Changes in the Northern Limit of Spruce at Dubawnt Lake, Northwest Territories

Аннотация

Larsen described the treeline west of Hudson Bay and particularly at Ennadi, Yathkyed and Dubawnt Lakes, as clumps of spruce, relict from a former more northerly distribution. ... Evidence collected by us in 1966 on the Dubawnt River system on the Mackenzie-Keewatin border, indicates that the spruce trees are re-establishing themselves and have moved northward and closer to Dubawnt Lake during the past one hundred years. ... Larsen's view that spruce has not re-establsihed itself during the last half century does not apply at Dubawnt Lake, but may be true at the Ennadai and Yathkyed Lake regions. ... The known changes in the treeline in the Dubawnt Lake area can be summarized as follows: the south arm of the Keewatin Glacier left the lake area possibly from 7.5 to 7.9 thousands of years before the present or as late as 5.5 thousand years ago. By 4 thousand years ago, a closed canopy forest extended half way up the east shore of Lake Dubawnt, leaving fossil podzols. Individual clumps and trees probably extended further north. A southern retraction of treeline followed, but a re-extension took place c. A.D. 1100 at the "little climatic optimum". A southern retraction again occurred and by 1770 Hearne recorded dead stumps 20 miles north of the treeline. Around 1870, satisfactory growth conditions existed within 2 miles of the south end of Dubawnt Lake and a minor northward extension took place. Re-establishment of spruce by means other than layering occurred by 1931. Less favourable growth conditions may have begun again in 1960.