Dwarf woolly-heads, specific populations, COSEWIC assessment status report: chapter 5

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Habitat

Habitat requirements

Southern Mountain Population

The Princeton unit occurs in a rainshadow cast by the Coast-Cascade Mountains. The resulting continental climate has cool winters with low to moderate snowfall. The growing season is relatively long (about 95 frost-free days), warm (about 1,028-1,266 growing degree days > 5°C) and dry (185-313 mm growing season precipitation). There are substantial growing season moisture deficits (Lloyd et al. 1990).

The species occurs on calcareous clay soils along pond margins and in shallow depressions which are dominated by annual plants which can take advantage of the brief period of favourable growing conditions. The leading species include Plagiobothrys scouleri (Scouler’s popcornflower) and Polygonum polygaloides ssp. confertiflorum (Close-flowered knotweed). Common associates include Myosurus minimus (tiny mousetail), Alopecurus carolinianus (Carolina meadow-foxtail), Gnaphalium palustre (lowland cudweed), and Deschampsia danthonioides (annual hairgrass). The most commonly associated perennial plant is Danthonia unispicata (One-spike oatgrass) (Douglas et al. 2003). The surrounding area is composed of shrub/grassland dominated by Artemisia tridentata, Pseudoroegneria spicata and Hesperostipa comata as well as open to closed woodlands dominated by Pinus ponderosa (Ponderosa pine) and Pseudotsuga menziesii (Douglas-fir).

Prairie Population

The prairie population occurs in a semi-arid region with very cold winters and short, warm summers. Most of the precipitation falls in summer, with 75-130 mm in June but an average of less than 50 mm per month in July and August (Hare and Thomas 1979).

In the Prairie Population, sites tend to occur on shallowly depressional, seasonally flooded sites such as Solonetzic pans, slough margins and ephemeral wetlands with sandy bottoms (Hudson pers. comm. 2005; Porter 2005 pers. comm., Romuld pers. comm. 2005; Wallis pers. comm. 2005; Bush pers. comm. 2005). There does not appear to be any consistent suite of associated species but vegetation data is lacking for most sites (Douglas et al.2000). The surrounding uplands tend to support grassland vegetation dominated by Hesperostipa comata, H. curtiseta, Pascopyrum smithii, Elymus lanceolatus, Koeleria macrantha and Bouteloua gracilis.

Trends

There is no reliable information regarding the rates of change in extent of occurrence, area of occupancy or habitat suitability in either unit.

Habitat protection/ownership

The three localities of the Southern Mountain Population occur on a private ranch within the Agricultural Land Reserve (Table 1). Two of the Prairie Population localities occur in protected areas. Most of the other localities occur on provincial crown land or land ownership is unknown.