The Pruned Log Index (PLI) was developed by former FRI scientist Jim Park in the late 80’s and is respected throughout New Zealand by forest owners and Log buyers a like as the absolute measure of pruned log quality. Interpine is now providing stand sampling and mill studies for Pruned Log Index (PLI) and Clear Veneer Potential (C
VP). This includes the incidence of resin and other randomly occurring defects. The results of these studies provide information on how much of the pruned resource can be turned into clear grade wood product, the most valuable grade to mill owners.
BENEFITS TO LOG BUYERS
- Greater confidence when purchasing pruned logs knowing their potential to be converted to high quality clear grade product.
- Greater confidence in purchasing wood from regions known for resin pocket problems.
- Improve interest and higher bidding on stumpage sales from buyers confident in what they are bidding on.
BENEFITS TO FOREST OWNERS
- Method of assessing true effectiveness of pruning and thinning regimes on ability to produce high quality clearwood.
- Establish suitability of the pruned resource to sell as peeler logs.
- Differentiating your pruned logs from the rest. Premiums paid for high PLI scored stands.
- Method for identifying which stands in the owners estate are prone to resin defects.
- Measure stand clearwood content where no or poor stand records exist.
- Ensure the best value is being realized for an expensive investment in pruning which has taken 25 years to mature.
- Understand value of clearwood resource for price negotiations
PRUNED LOG ATTRIBUTES
Our pruned log evaluations are completely independent of processing variables. They rely on three log charateristics alone, the three that have the largest baring on final clears grade output. These are:
The most commonly used measure of log size is SED however this is dependent on log length. Diameter at 1.3m under bark relates better to log volume for a given length so this is what’s used in the PLI formula to measure log size.
The main components of shape are sweep, crook, taper and ovality. Rather than considering shape in its individual components a new concept was derived, common volume (CVOL). Log volume can be reduced to two basic components, wood which is common to the whole log length and that which is not. For peeler logs CVOL is defined as the largest diameter possible common to the full length of the log but this is not appropriate for sawlogs. An indent on one side of a log, for instance, would reduce the whole cylinder available for peeling but for a sawlog it only affects one sawing face.
For this reason the expression of common volume most appropriate for pruned sawlogs was the column calculated from four quarter ellipses.
The defect core is defined as the cylinder of wood inside a pruned log containing the pith, branch stubs and occlusion scars. The spread of defects from the same knotty core can vary according to sawing system adopted. In order to standardize procedures and eliminate processing variation, defect cores (DC) were measured as the mean of two diameters measured at right angles to each other when the log is centrally aligned.
STUDY SAMPLE DESIGN
A good sample design is important to ensure the study results are an accurate representation of the stand. The sample design we use for pruned resource evaluations are based on stand history, topography, and inventory results.
There are two methods available for conducting the studies. The method chosen is dictated by machine accessibility to the sample sites and client requirements. The two methods are:
Via Cross-Sectional-Analysis – Study trees are dissected and analysed at forest site. Where terrain is adverse and road access limited, this is the only feasible method.
Via Sawing – Study trees are felled and extracted to the road side/skid. Stems are made into logs with the pruned component trucked to a sawmill for dissection and remainder of tree, in some situations, sold to partially recoup study costs.
The results from the two methods are directly comparable in all aspects except internal resin defect incidence. The sawing method allows for a more in depth assessment of the final wood products.
Costs are directly related to stand size, study method and distance to study site so vary greatly. Please contact Interpine for a detailed pricing assessment specific for your resource.
KEY OUTPUTS FROM THE STUDY
Pruned Log Index
This index evaluates pruned stands based only on key individual log characteristics making the evaluation independent of sawmill process. The characteristics measured include log size, shape and defect core, the three log attributes that dictate final clears grade output from saw logs.
Stand PLI values typically range between 1 and 10. Scores of 4-6 are average where 7 and above are considered very good. The PLI rating for a stand is a volume weighted score based on individual log PLI values from the entire forest population.
Clear Veneer Potential
CVP is the percentage of the peeler bolt which can be converted into continuous clear veneer ribbon. The stand CVP value is the population sample mean of CVP’s for individual logs. The size and shape of the log have biggest bearing on the “veneer potential” but size and position of the knotty core dictate how much of this is clear of defect. An off centre knotty core or a late pruned branch whorl can easily render a visually good peeler bolt to a poor CVP score.
Random Defect Incidence
Randomly occurring defects can downgrade pruned log quality.
Mills accept there will be a certain level of resin defects in wood consignments they buy but when the level gets too high they may become selective in where the logs are sourced from or only agree to purchase logs at a reduced rate. The incidence is expressed as defect frequency per m2 and as a percentage derived by dividing the surface area of board faces with that defect by the total surface area sampled.
ADD ON SERVICES
The standard study is based on providing an evaluation of the pruned component of a forest only. Further information can be collected in conjunction to the base study including log density and strength, branch index, volume-taper function reconciliation or a full yield analysis/valuation provided for the remaining log products contained within the forest. Please contact Interpine for further advice of whether further information would be beneficial to you.