Canadian Forest Service Publications

Effects of precommercial thinning on the tree growth and lumber quality of jack pine (Pinus banksiana Lamb.): results from a long-term study in the Acadian Forest Region, (Abstract only.) 2008. Swift, D.E.; Duchesne, I.; Zhang, S.Y.; Chauret, G., June 8-14, 2008, Koli, Finland. Natural Resources Canada, Canadian Forest Service, Canadian Wood Fibre Centre, Fredericton, N.B.

Year: 2008

Issued by: Atlantic Forestry Centre

Catalog ID: 28792

Language: English

CFS Availability: Not available through the CFS (click for more information).

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Jack pine (Pinus banksiana Lamb.), as with many conifers in the Acadian Forest Region, tends to regenerate at high densities (stems/ha) after natural distrubances and harvesting. As jack pine has one of the widest distributions of conifers across North America, forests containing this species have great value for producing forest products. Precommercial thinning operations are often conducted to reduce intraspecific competition and increase the merchantable growth rates by accelerating radial growth increments on individual tree stems, and decreasing rotation ages. Little information is available on the long-term effects of intensified silviculture on the growth and associated changes in wood properties of trees. Furthermore, long-term site-specific tree growth, stand dynamics, and effects on fiber attributes from thinning operations are lacking for jack pine.

In 1966, a precommercial thinning study was established by the New Brunswick Department of Natural Resources in a 25-year-old natural jack pine stand that had originated from wildfires during the early 1930s. The site is located near Eel River Bridge, New Brunswick, Canada, and is one of the oldest existing precommercial thinning studies for jack pine in eastern Canada. The following five thinning intensities were established on 2-ha treatment blocks: a) 1.2 m x 1.2 m, b) 1.5 m x 1.5 m, c) 2.1 m x 2.1 m, d) 2.7 m x 2.7 m, and e) variable release (releasing crop trees). The remaining and surrounding forest comprised the control area. In 2000, tree measurements were obtained from two temporary sample plots (400 m2) for the following thinning treatments for this study: a) control, b) 1.2 m x 1.2 m, c) 1.5 m x 1.5 m, and d) 2.1 m x 2.1 m. In each of the four treatment blocks, six trees were randomly selected in merchantable DBH classes that represented the range for diameter distribution. Additional tree measurements were recorded for these 154 sample trees before their logs were converted into lumber at a modern stud mill. Lumber was graded according to NLGA standard Grading rules by a qualified insepctor before and after kiln drying. The wood properties of all pieces of lumber were analyzed at the Forintek Division of FPInnovations in Quebec, Canada.

Based on this 34-year PCT study, the following results and conclusions can be made: Crown width, branch diameter, stem taper, and tree growth for jack pine crop trees increased with increasing thinning intensitie. In contrast, lumber strength (MOR) and stiffness (MOE) decreased with increasing thinning intensity. However, the control stand exhibited slightly more merchantable volume than the 1.2 m x 1.2 m and 1.5 m x 1.5 m thinning treatments, but less than the 2.1 m x. 2.1 m thinning treatment. Thus, the forester or landowner must make a choice (tradeoff) between increased growth (both tree diameter and stand volume) and lumber quality when selecting precommercial thinning intensities in young dense jack pine stands.