Canadian Forest Service Publications
Effects of precommercial thinning on the forest value chain in northwestern New Brunswick: Part 5 - kraft and thermomechanical pulping and pulp quality. 2013. Bicho, P.; Portillo, E.; Yuen, B.; Yan, D.; Pitt, D.G. The Forestry Chronicle. 89(4):490-501.
Issued by: Great Lakes Forestry Centre
Catalog ID: 35336
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Forty-eight years after application, three nominal precommercial thinning (PCT) spacings of 4 ft (1.2 m), 6 ft (1.8 m) and 8 ft (2.4 m) were compared to an unthinned control in six replicate, balsam fir (Abies balsamea [L.] Mill.)-dominated stands. Following the clearcut harvest of three of these replicates in 2008, chips produced from sawmilling trials (slab-wood) and from the top logs of the sampled trees (top-log) were kraft and thermomechanically (TMP) pulped. In general, top-log chips took longer to kraft pulp, had lower yields, and produced pulps with shorter, finer fibres than the corresponding slab-wood chips, across all PCT treatment levels. The main effects of PCT on pulping occurred with slab-wood chips and not top-log chips. While end-product quality in either kraft or TMP production was generally unaffected by wood from the range of thinnings tested, slight reductions in slab-wood chip density and H-factor suggest that kraft pulping productivity may be reduced by 1.8% with furnish from thinned stands. While these losses could be offset somewhat by lower chip consumption, the economic benefits for a kraft mill are marginal at best, and sharing of fiscal gains across the fibre value chain needs to be explored. Specific refining energy required in TMP production was, however, reduced by 4% with furnish from thinned stands. These results suggest that value-chain optimization is ultimately dependent on the segregation of fibre from different sources, including within-tree and among silvicultural treatments and sites.
Plain Language Summary
The effects of precommercial thinning on chemical (kraft) and thermomechanical pulping were assessed. Wood was harvested from balsam fir stands in New Brunswick that had been unthinned and thinned 48 years previously. Woodchips produced from both sawmilling (slab-wood) trials and top logs of sampled trees were subjected to rigorous pulping trials. The quality of pulp produced by both methods was unaffected by thinning, but a difference in manufacturing was noted. The main effect was a slight reduction in chip density and rate of delignification with slab-wood chips. This suggests that chemical pulping productivity may be reduced by 1.8% with chips from thinned stands, potentially resulting in a marginal economic loss. In thermomechanical pulping, however, refining energy was reduced by 4% with chips from thinned stands, potentially resulting in lower pulping costs. For pulp mills to realize economic benefits from thinning, segregation of fibre from different sources would be required.