This study examined the long-term effects of initial spacing on tree growth, wood characteristics and product quality and value in white spruce. The study is based on the oldest initial spacing trial established by the Ontario Ministry of Natural Resources in Thunder Bay. Three plantation spacings were examined: 1.8 m, 2.7 m and 3.6 m. 58 trees were sampled across the DBH classes present, bucked to maximize the production of 16 ft-long logs, and converted into lumber. Each piece of lumber was visually graded and tested in static bending to determine its lumber stiffness (modulus of elasticity, MOE) and strength (modulus of rupture, MOR), and MSR grade.
Sixty years after establishment, individual tree growth was greatly favoured by larger spacings. Tree diameter increased by 39% and 66% in the 2.7 m and 3.6 m spacings, respectively, compared to the narrowest 1.8 m spacing. This resulted in a remarkable volume increase of 129% and 159%. Stem taper increased from 0.93 cm/m in the 1.8 m spacing to 1.40 cm/m in the largest spacing. Lumber volume proportions of No.2 & Better grades were 85.7%, 86.8% and 80.4% in the 1.8, 2.7 and 3.6 m spacings, respectively. Expectedly, increased initial spacing favoured the production of large piece size. The volume proportion of 2x8 was 25.5% and 10.2% in the 3.6 m and 2.7 m spacings, but only 0.4% in the 1.8 m spacing. The 2.7 m spacing yielded the best total product value (lumber, chip, sawdust) per hectare ($50,817/ha), followed by the 1.8 m spacing ($44,043/ha). However, the 3.6 m spacing yielded the lowest plantation value ($37,231/ha) because of its low initial stocking.
Lumber stiffness decreased markedly with increasing spacing, from a maximum of 9427 MPa in the 1.8 m plantation, to 8031 MPa and 7476 MPa in the 2.7 and 3.6 m spacings. Similarly, through the same range of spacings, lumber strength decreased steadily from 37.2 MPa, to 30.1 MPa, and 27.1 MPa. The 2.7 and 3.6 m spacings had a major negative impact on lumber MOE (–15% and –21%), lumber strength (–19% and –27%), and a minor impact on wood density (–2% and –4%). MSR yields of No.2 & Better lumber grades decreased markedly with increased spacings. In the 1.8 m stand, 69.2 % of the lumber volume was graded MSR 1650f-1.5E, in comparison to 46.2% and 15% in the 2.7 m and 3.6 m stands, respectively.
In conclusion, this study indicates that initial spacing in white spruce should not exceed 1.8 m from a wood quality perspective, as wider spacings significantly decreased lumber stiffness and strength (MOE and MOR). However, if the silvicultural objective were to maximize economic value regardless of lumber mechanical properties, the 2.7 m spacing would give the highest plantation value.
Element 4 : Hardwood initiative - Development of new processes and technologies in the hardwood industry (Project 17) - Impact of partial harvesting on tree grade: projections for northern hardwoods of the Acadian Forest Region
The objective of commercial thinning and partial harvesting has traditionally been to improve and increase the amount of higher quality stems for sawlog and veneer products, reduce losses from mortality, and reduce the harvest rotations for even-aged silvicultural systems. Literature on the impact of partial harvesting on stand dynamics, tree grade changes, fibre attributes, and potential forest products to promote uneven-aged and structures and management is scare for the northern hardwood forests of the Acadian Forest Region. A long-term selection harvest study established in west-central New Brunswick provides the opportunity to obtain such information under the FPInnovations and Natural Resources Canada, Canadian Wood Fibre Centre Eastern Hardwood Research Initiative. Results from the study suggest that the treated stands did benefit in the terms of growth and improved quality, but stand restoration is a slow process in the second growth uneven-aged stands on a 20-year harvest cycles. Stand growth responses and tree grade changes for both the control and treated plots are within the values reported for northern hardwood stands and are influenced by a number of treatment and biological factors.
The results of fifteen years of observation are discussed in the context of the major publications existing in the literature for stand dynamics, tree grade changes, and the occurrence of ingrowth. In summary, greater is the basal area removal, the greater the diameter response of individual residual trees in the thinned plots. The thinned stands have not recovered the basal area values that existed at the initiation of this study Annual volume increment growth rates suggest that hardwood stands subjected to partial removals produced better growth response than was predicted at the start of the original study. Stand restoration and stem quality improvement are slow processes that may not be achieved with a first harvest entry in second-growth northern hardwood stands that have had the higher quality trees removed repeatedly in the past. Changes in tree grades were observed to be very dynamic in these second-growth northern hardwood stands because of a number of factors such as initial stem quality, stem growth, mortality rates, harvest rates (both regulated and unregulated), species, and site quality. As expected, ingrowth occurred more frequently in the thinned stands than the control stands. Except for one study site with more “mixedwood” characteristics ingrowth does not exist as a diverse mixture of desired tree species but a secondary canopy of dense American beech and sugar maple.
Hardwood Initiative - Part 5: Development of new processes and technologies in the hardwood industry (Project 16) ; Testing the impacts of tree and stand attributes on the variability of acoustic velocity in standing trees (ST300) and logs (HM200)
Transformative Technologies Program ; Project No. TT5.15
Hardwood Initiative Project is based on two paradigms. First, the end-use potential and value of a wood product basket can be determined by the properties of its wood and should be quantified as much as possible before trees are harvested. Second, as the correlations between site conditions and wood fibre attributes can be changed by silvicultural treatments, it would be possible to optimize the wood production in terms of quantity and quality through a better understanding of silvicultural impacts on changes in wood fibre properties. This document presents the preliminary results of a research component of the project related to acoustic velocity. It focuses on testing the impacts of tree and stand attributes on the variability of non-destructive velocity (ST300 non-destructive measurement in standing tree) and of destructive velocity (HM200 destructive measurement in log). The acoustic measurements were conducted in 30 plots of sugar maple mixed with yellow birch in New Brunswick. Among the trees measured, 64 trees have been subjected to both non-destructive and destructive velocity measurement. Regression analysis by mixed model showed no significant impact of stand attributes (stand basal area and stand height) on the variation of both velocities. In addition, the defects represented by stem deformation, hole, split, wound, and stump swelling, had no significant impact on both velocities. By cons, the test showed a significant correlation between both velocities and dbh and light crown area of the tree. Non-destructive velocity was better explained by dbh and light crown than the destructive velocity. These results open the potential to produce an equation to predict the non-destructive acoustic velocity of the tree using simple tree attributes (e.g., dbh and light crown) as predictors, and to prescribe the thinning intensity for a desired level of velocity and then a desired level of wood density or stiffness.
Full title: Hardwood Initiative - Part 5: Development of new processes and technologies in the hardwood industry (Project 16) : Testing the impacts of tree and stand attributes on the variability of acoustic velocity in standing trees (ST300) and logs (HM200)
The aim of the research project is to examine the long term (31 years) effects of late commercial thinning at wide spacing on tree growth, wood characteristics and product quality and value in a natural jack pine stand located in New Brunswick. Because mechanized commercial thinning has just recently become a more prevalent silvicultural prescription in the softwood forests and plantations of Eastern Canada, little information is available on the long-term effects of intensive silviculture on tree growth and concurrent changes in wood properties.
In 1976, when the even-aged jack pine stand was approximately 40 years old, Natural Resources Canada, Canadian Forest Service conducted an operational commercial thinning from below in a portion of the stand. The commercial thinning operations resembled current mechanized practices as the extraction trails were approximately 20 m apart and were 3 to 4 m in width. Trees were spaced to about 2.7 m to 2.7 m (50% removal of basal area) which represent the upper limit of what is done today in Eastern Canada.
Thirty-one years later in 2007, sample trees were collected from each tree DBH class in a control area (natural-origin) and the heavily thinned area for wood quality evaluation. A total of 85 trees was measured and bucked into 3.1 m (10-foot) long logs. Lumber conversion was carried out in two separate batches so that chip samples could be collected for fibre-based (MDF) panel manufacturing and quality evaluation. After kiln drying, each piece of lumber was visually graded and tested in static bending to determine its lumber stiffness (MOE) and strength (MOR). Based on the sample trees, the impact of commercial thinning was evaluated at the DBH class level and at the stand level. Finally, a benefit/cost analysis was made for the two treatments.
Commercial thinning had a positive effect on tree growth 31 years after treatment. The average tree diameter increased from 16.2 cm to 22.2 cm (37%) following heavy thinning. Average tree height increased from 15.4 m to 17.5 m (12%) and merchantable stem volume per tree increased from 171.3 to 347.3 dm3 (103%). The lumber volume recovery per tree was higher in the thinned area (50.5%) compared to the control area (45.7%).
Commercial thinning had a positive impact on the Select Structural lumber grade recovery with 14.8% for the thinned area as compared to 6.6% in the control area. The total lumber value per tree was 146% higher in the thinned trees compared to control trees. The economic analysis indicates that it is profitable to perform a one-entry commercial thinning at wide spacing with the stand conditions and assumptions described in this study. The benefit to cost ratio is 1.20 in the thinned stand, considering 1976 and 2007 revenues and costs, as compared to 1.56 in the control area.
Lumber stiffness and strength decreased following commercial thinning. The lumber modulus of elasticity (MOE) were 9859 MPa and 8783 MPa and the modulus of rupture (MOR) 40.6 and 36.5 MPa in the control and thinned trees, respectively. This represents a 12% and 11% decrease in MOE and MOR after commercial thinning. The results clearly show that the dominant fast-growing trees sampled in the largest diameter classes (32-34 cm) of the thinned area had the lowest mechanical properties.
In conclusion, based on this long-term study, commercial thinning operations should include removal of trees in the largest DBH classes, along with the more traditional removal of smaller diameter, suppressed trees and damaged trees. This prescription would make commercial thinning even more economically profitable at the time of treatment, while minimizing its effect on lumber mechanical properties. The resulting stand, comprising fewer fast-growing dominant trees and more co-dominant trees, will grow moderately and maintain desirable lumber mechanical properties.
This study examines the long term effects of precommercial thinning (PCT) on tree growth, wood characteristics and product quality and value in natural balsam fir stands. In Eastern Canada, little information is available on the long term effects of intensive silviculture on tree growth and concurrent changes in wood quality and value.
The Green River PCT trials, located about 80 km north of Edmundston in New Brunswick, were established between 1959 and 1961 to evaluate the long-term responses of balsam fir and spruce to PCT. Three nominal spacings, 4 ft (1.2 m), 6 ft (1.8 m), and 8 ft (2.4 m), were applied for comparison with an unthinned control in a randomized complete block design with 5 replicates. For the purpose of the present study, only 3 of the 5 replicates were assessed for wood quality. In 2008, or forty years after PCT treatment, sample trees were collected from each tree DBH class for wood quality evaluation. A total of 160 trees were measured, bucked into random-length (8-16-foot) logs, and converted into lumber in a modern sawmill. For each PCT spacing, wood chips were collected for evaluating the quality of medium density fibreboard (MDF) panels. Each piece of lumber was visually graded and tested in static bending to determine its lumber stiffness (MOE) and strength (MOR). Based on these sample trees, the impact of PCT spacing on product quality and value was evaluated at the DBH class level and at the stand level.
PCT had a positive effect on tree growth 48 years after treatment. The average tree diameter increased from 19.8 cm in unthinned control plots, to 23.5 cm (19%) in the 8’ spaced plots. Merchantable stem volume per tree increased from 277.1 dm3 to 381.1 dm3 (38%). Stand volumes from the control to the largest (8’) spacing were 281 m3/ha, 297 m3/ha, 310 m3/ha and 338 m3/ha, respectively. PCT had also a positive impact on Premium lumber grade recovery ranging from 18% in the unthinned control to 22% in the 8’ spacing. Through the same range of spacings, No. 2 & Better grade yields were 83.7%, 89.3%, 85.6% and 78.9 %, suggesting a slight decrease at the largest spacing. Total product value per tree was $29.09 in the unthinned control, and $31.07, $36.31 and $40.23 in the 4’, 6’ and 8’ spacings, respectively, representing a maximum value increase of 38%. PCT at 6' & 8' also increased the production of 2x6 & 2x8 by about 9 % compared to the control. Forty-eight years after treatment, all the spacings increased stand product value compared to the unthinned control: $25,222/ha (control), $29,942/ha (4’), $27,368/ha (6’) and $30,151/ha (8’). The Summit Road replicate, which was about 8 yrs older (70 years) than the two other replicates at Upper Belone (62 years), had markedly lower total product value recovery, indicating stand degradation. If the Summit Road plots are excluded, the stand product values for the control, 4’, 6’, and 8’ spacings become $27,402/ha, $35,200/ha, $32,948/ha and $31,911/ha, respectively.
Modulus of elasticity (MOE), or lumber stiffness, decreased slightly with increasing PCT spacing, from a maximum of 8233 MPa in the control, to 8175 MPa, 7937 MPa and 7961 MPa in the 4’, 6’ and 8’ spacings, respectively. Similarly, the modulus of rupture (MOR), or lumber strength, decreased steadily from 31 MPa in the control, to 30 MPa, 29 MPa and 28 MPa through the same range of spacings. Thus, compared to the control, the 8’ spacing had a minor negative impact on lumber MOE (–3.4 %) but a more appreciable negative impact on lumber strength (–8.9 %). Compared to the control, the 8’ spacing slightly decreased wood density by 3.7 % (340 kg/m3 vs. 328 kg/m3). Overall, the PCT spacings studied had a moderate negative impact on lumber mechanical properties. The sawmill wood chips from the control and the thinned stands (4’, 6’ & 8’) are all suitable for the production of good quality MDF panels. All MDF panels produced had very good strength (MOR) and stiffness (MOE), with little difference between product from thinned and unthinned stands.
In conclusion, this study shows that PCT in highly productive balsam fir stands is a viable silvicultural treatment that increases stand volume and solid-wood product value per hectare at the end of the rotation. On a total stand product value per ha basis, the 4’ spacing ranks as the best option, followed by the 6’ spacing. From a wood quality perspective, considering that the 8’ spacing decreased lumber MOE/MOR the most, it is recommended to thin young balsam fir stands to a maximum of 6’ (1.2 m) in order to limit the decrease in lumber mechanical properties. In this study, the 6’ spacing appears as the best compromise between stand volume production and solid-wood product quality and value. Thinning to a maximum of 6’ offers the advantage of minimizing the risk of loosing too many crop trees over time, in case natural perturbations occur, and potentially the opportunity to perform a commercial thinning if so desired.
Cette étude évalue l’impact du classement MSCR sur le rendement en volume et en valeur des sciages de bouleau blanc. Ce classement se base sur l’identification des défauts externes de l’arbre sur pied afin d’en évaluer sa vigueur et de déterminer sa priorité de récolte. Le code terrain MSCR signifie que les arbres classés M (Mourir – non growing stock) et S (Survie – poor growing stock) devraient être récoltés en priorité, tandis que les arbres classés C (Conserver – Acceptable growing stock) et R (Réserve – Premium growing stock) devraient être conservés en forêt. En plus de récupérer des volumes de bois en train de se perdre, le but ultime est d’augmenter la qualité des forêts feuillues québécoises à long terme en conservant des arbres vigoureux de qualité pour le futur. Cent bouleaux blancs matures et surannés, échantillonnés dans un peuplement situé dans les Hautes-Laurentides, ont été marqués selon le système de classification MSCR. Les arbres ont été sélectionnés pour obtenir un nombre adéquat d’arbres dans chaque classe MSCR.
Des 100 arbres échantillonnés, 59 ont produit des billes de qualité sciage (F-1, F-2, F-3, billon). Les 41 arbres restants ont été classés qualité « pâte ». Parmi ces derniers, 27 étaient classés M (mourir), 7 S (survie), 5 C (conserver) et 2 R (réserve). Les 100 bouleaux blancs ont majoritairement produit des billes de sciage de faible qualité (F-3) pour les classes d’arbres S, C et R. Pour les arbres en perdition (M), environ 70 % du volume des tiges livrées à l’usine a été classé impropre au sciage lors du mesurage (c. à d. qualité « pâte »). Pour les 3 autres catégories d’arbres, le pourcentage de bois à pâte variait entre 23 et 33 % du volume. Bien que les diamètres des arbres surannés de cette étude aient été importants (35 cm), les billes de qualité supérieure (F-1) étaient pratiquement inexistantes.
L’étude démontre qu’il faut environ deux fois plus d’arbres en perdition (M) que d’arbres productifs (R) pour produire 1000 pmp (2,36 m3) de sciages. Le revenu total moyen par m3 net de tige varie de 90,99 $/m3 pour les arbres en perdition (M) à 163,08 $/m3 pour les arbres en réserve (R) (sciages non triés). Pour les sciages triés selon la couleur, le revenu moyen passe de 95,50 $/m3 à 194,90 $/m3 pour les classes M et R respectivement. Si l’approvisionnement d’une scierie se fait uniquement à partir de bouleaux blancs en perdition (M), ceci diminuera considérablement ses revenus. De plus, on peut facilement prévoir un problème de surplus de copeaux puisque pour obtenir un volume suffisant de billes de sciages pour opérer une scierie, il faudra récolter encore plus d’arbres en perdition. Cette problématique, intimement associée à la transformation de billes de qualité inférieure, serait aggravée à moins de trouver de nouvelles utilisations pour cette ressource en perdition impropre au sciage. À long terme et s’il est appliqué avec rigueur dans les peuplements qui le permettent, le système de classification MSCR devrait contribuer à améliorer la qualité globale des forêts feuillues québécoises en conservant des arbres vigoureux de bonne qualité pour le futur.
This study examined the impact of initial spacing on tree characteristics, product quality and value recovery in jack pine. The study was based on one of the oldest initial spacing trials established in 1941 in Wellston, Michigan. In 2001, trees were collected from each tree DBH class in 3 initial spacings, 5x5 (1.52mx1.52m), 7x7 (2.13mx2.13m) and 9x9 (2.74mx2.74m). Trees were also collected from blocks that had been spaced (PCT) from 5x5 to 7x7 at age 13. The following were measured for each sample tree: crown width and length, total tree height, tree height up to 7.5cm top, tree height up to 9.1cm top (10cm DBH class) and average diameter of the 5 largest branches. Based on these measurements, stem volume, stem taper and length of the log below live crown were calculated. Each stem was then scanned in a log scanner for determining the impact of optimized bucking and sawing on lumber recovery using sawmilling simulation software. Stems were bucked into 8-foot long logs with a 4-inch overlength (2.54 m) according to sawmill practice. A 5-cm thick disk was collected from the base of each stem and from the top of each 8-foot sawlog for wood quality determinations. Lumber conversion was carried out in 4 separate batches so that chip samples could be collected for determining chip and pulp quality. Each piece of lumber was visually graded both before and after kiln drying. A static bending test was also performed to determine lumber strength and stiffness. Based on the sample trees, the impact of initial spacing and the PCT treatment was evaluated at the DBH class level and at the stand level. Finally, a benefit/cost analysis was made for the 4 treatments. Wood and pulp properties and sawing simulations will be reported separately.
Increasing initial spacing in jack pine from 5x5 to 7x7 had a considerable impact on average tree diameter (+14%) and volume (+30%) 57 years after planting. However, when spacing was further increased to 9x9 the additional gains in tree diameter (4%) and volume (3%) were considerably more modest. On the other hand, the PCT treatment in the 5x5 spacing in which stand density was decreased from approximately 4300 trees/ha to 2200 trees/ha, increased tree DBH by 6.6% and tree volume by 18%.
The negative impact of increasing initial spacing and PCT treatment on branch size and tree taper follows a similar trend. Average branch diameter in 5x5, 7x7 and 9x9 spacing was 30.1, 35.1 and 37.0mm respectively and 32.8mm in the thinned 5x5 stand. Average tree taper also increased considerably as spacing was increased from 5x5 (0.64cm/m) to 7x7 (0.79cm/m), the increase was much less as spacing was further increased to 9x9 (0.86cm/m).
Average nominal lumber volume recovery also increased considerably with increasing initial spacing. Once again the increase was more pronounced in narrow to moderate spacing than from moderate to wide spacing. On the other hand, lumber grade recovery did not decrease with increasing initial spacing in this study, as suggested by the increase in branch and knot size. In fact the highest yield of SS grade was in lumber from the 9x9 spacing, and its yield of SS & No. 1 lumber, is only marginally lower than that of lumber from the narrow 5x5 spacing. This is largely due to the fact that rot was also a major cause of downgrade in all stand densities and its impact was somewhat less important in the widest spacing. The presence of rot alone was responsible for 24.7% (9x9) to 56.9% (5x5) of lumber downgrade to No. 3 and Economy, which has a direct and significant impact on lumber value.
Lumber strength and stiffness decreased with increasing initial spacing. The modulus of elasticity (MOE) and modulus of rupture (MOR) of lumber from the widest spacing are 7.4% lower than those of lumber from the narrowest 5x5 spacing. But, the MOR of lumber from moderate (7x7) spacing is only approximately 3% higher than that of lumber from wide spacing (9x9). MOE and MOR of lumber from the thinned and unthinned 5x5 spacing are very similar which indicates that the PCT treatment did not seriously affect bending properties. In addition, the mechanical properties of those 2 stands compare well with those of lumber from young 50-year old natural stand. Generally, MOE and MOR decreased from butt log to top log in all spacings.
An economic analysis was carried out for a 47 and 57-year rotation using tree and lumber data that were generated for each tree DBH class in the 2001 study, as the initial spacing trial was 60-years old. The economic analysis was carried out in the context of sustainable forestry through intensive silviculture, which assumes that trees are planted each year at the same initial spacing. And for each year of operation, return on investment or benefit to cost ratio is estimated using current product values and costs.
The analyses indicate that benefit to cost ratios increase with increasing initial spacing both at 47 and 57-year rotations. However, none of the stand densities generated any profit at 47-year rotation mainly due to high harvesting and processing costs. It is nevertheless estimated that the widest initial spacing (9x9) would have shown a positive economic return on investment (B/C 0.96 in this analysis) had lumber values been based on 47-year old stems rather than 60-year old stems, since lumber downgrade due to rot would have been lower. In addition, improvements in lumber processing would also have a positive impact on stand value and profit. But, in order to be profitable on short rotations, plantations should be established in regions that are particularly favourable to jack pine growth.
In the 57-year rotation only the narrow 5x5spacing failed to generate profit (Benefit/cost 0.87). The economic impact of a precommercial thinning treatment in the dense 5x5 stand appears to be modest. However, in plantation-grown jack pine and especially in stands such as the one in the present study where tree form is a major problem, PCT treatments should be primarily aimed at eliminating deformed stems to have maximum impact on tree and stand value.
It appears that this stand should have been harvested before age 60 since there was high mortality in the last 10 years and essentially no additional volume growth. In fact, the only positive growth that was recorded from age 47 to 57, was in the 9x9 spacing with 8.6m3/ha over the 10-year period.
This study examined the impact of precommercial thinning (PCT) intensity on tree characteristics, product quality and value recovery in jack pine. The study was based on one of the oldest precommercial thinning trials established in 1966 on a poorly drained sandy-silty loam by the New Brunswick Department of Natural Resources and Energy. The trees on this site originated from fire in 1941. In 2000, 6 trees were collected from each commercial tree DBH class in 3 thinning intensities, 4x4 (1.22mx1.22m), 5x5 (1.52mx1.52m), 7x7 (2.13mx2.13m) and a control stand, for a total of 154 trees.
The following were measured for each sample tree: crown width and length, total tree height, tree height up to a 7-cm top, tree height up to 9.1-cm top (10-cm DBH class) and average diameter of the 5 largest branches. Based on these measurements, stem volume, stem taper and length of the log below live crown were calculated. Before bucking, the shape and size of each stem was determined using a laser transit and a target board overlaid with high precision graph paper. These virtual stems will be used to determine the impact of optimized processing on product volume and value recovery using a sawmilling simulation software developed by Forintek (Optitek).
Stems were bucked into 8-foot long logs according to sawmill practice. A 5-cm thick disk was collected from the base of each stem and from the top of each 8-foot sawlog for wood quality determinations. Lumber conversion was carried out in 4 separate batches so that chip samples could be collected for determining chip and pulp quality. Each piece of lumber was visually graded both before and after kiln drying. A static bending test was also performed to determine lumber strength and stiffness. Based on the sample trees, the impact of PCT intensity was evaluated at the DBH class level and at the stand level. Finally, a benefit/cost analysis was made for the 4 treatments. Wood and pulp properties and sawing simulations will be reported separately.
Since jack pine is a shade-intolerant species mortality decreased with increasing PCT intensity, as expected. Mortality in the 7x7, 5x5 and 4x4 thinning was 16.7, 20.6 and 24.2% respectively, and 29.6% in the control stand.
The impact of mild (thinned to 4x4) and moderate (thinned to 5x5) PCT treatment on tree growth was relatively modest 34 years after treatment. However, when thinning intensity is further increased to 7x7 (2200 stems/ha) the gains are considerable. Tree diameter increases by over 20%, from 15.1cm in the control stand to 18.3cm in the stand thinned to 7x7. Average tree height increases from 14.5m to 16.4m (13.1%) and merchantable stem volume per tree increases by more than 75%, from 105.1dm3 to 185.5dm3.
Total log volume recovery and green lumber volume recovery per tree is respectively 67% and 59% higher in trees from intensive thinning than in trees from the control stand. Lumber volume recovery per cubic meter of stem is slightly higher in trees from the 7x7 thinning than in trees from the control stand, and as a result wood consumption in the intensive thinning is somewhat lower. On the other hand, trees from the 5x5 thinning and control stand generally have similar log and lumber volume recoveries, which are higher than those from the 4x4 thinning.
Lumber quality generally increases with increasing thinning intensity. Yields of visually graded No. 2 and better lumber are 87.7%, 86.0% and 77.5% in stands thinned to 7x7, 5x5 and 4x4 respectively, and 79.2% in lumber from the control stand. The presence of large knots is the main downgrading defect in jack pine lumber from intensively thinned stands where it is responsible for 27.4% of the downgrade, while wane is responsible for approximately 25 to 30% of the downgrade in lumber from the control and mild thinning stand. Lumber and total product value recoveries per tree are approximately 70% higher in trees from intensive thinning than in control trees. And lumber value per thousand feet board, and per cubic meter of stem, are 14% higher in trees from intensive thinning. Once again trees from control and moderate thinning (5x5) have similar product value recoveries and these are superior to those of trees from mild thinning.
The economic analysis indicates that return on investment increases with increasing thinning intensity. Benefit to cost ratios, are 1.26, 1.31 and 1.46 for stands thinned to 4x4, 5x5 and 7x7 respectively. However, the unthinned control stand has a higher benefit to cost ratio (1.33) than stands from mild and moderate thinning. It thus appears that stand density has to be reduced to approximately 2200 stems/hectare (7x7) to be economically viable.
On the other hand, strength and stiffness properties of lumber decrease with increasing thinning intensity. The modulus of rupture (MOR) in stands thinned to 4x4, 5x5 and 7x7 is respectively, 57.2, 55.3 and 46.9 MPa, and the modulus of elasticity (MOE) is 11 242, 10 927 and 9823 MPa. MOR and MOE in lumber from the control stand are 51.9 MPa and 10 219 MPa, which is respectively 10.6% and 4.0% higher than those of lumber from intensive thinning. While bending properties of lumber from intensive thinning are the lowest in this study, they are nevertheless comparable to those of lumber from natural stands of good to excellent growth, as demonstrated in a recent study in 50, 73 and 90-year old jack pine stands from Northern Ontario. Lumber strength and stiffness also decrease fairly drastically from the butt log to the top log in all stands.
In summary, the results from this study indicate that mild and moderate thinning treatments do not have sufficient impact on tree and stand volume and value recoveries to generate a positive return on investment. A fairly intensive PCT treatment is thus required to be economically viable. It also appears that strength and stiffness properties of lumber from intensively thinned stands will be similar to those of lumber from natural stands of similar rotation age.
The impact of commercial thinning of jack pine stands on growth, yield and financial variables was examined. Data from 5 treated stands spread through Eastern Canada was used to calibrate individual tree and stand level models. Individual trees showed a good response to thinning, with the larger stems having the best reaction to thinning. Larger stems, however, could not take full advantage of the heavy thinning. At stand level, thinning had little effect on merchantable volume. Sawlog volume (merchantable volume of the stems with a diameter at breast height of 15.1 cm and more) showed a strong response to thinning, with heavy thinning having more sawlog volume. Thinning reduces the income of a stand, but reduces even more the cost to harvest and saw the stand. The return on investment and net present value (NPV) favour heavily thinned stands, with moderately thinned stands having the same NPV, but higher return on investment.
Impact of rotation age
This study examined the impact of rotation age on tree and wood characteristics, lumber quality and value recovery in natural jack pine forests. The study was based on three stands all established after forest fires in the region of Timmins, Ontario. These stands were 50, 73 and 90 years old. In 2002, a total of 142 sample trees were collected. For each stand, 6 trees per DBH class were selected to cover all diameter classes (DBH) in 2-cm interval. For each sample tree, major tree characteristics were measured: total tree height, tree height up to 9.1 cm diameter top (10 cm DBH class); DBH and stem diameter from the stump to the top at 1-m interval; live crown width and length and average diameter of the 5 largest branches. Based on these measurements, other tree characteristics were calculated: stem volume, stem taper, and length of the log without live crown. Each sample tree was bucked to 8-foot-long logs for lumber conversion. From the top of each log, a 3-cm-thick disc was removed for the evaluation of wood characteristics. Lumber conversion was carried out in a way which allows to keep track of the provenance of each piece of lumber. Logs from each stand were processed separately so that chip samples could be collected. Each piece of lumber was visually graded after drying and planing. Bending tests were performed to determine the mechanical properties (bending strength and stiffness) of the lumber pieces. Based on the sample trees, the impact of rotation age was evaluated first at the diameter class level and then at the stand level. Finally, a cost/benefit analysis was made for the three rotation ages.
For the three stands analyzed, tree height, tree diameter, tree volume, branch diameter and taper increased with diameter class (which is an effect of age). Basic density (90 yr-old stand data only) decreased from butt log to top log for all diameter classes.
Since the quality of the natural jack pine stands was excellent, the Economy grade accounted only for 2.4% or less of the total lumber volume production for each stand in this study. In the 90-yr-old stand, decay caused 20.6% of the downgrades, whereas for the 73- and 50-yr-old stands, downgrades due to decay was low or inexistent (5.2% and 0% respectively). When grades No. 2 and better were combined (current market practice), no significant differences were found among the three rotation ages.
The present study clearly shows that rotation age influences lumber quality. The 50-yr-old stand had a significantly lower lumber strength (MOR, 42 MPa) about 16% below that of the 73- and 90-yr-old stands (48 and 49 MPa). This can be partly explained by a higher proportion of juvenile (immature) wood at an age of 50 years. The lumber stiffness (MOE) at age 50 was also significantly lower (19 and 16%, 9441 MPa) compared to the 73- and 90-yr-old stands (11234 and 10927 MPa respectively). From the lumber strength and stiffness point of view, the 50-yr-old stand can be considered too young for harvest. The two older stands were similar in terms of lumber mechanical properties, which were very good (i.e. met or exceeded the mean-based MOE design values of the grade, unlike the 50-yr-old stand). For the three rotation ages, MOR and MOE decreases from the butt log to top log.
The benefits/cost analysis indicates that it is economically more profitable to harvest natural jack pine stands at an age of 90 years. However, regarding stand productivity, the 90-yr-old stand showed the lowest annual stand volume increment of 3.21 m3/ha/year, compared to 5.25 and 3.82 for the 50- and 73-yr-old stands, respectively. The stand also showed the highest mortality (loss of fibres) and rate of lumber downgrades due to decay. From the view point of lumber properties, downgrades due to decay and tree mortality, a moderate rotation age of about 70 years is preferred in jack pine.