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

Population Sizes and Trends

Search Effort

Searches have been most intense to date in the Nitinat watershed, due to road accessibility, and this watershed contains the largest number of known extant sites. The first observation of Scouler’s corydalis in British Columbia was by W. Carter in 1915 on the Nitinat River. Through the 1970s to early 1990s, a number of observations/ collections were made on the Nitinat and Klanawa Rivers and along Nitinat Lake. Pavlick (1989) also searched without success the Gordon, San Juan and Klanawa drainages. The most intensive searches to date, and the first to document population sizes, were conducted in 1997 and 2003 (Douglas and Jamison 2000, Douglas and Smith 2003; respectively). All of the searches have been conducted by vehicle along logging roads and therefore focus on creeks and wetlands adjacent to these roadways. A small portion of the less accessible Klanawa watershed has been searched, near the convergence of the East Klanawa and Klanawa Rivers, and downriver in and around the Klanawa River Ecological Reserve.

Potential habitat on all the drainages has been estimated, based on the surveys conducted in the Nitinat drainage. There is an estimated 65 km2 of potential habitat along the Nitinat River, 18 km2 in the Klanawa drainage, 10 km2 around Cowichan Lake, and 9 km and 10 km2 along Carmanah and Walbran Creeks, respectively.

It is estimated that less than 50% of the potential habitat for Scouler’s corydalis in the Nitinat River drainage has been searched to date (Douglas and Smith 2003), mostly on the accessible westerly side of the river (Figure 4). Since searches have been in the form of sporadic point surveys, the populations, which often occur in bands along streams and rivers, are probably much larger and more continuous than has been recorded.

The Klanawa River drainage has yet to be adequately searched, with only three small areas, or about 10% of the entire area, searched (Douglas and Smith 2003). Recently, additional populations have been observed in the upper Cowichan Lake and Carmanah River drainages. It is likely that many more populations of Scouler’s corydalis will be found in these unsearched areas (see Figure 4) in the future.


Abundance

There are presently 24 populations (36 sites) where Scouler’s corydalis has been observed (Table 2) in British Columbia within the last six years (1997 to 2004). These contain a total of about 848 000 stems. Since single clones may consist of numerous annual stems, spreading for at least tens of square metres (Ryberg, 1960), it is only possible to count stems and area covered to estimate population size. Stem counts by the authors were estimated after extrapolation from total counts made in 10 subpopulations in one-metre plots.Stem numbers range from one up to 462 000 per population. Seven of the populations have stem numbers over 20 000, which represent 95% of all the stems in British Columbia. The populations vary greatly in size from just a few square metres to 3.4 ha. Eight of the populations are over 0.5 ha in size. Total area currently occupied by these known populations is approximately 0.10 km2.

Using the ratio of area of extent to potential habitat found in the Nitinat drainage, it is estimated that there is an additional potential area of occupancy in the Klanawa, Carmanah, Walbran and Cowichan drainages totaling 0.143 km2.

The Conservation Data Centre recognizes Scouler’s corydalis in twenty-four populations or element occurrences in BC (J. Penny, pers. comm. 2006; Table 2). Populations are delineated from one another when they are separated by one kilometre or more. Five of the locations have not been mapped and therefore don’t have a number yet. Missing element occurrence numbers represent changes in spatial representation in the GIS and not a loss in numbers.


Fluctuations and Trends

The number of stems in the populations of Scouler’s corydalis have not been adequately monitored. However, at the few sites that have been visited more than once over the last five years, the number of stems appears to be stable.


Rescue Effect

The nearest population of Scouler’s corydalis, outside of British Columbia, is on the Olympic Peninsula, approximately 80 km to the south; therefore natural immigration from this source is highly unlikely. These populations to the south are considered to be healthy as these species are not ranked (SNR) in Washington and Oregon. However, there have been no genetic studies between the United States and the Canadian populations to determine evolutionary relationships. Potential habitat exists in the adjacent watersheds of the Carmanah and Walbran Creeks.

 

Table 2: Population Sizes for Scouler’s corydalis in British Columbia
CDC Element Occurrence # (=population)Sites (equal to subpopulations when more than one site per element occurrence)Last ObservationObserverNumber of Stems/Area
No # yetCowichan 12004Douglas6/2 m2
7Nitinat 12003Douglas and Smith34 700/5 784 m2
19Nitinat 21997Jamison16/60m2 in 3 clusters
6Nitinat 32003Douglas and Smith2 108/1 054 m2
6Nitinat 42003Douglas and Smith1 000/60 m2
6Nitinat 52003Douglas and Smith2 000/330 m2
24Nitinat 62003Douglas and Smith1 350/120 m2
No # yetNitinat 72004Penny and Ford10/4 m2
No # yetNitinat 82003FergusonNo data
No # yetNitinat 92003FergusonNo data
5Nitinat 102003Douglas and Smith18 000/1 600 m2
23Nitinat 112003Douglas and Smith150/15 m2
2Nitinat 122003Douglas and Smith50/150 m2
2Nitinat 132003Douglas and Smith40/150 m2
3Nitinat 142003Douglas and Smith462 600/34 068 m2
4Nitinat 151998Douglas2 000/5 000 m2
4Nitinat 162003Douglas and Smith2 000/7 000 m2
4Nitinat 282003Douglas and Smith44 850/24 800 m2
13Nitinat 172003Douglas and Smith94 800/7 900 m2
13Nitinat 182003Douglas and Smith21 867/7 275 m2
13Nitinat 192003Douglas and Smith6 820/1 026 m2
21Nitinat 202003Douglas and Smith540/36 m2
16Nitinat 211997Jamison1 000/1 000 m2
17Nitinat 222003Douglas and Smith105 700/5 000 m2
17Nitinat 232003Douglas and Smith5/6 m2
18Nitinat 242003Douglas and Smith60/60 m2
18Nitinat 252003Douglas and Smith44 000/5 500 m2
18Nitinat 261997Jamison100/60 m2
1Nitinat 272003Douglas and Smith1 080/300 m2
10Klanawa 12003Hoyt1 700/920 m2
15Klanawa 21997Roemer12 pls
15Klanawa 31998Douglas14/10 m2
15Klanawa 42004Douglas4/2m 2
20Klanawa 51998Douglas2/5 m2
11Klanawa 61998Douglas1/1 m2
No # yetCarmanah 12004MacKinnon7/500 m2
Total   848 592 stems

See Figure 4 for site locations.