Forked three-awned grass (Aristida basiramea) COSEWIC assessment and status report: chapter 6
Biology
Reproduction
Aristida basiramea is an annual, flowering and setting seed very late in the season. Mohlenbrock (1973) notes that the species flowers from August to early October in Illinois. In Maine it has been noted as fruiting from August to October (Maine Department of Conservation, 1999). From field observations in Ontario in 2001, it was striking how late flowering A. basiramea is. The majority of the plants were not yet exert (floral organs not yet visible) at Macey Lake on August 16th, and plants were still observed on October 7th as not exerted. Reznicek (pers. comm. 2001) notes that in Michigan, the plant “just keeps fruiting until the weather stops it.” Catling et al. (1977) note, with respect to A. longispica, that “Like other species of Aristida, this one begins to flower late in August, and does not develop fruit until September or October. Even then it may be relatively inconspicuous.”
Survival
The species appears to be very intolerant of competition, seems unable to compete in denser areas of herbaceous cover, and succumbs readily to succession and shading. It will be accorded the highest level of protection within the Tiny Township Official Plan -- Environmental Protection One. Permitted uses on lands designated Environmental Protection are limited to conservation and passive recreational uses. No buildings or structures are permitted, nor is any site alteration permitted in this designation. Golf courses are not considered to be passive recreational use; however, nothing in the official plan is intended to limit the ability of agricultural uses to continue on lands designated as Environmental Protection One (The Planning Partnership, 2000).
Physiology
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 (Gleason, 1952).
Catling et al. (1977) noted that the Macey Lake station of A. basiramea was 245 kms farther north than any other Aristida record in Ontario and is the only occurrence of a species of the genus north of the Carolinian zone. They also noted a similar situation for Michigan, with A. basiramea being the only member of the genus to be found north of the “tension” zone in that state, citing Voss (1972). Since that time Aristida dichotoma has been discovered as a native species in Ontario in Lennox & Addington County (Brownell et al.,1996), at approximately the same latitude as the native Ontario A. basiramea stations. 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 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).
Its northern distribution is likely restricted at least in part to the fact that it doesn’t even begin flowering until mid to late August, and individual plants are shut down by the advancing cold winter in the fall, prior to seed set.
Movements/dispersal
The divergent awns in Aristida aid in wind and animal transportation of the florets, and by holding the florets and the caryopses they contain, at an angle to the ground, in establishment (Allred, 2001).
At the Macey Lake station, the species certainly seems to be responsive enough to occupy newly created habitat in great numbers.
Nutrition and Interspecific Interactions
Although generally poor forage grasses, and despite the callus, which is potentially harmful to grazing animals, some species of Aristida are an important source of spring forage on western rangelands. Quail and small mammals eat small amounts of the seed (Allred, 2001).
Behaviour/adaptability
The species is adventive along sandy roadsides in some United States, e.g. Maine, where road management appears to be compatible with the species.
Wright et al. (1978) note that Aristida spp. are readily harmed by fire because their root crowns are close to or above the soil surface, while Lemon (1949) and Parrott (1967) have documented that Aristida stricta is a fire-adapted species, and dominates fire-maintained southeastern grasslands and savannahs. Its meristems are located about 3 cm below the soil surface, where they are insulated from the heat of fire. It can persist in the shade of invading hardwoods for 20 to 40 years, but is eliminated if fire does not occur after that time (Clewell, 1989).