Historical evidence and climatic implications of a shift in the boreal forest tundra transition in central Canada

✍ Scribed by Timothy F. Ball

• Publisher: Springer
• Year: 1986
• Tongue: English
• Weight: 968 KB
• Volume: 8
• Category: Article
• ISSN: 0165-0009
• DOI: 10.1007/bf00139750

✦ Synopsis

The line that marks the boundary between the boreal forest and the tundra regions is a relatively abrupt line in central Canada and appears to reflect a clearly defined climate boundary. Research suggests that relatively small changes in the climatic conditions should result in a movement of the treeline. Such a movement was apparently reported in 1772 by Samuel Hearne based upon the observations of generations of Indians who had lived in the area. A map of his voyages indicates a tree limit that was further west in the north/south section of western Canada and further south in the east/west section of central Canada. This location and subsequent movement appears to be logical in relation to the climatic conditions that occurred in the region as a result of the Little Ice Age and the warmer conditions thereafter.

The treeline in central Canada indicates a transition from the boreal forest to the tundra and is clearly defined on the west side of Hudson Bay and less clearly defined on the Quebec side. The transition zone on the west side of Hudson Bay is relatively narrow and Larsen (1974) suggests that it is relatively easy to plot the edge of the 'trees' with an accuracy of -+ 25-30 km. He also points out that the region is particularly suitable for determining the effects of climate on the forest because the cdaphic factors of geology and topography are relatively homogeneous.

Bryson (1966) suggested that the southern limits of Arctic air in winter and summer correlated with the northern and southern limits, respectively, of the boreal forest in central Canada. In a paper that examined the seasonal location of the Arctic Front over North America, Barry found support for this correlation, particularly 'in northwest Canada where the forest tundra boundary is extremely sharp'. (Barry, 1967, p. 90).

Many researchers have studied the relationship between climate and the treeline. Most of these studies use biologic indicators, such as pollen, which tend to have an insensitivity that precludes the measurement of relatively short term changes in climate and the vegetative response. The problem in trying to reconstruct continuous records of climate so that an accurate pattern of the trend and degree of change can be determined stems from the different sources of evidence and methodologies involved. For example, the transition from the instrumental records to the historical records involves a change from the precise objective measurement to the subjective data of weather diaries, proxy data, and other phenological indicators. Along the treeline of North America the problem is exacerbated by the lack of instrumental data and a paucity of historical information. The result is that there is very little evidence to provide an accurate determination of the effects of relatively short term but dramatic changes of climate such as the Little Ice Age.