PARENT SESSION
Contributed Oral Session 130: Forest Infestations and Mortality
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal

Mortality among mature sugar maple and yellow birch trees following selection harvest in the northern hardwoods of Quebec, Canada.

Hartmann, Henrik¹, Messier, Christian ¹, Beaudet, Marilou ¹, ¹ Université du Québec à Montréal, Montréal

ABSTRACT- Selection cutting is the most widely used type of harvest in the northern hardwoods of Quebec. Yield and rotation length estimates are based on experimental studies but recent investigations in stands under industrial management revealed higher than expected post-harvest mortality rates, leading to longer rotations than anticipated. Since mortality is a critical process of forest ecosystem dynamics, higher mortality rates also imply higher anthropogenic ecosystem disturbance. However, the underlying dynamics of these processes need further elucidation. The objectives of our study are to determine (1) if mortality rates, 10 years after harvest, vary with stand and site-specific characteristics allowing to identify sites with high mortality risk (2) if the probability of mortality of trees can be predicted from their recent history of radial increment, and if these probability estimates vary with tree vigor based on current tree classification guidelines, and (3) if harvest-induced disturbances affect the post-harvest radial increment of residual trees and their probability of mortality. The present study was undertaken in the deciduous forest of western Quebec. Since our study is at its very beginning, only preliminary results are available. We use different data sources (forest inventury, stem-mapped plots) at different scales (tree, stand) to investigate mortality rates and dynamics as well as spatial relationships between harvest-induced disturbances and the radial growth response and probability of mortality of residual trees. Mortality rates varied with site and stand specific variables (e.g. stand density, drainage) only for sugar maple but not for yellow birch. However, less vigorous yellow birch has more open crowns and shows more symptoms of dieback than vigorous trees but there is no such relationship for sugar maple. We found evidence for the persistence of machinery related disturbance even 11 years after harvest. In these stands, overall post-harvest mortality is close to natural mortality rates. Yet, higher mortality rates in the first 5 years after harvest corroborate results of other studies showing increased mortality for this period. Further analyses will be undertaken in the next few months in order to estimate mortality probabilities as a function of recent radial increment.

Key words: Selection system, Logging impact, Site characteristics, Stand characteristics