Forked three-awned grass (Aristida basiramea) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Limited Habitat
The species appears to be restricted to acidic, open sand barrens, associated with post-glacial shorelines. While not seemingly over restrictive, this habitat is in actually in very short supply in southern Ontario and southern Quebec. Undoubtedly more abundant at different times in history, such as during the hypsithermal (7,000 years BP) and more recently in Simcoe County during the period of large scale clearing of the forests from 1860 to 1880, these sand barrens have now been greatly reduced in quality and extent by development, planting of conifers to stabilize soils, and natural succession in the absence of periodic fire.
Sand Extraction
These Algonquin and Nipissing Shorelines where the sand barren habitat is supported are often utilized as wayside pits for sand extraction, both in southern Ontario and southern Quebec.
Successional Changes
The populations of A. basiramea in Ontario have been retained mainly through some sort of human disturbance which has set back the successional trend. At Christian Island, the placement of a baseball diamond, with relatively low levels of use, has helped to perpetuate tens of thousands of plants by preventing closure of the open habitat by invading shrubs. The Anten Mills station is virtually lost in the midst of conifers planted along the rim of the Algonquin Bluff. Fire was likely a factor, along with intense droughts, in maintaining the open character of these sand barrens, but fire suppression has been quite effective over the last one hundred years in Simcoe County, and many of these sand barrens would have been lost due to lack of the natural disturbance regimes.
Human Impacts
While the species obviously is threatened by permanent forms of development such as new subdivisions, it also owes its fragile existence to recent forms of light disturbance on its habitat, otherwise it succumbs to more competitive and shade tolerant species. At Beausoleil Island it grows today on the site of an old settlement; at Macey Lake it opportunistically moved to occupy prime habitat created by the activities associated with a peat mining operation; and at Christian Island it thrives in the tens of thousands across a baseball diamond. Only at the Anten Mills station and at Cazaville was any evidence of ATV or trail bike use noted. At Cazaville, ATVs pose a principal threat to A. basiramea, while at Anten Mills, ATV use is occurring at such low usage, that it may in fact be assisting the perpetuation of the species. In the absence of any intentional management for the species in Ontario, various types of human-induced disturbance seem to be compatible with or conducive to Aristida basiramea occurrences. On the other hand, the ATV use at Cazaville appears to be negatively impacting the population of A. basiramea.
Planting of Conifers
Many of the abandoned shorelines in Simcoe County have been planted in conifers, the result of very ambitious programs since the 1920s to stabilize and enhance these identified “wastelands”. Many of these today are dense canopy stands of Red and Scot’s Pine, totally unsuitable for an open sand barren species such as A. basiramea. Conifer plantations are a principal threat at the Cazaville station as well (Coursol, pers. comm. 2003).
Invasive Species
During fieldwork in 2001 the following invasive species were observed in the sand barren habitat of Aristida basiramea: Glossy Buckthorn (Rhamnus frangula), Spotted Knapweed (Centaurea maculosa), White Sweet Clover (Melilotus albus), and Scot’s Pine (Pinus sylvestris). In the dry, sandy habitat, especially with successive and severe drought years, only the latter species was noted as actually out-competing the Aristida, and it is quite common through the population at Macey Lake, and of course at Anten Mills.
Subdivision Development
This factor will certainly limit, if not eliminate entirely, the remnant habitat supporting the species at Anten Mills, and to some extent characterizes the type of subdivision development which is especially harmful to A. basiramea and other species which are relicts associated with post-glacial shorelines. That is the priority accorded such properties with striking vistas, as ideal for estate housing. New homes along the crest of the Algonquin Bluff in Anten Mills for example, will be afforded spectacular views of the Niagara Escarpment, 30 km to the west. The trend toward this location for new estates is on the rise, especially with the housing boom continuing unabated in Simcoe County.
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