Oregon forestsnail (Allogona townsendiana) COSEWIC assessment and status report 2013: chapter 7

Distribution

Global Range

The global range of Oregon Forestsnail is entirely within western North America (Figure 3). The northernmost extent of its range is in southwestern BC and southeastern Vancouver Island. The range extends south through the Puget Trough and Willamette Valley in Washington State to west-central Oregon. The easternmost records are west of Hope in BC, south-central Washington and north-central Oregon in the Columbia River Valley.


Figure 3 . Global range of Oregon Forestsnail (Allogona townsendiana)

Map showing the global range of Oregon Forestsnail (see long description below).

Based on Pilsbry (1940, figure 508) and Canadian records (BC Conservation Data Centre 2013). Originally published in COSEWIC (2002).

Description of Figure 3

Map showing the global range of Oregon Forestsnail, which is entirely within western North America. The northernmost extent of the range is in southwestern British Columbia and southeastern Vancouver Island. The range extends south through the Puget Trough and Willamette Valley in Washington State to west-central Oregon. The easternmost records are west of Hope in British Columbia, south-central Washington and north-central Oregon in the Columbia River Valley (information from report text).


Canadian Range

In Canada, Oregon Forestsnail is restricted to southwestern BC (Figure 4). The species ranges within the Lower Fraser Valley from Tsawwassen (western-most record) through the municipalities of Burnaby, Delta, Surrey, Langley, Coquitlam, Mission, Abbotsford, and Chilliwack to Hope (eastern-most record). On Vancouver Island, Oregon Forestsnail is known from Westholme near Crofton (BC Conservation Data Centre 2013). There are no known records on the Gulf Islands. All records are from elevations less than 360 m asl (above sea level).


Figure 4. Canadian distribution of Oregon Forestsnail (Allogona townsendiana)

Map showing the Canadian distribution of the Oregon Forestsnail (see long description below).

See Table 1. BC Conservation Data Centre 2013.

Description of Figure 4

Map showing the Canadian distribution of the Oregon Forestsnail, where the species is restricted to southwestern British Columbia. The Oregon Forestsnail ranges within the Lower Fraser Valley from Tsawwassen (westernmost record) through the municipalities of Burnaby, Delta, Surrey, Langley, Coquitlam, Mission, Abbotsford, and Chilliwack to Hope (easternmost record). On Vancouver Island, Oregon Forestsnail is known from Westholme near Crofton. There are no known records on the Gulf Islands. (Information from report text.)


Oregon Forestsnail records in BC date from 1901 (labelled ‘Chilliwack River’) (Appendix 1) to April 2012 (various sites, Table 1) (BC Conservation Data Centre 2013). There are 66 sites[1] for Oregon Forestsnail throughout the species’ range: 65 within the Lower Fraser Valley and one confirmed site on Vancouver Island at Westholme near Crofton (Table 1) (BC Conservation Data Centre 2013). Many sites were recorded during environmental assessment surveys during the past ten years (Malt pers. comm. 2012; Robbins pers. comm. 2012). The species’ range in the Lower Fraser Valley is well defined.

Table 1. Sites occupied and area of occupancy (AO) for Oregon Forestsnail (Allogona townsendiana) in BC up to April 2012 (BC Conservation Data Centre 2013). While the ASUChilliwack site is included, no additional data are provided due to the lack of a data-sharing agreement. A "Yes" for "Fragmentation & Isolation" suggests that the site is not viable for Oregon Forestsnail.
Site name Number of land owners Land ownership information Most recent observation Fragmentation & isolation AO (ha) General habitat description and threats summary[*]
Silver Creek 1 private ? 1959-07-09 - 0.00
  • No information available.
Vedder Crossing 1 private ? 1959-07-17 - 0.00
  • No information available.
Clayburn Creek 1 private 2005-07-07 No 0.21
  • Approximately 160 acres of potential unsearched high-quality habitat; site has been impacted by urban development.
Hope; Hunter Creek 1 BC crown 2006-07-07 No 78.14
  • Snails within mature Bigleaf Maple stands with a relatively open mossy understory with abundant large course woody debris.
Chilliwack, Mount Shannon 2 private ? 2010-01-28 No 9.55
  • This area has been heavily developed since the snails were historically collected in 1959.
  • Most of the recent snails were found near well-used trails. Several dead snails were found on the edge of a bike trail, which appeared to have been recently expanded (e.g., cut vegetation).
  • The surrounding areas of the mountain contain residential development.
  • The site is on the northwest-facing side of a mountain that is surrounded by residential and agricultural development.
  • Habitat is moist, with mature Bigleaf Maple and Stinging Nettle.
  • Threats: urban development, recreational activity
Poignant Creek 1 private ? 2006-02-27 No 12.50
  • The habitat is intact and a small amount of Himalayan Blackberry is growing in the area but is not dominant.
  • Roads fragment the forest stand to the north, east and south (also recent development to south). However, the habitat is relatively intact and connected to surrounding terrestrial and aquatic resources
  • Second growth, mixed deciduous/coniferous riparian forest with several mature conifers. The riparian habitat occurs in a ravine surrounding Dianne Brook, which runs through the north end of the survey property.
  • Threats: urban development
Abbotsford 2 private land 2010-05-19 No 23
  • Mature stand of mixed forest; description is that it is in good condition, with significant understory. There is a block of approximately 23 ha of similar forest where the snail was found.
  • One of the properties is in a block of forest within a fragmented landscape of agriculture and residences, with some riparian corridors; the other property is surrounded by agricultural land.
  • Threats: possible urban development
Chilliwack Mountain 2 private land 2009-08-08 No 12.96
  • Approximate 50-year-old Bigleaf Maple stand
  • The area is a surveyed, posted lot in a low-density residential area
  • Historical logging has occurred at the site resulting in the removal of conifer trees.
  • North side is a gravel road 15 - 20 m south of the occurrence, running east-west. There are residential areas toward the eastern end of the road approximately 300 m north of the occurrence. The area of occurrence and surrounding areas are not fragmented.
  • North side: The area is near the base of the slope of the mountain.
Chilliwack, Promontory 3 private ? 2007-06-19 Yes 0.39
  • This site is a transition zone between a wet and shady ravine to the north and a dry and sunny field and grassy trail.
Yarrow, south of 1 private ? 2008-05-09 No 4.47
  • The area is mature, second-growth mixed-wood forest, occurs on the north side of Vedder Mountain.
Chilliwack, Ryder Creek 3 private ? 2006-03-22 No 33.74
  • Both the crown land and private parcels on which the snails were recorded are very unlikely to be developed in the immediate future as they have major geotechnical hazards.
  • 65 shells and 2 live animals are within 0.3 square kilometres.
  • The occurrence is within moist, 60-year-old mixed-wood forest with large Bigleaf Maples along steep hillside and small creeks
Tamihi Creek 2 B.C. crown? 2008-05-04 No 4.10
  • Tamihi Creek south: primarily mature forest with an approximate age of 70 years; Tamihi Creek north: primarily a 60-year-old stand of deciduous trees
  • Tamihi Creek south: The occurrence is where the Tamihi Creek emerges from the Chilliwack River.
Cultus Lake, Northwest of; Vedder Mountain 2 B.C. crown, private 2009-06-26 No 19.18
  • The area of Vedder Mountain is primarily used for forestry activity. Situated within a Wildlife Habitat Management Area (zone length = 200 m) in an approved harvest cutblock (estimated to be less than 100 years old). Selective harvesting is permitted with Crown land, approved cutblock, under timber licence.
  • Threat: possible logging or road access through Wildlife Habitat Management Area.
Luckakuck Creek, Squiaala Indian Reserve 7 1 Indian Reserve (federal) Squiaala Indian Reserve 7 2007-09-21 No 5.39
  • The land is part of Squiaala Indian Reserve 7 and the original proposal included the creation of commercial property within the existing farmland. Present plans for property development are unknown.
Abbotsford, Downes Road 1 private 2005-12-14 No 12.50
  • Habitat is on an elevated knoll. Mixed stand dominated by mature Bigleaf Maple and Western Red-cedar with minor component of Douglas-fir, western Western Hemlock and Red Alder.
  • Threats: possible urban development.
Wharton Creek 1 private ? 2001-06-09 No 3.13
  • The area is primarily mature, second-growth forest.
  • The occurrence is in a regional park. The dominant vegetation species include Bigleaf Maple, The stand age is mature second growth.
Clayburn, Sahhacum Indian Reserve 1 1 Indian Reserve, Sahhacum Indian Reserve 1 2008-06-12 Yes 0.78
  • The western portion of Sahhacum Indian Reserve 1 is undeveloped and covered in natural vegetation. Historically, the western parcel has never been used and there is no existing infrastructure. It is inaccessible and undeveloped.
  • Sahhacum Indian Reserve 1 is bisected into eastern and western parcels by a transportation corridor occupied by Canadian Pacific Railway, Southern Railway of British Columbia, and the Abbotsford-Mission Highway Number 11.
  • Good quality wetland and riparian habitats with lowland wetland connected to surrounding terrestrial and aquatic resources within the western parcel.
  • Threats: in past, development for transportation corridors.
Coquitlam River, west of 1 Colony Farm Metro Vancouver Regional Park - local government 2010-05-20 Yes 5
  • Colony Farm Metro Vancouver Regional Park (Figure 10) surrounded by urban development.
  • Highway 7A and 7B are adjacent to the north and south borders of the park. Colony Farm Road divides the park north to south on the west side. The south end of the park borders the Fraser River.
  • Habitat is predominantly open fields and wetland complexes, colonized by dense Stinging Nettle, shrubs and tall grass, with only a few scattered deciduous trees.
  • Threats: in the past, transportation corridors and agricultural field, urban development
Abbotsford, South of Clayburn 1 private 2010-08-22 Yes 0.20
  • Watercourse enhancement works have occurred at the site; this has impacted Oregon Forestsnail individuals and habitat at this site.
  • Found within deciduous riparian corridor along a creek; greenbelt surrounded by suburban residential development. Snail likely occurred throughout similar habitat prior to urban development.
  • Threats: urban development
Abbotsford, south of Highway 11 1 private 2010-05-20 Yes 0.20
  • Residential developments, agricultural and industrial development surround the site.
  • Threats: urban development.
Nicomen Island 1 private ? 2000-05-23 Yes 2.09
  • Disturbed, second-growth forest on Nicomen Island, which is a river-island surrounded by dykes.
  • Threats: potential flooding may impact population persistence over time.
Mountain Slough 1? private ? 2007-03-23 Yes 3.13
  • This location was formerly a riparian area of Mountain Slough; the general area is predominantly Trembling Aspen and Black Cottonwood
  • The occurrence is within a recently cleared area of land, about 10-15 m from the adjacent water course.
  • Threats: urban development in the past, and likely future.
Mission, south of Wharton Creek (including Westminster Abbey) 3 private Westminster Abbey; other landowners unknown 2009 Yes 0.73
  • A permanent watercourse is present ~5 metres north of the sighting. A shrub wetland exists immediately south of the sighting for ~20-30 metres.
  • New residential housing exists to the north.
  • Beyond the riparian corridor to the west the area is fragmented from other adjacent, suitable habitat as a result of existing or planned housing development.
  • Threats: urban development (in part)
Mission, West Heights 1? private ? 2007-09-12 Yes 0.20
  • Mature deciduous forest vegetation situated along the upslope portion of the south side of the Canadian Pacific Railway right-of-way.
Sumas Mountain, McKee Peak 2 private ? 2007-05-30 Yes 6.86
  • Evidence of future development in area.
  • McKee Peak is a portion of Sumas Mountain and overall this area is large parcel of natural habitat within the Lower Fraser Valley. Sumas Mountain is experiencing extensive large-scale housing development, both at present and planned for the future.
Willband Creek 1 private ? 2006-07-07 Yes 0.78
  • BC Hydro substation to the east and south. Much of the nearby areas are farmed with road access.
  • In a Red Alder-dominated stand with Stinging Nettle understory surrounded by Himalayan Blackberry.
Tones Creek, south of 1 private ? 2007-09-12 Yes 0.20
  • Along the Canadian National Railway right-of-way south of the Fraser River surrounded by Matsqui Main 2 Indian Reserve.
  • Mature deciduous forest vegetation situated along the upslope portion of the south side of the Canadian National Railway right-of-way.
Abbotsford, Eleanor Avenue 1 private land 2006-11-02 Yes 0.20
  • This occurrence is found within mature deciduous-dominated forest habitat within a proposed development study area.
  • The proposed development study area includes the mature deciduous-dominated forest habitat in which this occurrence is found as well as disturbed/vacant habitat to the south within Lot:3 Sec:14 Twn:16 Plan LMP40494. The survey also extended north to Lonzo Creek.
  • Threats: urban development.
Abbotsford, Marshall Road 1 private land 2007-02-09 Yes 0.20
  • The Upper Ravine and the Ravine Pond area show many signs of human use including tracks, mountain bike jumps, wooden constructed pathways, a fort-like structure, garbage, evidence of campfires and the presence of an old camper top.
  • The property is surrounded by a large residential development, except for a few small treed areas in between the subdivisions. The plans are for further development if the surrounding area.
  • Currently, a ravine runs through the property from the northeast to the southwest. The ravine is a natural valley approximately 600 metres long, with slopes of varying heights and steepness. The habitat of the ravine is that of a mixed wood forest. The ravine at this site was partially filled in to allow for road development.
  • Threats: urban development, recreational use.
Chilliwack Prairie, Central and Patterson Road 3 private ? 2008-08-19 Yes 13.30
  • Habitat in a natural state, but selective tree removal was planned to occur in 2008 on the adjacent property. This will degrade the existing habitat, but riparian corridors and smaller tree retention is likely.
  • Historical logging in the area has removed most conifer trees; residential development is being implemented. Area remains intact, but the property north of the southern detection (7500 Patterson Road) is planned.
  • Threats: logging, urban development
Hatzic Prairie, Lagace Creek 1 Private 2006-06-11 Yes 0.38
  • Possibility of area having been mowed.
  • Potential habitat for the population is very limited and is not connected to other areas. The two live adults were found in a very isolated patch of forest on the corner of two paved roads and bordered on the other side by a creek
  • Threats: urban development, vegetation management.
Pemberton Hills 2 Private 2010-04-17 Yes 10.89
  • Site occurs in mixed-wood forest with a stand age of 70 - 80 years.
  • Strip of natural habitat surrounded by farmland and rural residences.
  • Both sites are in the Pemberton Hills area within 1 km of each other.
  • Threats: likely urban development.
Ridgedale, 5 km east of 1 Private 2008-06-07 Yes 0.01
  • The area has been logged in the past as evident by old stumps
  • snail was observed along and adjacent to an old logging road.
  • Deciduous and coniferous trees in the area are now mature.
  • Popular hiking area, although in some areas there is no disturbance from hikers
  • The area around the occurrence is in a natural state.
  • Threats: urban development, possible logging, recreational use.
Straiton, Poignant Creek 1 Private ? 2007-06-27 Yes 1.82
  • Ownership of the land is unknown, and extensive development in the area seems to be a major threat.
  • Straiton Road runs beside the ravine with an approximately 100-metre buffer between the stream and the road. A new residential area was in the process of development on the other side of the ravine
  • Habitat includes a riparian area that was very moist and in a ravine.
  • Threats: urban development
Sumas Mountain 1 private ? 2009-04-05 Yes 0.00
  • The occurrence is beside a poor trail and may be within an area not subject to development (on Sumas Mountain), but land ownership is unknown.
Tsawwassen 1 private 2008-04-15 Yes 0.73
  • Threats include dirt bikes, isolation and insularity of the population.
  • Occurrence is in a small forest block surrounded by agricultural fields, housing developments and roads (separating it from another forest block to the south in the United States). The area was to be developed into urban housing, but plans were delayed.
  • Threats: recreational use.
Watt Creek (Cultus Lake) 2 private 2007-05-29 Yes 2.35
  • Adjacent to a high-use trail, which is routinely raked, and a tree fort is nearby.
  • Camp Stillwod is used for summer programs, and often rented to large groups (adults and children) with various buildings, fields and trails to the west and Watt Creek to the east. It is a forested area, previously logged maybe 50 years ago.
  • Threats: recreational use.
Westholme , NE of Road/Rail junction, near Crofton, Vancouver Island 2 Indian Reserve; federal; perhaps some private 2007 Yes 8.83
  • The area is close to a railway track at the edge of a Bigleaf Maple stand that ranges from 40-80 years old.
  • From aerial photos, the occurrence appears to be surrounded by some suitable habitat, agricultural fields and roads.
  • The area is within a floodplain in a valley bottom with a high water table. It is close to a railway track at the edge of a mixed-wood forest with Bigleaf Maple that ranges between 40-80 years old.
City of Abbotsford, Douglas Taylor Park 1 local government Douglas Taylor Park, City of Abbotsford 2006-03-21 Yes 0.78
  • This site is within a 40-year-old mixed-wood forest.
  • Threats: recreational use.
Aldergrove Regional Park, Aldergrove 1 local government Aldergrove Regional Park Fraser Valley Regional District 2010-05-19 Yes 1.18
  • The wetland is off the park trail and is difficult to access.
  • The park is less than 2 kilometres north of the Canada/US border. Roads parallel the north and west borders of the park. Surrounding land use is primarily agricultural and residential. There are several gravel pits in the vicinity.
  • The site is within the floodplain of Pepin Creek within a regional park.
  • This wetland has large woody debris from years of beaver activity. The snail was found on a stump in a small patch of Skunk Cabbage.
  • Threat: low recreational use
Chester Creek, Mission 1 private 2007-02-16 Yes 0.28
  • Undisturbed forested area with creek running through it.
  • There are over 75 ha of similar undisturbed forest where the snail was found before any roads or clearings.
  • Forested area with agricultural clearings to the west and south (approximately 225 m and 175 m respectively). The forested area is more extensive to north and east with the first roads being about 500 m away. Generally the landscape is fragmented
  • Forested area with small creek running through it. Forest floor has large amount of leaf litter and course woody debris.
  • Threats: possible logging, urban development.
Sperling 1 private 1993-06-08 and 2010 Yes 3.12
  • Large forest block; adjacent southwest forest block private property and not protected.
  • Threats: logging, possible urban development.
Vedder Mountain, Browne Road 1 private 2005-04-05 Yes 0.78
  • Area is subject to cattle grazing and trampling of soil.
  • Habitat: 40-year-old Bigleaf Maple stand with disturbed understory on lower slope of mountain.
  • Threats: livestock grazing, possible urban development
Village of Kent; Cemetary Hill 1 private land Kent (Village) 2000-05-23 Yes 3.12
  • The area is primarily second growth, with some old trees.
  • Site is on east side of a hill in the Village of Kent.
Trinity Western University, Approximately 3 km south of Fort Langley 2 B.C. crown; private Trinity Western University Ecological Study Area 2001-09-08 Yes 0.78
  • The area is primarily mature second-growth forest with a large deciduous component.
  • This occurrence is in the Ecosystem Study Area of Western Trinity University campus, which contains part of the Salmon River and some tributaries.
  • Threats: possible recreational use, although there is good signage regarding habitat protection and respect for Oregon Forestsnail.
Sumas Mountain Road 1 private ? 2003-06-13 Yes 3.13
  • The area is near low-density housing, in a mixed-wood forest with a stand age of approx. 80 years.
  • The area is by a road on Sumas Mountain near low-density housing.
  • Threats: possible urban development.
Sumas Mountain, West Slope 1 private ? 2003-06-13 Yes 3.13
  • The area is mixed-wood forest with a stand age of approx. 70 years.
  • Site is near the base of the West slope of Sumas Mountain.
  • The stand age is approx. 70 years with moderate leaf litter, light soil and low, coarse woody debris.
  • Threats: possible urban development.
Sumas Mountain, Cox Road 1 private ? 2006-03-21 Yes 0.78
  • Steep hillside with large Bigleaf Maples and Stinging Nettle and Salmonberry understory.
  • Threats: possible urban development.
Bridal Veil Falls 3 private land; federal (Indian Reserve - Popkum); Bridal Veil Falls Provincial Park; BC crown 2011-07-12 Yes 3.91
  • Portion of this site is Bridal Veil Falls Provincial Park that is used by visitors primarily for day use. The park consists of mature, second-growth forest and large patches of Stinging Nettle. A number of snails were recorded adjacent to a recreational vehicle parking area (Figure 8), and were dispersing into mown grass and gravel.
  • The age of the stand is mature, second growth (< 70 years) with Bigleaf Maple and Western Redcedar
  • Threats: immediate plans for urban development on non-crown land; trampling and recreational use in the park.
Cheam Wetlands 1 local government Cheam Lake Regional Park Fraser Valley Regional District 2011-05-16 Yes 3.91
  • The site is within mature, mixed-wood forest in a regional park. The park has 2 km of trails, some walkways and a picnic area; dogs, watercraft and fishing are prohibited in the park.
  • Snails recorded from a strip of Stinging Nettle >250 m long and up to 50 m wide along a creek with lots of Oregon Forestsnails, a patch of Stinging Nettle at edge of parking lot lawn, approximately 85 m long and 15 m wide with OFS, scattered Stinging Nettle interspersed with other vegetation in a 1.5 loop around wetlands with Oregon Forestsnail.
  • Threats: recreation al use.
Chilliwack, Dunville Creek 3 B.C. crown and private 2005-04-08 Yes 2.34
  • Ongoing selective logging on lower slope on private land.
  • Habitat: 70-80-year-old mixed-wood forest stand with Bigleaf Maple (some large) on lower slope of mountain; abundant herbaceous plants in small forest openings.
  • Threats: logging
Hatzic Lake, 1 km north of 2 Private and B.C. crown 2005-04-13 Yes 1.56
  • Habitat: 40-50 year-old mixed-wood forest with Bigleaf Maple on lower slope of mountain; pockets of abundant herbaceous plants, especially near mountain base.
  • Threats: possible logging.
Hatzic Lake, 4.5 km north of 1 B.C. crown 2005-04-01 Yes 1.56
  • Habitat is within a mixed-wood, 60-year-old stand of Bigleaf Maple and alder with dense shrub understory.
  • Threats: possible logging.
Hope, southwest of 1? B.C. crown 2006-03-13 Yes 0.78
  • Recorded within 50-year-old, moist, mixed-wood forest that slopes steeply toward a creek.
  • Threats: possible logging.
Hopyard Hill > 2 private (numerous) 2005-04-07 Yes 3.91
  • Primarily young forest, with an approximate stand age of less than 50 years. This site is along a mowed road.
  • Threats: vegetation management along road.
South Surrey, Campbell Valley Metro Vancouver Regional Park 2 local government, Metro Vancouver Park 2006-03-06 and 2011 (unknown date) Yes 1.56
  • Snails were found on a south-facing creek bank adjacent to a floodplain. Site is within a 40-50-year-old mixed-wood forest.
  • Active recreational park with horseback riding and other recreational use.
Vedder Canal Bergman Road 1 private ? 2006-03-08 Yes 0.78
  • There is a recreational trail in the area.
  • Moist, 50-year-old, mixed-wood forest (mostly Red Alder and Black Cottonwood) with patches of Bigleaf Maple along Vedder Canal.
  • Threats: recreational use
Sumas Mountain, South Slope 5 private 2005-04-12 Yes 0.78
  • Site has been (sometime in the past) disturbed by ruminant station and a quarry/gravel pit.
  • Threats: urban development
D’herbomez Creek 1 private ? 2001-06-09 Yes 0.28
  • The site consists of mowed grass along a mature, second-growth forest edge
  • The age of the stand is mature, second-growth (greater than 100 years).
  • Threats: vegetation management, urban development.
Herrling Island Road 1? private ? 2000-05-22 Yes 3.12
  • Site located on a grassy surface at the edge of a road along the forest edge.
Nicomen Slough 1 private ? 2000-05-23 Yes 3.12
  • The area is primarily disturbed mature, mixed-wood forest near a road at Nicomen Slough.
Wren Creek, Mission 1 private 2012-05 (date not available) Yes < 3
  • Large private land development that includes the infilling and diversion of a creek with a large population of Oregon Forestsnail.
Brunette Fraser Greenway (Park) 1 local government, Metro Vancouver 2011-05-9 Yes < 0.5
  • Snail recorded from a small patch of Stinging Nettle adjacent to a well-used urban trail. Habitat is not connected to other areas and is highly isolated from other habitat.
Glen Valley 1 local government, Metro Vancouver 2011-05-11 Yes < 0.5
  • Found only at the poplar bar area of the park, three snails found in a patch approximately 80 mlong x 40 m at widest point on trail near parking lot
Neilson Park 1 local government, Fraser Valley Regional District 2011-05-24 Yes < 0.5
  • 150 m long Stinging Nettle strip approximately 10 m wide along base of steep hill at the edge of baseball field full of OFS. This connects to a strip of scattered Stinging Nettle, approximately 250 in length and 40 m wide in the forest east of the baseball field full of OFS
Brae Island 1 private, Metro Vancouver 2011-05-11 Yes < 0.5
  • Stinging Nettle mixed with other vegetation for approximately 800 m along the length of the loop trail, approximately 225 m in width at widest point
Department of National Defence Area Support Unit, Chilliwack 1 Federal 2011 (date unknown) No N/A
  • Information not available
South Perimetre Road, Surrey 1 B.C. Crown 2011 Yes N/A
  • There are a few sites along this highway expansion project that have Oregon Forestsnail. Some of the snails have been translocated to adjacent habitats, but the original habitat has since been converted to roadways as part of the expansion project.

*(Although not stated, all sites are subject to IUCN-CMPThreats: 7.1 (fire and fire suppression); 8.1 (invasive non-natives, particularly Himalayan Blackberry); 11.1 (Habitat shifting and alteration); 11.2 (droughts); 11.4 (storms and flooding).

Extent of Occurrence and Index of Area of Occupancy

Based on historical and recent records (within the past ten years) the extent of occurrence (EO) is 3,313 km2, including the single site on Vancouver Island. The current EO was calculated by the COSEWIC Secretariat using a minimum convex polygon within Canada’s extent of jurisdiction. The unsuitable habitat of the Strait of Georgia, between the island and mainland, is included in the EO calculation. The EO for the previous status report was approximately 1,863 km2 (based on map provided in COSEWIC 2002, calculated by the BC-CDC) and would have included only the Fraser Valley but not the Vancouver Island sites (in 2002 this island site was considered historical). New records that increased the EO include Colony Farm Regional Park (Coquitlam), Brunette-Fraser Regional Greenway (Burnaby), Tsawwassen and the confirmed site on Vancouver Island. Each of these four sites is fragmented, isolated and total less than 1 km2 biological area of occupancy (BCConservation Data Centre 2013).

The index of area of occupancy (IAO), calculated by the COSEWIC Secretariat, is 300 km2 (Figure 5) (= 75, 2 km x 2 km grids that cover all sites in Figure 4). The biological area of occupancy calculated by summing the area of all mapped sites is approximately 328 ha (Table 1) (BC Conservation Data Centre 2013).


Figure 5 . The index of area of occupancy (IAO) for Oregon Forestsnail

Map showing index of area of occupancy for the Oregon Forestsnail (see long description below).
Description of Figure 5

Map showing index of area of occupancy (IAO) for the Oregon Forestsnail in Canada. The IAO is 300 square kilometres, based on 2 kilometre by 2 kilometre blocks. Blocks indicate historical sites and extant sites.


If the three western-most records on the mainland (Burnaby - very small 20 m x 20 m area of Stinging Nettle on a right-of-way pedestrian walkway; Tsawwassen - private land up for development in the next ten years; and White Rock - municipal park; see Figure 5) were extirpated, the EO within Canada’s extent of jurisdiction would be reduced to 2,018 km2 (39%) and IAO would be reduced to 288 km2 (calculations by COSEWIC Secretariat).

Search Effort

From 2000 - 2011 substantial search effort for Oregon Forestsnail has resulted in additional sites within the species’ range in BC (Table 2). Search effort has focused on the edges of the species’ range on southeastern Vancouver Island, many southern Gulf Islands and areas throughout the Lower Fraser Valley and Sunshine Coast (Figure 6).

Table 2. Surveys for Oregon Forestsnail ( Allogona townsendiana) on Vancouver Island, Gulf Islands and Lower Fraser Valley, BC. Note: Search effort time (hours) and search effort distance ( km) have often not been measured during surveys.
Survey year Report citation Total number of sites surveyed Number of
Lower Mainland or Sunshine Coast sites surveyed
Number of Vancouver Island sites surveyed Number of Gulf Islands sites surveyed Search effort
time (hours)
Search effort distance (km)
1984 Cameron 1986 38 N/A N/A N/A N/A N/A
1999 - 2003 Ovaska and Sopuck 2000, 2001, 2002a, 2003a, Ovaska et al.2001 26 2 24 0 N/A N/A
2000-2001 Ovaska et al. 2001 142 38 104 0 196.6 N/A
2002 Ovaska and Sopuck 2002b 3 0 3 0 71.6 5.6
2003 Ovaska and Sopuck 2003b 52 30 22 0 19.25 N/A
2003 Ovaska and Sopuck 2003c, 2004a 43 0 30 13 N/A N/A
2003 - 2004 Ovaska and Sopuck 2004b 43 4 39 0 131.1 N/A
2005 Ovaska and Sopuck 2005a 47 47 0 0 57.9 N/A
2004 - 2005 Ovaska and Sopuck 2005b 47 47 0 0 57.9 N/A
2006 Ovaska and Sopuck 2006a 26 0 26 0 N/A N/A
2006 Ovaska and Sopuck 2006b 21 0 21 0 N/A N/A
2007 Ovaska and Sopuck 2007a 6 0 6 0 N/A 9.2
2007 Ovaska and Sopuck 2007b 6 0 6 0 N/A  
2008 COSEWIC 2010 17 4 13 0    
2008 Ovaska and Sopuck 2008 22 0 22 0 N/A N/A
2009 Bains et al. 2009 10 10 0 0 43 49.6
2008 Ovaska and Sopuck 2009a 6 0 6 0 N/A N/A
2008 Ovaska and Sopuck 2009b 22 0 22 0 N/A N/A
2008 - 2009 Ovaska and Sopuck 2009c 22 0 22 0 N/A N/A
2009 Department of National Defence Formation Environment Natural Resources Program 2009 6 0 6 0 N/A N/A
2010 Ovaska and Sopuck 2010 10 0 10 0 N/A 7.2
2010 Parkinson and Heron 2010 5 5 0 0 30 34.3
2009 Sopuck and Ovaska 2010a 5 0 0 5 N/A N/A
2010 Sopuck and Ovaska 2010b 1 1 0 0 N/A N/A
2011 Heron, personal data 2011 39 39 0 0 144 418.9
2009 - 2011 Ovaska et al. 2011 5 5 0 0 N/A N/A
1990 - 2011 Forsyth personal data 2011 450 N/A N/A N/A 75.5 N/A
Total: 1984 - 2011   1083 232 382 18 826.85 524.8


Figure 6. Search effort for terrestrial snails within and adjacent to the known range of the Oregon Forestsnail

Map showing sites searched for terrestrial snails (see long description below).

The current extant sites and historically occupied sites also are shown. Data from the BC Conservation Data Centre (2013) up to April 2012 as well as Forsyth (unpubl. data up to 2011) are included (map produced by COSEWIC Secretariat).

Description of Figure 6

Map showing sites searched for terrestrial snails within and adjacent to the known range of the Oregon Forestsnail. Extant sites and historically occupied sites for the Oregon Forestsnail are also indicated.


Surveys for Oregon Forestsnail have primarily been by wandering transects through suitable habitat with the main objective to record snail presence, abundance and habitat information (Table 2). Wandering transects follow no pre-determined grid or fixed route and allow the surveyor to change course depending on habitat suitability. Transect routes are usually tracked using a handheld geographic positioning system (GPS) unit to also quantify search effort. This methodology has not allowed for population size or trend evaluations, mostly because surveys have been to assess environmental values prior to development and sites are not revisited.

The presence of Oregon Forestsnail shells is considered evidence of recent live individuals at a site. Oregon Forestsnail is typically reported incidentally during other wildlife surveys and not during the ideal survey window (e.g., snails may be hibernating or aestivating). Pearce (2008) found clearly identifiable terrestrial snail shells after 4 to 7 years exposure in forests of Delaware and northern Michigan but cautions that decomposition rates varied among species but not between the two habitats he tested.

Since 2000, gastropod surveys within the range of Oregon Forestsnail amount to a minimum of 1083 sites surveyed (232 sites in the Lower Fraser Valley; 382 sites on Vancouver Island, 18 sites on the southern Gulf Islands) (Figure 6). From 2009 - 2011, there is a minimum of 827 hours and 525 km of search effort for Oregon Forestsnail, including surveys completed as part of the updated status report preparation. The actual search effort since 2000 (hours and kilometres) is much higher because many surveyors did not record this information (Table 2). For this reason, the number of sites surveyed is the best indication of search effort.

Oregon Forestsnail is often recorded as an incidental observation and in the past ten years, biologists, naturalists, and members of the public have voluntarily submitted new observations to the BC Conservation Data Centre (2013), which has increased the knowledge on distribution and habitat association. Of particular importance, professional biologists working on environmental assessments often contribute null data (e.g., search effort for Oregon Forestsnail with no specimens found) (Ferguson pers. comm. 2011; Bianchini pers. comm. 2012; Durand pers. comm.2012; Knopp pers. comm.2012; Malt pers. comm.2012). The null data are not possible to quantify yet the contribution to overall search effort is notable.

The following conservancy groups working on various Gulf Islands have not recorded Oregon Forestsnail during surveys: Salt Spring Island (Annschild pers. comm. 2011), Denman Island (Fyson pers. comm. 2012), Hornby Island (Law pers. comm. 2011), Mayne Island (Dunn pers. comm. 2011) and Galiano Island (Crowe pers. comm. 2011).

1Site refers to a record of one or more Oregon Forestsnail individuals from a habitat patch. A site is a "spatial representation of a species or ecological community at a specific area, generally delineates a species population or ecological community stand, and represents the geo-referenced biological feature that is of conservation or management interest. Sites are documented by voucher specimens (where appropriate) or other forms of observations. A single site may be documented by multiple specimens or observations taken from different parts of the same population, or from the same population over multiple years" (Natureserve 2012).

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