Establishment of White Spruce Populations and Responses to Climatic Change at the Treeline, Churchill, Manitoba, Canada

Abstract

Studies on recruitment of white spruce from 1785 to present document the open forest succession at Churchill, Manitoba. Advance of trees onto land emerging from Hudson Bay due to isostatic uplift and permafrost intrusion has resulted in the development of two distinct systems. Open forest and forest-tundra are distinguished by seedling establishment, crown forms, and the growth patterns of the trees. Forest-tundra plots which demonstrate transition to open forest are documented. Where the two systems were established prior to the major climatic warming, they are resistant to invasion and there is little resultant change in the position of the treeline. Once started, population growth within the open forest system tends to be self generating and is little affected by subsequent climatic cooling. The mature open forest established prior to 1800 has shown a decline in seedling establishment during the climatic warming. These sites are characterized by extensive lichen cover.