Standing dead trees and their decay-class dynamics in the northeastern boreal old-growth forests of Quebec

In unmanaged boreal forests standing dead trees are an important component of stand structure, but knowledge on their quantities and dynamics is limited. We characterized the populations of standing dead trees, and modeled their decay-class dynamics in the northeastern boreal old-growth forests of Quebec, Canada. Using 40 m × 400 m plots, we sampled five Picea mariana-dominated, five mixed P. mariana-Abies balsamea, and five A. balsamea-dominated stands. We classified dead trees into five decay classes, extracted sample disks, and crossdated the year of death of 190 trees. Mean times since death in each decay class were used to construct a matrix model for transition dynamics between the classes. Standing dead trees were abundant in all stands, but with large between-stand variation (density, 89.4–229.4 trees ha−1; volume, 8.3–49.2 m3 ha−1). On average, dead trees represented 21.4% of the number of all standing trees in P. mariana-dominated stands, 34.0% in mixed P. mariana-A. balsamea stands, and 33.7% in A. balsamea-dominated stands. Modeling indicated lower transition rates between decay classes for P. mariana than for A. balsamea. Half-life as standing dead trees was 35–40 years for P. mariana and 30–35 years for A. balsamea. Our results showed that standing dead trees are an important and long-lasting structural component of the stands studied. To retain stand structural complexity and the associated species diversity in managed forests of this region, strategies for managing standing dead trees need to be developed.