False rings in the white pine (Pinus strobus) of the Outaouais Hills, Québec (Canada), as indicators of water stress

False rings are intra-annual bands of wood darker than the adjacent wood. They have been reported for several species of Pinus, although not previously for white pine (Pinus strobus L.). In southwestern Quebec, false rings were found to be very common among white pine, an indication that the species is sensitive to water stress in this region. False rings were analyzed on 110 trees from 12 mature stands. A false ring database was built, and false ring chronologies were established and analyzed for two groups of sites (rocky outcrops and shallow soils). The years 1955, 1959, and 1988 were those with the highest occurrence of false rings (62% to 90% of all stems). Factors predisposing false ring formation include the cambial age of stems bearing false rings and drainage conditions (dry rocky outcrop sites). Triggering factors were climatic events occurring during the four-month growing season. Years with low precipitation correlate with years featuring a higher occurrence of false rings. High summer temperatures may also be involved, as they explain the distribution of false rings in all frequency classes. In areas where they form, false rings in white pine can be used as diagnostic rings and as indicators of water stress.