Scouler’s corydalis (Corydalis scouleri) COSEWIC assessment and status report: chapter 9

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 Observation Observer Number of Stems/Area
No # yet Cowichan 1 2004 Douglas 6/2 m2
7 Nitinat 1 2003 Douglas and Smith 34 700/5 784 m2
19 Nitinat 2 1997 Jamison 16/60m2 in 3 clusters
6 Nitinat 3 2003 Douglas and Smith 2 108/1 054 m2
6 Nitinat 4 2003 Douglas and Smith 1 000/60 m2
6 Nitinat 5 2003 Douglas and Smith 2 000/330 m2
24 Nitinat 6 2003 Douglas and Smith 1 350/120 m2
No # yet Nitinat 7 2004 Penny and Ford 10/4 m2
No # yet Nitinat 8 2003 Ferguson No data
No # yet Nitinat 9 2003 Ferguson No data
5 Nitinat 10 2003 Douglas and Smith 18 000/1 600 m2
23 Nitinat 11 2003 Douglas and Smith 150/15 m2
2 Nitinat 12 2003 Douglas and Smith 50/150 m2
2 Nitinat 13 2003 Douglas and Smith 40/150 m2
3 Nitinat 14 2003 Douglas and Smith 462 600/34 068 m2
4 Nitinat 15 1998 Douglas 2 000/5 000 m2
4 Nitinat 16 2003 Douglas and Smith 2 000/7 000 m2
4 Nitinat 28 2003 Douglas and Smith 44 850/24 800 m2
13 Nitinat 17 2003 Douglas and Smith 94 800/7 900 m2
13 Nitinat 18 2003 Douglas and Smith 21 867/7 275 m2
13 Nitinat 19 2003 Douglas and Smith 6 820/1 026 m2
21 Nitinat 20 2003 Douglas and Smith 540/36 m2
16 Nitinat 21 1997 Jamison 1 000/1 000 m2
17 Nitinat 22 2003 Douglas and Smith 105 700/5 000 m2
17 Nitinat 23 2003 Douglas and Smith 5/6 m2
18 Nitinat 24 2003 Douglas and Smith 60/60 m2
18 Nitinat 25 2003 Douglas and Smith 44 000/5 500 m2
18 Nitinat 26 1997 Jamison 100/60 m2
1 Nitinat 27 2003 Douglas and Smith 1 080/300 m2
10 Klanawa 1 2003 Hoyt 1 700/920 m2
15 Klanawa 2 1997 Roemer 12 pls
15 Klanawa 3 1998 Douglas 14/10 m2
15 Klanawa 4 2004 Douglas 4/2m 2
20 Klanawa 5 1998 Douglas 2/5 m2
11 Klanawa 6 1998 Douglas 1/1 m2
No # yet Carmanah 1 2004 MacKinnon 7/500 m2
Total       848 592 stems

See Figure 4 for site locations.

 

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