Forked three-awned grass (Aristida basiramea) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species information

This tufted, wiry-stemmed annual grass grows erect to 30 to 60 cm. It has very narrow leaves (1 mm wide), and terminal fruiting clusters 5-10 cm long that feature long bristly awns. The glumes (lowest bracts around the spikelet) have a single vein and they are unequal in length, the second being longer than the first. It characteristically branches freely at the base, sparingly so above.

Distribution

The species is endemic to North America, with a range that is primarily mid-western, with outliers west to Colorado, south to Texas, east to Maine, and north as far as the Upper Peninsula of Michigan. The Canadian range is restricted to southern Ontario and southern Quebec, where it is known from five extant naturally-occurring sites. In addition, it is known from one adventive station in northwestern Ontario, near Fort Frances, Rainy River District.

Habitat

In the US the species occurs in rare habitats such as pine barrens, but can also tend to more weedy habitats, such as roadsides, pastures and waste ground. In Canada, native populations appear to be restricted to dry, open, acidic sand barrens, but the species will exploit weedy habitats associated with these sites, such as roadside ditches and old fields. The five native Canadian populations occur on low, sand ridges or dunes, associated with post-glacial shorelines of Algonquin or Nipissing age (12,000 and 5,000 years B.P. respectively).

Biology

The Aristida genus is chiefly of subtropical and warm temperate climates in both hemispheres, where the more than 300 species prefer dry, sterile, or sandy soil. In North America the genus is most abundant in the arid regions. Although apparently the hardiest member of its genus, habitat and soils may be limiting Aristida basiramea in Canada, since the dry, open sand barrens habitat used by the species in Ontario and Quebec is limited, and in Ontario at least does not occur commonly in the Georgian Bay area north of the known locations. A. basiramea is not currently known natively north of the northern Upper Peninsula of Michigan (approximately 48 degrees latitude).

Population sizes and trends

Forked Three-awned Grass appears to be a species that has always been extremely rare in Canada, at least in recent times. Through this long history of botanical exploration, a total of only five naturally-occurring stations have been discovered for the species, all in two of the most intensively botanized regions of the country, southern Ontario and southern Quebec. Other populations may yet be discovered. The species is difficult to find because of its inconspicuous nature, its very late flowering and seed set, and because its habitat can be hidden in small sites ‘off the beaten track’.

For this species it is impossible to provide population trend data, given that three of the stations were only discovered in 2001, the Christian Island station was only known from a now-extirpated sub-population when last observed in 1981, and the Macey Lake population experienced an explosion in numbers in the last six years through exploiting newly created habitat. The species was never known from any other historical stations, thus offering up no clues to declines.

The total number of plants for the five stations is in excess of 20,000, with the bulk of these at two sites, and the total area of occupancy is less than 3 sq kms. The total extent of occurrence for the five populations is 502 sq kms, and this sand barren habitat is in very short supply, and continues to be shifted to other uses and community types.

The species is rare in three US states, but the number where it is secure is unknown, as no states have ranked it as S4 or S5.

Limiting factors and threats

The species is subject to several limiting factors, the most important of which are the fact that its sand barren habitat is very restricted, fragmented, and in decline; and what little remains is quickly being lost to succession in the absence of natural disturbance regimes, in particular fire, which served to maintain the open character of these barrens.

Special significance of the species

Forked Three-awned Grass is a very low profile species, with no reason to date to be of interest to the public, and for which there is no known special significance.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

Species

Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)^Footnoteb

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)^Footnotec

A species for which there is insufficient scientific information to support status designation.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.