Forked three-awned grass (Aristida basiramea) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

From the botanical history of the last 200 years, A. basiramea appears to be a species which has always been extremely rare in Canada. 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, owing to its habitat in sand barrens which can easily be localized in small sites ‘off the beaten track’, and by the inconspicuous nature of A. basiramea, which requires a fair level of botanical competency by the observer to note and identify it.

For this species it is impossible to provide population trend data at native Canadian sites, 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.

Population numbers for the species in 2001 were as follows:

  • Anten Mills: ca. 800 plants
  • Beausoleil Island: >500 plants
  • Macey Lake: 1000s of plants
  • Christian Island: tens of 1000s of plants
  • Cazaville: >10,000 plants

Total number of plants is estimated as well in excess of 20,000, but the bulk of these are 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. There have been discussions by the Beausoleil First Nation regarding development on the Christian Island site where the A. basiramea occurs, and the station at Anten Mills will largely be lost through subdivision development, where construction commenced in 2002.

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 (NatureServe, 2001).

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