Prairie skink (Eumeces septentrionalis) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Prairie Skinks are at their northern limit in southern Manitoba. Within this area, they are limited by the presence of mixed grass prairie on sandy soils. In winters with poor snow cover, skinks may be killed in their hibernacula when freezing temperatures penetrate more deeply. This winter kill can be a limiting factor (Bredin, 1989). Prairie Skinks are limited to a small area of southwestern Manitoba and mixed grass prairie in this area is decreasing and becoming increasingly fragmented. Habitat loss is resulting from succession to Aspen Parkland, invasion by the exotic Leafy Spurge, cultivation, tree planting programs, and home and road construction.

Fire suppression is encouraging the succession of mixed grass prairie towards Aspen Parkland. With over 20% of prairie lost to forest succession at one site over the last half century (Mansell and Moore 1999) habitat loss is a significant threat to Prairie Skinks (Figure 5). Fire suppression may also reduce habitat quality by increasing the layer of thatch – dead plant material. Such accumulation may insulate the ground and reduce the potential active season. Although this hypothesis has not been tested, Prairie Skinks are more abundant on old fields that are burned regularly (Pitt 2001). Grazing by cattle is not adequate to prevent this succession, for even in grazed pastures, the amount of land covered by aspen increases on average 7% per year in Manitoba (G. Oliver, pers. comm., 2003). There are fire restrictions on the land surrounding Spruce Woods Provincial Park. Within the park, controlled burns have occurred to maintain major prairie sites but the park is not attempting to reclaim prairie lost to forest encroachment over the last few decades (G. Oliver, pers. comm., 2003).

Tree planting programs have also reduced skink habitat by increasing forest cover and destroying prairie soils. For example, in 1994, the Manitoba Agro Woodlot Program plowed almost 3 ha of mixed grass prairie supporting a population of Prairie Skinks in Spruce Woods Provincial Forest. Then over 200 Boy Scouts and Girl Guides planted 14 000 Scots Pines (Pinus sylvestris). From the mid-1980s to mid-1990s, Scouts and

Figure 5. Photo illustrating isolation of mixed grass prairie areas as a result of forest succession. Photo by Errol Bredin.

Guides planted approximately 80 000 Scots Pine trees in this area, thereby eliminating considerable areas of the rare mixed grass prairie required by Prairie Skinks.

Leafy Spurge (Euphorbia esula) is an herbaceous, deep-rooted perennial of the Spurge (Euphorbiaceae Family). It can reproduce vegetatively or by seed. It was first observed in North America in 1827 in Massachusetts (Britton 1921). Leafy Spurge was first noted in Manitoba in 1900 (Bird 1961). Bird (1961) wrote, Leafy Spurge “is now widely established. This is particularly well demonstrated in the Spruce Woods Forest Reserve, where many hundreds of patches now occur. On a special survey of the Shilo area alone, by the Manitoba Weeds Commission in 1950, 1435 patches were counted.” The US Department of Agriculture has a Leafy Spurge team dedicating to controlling and eradicating this species (Team Leafy Spurge website). They estimate that there are approximately five million acres of land in Canada and the US with Leafy Spurge and that the amount of acreage has doubled every 10 years since the early 1900s.

The vast majority of prime skink habitat throughout the Carberry Sandhills is threatened by colonization of Leafy Spurge. In dense patches of Leafy Spurge, there is an average of 96 stems/m² (Bredin 1988). South-facing slopes have often become completely covered in Leafy Spurge in areas of the Carberry Sandhills. Such locations are preferred Prairie Skink habitat, yet in three areas, with the colonization of Leafy Spurge, the south-facing slopes were abandoned by the skinks (Bredin 1988). Leafy Spurge also negatively affects other species. In areas of high Leafy Spurge infestation, there are fewer nests of ground-nesting birds (Scheiman et al. 2003). To date grazing by goats has proven to be an effective control (G. Oliver, pers. com., 2003). Controlled burns are not effective, because rootstocks can extend more than 3 m below ground and survive a grass fire. Manitoba Agriculture and Food is distributing flea beetles to farmers to control Leafy Spurge, but it can take up to 10 years for a large population of beetles to build up and become an effective control (J. Thornton, pers. comm., 2003). Indeed, there is evidence of dramatic reduction in Leafy Spurge where flea beetles were released in Spruce Woods Provincial Park several years ago in a control program operated by Manitoba Parks and Natural Areas Branch (W. Watkins, pers. comm. 2003).

Cultivation of mixed grass prairie is a major threat to the Prairie Skink. Over 5000 ha of mixed grass prairie was lost from 1995-1998 as a result of cultivation (Mansell and Moore 1999). In the Carberry area alone approximately 7000 ha of land has been lost to potato farming from 1961-2000 (Town of Carberry 2003).

Combined, these losses of habitats are increasing the fragmentation of the naturally fragmented distribution of the Prairie Skink. Populations are cut off from one another by rivers, streams and large wetlands. The expansion of aspen Parkland surrounds pockets of prairie occupied by skinks (e. g. Figure 5), and these areas shrink every year such that many of these “islands” will be lost within a decade or less (Bredin pers. obs.). This separation and shrinkage of habitat is particularly important in a species with low population densities, limited ability to disperse and at its extreme northern limit.