Initial spacing
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.
Precommercial thinning
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.
Commercial thinning
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.