Abstract
We evaluated the effectiveness of commercial thinning mainly from below (CT; 0, 26%, 32% and 40% merchantable basal area removals) in meeting wood production demands and developing structural heterogeneity in a balsam fir (Abies balsamea (L.) Mill) and spruce (Picea spp.) stand. After 10 years, 32%–40% removals showed a 12%–18% increase in mean diameter and 27%–38% increase in gross merchantable volume (GMV) per tree compared to the unthinned control. At the stand level, all thinning treatments generated as much cumulative GMV (harvested volume + GMV after 10 years) and gross sawlog volume per hectare as the unthinned control. As for stand structure, eight out of nine thinned experimental units showed increased structural heterogeneity after 10 years, i.e., irregular, positively-skewed diameter distribution with an elongated right tail toward larger trees. The diameter distribution in the unthinned control became more symmetric, unimodal and regular over time, with fewer saplings than at the beginning of the experiment and lower density of larger trees compared to CT. Regeneration density and stocking were abundant in all treatments, largely dominated by balsam fir. Results indicate that thinning can be used to meet wood production objectives and help develop structural heterogeneity in this forest.
Highlights
The notion of using silviculture to help reach multiple management objectives in a sustainable manner has been evoked by generations of foresters
For Objective 2, we hypothesized that commercial thinning (CT) will increase: (a) the number of large trees; (b) the heterogeneity of the shape of the diameter distribution; and (c) the regeneration density and stocking compared to the unthinned control
Cumulative gross merchantable volume (CGMV) production was calculated as the sum of harvested merchantable volume and GMV after 10 years
Summary
The notion of using silviculture to help reach multiple management objectives in a sustainable manner has been evoked by generations of foresters. In North America, contemporary scientists that addressed this notion using old-growth attributes or structural heterogeneity in response to societal concerns over biodiversity are numerous [4,5,6,7,8] These references are examples of the use of natural variability concepts in managing ecological systems [9]. There is some evidence suggesting that thinning could serve as a tool to increase structural heterogeneity and help accelerate the development of old-growth structural attributes Studies where this was demonstrated include various forest types in North America and Europe [16,17,18,19,20,21,22]. For Objective 2, we hypothesized that CT will increase: (a) the number of large trees; (b) the heterogeneity of the shape of the diameter distribution; and (c) the regeneration density and stocking compared to the unthinned control
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