Oregon forestsnail (Allogona townsendiana) COSEWIC assessment and status report 2013: chapter 11

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Threats and limiting factors

Threats to Oregon Forestsnail

The International Union for Conservation of Nature-Conservation Measures Partnership (2006) (IUCN-CMP) threats calculator was used to classify and list threats to Oregon Forestsnail (Salafskyet al. 2008; Master et al. 2009). This exercise was completed by the Oregon Forestsnail Recovery Team, chaired by the status report writer; Molluscs SSC (Species Specialist Sub-committee) co-chairs and an expert on applying the threats calculator attended a subsequent teleconference (6 June 2012) where initial results were re-evaluated. The overall Threat Impact for Oregon Forestsnail is Very High (Table 3). Major level 1 threats (highest to lowest impact) include Threat #1. Residential and commercial development; Threat #4. Transportation and service corridors; Threat # 8. Invasive and other problematic species and genes; and Threat #6. Human intrusions and disturbance. Threats that are applicable to Oregon Forestsnail are further discussed below under the IUCN-CMP level 1 headings, from highest to lowest impact.

^a Impact – The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each stress is based on Severity and Scope rating and considers only present and future threats. Threat impact reflects a reduction of a species population or decline/degradation of the area of an ecosystem. The median rate of population reduction or area decline for each combination of scope and severity corresponds to the following classes of threat impact: very high (75% declines), high (40%), medium (15%), and low (3%). Unknown: used when impact cannot be determined (e.g., if values for either scope or severity are unknown).

^b Scope – Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species’ population in the area of interest. (Pervasive = 71-100%; Large = 31-70%; Restricted = 11-30%; Small = 1-10%)

^c Severity – Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or three-generation timeframe. Usually measured as the degree of reduction of the species’ population (Extreme = 71-100%; Serious = 31-70%; Moderate = 11-30%; Slight = 1-10%).

^d Timing – High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.

Residential & commercial development: Calculated Impact – High; Scope – Large; Severity – Extreme (IUCN-CMP Threat 1)

Housing and urban areas (Threat 1.1) and commercial and industrial areas (Threat 1.2)

Natural habitats, large ravines and riparian areas that represent core habitats for Oregon Forestsnail, coincide with the local government jurisdictions of Abbotsford, Mission, Chilliwack, Langley and Hope. Expanding human population in these lowland urban areas threatens habitat. Human activities associated with urban developments, specifically those that include clearing or removing Oregon Forestsnail habitat and/or altering natural hydrological patterns that result in habitat conditions that are too dry or wet for prolonged periods, can impact the microhabitat and overall forest stand structure necessary to sustain populations of Oregon Forestsnail.

At a minimum, there have been 73 separate urban housing developments within the core geographic range of Oregon Forestsnail (Abbotsford, Chilliwack, Agassiz, Maple Ridge, Mission and Langley). Of these developments, at least 17 urban housing developments (see Greater Vancouver Real Estate 2011) within the municipalities of Mission, Abbotsford (Figure 12), and Chilliwack appear to have resulted in direct natural deciduous forest habitat conversion and may have impacted Oregon Forestsnail habitat or populations (estimated from Google Earth satellite imagery viewing through Greater Vancouver Real Estate 2011). These urban developments include large-scale new communities with new infrastructure, such as schools, roads, and central shopping amenities and in some cases golf courses and other recreational infrastructure. Most of this development has been within privately owned natural land on Sumas Mountain and other areas of rural Abbotsford, Vedder Mountain, Whatcom and other natural areas of Chilliwack, within the Lower Fraser Valley (Greater Vancouver Real Estate 2011).

Figure 12. Urban housing projects (red dots on map) in the City of Abbotsford (Greater Vancouver Real Estate 2011)

Note the large natural green area to the east is Sumas Mountain.

Today, most of the remaining large natural habitats within the core range of Oregon Forestsnail are in private ownership (either owned by the local government or by a private development company [proponent]) (Table 1). Each municipal government has an Official Community Plan with specific areas designated for future housing and commercial development to service the increase in human population. The Local Government Act requires a private landowner who is subdividing their property to dedicate 5% of the land subject to subdivision as a park or to pay cash in lieu of the land. This does not necessarily provide habitat for species at risk, however, as local government may be more inclined to take monetary compensation that can then be allocated to community projects elsewhere in the municipality over park land if the Official Community Plan does not designate the type and site of future parkland. As well, if someone is developing a property but is not subdividing (e.g., building a home, barn, etc.), this dedication is not required (Wetland Stewardship Partnership 2007). Some municipalities have environmentally sensitive development permit areas and can direct development away from these sensitive areas with high ecological (e.g., species at risk) values; however, if this is a gap in a municipality’s Official Community Plan, then ecosystem values such as Oregon Forestsnail do not get protected.

Industrial and business park expansion plans are published for some municipalities within the Lower Fraser Valley, such as, for example, the City in the Country Plan specific to the City of Abbotsford. This plan projects the need for “1,300 acres of employment-generating industrial and business park lands over the next 20 years” with “future residential development accommodated through hillside development … not accommodated by expansion into the Agricultural Land Reserve” (City of Abbotsford 2004).

Tourism and recreational areas (Threat 1.3)

The demand for tourism and recreational areas within the Lower Fraser Valley and southeastern Vancouver has increased substantially within the past decade. Natural areas continue to be developed into golf courses, campgrounds, parks and recreation facilities.

This threat applies to two known Oregon Forestsnail sites, although likely more sites because golf course or recreational developments within existing protected areas often are not accurately captured in threat assessments. In the past 10 years, numerous golf courses have been developed within the Lower Fraser Valley within natural habitat that may have had occurrences of Oregon Forestsnail: Abbotsford (two courses), Chilliwack (five courses), Langley (two courses), Aldergrove (part of Abbotsford) (one course), and Hope (one course).

Within existing parks, as well as regional and municipal properties, habitat conservation and recreational development potentially conflicts with Oregon Forestsnail conservation. Potential threats include construction of new trails and rights-of-way within highly used Metro Vancouver regional parks such as Colony Farm (Figure 10), Brunette-Fraser Greenway, Brae Island, Cheam Wetlands; creation of new camp sites (e.g., Hope and Chilliwack areas – at least two sites); creation of golf courses in the Abbotsford, Chilliwack, and Hope areas. For example, within Neilson Regional Park (Fraser Valley Regional District) there is a planned expansion of a children’s playground into a large patch of Stinging Nettle where Oregon Forestsnail is known to occur (Heron pers. obs. 2011). In a separate site also within Neilson Park, Oregon Forestsnail is known to occupy patches of Stinging Nettle that border a baseball diamond.

Expansion of recreational areas increases the frequency of road and trail building, which may act as corridors (into natural habitats) that facilitate the rapid spread of invasive species (e.g., plant seeds attach to car tires and become dislodged at new sites) (Trombulak and Frissell 2000) and movement of non-native molluscs, especially Arion slugs (see IUCN-CMP Threat 8.1).

Transportation and service corridors: Calculated Impact – High; Scope – Large; Severity – Serious (IUCN-CMP Threat 4)

Roads and railroads (Threat 4.1)

With increasing human population comes the need for associated transportation infrastructure and access to both new and existing urban areas. Proposed transportation routes are often planned through areas that have the least impact to existing private landowners, e.g., land (frequently also natural areas) owned by the local or provincial government, land currently within the agricultural land reserve (although the land may be privately owned); or land through natural areas owned by one private landowner or company.

Oregon Forestsnail habitat includes ravines and gullies where both ephemeral and permanent natural watercourses flow. Proposed transportation routes through natural areas frequently result in changes to existing watercourses (e.g., if a roadway bisects a creek; ongoing road and highway expansion projects include plans to divert, infill and alter watercourses). At least 10 sites with Oregon Forestsnail have ongoing/finished major works within the past ten years (e.g., Marshall Road, Wren Creek, South Perimeter Road [Table 1]). Additional sites include areas near Westholme (Vancouver Island) along a railway right-of-way.

Within the range of Oregon Forestsnail extensive roads and other similar transportation corridors already fragment much of the remaining natural habitat and contribute to other threats including increased frequency of use by humans (IUCN-CMP Threat 6.1). Roadsides act as corridors into natural habitats and are known to facilitate the rapid spread of introduced species (e.g., plant seeds attach to car tires) (Trombulak and Frissell 2000) (see IUCN-CMP Threat 8.1). Roads are also effective barriers to snail dispersal and fragment habitat but also fragment and isolate populations that may have once been connected (Baur and Baur 1990).

Utility and service lines (Threat 4.2)

Service lines lead to population isolation and increased drought from edge effects and stand/wind penetration, leading to increased mortality and ecosystem changes through introduced species. Plans for expansion of hydro rights-of-way and infrastructure are ongoing throughout the Lower Fraser Valley, particularly in areas within large urban developments that require new/improved utility infrastructure. This threat applies to at least five known sites.

At present, there is ongoing construction of a transmission line from Coquitlam to Hope through much potential and unchecked habitat for Oregon Forestsnail. This habitat loss is not in the same areas as are the roads and the overall impacts are cumulative.

Invasive and other problematic species and genes: Calculated Impact – Medium-Low; Scope – Pervasive; Severity – Moderate-Slight (IUCN-CMP Threat 8)

Invasive non-native/alien species (Threat 8.1)

Introduced gastropods, invertebrates and plant species have been recorded from most Oregon Forestsnail habitats, although the scope of introduction and suite of species present is not fully known. Greater than 90% of sites have introduced species present, particularly Himalayan Blackberry (Rubus armeniacus)and other non-native plants, introduced gastropods, earthworms and various introduced carabid beetles. Invasive terrestrial gastropods can potentially out-compete and prey upon Oregon Forestsnail.

Introduced invertebrates, particularly introduced gastropods, may pose a threat to Oregon Forestsnail through competition for food and shelter or through predation. Rollo and Wellington (1979) demonstrated intra- and interspecific aggression among slugs and competition for refuges. Introduced gastropods of European origin are widespread within urban and agricultural areas within the Lower Fraser Valley and southern Vancouver Island, and several species have penetrated forested habitats (Forsyth 1999b, 2001). These species continue to spread into new areas with inadvertent assistance from humans when nursery plants, garden ornamentals, or other materials with adhering soil are transported or when garden waste is discarded (Forsyth 1999b). Roads are also known to increase the spread of introduced species and predation pressure on gastropods (Trombulak and Frissell 2000).

Three introduced species locally common in the Lower Fraser Valley, Giant Gardenslug (Limax maximus), Dusky Arion (Arion subfuscus), Chocolate Arion (Arion rufus) and Longneck Fieldslug (Deroceras invadens), are particularly aggressive. The introduced, carnivorous Dark-bodied Glass-snail (Oxychilus draparnaudi) is locally common in southern Vancouver Island (Victoria area) and greater Vancouver areas (Forsyth 1999b) and probably also occurs within the range of Oregon Forestsnail in the Lower Fraser Valley. Dark-bodied Glass-snail could potentially be a significant predator of Oregon Forestsnail eggs and young (Ovaska pers. comm. 2012). This species has been identified as a potential threat to native gastropods in other areas where it has been introduced (Frest and Rhodes 1982). Other introduced gastropod species that may compete with Oregon Forestsnail include Grovesnail and other species of slugs, such as the Chocolate Arion and the Gray Fieldslug (Deroceras reticulatum).

Although most invasive gastropods are primarily in areas of high human use and alteration, some have spread into intact coniferous forest habitats and increased their range (Ovaska pers. comm. 2012). Within forests in Washington State, Chocolate Arion is documented from within old growth forests, and may be displacing native Banana Slug (Ariolimax columbianus) (Burke et al. 1999). Concentration of snails into small habitat patches with less overall shelter and escape cover is likely to increase their vulnerability to predation.

Some invasive plant species are known to change the forest floor vegetation and soil structure and facilitate an increase in light penetrating to the forest floor. Increases in light levels lead to dryer microclimate, understory conditions and forest floor desiccation, and increases dehydration stress to gastropods that depend upon high water and humidity levels. Invasive plants, such as English Holly (Ilex aquifolium) and Spurge-laurel (Daphne laureola) are likely to invade disturbed areas. English Ivy (Hedera helix) is known to spread and displace native vegetation on forest floors. English Holly and Himalayan Blackberry are also widely spread invasive plants within native ecosystems within southern Vancouver Island, and are known to displace native vegetation and may impact native Stinging Nettle. Oregon Forestsnail appears to be able to survive within habitat that has Himalayan Blackberry (e.g., Colony Farm Regional Park [Figure 10]).

The threat of invasive species likely exists at all Oregon Forestsnail sites; however, there is some uncertainty of the impact.

Human intrusions and disturbance: Calculated Impact – Low; Scope – Large; Severity – Slight (IUCN-CMP Threat 6)

Recreational activities (Threat 6.1)

Recreational activities within Oregon Forestsnail habitat include camping, hiking (e.g., Sumas Mountain Regional Park), foot and bicycle traffic (e.g., Brunette-Fraser Regional Greenway), horseback riding (Campbell Valley Regional Park [Figure 7]) and the use of all terrain vehicles (ATVs) and trail bikes (e.g., private land), especially off-trail bikes (e.g., Sumas Mountain). Such activities can result in degradation of habitat quality through soil compaction and can also cause accidental mortality especially along trail edges.

Effects from recreational activities can be pronounced in areas where the species is restricted to small habitat patches (e.g., Brunette-Fraser Regional Greenway – Metro Vancouver Regional District; Neilson Regional Park – Fraser Valley Regional District). For example, inadvertent trampling of the site could result in significant mortality, especially during the spring breeding period when the snails are active.

Areas with particularly high recreational use include habitats within Metro Vancouver and Fraser Valley regional districts parks; habitats on Sumas Mountain on BC Crown and private land (including local government land); portions of the TSU-ESA, and provincial parks such as Cultus Lake Provincial Park (Chilliwack) and Bridal Veil Falls Provincial Park (outside Hope) (Figure 9).

Hiking, ATV and related activities may also increase the spread of introduced species (see IUCN-CMP Threat 8.1). Recreational use of trails for horseback riding also likely impacts habitat (e.g., trampling of trails/edges and defecation which increases the spread of fungus, seeds, etc.).

The threat of recreational activities applies to at least 58 sites, although at many sites the damage to the species or its habitat is likely limited in scope to trail sides.

War, civil unrest and military exercises (Threat 6.2)

Activities occurring on DND land that are considered necessary for national security include not only military training but training by other organizations, such as police. The Canadian Forces and Royal Canadian Mounted Police (RCMP) both conduct dismounted (on foot) training in forested areas belonging to DND. In addition to training, development to meet operational requirements and maintenance (such as road maintenance) are necessary on training areas to maintain their usefulness.

Populations of Oregon Forestsnail on DND land have been found away from roads in forested areas that will continue to be maintained as such, and are only occasionally used for dismounted training. Although training has been ongoing at one site for over 25 years, the soils do not appear to have been compacted. The fact that there are still extant populations with juveniles indicates that this threat is negligible.

Agriculture and aquaculture: Calculated Impact – Low; Scope – Restricted; Severity – Moderate (IUCN-CMP Threat 2)

Annual and perennial non-timber crops (Threat 2.1)

Coniferous forest habitat that is within the agricultural land reserve is subject to clearing and conversion. In some cases, landowners/managers may clear land in anticipation of agricultural development, although no actual crops, grazing or agricultural practices will occur on the land for a number of years. At present, there is no environmental assessment required for species at risk presence surveys prior to the clearing of land for agriculture. This is a potential threat at many agricultural sites within the Lower Fraser Valley with verges of natural habitat surrounding the agricultural field (e.g., Oregon Forestsnail has been observed adjacent to fields) (Bianchini pers. comm. 2012). This applies to remnant areas of habitat (e.g., ditchside verges, crop verges and the perimeter of agricultural fields) where Oregon Forestsnail may remain in small habitat patches.

Wood and pulp plantations (Threat 2.2)

Wood and pulp plantations are throughout the Chilliwack and Hope areas. The first hardwood tree-farm licence in the Lower Fraser Valley was granted in 1985 and as a result much of the old growth cottonwood stands were harvested (Pollon 2010). Conifer plantations do not manage for a diverse multi-layer understory. Small gaps in wet areas may act as a population sink where Oregon Forestsnail may remain. As well, ongoing harvesting within these stands continues to take place and destroy habitat and these remaining patches.

Livestock farming and ranching (Threat 2.3)

Detrimental impacts to Oregon Forestsnail habitat from livestock grazing have been recorded from at least three sites (BC Conservation Data Centre 2013). The impacts to gastropods from grazing are unknown, but trampling of sensitive riparian areas is often a result of livestock congregating near watercourses and there would be direct mortality caused by trampling of individuals and habitat (e.g., Stinging Nettle and other herbaceous plants).

Energy production and mining: Calculated Impact – Low; Scope – Small; Severity – Extreme (IUCN-CMP Threat 3)

Mining and quarrying (Threat 3.2)

Gravel mining is a localized threat at sites in the Lower Fraser Valley, particularly on areas of Sumas Mountain. The overall footprint is small at this time but may expand in the future and results in complete habitat loss where it occurs.

Renewable energy (Threat 3.3)

Independent Power Projects are numerous throughout the Lower Fraser Valley and impact potential habitat (riparian areas) where Oregon Forestsnail may occur. The overall footprint from these power projects is small; however, the cumulative riparian habitat loss due to these substations has potential to impact the species overall.

Biological resource use: Calculated Impact – Low; Scope – Small; Severity – Serious-Moderate (IUCN-CMP Threat 5)

Hunting and collecting terrestrial animals (Threat 5.1)

There are a few observations of citizens collecting terrestrial snails for consumption (Bianchini pers. comm. 2012); therefore, the scope of this threat is negligible at this time. It is also likely that once an individual has removed the readily available snails (e.g., they’ve cleaned out the snails, up to 70% in an area), the same area will not be revisited in the future.

Gathering terrestrial plants (Threat 5.2)

Stinging Nettle is of cultural significance to First Nations people in the region. As well, many people consume the plant. With an increased awareness of local native plants, the consumption of native species and the widespread social trend to consume locally grown produce, some local farms provide Stinging Nettle. It is likely that these farms are just gathering the plant and not cultivating it (e.g., crops). Currently, this threat has a negligible impact on Oregon Forestsnail.

Logging and wood harvesting (Threat 5.3)

The BC range of Oregon Forestsnail has been impacted from extensive historical logging and forest resource extraction activities. The forest land base, particularly within the rural areas of Mission, Chilliwack and Hope, continues to be intensively managed due to the high demand for forest products. Forest management practices, including pre-commercial thinning, pruning, removal of select tree species, fertilization, patch-size harvesting, and clear-cut harvesting, likely have detrimental effects on populations of Oregon Forestsnail.

Pre-commercial thinning and pruning reduce the quantity and/or alter the timing of leaf and branch litter that would otherwise fall to the forest floor and provide shelter for Oregon Forestsnail. Pruning that removes lateral branches reduces the overall forest canopy, which results in lower relative humidity and subsequent desiccation of the forest floor. The removal of trees and use of machinery may compact ground cover, crush individuals of Oregon Forestsnail, disturb coarse woody debris and shelter sites, and cause localized impacts.Present-day intensive forest management practices target large dead coarse woody debris removal during the second rotation of harvesting. Thus, large coarse woody debris may be in short supply in intensively managed forests. These logs are likely important for maintaining stable microclimates for developing e.g., and thus suitable microhabitat for Oregon Forestsnail.

Harvest of forest stands isolates subpopulations further, decreases available habitat and increases drought from edge effects and stand/wind penetration, leading to increased mortality and ecosystem changes through introduced species. Numerous Oregon Forestsnail records are from provincial Crown land operating under the Chilliwack Forest District (BC Ministry of Forests, Lands and Natural Resource Operations 2012). The Chilliwack Forest District covers approximately 1.4 million ha (BC Ministry of Forests, Lands and Natural Resource Operations 2012). Stands under 350 m elevation are potential Oregon Forestsnail habitat.

Areas on Sumas and Vedder Mountain still have small habitat patches used for logging, although once logged the land use will likely change. Hope and Chilliwack (easternmost range extent) have ongoing logging. This threat applies to 11 sites.

There is also ongoing illegal harvest of older growth cedar and hardwood trees throughout the range of Oregon Forestsnail. The impacts of illegal harvest are unknown.

Natural system modifications: Calculated Impact – Low; Scope – Small; Severity – Serious (IUCN-CMP Threat 7)

Fire and fire suppression (Threat 7.1)

Burke et al. (1999) cite fire as a threat to gastropod populations in Washington State. The threat of fire is present throughout the entire range of Oregon Forestsnail, particularly within large natural tracts of land, areas adjacent to roadways and rights-of-way and in recreational areas where campfires occur.

Deciduous forests within the range of Oregon Forestsnail remain moist and wet throughout the year, but the threat of forest fires is possible, particularly in July through September.

Human activities that increase the threat of fire include careless attendance to campfires, discarded cigarettes, improperly wired camping equipment and machinery. Forests fires occur yearly, although efforts are made to control the frequency, size, and spread of fire through fire suppression programs (e.g., brush burning).

Brush clearing, piling and periodic burning of vegetation and woody debris occur on private and public lands throughout the range of Oregon Forestsnail. Although burning would only impact small areas of land, there is the possibility of overlap with unknown occurrences of Oregon Forestsnail. The smoke generated from periodic brush burning, and the resultant char and burned debris are also detrimental to habitat quality.

All Oregon Forestsnail sites are threatened by fire, however not at the same time. If or when a fire will occur at a particular site is unknown thus the overall impact from fire is unknown.

Other ecosystem modifications (Threat 7.3)

Mowing and cutting of vegetation within sites (often as a form of fire suppression) adversely affects Oregon Forestsnail. Removal of vegetation may impact Oregon Forestsnail through decreasing available moisture retention within habitats and increasing dehydration stress to individuals and direct mortality as gastropod activity patterns predominantly coincide with preventing dehydration (Prior 1985). This threat is present throughout a small portion of its range especially at the urban interface; roadsides, trails and other right-of-ways; agricultural areas and in recreational areas to control campfires.

The close association Oregon Forestsnail has with Stinging Nettle may indirectly be detrimental to Oregon Forestsnail habitat. This is because Stinging Nettle may be targeted for removal in recreational areas with high human use due to the plant’s ability to irritate skin.

Pollution: Calculated Impact – Unknown; Scope – Small; Severity – Unknown (IUCN-CMP Threat 9)

Agricultural and forestry effluents (Threat 9.3)

The use of pesticides, especially those aimed at gastropods, has potential to harm Oregon Forestsnail populations by directly killing both individuals and eggs. The only application of pesticides that specifically target gastropods that is likely to occur is on privately owned properties within close proximity to houses, barns or other human structures where Oregon Forestsnail is mistaken for a pest species. Overall, the general use of herbicides within parks and protected areas is diminishing due to municipal and regional bylaws that limit the use of these chemicals (e.g., City of Richmond). Provincial initiatives that consider the ban on home use of pesticides for cosmetic purposes throughout BC are ongoing (Nagel 2011). However, pesticide bans are controversial in some municipalities (e.g., Cassidy 2011).

Agricultural and forestry effluents are likely to cause harm to Oregon Forestsnail habitat and individuals. For example, the use of herbicides to control regeneration of Bigleaf Maple on commercial forestry lands may also impact snail populations in adjacent, mature stands, through run-off. Young Bigleaf Maple regeneration within conifer plantations competes with commercial tree species, and herbicide treatments (either stump or foliage applications) are applied to control competing vegetation. This herbicide treatment can potentially harm or reduce habitat available to land snails.

Oregon Forestsnail is frequently recorded from forest and trail edge habitats, with at least three sites known to occur adjacent to well-used recreational trails within urban parks. Other land snails, such as Copse Snail (Arianta arbustorum) prefers moving along road verges and avoids crossing roads, including unpaved roads only 3 m wide (Baur and Baur 1990). Spraying herbicides (and mowing, see above) to control road or trail-side vegetation likely harms gastropods within these verges, and the cumulative and persistent effects of herbicides within these environments may lead to long-term declines in gastropod numbers. Herbicides are used less today and many municipalities have bans on certain herbicides, but it is unclear how extensive this practice was (or is currently) within the range of Oregon Forestsnail.

It is possible agricultural run-off could impact the species. The snail has been found adjacent to agricultural and urban run-off areas, but the overall impact to the species is unknown. Increasing blueberry acreage throughout the Lower Fraser Valley includes many sites potentially adjacent to Oregon Forestsnail habitat. Concern for fruit pests such as Spotted Wing Drosophila (Drosophila suzukii) has resulted in intensive spraying of hedgerows, riparian areas and other vegetation that includes wild fruits capable of serving as refuge for Spotted Wing Drosophila. This may in turn be a problem for edge species such as Oregon Forestsnail. Pesticides and fertilizers threaten Oregon Forestsnail in much of the suitable habitat, particularly adjacent to the urban/agricultural interface.

This threat applies to 13 known sites, although there are likely additional sites adjacent to agricultural areas where effluent run-off occurs. The impact of this threat is unknown and requires study.

Geological events: Calculated Impact – Not calculated; Scope – Small; Severity – Serious (IUCN-CMP Threat 10)

Earthquakes/tsunamis (Threat 10.2)

Oregon Forestsnail records and potential habitat includes areas of the Lower Fraser Valley that could potentially be impacted from rising water levels as a result of earthquakes or tsunamis. The timing of such events, however, is unknown.

Avalanches/landslides (Threat 10.3)

Oregon Forestsnail habitat includes steeper hillsides and riparian areas where minor landslides and washouts could occur, particularly in areas with unstable historical road construction and improper culvert drainage. The forested areas of Chilliwack and Hope are where this threat is most likely to apply. Overall, this threat is thought to be negligible because the scope is negligible.

Climate change and severe weather: Calculated Impact – Not calculated; Scope – Restricted-Small; Severity – Slight (IUCN-CMP Threat 11)

Droughts (Threat 11.2)

Increased summer droughts may affect occupied Oregon Forestsnail habitats and will decrease the available site moisture that allows for suitable microhabitat. Combined with other threats, such as water diversion and infilling, drought within natural habitat may increase in the next ten years. The impact of this threat is unknown.

Storms and flooding (Threat 11.4)

Some areas of Oregon Forestsnail habitat such as the valley bottom within the Lower Fraser Valley is within the potential flood zone of the Fraser River (BC Ministry of Environment 2011b). The greatest vulnerability to flood risk within the range of Oregon Forestsnail includes parts of Langley, Pitt Meadows, Chilliwack, Kent, Abbotsford, Tsawwassen, Mission, Hope, Port Coquitlam and Surrey (Fraser Basin Council 2011). The Lower Fraser Valley has experienced major floods: the largest in 1894 and the second largest in 1948. Within the next 50 years there is a one-in-three prediction that a flood of similar magnitude will occur within the Lower Fraser Valley (Fraser Basin Council 2011). Overall the severity of this threat is slight.

Number of locations

The most serious, predominant threat to Oregon Forestsnail in Canada is IUCN-CMP Threat #1 Residential and Commercial Development, which is likely to affect most large pieces of private riparian and lowland forested land.At present there are 66 known occupied sites for Oregon Forestsnail spanning at least 95 different landowners (e.g., property where Oregon Forestsnail habitat spans numerous landowners but ownership is unknown). At least 56 sites are privately owned (including local government land which is considered private land in BC). If each separate parcel of land occupied by the snail and owned by a different person, business, or organization is considered a location, then the number of locations for the Oregon Forestsnail in Canada is well above the COSEWIC threshold of 10 given the rate and scope of development will most likely vary among owners.

Limiting factors for Oregon Forestsnail

Dispersal ability

The dispersal ability of Oregon Forestsnail is likely poor, and it is unclear how much habitat is required to sustain a population within a site or habitat patch. By their very nature, snails are sedentary and cryptic animals, and their natural ability to colonize new areas is likely poor.

Northernmost extent of global range

Oregon Forestsnail is at the northernmost extent of its global range, which likely increases the species’ susceptibility to climatic changes and stochastic population fluctuations.

Require humid environments

When the forest floor becomes increasingly exposed to wind and sunlight and there is less vegetation growing throughout the understory, terrestrial molluscs are more vulnerable to dehydration (Prior 1985; Burke et al. 1999) and experience high rates of evaporative water loss through their skin (Dainton 1954a,b; Machin 1964a,b,c; Burton1966; Prior 1983; Prior et al. 1983; Prior 1985). Snails are known to initiate “water seeking” responses to dehydration after a short-term reduction in locomotor activity (Prior 1985). The physiology and activity patterns of Oregon Forestsnail inherently make them susceptible to continuous water loss through dehydration. All snails deposit a dilute mucus trail, and experience constant evaporative water loss through the lung surface and integument. Numerous ecological and physiological studies show a relationship between body temperature, hydration and locomotor activity (Machin 1975; Peake 1978; Burton 1983; Riddle 1983; Martin 1983 as cited in Prior 1985). Within two hours, active slugs can lose 30 - 40% of their initial body weight and habitat selection by slugs is correlated with water availability (Prior 1985). Although this information pertains to slugs, it is likely similar for Oregon Forestsnail.

Soil mineral composition

Soil mineral content (including magnesium and calcium) and pH may play an important factor in snail microhabitat preference. Although unstudied in Oregon Forestsnail, these factors have been known to affect habitat preferences in other gastropods (Wareborn 1969; Hylander et al. 2004).

Native predators

Potential native invertebrate predators include the carnivorous snail Robust Lancetooth and ground beetles (e.g., Snail-killer Carabid, Scaphinotus angusticollis) (Ovaska pers. comm. 2012; Sopuck pers. comm. 2012). Both species are believed to be gastropod specialists (Thiele 1977) and will follow the mucus trails of slugs. Robust Lancetooth has been observed to attack and kill slugs (Ovaska and Sopuck unpubl. data 2000). These (and other) invertebrate predators are common throughout the same habitats as Oregon Forestsnail although there are no known obligate associations. Concentration of predators in small habitat patches where little escape cover is available will potentially increase predation rates on Oregon Forestsnail. Competition and predation as a limiting factor may become more of a threat when combined with competition and predation from introduced species and further development pressures.