Short-rayed alkali aster (Symphyotrichum frondosum) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

In Canada, S. frondosum is a late emergent shoreline species reported primarily from lakeshore habitats in moist drawdown zones of sandy beaches and perimeters of alkali lakes and ponds. It is found in the bunchgrass biogeoclimatic zone (Douglas et al. 1998) of the sagebrush steppe in the southern Okanagan Valley. In these sites, the water draws down in the late summer and early fall, exposing suitable shallowly sloping moist sites for flowering and seed dispersal. It has also been found in drier sand beach proximal to drawdown zones by the authors. In general, suitable habitat for this species is found throughout the southern portion of the Okanagan Valley. In California, this species is also known from granitic soil of meadows and mountain slopes, and from around moist alkaline flats, marshes, ponds and ditches (Munz and Keck 1970, Wiggins 1980).

The single ephemeral coastal station from Surrey BC was found along the shore of the Fraser River in river sand dredgings, but likely originated in material washed down the Fraser from the interior of BC (Lomer 1996, 2001).

Habitat in BC is typified by the following:

  • Symphyotrichum frondosum was observed at Skaha and Vaseux Lakes in August 2002 and 2003 growing in moist sand in narrow bands of beach just below the mean summer water line, in the drawdown zone. Because of the disturbed nature of these sites, associate species included alien species such as Plantago major, Poa annua, Chenopodium glaucum, Lythrum salicaria, Melilotus alba and Polygonum aviculare. Associated native plants include alkali-tolerant Symphyotrichum ciliatum (Aster brachyactis) and Distichlis spicata var. stricta (personal observation, and Lomer collection # 3908).
  • At Osoyoos Lake, the majority of the east shoreline and beach areas were not examined. S. frondosum was found in 2002 in a public campground on a low sand beach above, but proximal to, the drawdown zone, in part sun, under poplar trees. This may represent a relict of what was once a larger population that also occupied the drawdown zone.
  • At Max Lake, S. frondosum was found on exposed saline lake edges following summer drawdown (Baumbrough 2003 pers. comm.). It is notable that this site has been predominantly dry over the last three years (Baumbrough pers. com. 2003).
  • Lomer’s 1994 collection from Surrey was from “a small patch found in temporary pilings of Fraser river sand dredgings…in compacted depressions that showed traces of salty deposits washed out from the surrounding sand” (Lomer pers. comm. 2002).

Habitat trends

Habitat at Vaseux Lake is in decline. Disturbance on the beach from park users presently limits the population to the less disturbed edges. Disturbance includes trampling, boat placement, and hole digging in the sandy beach. Additionally, in 2003, a heavy invasion of white sweet clover had moved in and was shading the spots where the aster grows.

At Skaha Lake, roto-tilling by maintenance personnel severely reduced numbers of plants in 2002. Roto-tilling has been occurring for years to maintain the beach for swimming (Harrison pers. comm. 2002), but timing and areal scope of the roto-tilling influences habitat suitability for the aster.

At Osoyoos Lake, no habitat trend information is available for the confirmed sub-population, but as with the other beach sites, lake management, heavy beach use and beach maintenance has no doubt resulted in habitat decline. An additional sub-population was extirpated as a result of site development.  

No information is available on habitat changes at Penticton, but no active management is reported. 

The site in Surrey was ephemeral, found on dredged sand landfill material in a development site.

Habitat protection/ownership

The Vaseux Lake site is a provincial park; however, no special protection measures are in place (Gunoff pers. comm. 2003) for the beach area. The site at Skaha Lake is owned by two jurisdictions: the provincial government (provincial park, provides legal protection) and the Regional District of Okanagan-Similkameen (regional park) (Harrison pers. comm. 2003). Neither agency was aware of any rare plants on their lands and had no management actions in place to protect any rare plants at the time they were contacted (Gunoff pers. comm. 2003 and Harrison pers. comm. 2003).  The Osoyoos Lake population occurs in a public campground on a heavily used public beach. The campground is part of the adjacent Indian Reserve. The Penticton site is privately owned, but is protected now by a formal conservation covenant with the landowners because of the site's role as a valuable wildlife site.

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