The evolution and maintenance of white spruce woodlands on the Mackenzie Delta, N.W.T., Canada

White spruce forests on the most elevated surfaces of the Mackenzie Delta are dying out and are being replaced by open spruce/lichen-heath or spruce/bog woodlands. Soil profiles indicate that these woodlands have not received flood-deposited sediments for many years. The active layer is only 20 to 50 cm deep by mid-summer, and the organic soils are colder and more acidic than soils under white spruce forests flooded during spring ice breakup in 1961, 1972, and 1982. Spruce regeneration is limited to those stands that are flooded periodically, have moderately-closed canopies, and have a ground cover of herbs rather than feathermosses and lichens. It is proposed that a decrease in flood frequency is primarily responsible for the poor regeneration of white spruce on the most elevated delta surfaces. Spruce woodlands on the delta could succeed to tundra vegetation if present fluvial regimes continue.