This study examined the impact of pre-commercial thinning (PCT) on tree growth, product recovery, stand value and financial return in jack pine stands in Northern Ontario. This study was based on 10 sites composed of both control and thinned stands, and the sites represent various stand densities and stand ages. In each site, 5 circular plots of 5.64 m in radius were randomly selected from each of the control and thinned stands. In each plot, all trees were measured for tree DBH and total tree height. A total of 3118 trees were measured from the 100 plots within the 10 sites. These measurements were used to estimate tree volume, merchantable stem volume, and product recovery. Tree or stem volume were estimated using a general volume equation developed by the Canadian Forest Service in Fredericton, while lumber volume and value recovery from each tree were assessed using models for describing the relationship of lumber recovery to jack pine tree characteristics (DBH and tree height) developed by Forintek. Both dimension and stud mills were considered for the product recovery. Sawdust was assumed to be 5% of the merchantable stem volume, whilst volume of the chips from each tree was calculated by subtracting lumber and sawdust volume from the merchantable stem volume.
PCT treatment in jack pine has a positive effect on both diameter and tree height growth of individual trees. Average diameter of trees from thinned stands was larger than for those from control stands for all 10 sites, and a similar trend was noticed for total tree height.
When stand density ranged from 2,000 to 3,000 trees/ha, average DBH in the control stands tended to decrease moderately with increasing stand density, however, when stand density increased to between 3000 and 6000 trees/ha, average DBH appeared to decrease slowly. With increasing stand density, no consistent pattern could be recognized for the DBH of the thinned stands. However, the magnitude of the increment in average DBH due to PCT increases with increasing thinning intensity.
PCT treatment accelerates tree diameter and height growth of individual trees, but it generally reduces total tree volume and merchantable stem volume per hectare due to the reduced number of trees. Thanks to a considerably higher lumber volume recovery per m3 associated with larger tree diameter, however, the total lumber volume and value recovery per hectare in the thinned stands are still improved. Compared to the control stands, the thinned stands on average produced 6.92 Mfbm (18%) or $2658.92 (20%) (from the dimension mill) and 3.86 Mfbm (22%) or $1783.68 (29%) (from the stud mill) more lumber per hectare. In contrast, the control stands produced 24.4 m3 or $1,142 (39.5%) (from the dimension mill) and 17.7 m3 or $828 (16.6%) (from the stud mill) more chip recovery per hectare.
PCT has a positive effect on total product value recovery. About half of the 10 stands receiving PCT had a higher total product value (from $1850 to $7147 per hectare for the dimension mill and from $3698 to $6634 per hectare for the stud mill, respectively) than the control stands, while the rest of the thinned stands produced lower total values than the control stands. On average, the thinned stands produced approximately $1,500 and $960 (or 9.9% and 8.6%) more product value per hectare for the dimension mill and stud mill, respectively.
PCT also has a positive effect on logging and lumber conversion costs thanks to a larger tree diameter. As a result, the total costs for the thinned stands including the PCT treatment cost, interest charges, stumpage fee, costs for harvesting, transportation and lumber conversion were lower than those for the control stands. Therefore, the thinned stands had a higher ratio of benefits/costs.
Overall, this study indicates that PCT appears to be an economically viable silvicultural investment for jack pine stands in Northwestern Ontario.