Dense-flowered lupine (Lupinus densiflorus) COSEWIC assessment and status report: chapter 9

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Population Sizes and Trends

• Search Effort
• Abundance
• Fluctuations and Trends
• Rescue Effect

Search Effort

Search effort for this species included assembling locations for this species from herbaria (Royal British Columbia Museum, University of British Columbia and the University of Washington) and from the BC Conservation Data Centre and laying out transects between known sites. Prior to refining habitat requirements and a species search image, the surveying extended well beyond the known locations. Searching was initially conducted in the late summer and the distinctive foliage of Lupinus densiflorus made searching relatively easy. Additional searches were conducted in the fall and spring once it was determined that this species was a winter annual. The large, distinctive cotyledons of this species enhanced these searches and fall die-back of other competing species made searching easier. Summer search effort and measurement for the primary report writer was 16 hours and winter search effort was an additional 4 hours.

Although there is a high confidence that the primary report writers accurately delineated the current populations, there is little confidence in the numbers of individuals. Fine-scale studies of demographic patterns over a three-year period indicate that populations may fluctuate even more than has been documented in this report, although they still tend to be less than one order of magnitude (Fairbarns in prep.].

Abundance

The current areal extent of Lupinus densiflorus in Canada is 2 km² and the populations occur over 0.12 ha within that area. One of four known populations has been extirpated. Past observations of the other populations have included estimates of abundance but these appear to be too unreliable to use as a basis for tracking trends (see Fluctuations andtrends section below). The populations, however, do experience sizeable fluctuations. Estimates from 2000 and 2001 suggest a total of between 1800 and 2100 individuals among the three main populations (Table 1).

Fluctuations and Trends

Lupinus densiflorus has not been sampled regularly or consistently over the three extant populations,which hampers any attempts at relaying accurate trend data. However, for annual species, trend data on numbers of individuals is of limited value as it is difficult to assess the seed bank constituents and also to standardize for variability in growing conditions year-to-year. Currently, the BC Conservation Data Centre has the following records,which are rough periodic counts of all or portions of the three extant populations:

Rescue Effect

The United States populations of Lupinus densiflorus in Washington and California were not assessed for their health and viability. Inquiries to NatureServe Heritage program staff and web sites indicated that this species was not tracked. As mentioned in the previous section on name and classification, there is some question about the taxonomy of the southern and northern populations of Lupinus densiflorus, so it is likely that the Washington populations would provide the only viable seed source for species replacement in the present habitats of the Canadian populations. Having said that, the likelihood of natural transfer of seeds between BC and Washington State populations is very low due to the large expanse of hostile marine environments between the Victoria area of Vancouver Island, BC,and San Juan Island, Washington.