Late-Holocene light-ring chronologies from subfossil black spruce stems in mires of subarctic Québec
1997
Lavoie, Claude | Payette, Serge
Subfossil black spruce (Picea mariana [Mill.] B.S.P.) stems from permafrost mires in a 250-km² area at the arctic tree-line, near the eastern coast of Hudson Bay, were sampled for the construction of a long 'light-ring' chronology spanning the late Holocene. Thirty-three out of the 143 sampled spruce logs were ¹⁴C- dated yielding dates between 4580 and 1540 BP (3550-3010 cal. BC - cal. AD 377-649). Light rings (rings with thin-walled latewood cells or showing reduced latewood cell development) were numerous in all the studied stem discs and a set of 47 logs was successfully cross-dated. The cross-dated trees were used to build seven 'floating' light-ring chronologies located between c. 1200 cal. BC and cal. AD 500 (i.e., c. 1200 to 1000 cal. BC, 900 to 800 cal. BC, 700 to 400 cal. BC, 700 to 500 cal. BC, 100 cal. BC to cal. AD 300, cal. AD 50 to 450 and cal. AD 400 to 500). The large number of light rings in mire spruces appears to be associated with particular growth conditions in mires. A comparison of the frequency of light rings in extant spruce growing in mires and in dry-mesic sites showed that light rings were more common in peatland trees during this century. A delayed growing season caused by late peat thaw may possibly explain the difference between the two groups of sampled trees.
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