Streambank lupine (Lupinus rivularis) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Limiting factors

There are several critical limiting factors for the occurrence of this species in Canada. These include severe habitat loss and biogeographic range limits. 

This is a species that occurs at the extreme northern limits of its range and is, therefore, probably limited in the extent to which it will occur in our region. 

In the past, we believe this species was somewhat more extensive in coastal areas in the lower Fraser Valley, but that the extensive dyking introduced for flood control has significantly reduced its available habitat. It may be a species that is tied to flooding and the associated scouring and siltation. These factors are now severely limited in our range by dyking and flood control. Most of the few isolated populations that remain may be relicts from pre-dyking populations that might once have been more frequent along the river and creek banks of our area. These populations may simply be subsisting in conditions that might otherwise have allowed further seed/population dispersal and establishment of colonies. The presence of seedlings at our populations may indicate vigour, or they may actually be occurring in much lower numbers that they would have in more natural settings. Further investigation of this is needed. Other areas of suitable habitat--secondary shoreline floodplain sites in the lower Fraser Valley--have been drastically altered and now support, for the most part, industrial subdivisions. No plants have yet been found on the gravel bars of the Fraser in the Mission area, although this requires further investigation.

Threats

Several major imminent threats exist for this species, including 1) genetic swamping and hybridization, 2) site maintenance and herbicide spraying, 3) introduced invertebrates, and 4) wildflower picking. In addition, given the very small areal extent of the populations and the complete lack of protection for them, we feel that they are in a precarious position. All sites have the potential for catastrophic (human or natural) occurrences that could have a major impact on the species in Canada. The entire species could be eliminated within its Canadian range with very little effort. Serious damage from ground maintenance has already occurred in 2001.

1. Lupine rivularis is a species that is threatened throughout its entire range by genetic swamping by the highly aggressive Lupinus arboreus, and the threat is imminent. In our region, L. arboreus has been introduced, and is now being planted extensively on Vancouver Island by the Ministry of Highways (Fraser 2001 pers. comm.). We have observed its occurrence now in the lower Fraser Valley, where hybrids between the two species have been observed. In addition to ‘natural’ invasion, highways crews are actively planting L. arboreus on Vancouver Island, and seeds are presently being sold in garden shops throughout our region. Further, wildflower seeds from packages are being planted/scattered in our area and on the island as part of a beautification effort. The lupine seeds in these packages, which contain other plants such as California poppy, may have originated from California stock where L. rivularis/arboreus hybrids are common. Even without the hybridization threat, these seeds are introducing a completely different gene pool in our region.
   
   This threat by Lupinus arboreus is substantial, and probably is the single greatest threat facing the continued existence of Lupinus rivularis throughout its global range. Teresa Sholars (2001 pers. comm.) has indicated that pure populations of the species in the US might be extremely rare: most populations south of us show introgression with L. arboreus, and this may make our populations the most “pure” that still exist along the coast. This genetic purity needs to be investigated, and Sholars has indicated that status reassessment may result from her present work on Lupinusfor Flora North America. Introgression with L. littoralisis probably less of a concern, and would likely be a natural occurrence.
   
2. Further threat comes from direct site maintenance/roadside maintenance activities such as herbicide spraying. Die-off was observed this year at one site as a result of spraying. Mowing, and in particular repeated mowing, may also kill off individuals, though this requires investigation. Mowing is occurring at one site. 
   
3. In cultivation this species is very prone to predation by slugs, particularly the European Furrowed Slug (Arion ater). It is almost impossible to grow this species on southern Vancouver Island and on Saltspring Island without diligent slug control. Since this slug, and several other non-native slugs and snails are rapidly spreading within the range of Lupinus rivularis, this threat may be preventing or limiting seedling establishment at some locations (Fraser 2002 pers. comm.)
   
4. Wildflower picking of this species because of its lovely flowers has been observed, and will significantly reduce seed set. Because this species often occurs on road and railway edges where there is human access, wildflower picking is likely.
   
5. "The water district for Greater Victoria and DFO are raising the water level in the Victoria watershed an additional meter in order to redirect water flows down the Sooke River, in order to create additional salmon spawning habitat. This will change the hydrological regimes of the river, and may or may not impact the gravel bars were L. rivularis grow. Environmental Impact Assessment of this project appears to be limited to the impacts of the expanded water reservoir only, not the changes in the river." (Fraser 2002 pers. comm.).

Significant habitat loss has, we believe, already occurred for this species, and the remaining populations may well be relicts of populations that survived, for the most part, opportunistically. We believe that substantial potential habitat would have existed in the lower Fraser Valley prior to the building of the dyking system. This, combined with extensive industrial use of low floodplain sites that are ideal habitat for the species, has resulted in a major decline of the species in Canada. Further habitat loss is not likely; however, any expansion of the species in Canada is unlikely without direct intervention.