Recovery Strategy for the Dense-flowered Lupine in Canada [Proposed] 2011: Background

Date of Assessment: May 2005
Common Name (population): Dense-flowered Lupine
Scientific Name: Lupinus densiflorus
COSEWIC Status: Endangered
Reason for designation: An annual with a highly restricted distribution known from three Canadian locations. The total population size is small and fluctuates considerably depending on climatic conditions. These populations are subject to continued risks from habitat loss and degradation due to activities such as urban development, trampling, mowing, and competition with invasive exotic plants.
Canadian Occurrence: BC
COSEWIC Status History: Designated Endangered in May 2005.

Dense-flowered Lupine is an annual, tap-rooted plant that is usually branched and grows 20-30 cm in height (Figure 1). The stems are usually hollow and cylindrical at the base, and sparsely to copiously soft-hairy with long, brownish hairs. The leaves are palmately compound and occur basally and alternately along the stem but tend to cluster near the top. Further details can be found in the COSEWIC status report (COSEWIC 2005).

Dense-flowered Lupine occurs from Vancouver Island and coastal Puget Sound, south to Baja California (Figure 2). Canadian plants are sometimes (e.g. Hitchcock et al. 1961) recognized as belonging to the scopulorum variety, which is restricted to the area of Victoria, British Columbia, and adjacent islands of Washington State. These populations are disjunct from the main range of the species (Figure 2).

Conservation ranks are provided in Table 1. The proposed scopulorum variety, though much more rare, has not been ranked separately.

In Canada, populations of Dense-flowered Lupine occur in maritime meadows in the vicinity of Victoria, British Columbia (Figure 3, Table 2).

Figure 1. Illustration of Dense-flowered Lupine. Plant habit (left), flower (top right) and seedpod (bottom right). Line drawing by Ronald in Taylor (1974).

Figure 2. Distribution of Dense-flowered Lupine in North America (from COSEWIC 2005). The proposed scopulorum variety is restricted to a small area near Victoria, well separated from the range of other varieties of the species.

^?denotes an inexact rank

Figure 3. Distribution of Dense-flowered Lupine in Canada (from COSEWIC 2005). Numbers refer to population numbers in Table 2. Closed circles: extant populations; open circle: extirpated population.

The extent of occurrence in Canada is approximately 2 km²(Fairbarns unpublished data 2005). The average number of mature individuals in the Canadian population is likely in the low 1000’s, but the population varies greatly in size from year to year and survey effort has been inconsistent (Table 2). The Canadian extent of occurrence, area of occupancy, and population size represent less than 1% of the corresponding global values for the species. The status report does not treat the proposed scopulorum variety separately, but based on reports from Atkinson and Sharpe (1993) the Canadian extent of occurrence would constitute approximately 40% of the global extent of occurrence (M. Fairbarns, unpublished data 2005).

^†Counts presented in this table are not population estimates. These numbers represent the most recent survey data for a given population and due to high annual variation these numbers can not be interpreted as the average population size.

^††Populations numbered as in COSEWIC status report.

In British Columbia, Dense-flowered Lupine is restricted to the Southern Gulf Islands and Nanaimo Lowlands Ecosections, where it occurs in the Coastal Douglas-fir Biogeoclimatic Zone (BC Ministry of Environment n.d.; BC Ministry of Forests 2003). It occurs in dry to moist grassy openings, clay cliffs, and eroding grassy banks and benches above the seashore. The sites are either level or steep, and are southeast to southwest facing. The soils are deep and remain moist through the winter but are very dry by mid-summer. The plant communities are dominated by low-growing forbs and grasses and have little or no bryophyte cover. The sites are open and sunny with few trees, shrubs or even dense and taller growing herbaceous plants.

This species is dependent on various ecosystem processes to reduce competition with other species and provide safe sites for seed germination and seedling growth. These processes include natural erosion of clay banks, periodic exposure to harsh marine conditions (wind and salt spray), an annual cycle of summer drought, and occasional wildfire. In general, these processes serve to keep perennial species from dominating, allowing space for Dense-flowered Lupine germination and growth. Many of these processes have been altered by human activities within the last few hundred years.

While southern (California) populations of Dense-flowered Lupine are self-pollinated, the Canadian plants have a different flower structure and are pollinated by bumblebees.

Dense-flowered Lupine does not reproduce vegetatively, therefore dispersal of the species is dependent on seeds. It is an annual species, so populations are replenished either by recruitment from a local seed bank and/or by dispersal from other populations. Long-distance dispersal between populations is probably a rare event, so banked seeds are essential to the persistence of populations.

Three-year demographic studies reported after the COSEWIC status report was prepared provide new information on demographic characteristics (Fairbarns 2005a). The number of seedlings that survived to produce fruiting plants varied considerably (20-91%), both among locations and between years. Mortality was concentrated during the seedling stage and the major factors were invertebrate herbivory and fungal attack. Fruiting plants produced an average of 26.5 ripe seeds. There was little damage to seeds while they were still on the plant, but there were only about 10-20% as many seedlings as seeds produced in the previous year. The rest of the seeds may enter deep dormancy or be attacked by soil fungi or invertebrates. In a two year study the number of flowering individuals varied among three study plots from a decrease of 71% to an increase of 239%. Long-term fluctuations are probably much greater.

Dense-flowered Lupine populations appear limited by poor dispersal, high seedling mortality, and extreme population fluctuations.

Except where otherwise stated, this section is adapted from COSEWIC 2005. Threats are listed in the order they appear in Table 3).

Trampling and Soil Disturbance

Trampling and elevated levels of soil instability pose one of the greatest threats to Dense-flowered Lupine. The Macaulay Point and Dallas Bluffs populations occur mainly along the coastlines of heavily used municipal parks and many plants are trampled and killed each year. Trampling also poses an indirect threat at both locations, because the informal network of trails has accelerated soil erosion, exceeding the species needs, and destroying significant amounts of habitat through small landslides. Based on information presented in the COSEWIC status report and field work (Fairbarns 2010a) this threat is believed be of high severity and concern.

Invasive alien plants

Invasions of alien herbaceous plant species pose as great a threat as trampling and soil disturbance. All three populations are threatened by the encroachment of exotic shrubs and grasses, most notably Scotch Broom (Cytisus scoparius), English Ivy (Hedera helix), Gorse (Ulex europaeus), Orchard Grass (Dactylis glomerata), Sweet Vernal Grass (Anthoxanthum odoratum), Perennial Ryegrass (Lolium perenne), Barren Brome (Bromus sterilis), and Soft Brome (B. hordeaceus. Based on information presented in the COSEWIC status report and field work (Fairbarns 2010a) this threat is believed be of high severity and concern.

Land Development

Land conversion poses a significant threat to Dense-flowered Lupine. A portion of the Macaulay Point population was destroyed in 2003 when an existing road was upgraded. The Clover Point population has also been lost, apparently when a sewage pumping station was developed or the seawall was improved.

The developments described above continue a century-long trend that has seen the loss of more than 95% of Garry Oak ecosystems in the Victoria area (Lea 2002). Because the habitat of Dense-flowered Lupine is closely associated with Garry Oak ecosystems, the historical loss of Garry Oak ecosystems probably reflects a similar decline in habitat suitable for survival and recovery of this species.

While this threat has the potential for severe population level effects through land conversion, it is of medium concern as the species occurs on public land and land managers are aware of the species.

Fire Suppression

Aboriginal people may have burned some Dense-flowered Lupine sites on a regular basis to improve production of food plants and increase habitat suitability for game species (Turner 1999). There is no information about whether Dense-flowered Lupine was harvested by Aboriginal people, but burning activity would have maintained suitable habitat for this species. Fire has been suppressed throughout the Canadian extent of occurrence for over a century and this has favoured encroachment by forests, shrublands, and tall herbaceous perennials within which the lupine cannot grow.

This threat has the potential for large population level effects as it can result in habitat becoming unsuitable. However, two out of the three populations currently have habitat stewardship activities underway to reduce encroachment of shrubs. This threat is of medium concern.

Mowing

The majority of the Trial Island population has been regularly mown to reduce the risk of fire. At one time, mowing began before most of the plants could produce mature fruit. Over the past decade, mowing has usually been deferred until the majority of the seed has been dispersed (McNeill pers. comm. 2005). The site was not mowed at all in 2004 and by mid-summer, aspen along the meadow fringe had sent numerous suckers into the meadow. It therefore appears that properly timed mowing is beneficial to populations on deep, stable soils susceptible to woody plant encroachment. Elsewhere, mowing may have detrimental effects on Dense-flowered Lupine and/or co-occurring species at risk. Mowing on Trial island was resumed in 2005 to stop aspen encroachment.

While this threat has the potential to severely reduce plant growth and reproduction in a given population it is not occurring range wide and mowing practices have been altered to benefit the species making this threat currently of low concern.

Further information is needed on seedbank longevity and minimum viable population size. Techniques for population establishment/augmentation still need to be developed. Taxonomic studies are required to determine whether the Canadian/Puget Sound populations constitute a distinct taxonomic element within the species. Knowledge gaps relating to critical habitat identification are listed in section 2.5.4.