Gold-edged gem (Schinia avemensis) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Gold-edged Gems are habitat specialists in active sand dunes and dune blow-outs. They have been found only in, or immediately adjacent to, areas of active sand (J. Troubridge, pers. comm., 2004; C. Harp, pers. comm., 2004; B. C. Schmidt, pers. comm., 2004; G. Anweiler, unpublished data). Within active sand areas, Gold-edged Gems are found in close association with colonies of the only known host plant, prairie sunflower, Helianthus petiolaris Nutt. (Hardwick, 1996) (Figure 3).  At the colonies near Bindloss and Pakowki Lake, Alberta, the moths were only found associated with sunflowers growing in the centre of the blow-out (B.C. Schmidt, pers. comm., 2004; Anweiler, unpublished data).

A suitable nectar source for adults is also an important habitat element. Gold-edged Gems were observed nectaring only at blossoms of skeletonweed (Lygodesmia juncea (Pursh) D. Don ex Hook.) in all four populations for which there are data (C. Harp, pers, comm., 2004; B.C. Schmidt, pers. comm., 2004; G. Anweiler, unpublished data).

Although stabilized dune fields cover extensive areas of the southern prairie provinces, active sand dunes and blow-outs occur infrequently and comprise only a very small fraction of the total area of dune fields; many dunes entirely lack significant areas of active sand (David, 1977; S. Wolfe, pers. comm., July 2004). Suitable habitat for Gold-edged Gems is thus extremely fragmented and patchy. Active dunes may also lack both Gold-edged Gems and prairie sunflowers, possibly due to factors such as topography and moisture (i.e. ridges and swales vs. extensive level sand sheets) and differences in sand particle size. Large, active, sand dunes in the Great Sandhills south of Prelate, Saskatchewan and the adjacent Burstall dunes were more sheet-like and had little topographic relief (Figure 7). They also appeared to be comprised of finer sand particles that had formed a light surface crust. Vegetation on these dunes was very sparse to absent except along the dune edges and face. Only two species of plants were abundant on these dunes, scurf-pea Psoralea lanceolatum (Pursh) and sand dock Rumex venosus Pursh; prairie sunflower was entirely absent, although it occurred as scattered individuals in adjacent grasslands, and along nearby roadside edges at the Burstall site (G. Anweiler, unpublished data).

Figure 3. Colony of prairie sunflowers occupied by Gold-edged Gems at Spirit Dunes, Spruce Woods Provincial Park, Manitoba. Note location of sunflowers on the lower slope at the edge of the active sand. August 4, 2004.

Figure 3. Colony of prairie sunflowers occupied by Gold-edged Gems at Spirit Dunes, Spruce Woods Provincial Park, Manitoba. Note location of sunflowers on the lower slope at the edge of the active sand. August 4, 2004.

Figure 4. Burstall dunes,Saskatchewan. Note sheet-like formations with smooth topography and little vegetation. Plants in foreground are scurf-pea. August 6, 2004

Figure 4. Burstall dunes,Saskatchewan. Note sheet-like formations with smooth topography and little vegetation. Plants in foreground are scurf-pea. August 6, 2004

Figure 5. Massive stand of prairie sunflowers on fallow field, east of Burstall, Saskatchewan. August 6, 2004.

Figure 5 Massive stand of prairie sunflowers on fallow field, east ofBurstall, Saskatchewan. August 6, 2004.

Figure 6. Prairie sunflowers in full bloom on dune front, Spirit Dunes, Spruce Woods Provincial Park, Manitoba. August 27, 2004.

Figure 6. Prairie sunflowers in full bloom on dune front, Spirit Dunes, Spruce Woods Provincial Park, Manitoba.  August 27, 2004.

Figure 7. Prairie sunflowers growing on disturbed area, Canadian Forces Base (CFB) Shilo road/fireguard. August 4, 2004.

Figure 7. Prairie sunflowers growing on disturbed area, CFB Shilo road/fireguard. August 4, 2004.

Dependency on a narrow range of host plants is usual in the genus Schinia, with many individual Schinia species restricted to one or several host plant species in a single genus, or to a few closely related genera of host plants (Hardwick, 1996).

Helianthus petiolaris is a native plant in the family Asteraceae. It grows on light or sandy soils throughout much of southern Canada and the continental USA, and appears to have expanded its range since settlement (Heiser, 1969). Unlike most native sunflower species, it is an annual and thus one of the last species of sunflowers to blossom. It is more or less restricted to disturbed areas on sand or sandy soils, including roadsides, fallow fields (Figure 6), active sand dunes and beaches (G. Anweiler, pers. obs.). In southwestern Saskatchewan and southeastern Alberta, it forms almost continuous stands for many kilometrer along the edges of gravel roads and highways. At the Spirit Dunes site, prairie sunflowers occurred in essentially pure stands as an early pioneer on active sand above and below the active dune crests (Figures 4 and figure5). They were rarely observed growing mixed with other dune vegetation, with the exception of sand dock at some sites (G. Anweiler, unpublished data, 2004). 

The active dune habitat occupied by Gold-edged Gems in the Spirit Dunes of Spruce Woods Provincial Park is known to also harbour a suite of other rare moths, including Schinia bimatris (Harv.), Schinia roseitincta (Harv.), Pygarctia spraguei (Grt.), and at least three species of Copablepharon (J. Troubridge, pers. comm., 2004; Schmidt and Anweiler, 2004; G. Anweiler, unpublished data).

Habitat trends

According to Wolfe (2001), many active dunes on the southern Prairie Provinces have been stabilized by vegetation at a rate of 10-20% per decade, and some have become nearly completely stabilized over the last century. The causative factors for the evolution of these active dune areas to stabilized, vegetated dunes is not well understood.  Changes in land use activities and the frequency of disturbance, as well as changes in climatic conditions on the prairies over the last century, each play a role in dune stabilization (Wolfe, 2001).

Aerial photographs show that the Middle Sand Hills in Alberta, covering about 400 km², had extensive active dunes in 1937, but were reduced to a fraction of the area by 1998 (see Geological Survey of Canada, 2001). Vance and Wolfe (1966) and Mahus and Wolfe (1999) studied historical photographs of the dunes and concluded that there was significantly less bare sand in the Middle Sand Hills since the 1930s.  Bender et al. (2005) quantified changes in the Middle Sand Hills from 1949 to 1998 using air photos and satellite imagery.  They found that many individual dunes were becoming completely stabilized by vegetation at a mean rate of loss of seven dunes per decade and that in the overall dune complex, areas of exposed sand had declined at an average rate of 40% per decade.  Furthermore, Gummer and Bender (COSEWIC, 2006) extrapolated dune loss in the Middle Sand Hills to be 53% from 1995 to 2005 and concluded that all active sand dunes in the complex will disappear by 2014. 

Within the Great Sand Hills of adjacent Saskatchewan, covering some 2,000 km², the number of sections of land with blowing, active sand had been reduced by 60% between the 1880s and 1980. This has been attributed largely to “diligent management practices that contributed to the reduction in bare, blowing sand, and the increase in vegetative cover in sensitive dune areas” (Wolfe, 2001). The active sand areas of the Manitoba Spirit Sand Hills (Spirit Dunes) have decreased as they have become progressively more vegetated since the earliest air photos in the late 1920s. In 1928, the active portion of the Spirit Dunes was about 145 ha, reduced to 23 ha in 1958 and 15 ha in 1969; about 20 ha remain today (Wolfe 2001; Geological Survey of Canada, 2001).

Habitat protection/ownership

The Manitoba population of Gold-edged Gems is largely, or entirely, contained within the boundaries of Spruce Woods Provincial Park, although it is possible that the species also occurs in parts of adjacent CFB Shilo. The park is under provincial jurisdiction, while the CFB Shilo lands are under federal jurisdiction. The Bindloss, Alberta and Burstall, Saskatchewan colonies of Gold-edged Gems are located on private lands, and the Pakowki Lake colony on leased, provincially owned grazing land.

Much of the potential habitat in Alberta occurs in the Middle Sandhills, on federal lands within CFB Suffield. Other potential habitat in southern Alberta and Saskatchewan occurs on provincially owned lands currently used for grazing, either as land leased for agricultural uses or within Community Pasture. Additional fieldwork is needed to determine if any of these areas are occupied by Gold-edged Gems.

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