VEGETATION COMMUNITIES AND PLANT-DISTRIBUTIONS AND THEIR RELATIONSHIPS WITH PARENT MATERIALS IN THE FOREST-TUNDRA OF NORTHWESTERN CANADA

Vegetation data from 95 sites and chemical and textural data for paren t materials from 98 sites in subarctic northwestern Canada were analyz ed by ordination, classification, and statistical techniques. A discon tinuity in plant species occurrence, vegetation communities, and paren t materials takes place near the southeast/northwest boundary north of Great Slave Lake. Till parent materials in the forest-tundra show reg ional differences in nutrient concentration and texture that correlate with the local bedrock. Northwestern tills, as a group, are markedly richer in nutrients and finer-textured than Shield tills, with much hi gher levels of cation exchange capacity, nitrogen, potassium, calcium, magnesium, hydrogen, and organic carbon, and more silt and clay than Shield tills. Plant species occurrence and vegetation community compos ition show strong relationships with soil pH, moisture, texture, and l atitude. The northwest is characterized by calciphilic white spruce, D ryas, legume, and bryophyte communities, and high species diversity, o n basic loamy Cryosols. The southeast is characterized by acidophiles and widespread generalist black spruce, ericad, and lichen communities , and low species diversity, on acidic loamy sand and sandy loam Bruni sols.