Lodgepole pine and trembling aspen mixedwoods: Growth and yield within 22 to 39 year old pine plantations of northern interior British Columbia

Abstract

Six lodgepole pine plantations located in the Sub Boreal Spruce (SBS) biogeoclimatic zone of northern interior British Columbia were chosen to study the impacts of aspen competition on the growth and yield of lodgepole pine. The six sites from four different zonal variants (dw2, dw3, dk1 and mc2) ranged in age from 22 to 39 years. Site preparation treatments occurred on all sites: drag scarification, disking, or a broadcast burn post clear-cut logging. Four of the sites received at least one operational brushing treatment for aspen (chemical or manual). At each site, 30 pine trees (CP) were selected as plot centres to represent the observed range of aspen competition. A series of nested plots up to 7.98 m radius was used to evaluate effects of % pine composition on stand density and stand volume using linear and non-linear models. At five of the six sites total volume was unchanged across the range of pine composition. The growth interaction between aspen and pine was found to be a linear relationship of competitive reduction where pine volume, basal area and merchantable volume was highly sensitive to any increase in aspen density or composition.Keywords: Lodgepole pine, aspen, boreal mixedwoods, growth and yield, merchantable volume, basal area, competition. RÉSUMÉSix plantations de pin lodgepole situées dans le sud de la zone biogéoclimatique de l' épinette subboréale (SBS) dans la région nord de l'intérieur de la Colombie-Britannique ont été choisies pour étudier les effets de la compétition par le tremble sur la croissance et le rendement du pin lodgepole. Les six plantations établies dans quatre variantes zonales (dw2, dw3, dk1 et mc2) étaient âgées de 22 à 39 ans. Des travaux de préparation du site ont été réalisés sur tous les sites : scarifiage par traînage et au moyen de disques ou encore par brûlage contrôlé après coupe à blanc. Quatre des six plantations ont fait l' objet d'au moins un traitement de débroussaillage (chimique ou manuel) afin de contrôler le tremble. Dans chaque plantation, 30 pins (CP) ont été choisis comme centres de parcelles-échantillons destinées à étudier l'importance de la compétition par le tremble. Une série de parcelles regroupées jusqu'à un rayon de 7,98 m a été utilisée pour évaluer les effets du pourcentage de la composition en pin sur la densité et le volume du peuplement en se servant de modèles linéaires et non linéaires. Pour cinq des six plantations, le volume total est demeuré inchangé, peu importe la composition en pin. L' effet de l'interaction entre le tremble et le pin sur la croissance se traduit par une relation linéaire où le volume du pin, sa surface terrière et son volume marchand diminuaient significativement avec tout accroissement de la densité ou de la composition en tremble.

Lodgepole pine and trembling aspen competition: Neighbourhood studies within 22 to 39 year-old pine plantations of northern British Columbia

“…Nearest neighbour assessments were used to explore the aspen -pine tree level competition providing linkage to the previously published stand level forest productivity results (Harper 2015). Impacts to pine stand volume and basal area due to increases in aspen composition and density were noted at all six sites (Harper 2015).…”

“…Aspen density ranged from 0 to 15500 trees/hectare (tph) and pine density from 100 to 8900 tph. Stand canopies were dominated by pine, aspen or a mix of the two with a total density from 1350 to 18100 tph (Harper 2015). Centre pine DBH and height declined with density at four of the six sites (BE and CC were the exceptions) with linear models used to describe the site-dependent tree size decline (Table 3).…”

“…The following methods are a shorter version of those in Harper (2015). Six pine plantation sites were selected during the summers of 2013 and 2014, all located within the SBS zone of British Columbia (Table 1).…”

“…Overtopping aspen has been shown to influence the growing conditions of understorey trees through impacts on suggest aspen threshold densities exist for unimpeded pine growth appear to contradict generally established principles of forest dynamics where tree growth is inversely related to density (Zeide 2002, Pretzsch 2009). Although total stand productivity may remain unchanged with increased levels of aspen, there is a significant decline in pine component growth and yield (Harper 2015) and several studies have documented diameter growth impacts in young pine (Newsome et al 2008, Harper et al 2009). Most published studies have focused on early establishment performance prior to canopy closure based on measurements of aspen competition in young pine from small plots.…”

“…In this paper, tree-level competition results are presented as a companion study to Harper (2015), where stand growth and yield information were presented from a retrospective study of six post-free growing SBS pine plantations. The objectives of this paper are to provide a linkage between stand growth and yield and individual tree-based measures of competition through a focus on understanding interspecific treelevel competition between aspen and pine neighbours.…”