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Log quality, conversion and grading

Log quality is a function of size (diameter, length) shape (straightness, ovality, taper), and other external (branching) and internal (wood properties) features which can affect the suitability for a particular end use.

Adaptability of New Zealand pine (which comprises the most part of New Zealand’s plantation forestry) to varying site and management regimes results in the production of a range of log types. Grades based on quality characteristics are used in New Zealand to allow buyers to specify the preferred quality. The key to the appropriate use of these logs is to recognise associated quality variations and to match them to the intended process and product.

Log quality is a function of size (diameter, length) shape (straightness, ovality, taper), and other external (branching) and internal (wood properties) features which can affect the suitability for a particular end use.

Some log types

Pruned Peelers – High quality, large, straight logs for sliced or peeled veneer, plywood and LVL manufacture
Industrial Peelers – Large, straight unpruned logs for knotty grades of plywood and LVL manufacture
Pruned Sawlogs – high quality, large, straight logs for sawmills to produce clear and appearance grade lumber
Small branch sawlogs (s) – suitable for production of structural lumber, available in small, medium and large diameter groups
Large branch sawlogs (l) – suitable for production of industrial and appearance lumber, available in medium and large diameter classes
Posts and poles – small to medium size, straight logs, used fo engineering and ground contact end uses, must be chemically treated to extend lifespan
Residual logs (pulp and panel products) – sound logs not fitting into any of the above categories

The wood of New Zealand pine has medium density, even texture, and average shrinkage for softwoods. The logs yield the full range of lumber grades from long length clear wood to industrial grades. The strongest, most stable wood for structural uses is derived from the outer region of the log, while lumber from the juvenile zone is suited to packaging and similar products.

Contrary to popular belief, the wide growth rings typical of managed plantations of New Zealand pine are not a reflection of poor wood quality. Correctly graded, New Zealand pine conforms to grade requirements for structural lumber worldwide.

Reference: NZ Pine User Guide, courtesy of NZ Pine Manufacturers Association