Effects of Planting, Vegetation Management, and Pre-Commercial Thinning on the Growth and Yield of Lodgepole Pine Regenerated after Harvesting in Alberta, Canada

Abstract

A large long-term field trial was established in the Upper and Lower Foothills sub-regions of the Canadian boreal forest to monitor the effects of planting, vegetation management, and pre-commercial thinning on the development of lodgepole pine stands following harvesting. Data collected at the end of the trial’s regeneration phase, 17 to 20 years after its establishment, were tested for treatment effects and projected to rotation age. Planting generally improved stocking and increased projected growth and yield of lodgepole pine. On modal sites, planted trees were often greatly outnumbered by natural regeneration; however, on others, typically with either poorer or richer soils, satisfactory restocking was not achieved without planting. Control of competing vegetation by herbicide application facilitated regeneration of pine where it was otherwise difficult or impossible on sites with excessive herbaceous or hardwood competition. Pre-commercial thinning accelerated the growth of individual trees and was projected to shorten rotations in dense stands. Responses to the treatments varied depending on environmental factors. Particular treatments may be effective to meet management objectives under some site conditions but unnecessary or counterproductive elsewhere.

Lodgepole Pine and White Spruce Thinning in Alberta―A Review of North American and European Best Practices

“…To this end, several pre-commercial [32,33] and commercial [19] thinning research trials in lodgepole pole pine have been recently initiated, largely focused on the foothill subregions in Alberta and following a more robust statistical procedure. However, the information on thinning of lodgepole pine stands gathered from current experiments in Alberta does not provide a sufficient baseline for developing a thinning practice for the species.…”

Thinning Increases Individual Tree Growth While Reducing the Growth Heterogeneity of Lodgepole Pine

“…However, there is a pending midterm timber supply shortage in Alberta due to past natural disturbances and a shrinking forestry land base giving rise to recent research on the thinning response of lodgepole pine. Recent studies have shown the effect of thinning (both pre-commercial (PCT) and commercial thinning (CT)) on the growth and productivity of lodgepole pine at the stand level [24][25][26]. However, the thinning response of individual trees and their growth dynamics over time has not been addressed intensively, especially with different thinning intensities and combinations of PCT and CT. Thinning intensities are one of the most important factors affecting growth response after thinning [27][28][29].…”