioneer species. Densiometer readings within Oregon populations found the percent canopy closure to range from 0 to 100 percent with a median of 84 percent (Goldenberg 1992). Both Goldenberg and Gamon came to a similar conclusion, that the species seems best suited to habitats in which a high, partial canopy allows sufficient light for growth and reproduction, but hinders the establishment of competing vegetation. A general distinction can be made between Oregon and Washington populations in terms of the stream order they are associated with. Oregon populations are most numerous in headwater areas (stream order 0) and 3rd, 4th, and 5th order streams, but largely absent from 1st and 2nd order streams. In Washington most populations are associated with headwaters and 1st and 2nd order streams. This difference may simply be due to the greater number of 3rd, 4th and 5th order streams that occur within the range of Corydalis aquae-gelidae in Oregon.

Sites vary in slope from 90 percent to flat and most often have an aspect of northwest to northeast, although all aspects have been recorded. Precipitation within the species' range varies from 1500-2500 mm (60-100 inches) annually.

Diaz and Mellen (1996) have described the Corydalis aquae-gelidae Plant Community from 3 plots located on the Mt. Hood National Forest. The Community represents sites with gravel and sand deposition, very close to the high water line, where Corydalis is dominant. Associates included Senecio triangularis (arrowleaf groundsel), Senecio pseudaureus (streambank butterweed), Delphinium trollifolium (Columbia larkspur), Aconitum columbianum (monkshood), Aster modestus (few-flowered aster), Alnus incana (mountain alder), Physocarpus capitatus (nine bark), and a well developed moss layer. The Community had an average 10.7 vascular plant species per plot, the lowest value among riparian plant communities recorded for the Mt. Hood and Gifford Pinchot National Forests. This reflects the strong dominance of Corydalis aquae-gelidae at these sites. It should be noted that Corydalis aquae-gelidae is likely to occur as a less dominant associate of other plant communities and is not restricted to one described community. Sensitive plant site information from the Salem District BLM, Gifford Pinchot NF, and Mt Hood NF list associated species as Saxifraga arguta (brook saxifrage), Mimulus guttatus (common monkey-flower), Tolmiea menziesii (pig-a-Back Plant), Tiarella unifoliata (coolwort), Oxalis oregana (Oregon oxalis), Isopyron hallii (rue-anemone), Polysticum munitum (sword fern), Veronica americana (speedwell), Montia siberica (Siberian montia), Alnus rubra (red alder), Oplopanax horridum (devil's club), Acer circinatum (vine maple), Ribes lacustre (swamp currant), Thuja plicata (western redcedar), Taxus brevifolia (Pacific yew), Tsuga heterophylla (western hemlock), Abies procera (noble fir), Abies amabilis (Pacific silver fir) and Pseudotsuga menziesii (Douglas-fir).

The Corydalis aquae-gelidae Plant Community is found within Rosgen B and C channel types in Oregon (Diaz et al. 1996). C channel types are described as having a low gradient, meandering, with a broad, well defined floodplain (Rosgen 1994). B channel types have a higher gradient, more defined channel, and are less meandering.

II. CURRENT SPECIES SITUATION

A. Why Species is Listed Under Survey and Manage Standards and Guidelines

Corydalis aquae-gelidae was rated 10-48-40-2 for Outcomes A, B, C, and D respectively under Option 9 (USDA-USDI FEMAT, 1994). Outcome B (48%), where the species would be expected to stabilize with significant gaps in the historic distribution on federal lands was given the greatest probability, followed by Outcome C (40%), where the species is restricted to refugia with strong limitations on interactions among local populations. Other factors contributing to the species' designation include: approximately 67 percent of known populations occur within the Matrix, and there has been a loss of individuals and habitat due to hydroelectric projects, timber harvest, road construction, and fish habitat improvement projects (USDA-USDI Appendix J-2 1994). The species has limited potential to establish outside of known population areas due to its specific habitat requirements.

B. Major Habitat and Viability Considerations

Major considerations for Corydalis aquae-gelidae habitat and viability include light levels, hydrologic function, water temperature, substrate, and vegetative competition.

Based on a median value of 84 percent canopy closure of the overstory for populations in Oregon (Goldenberg 1992), canopy closures of 70 to 90 percent should provide an optimal range for shade. At this level, vegetative competition will also be held to acceptable levels.

Hydrologic function is best described as the maintenance of perennial water within acceptable vertical and horizontal distances from plants. Goldenberg (1990) found the horizontal distance of individual plants to water ranged from 20 centimeters (-0.7 feet) from the water's edge into the stream to 290 centimeters (9.6 feet) away from the water's edge on land, with a vertical distance ranging from 12 centimeters (-0.3 feet) below the waterline to 95 centimeters (3.1 feet) above the waterline. The extreme values within these ranges may represent outliers or relict plants and not necessarily optimal habitat. To determine the optimal range, one standard deviation of the mean is used. This equates to a horizontal distance of 18 centimeters (-0.6 feet) into water from the water's edge to 86 centimeters (2.8 feet) away from the water edge and a vertical distance of 7 centimeters (-0.2 feet) below the waterline to 21 centimeters (0.7 feet) above the waterline. Water temperature is also an important habitat consideration. Stream temperature ranged from 5.9^oC. (43^oF.) to 14^oC. (57^oF.) at Oregon populations during the growing season (Goldenberg 1990). The upper temperature limit of 14^oC. is viewed as the critical threshold.

Substrates are a mixture of cobble and sand. Plants occurring on silt-textured substrates or soils high in organic matter occur only rarely and are totally absent from bogs and marshes. A typical substrate in Oregon is greater than 50 percent gravel with coarse sand filling the interstices (Goldenberg 1990).

C. Threats to the Species

Threats to habitat and viability include effects to hydrologic function, an increase in stream temperatures beyond the identified upper threshold during the growing season, changes in shade above or below threshold levels, increases in vegetative competition, and mechanical damage to plants.

Changes in hydrology, which result in lowering of water levels or inundation of Corydalis aquae-gelidae sites, can adversely affect populations by reducing seed germination and recruitment and plant growth. Distances to water outside of the horizontal and vertical ranges of negative 18 centimeters to positive 86 centimeters (-0.6-2.8 feet) from the water's edge and negative 7 to positive 21 centimeters (-0.2-0.7 feet) from the water level are assessed to be adverse to habitat and viability. A stream temperature of 14^oC. (57^oF.) during the growing season is the upper threshold for those Corydalis aquae-gelidae habitats measured in Oregon. Temperatures greater than this will result in unsuitable habitat. Increases in stream temperature are most often caused by a decrease in shade or stream flow. The resulting higher temperatures will affect areas downstream; therefore, Corydalis may be threatened by actions that occur some distance upstream of the actual habitat.

Canopy cover that falls outside of the 70 to 90 percent range can affect viability. Plants under canopy closure less than 25 percent were found to be chlorotic and stunted (Goldenberg 1990) while plants with 100 percent canopy closure had a lower incidence of flowering (Gamon 1983). An increase in the availability of light will result in increased vegetative competition from early-sere species. Maintaining a high partial canopy of 70 to 90 percent closure will maintain unsuitable habitat for these competitive species.

The stems of Corydalis aquae-gelidae are hollow, fragile, and are easily damaged. Mechanical damage could result from equipment or trampling. The resulting loss of leaves, flowers, or fruit can affect long-term population viability.

Trampling from recreational activity is a concern but is judged to be minor at this time.

D. Distribution Relative to Land Allocations

All known sites are within Riparian Reserves, of which approximately 67 percent are within the Matrix land allocation (USDA-USDI Appendix J2 1994). The majority of the remaining sites occur within Late-Successional Reserves. Because some Corydalis aquae-gelidae sites are associated with small seeps and springs, these Riparian Reserves may not be mapped.

III. MANAGEMENT GOALS AND OBJECTIVES

A. Management Goals for the Taxon

The management goal for Corydalis aquae-gelidae is to assist in maintaining species viability within the range of the northern spotted owl.

B. Specific Objectives

• Maintain hydrologic function within parameters defined for Corydalis aquae-gelidae at known sites.
• Maintain upper-story canopy levels between 70 and 90 percent closure at known sites.
• Maintain cold water temperatures for streams with known sites.
• Avoid ground disturbance and mechanical damage within known sites.

IV. HABITAT MANAGEMENT

A. Lessons from History

Management activities that have affected Corydalis aquae-gelidae sites include timber harvest, road construction, hydroelectric development, and fish habitat improvement projects (USDA-USDI Appendix J2 1994).

Conclusions can be made as to the response of Corydalis aquae-gelidae to timber harvest activities based on formal data collection and casual observation. Gamon (1991) revisited 26 of 39 known sites on the Gifford Pinchot National Forest in 1990. Sites that occur in relatively undisturbed habitat were found to be doing well. Sites located within or adjacent to timber harvest areas were found to be in decline as demonstrated by a decrease in the number of plants at these sites. This decline was attributed to increased vegetative competition on the ground, a decrease in light penetration resulting from an increase in dense deciduous tree and shrub cover following timber harvest, and altered hydrology. Plants growing in clear-cut units with little or no overstory canopy on the Mt Hood National Forest exhibited small, curled, and discolored leaves as well as reduced seed production and a higher incidence of downy mildew damage (Goldenberg 1990). The Stone Creek Hydroelectric Project, implemented in 1992, resulted in the loss of some plants during the construction phase. To determine how Corydalis aquae-gelidae will be affected by lower water levels within the diversion reach, monitoring plots were established at the site. Data is scheduled to be collected annually from 1994 through 1998 and every 5 years thereafter. Preliminary results after 3 years of data collection are inconclusive (Draft Stone Creek Hydroelectric Project Annual Corydalis Monitoring Report 1996).

B. Identification of Habitat Areas for Management

All known sites of Corydalis aquae-gelidae on the Gifford Pinchot National Forest, Mt. Hood National Forest, and Salem District of the Bureau of Land Management should be managed to maintain species viability. Unknown is the degree of genetic variability within and between populations and, therefore, the relative contribution of individual plants or populations to the overall maintenance of species viability. Until this assessment can be made, it will be important to maintain the entire gene pool.

C. Management Within Habitat Areas

Specific management goals and objectives to maintain Corydalis aquae-gelidae viability include the maintenance or restoration of hydrologic function, cold water temperatures, gravelly-sand substrate, the maintenance of a high partial overstory, and the avoidance of ground disturbance.

To manage known sites of Corydalis aquae-gelidae, the following recommendations are offered.

1. Evaluate known sites and assess whether habitat conditions are within described parameters.
2. Maintain or restore habitat conditions at sites to meet parameters for hydrologic function, canopy closure of the overstory, stream temperature, and substrate.
3. Activities, such as thinning of the tree and shrub component, may be useful in cases where excessive shading is resulting in reduced population vigor. The threshold for excessive shading is considered to be 90 percent and above. Planting of fast-growing conifer or deciduous species appropriate to the site may be used to provide shade on sites that have less than 70 percent canopy closure.
4. Where stream temperatures are greater than acceptable levels (5.9^oC. (43^oF.) to 14^oC. (57^oF)) maintain existing cover and augment shading by planting trees and shrubs appropriate to the site. The source of the high temperatures may not be at the Corydalis site itself, but upstream some distance.
5. Sites that appear to be outside of prescribed hydrologic parameters will need further investigation to determine the exact cause. Changes in hydrology are most often the result of culvert placement and can be remedied by either removing or replacing the culvert. Changes may also occur as the result of road placement or water diversion.
6. Projects designed to trap gravels and sand to enhance fish spawning habitat may also serve to provide required substrates for Corydalis establishment. Efforts should be made to incorporate the needs of Corydalis aquae-gelidae into project design.
7. Avoid trampling, digging, or any other activity that will result in mechanical damage to plants, including habitat restoration projects.

D. Other Management Issues and Considerations

All Corydalis aquae-gelidae sites occur within interim Riparian Reserve Areas. As a component of the Aquatic Conservation Strategy, the objectives for the Reserves are to maintain and restore the distribution, diversity, and complexity of features to which riparian dependent species are adapted. These features include, but are not limited to, spatial connectivity within and between watersheds, water quality, sediment regimes, in-stream flows, and thermal regulation. Current management objectives for the Riparian Reserve Areas are, therefore, compatible with those identified for Corydalis aquae-gelidae.

For sites affected by past management activities, develop habitat restoration plans on a site specific basis. Highest priority should be placed on sites with altered hydrology and those with excessive shading or lacking shade.

V. RESEARCH, INVENTORY, AND MONITORING NEEDS

The objective of this section is to identify opportunities for additional information which could contribute to more effective species management. The content of this section has not been prioritized or reviewed as to how important the particular items are for species management. While the inventory, research, and monitoring identified below are not required, these recommendations should be addressed by a regional coordinating body at the Northwest Forest Plan level.

A. Data Gaps and Information Needs

Most known Corydalis aquae-gelidae sites have been located through project-level surveys. For watersheds that have had a relatively low level of management activity, and few surveys for Corydalis, an inventory of potential habitat will be useful in determining the full extent of the species' range and numbers. Inventories should be conducted within administrative units adjacent to those with known Corydalis sites.

No information exists on the effectiveness of Corydalis aquae-gelidae habitat restoration or manipulation. As projects are implemented it will be useful to measure the response of the plants to help in future project design.

There is currently no information on the genetics of Corydalis aquae-gelidae. Knowing the genetic variability of the species within and between populations will help managers determine population boundaries and assess the contribution of individual populations toward viability of the species range-wide.

B. Research Questions

• What are the genetic variability of Corydalis aquae-gelidae within and between populations?
• What are the dispersal mechanisms for Corydalis aquae-gelidae?
• How does Corydalis aquae-gelidae respond to habitat enhancement?
• Will Corydalis aquae-gelidae colonize newly created habitat and at what rate?

C. Monitoring Needs and Recommendations

Continue to support monitoring of the Corydalis aquae-gelidae population at the Stone Creek Hydroelectric Project to determine the effects of water diversion.

Where management actions are done within Corydalis aquae-gelidae populations, including habitat enhancement, monitor for abundance and reproduction of plants as well as habitat parameters (hydrology, shade, stream temperature, substrate).

VI. REFERENCES

Brockway, D. G., C. Topik, M. A. Hemstrom, and W. H. Emmingham. 1983. Plant Association and Management Guide for the Pacific Silver Fir Zone, Gifford Pinchot National Forest, USDA Forest Service, Pacific Northwest Region. Portland, Oregon. R6-Ecol-130a-1983. 122 pp.

Diaz, N. M. and T. K. Mellen. 1996. Riparian Ecology Types; Gifford Pinchot and Mt. Hood National Forest and Columbia River Gorge National Scenic Area. USDA Forest Service, Pacific Northwest Region. Portland, Oregon. R6-NR-TP-96.

Draft Stone Creek Hydroelectric Project Annual Corydalis Monitoring Report for 1995. Eugene Water and Electric Board, Eugene, Oregon. Unpublished Report. 24 pp.

Gamon, J. 1983. Species Management Guide for Corydalis aquae-gelidae on the Gifford Pinchot National Forest. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. 15 pp.

Gamon, J. 1991. Review of the Species Management Guide for Corydalis aqaue-gelidae on the Gifford Pinchot National Forest. Washington Department of Natural Resources, Olympia, Washington. Unpublished Report. 20 pp.

Goldenberg, D. M. 1990. Draft Species Management Guide for Corydalis aquae-gelidae (Peck and Wilson). Unpublished report submitted to the Mt. Hood National Forest, Gresham, Oregon.

Goldenberg, D. M. 1992. Ecology of Corydalis aquae-gelidae, a Rare Riparian Plant. Unpublished M.S. thesis, Oregon State University, Corvallis, Oregon.

Goldenberg, D. M. and D. B. Zobel. 1997. Allocation, Growth and Estimated Population Structure of Corydalis aquae-gelidae, a Rare Riparian Plant. Northwest Science, 71:196-204.

Guerrant, E. 1995. Personal Communication.

Halverson, N. M., C. Topik, and R. Van Vickle. 1986. Plant Association and Management Guide for the Western Hemlock Zone. Mt. Hood National Forest. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. R6-ECOL-232A-1986. 111 pp.

Hemstrom, M. A., W. H. Emmingham, N. M. Halverson, S. E. Logan, and C. Topik. 1982. Plant Association and Management Guide for the Pacific Silver Fir Zone, Mt. Hood and Willamette National Forests. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. R6-ECOL-100-1982a. 104 p.

Hitchcock, C. L., A. Cronquist, M. Ownbey, and J. W. Thompson. 1964. Vascular Plants of the Pacific Northwest. Part 2: Salicaceae to Saxifragaceae. University of Washington Press, Seattle. 597 pp.

Oregon Natural Heritage Program. 1995. Rare, Threatened and Endangered Plants and Animals of Oregon. Oregon Natural Heritage Program, Portland, Oregon. 84 pp.

Rosgen, D. L. 1994. A Classification of Natural Rivers. CATENA. 22, (1994) 169-199.

Topik, C., N. M. Halverson, and D. G. Brockway. 1986. Plant Association and Management Guide for the Western Hemlock Zone, Gifford Pinchot National Forest. USDA Forest Service, Pacific Northwest Region, Portland, Oregon. R6-ECOL-230A-1986. 132 p.

USDA, Forest Service, and Department of the Interior, Bureau of Land Management. 1994. Record of Decision for Amendments to Forest Service and Bureau of Land Management Planning Documents within the Range of the Northern Spotted Owl and Standards and Guidelines for Management of Habitat for Late-Successional and Old-Growth Related Species within the Range of the Northern Spotted Owl. Portland, OR.

USDA Forest Service, and Department of the Interior, Bureau of Land Management. 1994. Final Supplemental Environmental Impact Statement on Management of Habitat for Late-Successional and Old-Growth Forest Related Species within the Range of the Northern Spotted Owl, Appendix A, Forest Ecosystem Management: An Ecological, Economic, and Social Assessment. Portland, OR.

USDA Forest Service, and Department of the Interior, Bureau of Land Management. 1994. Final Supplemental Environmental Impact Statement on Management of Habitat for Late-Successional and Old-Growth Forest Related Species within the Range of the Northern Spotted Owl, Appendix J2, Results of Additional Species Analysis. Portland, OR.

Washington Natural Heritage Program. 1994. Endangered, Threatened and Sensitive Vascular Plants of Washington. Washington State Department of Natural Resources, Olympia, Washington. 42 pp.