Long-term tree and stand growth dynamics after thinning of various intensities in a temperate mixed forest

Abstract In mixed forests, the presence of several tree species with various ecological characteristics leads to complex stand dynamics driven by the species-specific resource-use efficiencies that ultimately drive forest productivity. In this study, we applied the concept of stand growth dominance (GD), together with the growth rates of trees as a function of their allometric expectations (AE) under size-symmetric competition, as an analytical framework to identify the strong and weak contributors to the growth of thinned, mixed larch-spruce-fir stands. We used periodic surveys on approximately 2000 trees over a 25-year period following the application of four different intensities of thinning from below (TI): light (20% BA removed), moderate (30%), heavy (40%) and a control (0%). Results showed that stand GD became more negative with increasing TI and increased with increasing years since thinning except for the 20% TI, for which GD was always positive and had a small increase over time. Twenty-five years after treatment application, shade-intolerant larch trees contributed more to stand growth than their AE, particularly for medium- to large-sized trees, suggesting that they had acquired a large proportion of the available resources. Conversely, the shade tolerant coniferous and broad-leaved trees contributed less than their AE in all treatments, making them weak contributors to the overall stand growth. The analytical framework proposed in this study was useful to identify tree groups that were either weak or strong contributors to stand growth after partial cutting. This information can be used to help prioritise trees for removal during partial cutting operations and to identify successional pathways that will lead to the composition of the future stand.