. The Canadian field-naturalist. h s1 .:V: Figure 2a. A small grove of white spruce in a drainage line at the south end of Artillery apparent that the trees survive in sheltered spots created by rocky bluffs and hills along the McDonald Fault. It is conceivable that timberline swings to the south from Artillery Lake eastward because here, too, till rather than outcropping bedrock is the dominant sur- ficial geological formation. The term "forest border" is a more mean- ingful bioclimatological reference than the "limit of trees", since this latter does not coin- cide
. The Canadian field-naturalist. h s1 .:V: Figure 2a. A small grove of white spruce in a drainage line at the south end of Artillery apparent that the trees survive in sheltered spots created by rocky bluffs and hills along the McDonald Fault. It is conceivable that timberline swings to the south from Artillery Lake eastward because here, too, till rather than outcropping bedrock is the dominant sur- ficial geological formation. The term "forest border" is a more mean- ingful bioclimatological reference than the "limit of trees", since this latter does not coin- cide as closely with the apparently limiting macroclimatic parameters as does the forest border. It appears that the climatic transition across the Great Slave Lake-Artillery Lake forest- tundra transition zone is more abrupt than farther to the east (McFadden 1965). Along Pike's Portage, the zone of transition from forest to tundra is much compressed over the transition in, for example, the Ennadai Lake area, environmental gradients must be steeper, and southern boreal and tundra components of the vegetation range much closer to one another if they do not actually overlap (which many do). The nature of the substrata at least helps account in part for the increased import- ance of white spruce in this area as compared to the role of white spruce in the timberline forest in areas to the east. White spruce fails to occupy the till-dominated terrain beyond the south end of Artillery Lake because, north- ward, there is both an absence of nutrients. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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