We modelled how pre-commercial and commercial thinning affects development of merchantable timber, specifically large sawlogs (> 20 cm diameter), on various site qualities and at different harvest ages. Data from juvenile permanent sample plots from post-harvest regenerated lodgepole pine stands in Alberta were projected using the Mixedwood Growth Model (MGM 21). Pre-commercial thinning (PCT) and different levels of commercial thinning (CT) with PCT were assessed on stands of good, medium and fair site quality. Results show site quality alone had the greatest impact on merchantable yields with good sites producing ~1.5 times the yield of medium and ~4.3 times that of the fair sites. Moderate thinning on good sites produced a greater quantity of large sawlogs (> 20 cm diameter) and their associated volume over unthinned stands than that on medium or fair sites, though thinning positively influenced total yield on these sites as well. On good sites, at age 50, CT treatments produced about ~50 m3/ha more volume of large sawlogs (> 20 cm) than the control; such gain drops to 18 m3/ha on medium sites. In addition, mean annual increment culminated earlier on good sites, also enabling earlier harvest.

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Intensive silviculture is practiced in many parts of the world but is rare in the public forests of western Canada. Here, we make the argument that intensive silviculture could be justified in Alberta but has not been implemented due to philosophies and policy decisions by foresters from government, industry and academia. These include adherence to long rotations, management goals that are aimed at sustained total volume yield rather than economic value, limitations in the types of stands that are allowed to be regenerated and models that do not include intensive silviculture options. In Mixedwood Growth Model projections, we demonstrate the potential of intensive silviculture that includes combinations of selecting good sites and thinning to produce merchantable stands by age 50 compared to the standard rotation age of 80 with basic silviculture. There could be even more gains if forest level constraints in timber flow were removed due to the increased growth of regenerating stands. Finally, we examine the attitude and policy changes that we believe are necessary for adoption of more intensive silviculture systems on parts of Alberta’s forest landbase.

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Competitive exclusion can lead to a loss of species diversity within small forest gaps. Thus, it poses a potential concern for mixed species regeneration following strip-cut harvesting in the species rich interior moist forests of British Columbia. In this study, we compare nine tree species widely used in reforestation for their growth rates along a light/gap-position gradient in 50 m wide east-west oriented strip-cuts. Data after 15 growing seasons reveal that a crossover of species’ growth patterns along the light gradient can be linked to their shade tolerance ranking, and competitive hierarchy processes can be observed between species. The growth of two shade-intolerant (lodgepole pine and ponderosa pine), and two moderately tolerant (Douglas fir and white pine) species did surpass the growth of other more tolerant species under high light conditions in this study. Thus, we conclude that maintaining shade-intolerant species within 50 m wide strip-cuts is feasible, but species need to be planted in locations that suit their light requirements.

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We modelled the potential impact of intensification of plantation management and thinning, on timber supply of an ~500,000 ha forest in Alberta, Canada over a 200-year planning horizon. Pre-commercial and commercial thinning were applied to a portion of the better sites, which allowed shortening of the time to merchantability and earlier harvest than unthinned stands; less than 25% of the forest was thinned over the course of the plan. The sustainable harvest rate, represented here as the annual allowable cut (AAC), increased by ~14% above baseline, when thinning was applied. Similarly, there was a 20.7% increase in AAC projected with the relaxation of even flow rules if thinning was also applied. Finally, thinning offset the expected decline in AAC after a 20-year surge in cutting of mature pine, designed to slow an epidemic of mountain pine beetle. In terms of wood supply, the volume extracted at thinning was <2% of annual supply but volume from final harvest from thinned stands, at times, surpassed that of unthinned stands of the forest. Individual tree size from thinned stands was ~twice that from unthinned areas in the second part of the planning period, offsetting the expected decline in piece size after the era of harvest of natural forests.