. The Canadian field-naturalist. 1991 Downing, Bayer, and Vitt: Rare and Disjunct Plants 377 120° NORTHWEST TERRITORIES. Ft. McMurray i STUDY AREA EDMONTON rO, CALGARY % â Figure 1. Location of Whitemud Falls Ecological Reserve "Study Area" in Alberta. (a) Erosional bedrock features. Rock expo- sures, cliffs and gullies adjacent to the Clearwater River provide a variety of microsites. Extremely dry rock faces are dominated by crustose lichens and drought- tolerant mosses, with a variety of vascular and non-vascular species in slightly moister environments, rock crevices
. The Canadian field-naturalist. 1991 Downing, Bayer, and Vitt: Rare and Disjunct Plants 377 120° NORTHWEST TERRITORIES. Ft. McMurray i STUDY AREA EDMONTON rO, CALGARY % â Figure 1. Location of Whitemud Falls Ecological Reserve "Study Area" in Alberta. (a) Erosional bedrock features. Rock expo- sures, cliffs and gullies adjacent to the Clearwater River provide a variety of microsites. Extremely dry rock faces are dominated by crustose lichens and drought- tolerant mosses, with a variety of vascular and non-vascular species in slightly moister environments, rock crevices or rock ledges. Deep gullies between bedrock ex- posures provide moist, cool conditions un- der which many boreal species flourish. Stunted Jackpine (Pinus banksiana Lamb) forests with a Bearberry (Arctostaphylos uva-ursi (L.) Spreng.) dominated understory are characteristic of very shallow sandy Brunisolic soils overlying bedrock. Lime- stone bedrock probably exerts a controlling influence on soil and water chemistry. (b) Dry sand plains and dunes. Jackpine com- munities with an understory characterized by Bearberry and lichens (Cladina spp.) occur on rapidly drained, mainly south or west facing sites. Green Alder (Alnus crispa (Ait.) Pursh), Bunchberry (Cornus canadensis L.) and Feathermoss (Pleurozium schreberi (Brid.) Mitt.) are understory as- sociates on moister sites (usually north and east facing slopes). (c) Sandy veneers and blankets mantling bed- rock. Dry aspen (Populus tremuloides Michx.) communities with an understory dominated by Bearberry, Prickly Rose and Wild Rose (Rosa acicularis Lindl., R. woodsii Lindl.) occur on rapidly to well drained thick sand blankets. These sites are not as dry as those occupied by Jackpine/ Bearberry/lichen communities on habitats (a) and (b). (d) Wet, poorly drained depressions, often with organic deposits over mineral soils. Two community types are common in this habi- tat: shrub-herb communities dominated by willows (Salix spp.)
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