Dendrochronological procedures improve the precision and accuracy of tree and stand age estimates in the western Canadian boreal forest

Abstract

Tree and stand age are critical information needed for understanding forest ecosystems. Tree age estimates are usually derived from ring counts, but these are not dendrochronological estimates unless procedures like ring measurement and cross-dating are used. Stand age is usually estimated from the mean ring count on a sample of trees. However, the oldest trees may better represent time since stand replacing disturbance. Using a forest inventory dataset from Manitoba, Canada, standard ring counts were found to underestimate true ring counts obtained using dendrochronological procedures for all black spruce (Picea mariana) trees, and older jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides) trees. Data from whole stand reconstruction plots for these same species demonstrated that mean ring counts from a sample of trees underestimate the time since last stand replacing disturbance, particularly for black spruce stands where ring counts at breast height were highly variable among individuals. The evidence in this study, and from similar existing studies, suggests that tree age, stand age, and time since last stand replacing disturbance are more likely underestimated than overestimated in the boreal forest of western Canada. Dendrochronological procedures can improve both the precision and accuracy of tree age estimates, but some aspects of age uncertainty may be irreducible, especially in older stands. Age uncertainty should be more widely acknowledged and where possible incorporated into forest science models.