Light Rings in Subarctic Conifers as a Dendrochronological Tool

Abstract

Light rings are characterized by one or a very few latewood-cell layers, an indication of shortened growing seasons, and are particularly frequent in black spruce (Picea mariana (Mill.) BSP) at the treeline in Québec. The construction of a light-ring chronology spanning the period AD 1398–1982 showed that the highest frequency (>25%) of light rings among 160 trees and krummholz occurred in 1593, 1620, 1634, 1784, 1816, 1817, 1853, 1969, and 1972. These diagnostic rings be a useful cross-dating tool for dendroecologists working with living and dead krummholz with a low-growth variability. About two-thirds of the 65 light-ring years coincide with years (or triads) of major volcanic eruptions. The climatic conditions (low temperature) occurring at the end of the growing season, in part induced by the climatic effect of volcanism, seem to initiate light rings.