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Old cedars and dendroclimatology

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Even though islands are frequently affected by fires, a number of islands in Lake Duparquet have managed to remain unburned for thousands of years. Absence of fires and the presence of slow growing conditions have allowed certain cedars to attain venerable ages, approaching 1,000 years. Discovery of these specimens provided a means of reconstructing climate changes over the last 800 years, using fluctuations in radial growth of these old cedars (fire history map; Archambault and Bergeron, 1992). Periods of good growth correspond to hot and humid conditions, whereas periods of slow growth are associated with cold and dry conditions. The slow growth between 1600 and 1850, corresponds to the period known as the "Little Ice Age" ; a period of better growth since 1850, is possibly associated with global warming. This recent warming, associated with an augmentation in summer precipitation, explains the marked decrease in fire frequencies during the last 100 years (fig. 1; Bergeron and Archambault, 1993). Moreover, the presence of the dwarf mistletoe (Arceuthobium pussillum), a parasite of black spruce occurs on some islands that have not burned for a very long time.

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Fig. 1. a) Fire occurence in lake Duparquet area, b) Burned area on shore perimeter and c) Burned area on islands, d) Long term change of white cedar radial growth from lake Duparquet islands, e) Summary of global deviation to average temperature for the period 1680-1990 according to the Intergovernmental Expert Group for the Study of Climate Change.



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