Estimating time since death of Picea glauca x P-engelmannii and Abies lasiocarpa in wet cool sub-boreal spruce forest in east-central British Columbia

A new method for studying stand disturbance regimes, which could be used alone or combined with other approaches (e.g., age class analysis, tree ring analysis, direct gap measurements), is presented. The method is a set of multiple regression models that estimate the year of death of trees on the basis of external characteristics (e.g., bark presence) and tree position (standing or down). The models were calibrated for Picea glauca (Moench) Voss x P. engelmannii Parry ex Engelm. and Abies lasiocarpa (Hook.) Nutt. trees with known dates of death determined from permanent sample plot data obtained from the Aleza Lake Research Forest, in east-central British Columbia, in the wet cool foothills of the Rocky Mountains. The P. glauca x P. engelmannii model explained 95.3% and 79.3%, and the A. lasiocarpa model explained 81.2% and 78.2%, of the variation in years since death for standing and down trees, respectively. The models were validated by an independent sample of dead trees, where the model estimate was compared with year of release determined from tree ring cores in subordinate understory trees. The two estimates were related (R-2 = 61.3%, for both species), indicating that the model provides acceptable estimates for year of death in the two species. This approach may be particularly useful for determining year of death for trees that do not have subordinate individuals that release following overstory mortality.