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UBC Theses and Dissertations

The effect of pre-commercial thinning on growth and development of paper birch leading stands in British Columbia's Interior Leclerc, Marie-Eve


With shifting disturbance regimes negatively impacting timber supply in British Columbia (BC), broadleaf and mixedwood stands present an opportunity to supplement timber loss and create resilient forests to natural disturbances. This study assessed the effects of thinning of paper birch leading stands on growth of the overstory and the diversity of the naturally regenerated understory in the Interior Cedar Hemlock (ICH) zone in southern BC. Pre-commercial thinning was applied to naturally regenerated paper birch stands to reach three densities: 3,000 stems/ha, 1,000 stems/ha and 400 stems/ha. Thinning effects on tree growth were analyzed at both the stand and tree level. The stand level analysis was performed on trees greater than or equal to 4cm in diameter at breast height (DBH) that were alive throughout all measurements. The tree level analysis was performed on the tallest 250 paper birch trees/ha. After 25 years, height and height growth were greater in thinned stands relative to the control stands at both the stand and tree level. At the stand level, basal area/ha and volume/ha were greatest in the control stands and were lowest in stand densities of 400 stems/ha. At the tree level, height and height growth were significantly greater (p < 0.0036) in thinned stands relative to the control stands. DBH and volume were significantly greater (p < 0.0001) in 1,000 stems/ha and 400 stems/ha relative to the control stands; the same result was found for DBH and volume increment. In 2016, diversity of ingrowth and seedlings was calculated using Simpson and Shannon-Weiner’s index, and increased with increasing thinning intensity. From a forest manager’s perspective, among the thinning treatments from this study, 1,000 stems/ha provides the best option. Thinning to 1,000 stems/ha allowed an increase in diameter growth without compromising stand volume for timber objectives, while simultaneously promoting diverse natural regeneration for future resilient forests.

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