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Use of Tools to Predict Aspects of Wood QualityJohn Moore, Dave Cown, Euan Mason

Some Important Wood Properties & Attributes

Structural Appearance Other

Basic density Colour Tracheid length

Modulus of elasticity Resin features Cell wall thickness

Modulus of rupture Checking Density

Stability Stability Extractives content

Knots Durability Cellulose content

(Microfibril angle) Heartwood

Knots

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Some Major Drivers of Wood Property Variation

• Within-tree variation – biological phenomenon• Site – climate and soil driven• Genetics – contributes to properties and variation• Silviculture – control of growing space + pruning

Timeline for Wood Quality Research in NZ

1960 - 1980 1980 - 2000 2010 +

WQ Site Variation

2000 - 2010

Link WQ Performance

Link WQ to Silviculture

WQI/SWI

FFR

Cambial Modelling

Segregation Tools

Value Recovery

ConversionPlanning

Effect of Silviculture

Genetics of Wood Properties

Sawing Studies

Model Property Patterns

Non-destructive Tools

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Regional Variation in Wood Density

Intra-Stem Variation in Wood Density

(Example from Tarawera stocking trial)

Density = f(RN, RW, Density Index)

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Effect of Genetic Gain on Wood Density

Density Index = 398 + 1.85 GFPlus

350

400

450

500

550

-20 0 20 40 60

De

nsi

ty In

de

x (

kg

/m3)

GF Plus rating

Microfibril Angle

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Source:Walker (1993)

Modulus of Elasticity

• Traditionally measured in bending tests• Can be estimated from:

− portable acoustic tools− density and microfibril angle

MOE = ρV2

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Appearance Characteristics – Resin Features

• Incidence has been recorded across NZ• Range of causal mechanisms suggested

− Wind− Drought− Nutrition (boron deficiency)

(Woollons & Manley 2008– NZ J For. Sci.)

Shrinkage and Distortion

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Spiral Grain

New Insights into Spiral Grain

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Growth Stresses

• Not really a problem in radiata pine, but can be a major problem in Eucalypts

Juvenile Wood – A Challenge for Plantation Softwoods

• Juvenile wood refers to the relatively poor properties of the wood formed near the pith

− Often defined as innermost 10 rings

• Characteristics include: − wider growth rings, − lower wood density, − higher spiral grain− higher shrinkage

• Other features such as heartwood, resin content and intra-ring checking are much more prevalent in the juvenile wood

• Main influences on juvenile wood content are:

− Rotation length− Stocking

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Inherent Characteristics of Plantation-grown Softwoods

Levels vary with site, silviculture and genetics

Drivers of Juvenile Wood Content

05

101520253035404550

25 30 35

Juve

nile

Co

rew

oo

d

Co

nte

nt

(%)

Clearfell Age (years)

Clearfell Age

ClearwoodFraming

0102030405060708090

100

0 2 4 6 8 10

Juve

nile

Co

rew

oo

dC

on

ten

t (%

)

Log Position in Stem (5m height classes)

Position of Log in Stem

Clearwood Framing

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Silvicultural Interventions to Improve Wood Quality

• Choice of planting stock• Site preparation (weed control)• Initial planting density• Fertilisation• Timing & intensity of thinning• Pruning• Rotation length

Effect of Growing Space on Wood Properties

1000 1500 2000 2500

0

2

4

6

8

Stocking (stems ha−1)

Stif

fne

ss (G

Pa

)

Clone 6Clone 9Others

Lasserre et al (2005) Carson et al (in review)

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Structural volume needs high final stocking and age

< 100m3

>600m3

Source: Brian Rawley

What Can We Model Now?

• Models are available in Forecaster for the following:− Wood density

− MOE (acoustic velocity)

− Heartwood

− Branch size

− Stem form (sweep/forking – probabilistic)

− MfA

− Spiral grain

− Juvenile wood content

• Explicit models do not exist for the following:− Resin blemishes

− Compression wood

− Intra-ring checking

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Linking end product performance back to the forest

Tree Board

Measured and simulated distributions of board

properties are in agreement

MOE Twist

Crook Bow

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Summary

• Variability in wood quality within stems is high for radiata pine anda function of age (juvenile wood – density, fibre length, spiralgrain, etc.)

• Variability between stems within a site is high and can be greaterthan site effects

• Site factors determine average fundamental wood characteristics(wood density, resin features)

• Silviculture (spacing, pruning, fertilisers and rotation) has a majorimpact on stem growth rate, variability and quality (juvenile wood,branching)

• Genetics can potentially alter average wood quality and variability