Oregon forestsnail (Allogona townsendiana) COSEWIC assessment and status report 2013: chapter 7
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)
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).
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)
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.
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 |
|
Vedder Crossing | 1 | private ? | 1959-07-17 | - | 0.00 |
|
Clayburn Creek | 1 | private | 2005-07-07 | No | 0.21 |
|
Hope; Hunter Creek | 1 | BC crown | 2006-07-07 | No | 78.14 |
|
Chilliwack, Mount Shannon | 2 | private ? | 2010-01-28 | No | 9.55 |
|
Poignant Creek | 1 | private ? | 2006-02-27 | No | 12.50 |
|
Abbotsford | 2 | private land | 2010-05-19 | No | 23 |
|
Chilliwack Mountain | 2 | private land | 2009-08-08 | No | 12.96 |
|
Chilliwack, Promontory | 3 | private ? | 2007-06-19 | Yes | 0.39 |
|
Yarrow, south of | 1 | private ? | 2008-05-09 | No | 4.47 |
|
Chilliwack, Ryder Creek | 3 | private ? | 2006-03-22 | No | 33.74 |
|
Tamihi Creek | 2 | B.C. crown? | 2008-05-04 | No | 4.10 |
|
Cultus Lake, Northwest of; Vedder Mountain | 2 | B.C. crown, private | 2009-06-26 | No | 19.18 |
|
Luckakuck Creek, Squiaala Indian Reserve 7 | 1 | Indian Reserve (federal) Squiaala Indian Reserve 7 | 2007-09-21 | No | 5.39 |
|
Abbotsford, Downes Road | 1 | private | 2005-12-14 | No | 12.50 |
|
Wharton Creek | 1 | private ? | 2001-06-09 | No | 3.13 |
|
Clayburn, Sahhacum Indian Reserve 1 | 1 | Indian Reserve, Sahhacum Indian Reserve 1 | 2008-06-12 | Yes | 0.78 |
|
Coquitlam River, west of | 1 | Colony Farm Metro Vancouver Regional Park - local government | 2010-05-20 | Yes | 5 |
|
Abbotsford, South of Clayburn | 1 | private | 2010-08-22 | Yes | 0.20 |
|
Abbotsford, south of Highway 11 | 1 | private | 2010-05-20 | Yes | 0.20 |
|
Nicomen Island | 1 | private ? | 2000-05-23 | Yes | 2.09 |
|
Mountain Slough | 1? | private ? | 2007-03-23 | Yes | 3.13 |
|
Mission, south of Wharton Creek (including Westminster Abbey) | 3 | private Westminster Abbey; other landowners unknown | 2009 | Yes | 0.73 |
|
Mission, West Heights | 1? | private ? | 2007-09-12 | Yes | 0.20 |
|
Sumas Mountain, McKee Peak | 2 | private ? | 2007-05-30 | Yes | 6.86 |
|
Willband Creek | 1 | private ? | 2006-07-07 | Yes | 0.78 |
|
Tones Creek, south of | 1 | private ? | 2007-09-12 | Yes | 0.20 |
|
Abbotsford, Eleanor Avenue | 1 | private land | 2006-11-02 | Yes | 0.20 |
|
Abbotsford, Marshall Road | 1 | private land | 2007-02-09 | Yes | 0.20 |
|
Chilliwack Prairie, Central and Patterson Road | 3 | private ? | 2008-08-19 | Yes | 13.30 |
|
Hatzic Prairie, Lagace Creek | 1 | Private | 2006-06-11 | Yes | 0.38 |
|
Pemberton Hills | 2 | Private | 2010-04-17 | Yes | 10.89 |
|
Ridgedale, 5 km east of | 1 | Private | 2008-06-07 | Yes | 0.01 |
|
Straiton, Poignant Creek | 1 | Private ? | 2007-06-27 | Yes | 1.82 |
|
Sumas Mountain | 1 | private ? | 2009-04-05 | Yes | 0.00 |
|
Tsawwassen | 1 | private | 2008-04-15 | Yes | 0.73 |
|
Watt Creek (Cultus Lake) | 2 | private | 2007-05-29 | Yes | 2.35 |
|
Westholme , NE of Road/Rail junction, near Crofton, Vancouver Island | 2 | Indian Reserve; federal; perhaps some private | 2007 | Yes | 8.83 |
|
City of Abbotsford, Douglas Taylor Park | 1 | local government Douglas Taylor Park, City of Abbotsford | 2006-03-21 | Yes | 0.78 |
|
Aldergrove Regional Park, Aldergrove | 1 | local government Aldergrove Regional Park Fraser Valley Regional District | 2010-05-19 | Yes | 1.18 |
|
Chester Creek, Mission | 1 | private | 2007-02-16 | Yes | 0.28 |
|
Sperling | 1 | private | 1993-06-08 and 2010 | Yes | 3.12 |
|
Vedder Mountain, Browne Road | 1 | private | 2005-04-05 | Yes | 0.78 |
|
Village of Kent; Cemetary Hill | 1 | private land Kent (Village) | 2000-05-23 | Yes | 3.12 |
|
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 |
|
Sumas Mountain Road | 1 | private ? | 2003-06-13 | Yes | 3.13 |
|
Sumas Mountain, West Slope | 1 | private ? | 2003-06-13 | Yes | 3.13 |
|
Sumas Mountain, Cox Road | 1 | private ? | 2006-03-21 | Yes | 0.78 |
|
Bridal Veil Falls | 3 | private land; federal (Indian Reserve - Popkum); Bridal Veil Falls Provincial Park; BC crown | 2011-07-12 | Yes | 3.91 |
|
Cheam Wetlands | 1 | local government Cheam Lake Regional Park Fraser Valley Regional District | 2011-05-16 | Yes | 3.91 |
|
Chilliwack, Dunville Creek | 3 | B.C. crown and private | 2005-04-08 | Yes | 2.34 |
|
Hatzic Lake, 1 km north of | 2 | Private and B.C. crown | 2005-04-13 | Yes | 1.56 |
|
Hatzic Lake, 4.5 km north of | 1 | B.C. crown | 2005-04-01 | Yes | 1.56 |
|
Hope, southwest of | 1? | B.C. crown | 2006-03-13 | Yes | 0.78 |
|
Hopyard Hill | > 2 | private (numerous) | 2005-04-07 | Yes | 3.91 |
|
South Surrey, Campbell Valley Metro Vancouver Regional Park | 2 | local government, Metro Vancouver Park | 2006-03-06 and 2011 (unknown date) | Yes | 1.56 |
|
Vedder Canal Bergman Road | 1 | private ? | 2006-03-08 | Yes | 0.78 |
|
Sumas Mountain, South Slope | 5 | private | 2005-04-12 | Yes | 0.78 |
|
D’herbomez Creek | 1 | private ? | 2001-06-09 | Yes | 0.28 |
|
Herrling Island Road | 1? | private ? | 2000-05-22 | Yes | 3.12 |
|
Nicomen Slough | 1 | private ? | 2000-05-23 | Yes | 3.12 |
|
Wren Creek, Mission | 1 | private | 2012-05 (date not available) | Yes | < 3 |
|
Brunette Fraser Greenway (Park) | 1 | local government, Metro Vancouver | 2011-05-9 | Yes | < 0.5 |
|
Glen Valley | 1 | local government, Metro Vancouver | 2011-05-11 | Yes | < 0.5 |
|
Neilson Park | 1 | local government, Fraser Valley Regional District | 2011-05-24 | Yes | < 0.5 |
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Brae Island | 1 | private, Metro Vancouver | 2011-05-11 | Yes | < 0.5 |
|
Department of National Defence Area Support Unit, Chilliwack | 1 | Federal | 2011 (date unknown) | No | N/A |
|
South Perimetre Road, Surrey | 1 | B.C. Crown | 2011 | Yes | N/A |
|
*(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).
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
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).
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).
Figure 6. Search effort for terrestrial snails within and adjacent to the known range of the Oregon Forestsnail
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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