Bradwell National Wildlife Area Management Plan: chapter 2


2 Ecological resources

2.1 Terrestrial and Aquatic Habitats

Bradwell National Wildlife Area (NWA) contains modified elements of the Moist Mixed Grassland Ecoregion of the Prairie Ecozone (Ecological Stratification Working Group 1995). Upland ecosites occupy 77 ha (70%) of Bradwell NWA, and consist of dark-brown sandy-loam soils of the orthic chernozemic suborder on glacio-fluvial outwash. Originally, the typical upland ecosites would have been dominated by grasslands of western porcupine grass - northern wheat grass - needle and thread (Hesperostipa curtiseta - Elymus lanceolatus - Hesperostipa comata) (Thorpe 2007). Recent inventories confirm that small remnants of this grassland type occur on three uncultivated hill tops, with a high proportion of upland sedges (Carex obtusata, C. filifolia, C. heliophila) and fringed sage (Artemisia frigida).

Upland ecosites have been modified by deliberate and unintended human activity over the last century. Historically, approximately half (46 ha) of the uplands were plowed for agricultural crop production. Most of that land is now dominated by planted perennial forages of European origin, mostly Smooth Brome, Intermediate Wheatgrass, and Alfalfa. Some smaller areas were seeded to different native and tame grass and legume mixes on a trial basis in 1979 (Canadian Wildlife Service 1985). Vegetation inventories in 2012 indicate none of the seeded native species remain, and all formerly disturbed upland sites are now dominated by Smooth Brome and Intermediate Wheatgrass.

Due to active fire suppression to protect infrastructure and forage supplies, many native grassland habitats within Bradwell NWA now support expanding patches of tree and shrubland habitats, including Trembling Aspen (Populus tremuloides), Willow (Salix spp.), Western Snowberry (Symphoricarpos occidentalis), Prairie Rose (Rosa arkansana), Silverberry (Elaeagnus commutata), and Gooseberry (Ribes oxyacanthoides). Long-term exclusion of fire, grazing, or haying at Bradwell NWA has resulted in unfettered seed production and wind dispersal of Smooth Brome, Canada Thistle, Perennial Sow-thistle (Sonchus arvensis), Absinthe, and Yellow Sweet Clover, which have invaded and now dominate nearly all 45 ha of remnant native grasslands and wet meadows.

Lowland ecosites and ponds with waters ranging from fresh to saline occupy 37 ha (30%) of Bradwell NWA. Soils consist of dark-brown gleyed chernozems and humic gleysols with a loam texture. In the wetlands, common emergent species include Spike Rush (Eleocharis palustris), Bulrush (Scirpus spp.), and Cattail (Typha latifolia). Owing to the water-level manipulations and supply of fresh river water through the canal, there are also several emergent stands of Giant Reedgrass (Phragmites communis) in canals and at the inlets and outlets of ponds. Water-milfoil (Myriophyllum spp.) and Pondweed (Potamogeton spp.) are the dominant submergent plants. In wet meadow areas, Rush (Juncus balticus), Sedge (Carex spp.), Reedgrass (Calamagrostis inexpansa), Sloughgrass (Beckmannia syzigachne), Dandelion (Taraxacum officinale), and Sea-side Arrowgrass (Triglochin maritima) are common. In saline areas, Saltgrass (Distichlis spicata) and Foxtail Barley (Hordeum jubatum) are common (Millar 1976).

2.2 Wildlife Species

Over 100 species of birds have been seen in Bradwell NWA. Major species groups of migratory birds that currently use the NWA include waterfowl, grebes, and shorebirds. Many of the waterfowl found in the area are suspected to breed there, though this has only been confirmed for Canada Goose (Branta Canadensis), Northern Pintail (Anas acuta), Gadwall (Anas strepera), and Ruddy Duck (Oxyura jamaicensis). Many shorebirds found in the Bradwell NWA region stage there during spring and fall migration; however, Killdeer (Charadrius vociferous), Marbled Godwit (Limosa fedoa), and Wilson’s Phalarope (Phalaropus tricolor) are confirmed to breed in the area. Avian predators sometimes seen in the area include Northern Harrier(Circus cyaneus), Swainson’s Hawk (Buteo swainsoni), Great Horned Owl (Bubo virginianus), Short-eared Owl (Asio flammeus), Black-billed Magpie (Pica hudsonia), and American Crow (Corvus brachyrhynchos). Most passerine species are regular summer visitors that likely breed locally (Canadian Wildlife Service 1985).

At least 19 species of mammals occur on Bradwell NWA. Upland soil and vegetation is frequently disturbed by earthen mounds created by Northern Pocket Gopher (Thomomys talpoides), while wetland and lowland vegetation is largely impacted by Muskrat and Beaver. Other mammal species that are abundant and significant predators of birds, eggs, and/or nestlings include Red Fox (Vulpes vulpes), Coyote (Canis latrans), Racoon (Procyon lotor), Short-tailed Weasel (Mustela erminea), American Mink (Neovision vision), Striped Skunk (Mephitis mephitis), Franklin’s Ground Squirrel (Spermophilus franklinii), and Thirteen-lined Ground Squirrel (Spermophilus tridecemlineatus) (see Pasitschinak-Arts et al. 1998). Whitetailed Deer (Odocoileus virginiana) are frequently observed resting in forest and shrubland cover and feeding in perennial forage crops.

Three amphibians are known to use the wetland and adjacent upland habitats at Bradwell NWA, namely Wood Frog (Rana sylvatica), Boreal Chorus Frog (Pseudacris maculata), and Canadian Toad (Bufo hemiophrys). Fathead Minnow (Pimephales promelas) was detected in the wetlands in 1983 and likely arrived through the canal system.

Among invertebrates, several aquatic groups are abundant and important as food sources for wildlife or indicators of environmental change. Groups best represented at Bradwell NWA include crustaceans (for example, Cladocera, Hyalella spp., Gammarus spp.), insect larvae (for example, Diptera, Ephemeroptera, Odonata), and adult beetles (for example, Dytiscidae, Chrysomelidae) (Euliss et al. 1999).

2.3 Species at Risk

Two species that have been recommended for listing under the Species at Risk Act, Bobolink (Dolichonyx oryzivorus) and Horned Grebe (Podiceps auritus), were observed on Bradwell NWA in 2012. Five other species at risk are known to occur in the surrounding landscape (Table 3). The International Piping Plover Census, conducted every five years since its initiation in 1991, includes the nearby Bradwell Reservoir (Elliot-Smith et al. 2009), but no individuals have been recorded at that site to date (M. Ranalli, pers. comm.). No critical habitat for any species at risk listed under the Species at Risk Act has been identified at Bradwell NWA.

Table 3: Species at risk detected either in Bradwell National Wildlife Area or in the surrounding landscape
Species Common names of species Scientific names of species Status/
Canada/
Species at Risk Act (SARA)a
Status/
Canada/
Committee on the Status of Endangered Wildlife in Canada (COSEWIC)b
Status/
Saskatchewan/
Provincial rankingc
Presence or Potential of Presence
Birds Barn Swallow Hirundo rustica No status Threatened S5B, S5M Potential
Birds Bobolink Dolichonyx oryzivorus No status Threatened S5B Confirmed
Birds Horned Grebe Podiceps auritus No status Special Concern S5B Confirmed
Birds Piping Plover Charadrius melodus circumcinctus Endangered Endangered S3B Potential
Birds Short-eared Owl Asio flammeus Special Concern Special Concern S3B, S2N Potential
Birds Sprague's Pipit Anthus spragueii Threatened Threatened S4B Potential
Amphibians Northern Leopard Frog Lithobates pipiens (syn. Rana pipiens) Special concern Special concern S3 Potential

a Species at Risk Act : Extinct, extirpated, endangered, threatened, special concern, not at risk (assessed and deemed not at risk of extinction) or no status (not rated)

bCommittee on the Status of Endangered Wildlife in Canada

c Saskatchewan Conservation Data Centre (SKCDC) Provincial Rank (PDF; 32KB)

2.4 Invasive species

Canada Thistle, Perennial Sow-thistle, Absinthe and Sweet Clover have invaded most of the remaining native grassland uplands within Bradwell NWA. Most tame uplands were seeded to Smooth Brome and Alfalfa and, as a result, Smooth Brome has invaded downslope into most wetland margins. The canal along the southern edge of Bradwell NWA contains substantial populations of Reed Canary Grass (Phalaris arundinacea) and giant reed (Phragmites), though it is unknown if the latter is the exotic (Phragmites australis) or native species (Phragmites communis).

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