The boreal forest in North America owes much of its floristic and faunistic diversity to periodic fires ignited by lightning and by man since he appeared on the scene. The indirect evidences of buring in vegetation and soils, and recent direct observations of fires, are reviewed. Fire is shown to exert a significant effect on vegetational composition, on soil chemical properties and thermal regime, and on animal populations through the particular mosaic of habitats created. In turn, fire is itselt influenced by the nature of geographic landscape ecosystems according to their surface forms, accumulations of organic materials, and susceptibility to drought. It is concluded that fire should be viewed as a normal ecological process in the boreal forest. A thorough understanding of its long-term role in terrestrial and aquatic ecosystems is needed.
The effects of forest fires on some physical and chemical soil properties in the Black Lake region of northern Saskatchewan were determined on four burned-over areas, and results were compared with corresponding mature forested areas. Formerly, two of the burns supported jack pine forests and the other two supported black spruce forests.Temperatures, water infiltration rates, and erosion were the physical soil properties considered. Temperatures at the 1-inch and 3-inch depths in the burned-over soils averaged 10.5 F and 9.7 F respectively, higher than soil temperatures under mature forests. Water infiltration rates, compared at one location only, were not impaired. Erosion following fire was slight.Soil nutrients and soil pH were the chemical properties considered. Total exchange capacity decreased on three of the four burns, when compared with mature forests. Exchangeable hydrogen was reduced and available phosphorus increased on each of the burned-over soils. Exchangeable calcium increased on three of the four burned-over soils. No conclusions could be reached for alterations in total nitrogen, exchangeable magnesium, potassium, and sodium. On the burned-over areas acidity decreased at 1-inch depths and 3-inch depths.Forest fire influence both chemical and physical soil properties on the winter range of barren-ground caribou in northern Saskatchewan. These alterations may be important in changing the habitat to one less favorable for the germination and growth of preferred food plants.
Data on the growth rate of lichens are essential to the understanding of the carrying capacities of rangelands used by caribou and reindeer in Canada. Recent Russian literature suggests fruticose lichens have three growth stages. The first stage is one of podetium accumulation. During the second stage, accumulation rate and decomposition rate are similar, while, in the third stage, decomposition of the Podetium is more rapid than accumulation. In the Taltson River region, the average annual linear growth rates of Cladonia alpestris, Cladonia mitis, and Cladonia rangiferina as determined by dividing the number of joints on the living podetium by the height of the living portion of the podetium, are 3.4, 3.6, and 4.1 mm, respectively. These rates are less than those reported from Russia, Newfoundland, and northern Saskatchewan.
The distribution and general ecology of 249 macrolichen taxa is described for 230 000 km2 of coniferous forest, open fens, and alpine terrain along the Mackenzie River in the District of Mackenzie, Northwest Territories, and the Peel River, a major tributary which rises in the Yukon Territory. Permafrost plays a major role in determining the plant communities that are present. Fire and man-made disturbances initiate succession. There are 45 new reports for the District of Mackenzie and 30 for the Yukon. Of the taxa, 86% are found in Europe, Asia, and North America, 9% are known from Asia and North America, whereas only 4% are restricted to North America. Pilophorus robustus is new to Canada. High mountains in the western part of the area, generally nonglaciated during the Wisconsinian, support a flora that contains many Arctic and Arctic–Alpine taxa. Amphi-Beringian species occur primarily in the north.
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