Tway National Wildlife Area Management Plan, 2016: chapter 2

2 Ecological Resources

2.1 Terrestrial and aquatic habitats

Tway NWA straddles the Aspen Parkland Ecoregion of the Prairie Ecozone and the Boreal Transition Ecoregion of the Boreal Ecozone of Saskatchewan. Upland ecosites occupy 71 ha (23%) of the Tway NWA (Table 4). The Saskatchewan Soil Survey (1989) reports the uplands at Tway NWA are Black Chernozomic soils with an average slope of 2-3%. Upland soil textures range from sandy loams on gravely fluvial materials (Whitesand series) to more silty lacustrine materials (Hoey series).

Originally, upland ecosites would have been dominated by grasslands of Plains Rough Fescue-Northern Wheatgrass-Western Porcupine Grass (Festuca hallii-Elymus lanceolatus-Hesperostipa curtiseta) on loamy sites (Thorpe 2007a) and Western Porcupine Grass (Hesperostipa curtiseta) on sandy loam sites (Thorpe 2007b).

Upland ecosites have been modified by deliberate and unintended human activity over the last century. Historically, the majority of uplands were plowed for agricultural crop production. All cultivated areas were subsequently either sown to dense nesting cover (a mixture of Sweet Clover [Melilotus spp.], Alfalfa [Medicago saliva], Intermediate Wheatgrass [Thinopyrum intermedium] and Tall Wheatgrass [Thinopyrum ponticum]) or reverted to native upland through natural succession. Most of that land is now dominated by perennial forages of European origin, mostly Smooth Brome (Bromus inermis) and Kentucky Bluegrass (Poa pratensis).

Due to active fire suppression to protect infrastructure and forage supplies, many native grassland habitats within Tway NWA now support expanding patches of trees and shrublands, which may include Trembling Aspen (Populus tremuloides), Willow (Salixspp.), Western Snowberry (Symphoricarpos occidentalis), Saskatoon (Amelanchier alnifolia), Beaked Hazelnut (Corylus cornuta) and Red-osier Dogwood (Cornus stolonifera). Long-term exclusion of fire, grazing or haying at Tway NWA has resulted in unfettered seed production and wind dispersal of Smooth Brome, Canada Thistle (Cirsium arvense), Perennial Sow Thistle (Sonchus arvensis), Dandelion (Taraxacum officinale) and Yellow Sweet Clover (Melilotus officinalis), which have invaded and now dominate the once-remnant native grasslands and the wet meadows.

No vegetation inventories have been completed on the NWA nor have there been any ecological health assessments of the upland and lentic riparian communities.

Lowland ecosites with open water, wetlands and wet meadows that range from fresh to saline occupy 163 ha (77%) of Tway NWA (Table 4). The dominant soils are Humic Gleysolic that underly shallow open water and poorly drained soils found in marginal areas (Saskatchewan Soil Survey 1989). The emergent vegetation around the large wetland basin is dominated by Great Bulrush (Scirpus acutus) and Common Cattail (Typha latifolia), with Creeping Spike Rush (Eleocharis palustris) and Sedges (Carex sp.). The submergent vegetation includes Sago Pondweed (Potamogeton pectinatus), Hornwort (Ceratophyllum demersum), Water-milfoil (Myriophyllum exalbescens), Common Duckweed (Lemna minor) and Muskgrass (Chara vulgaris) (Whyte 1986). Wet meadow communities have not been inventoried.

In general, the flowing surface waters in the Tway region are intermittent. Local creeks and streams are largely dependent on spring runoff, and they show seasonal and annual fluctuations in salinity. The area covered by water at Tway NWA changes drastically among seasons and years. In some years, water is virtually absent from the NWA except for Tway Lake. The Carrot River, which supplies Tway NWA, is intermittent and typically has a no-flow period between November and February. In dry years, the no-flow period can extend from July to March. Flows generally peak in May and rapidly decline in October.

2.2 Wildlife species

Nearly 140 species of birds have been observed at Tway NWA (unpublished data: Saskatoon Nature Society 1991). Major species groups of migratory birds that currently use the NWA include wetland species such as waterfowl, grebes and shorebirds, and grassland and forest species such as woodpeckers, warblers and sparrows. The large wetland basin created by the water control structure is noted for production of diving ducks, especially for use during moulting (Whyte 1986). Waterfowl that are known to breed in Tway NWA are Canada Goose (Branta canadensis), Mallard (Anas platyrhynchos), Northern Pintail (Anas acuta), Blue-winged Teal (Anas discors), Green-winged Teal (Anas crecca), American Wigeon (Anas clypeata), Canvasback (Aythya valisineria), Redhead (Aythya americana), Lesser Scaup (Aythya affinis) and Ruddy Duck (Oxyura jamaicensis).

No inventories have been completed for plants, bryophytes, mammals, reptiles or amphibians in Tway NWA. Large ungulates such as White-tailed Deer (Odocoileus virginianus), Mule Deer (Odocoileus hemionus), Elk (Cervus canadensis) and Moose (Alces alces) are common in the area and are likely present in the NWA during certain times of the year. Beaver (Castor canadensis) and Muskrat (Ondatra zibethicus) inhabit Tway NWA and pose management challenges by plugging the water control structures with branches, reeds and mud, and burrowing in the dykes and dams. Mounds created by Northern Pocket Gophers (Thomomys talpoides) are widespread in the seeded upland grasslands.

The 1986 Management Plan provides a list of potential species that may occur on the NWA or the vicinity (Whyte 1986).

2.3 Species at risk

Two species at risk, Common Nighthawk (Chordeiles minor) and Yellow Rail (Coturnicops noveboracensis), which are listed as threatened and special concern under Schedule 1 of the Species at Risk Act, respectively, are known to breed in Tway NWA (Table 5). Also recorded at Tway NWA are Baird's Sparrow (Ammodramus bairdii), Horned Grebe (Podiceps auritus), Barn Swallow (Hirundo rustica) and Bobolink (Dolichonyx oryzivorus), which have been recommended for listing under the Species at Risk Act (Table 5). Short-eared Owl (Asio flammeus), which is listed as special concern under Schedule 1 of the Species at Risk Act, inhabits the area surrounding Tway NWA and may frequent the property.

The following species have been observed in Tway NWA and are on the provincial Saskatchewan Conservation Data Centre tracking list: American White Pelican (Pelecanus erythrorhynchos), Cooper's Hawk (Accipiter cooperii), Forster's Tern (Sterna forsteri), Great Blue-heron (Ardea herodias), Short-billed Dowitcher (Limnodromus griseus), Turkey Vulture (Cathartes aura) and Western Grebe (Aechmophorus occidentalis) (Saskatchewan Conservation Data Centre 2012). One tracked mammal species, the Olive-backed Pocket Mouse (Perognathus fasciatus), has been historically recorded in the vicinity (Saskatchewan Conservation Data Centre Wildlife Application 2014) (Table 5).

Potential habitat for the Northern Leopard Frog (Lithobates pipiens), considered special concern under Schedule 1 of the Species at Risk Act, is present in Tway NWA (Table 5) (Gerry and Pepper 2000).

The Saskatchewan Conservation Data Centre (2011) has listed 13 element occurrences of rare and endangered species found in the Rural Municipality of Invergordon surrounding Tway NWA, many of which are historic occurrences, and the species' current range no longer extends into this area (e.g., Burrowing Owl [Athene cunicularia]).

2.4 Invasive species

The tame grass upland community is dominated by Smooth Brome (Bromus inermis), Quackgrass (Elymus repens), Kentucky Bluegrass (Poa pratensis), Sweet Clover (Melilotus sp.) and Alfalfa (Medicago sativa). Canada thistle (Cirsium arvense), Perennial Sow-thistle (Sonchus arvensis) and Dandelion (Taraxacum officinale) are common throughout.

Common Tansy (Tanacetum vulgare), a provincially listed noxious weed, is a major invasive alien plant species of concern in the Rural Municipalities of Invergordon and Three Lakes. It has been observed on the NWA and vicinity in road ditches, hayfields and pastures. Wild Caraway (Carum carvi) is another invasive alien plant species found in the vicinity along road ditches.

Wild Boar (Sus scrofa), an agricultural livestock species in Saskatchewan, is feral in the Rural Municipality of Invergordon and surrounding areas.