Early development of tended mixtures of aspen and spruce in western Canadian boreal forests

Bokalo, Mykola; Comeau, Philip G.; Titus, Stephen J.

doi:10.1016/j.foreco.2007.01.038

Cited by 43 publications

(49 citation statements)

References 30 publications

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“…This is consistent with high natural mortality that has been observed in young aspen stands (e.g., Bokalo et al 2007) and exemplifies the self-thinning ability of this pioneer species (Perala 1990). Our results indicate that PCT lowered aspen mortality, while greatly improving spruce survival.…”

Section: Mortality and Browsingsupporting

confidence: 87%

“…Although the response was detected later on conifers, their DBH increment and height growth doubled without affecting aspen DBH response, thereby confirming our third hypothesis. The height growth response of conifers was only detected after 10 years; such a delay could explain why Bokalo et al (2007) found no effect of aspen spacing on white spruce height after 3-4 years in western Canada. Furthermore, the 100% decennial gain was lower than the 200-300% gains that were reported for understory balsam fir in the Saguenay-LacSaint-Jean region of Quebec (Prévost and Gauthier 2012).…”

Section: Growthmentioning

confidence: 98%

“…The widespread presence of aspen on the landscape and the increasing protection of conifer advance growth in current management practices (Groot et al 2005) should favour development of this type of even-aged stratified mixture along successional pathways (Smith et al 1997). In such stands, PCT has traditionally prioritized conifers over early successional broadleaved species (e.g., Pitt and Bell 2005), whereas growing species in mixtures has received little attention so far (e.g., Bokalo et al 2007, Kabzems et al 2016. For example, Rice et al (2001) suggested that PCT be considered as a means of increasing aspen diameter and allowing conifer ingress to be established within the resultant openings.…”

Section: Introductionmentioning

confidence: 99%

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Precommercial thinning of overtopping aspen to release coniferous regeneration in a boreal mixedwood stand

Prévost

Charette

2017

The Forestry Chronicle

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We used precommercial thinning (PCT) to accelerate natural succession in an 8-year-old, even-aged stratified mixture, in which trembling aspen (Populus tremuloides) overtopped a dense understory of balsam fir (Abies balsamea) and spruce (Picea mariana, P. glauca). In addition to an unthinned control, we applied three residual aspen spacings (2.5, 3.0 and 3.5 m) while retaining all understory conifers, and a 3.0-m spacing retaining only small conifers (<1/3 of the aspen crop tree height). PCT improved survival of spruce, increased diameter growth of aspen by 90% and doubled diameter and height growth of conifers, without differences among spacings or between levels of conifer retention after 10 years. The level of conifer retention did not affect aspen growth response, but appeared to influence the occurrence of browsing on aspen and balsam fir. Retaining only small conifers decreased regeneration density of balsam fir in favour of abundant vegetative reproduction of red maple (Acer rubrum) and beaked hazelnut (Corylus cornuta). Live crown characteristics and stand structure indicate that thinning caused a shift from overtopping of aspen to an intimate mixture of species sharing the growing space. This study confirms PCT as a means of accelerating natural succession in a boreal mixedwood stand, thereby securing the coniferous component at the early stage of development.Key words: ecosystem-based forest management; hardwood conversion; stratified species mixture; precommercial thinning; live crown characteristics. RÉSUMÉNous avons utilisé l' éclaircie précommerciale (EPC) afin d'accélérer la succession naturelle dans un mélange équien stratifié de 8 ans, dans lequel le peuplier faux-tremble (Populus tremuloides) surplombait une dense régénération de sapin baumier (Abies balsamea) et d' épinette (Picea mariana, P. glauca). En plus d'un témoin non éclairci, nous avons appliqué trois espacements résiduels entre les trembles (2,5, 3,0 et 3,5 m) en conservant tous les conifères du sous-étage, et un espacement de 3,0 m en conservant seulement les petits conifères (<1/3 de la hauteur du tremble éclairci). L'EPC a amélioré la survie de l' épinette, augmenté la croissance en diamètre du tremble de 90% et doublé la croissance en diamètre et en hauteur des conifères, sans différences entre les espacements ou entre les niveaux de rétention des conifères après 10 ans. Le niveau de rétention des conifères n'a pas affecté la réponse de croissance du tremble, mais a semblé influencer la fré-quence du broutement sur le tremble et le sapin. La rétention des petits conifères seulement a diminué la densité de la régénération de sapin au profit d'une abondante reproduction végétative d' érable rouge (Acer rubrum) et de noisetier à long bec (Corylus cornuta). Les caractéristiques des cimes vivantes et la structure du peuplement indiquent que l' éclaircie a amené le peuplement à passer d'une dominance du tremble à un mélange intime d' espèces se partageant l' espace de croissance. Cette étude confirme que l'EPC est un moyen d'ac...

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Section: Mortality and Browsingsupporting

confidence: 87%

Section: Growthmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Precommercial thinning of overtopping aspen to release coniferous regeneration in a boreal mixedwood stand

Prévost

Charette

2017

The Forestry Chronicle

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“…Early tending, such as various PCT methods, usually show a positive response for the future yield of target tree species (Johansson 1996;Bokalo et al 2007;Rytter and Werner 2007;Thiffault and Roy 2011;Uotila and Saksa 2014). In general, PCT could also have a long-term impact on the ground vegetation cover since high stocking is a severe limitation due to the reduction in light to the ground and the stocking is more important than the canopy species composition per se.…”

Section: Introductionmentioning

confidence: 99%

Scenario analysis of planting density and pre-commercial thinning: will the mixed forest have a chance?

Holmström¹,

Hjelm

Karlsson³

et al. 2016

Eur J Forest Res

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In the establishment phase, several management alternatives could be applied that affect the species composition of the future stand. In this study, tree seedling data from experiments with planted Norway spruce (Picea abies L. Karst) and naturally regenerated species, mainly Silver birch (Betula pendula Roth), were used for six simulated pre-commercial thinning (PCT) scenarios. The scenarios included both monocultures and mixed stand alternatives with various initial spacing of the planted Norway spruce (0, 1600 or 2800 seedlings) and selection of main stems based on relative heights. Further stand development and individual tree growth were simulated until final harvest. Potentially, based on findings of the seedling measurements, the stands could be mixed with five to six species, but the browsing pressure from ungulates reduced this possibility since the height growth for all species except Norway spruce was highly affected by browsing. The simulated mixtures had a small variation between the PCT scenarios for the maximum mean annual increment (about 10 %). Although the growth was similar for Norway spruce, the proportion of birch in the final stands differed from 3 to 21 % between treatments and none of the highdensity planting treatments generated a mixed Norway spruce-birch forest at the time of final felling.

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“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Kabzems

Bokalo

Comeau

et al. 2015

Forests

Self Cite

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Intimate mixtures of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) are a key feature of western Canadian boreal forests. These mixtures have the potential to produce high yields of merchantable fibre and provide numerous ecological services. Achievement of this potential has been difficult, and often expensive, to realize as a regeneration goal in managed forests. We report 21 to 25 year results of managed mixtures on two study sites where the white spruce was planted, and the density of aspen natural regeneration manipulated within five years of the stand initiation disturbance. On both sites, white spruce mortality did not increase with increasing aspen density. While height and diameter growth of white spruce declined with increasing aspen density, the effect was not entirely consistent across the two sites. Abrasion from aspen branches was the most common source of damage to spruce crowns. Mixed stands had greater merchantable volume production than pure spruce stands based on model projections. Application of aspen harvest at year 60, while protecting the spruce component for a second harvest entry at year 90, was projected to optimize combined yield for the mixedwood stands.

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Early development of tended mixtures of aspen and spruce in western Canadian boreal forests

Cited by 43 publications

References 30 publications

Precommercial thinning of overtopping aspen to release coniferous regeneration in a boreal mixedwood stand

Precommercial thinning of overtopping aspen to release coniferous regeneration in a boreal mixedwood stand

Scenario analysis of planting density and pre-commercial thinning: will the mixed forest have a chance?

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

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