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Long-term outcome of precommercial thinning in northwestern New Brunswick: growth and yield of balsam fir and red spruce

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A study was established between 1959 and 1961 to study the long-term responses of balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) to precommercial thinning. Three nominal spacings of 4 ft (1.2 m), 6 ft (1.8 m), and 8 ft (2.4 m) were compared with an unthinned control in a randomized complete block design with five replicates. At the time of thinning, natural regeneration averaged 16years of age, 8years after harvest. Although thinning had minimal effect on gross total volume production over a 42 to 44year observation period, actual spacings between 2.1 and 2.5m produced an average of 360m3·ha–1 gross merchantable volume (GMV), representing a 21% gain over unthinned stands. The same spacings produced quadratic mean diameters of 21 and 23cm, respectively, compared with 18cm in the unthinned stands. These size increases translated to individual stem volume gains of 33% and 62%, significantly reducing the age at which thinned stands would meet a specified minimum requirement for merchantability or habitat. The mean annual increment of GMV ranged from 6m3·ha–1·year–1 in unthinned stands, to more than 7m3·ha·–1·year–1 in the thinned stands, and had not yet culminated an average of 50years postharvest.

Une expérience a été établie entre 1959 et 1961 pour étudier la réaction à long terme du sapin baumier (Abies balsamea (L.) Mill.) et de l’épinette rouge (Picea rubens Sarg.) à la suite d’une éclaircie précommerciale. Trois espacements nominaux de 4pi. (1,2m), 6pi. (1,8m) et 8pi. (2,4m) ont été comparés à un témoin non éclairci dans le cadre d’un plan expérimental en blocs aléatoires complets comportant cinq répétitions. Au moment de l’éclaircie, huit ans après la coupe du peuplement, les arbres qui composaient la régénération naturelle avaient en moyenne 16ans. Quoique l’éclaircie n’ait eu qu’un effet minimal sur la production brute en volume total après une période d’observation de 42 à 44 ans, les espacements réels variant entre 2,1 et 2,5m ont produit un volume marchand brut (VMB) de 360m3·ha–1, ce qui représente un gain de 21% par rapport aux peuplements non éclaircis. Les mêmes espacements ont produit des diamètres moyens quadratiques de respectivement 21 et 23cm comparativement à 18cm dans les peuplements non éclaircis. Cet accroissement se traduisait chez les tiges individuelles par des gains en volume de 33% et 62%, ce qui réduit significativement l’âge auquel les peuplements éclaircis atteindraient les dimensions minimales requises pour avoir une valeur commerciale ou servir d’habitat. L’accroissement annuel moyen en VMB variait de 6m3·ha–1·an–1 dans les peuplements non éclaircis à plus de 7m3·ha–1·an–1 dans les peuplements éclaircis et n’avait pas encore atteint sa valeur maximale 50 en moyenne ans après la coupe de régénération.

Document Type: Research Article

Publication date: March 1, 2008

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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