Aspen competition affects light and white spruce growth across several boreal sites in western Canada

Abstract

The effectiveness of competition indices for predicting light transmittance and white spruce (Picea glauca (Moench) Voss) growth were examined across trembling aspen (Populus tremuloides Michx.) density gradients using sites from a long-term study of mixedwood growth and development in Alberta and Saskatchewan. Competition indices based on density (number of trees, basal area, and spacing factor), distance-dependent and -independent size ratio (Hegyi's and Lorimer's), and crown characteristics (crown volume, surface area, and cross-sectional area) were tested. Transmittance was effectively predicted by crown competition indices followed closely by aspen basal area and size ratio indices. Models of spruce growth indicated better results for stem volume compared with diameter or height. Competition alone accounted for less than 60% of stem growth variation, with basal area and transmittance providing some of the best models. The predictive ability of spruce growth was increased up to 93% by adding initial size as a second explanatory variable. In this respect, initial diameter was superior to initial height, crown volume, and surface area. Relationships between competition, transmittance, and spruce growth were found to differ significantly between geographical locations. These results suggest the need for local development of models relating tree growth to competition.Résumé : L'efficacité d'indices de compétition à prédire la transmittance de la lumière et la croissance de l'épinette blanche (Picea glauca (Moench) Voss) a été étudiée le long de gradients de densité de peuplier faux-tremble (Populus tremuloides Michx.) en utilisant les stations d'une étude à long terme de la croissance et du développement de peuplements mixtes en Alberta et en Saskatchewan. Parmi les indices de compétition testés, certains étaient basés sur la densité (nombre d'arbres, surface terrière et facteur d'espacement), d'autres étaient dépendants de la distance et indépendants de la taille relative (indices de Hegyi et de Lorimer) et d'autres considéraient les caractéristiques de la cime (volume, surface ou surface projetée de la cime). La transmittance était efficacement prédite par les indices de compétition basés sur la cime, suivis étroitement par les indices basés sur la surface terrière en peuplier et la taille relative. Les modèles de croissance de l'épinette donnaient de meilleurs résultats pour le volume de la tige que pour le diamètre ou la hauteur. Moins de 60 % de la variation de la croissance des arbres était expliquée par la compétition et les meilleurs modèles incluaient la surface terrière et la transmittance. L'efficacité à prédire la croissance de l'épinette a pu être augmentée jusqu'à 93 % en ajoutant la taille initiale comme deuxième variable explicative. À cet égard, le diamètre initial était meilleur que la hauteur initiale, le volume de la cime ou la surface de la cime. Les relations entre la compétition, la transmittance et la croissance de l'épinette étaient significativement différentes selon l'endroit. Ces résul...

Managed Mixtures of Aspen and White Spruce 21 to 25 Years after Establishment

“…The average height growth of white spruce between the last two assessments also demonstrates that there was a stronger environmental gradient created by the aspen densities at Bear Mountain which influenced white spruce height growth. Another source of variability results from the fact that density does not represent competition effects as well as other variables such as basal area that incorporate both density and tree size [12].…”

“…Quantitative comparisons of mixed and pure-species stands growing under similar site conditions are limited [11]. Several studies demonstrate that aspen can reduce growth of overtopped white spruce when it is present at densities above about 1000 st ha´1 (stems per hectare) [12,13]. Studies also indicate that reducing aspen densities can increase light levels [10,12] and spruce growth [14][15][16].…”

“…Several studies demonstrate that aspen can reduce growth of overtopped white spruce when it is present at densities above about 1000 st ha´1 (stems per hectare) [12,13]. Studies also indicate that reducing aspen densities can increase light levels [10,12] and spruce growth [14][15][16]. Treatments which reduce competition from aspen and other broadleaved trees can provide substantial increases in growth of white spruce [17,18].…”

Effects of aerial strip spraying on mixedwood stand structure and tree growth

“…Despite these potential benefits, several studies demonstrate that aspen reduces growth of overtopped white spruce when it is present at moderate or higher densities (Filipescu and Comeau 2007). Reducing aspen densities has been shown to increase light levels (Comeau et al 2006, Filipescu and and spruce growth (Lees 1966, Pitt et al 2004, Bokalo et al 2007, Pitt et al 2010.…”

Identifying and Characterizing Important Trembling Aspen Competitors with Juvenile Lodgepole Pine in Three South-Central British Columbia Ecosystems

“…We now know that within a relatively small geographic range in south-central British Columbia, aspen has greater ability to intercept light and to compete with neighbouring lodgepole pine in productive Sub-Boreal Spruce (SBS) ecological units than in the drier, less productive Interior Douglas-fir (IDF), and the even drier and colder Sub-Boreal Pine Spruce (SBPS) units [9][10][11][12]. However, competitive interactions have been highly variable between sites even within the same ecological unit, which Filipescu and Comeau [13] also observed for trembling aspen-white spruce (Picea glauca (Moench) Voss) interactions.…”