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

Abstract

A significant portion of the harvested land base in western Canada is becoming old enough or entering a phase where thinning is a legitimate forest management option. A comprehensive review of the existing knowledge of commercial thinning (CT) treatments applied to pine and spruce-dominated stands in Alberta was conducted, with particular regard to the intensity, timing of interventions, method, and impacts on crop tree growth responses. Although the geographical focus of this review is Alberta, information on this topic is more complete in other areas of North America and Europe, where there is a long history of density management. In areas of eastern North America, our review revealed that CT from below, with tree removal levels from 27 to 43% of the basal area, could increase total merchantable wood produced from 11 to 60 m3 ha−1 over a rotation, depending on stand age and intensity of thinning. For Alberta conditions, and considering the risks, we conclude that commercial thinning basal area removal should be in the range of 25 to 40%, depending on a variety of factors such as species, wind firmness, and insect or disease incidence and risk. Thinning too aggressively and/or too late will increase the blowdown risk but the literature is fairly consistent in suggesting that live crown ratios should be >40% to maximize the chance of growth response and minimize the blowdown risk. In cases where stands are also threatened by stressors such as drought, wind, and insect or disease outbreaks, CT treatments likely offer the potential at limiting the overall risk, but localized knowledge and experience are critical. It is intended that the information presented may support ongoing and future research trials and growth and yield (G&Y) model development about potential CT treatments to apply and the likely results of practical application to commercial forestry.

Characterizing the speed and severity of mountain pine beetle spread under climate change with a mechanistic model

“…With the central projected values of N = 55 and s = 0.994, this fraction increases to 0.994 55 = 0.72, and so there are more susceptible trees for the beetles to consume on subsequent outbreaks with higher juvenile survival. However, note that these subsequent outbreaks and the juvenile survival after an outbreak depend strongly on forestry practices (Baah-Acheamfour et al 2023). Additionally, in regions that are no longer suitable for lodgepole pine, this parameter may decrease more dramatically, leading to smaller, lower vigor pine trees that may not be as suitable of hosts for MPB.…”

“…We set each discrete cell to have total tree density T = 1, which allows us to interpret the values of S t ( x ), j i , t ( x ), and I t −1 ( x ) or I t −2 ( x ) as fractions of the total tree density in the stand at location x . We note that typical stands of lodgepole pine in Alberta have densities of a few thousand stems per ha (Baah-Acheamfour et al 2023; Safranyik and Wilson 2006), and so with Δ x =16 m each cell contains approximately 50 to 500 trees.…”