False rings in jack pine and black spruce trees from eastern Manitoba as indicators of dry summers

Abstract

False rings (FRs) are a tree-ring anomaly that can be used to better understand tree growth and potentially reconstruct past climatic events. The main objective of this study was to explore the association between FRs and climate, especially drought occurrence. Sampling was conducted in Nopiming Provincial Park. Wood cores were extracted from jack pine ( Pinus banksiana Lamb.) in five stands and from co-occurring black spruce ( Picea mariana (Mill.) BSP) in three of these stands. After cross-dating, earlywood, latewood, and total ring width were measured on all cores. All FRs were identified, and their position within a tree ring was determined. Both species showed similar radial growth and FR patterns. Jack pine and to a lesser extent black spruce both showed abundant FRs in the juvenile period. Springs with cool and snowy conditions and summers with severe drought were associated with a higher frequency of FRs. These anomalies could be formed partly in response to timing of the start of the growing season and to conditions during that growing season that lead to interruption and subsequent resumption of normal growth. Jack pine radial growth was found to be more sensitive to precipitation, whereas that of black spruce was more sensitive to temperature.