Dusky dune moth (Copablepharon longipenne) COSEWIC assessment and status report: chapter 7

Habitat

Habitat Requirements

Copablepharon longipenne is associated with sparsely vegetated active sand dunes and blowouts. It is considered a habitat specialist because it occurs only in a specific habitat type. During sampling in 2004–2005, the highest abundance of C. longipenne adults (up to 142 moths per trap) occurred in open dunes with >75% of the surface made up of open sand. The species was never captured in stable or semi-stable dunes unless they were immediately adjacent to an active dune. Field observations of ovipositing behaviour in 2004–2005 suggest that the presence of open sand is important for reproduction; C. longipenne was observed ovipositing on the leeward edge (slip face) of active dunes or other depositional areas. Sand deposition may prevent exposure or predation of eggs. Movement of sand by wind is considered an essential process for maintaining habitat for C. longipenne.

Substrates in active sand dunes in the southern Canadian prairies are characterized by fine or moderately fine sand, moderately high pH (8.1–8.3), less than 0.5% organic matter, and small amounts of silt and clay (<8% of total mass) (Hullett et al., 1966). The water-holding capacity of these substrates is very low, and only specialized plants are able to establish and grow on them. These soils are classified as regosols by the Canadian Soil Classification System.

Sand dunes are spatially discrete habitat patches. If sand supply is low, wind movement of sand is weak, or colonization by vegetation is rapid, active dunes are small and scattered. The smallest size of a sand dune or group of dunes in which a population of C. longipenne will persist is unknown. However, the moth was captured in isolated dunes around 0.5 ha in size at Cramersburg Sand Hills, SK and Dune Point, AB. Most sites in which C. longipenne was captured have multiple active dunes or blowouts within a landscape of dry grasslands (Figure 5).


Figure 5: Sand dune habitat characteristics: a) human-made fireguard with open sand in which C. longipenne was abundant (Dundurn Sand Hills, SK); b) semi-stabilized dune blowout in which C. longipenne was not captured (Dundurn Sand Hills, SK); c) dune margin with high abundance of C. longipenne (Seward Sand Hills, SK); d) dry grassland near open dune in which C. longipenne was not captured (Great Sand Hills, SK); e) active dune complex with lance-leaved psoralea and Canada wildrye on the slip face (Cramersburg Sand Hills, SK; C. longipenne was captured); and f) sparsely vegetated margin of active dune in Burstall Sand Hills, SK with lance-leaved psoralea and sand dock colonization (not sampled in 2004–2005 but C. longipenne found several times previously)

Figure 5. Sand dune habitat characteristics.

All photos by N.A. Page (a, b: August 2004; c–f: July 2005).

Plants and plant communities in active dunes and sparsely vegetated dune margins in the southern Canadian prairies have been described by Hullett et al. (1966), Epp and Townley-Smith (1980), Radenbaugh (1988), Coenen and Bentz (2003), and Gerry and Anderson (2003). Plants with adaptations to dry, nutrient-poor conditions in sand dunes include lance-leaved psoralea (Psoralea lanceolata Pursh), wheat grass (Agropyron spp.), Indian rice grass (Achnatherum hymenoides (Roemer & J.A. Schultes) Barkworth), Canada wildrye (Leymus canadensis L.), prairie sandreed (Calamovilfa longifolia (Hook.) Scribn.), prairie Junegrass (Koeleria macrantha (Ledeb.) J.A. Schultes), sand dropseed grass (Sporobolus cryptandrus (Torr.) Gray), skeleton-weed (Lygodesmia juncea (Pursh) D. Don ex Hook.), sand-dock (Rumex venosus Pursh), petiolate sunflower (Helianthus petiolaris Nutt.), prickly rose (Rosaacicularis Lindl.), and silverberry (Elaeagnus commutata Bernh. ex Rydb.). Plant communities described from active and semi-stable dunes include a sand dock herbaceous association from Pakowki Lake (Coenen and Bentz, 2003), an Indian rice grass–Canada wildrye Sparsely Vegetated Association (Wallis, 1980 in Allen, 2004), and two mixed herb alliances described from the Great Sand Hills: sand dropseed Sand Hill Herbaceous Vegetation and sand grass Sand Hill Herbaceous Vegetation (Gerry and Anderson, 2003). More sampling and analysis is needed to develop a comprehensive classification of sand dune vegetation in the Canadian prairies.

Fauske (1992) stated that C. longipenne was often associated with grama-needlegrass-wheatgrass steppe, and recorded from aeolian drift areas.


Habitat Trends

Sand deposits are widespread in the southern Canadian prairies. Wolfe (2001) mapped 5900 km2 of aeolian deposits (sand or silt moved by wind) in the portion of the Canadian prairies in which C. longipenne occurs. However, active dunes are rare. Based on data in Hugenholtz and Wolfe (2005), active dunes in the Tunstall Sand Hills account for 0.5% of the total area, while active dunes in the Seward and Great Sand Hills encompass 0.4% and 0.2% of the total area of the dune field respectively. Similarly, an assessment of land cover in the Great Sand Hills, the largest and most well-known of sand dune areas in the Canadian prairies, found that active dunes comprise less than 0.5% of the total area of 1136 km2 (Saskatchewan Environment and Public Safety, 1991). Most areas of sand hills are vegetated and lack open sand habitat except in isolated blowouts, road cuts, and other disturbed sites. Sand deposits in the southern Canadian prairies are glaciofluvial, glaciolacustrine, and deltaic sediments from the last glaciation that have been reworked by wind action (David, 1977).

Based on the sampling records and field observations that suggest C. longipenne is associated with active sand dunes, natural dune stabilization has reduced the amount of its habitat in Canada. Stabilization of sand dunes in the southern prairies in the past 100 years has been well documented (Figure 6) (Vance and Wolfe. 1996; Wolfe, 1997; Wolfe et al., 2001; Wolfe and Thorpe, 2005; Hugenholtz and Wolfe, 2005). Dune stabilization is driven by changes in regional precipitation. Vegetation colonizes dune surfaces during periods of increased precipitation while prolonged drought results in reduced vegetation cover and an increase in dune activity (Wolfe et al., 2001). Unlike other dune ecosystems, such as those on the Pacific Coast, stabilization of sand dunes in the Canadian prairies appears to be a largely natural phenomenon (Wolfe, 2001). Vance and Wolfe (1996) found that most dune fields in southern Alberta, Saskatchewan and Manitoba have become vegetated at a rate of 10% to 20% per decade. For example, the total area of active sand dunes in the northwest portion of Great Sand Hills has declined from 207 ha in 1946 to 161 ha in 1991 (Hugenholtz and Wolfe, 2005). During this time, the number of active sand patches declined from 340 to 130. Bender and Gummer (2005), using air and satellite photo data, recently found that open sandy areas in the Middle Sand Hills (an area along the South Saskatchewan River north of Medicine Hat) have declined by up to 57% per decade. Wolfe (2001) also noted that droughts in the 1930s, 1960s, and 1980s did not slow vegetation stabilization of dunes in the Canadian prairies, but that the present trend to a warmer and drier climate in the region may result in increased dune activity.


Figure 6: Historical Change in Active Dunes at Seven Dune Sites in Canada

Figure 6. Historical change in active dunes at seven dune sites in Canada.

From Hugenholtz and Wolfe, 2005. Note, Brandon North and South are referred to as the “Spirit Dunes” in this report; GSH-NW refers to dunes in the northwest portion of the Great Sand Hills and GSH-WC to dunes in the south-central portion. Figure used with permission.

Invasive plant species do not appear to be a major contributor to sand dune stabilization in the Canadian prairies. Gerry and Anderson (2003) documented 18 non-native plants in the Great Sand Hills area and found at least one exotic species in 91% of assessed sites. However, few are abundant. Non-native plants were more common in areas affected by agriculture and grazing.

Longer-term changes (>100 years) to sand dune activity in the southern prairies have also been documented through geological research (Wolfe et al., 2001). Optical dating of sand grains and climate records from tree rings suggests that widespread sand dune activity was initiated by below-average precipitation during the 1700s and a drought in the 1790s. Dunes have been stabilizing in the Canadian prairies since the 1820s when regional precipitation increased (Figure 7).


Figure 7: Long-term Trends in Dune Activity in the Southern Canadian Prairies

Figure 7. Long-term trends in dune activity in the southern Canadian prairies.

From Wolfe et al., 2001. The number of optical ages is a measure of sand grain exposure to sunlight. Figure used with permission.

Land development activities such as roads, buildings, gas wells, and transmission lines have also degraded C. longipenne habitat where disturbance is intense. However, some disturbance may initiate dune activity or increase open sand in stabilized sand hills. For example, C. longipenne was captured in an unvegetated fire break in the Dundurn Sand Hills south of Saskatoon.

Cattle grazing occurs within, or adjacent to, most dune sites visited in Saskatchewan and Alberta. Minor grazing may initiate dune activity (Hugenholtz and Wolfe, 2005), but intensive grazing is likely detrimental to C. longipenne because trampling disturbs vegetation, compacts soil, and may crush eggs, larvae, or pupae. Recent increases in dune activity in some dune fields, such as the northwest portion of the Great Sand Hills, may reflect localized effects of increased grazing (Hugenholtz and Wolfe, 2005). Other agricultural activities are not a threat to C. longipenne because, as shown in the satellite image in Figure 4, grain or oil seed cultivators avoid sandy soils.

Increases in fire frequency may also increase dune activity by decreasing vegetation cover. Fire of both natural and anthropogenic origin was likely more common in the Canadian prairies in the past (Boyd, 2002); however, the effects of fire on sand dune ecosystems are poorly understood.

Recreation, including the development of trails, may degrade C. longipenne habitat. Localized disturbance may help sustain open dunes, but intensive, widespread disturbance may destroy vegetation, compact soil, and destroy eggs, larvae, or pupae. Off-road vehicle use was observed in the Burstall Sand Hills and in the protected portion of the Great Sand Hills in July 2005. It was likely more common and widespread in the past.


Protection and Ownership

Most Canadian sites with known or suspected C. longipenne populations occur in publicly owned lands, primarily provincial lands that are leased for cattle grazing. Ownership and protection status of these sites is summarized in Table 1. Three known or suspected populations of C. longipenne occur in protected areas: the Great Sand Hills Representative Area Ecological Reserve that was protected in 2005 and encompasses the largest of the active dune fields; Elbow dunes in Douglas Lake Provincial Park (SK) (suspected C. longipenne population); and Spruce Wood Provincial Park (MB). A portion of the Pakowki Lake area is a wildlife viewing site but it is not formally protected. The ownership of US sites is not known.

 

Table 1 (Known Populations): Land Ownership and Protection Status for known or Suspected Canadian Populations of C. longipenne
Population/Locality Province Land Ownership and Protection Status
Lethbridge AB Recent presence unconfirmed; exact location unknown
Pakowki Lake (Manyberries) AB Province of Alberta; grazing leases
Onefour, Dominion Range Station AB Recent presence unconfirmed; exact location unknown; Onefour Agricultural Research Substation (federal)
Sunnydale (Oyen?) AB Exact location unknown (may be Dune Point)
Dune Point (Bindloss) AB Unknown; provincial grazing land?
Spirit Dunes MB Spruce Woods Provincial Park; Department of National Defence (CFB Shilo)
Burstall Dunes SK Unknown; provincial grazing land?
Bigstick Sand Hills (Tompkins) SK Big Stick Community Pasture, PFRA
Great Sand Hills SK Ecological reserve; Provincial grazing land (leased)
Dundurn Sand Hills SK Department of National Defence (CFB Dundurn); Dundurn PFRA
Seward (Webb) Sand Hills SK Swift Current-Webb Community Pasture, PFRA
Cramersburg Sand Hills SK Unknown; likely provincial grazing land

Based on current or historic sampling records

 

Table 1 (Suspected Populations): Land Ownership and Protection Status for known or Suspected Canadian Populations of C. longipenne
Population/Locality Province Land Ownership and Protection Status
Tunstall Lake Sand Hills SK Bitter Lake Community Pasture, PFRA
Bigstick Sand Hills SK Unknown; provincial grazing land?
Elbow / Douglas Lake SK Douglas Lake Provincial Park
Westerham Sand Hills SK Unknown; provincial grazing land?
Middle Sand Hills AB Suffield NWA; CFB Suffield

Based on presence of suitable habitat

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