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COSEWIC Assessment and Update Status Report on the Scouler’s Corydalis in Canada


Habitat Requirements

Lush stands of Scouler’s corydalis are found in wet, cool habitats associated with watercourses – ranging from large rivers to small tributary streams. Elevations range from sea level to approximately 200 m in British Columbia (Douglas and Jamison 2000). In British Columbia, this species is found in the CWHvm1 (submontane very wet maritime) variant of the Coastal Western Hemlock Biogeoclimatic Zone (Pojar et al. 1991). In regions where Scouler’s corydalis is locally abundant, such as lower elevations of Washington State’s Mt. Rainier National Park (Brockman, 1947) and the Nitinat River and Klanawa River drainages, the species occurs on gradually sloping alluvial floodplains and river terraces with slopes typically between 0-10%, although sometimes up to 40% (Douglas and Smith 2003). Larger and healthier populations were found on gently sloping or relatively flat sites. When not found on these flat flood plains, the aspect of sites was typically NW to NE, although one site had a SSW aspect. The substrate was typically composed of fine loam or silty-clay to sandy or gravelly sediments, sometimes along with larger gravels and cobbles. In the Nitinat Valley, this species is an understory component of the early seral mixed or deciduous forest habitat. All the red alder (Alnus rubra) stands of approximately 30 years and older surveyed in the Nitinat, were found to contain Scouler’s corydalis. In addition to red alder, other associated overstory tree species include Acer macrophyllum and Picea sitchensis, and with lesser frequency, Tsuga heterophylla and Thuja plicata. Prominent understory species include Polystichum munitum, Oplopanax horridus, Sambucus racemosa, Petasites frigidus var. palmatus, Ribes bracteosum, and Rubus spectabilis.

Scouler’s corydalisalso grows in roadside gravel banks and ditches. These sites, when sufficiently moist during the growing season, mimic the gravelly, natural habitats of the floodplains. Only one population of this type (with at least 500 stems) was sampled.

Habitat Trends

Habitat trends for Scouler’s corydalis are largely unknown; however, the species has been seen to colonize disturbed habitats, which reflects the species’ adaptable nature. The largest stands (over 400 000 stems or almost one-half of the total known stems) of Scouler’s corydalis in Canada have now been protected within Wildlife Habitat Areas under the provincial Forest and Range Protection Act. These areas are to be managed primarily for Scouler’s corydalis to protect it from forestry management activities.

There has likely been a very minor loss of habitat over the last 50 years to road and bridge construction in the Nitinat River drainage, although this is not likely to have significantly affected the amount of habitat available. There is substantial additional potential habitat that has not been surveyed due to inaccessibility (Figure 4). Because Scouler’s corydalis occurs in early seral forests developing on floodplains, suitable sites are likely continually in a process of gradual change, with new sites becoming available and older, established sites declining in suitability.

Direct human disturbance to the alluvial floodplain habitat has been minimal despite logging activity throughout the Nitinat valley. No sites have been affected by recent forestry practices, partly because of protection of riparian areas under the provincial Forest and Range Practices Act and the lack of commercially available species at these sites. However, one population (#23, Nitinat River drainage, see Figure 4) was degraded due to heavy equipment work during creek restoration, with only 6 stems remaining in 2003, from 30 stems in 1997. This small population may recover in the future because ample gravels are still exposed.

Habitat Protection/Ownership

Almost all the large Scouler’s corydalis populations on south-western Vancouver Island have some type of protection. Although not stated in the original status report, populations of the species were known to occur in one Provincial Park (44 850 stems) and an Ecological Reserve (less than 15 stems). Another population of approximately 7 stems was recently discovered in a second Provincial Park (Carmanah-Walbran), although a thorough inventory has not been done of this area (see Table 1; Figures 5 and 6). These are therefore protected by provincial parks legislation from the threat of forest management activities.


Table 1: Protected Areas summary table – Area and number of stems
EO #
WHA or Protected
Area Name
WHA Core
size (ha)
WHA Buffer
size (ha)
Total size (ha)
Estimated #
of stems
 Sum462479481 972
2 (part)Upper Nitinat River-1-19083117 500
3 (part)Jasper Creek-1-19116521293 500
13 (part)Mid Nitinat River-1-19211294 800
21Lower Nitinat river-1-1934151 500
5Upper Granite Creek-1-19412318 000
5Lower Granite Creek-1-195123200
10Klanawa Creek-1-19645911 600
6Vernon Creek-1-19715102510 000
4 (part)Nitinat River Prov. ParkN/AN/AN/A44 850
15Klanawa Ecological ReserveN/AN/AN/A<15
No #Carmanah-Walbran Prov. ParkN/AN/AN/A7

EO = “Element Occurrence” is an area of land and/or water in which a species or natural community is present. A principal EO may be a single contiguous area or may be composed of discrete patches or subpopulations. (NatureServe, 2006a).

WHA = Wildlife Habitat Area

Under the Forest and Range Practices Act (FRPA), larger fish-bearing streams such as the Nitinat, Klanawa and Carmanah-Walbran where Scouler’s corydalis is found are managed under a default standard that requires a riparian reserve zone associated with a management zone. The reserve zone is legislated and is to remain intact to ensure that characteristics necessary to keep the stream properly functioning and to also manage for wildlife. Therefore, licensees can be encouraged to leave the management zones intact and associate their wildlife tree retention to help protect and buffer potential Scouler’s corydalis habitat within these areas.

In May of 2006, the province established, under the FRPA, eight Wildlife Habitat Areas (WHAs) for significant populations (over 400 000 stems) of Scouler’s corydalis. These areas included the range of the species in the Nitinat and Klanawa Rivers (see Table 1 and Figures 5 and 6). Under this Act, the forestry companies are legally compelled to protect these populations from forest management activities. WHAs provide a similar level of protection for the species as the provincial Parks Act with regard to forestry management activities, which are the main threat to this species. Such activities are not permitted within WHAs or parks.

Figure 5: Protected Areas for Scouler’s Corydalis in the Nitinat River Drainage Area

Figure 5: Protected areas for Scouler’s corydalis in the Nitinat River drainage area. Those sites indicated by an asterisk and numbered 1-190 to 1-195 and 1-197 occur within Wildlife Habitat Areas designated for the protection of the species.

Those sites indicated by an asterisk and numbered 1-190 to 1-195 and 1-197 occur within Wildlife Habitat Areas designated for the protection of the species.

Figure 6: Protected Areas for Scouler’s Corydalis in Klanawa River and Carmanah Creek

Figure 6: Protected areas for Scouler’s corydalis in Klanawa River and Carmanah Creek. Site 1-196 occurs within a Wildlife Habitat Area designated for the protection of the species.

Site 1-196 occurs within a Wildlife Habitat Area designated for the protection of the species.

The majority of the current locations of Scouler’s corydalis occur on Crown Land within Tree Farm Licence (TFL) #44. This licence is presently held by Western Products (formerly Weyerhaeuser Canada). A second Tree Farm Licence (# 46) is now held by Teal-Jones Group (originally held by TimberWest until January 2004); this currently has three sites (#7, #8 & #9, Nitinat River drainage; see Figure 4). All of the Scouler’s corydalis populations that could be impacted by forestry operations have been identified and appear on forest management plans (Bill Beese, pers. comm.; Bo Ferguson, pers. comm.).

A portion of the largest site (#14, Nitinat River drainage; see Figure 4) occurs on the Ditidaht Band’s Chuchummisapo Reserve. There is no known threat to this population. At the time of the field survey by Douglas and Smith in 2003, Douglas recognized that they were near the edge of the Indian Reserve based on topographic maps but did not think that they were within its boundary (S. Smith, pers. comm. 2006). The Ditidaht Band has participated in the recovery team and is aware of the occurrence of the population.