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

Abstract

Six lodgepole pine plantations located within the Sub Boreal Spruce (SBS) biogeoclimatic zone of the northern interior of British Columbia were chosen to study the impacts of neighbourhood aspen competition on the growth of planted lodgepole pine (22-39 years old). At each site, 30 pine trees (CP) were selected as plot centres across the observed range of aspen competition. Information on the six nearest neighbours (NN) and a variety of competition indices were evaluated using linear and nonlinear models. Competition indices based on diameter or height relative to size were found as the best overall predictors of CP growth. Proximity of NN to the CP was found to be inconsistent as a predictor of growth. Individual pine and aspen NN modelling suggested aspen competition had the greatest influence on CP growth restriction. The results do not support aspen thresholds for optimizing the growth of free growing pine plantations. It is recommended that performance-based standards be developed that account for aspen competition intensity and provide guidance for the management of pine stand productivity.Key words: Lodgepole pine, aspen, boreal mixedwoods, nearest neighbours, stem volume, competition. RÉSUMÉOn a identifié six plantations de pin tordu situées dans la zone biogéoclimatique de l' épinette sub-boréale (Sub Boreal Spruce-SBS) dans le nord de la Colombie-Britannique intérieure pour y étudier l'impact de la compétition du peuplier environnant sur la croissance de pin tordu dans des plantations de 22 à 39 ans. À chaque endroit, 30 pins (CP) ont été choisis comme centre de placette de manière à représenter tous les niveaux de compétition par le peuplier. Les renseignements pris sur les voisins les plus rapprochés (NN) ont servi à évaluer une variété d'indices de compétition à l'aide de régressions linéaires et non linéaires. On a observé que les indices de compétition basés sur le diamètre ou la hauteur par rapport à la taille donnaient les meilleures prédictions de croissance du CP. La proximité des NN par rapport au CP a donné des prédictions de croissance qui se sont avérées incohérentes. Le modèle individuel pin et peuplier le plus rapproché laisse voir que c' est la compétition exercée par le peuplier qui limite le plus la croissance du CP. Les résultats ne permettent pas d' établir de seuils de compétition du peuplier pour optimiser la croissance des plantations de pins. Nous recommandons d' établir des normes de performance qui tiennent compte de l'intensité de la compétition par le peuplier et qui puisse servir de guides pour gérer la productivité des plantations de pins.

Effects of manual brushing on 10-year survival and growth of Douglas-fir in the mixed broadleaf – shrub complex of southern interior British Columbia

“…An alternative broadleaf competition measure that considers only broadleaf densities that are as tall as or taller than the crop trees, has been promoted to integrate with BC's free growing regulations (Heineman et al 2009;Newsome et al 2012). However, this approach does not consider the "smaller than" component of broadleaf competition, stand density and canopy composition (Harper 2017) and, effectively truncates the vertical dimension of the competition neighbourhood and the lower competition intensity distribution where maximum response is correlated (Wagner 2000;Simard et al 2005;Harper 2015).…”

“…Model (eq. 1) coefficients a and b respectively, can be used to estimate maximum size at low competition intensity or, highlight the rate of decline (Zeide 1989;Harper 2017). The model b coefficients (Table 4) indicated the decline in Douglas-fir diameter and height with increased broadleaf competition varied with treatment (brushed or untreated) and the competition measure used (CRH vs DRH).…”