Abstract
Careful logging around small merchantable stems (CLASS) is a partial cutting treatment that consists of the harvest of 70%–90% of the merchantable volume of an irregular coniferous stand. In this treatment, regeneration, saplings and small merchantable stems (DBH < 15 cm) are preserved and can continue to grow and develop into the dominant layer of the new stand. The aim of this project was to examine the effects of CLASS on the primary and secondary growth of branches, as well as on branch diameter in black spruce and balsam fir trees in the boreal forest of Quebec, Canada. Primary and secondary growth were measured on five branches per tree while branch diameter was analysed from 15 whorls distributed within the crown of the 48 black spruce and 48 balsam fir trees sampled. Branch primary and secondary growth significantly increased after CLASS in the lower part of the crown in both species, and both types of growth increased proportionally. These findings suggest that CLASS may delay crown recession as the lower branches tend to survive and grow for a longer period. However, although radial growth increased in the years post-CLASS, this did not significantly influence the final branch diameter and should not lead to lumber downgrade.
Highlights
In the province of Quebec, Canada, the application and study of the partial cutting treatment known as careful logging around small merchantable stems (CLASS) began in 1997 [1].Careful logging around small merchantable stems (CLASS) consists of the harvest of 70%–90% of the merchantable volume of an irregular coniferous stand, while regeneration, saplings—diameter at breast height (DBH) = 1.1–9.0 cm—and small merchantable stems (DBH = 9.1–15.0 cm) are preserved [1,2]
Branch primary growth increased after CLASS in the lower part of the live crown (Figure 3)
Annual primary growth in branches was ca. 28 mm in the lower two sections of the crown in CLASS trees, an increase of 20% compared to increments before CLASS
Summary
CLASS consists of the harvest of 70%–90% of the merchantable volume of an irregular coniferous stand, while regeneration, saplings—diameter at breast height (DBH) = 1.1–9.0 cm—and small merchantable stems (DBH = 9.1–15.0 cm) are preserved [1,2]. These residual protected stems can continue to grow and develop into the dominant layer of the new stand [3], which can be harvested in a shortened rotation. Stand thinning and partial cutting can increase space and light availability for the lower branches of the crown, thereby allowing residual trees to have a larger, more productive green crown for photosynthesis. A decrease in stand density can increase the radial growth of branches and produce larger branches that can affect
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