FROST RINGS AND WHITE EARLYWOOD RINGS IN PICEA MARIANA TREES FROM THE BOREAL PLAINS, CENTRAL CANADA

Dendroecological analysis of tree-ring anomalies can facilitate better environmental reconstructions provided that conditions leading to their formation are well understood. White earlywood rings (WER) constitute an anomaly not previously described and, like frost rings (FR), occur often in boreal coniferous species in central Canada. The objectives of this study were i) to examine the distribution of FR and WER in black spruce trees, ii) to measure and compare tracheid dimensions in WER and control rings and iii) to investigate potential causes of WER formation. Sampling was conducted in two regions of western Manitoba. At each of four sampling sites, ten black spruce trees were selected for stem analysis. Results indicated that FR were mainly formed in the smaller diameter, thin barked portion of the stem up to a height of 16m, whereas WER were almost uniformly distributed along the stem. Tracheids were measured for WER occurring in 1916, 1943 and 1970 and WER were found to have earlywood tracheids with significantly thinner cell walls compared to control rings. It is speculated that the formation of WER may be related to reduced hormone and carbohydrate availability in the early growing season. The potential linkage between WER and frost events, or other agents of defoliation, prior to ring formation merits further investigation.