Streambank lupine (Lupinus rivularis) COSEWIC assessment and status report: chapter 5

• Previous page
• Table of contents
• Next page

Habitat

Habitat requirements

This species occupies open sandy or gravelly, moist, river or creek bank sites subject to flooding and proximal to the coast with generally little ground cover. Scoggan (1978) and others describe it as occurring in gravelly prairies, streambanks and open wood, always at low elevations. Like other lupines, it shows a distinct preference for nutrient-poor sites in disturbed, but not weedy, situations, including dykes and railway tracks adjacent to waterways (Sholars 2001 pers. comm.). Because these are disturbed sites, associated species vary but include Plantago lanceolata, Solidago canadensis, Juncus tenuis, Hypericum perforatum, and Epilobium angustifolium.

In British Columbia we have observed that Lupinus rivularis grows preferentially within a short distance from a stream or creek, most frequently within 30 meters. It occurs in both natural riverbank situations and on gravelly railway beds and dykes that have been located proximal to natural creek or riverbanks sites. Where it occurs in these man-made situations, we believe that this is coincident, and that the species opportunistically invades from already present populations. In fact, the railway beds and dykes might well have allowed survival of some populations in the face of immense habitat destruction. In natural unaltered situations, it occurs on gravel or sandy/gravelly sites that are located behind low banks. Only one population of Lupinus rivularis has been found on a completely unaltered site. This is a natural site that occurs in a gravel bed behind a low “beach” ridge on a riverbank that might lie within a provincial park. 

At one site, a sub-population of the plant was found about 300 metres from the Fraser River, growing along the roadside. However this site appears to be comprised of river dredging material, and is substantially disturbed due to subdivision preparation. A relatively new subdivision occurs just across the road. It is possible that a natural creek once ran through the area. This population may be either a relict, or has resulted from seed dispersal during equipment or dredging material transport and is effectively non-viable. No seedlings were observed here.

Prior to dyking, L. rivularis likely occurred more frequently along the banks of creeks and rivers in the coastal reaches of the lower Fraser Valley. Today in this area only remnant pockets of suitable natural habitat for this species occur along the Fraser River, Pitt River, Coquitlam River, and other creeks and rivers in the area, although dykes may provide an alternative. However, natural habitat either has been heavily developed for industrial use, or has been buried by the extensive dyking system now present. The dyking has probably eliminated many populations of the plant. Natural floodplain sites, while heavily industrialized, still retain fragments of suitable natural habitat for this species and, thus, are critical for species recovery. 

In situations where the sites are unaltered by the building of dykes or railway beds, the species shows preferences for floodplain sites. Sites appear to be moister than the adjacent landscape, as is indicated in the more disturbed stations by the frequent presence of Juncus spp. 

Although this species is a pioneer species that shows preference for open sites with low soil nutrients, it does occur in two stations in shade or partial shade.

1. It shows persistence in one location where some plant succession has occurred along a roadside, adjacent to a fence: the site supports substantial tree growth with a canopy cover of approximately 75%. 
2. It also occurs in a second location on a shaded riverbank (morning sun, afternoon shade).

As a perennial species, it is well adapted to persisting under such adverse conditions and, in fact, may benefit from other disturbances, such as mowing, where the mowing aids in a somewhat broader seed dispersal than might otherwise be the case, especially where mowing occurs after seed set. Part of one site is regularly mowed, and another site has been sprayed. In both instances, however, healthy seedlings have been observed, both in the early spring, and in the fall. 

Additional suitable habitat for the species appears to occur on the gravel bars/islands that become more frequent in the Fraser River closer to the town of Mission. However, no populations have yet been discovered in these sites.

Trends

LowerFraser Valley

A cluster of records (five of six) for Lupinus rivularis occurs in the lower Fraser Valley, and all are unprotected, leaving the future of the species in Canada in jeopardy. In this region, we believe significant habitat loss has occurred as a result of the extensive dyking of our river system, and heavy industrialization of floodplains in the lower, more coastal, reaches of the Fraser. We can see some evidence of gravel pockets along the banks of the Fraser where erosion has exposed the substrate. If these were more extensive before dyking, they undoubtedly would have supported some populations of this rare species.

However, although this trend may well be responsible for the presently perilous existence of this species, it was likely already an uncommon or rare species in our region because of its occurrence at the northern limits of its range.

While more extensive gravel substrate is found further upriver, closer to Mission, including several gravel bar systems in the river, no populations of the plant have so far been discovered in this region. As it is primarily a coastal species, this may be expected. Harsher conditions further inland may be beyond the environmental capability of the species.

A further potentially restricting factor for a more inland distribution may be the impact of spring flooding.  Spring melt flooding further upstream on the Fraser River and its tributaries is more intensive, and flood water levels in the Mission to Hope area are higher, resulting in greater and more frequent scouring of riverbanks and gravel bars that may inhibit the establishment of any permanent populations.

Today, abundance of the species may be also partly limited by maintenance practices, such as spraying, along the railway tracks where it occurs. While this spraying reduces competition and opens up habitat where seedlings can establish, it also eliminates the parent plants. If it occurs next year before seed set, then this will impact seriously on the two railway bed populations. These populations will be entirely dependent, then, on a buried seed bank.

Southern Vancouver Island

Field work to date in the southern portion of the Island has not turned up any other records for this species besides the Sooke station. Further investigations should be undertaken, however. An abundance of yellow bush lupine (Lupinus arboreus) grows along the Sooke coastline less than two kilometres from the single station for L. rivularis, and hybridization is a real concern here. 

Protection/ownership

Only one population of Lupinus rivularis might be occurring in a protected site (provincial park), however, as the population was previously unreported, no active protection measures are in place. The other populations occur on railway beds, dykes, and along roadsides in private industrial lands, areas where disturbances are regular. Spraying occurred in 2001 along all railways lines in the vicinity.