Criteria for estimating old growth in boreal mixedwoods from standard timber inventory data

This paper quantifies the amount of old growth forest in a boreal mixedwood landscape using the profile of tree sizes within stands. In the boreal mixedwood, successional trajectories exhibit significant variability, thereby making classification systems based on age or seral stage difficult to apply. Furthermore, a lack of extensive datasets on forest structure prevents comprehensive, multivariate classification of stands. Alternatively, we designated old growth status using the proportion (greater than or equal to 15%) of large trees (greater than or equal to 40 cm DBH) and the subcanopy/canopy tree ratios (>1.5). With these riteria, approximately 11.4% of the boreal mixedwood landbase within northeastern Alberta has an old growth structure. Proportionally, more old growth structure was found in aspen and white spruce mixedwood types, with lesser proportions in pure aspen and white spruce stands. Sensitivity analysis revealed that the tree size criteria was the most important driving variable in determining the amount of old growth. (C) 2000 Elsevier Science B.V. All rights reserved.