Factors determining the distribution of Opuntia fragilis in the boreal forest of southeastern Manitoba

Abstract

Opuntia fragilis (Nutt.) Haw. is restricted to south-facing rock outcrops on the shores of certain rivers and lakes in the boreal forest of southeastern Manitoba. Limitations in propagule dispersal, establishment, and maintenance were studied at Bird River (50°25′ N, 95°41′ W) between October 1979 and October 1982. Propagules studied were stem units (pads) because this cactus propagates entirely by vegetative means in this region. Mature terminal pads broke off most easily in the late spring while turgid and rolled downhill (geochory), thus establishing new plants locally. Some pads fell into the river and could float long distances (hydrochory) before being washed ashore. Perhaps less frequently, pads were dispersed over long distances on animals (epizoochory). Marked pads placed in potential habitats showed significantly greater establishment (α = 0.05) on south-facing outcrops than on north-facing or forest sites. Censuses (1979–1982) of an established colony indicated that pad number was increasing by 51% per year. Approximately 6% of the pads were dispersed from the outcrop. The present distribution of O. fragilis appears to be both habitat and dispersal limited.

Reproductive biology of Opuntia: A review

“…In several populations the higher recruitment of individuals by multiplication is evident (Bobich and Nobel, 2001a;Mandujano et al, 2001). Vegetative propagules display a short-range dispersal (Bobich and Nobel, 2001a), resulting in high-density populations surrounding the mother plant (Bobich and Nobel, 2001b), although in O. fragilis, dispersion of joints may be very broad (Frego and Staniforth, 1985), especially when animals cause detachment (Anthony, 1954;Bobich and Nobel, 2001b) and dispersal (Frego and Staniforth, 1985) of the joints. Furthermore, it seems likely that in the absence of multiplication, most plants live no longer than 20-25 years (Bowers, 1996b).…”

“…Cladode survival percentage 13 months after being deposited on a number of substrates ranged from 63% to 100% and 86% of surviving cladodes developed roots, mainly in mossy substrates and barren soil. Epizoochory by humans and deer is also frequent in this species and birds and small mammals are also likely to participate (Frego and Staniforth, 1985).…”

Freezing and heat tolerance ofOpuntiacacti native to the Canadian prairie provinces

“…0. fragilis. Opuntia fragilis vegetatively propagates by detaching the terminal cladodes (Frego and Staniforth 1985). In the summer of 1986, four flowers were observed in this population, but none of them set seeds.…”

“…The terminal cladodes of 0. fragilis (Fig. l), which are readily detachable to facilitate dispersal (Frego and Staniforth 1985), were used to determine seasonal changes in water content and freezing and heat tolerance. Only freezing tolerance was determined for the terminal cladodes of 0. polyacanrha (5-13 cm long, 4-10 cm across, and about 1 cm thick), which are larger than those of 0 .…”

“…It is possible that the present northern limit may simply be a result of such migration patterns. This species is also reported to occur on south-facing rocky shores of waterways in the boreal forest of southern Manitoba (Frego and Staniforth 1985). A high freezing tolerance and the ability to rapidly cold acclimate would enable 0. fragilis to establish in cold climates.…”