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Analysing the growth dynamics of mixed stands composed of balsam fir and broadleaved species of various shade tolerances

Pothier, David
Forest ecology and management 2019 v.444 pp. 21-29
Abies balsamea, allometry, cutting, mixed stands, shade tolerance, trees, understory
The presence of shade-tolerant trees in the understory of mixed-species stands could produce a state of reverse growth dominance, but the growth dynamics between species has been little studied. Here, an analytical framework that was based upon the concepts of growth dominance (GD) and competition mode was used to study the growth dynamics of mixed-species stands. Because shade tolerance is an important trait that influences stand growth dynamics, stands in this study were composed of balsam fir (Abies balsamea [L.] Mill.) and one of four broadleaved species that together form a shade-tolerance gradient. The relative contribution of trees to entire stand growth was determined and then analyzed as a function of their size, species and allometric expectations based upon size-symmetric competition. Balsam fir trees were generally smaller than companion broadleaved species in each type of mixed stands. The small sizes and vigorous growth rates of balsam fir trees were typical of mixed stands that were characterized by negative GD values, i.e., reverse growth dominance. The low number of stands that had positive GD values was generally characterized by higher growth of broadleaved species compared to balsam fir. The growth rates of balsam fir as a function of its allometric expectations play a key role in explaining GD values of mixed-species stands, whereas that of broadleaved species is apparently insensitive to GD values. The concept of stand growth dominance, together with the prevailing mode of competition between trees, identified tree groups that are poor contributors to stand growth. This information can be used in selecting trees for harvest during partial cutting operations, if the purpose of the treatment is to maximize growth of residual stands.