A new technology for measuring growth stress in Eucalypts
Norashikin Kamarudin
Submitted in total fulfilment of the requirements of the degree of
MWoodSc (by Research)
June 2014
School of Land and Environment
The University of Melbourne
i
ACKNOWLEDGEMENTS
First and foremost praise to Allah the Almighty for his mercy. With his approval I
successfully completed my research project. Committing to a Masters Degree is a
challenging undertaking, especially daunting for a person with English as a second
language.
This study would not have been possible without the strong support from dedicated
supervisors Professor Peter Vinden, Dr Simon Przewloka and Dr Graham Brodie. I
would like to express my profound heart-felt gratitude and appreciation for their
invaluable guidance, advice, reviews and comments during the writing of this thesis
as well as for their kindness, patience, wonderful thoughts, assistance and providing
continuous encouragement throughout the study.
My special thanks go to my co-supervisor Mr Ken James for his lovely thoughts and
the contribution he made in providing me use of his fantastic equipment (GSM10) for
my project. Ken had faith in me and fully supported my research using his novel
equipment and allowed me to explore much information for measuring growth stress
with his novel method. It was not easy and quite challenging to introduce this new
method to me but he always had belief in my ability to make this project successful. I
will ever remain grateful to him.
I am most grateful to the Jun Li Yang, researcher of CSIRO, for meeting with me and
sharing her ideas and resources for my project. I also want to give deep appreciation
and sincere thanks to all staff of the Department of Forest and Ecosystem Science,
The University of Melbourne who were involved directly or indirectly in my project.
I also would like to express my thanks to my Scholarship, University Technology
MARA Malaysia who readily gave me fund to achieve my study in University of
Melbourne. Without their support and encourage, my dream would never come true to
pursue my master in Australia. I hope all knowledges, ideas and experiences that I
obtained and share with my nation. Thank you so much once again for making my
dream comes true.
ii
I am also grateful to my lovely friends Nur hannani Abdul Latif and Muliyana
Arifudin for their help, support and invaluable interaction when I was working in the
field and laboratory. I will never forget their kindness and sincerity in accompanying
me during progression of this project. I am indebted to my colleague Krisdiyanto
Sugiyanto and Anil Sethy for their ready assistance, advice and unflagging
encouragement.
Finally, I wish to express my special thanks to my beloved mother Zaiton Ahmad,
sister Nurulafiza and my brothers Nur Shamin and Nur Shamil for letting me put my
studies ahead of their needs. I am also indebt to my best friends Suzi anah, Khadijah,
Norizan and Zaida for their invaluable moral support and encouragement during my
study even though they were far away from me. Thank you once again to all of you.
iii
STATEMENT OF ORIGINALITY
This is to declare that this thesis comprises my own work, except acknowledgement
has been indicated in the text and other materials used.
Norashikin Kamarudin
June 2014
iv
DECLARATION
This is to certify that:
i) the thesis comprises only my original work towards the masters
ii) due acknowledgement has been made in the text to all other material used
iii) the thesis is 22, 463 words as approved by the Research Higher Degrees
Committee.
__________________________
Norashikin Kamarudin (341588)
June 2014
v
ABSTRACT
A new method of measuring growth stresses in standing trees for example Blue Gums
(Eucalyptus globulus) has been developed at the University of Melbourne, Burnley
Campus. The Objective is to compare the technique with traditional methods such as
the CIRAD Foret method that was developed in France. Preliminary results indicate
the GSM10 method (Ken James Apparatus) is more sensitive and potentially a more
accurate method of measuring growth stresses in round wood. In this research there
are a few relationships have been evaluated to determine their effect on growth
stresses. Different tree heights (0.5 m and 1.3 m), direction or orientation of the tree
stem (North, East, West and South), age, diameter, species, and distance between
trees were evaluated. Growth stress measurements show that the GSM10 method is
more sensitive than the CIRAD method. The strain of wood by using the GSM10
method was found to be approximately half the strain measured using the CIRAD
Foret method. Three assessments have been undertaken. Firstly, the growth stress of
trees between CIRAD Forêt method and GSM10 are compared by drilling 20 mm
holes. Secondly, growth stress has been tested for the GSM10 method by drilling the
top of the 20 mm hole. Thirdly, growth stresses have been tested using the GSM10
method by drilled a hole at the bottom of the 20 mm hole. The GSM10 method is
quick and accurate, hand held and provides computer print-out of results. Most
importantly and unlike existing technologies, the new method provides relatively little
damage to standing trees.
vi
TABLE OF CONTENT
Title Page
Acknowledgement i
Statement of Originality iii
Declaration iv
Abstract v
Table of Content vi
List of Figures viii
List of Tables ix
Abbreviation x
Chapter
1.0 General Introduction 1
Objectives 9
2.0 Biological Processes and Wood Quality 10
2.1 Biological process 10
2.2 Wood Quality 11
2.2.1 Wood Quality – Eucalypts 11
2.2.2 Biological factors affecting wood properties 12
2.2.2.1 Forest Pest and Wood Diseases 12
2.2.2.2 Compass Direction in the Tree Stem 13
2.2.2.3 Temperature, Light and Wood Production 14
2.2.2.4 Position of the Tree in the Stand 15
3.0 The Effect of Silviculture on the Quality of Wood from Eucalypt
Plantations 17
3.1 Introduction 17
3.2 Tree Spacing 18
3.3 Thinning 19
3.4 Pruning 21
4.0 Growth Stress 22
4.1 Mechanism of Growth Stress 22
4.2 Strain Distribution 24
5.0 Methods of Measuring Stress 28
5.1 Introduction 28
5.2 Nicholson Technique 28
5.3 CIRAD Forêt Method 32
5.4 Strain Gauge Method 34
6.0 New Growth Stress Measurement- GSM10 Method 36
6.1 General Introduction 36
6.2 Comparison between two methods of measuring growth stress;
CIRAD Forêt method and GSM10 method. 38
6.2.1 Introduction 38
6.2.2 Materials and Methods 39
vii
6.2.3 Results and Discussions 42
6.2.4 Conclusion 47
6.3 Measuring growth stress at different height 48
6.3.1 Introduction 48
6.3.2 Materials and Methods 48
6.3.3 Results and Discussions 50
6.3.4 Conclusion 52
6.4 Measurement of growth stress at different tree faces 53
6.4.1 Introduction 53
6.4.2 Materials and Methods 54
6.4.3 Results and Discussions 56
6.4.4 Conclusion 56
6.5 Measuring of growth stress at different sites 57
6.5.1 Introduction 57
6.5.2 Materials and Methods 58
6.5.3 Results and Discussions 59
6.5.4 Conclusion 60
7.0 General Conclusions 61
7.1 Recommendation 64
References 65
Appendices 70
Appendix A-1 70
Appendix A-2 72
Appendix A-3 74
Appendix A-4 76
Appendix A-5 79
viii
LIST OF FIGURES
No Title Page
Figure 1 Log end splitting due to the release of growth stresses following
cross cutting (Eucalyptus spp.).
4
Figure 2 Near full length log splitting due to the release of growth stresses
following cross cutting (Eucalyptus spp.).
4
Figure 3 Distortion of sawn boards due to the growth strain differential
(Eucalyptus spp.).
5
Figure 4 End face 5 minutes after cross cutting - no heart cracking present. 6
Figure 5 Small cracking developed 1 hour after cross cutting 6
Figure 6 Log showing worsening heart cracking 4 days after felling 7
Figure 7 Leaning stems showing direction of growth stress induced forces
acting to maintain upright habit or stabilise the stems. CW=
compression wood; TW= tension wood.
18
Figure 8 The importance of even tree spacing. 19
Figure 9 The effects of stocking upon tree characteristics 20
Figure 10 The importance of attaining large diameter. (Shading represents the
defect core)
21
Figure 11 Accumulation process of longitudinal stresses in tree 23
Figure 12 Preparation of a diametrical plank for the measurement of growth
stresses
25
Figure 13 Strain distribution across a stem as calculated using (Kubler,1987)
model.
26
Figure 14 (a) Front and side view of a wood segment to be removed as
specified in the Nicholson primary procedure (1971);
(b) The side and top view of the wood segment after removal.
29
Figure 15 Measurement of longitudinal strain near the tree surface with a
classical extensometer.
31
Figure 16 The point and site view of the CIRAD Forêt strain measurement. 33
Figure 17 a) The strain gauge method
b) Measurement of the released strains of two-dimensional surface
growth stress on the outermost surface of the xylem by the strain-
gauge method
34
35
Figure 18 CIRAD Forêt method of growth stress measurement on a standing
tree.
40
Figure 19 The GSM10 and placement guide. 41
Figure 20 Measurement of longitudinal released strain growth stress. 42
Figure 21 Relationship between growth stress for CIRAD Forêt and GSM10
methods
44
Figure 22 Strain measured with strain gauge before and after releasing growth
stress
45
Figure 23 Effect of the release position on the growth stress strain released 46
Figure 24 Diagrammatic representation of sampling strategy 49
Figure 25 Mean growth stress at 10 heights 51
Figure 26 Growth stress measurement at four difference faces 55
Figure 27 Changes in mean growth stress with different tree faces 56
Figure 28 Mean growth stress of 10 individual trees averaged from
measurements at two sites
60
ix
LIST OF TABLES
Table Title Page
6.0 The readings of CIRAD Forêt and GSM10 method 43
6.2 Analysis of tree mean value of growth stress 59
x
ABBREVIATION
cm centimetre
CSIRO Commonwealth Scientific and Industrial
Research Organization
CW compression wood
DBHOB Diameter Breast Height Over Bark
DOS Diameter Over Stub
E East
e.g example given
GSM10 Growth Stress Method
ha hectare
in inch
m metre
mm millimetre
MOE Modulus of Elasticity
N North
NAP National Afforestation Program
S South
SA South Australia
SE South East
TW tension wood
USD United Stated Dollar
W West
1
CHAPTER 1.0: GENERAL INTRODUCTION
Wood has long served as a most versatile and widely used raw material. Wood
products include: solid wood for structural and ornamental applications, composite
products in the form of panels and beams, numerous paper products, chemicals and
fuel. Foresters have worked for many years to increase wood yield from forests, while
manufacturers have refined their techniques to become increasingly efficient in
producing wood products. To a large extent, however, work has been carried out
without a true understanding of the needs and constraints.
Wood results from biological processes. Growth occurs under a wide range of genetic
and environmental influences resulting in a similarly wide range of wood properties
and characteristics (Punches, 2004). Understanding the process by which trees grow
allows foresters to anticipate the effects of their activities on the products that will
ultimately be produced. Similarly, understanding tree growth processes helps wood
product manufacturers to comprehend how various wood characteristics develop and
what constraints foresters face while guiding the growth process (Punches, 2004).
Wood that is intended for structural applications may be judged by its strength,
stiffness and dimensional stability, while wood for architectural millwork may require
specific grain patterns or colour (Punches, 2004). In the pulp and paper industry,
wood quality may be based upon fibre length and relative proportions of cellulose and
lignin (Ververis et al., 2004). Several wood attributes (density, fibre length,
compression wood, growth rings, juvenile wood and growth stresses) are applicable
across applications (Vinden, 2009) Foresters understand the quality of wood depends
upon environmental issues, growth rate, disease resistance, uniformity between trees
and genetic variability (Vinden, 2009).
The productivity of most forest plantations is less than their physiological potential as
defined by prevailing climate, because the supply or capture of light, water and
nutrients is less than optimal. However, maximum growth does not equate to
maximum wood value. The silviculture challenge is to design and use management
regimes that achieve target growth rates and wood quality by manipulating resource
2
supply, capture or use (Gonçalves et al., 2004). There are some impacts of forest
operation upon wood quality such as seed source or selection and genetic
improvement, site, spacing and weed competition, thinning, pruning, fertilizers and
age at harvesting (Vinden, 2009).
Forestry in South Australia has been dominated by plantations of radiata pine (Pinus
radiata D. Don) since the early 1900‟s following a series of species and provenance
trials conducted after which it was decided by the Forestry Board that the indigenous
eucalypt species had little potential to support a forest industry (Boardman, 1988).
Radiata pine out performed a range of exotic species that were investigated. No
further detailed examination of the potential of eucalypt species for plantation forestry
was undertaken until the late 1970‟s when an experiment involving 36 species and 88
provenances of eucalypts was established at Mount Gambier in the south-east of
South Australia (Cotterill et al., 1985). This work indicated that a number of eucalypt
species could grow at satisfactory rates using prevailing silviculture which involved
complete weed control to maximize water availability to the tree crop (Yang et al.,
2001). Tasmanian blue gum (Eucalypts globulus) was one of the eucalypts species
that was identified as having potential and further research was undertaken by the
National Afforestation Program in 1998 with 114 ha being planted in South Australia
(Woods and Forests, 1989). The tree plantation program, known as the Green
Triangle Region (TGR), undertaken by Apcel (now Kimberly Clark, Australia.) in
south-eastern South Australia and south-western Victoria, is one of the continuing
efforts to encourage plantation establishment of up to 500 ha of blue gum annually to
supply hardwood chips to the paper mill at Snuggery, SA (Woods and Forests
1990/91). Annual planting of blue gum increased rapidly with 3380, 8000 and 20000
ha being planted in 1997, 1998 and 1999 respectively (Yang et al., 2001).
In most countries where large areas of eucalypts have been planted, the primary use
has been for wood chips, firewood, mining timber and shelter belts. Higher value uses
such as furniture and internal decoration are very limited due to unsatisfactory quality
of the raw material and the lack of knowledge and experience in handling growth
stresses during sawlog processing and subsequent timber drying (Yang and Waugh,
2001). The motivating factors for developing higher quality timber products from
these resources are the vast areas of plantations, the decline in hardwood pulpwood
3
prices, better financial prospects from higher value products, environmental concern
over the deleterious impacts of short rotation management, emerging conversion and
processing technologies and the potential to substitute eucalypt products for tropical
hardwoods (Flynn and Shield, 1999).
One of the key factors limiting higher value use of young eucalypts as sawlogs is high
growth stress (Maree and Malan, 2000). The release of residual growth stresses results
in log end splitting, flitch moment and further splitting of the log end splits during
sawing, sawn board distortion and thickness variation and reduced choices of sawing
patterns (Yang, 2005).
Major problems for plantation grown logs are:
a) End splits – Growth stress can result in end splitting of logs after felling. It
can also occur when a log is cross cut. The longitudinal growth stress of a
fresh cut is transformed into secondary radial and tangential tensile stresses at
the cut end (Yang, 2005). It becomes worse when the tangential stress is near
the pith. When the tangential stress exceeds the tangential tensile strength of
the wood, splits, originating from the pith, develop on the log end (Figure 1).
Log end splitting happened because of growth stresses but is accentuated by
careless tree felling, incorrect stem cross cutting and rough log handling.
These end splits can become continuous splits along the entire length of the
log (Figure 2). End splits usually reach its worst in the first week following
cross cutting, then slowly becomes wider and longer with time (Yang and
Waugh, 2001).
4
Figure 1: Log end splitting due to the release of growth stresses following cross
cutting (Eucalyptus spp.).
Figure 2: Near full length log splitting due to the release of growth stresses following
cross cutting (Eucalyptus spp.).
b) Distortion during sawing – Sawn boards distort as a consequence of the re-
balancing of residual growth stresses in the boards upon being sawn from logs
(Figure 3). Quarter sawn boards spring and back sawn boards bow. Bow can
be corrected throughout by resizing (Yang, 2001).
5
Figure 3: Distortion of sawn boards due to the growth strain differential
(Eucalyptus spp.).
c) Heart checks – Radial heart cracks are commonly found on the end faces of
logs immediately or soon after felled trees have been crosscut. These cracks
are frequently attributed solely to the relief of longitudinal growth stresses and
their development is influenced by steepness of the site, altitude, log diameter
and external stresses on the log during felling and cross cutting (Barnacle,
1971). Trees and logs are also subjected to external stresses which could
contribute to the development of radial cracks. External stresses during felling
and cross cutting may be due to the stem leaning over while the felling cut is
being made or to the force of impact as the stem and branches strike the
ground (Barnacle, 1971). Bending of the stem across supports during
crosscutting or rough handling of logs after cutting can also contribute to
stresses in the log (Barnacle, 1971). Cracks are found in the end faces
immediately after cross cutting (Figure 4). Heart cracking can appear up to 4
cm in length after initial exposure (1 hour after cross cutting) (Figure 5). Logs
exposed for longer times results in cracks worsening after 4 days (Figure 6)
(Barnacle, 1971).
6
Figure 4: End face 5 minutes after cross cutting - no heart cracking present.
Figure 5: Small cracking developed 1 hour after cross cutting.
4 cm
7
Figure 6: Log showing worsening heart cracking 4 days after felling.
d) Some other minor problems that also contribute to undesirable effects in
sawlogs utilization are:
i) Sawn board thickness inaccuracies
When a log is cut, both the board being removed and the remaining
flitch will move or distort as they attain a new state of stress
equilibrium. Flitch remaining on the carriage curves away from the
straight saw line thus, the next board cut will be below the nominal
thickness at the ends of the board and above the thickness at its
centre if appropriate sawing equipment is not used to manage this
problem (Yang, 2001)
ii) Loss of productivity
To resize quarter sawn boards that have excessive spring and resize
sawn boards to the correct thickness at a later stage, is to add one
more step of processing, thus reducing productivity. (Barnacle,
1971).
8
iii) Drying degrade due to tension wood
Growth stresses are generated in newly formed wood cells. The
highest growth stresses are usually found during the formation of
tension wood. Trees that show high growth stresses are suspected
of having more tension wood, or at least have wood cells that are
different from less stressed wood (Nicholson et al., 1975). A
number of eucalypt species are prone to collapse checking during
drying. The presence of tension wood makes this collapse checking
worse (Dadswell et al., 1959). Sawn boards from highly stressed
trees have been observed to collapse more severely than normal
material (Nicholson et al., 1972). The presence of collapse
checking in seasoned wood has a limited effect on structural sawn
products, but, depending on the severity of the checking, it may
exclude the use of this seasoned wood for higher value appearance
products.
iv) Weak material in the core wood zone caused by brittle heart
Brittle heart starts to form during tree growth when the
compression stress induced by growth stresses towards the tree
centre exceeds a certain percentage of the compression strength of
the wood (Yang, 2001). Severity and radial extent are associated
with the magnitude of growth stresses and the tree‟s diameter.
Brittle heart has low strength properties, in particular impact
strength, and fails with a brash fracture (Dadswell and Lanlands,
1938). Yang (2000) found that the bending strength of brittle heart
in Tasmanian E. obliqua regrowth was approximately 97% of that
of the clear material. The incidence of brittle heart has also been
reported in Zambian grown E. grandis (Hillis et al., 1975) and
South Africa grown E. grandis. Brittle heart appears to a minor
problem for small size trees which are becoming the major supply
in the log market.
9
OBJECTIVES
The aim of this study is to find more efficient methods of measuring growth stress in
both standing trees and trees that have been felled. The new method of measuring
growth stress developed by James (2008), “GSM10” is one of the practical methods
of measuring stress in trees and logs. The accuracy of this method in measuring
growth stress will be compared with a widely used method, the CIRAD Forêt method.
The Objectives of this study are to:
1) Measure growth stress and compare both CIRAD Forêt and GSM10 methods
(drilled in 20 mm hole).
2) Measure growth stress using the GSM10 method by drilling 6 mm hole at the
top and bottom of 20 mm hole.
3) Compare the growth stress at different tree heights and faces (north, east, west
and south).
4) Compare the growth stress between 2 different growing sites.
10
CHAPTER 2.0: BIOLOGICAL PROCESSES AND WOOD QUALITY
2.1 Biological process
Wood in standing trees is subjected to stress during the whole life of the tree. That
means a potential ability of the material to strain or even to crack when processed
(Archer, 1986; Kubler, 1987). Various methods allow the measurement of released
longitudinal, εL , and tangential strains, εт , at the stem periphery. Longitudinal strain is
usually negative (shortening) and exceeds 10-3
; tangential stress is positive, of the
order of about 2 times the longitudinal strain. Accordingly as, εт > -vLT εL (v LT :
Poisson‟s ratio), it can be assessed that in most standing trees, the longitudinal
component of stress is tensile and the tangential component is compressive (Ferrand,
1981). However, this assessment may not apply in case of reaction wood and juvenile
wood (i.e. small diameter logs).
The living tree takes advantage of these stresses: tensile longitudinal stresses protect
sapwood against excessive wind induced compressive bending stresses, and
compressive tangential stresses counteract frost or drying crack propagation (Kubler,
1987). To describe the origin of growth stresses, the following assumption may agree
with anatomical, physiological and chemical observations, according to many authors
(e.g. Boyd, 1972; Bamber, 1987). During radial growth, cells of outermost layers, just
after differentiation, have a tendency to shrink in the fibre direction and swell in the
transverse direction. These strains are impeded by the central part of the trunk that
leads to internal stresses in the whole tree.
Many biological processes in wood occur during the formation of cell wall. The
behaviour of a wood during use is correlated with its chemical composition, the fine
structure of the fibre wall, and its anatomy. The thickness of the cell wall of the fibre
can vary from species to species, latewood to earlywood, or normal wood to tension
wood. The wall very largely consists of the secondary wall of which the S2 layer is the
main portion. The cell wall is made up of cellulose microfibrils in a matrix of lignin
and hemicelluloses. The microfibrils comprise elementary fibrils that are surrounded
by hemicelluloses (Fengel, 1971). The microfibrils in the S2 layer of the cell wall are
arranged in a spiral with respect to the cell axis and variation in this angle of
11
orientation can cause considerable variation in wood properties. The angle becomes
less with increasing cell length.
Only about one fifth of the components in the secondary wall are lignin, but the major
portion of the total lignin is found there because of its larger volume in comparison
with the remainder. The concentration of lignin in the middle lamella region is,
however, greater than 50%. This highly lignified middle lamella probably restrains
the shrinkage of wood more than the lignin in secondary wall (Kelsey, 1963).
The microfibrils in the cell wall do not pack completely together and the space
between them which is accessible to water occupies about one quarter of the volume
of the fibre walls of undried sapwood. The size of capillaries which make up this free
space is uncertain, but is large enough to enable the penetration of substantial amounts
of extractives of low molecular weight, or of other material (Hillis, 1971). This
penetration results in greater durability, stability etc. of heartwood or of treated
sapwood.
Wood elements – The arrangement of the vessels, parenchyma and generally, the type
of fibre-tracheids which constitute the ground mass of eucalypt wood varies between
different groups of species. Because of variations within species, and the similarity of
anatomy between some species (Dadswell, 1972), it is not always possible to identify
woods of particular species from their anatomy (Hillis, 1978).
2.2. Wood Quality
Variation in the quality of wood depends on variations at the cellular level, in the
chemical composition, ultrastructure and microscopic characters of the wood.
Substantial variation also occurs at higher levels of organization, not only
interspecifically, but also within and between trees of the same eucalypt species, in
cell dimensions and the relative proportions and arrangement of different tissue
elements. A better understanding of the relationship between the chemical,
morphological and physical characteristics, and the conversion and utilization
properties of eucalypt wood will assist in the planning of research programmes to
improve wood properties of future generations of eucalypts.
2.2.1 Wood Quality – Eucalypts
There are about 500 species and subspecies within the genus Eucalyptus (Pryor and
Johnson, 1971), but in practical terms only about ten species have been planted
12
extensively outside Australia: furthermore, within Australia the so-called “ash” group
of eucalpyts, mainly Eucalpytus delegatensis, E. obliqua and E. regnan, provide for
most of the industrial timber produce (Brown and Hilis, 1978).
Now, largely as the result of intensive development work and improved technology,
eucalypt timbers are used extensively for building, as decorative woods for furniture
and veneers, and for a variety of paper pulps. It would be fair to say that many of
these uses came about not because eucalypts would have been the first choice for a
particular product, but because the timbers were available in great quantity and were
cheap. The technologies were developed to make full use of the unfamiliar raw
material, and now many of these timbers are greatly prized for specific purposes.
These comments would particularly apply to the use of eucalypts for pulp and paper.
New technologies, in forestry as well as pulping, were required to produce high
quality paper from these short-fibred hardwoods. Once the technology was
established, eucalypts became species of interest to forestry outside Australia.
Hillis (1978) states that „plantation eucalypts will be used most effectively when it is
realized that fast grown- eucalypt wood is in many ways, “new” wood. It has
properties requiring improved conversion processes and different methods of
utilization. Furthermore, knowledge of the structure and formation of wood in young
trees will facilitate the modification of wood properties through silviculture. The short
rotation cycle involved will assist the introduction of trees with wood properties
improved by genetic manipulation or selection. The shorter rotation periods of
intensively grown plantations also enable decisions concerning their likely end-use to
be made with greater certainty‟.
2.2.2 Biological factors affecting wood properties
There are many biological factors that can alter wood quality, but do not fit neatly into
any category. Factors that affect wood quality are:
2.2.2.1 Forest Pests and Wood diseases.
Insect and diseases that do not actually kill trees often cause
deformation or changes in wood properties that render the wood of
limited utility. Others that kill trees can cause a rapid deterioration of
wood quality, reducing its usefulness for some products and making
the wood useless for others.
13
a) Disease and Wood Properties
The most common infections that cause variation in wood colour
are the blue-stain fungi. The degrade and loss of wood quality due
to the stains decay fungi and heart rots are so large and important
that they deserve special, full coverage in a separate publication
and will be dealt with no further here, other than to recognize that
severe wood variability is caused by decay and stain organisms.
There are diseases which do not kill the tree, but do a great amount
of damage to the wood. Diseases commonly attack wood in trees
destroyed by fire, wind-blow or other causes. The wood can be
severely affected and one of the most puzzling problems is what
use can be made of such wood.
b) The Influence of Insects on Wood Quality
There are both direct and indirect reasons for changes in wood
properties following insect attack. When trees are killed by bark
beetles, spruce budworm, defoliators, or similar insects, the wood
is usually degraded by subsequent fungal attack or from attack by
secondary insects, rather than directly from the insect that killed
the tree.
c) Effects of Other Pests on Wood Properties
Numerous other organisms that attack a tree can affect wood
quality. For example, Pirito et al. (1974) studied the effects of
mistletoe (Phoradendron sp. and Arceuthobium spp.), common
pests of both conifers and hardwoods, on lodge-pole pine. They
found that the infected wood had a higher specific gravity, more
alcohol-benzene extractives, shorter tracheids, and an increased
fibril angle, resulting in an increase in longitudinal shrinkage of
boards made from it. An important finding was that both infected
and non-infected wood in the same tree was affected by mistletoe.
2.2.2.2 Compass Direction in the Tree Stem
Especially in the higher latitudes, it is sometimes found that wood
formed on the side of the stem that receives more sunlight or is subject
to prevailing winds is different from wood on the shaded or protected
14
side of the tree. In diffuse-porous hardwoods, the cardinal direction
seems to have little effect, even in the far North. For example,
Yangchuk et al. (1983) found no significant differences with cardinal
direction in trembling aspen (Populus tremuloides) in Alberta, Canada.
There was also no difference between north and south part of the tree
in Populus deltoids, according to Walters and Bruckman
(1965).Knigge and Koltzerbburg (1965) cited several authors who
concluded that fibre length in poplars was greatest on the sunny side of
the tree. They then cite several other authors who found no differences
(for Eucalyptus and Populus species). Meyer (1957) reported a smaller
proportion of fibres and more rays and vessels on the sunny side of
poplar. Several of the authors identified that position of an individual
tree within the forest stand can modify the effect of compass direction
(Zobel and Buuijtenan, 1989). The wind direction from prevailing
winds can also have a considerable effect on wood properties. One of
the summary points of Olesen (1973) on Norway spruce is “…. wind is
thus directly the main cause of the systematic variation in basic density
between directions within a stand”.
2.2.2.3 Temperature, Light and Wood Production
Although temperature is one of the integral parts of the climate, only a
few studies have been made directly on temperature effects, other than
those cited above related to compass direction. When young red pine
trees from widely separated natural stands were grown at four
temperatures for 23 weeks, differences were found for most wood
characteristics although only minor differences were observed among
the source population (Larson, 1967).
In Picea sitchensis, Richardson (1964) found that higher temperatures
increased tracheid length and radial lumen diameter, but cell wall
thickness was not affected. Tracheid length increased with increases in
temperature, both day and night. From this, he hypothesized that cell
elongation is a direct function of temperature, while cell wall thickness
is determined by net assimilation rate.
15
It is often considered that the total sum of light hours is important for
growth patterns and thus for wood properties. To determine this for
tracheid wall formation in Larix deciduas var. polonica grown in a
greenhouse, Wodzicki (1961) treated the plants with differing
combinations of day length. He found that when daylight was
supplemented by low light intensity during the night, thick-walled
tracheids were formed. Similar results were obtained when two and six
hours periods of light and darkness were used. Contrary to most reports
he did not find a relationship between cessation of shoot growth and
tracheid wall thickening.
2.2.2.4 Position of the Tree in the Stand
A surprising number of studies have been made relative to the position
of the tree in the stand, i.e., whether the tree is dominant, codominant,
intermediate, or suppressed. Much of the European literature refers to
this as “sociological position” of the tree. Certainly sociological
positions affect crown function through light availability and crown
size so it would be expected to have some affect on wood properties
(Larson, 1963). Hildebrandt (1960) generalizes that in even-aged
stands dominant trees have a lower density than co-dominant ones.
In a study of beech (Fagus sylvatica) Koltzenburg (1967) found that
the larger amount of light available to the more dominant crown
classes produced larger vessels in the wood along with wider annual
rings. On the other hand, fiber length of beech showed no relationship
to crown class or light availability. In the dominant tree class, ring
width had little relation to wood weight, but suppressed trees had lower
specific gravity when ring width was larger. It is evident that the
position of a tree in the canopy can have an effect on wood properties.
It is of little practical importance in well-managed forests where the
intermediate and suppressed trees are removed. Little wood variation
occurs between the dominant and codominant trees within a stand
(Zobel and Buijtenen, 1989).
16
One type of defect in wood that causes extensive degrade, especially for solid wood
products are cracks and rings shakes caused by frost damage, wind, and internal tree
stresses. These are usually found in severe climates and only in some species, but the
overall degrade is much larger than commonly realized.
Dietrichson (1963) studied the relationship between wood maturation and climate in
Picea abies. After a warm summer there is a late maturation, which results in hidden
frost damage. This occurs most in southwest continental European provenances.
(Dietrichson et al., 1985) feel that the triggering mechanism for stem cracks is a late
summer drought. They also state that a growth rhythm out of phase with the climate
makes the trees more susceptible to stem cracks.
An unusual degrade of wood quality is caused by sapsuckers; a bird pecks holes in the
cambium, which results in the formation of abnormal wood and sometimes in the
death of the tree. The yellow-bellied sapsucker (Sphyrapicus varius) is a member of
the American woodpecker family of migratory birds. This bird overwinters in Central
America and southern North America. It spends the summer in Canada and northern
United States. This group of woodpeckers pecks holes in trees and larger woody
shrubs, feeding on the bark, sap and insects. This sapsucker tends to rely more on
plant sap than insects for its diet. Typically, these holes are not harmful, but some
trees or shrubs may die of holes extensive enough to girdle the trunk or stem. Their
feeding habits can also degrade wood quality or trees used for commercial purposes.
For example, feeding is more likely on red maple than Southern red oak trees.
Favorite southern trees of the yellow-bellied sapsuckers include maple (Acer spp.),
pecan (Carya), birch (Betula spp.), pine (Pinus spp.), elm (Ulmus spp.), and some
oaks (quercus spp.). Trees released by thinning are more severely damaged by this
bird than unreleased trees (Erdman and Peterson, 1972). For some species,
abnormalities in the wood caused by pecking are used for decorative purposes.
17
CHAPTER 3.0: THE EFFECT OF SILVICULTURE ON THE QUALITY OF
WOOD FROM EUCALYPT PLANTATIONS
3.1 Introduction
With increasing tree and wood maturity, cells that form new wood under the bark
contract longitudinally compared to those formed at a younger age (Private Forest
Tasmania, 2004). A tension stress forms along the grain, placing the centre of the tree
under increasing compression forces. This results in the outside of a log being under
tension while the inside is under compression, producing growth stress. The amount
of stress can vary between trees of the same species and between species.
The natural habit of trees is upright growth. If the natural habit is disturbed, for
example by soil subsidence or exposure to strong prevailing winds, the resultant
leaning stem develops abnormal wood which serves either to reorient the stem, if the
stem is not too large, or to stabilise the tree and prevent further lean (Bamber, 2001).
When a tree is not parallel to the gravity vector, a kind of wood called reaction wood
is formed (Zobel and van Buijtenen, 1989). To effect righting of the tree, compression
wood develops a compressive strength that serves to push the stem upright or stabilise
it whereas tension wood develops a contractile stress which serves to pull the stem
upright or stabilise it (Figure 7). While stresses are no doubt present in all tree trunks
they are more or less unevenly distributed and as a consequence can cause
considerable problems during sawing or drying with resultant degrade of timber
(Bamber, 2001).
In reaction wood, however, growth stresses are unevenly distributed and as a
consequence can cause considerable problems during conversion and drying. The
presence of compression wood can cause degrade in solid wood products because of
its effect on shrinkage and related seasoning defects. The flat fibril angle in
compression wood tracheids result in excessive shrinkage along the grain and reduced
shrinkage in the radial and tangential directions. Wood normally shrinks very little
longitudinally (generally 0.1% to 0.3%), but compression wood can have shrinkage in
excess of 3%. Thus, rather than the normal shortening of a 16-ft board by 0.2 in, upon
drying, the board with severe compression wood will shrink 5.7 in. or more (Wooten,
1968). The real problem occurs when part of a board is compression wood and part is
normal wood. Boards with reaction wood will affect during sawing or drying and also
18
will degrade the timber. The differential shrinkage results in all kinds of defects, such
as warping (Wooten, 1968). Even though longitudinal shrinkage increases with
increasing amounts of compression wood, careful seasoning using kilns can reduce
degrade, according to Boone and Chudnoff, (1972).
Figure 7: Leaning stems showing direction of growth stress induced forces acting to
maintain the upright habit or stabilise the stems. CW= compression wood; TW=
tension wood.
3.2 Tree spacing
Competition can have both a positive and a negative effect on tree growth and wood
quality. In young plantations a dense forest encourages rapid tree growth by
suppressing weed and providing mutual shelter from strong winds. Figure 8 illustrates
the tree on the right is evenly spaced in relation to its neighbours, resulting in a
balanced crown. If the trees are planted too close, it results in unbalanced crowns.
Such growth will also cause the development of tension wood within the stem. The
lower diagram shows indicative cross sections of stems corresponding to the trees on
the left. The shading indicates tension wood that forms within the stem on the
opposite side of additional crown development. In such cases it is common for pith to
be off-centre (Private Forests Tasmania, 2004). However, the cross section on the
right is indicative of evenly spaced trees with balanced crowns and central pith. When
even spacing is achieved in combination with thinning to low stockings at a young
age, tension wood is greatly reduced and higher quality timber can be produced.
19
Figure 8: The importance of even tree spacing. (Private Forest Tasmania, 2004)
3.3 Thinning
Thinning at an early age results in fast diameter growth and shorter trees. In contrast
when stands are left unthinned, trees are taller and smaller in diameter trees. New
Zealand experience has shown that fast-grown tall trees are difficult to mill due to
growth stresses, whereas fast-grown, large diameter logs can remain stable (Farm
Forests Tasmania, 2004). Tree planting with low stockings / hectare tend to achieve
faster growth in diameter that will reduce competition between trees (Figure 9a). The
reduced height will result in wide crowns and also reduce wind sway. Trees also have
lower growth stresses and tension wood within stem and that improves the recovery
of quality timber. The tree on the right (Figure 9b) illustrates the influence of high
stocking. Normally diameter growth will be slower and because of that the tree tends
to be tall and influenced by wind sway. It results in higher growth stresses and
tension-wood and reduced recovery of quality timber.
20
(a) (b)
Figure 9: The effects of stocking upon tree characteristics.
A reduction in growth stress is achieved with fast diameter growth. Log diameter is
important when sawing eucalypts. The amount of growth stress present is determined
by tree age, rather than growth rate. The outside of a log is under tension, while the
inside is under compression. This results in a stress gradient between the centres of
the tree and the outer periphery. A small diameter tree will have a similar level of
growth stress to a large diameter tree of the same age. The growth stress within the
larger diameter is spread across a greater distance, resulting in a relatively flat stress
gradient. As a result, there is less distortion during sawing. Figure 10 illustrates “back
sawing” (top). This enables wide boards to be cut from relatively small diameter trees.
Growth stress and tension wood can result in significant sawing and drying
difficulties. Quarter sawing (bottom) is the preferred sawing option for eucalypts with
growth stress and tension wood. Drying degrade can be significantly reduced.
However, wide boards can only be cut from larger diameter logs (Private Forests
Tasmania, 2004).
21
(Top)
(Bottom)
Figure 10: The importance of attaining large diameter. (Shading represents the defect
core). (Source: Farm Forests Tasmania, 2004).
3.4 Pruning
Unlike softwood species such as Pinus radiata, eucalypts do not tolerate intense
between-tree competition. In order to achieve larger diameter trees in relatively short
rotations, a final stocking of 150 stems/ha or less is recommended (Farm Forests
Tasmania, 2004). This requires an average spacing of 8 metres or more between trees.
Pruning is usually carried out in „lifts‟ of about two to three lifts often occurring on
selected trees at a frequency determined by the growth rates of the stand.
The objective of pruning is to select trees with suitable spacing, form and vigour and
achieve a consistent maximum Diameter Over Stub (DOS) of approximately 15cm for
all lifts. Pruning to achieve a maximum DOS significantly smaller than 15cm
achieves little with respect to clearwood recovery while tree growth can be adversely
affected. Green pruning of live branches can minimise the defect core. To reduce the
size of the pruning wounds and increase the rate of occlusion (healing) of pruned
branch stubs running operations are conducted when branches are small (<3cm).
Pruning also retains sufficient foliage to maintain growth rate to ensure rapid
occlusion.
22
CHAPTER 4.0: GROWTH STRESS
4.1 Mechanism of growth stress
One of the main functions of growth stress is to reorient the tree stem and crown to a
more favourable position (Kubler, 1988). Growth stresses result from self-generated
forces during the differentiation and maturation of new cells (Jacobs, 1938;
Yamamoto et al., 1992). In the cambium, when a new cell is initiated, the
development of its cell wall layers takes several days or weeks to complete. This
development is the so-called „maturation‟ period in which complex biochemical
reactions occur, i.e. the active construction of a cellulose network and the deposition
of lignin and hemicellulose (Yang et al., 2004). Each of these chemical components
contributes uniquely to the properties and behaviour of wood. In hardwood species
and to a lesser extent softwood species, the direct physical consequence of the
maturation is a longitudinal shortening and a tangential swelling of the new wood cell.
However, maturing cells cannot shorten completely as they are joined to older,
already lignified cells. Hence they are held in a state of tensile stress. This tensile
stress is released when a cross-grain cut is made in the wood.
Wood cells at the surface of hardwood trunks are generally held in tension. However,
the wood cells inside the trunk slowly compress until they are held in compression of
increasing severity towards the centre of the trunk due to the formation of new wood
cells (Figure 11). This gradient of mechanical stress in standing trees constitutes a
self-balanced prestressed field, whereby the outer part of the tree trunk is held in
tension and the inner part in compression (Yang et al., 2005).
23
Figure 11: Accumulation process of longitudinal stresses in tree (Baillères, 1994).
Stress is defined as the force per unit area. Objects subjected to stress will change
their dimensions and shape. The dimensional change per unit of original length is the
strain (tensile or compressive). Within the proportional limit of elasticity, stress is
equal to strain multiplied by Young‟s modulus, a measure of the rigidity of the
material (Yang et al., 2004). Growth stresses are usually impossible to measure
directly, whereas the strains are comparatively easy to assess. As the stress near the
tree surface is within the proportional limit of elasticity, it can be calculated from the
measurement of the strain and Young‟s modulus.
One of the key factors limiting the use of young plantation-grown eucalypts as
sawlogs is high growth stress within the log. The continuous formation of growth
stresses during tree growth results in as uneven distribution of residual stresses across
tree stems (Kubler, 1987). When logs are sawn longitudinally, these residual stresses
are largely released. The gradient of longitudinal residual stress causes sawing
inaccuracy and sawn product distortion which result in downgrade or rejection of the
sawn products (Jacobs, 1938; Page, 1984; Kubler, 1987; Malan, 1997).
Two explanations of how growth stresses are generated exist. They may occur during
lignification, maturation or the formation of new cells. Polymerization of lignin
24
causes contraction or swelling of the cell‟s lateral directions and simultaneous
elongation or shortening of fibres or tracheids in the axial direction (Munch 1938;
Boyd, 1972) depending on the microfibril angles in these cells (Boyd 1973a, 1973b).
The contraction of microfibrils in the formation of new cells during their continuing
crystallization is inhibited by the deposition of lignin (Yang and Waugh, 2001).
Neither explanation is applicable in all circumstances. Other factors may contribute to
the formation of growth stresses including microfibril angle, cellulose and lignin
content and cellulose crystallinity. Regardless of the mechanism, the consequence is
that dimensional changes of the cells in longitudinal and lateral directions are
restrained by already-lignified neighbouring cells, which in turn gives rise to the
formation of longitudinal and lateral growth stresses in the maturing cells.
4.2 Strain distribution
Traditionally growth stress has been assessed by harvesting trees and measuring
changes in board length (in and out of the tree) or the degree of deformation in sawn
boards. This type of sampling is destructive. Jacobs (1938) developed a method for
evaluating growth stresses in stems by cutting a full diameter plank within a log,
whilst leaving the log attached at both ends of the plank to minimise splitting as
shown in Figure 12. Guidelines representing lines which were straight in the standing
tree are marked on the plank (Figure 12a). The distance between fixed points near the
ends of the guide lines should be accurately measured. The plank should then be cut
into strips in the manner shown in Figure 12b. When the stresses are released the
strips will curve so that the concave side faces the periphery of the stem on each side
of the central strip. The strips should then be straightened and the distance between
the fixed points on the guide lines remeasured. There is a systematic variation
between the in-tree and out-of-tree lengths in the case of the strips across the plank.
The out-of-tree and lengths will be less than the in-tree lengths in the case of the strips
close to the periphery of the trunk. The strips cut from near the centre of the plank
will be longer out-of tree than in-tree. A diagrammatic representation of the change in
lengths is shown in Figure 12c. The meaning of this change of length as strips are cut
from the plank is that the outer strips must have been in a state of longitudinal tension
within the tree and the inner strips in a state of longitudinal compression (Jacobs,
1955). The amount of curvature or “deflection” (Figure 12d) is a useful measure of
25
the rate at which the axis is being compressed. The difference between the lengths of
the inside and outside edges of a strip represents the change in length of the side of
the log from which the strip was cut as the log grew the width of the strip. This
difference does not necessarily indicate the true shortening of the central axis, but
with erect stems gives a close approximation.
Figure 12: Preparation of a diametrical plank for the measurement of growth stresses.
In 70 years since Jacob‟s original work many scientific papers have been written on
theories about the origin of growth stresses and many models produced for the
distribution of such stresses within the tree. All the details have been reviewed by
Boyd, (1950) and Kubler, (1987). Recent theories have been proposed by Yang and
Waugh, (2001) where they summarise research into growth stress, their effects and
assessment methods. Very little data is available on the effects of the stress on
26
subsequent processing. Most experimental work has concentrated on assessing strain
levels and/or the behaviour of sawn boards (Raymond et al., 2004). The most
commonly quoted model defines longitudinal strain levels as a function of peripheral
strain and logarithmic function of distance across the radius of the stem (equation 1).
εl = εlp 1 + 2 ln r/R ------------------------------------------------------- Equation 1
where εl is the longitudinal strain across the stem, εlp the constant peripheral strain, r
the distance from the pith and R the stem radius (Kubler, 1987). The shape of the
calculated strain distribution from Equation 1 is illustrated in figure 13. The level of
stress present is a function of strain and the MOE (Modulus of Elasticity). Thus, if a
constant MOE is assumed, Figure 13 would represent stress rather than strain. This
model indicates that boards cut from near the cambium would be under longitudinal
tension and could be expected to shorten once released from logs, whilst boards cut
from near the pith would be under longitudinal compression and would thus be
expected to increase in length once released (Raymond et al., 2004).
Figure 13: Strain distribution across a stem as calculated using the Kubler, (1987)
model.
Peripheral strain (strain levels on the outside of the tree) can be measured on standing
trees. If the MOE is known, it can be used to estimate growth stresses without the
need for harvesting trees. Several techniques for assessing growth strain are available
(Yang and Waugh, 2001. These will be discussed in chapter 5.
27
CHAPTER 5.0: METHODS OF MEASURING STRESS
5.1 Introduction
In considering the most suitable method for estimating the level of longitudinal stress
present in logs and trees, the various techniques used in previous research were
evaluated. None of the methods previously used (Nicholson, 1971) was found to meet
the requirements of the present study. It was decided that a new technique should be
developed. Most of the techniques for assessing growth strain rely on attaching pins to
the outside of the tree, cutting or drilling holes into the wood to release some or all of
the stress and then measuring the displacement of the pins. Existing methods for
measuring surface strain as a consequence of stress release in trees are:
Primary Nicholson procedure
Simplified Nicholson procedure
CIRAD Forêt method
Strain gauge method
5.2 Nicholson technique
The Nicholson‟s technique (1971) was developed using an engineering approach. It
has been the method used by the Australian Commonwealth Scientific and Industrial
Research Organisation (CSIRO). No modifications to the procedure have been made,
despite a recent attempt to examine its validity by passing the step of curvature
adjustment (Yang and Hunter 2000). The Nicholson technique has two versions, the
primary and simplified procedures.
Primary Nicholson procedure
Two steel studs are glued to the surface of a tree stem or log which has had the bark
removed (Figure 14). The studs are 50 mm apart and aligned parallel to the wood
grain. The linear distance between the studs is measured before and after a wood
segment is removed from the tree or log. The segment is 19 x 90 mm and
approximately 10 mm thick and contains the two studs centrally. The wood segment
may develop a curvature upon its removal because of the gradient of longitudinal
growth strain along the tree radius (Kubler 1959). The elimination of this secondary
28
curvature is accomplished by using an apparatus to bend the wood segment in an
opposite direction and restore its original conformation. Following the curvature
adjustment, the distance between the studs represents the linear measurement after
strain release. Strain is calculated from the difference between the before and after
removal measurements (Yang and Waugh, 2001).
Figure 14: (a) Front and side view of a wood segment to be removed as specified in
the Nicholson primary procedure (1971); (b) The side and top view of the wood
segment after removal.
The advantage of the primary Nicholson technique is that it allows for the release of
most internal stress in the wood segment when the segment is completely removed
from the tree. It also enables the direct determination of average longitudinal strain in
the wood segment. The technique has low running cost as the pins are reusable and
durable. The tool kit costs less than USD3000. The equipment is portable and allows
for the evaluation of sequential changes in strain, when the stress field is disturbed by
drilling or grooving at nearby areas.
29
The proper removal of the segment is challenging and requires well designed,
efficient tools (chisels and saws). Poor operation is either inefficient or results in
unnecessary damage to the tree. Further, it is difficult to precisely control the segment
thickness during bark removal and to physically correct it afterwards. Cambium is
also injured as a window of bark (50 (tang) x 130 (long) mm) is removed; such an
injury is traumatic for small trees (<150 mm diameter at breast height over bark).
Measurement errors are introduced when the gauge contact with the pins differs
between the first and second distance measurements. The curvature adjustment step
takes about 20% of the whole measurement time.
Simplified Nicholson procedure
Two horizontal cuts are made in the tree, one above and one below the metal studs,
with linear measurements made before and after the cuts. Nicholson did not quote the
time saved by omitting the two vertical cuts and the removal of the sample from tree,
but from current field experience it has been estimated to be approximately 15%
(Yang and Waugh 2001). A close relationship between the primary and the simplified
procedure was suggested by Nicholson (1971) for use on large logs only (diameter
>76 mm) in order not to lose accuracy (Figure 15).
30
Figure 15 - Measurement of longitudinal strain near the tree surface with a classical
extensometer. The total longitudinal stress is relieved by sawing two grooves, above
and below the sensor. The longitudinal strain is detected and displayed in microstrain
(µm m-1
) (Baillères 1994).
An advantage of the simplified technique is a time saving of up to 15% when
removing a wood segment and given that no curvature adjustment is required,
potentially there is a further time saving of up to 20%. The error in the measured
strain due to variation in thickness between removed segments is minimized. The
procedure decreases injury to the cambium because a smaller window of bark needs
to be removed and fewer cuts are necessary.
The disadvantages of the simplified Nicholson technique are that the measured strain
is less accurate because of incomplete release of the internal stresses and it has been
tested on large trees/logs only. Methods for use on young trees are currently more
important.
31
5.3 CIRAD Forêt method
This method has undergone refinement over 20 years and the latest model is described
by Gerard et al. (1995). It is primarily used in France but has gained international
popularity. The method is based on measurement of the distance between two drilled
holes at different points. A piece of bark (200 x 100 mm) is removed from a standing
tree to expose the cambium. Using a guide to aid vertical alignment, two notched pins
are punched into the wood and an indentation is made at the same time at the mid-
point between the two pins. A steel measurement frame that is fitted with a dial gauge
is then hung on the upper pin, with a spring feeler touching the lower pin. The
distance between the two pins is measured before and after a hole of approximately 20
mm in diameter and 30 mm depth is drilled radially where the small indentation was
made (Figure 16).
32
Figure 16: The point and site view of the CIRAD Forêt strain measurement. Device in
use (after CIRAD-Forêt sensor documentation). The drilling jig is for making the
position of the hole and inserting the pins.
An advantage of the “one hole” method (CIRAD Forêt method) is the tool kit is
supplied from single source (CIRAD Forêt) as a finished product with documentation.
The method is therefore standardized among users with measured displacement
values. This method has a low running cost since the pins are reusable and durable.
The tool kit is compact, transportable and safe to operate. Cost is €2900 (in 2010) and
allows for the evaluation of sequential changes in strain, when the stress field is
disturbed by drilling or grooving at nearby areas.
Disadvantages of the “one hole” CIRAD Forêt method is that it causes more damage
to the cambium than the primary Nicholson procedure because of debarking. The
damage is worse for small trees and the hole size is fixed for trees of all diameters. It
33
is uncertain whether displacement values should be adjusted for tree diameter
differences although, given accompanying variation in the stress gradient, this would
seem likely.
5.4 Strain gauge method
The strain gauge method is predominantly used in Japan (Okuyama, 1997). Nagoya
University of Japan was the first to use strain gauges in growth stress studies (Kikata,
1972), (Figure 17a). Modified versions have also been developed and used in
Australia (Wilkin and Kitahara, 1991) and India (Aggarwal et al. 1997). A flexible,
waterproof, resistant strain gauge that has a polyamide base is glued on a freshly
exposed wood surface. The growth stresses are released by kerfing or boring the wood
around the gauge, above and below the gauge for longitudinal strain, and on both
sides of the strain gauge for tangential strain. The longitudinal and tangential strains
can be measured immediately. It is possible to carry out the measurements close
together with little interference between the measurements (Okuyama 1997). In the
latest study Yamamoto, (2005) measured the growth stresses on standing trees by
using the strain gauge method with removal of the phloem and the immature xylem at
each measuring position, and exposure of the surface of the mature xylem. The two
strain gauges were pasted together in the direction parallel and perpendicular to the
grain respectively. The surface stresses were released by making grooves of 1- 2 cm
in depth around the strain-gauges with a handsaw and a chisel (Figure 17b).
Figure 17(a) - The strain gauge method (after Kikata and Miwa 1977).
34
Figure 17(b): Measurement of the released strains of two-dimensional surface growth
stress on the outermost surface of the xylem by the strain-gauge method.
An advantage of the strain gauge method is that it is more suitable than the previous
two methods for measuring longitudinal strain in a very thin layer of wood and does
not require complex adjustment. Yoshida and Okuyama (2002) recommended 5-10
mm as the best groove depth and 3-5 mm as the best distance between a groove and
the nearest edge of the strain gauge. For tangential strain measurement, no
mathematical corrections are necessary because the strain gauges are glued to the
wood surface and their shortening occurs in the circumferential contour of the tree.
The technique is also less destructive than the previous two methods because only a
small area of bark needs to be removed. Using this method many strain values can be
automatically and simultaneously obtained over time through the use of a data logger
and control system.
A disadvantage of the strain gauge method is that its operation is expensive due to the
cost of the strain gauge. Each measurement represents a smaller volume of wood than
the previous two methods, so more measurements are needed per tree to estimate with
confidence. It is also highly sensitive so that calm weather is required otherwise
operators have to wait for trees to temporarily stop moving
35
CHAPTER 6.0: NEW GROWTH STRESS MEASUREMENT –
GSM10 METHOD
6.1 General Introduction
One of the objectives of this study is to find a practical method of treating logs and
trees to reduce stress. A prerequisite for this is the identification of a technology that
can measure growth strain accurately. A main requirement for a stress measuring
technique is that the logs and trees should not be destroyed or significantly altered
during the course of the initial measurement.
A novel growth stress measurement tool developed at The University of Melbourne
uses growth strain gauges in growth stress analysis and is known as the GSM10
method. This method has been applied by James (2008) to investigate the effect of
microwaves on the modification of growth stress in 7 year old blue gum (E. globulus)
timber, approximately 20-30 cm in diameter, obtained from Timbercorp plantations
grown in south western Victoria, Australia. The study then investigated the
development of new instrumentation to measure growth stress more accurately
(James, 2008). A novel growth stress meter prototype, based on electronic digital
sensors which could be connected to a computer was developed, so that accurate data
could be recorded and analysed. The instruments were accurate to 1 micron and initial
laboratory testing demonstrated superiority to the CIRAD Forêt strain measuring
device which is a standard in the timber industry. Several versions of the prototype
were developed and tested in field conditions and in microwave laboratories with
encouraging initial results (James, 2006).
GSM10 was developed by James (2008) after improving the accuracy of the GSM1,
GSM2, GSM3 and GSM4 prototypes to 10 microns. GSM10 is a digital instrument
connected to a computer so that accurate calibrated data can be generated for
measuring growth stress. The instrument has little damage impact to the tree because
of the small area bark removed. GSM10 is applicable to both standing and felled trees
(Figure 18 and 19).
36
In reviewing the various options available for measuring growth stress in standing and
felled trees various deficiencies are apparent in existing methods. Most importantly
the methods are quite destructive in that fairly large samples of bark have to be
removed from logs that inhibit the number of readings that can be taken from a tree.
Also the sampling may be detrimental for the continuing growth of the tree.
A eucalyptus plantation at The University of Melbourne (Creswick campus) was
selected for experimental studies. The sampling area was sloping with a small gully.
Growth stresses of eucalypts were measured on standing trees and felled trees. Ten,
fast grown trees with round stem characteristics (straight, non-leaning, low taper,
single stem, few large branches, and few injuries) were randomly selected and their
diameter at breast height, nominally 1.3 m, over bark measured. The growth stress of
each tree was measured on the surface using the CIRAD Forêt method (Gerard et al.,
1995) and GSM10 method (James, 2008) at 0.5 m and nominal height 1.3 m. The
growth stress was also measured on tree faces of north, east, west and south. The
condition of end log (where the log has been cut) was recorded as mentioned on Page
5. The growth stress before and after felling was 22 microns and 16 microns
respectively at 0.5 m height whilst at 1.3 m height, the growth stress before and after
felling was 24 micron and 29 micron respectively. After measuring the 10 standing
trees, 2 were felled. Total tree height and height of lower crown were measured. The
felled trees were cut into 3 metre lengths. All log ends were marked top and bottom as
they were cut and labels written on the log surface for identification. The logs were
transported to the laboratory 4 days after felling. End splitting was recorded and
growth stress measured on the log surfaces at eight heights, equivalent to 3.0 m, 3.4
m, 3.8 m, 4.2 m, 5.0 m, 5.6 m, 6.0 m and 6.1 m. At each tree height, growth stress was
measured at 4 faces (north, east, west and south).
In this study, the growth strain was measured by the CIRAD Forêt and GSM10
methods and a comparison made. The area of bark removed for each measured area
was 15 x 10 cm. Both the CIRAD Forêt and GSM10 were set up and the growth strain
(microns) measured at the same time by drilling a 20 mm hole. Using the GSM10
method, growth strain was measured by drilling a 6 mm hole at the top and bottom of
a 20 mm hole.
37
Four experiments were conducted and are described below:
(1) Growth strain readings are calculated between two different methods (CIRAD
Forêt and GSM10). (Section 6.2)
(2) The significance between tree heights and tree faces (north, east, west and
south) are examined. (Section 6.3)
(3) Growth strain are calculated separately using GSM10 only to see whether the
CIRAD Forêt releases all growth stress with a 20 mm drilled hole and the
relationship of growth strain by drilling a 6 mm hole at the top and bottom of
the 20 mm hole. (Section 6.4)
(4) The complete data set was analysed to compare the differences of growth
stress at different sites. (Section 6.5)
6.2 Comparison between two methods of measuring growth stress; CIRAD
Forêt method and GSM10 method.
6.2.1 Introduction
The GSM10 method was compared with Nicholson in preference to the strain gauge
method. The reasons for this arise from the greater similarity of the GSM10 method to
the Nicholson method. Cuts or holes are made above and below the strain gauge to
partially release the stresses between the cuts and holes. The longitudinal strain
determined by this method is likely to be smaller than that obtained with the
Nicholson method because of incomplete release of the stresses.
The second reason for selecting the CIRAD Foret method arises from being able to
monitor changes at the same time; the stress released can be visualized from the
software (screen). Even the CIRAD Foret method shows the reading of total amount
of stress released but GSM10 will show an extension of the stress that can still occur
in the tree. Most of the readings demonstrate that the GSM10 method is about half
that obtained with the CIRAD Foret method.
The amount of growth stress generated in the secondary xylem of the trunk is
calculated from the stress induced by releasing the growth stress and from the
elasticity. This stress is referred to as released stress of growth stress, released stress
or growth stress (Yoshida and Okuyama, 2002). Currently, the most commonly used
method of measuring growth stress is the CIRAD Forêt method (French method). In
38
this study, a novel instrument (GSM10) was used to compare with the CIRAD Forêt
technique and suggests a technique for accuracy and stability of stress measurements.
This study also investigated the stability of GSM10 before and after releasing growth
stress and the effect of groove location in the CIRAD Forêt method.
6.2.2 Materials and Methods
In this study 16 tests and measurements were conducted randomly on one felled tree
(diameter 28 cm) estimated to be 15 years old. The data from this 16 testing will be a
reference to the next experiments. This testing is really important to make sure that
GSM10 better than CIRAD Forêt in measuring growth stress. For this study, both
GSM10 and CIRAD Forêt measurements were taken simultaneously.
CIRAD Forêt method
Before installation of the two test instruments, bark was removed from the outer
surface of the tree using a chisel and hammer until the xylem was exposed (preventing
cambium damage). The area of bark removed was 15 cm long by 10 cm wide (Figure
18). Both target pins were hammered longitudinally into the measured area. There
was one small point marked where a hole was drilled (Figure 18(d)). The
displacement of the pin targets induced by releasing the growth stresses were
measured to a precision of 0.001 mm. The 20 mm drill hole, released stresses (due to
wood tension) and both pins were pushed apart. The results obtained using the
CIRAD Forêt method were recorded.
GSM10 method
In order to determine whether the GSM10 method provides similar results to the
CIRAD Forêt method, the instruments were installed adjacent to one another such that
testing occurred simultaneously when the hole was drilled. The juxtaposition of
GSM10 method relative to the hole that was drilled is given in Figure 19. The GSM10
sensor pin corrects for errors that may be caused in the field by changes in the
resistance of the sensor pin due to wind. After measuring initial strain (S1), the strain
released was then measured again (S2) after two grooves were prepared using a 6 mm
drill cut in the trunk, one above the hole and one below the hole (Figure 20(ii)).
Initially, the distance was 1 cm with subsequent grooves made closer to the hole
(Figure 20(i)).
39
The depth of the groove made to release the growth stress was kept constant at 10
mm. The amount of strain released was calculated by subtracting the initial
measurement from the second [S2 – S1 = S3 (actual growth stress)]
(a) (b)
(c) (d)
Figure 18: CIRAD Forêt method of growth stress measurement on a standing tree. (a)
insertion of two pins using a template (after bark removal), (b) two pins spread 45 mm
apart, (c) attachment of measuring cradle and micrometer and, (d) 20 mm hole drilled
between the two pins and result recorded by instrument.
40
Figure 19: The GSM10 and placement guide.
41
Pin
Drill cut Drill cut
(ii)
hole (i) hole
Drill cut (ii)
Drill cut
Trunk Trunk
(a) Side view (b) Front view
Figure 20: Measurement of longitudinally released strain growth stress. (i) 20 mm
drill hole used in CIRAD Forêt method and; (ii): additional cut used 6 mm drill cut to
release additional growth stress.
6.2.3 Results and Discussions
The growth stress readings showed large variation between the two methods (Table
6.0). The released stress values as measured by the CIRAD Forêt and GSM10
methods were linearly correlated (Figure 21). The absolute values of the released
stress as measured by the GSM10 method were approximately half those of the
CIRAD Forêt method. As the one 20 mm hole was drilled or two grooves were cut
between two pins, differences in the measurements by the two methods are likely
caused by the position of the cut. Thus, if the 20 mm hole was drilled between two
pin, the released stresses should be the same by either method, when referring to the
data, CIRAD Forêt and GSM10 methods must be measured simultaneously, and, if
the latter, whether both methods were measured accurately by 20 mm hole or two
42
grooves. The standard deviation for the GSM10 was 0.16%, while for the CIRAD
Forêt method 0.22%. Generally, if a measured value is twice as great, the calculated
standard deviation also doubles. From the equation y = 0.6291x – 9.3335 (Figure 21),
the measured value was 0.63 times greater with the CIRAD Forêt method than with
the GSM10 method. The adjusted standard deviation of the CIRAD Forêt method,
0.35% (0.22/0.63), is therefore greater than that of the GSM10 method, 0.16%
suggesting that dispersion is greater in the former than in the latter. Since the
dispersion of CIRAD Forêt method (0.001%) is sufficient to measure the released
stress, the largest dispersion of the CIRAD Forêt method is due to inconsistencies in
manual instruments. Thus, the GSM10 method is preferable for more consistent
measurements. Throughout this study, drill cuts (sawn grooves) were used to release
growth stress. In some cases, growth stress is not released sufficiently by drilling
holes, making additional calculations necessary.
Table 6.0: Matched readings for the CIRAD Forêt and GSM10 method.
Sample CIRAD Forêt (micron) GSM10 (micron)
C1 93 58
C9 45 26
C10 43 18
C11 64 25
C12 95 45
C13 78 55
C14 83 40
C15 36 10
C16 104 55
C17 66 35
C18 82 40
C19 71 36
C20 96 40
C21 87 60
C22 104 50
C23 52 12
43
y = 0.6291x - 9.3335R² = 0.7505
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120
GSM
10
(m
icro
n)
CIRAD Foret (micron)
CIRAD Foret vs GSM10
Figure 21: Relationship between growth stress for CIRAD Forêt and GSM10
methods.
i) Measurement of stability using the GSM10 method, before and after
releasing growth stress.
Strain was measured continuously for a few minutes using a GSM10 on the surface
where bark had been removed. After releasing the growth stress, the strain was again
measured continuously. The grooves for releasing the growth stress were cut 1 cm
from the end of the GSM10 and 1 cm deep.
Release of tensile growth stress in normal wood induces shrinkage and therefore,
negative longitudinal strain. The y-axis in the (Figure 22) indicates negative values.
Strain measurements remained stable (±0.001%) for 1h after the GSM10 was glued to
the secondary xylem surface immediately after exposure. After releasing the growth
stress, the negative strain (the tensile strain released in the absence of growth stress)
was measured, and was stable for 1 hour.
44
Figure 22: Strain measured with GSM10 before and after releasing growth stress
This result observed that the strain GSM10 had no drift as drying did not shrink the
newly exposed fresh green xylem surface for several hours. Most of the growth stress
was released as soon as the grooves were sawn and subsequent changes in the
measurements were negligible. Therefore, the initial strain can be measured soon after
gluing on the strain gauge, waiting only until the solder cools, and the growth stress
can then be released and the strain measured immediately.
ii) Effect of groove location in the CIRAD Foret method
There are two places that grooves can be sawn to release growth stress in the dial
gauge method: inside or outside the pair of pin targets. In normal wood, the distance
between the two pins will increase when the grooves are cut between pin targets and
decrease when the grooves are cut outside them. The absolute value of the strain
released after sawing grooves inside the pin targets was twice that measured when the
cuts were made outside them. This two-fold relationship did not always hold,
probably because growth stresses were not exactly equivalent at each measuring
point.
When one groove is made at the centre of a long trunk, the xylem surfaces are
distorted to a similar degree on each side of the groove. With subsequent grooves, the
distortion is not equal. The distortion induced by a subsequent groove is minimal on
45
the side adjacent to the first groove, because the growth stress has been almost
completely released by the first groove. However, on the other side of the cut, the
distortion is as great as that induced by the initial groove (Figure 23).
Figure 23: Effect of the release position on the growth stress strain released. A: Closer
release positions increased the released strain, B: while position under 1 cm decreased
it, C: The xylem surface and GSM10 may be extended by sawing cutting (Yoshida
and Okuyama, 2002).
46
6.2.4 Conclusion
This study found that GSM10 potentially gave more accurate readings compared to
the CIRAD Forêt Methodology when using a 20 mm drill hole and 6 mm drill cut.
The results also found that the mean growth stress using the GSM10 was
approximately half that of the CIRAD Forêt method. There are some extensions of
growth stress when using the GSM10 method just after CIRAD Forêt was applied.
To achieve accurate reading by both the CIRAD Forêt and GSM10 methods, a few
protocols have to be observed:
i) Remove the bark and the differentiating xylem with a hand chisel, so
as not to cut the xylem surface. Scrape the xylem surface with edge of
the hand chisel to remove differentiating xylem and smooth the xylem
surface.
ii) The position of GSM10 must be placed at the upper pin of the CIRAD
Forêt method to make sure the reading gives accurate readings when
the first hole is drilled using the 20 mm drill.
iii) Release the growth stress by sawing grooves above and below pin of
CIRAD Forêt, 0.5 to 1 mm from the ends of GSM10 and 5 to 10 mm
deep, using a 6 mm drill cut.
iv) Measure the stress immediately after releasing the growth stress.
Growth stresses are almost completely released immediately after the
grooves are sawn.
v) Calculate the amount of stress released by subtracting the initial
measurement from that made after releasing the growth stress.
If the CIRAD Forêt method is used, the released stress induced by sawing the grooves
outside the pin targets is equal to that induced using the GSM10 method. The stress
released by sawing the grooves inside the pin targets is about two-fold the absolute
value measured using the GSM10. It would appear that the GSM10 is more accurate
in measuring growth stress, sawing grooves inside the pin targets is preferable.
By using GSM10, appropriate procedures and techniques for harvesting and log
handling could minimize the impact and hence minimize damage after felling.
47
6.3 Measuring growth stress at different tree heights.
6.3.1 Introduction
High levels of growth stress are implicated in causing end splitting of logs, deflection
during sawing and deformation of boards as stresses are released during resawing
operations. The level of stress is a function of strain and the elastic modulus of wood
(MOE). Levels of peripheral strain can be measured on standing trees and felled trees
and if the MOE is known, stresses can be estimated. Peripheral strain levels were
extremely variable within the bottom log and little evidence was found for consistent
patterns of variation, although measurements generally increased with increasing
height above ground. This study investigates growth stress at different tree heights.
Although the development of growth stress is a dynamic process, few studies have
investigated tree growth stress at different stages of development. A few variables
should be investigated, such as crown width, DBH (Diameter at Breast Height) and
individual tree competition in stands to determine whether they may influence growth
stress (Biechele et al., 2009). The objective of measuring growth strain in this study is
to determine the relative importance of genetic and environmental effects on growth
stress in Eucalyptus globulus.
6.3.2 Materials and Methods
In this study growth stress was measured on standing and freshly felled trees. Basal
area growth was determined by measuring the DBHOB (diameter at breast height,
normally 1.3 m, over bark) of all trees growing within a randomly selected Eucalyptus
globulus forest plantation at The University of Melbourne, Creswick Campus. Ten
trees with comparatively fast growth and better stem characteristics (straight, non-
leaning, low taper, single stem, fewer large branches, fewer injuries, etc.) were
selected as the study trees and their DBHOB measured. Growth strain was measured
on the surface of each tree using the GSM10 method (James, 2008) at four different
positions. Each tree was measured at the height of 0.5 m and 1.3 m before felling.
After measurement of all standing trees, one was felled and cut into 2 m lengths, due
to the difficulties of measuring higher heights on standing trees. Three logs were
obtained over a total of eight different heights (3.0, 3.4, 3.8, 4.2, 5.0, 5.6, 6.0 and 6.3
m) and marked for laboratory analysis (Figure 24). The ends of all logs also were
48
marked as soon as they were cut. Growth stress was measured in the laboratory using
the GSM10 instrument.
Figure 24: Diagrammatic representation of sampling strategy
49
6.3.3 Results and Discussion
The results of stress measurement are given in detail in (Appendix A-3 and A-5) and
summarized in Figure 24. Growth stress was extremely variable within the log and
little evidence was found for any consistent patterns of variation. Although large and
significant differences in growth stresses were found between the trees, there were
also large amounts of variation within each tree (Figure 25). From the chart, readings
for growth stress fluctuate. The stresses increase from height 0.5 m to 1.3, 3.0 m to
3.8 and 5.6 m to 6.3 m. Yang et al. (2001) found that growth stresses at 6.1 m height
was greater than at some lower heights. High growth stress also appeared to relate
closely to tree growth characteristics, i.e. stem straightness, tree height, length of the
crown, DBHOB and taper. From the results, the largest variation was found between
the heights of 0.5 m to 1.3 m. This was followed by the region 3.8 m to 4.2 m. There
was very small variation from 5.0 m to 5.6 m. There is strong reason to support these
circumstances where the height of 1.3 m, 3.0 m, 3.8 m, 4.2 m and 5.0 m are at the log
end. Refer to Figure 5 and 6 (Chapter 1); those logs have been measured after 4 days
they felled. There were small cracks (4 cm) appeared at the end of log when it freshly
cut down. When the logs exposed to the environment for 4 days, the cracks became
worse. It is probably one of the reason how the cracks affect the reading of growth
stress at those height. Chafe (1985) found a significant negative relationship between
growth strain and height measurement in eight-year-old plantation E.nitens Maiden
over a 15 m span. Chafe (1985) suggests that these different results can be interpreted
in terms of different stages of tree maturity. This has been analysed extensively by
investigating the origin of growth stress. Firstly, there is maturation of the wood cells
causing stress, termed „maturation stress‟, and, secondly, crown weight and bending
as a result of wind causing stress termed „supported stress‟. During the maturation of
the newly formed wood, the cells, which grow every year on the stem periphery,
contract longitudinally while the lignified wood cells already formed impede this
contraction. This causes tension inside the stems, which contributes to the protection
of new wood cells from bruising. In keeping with the theory from Kubler, (1959),
growth stresses are highest at the periphery to prevent non-lignified cambium cells
becoming compacted in the event that external forces, such as wind, causes young
trees to bend.
50
Figure 25: Mean growth stress at 10 heights. Values each height are the mean of four
different positions.
One may argue that lower mean growth strain in bush-logs than that measured in the
standing tree at 1.3 m was a result of stress release upon tree falling (Yang et.al,
2001). It is true that a change in pattern and range of growth stress did occur when a
tree was felled. However, the mean value before and after felling, at approximately
the same height (eg 1.5 m), changes only slightly, and hence are comparable
(Nicholson, 1973; Chafe, 1985). Additional growth stress reduction in bush-logs
probably had also occurred during the six weeks of log storage. However, such a
reduction should have occurred at all heights in the bush-logs. Therefore the original
stain-height pattern in trees should have been reflected in the bush-logs after felling.
Yang et.al (2001) found that if mean growth stress does decrease with height in
younger trees, it would have significant implications for growth stain sampling,
especially if growth strains at a lower height (e.g. breast height) were closely
correlated with those at other heights as well as correlation with the mean growth
strain over several heights. Firstly, the measurement of strain at several heights in the
forest is highly impractical. Yang et.al (2001) also suggests that the breast height
measurements have a modest relationship with bush log growth stress. Future research
needs to investigate the full-stem growth strain distribution with height in trees of
various ages. When it known how tree dimensions affect growth stress level, the
0.0000
10.0000
20.0000
30.0000
40.0000
50.0000
60.0000
70.0000
.5 1.3 3.0 3.4 3.8 4.2 5.0 5.6 6.0 6.3
Height in tree (m)
Mean growth stress (micron)
.5
1.3
3.0
3.4
3.8
4.2
5.0
5.6
6.0
6.3
51
within tree distribution of growth stress (e.g. height distribution) might be
manipulated through forest management.
6.3.4 Conclusion
From this study, there was no significant difference in mean growth stress between
tree heights. However, measurements of a single tree at different heights may be
insufficient to detect large variation in heights differences. Sampling of large numbers
of trees is required to determine the influence of tree parameters on growth stress.
One of the objectives in this study was to determine whether growth stress was
influenced by genetic or environmental factors. The determination of the relative
importance of environmental or genetic control of wood properties is difficult because
the relationship is often influenced by genetic and environment interactions. Thus, an
individual tree of a species (or a species as a unit) may produce one type of wood in a
given environment and similar wood in another environment, while another tree (or
species) may produce a different kind of wood in the second environment.
Large growth stresses are generated in reaction wood. Research undertaken by
Yamamoto et al., (1991). To clarify the mechanisms by which growth stress is
generated has revealed that changes in cell wall structure and properties are primary
causes of change in growth stress. Therefore, there are clear relationships between
growth stress and the anatomical properties of wood (Yamamoto et al., 1991).
Environmental factors such as high temperature or soil compaction can influence
physiological processes such as photosynthesis and in turn impact growth. Altering
the environment or management practices to decrease stress, and selecting the right
tree for the right place will promote growth and longevity. Growth stress also can be
minimized by adopting silvicultural practices. As only a limited number of trees were
available for the current study, the results will need to be confirm by further research.
To discuss the influence of growth stress on wood properties, it is useful to have a
closer look at the growth stress levels found in other investigations on hardwood
species. There are no studies available that describe the growth stress level at which
the liberation of growth stresses occurs, while processing the logs or the defects that
result in reduced of wood quality (Biechele et al., 2009). Of course, other forces also
may influence wood quality, like drying stresses for instance. In combination with
high growth stresses they may lead to warping and splitting of wood (Ormarsson and
52
Dahlblom, 2008). Some logs are less prone to splitting and warping than others, even
though growth stress levels are comparable or higher.
6.4. Measurement of growth stress at different tree faces.
6.4.1 Introduction
Growth stress is one of the key factors limiting the higher-value use of young
eucalypts (Yang and Waugh, 2001). The release of residual internal stresses results in
the splitting of log ends, further splitting of the log end during sawing, sawn board
distortion and thickness variation and reduced choices of cutting pattern are also
consequences of growth stresses. Very little is known about the quantitative effect of
the growth stresses on sawn timber quality and recovery (Yang and Pongracic, 2004).
However, there is evidence that shows that the growth stress exists naturally in tree
(Jacobs, 1955) and gets worse during felling (Barnacle, 1971), causing board
deflection during sawing. This study also investigates factors that influence growth
stress in standing trees.
The mechanism of heat injury is complex and it can be difficult to distinguish this
type of damage from high levels of stress. The temperature extremes experienced by
trees depends on where the tree is planted and its location. However, there have been
very few reports of death from heat (other than fire) of trees in their natural growing
conditions (Larcher, 1995 and Moore, 1981). Stress of individual trees has occurred in
heavily thinned forest stands of trees. The effects include leaf chlorosis, reduced
growth, sunscald, production of epicormic shoots and death of trees (Kozlowski et al.,
1991). This may be similar for a tree coming from a relatively sheltered nursery and
then being transplanted into an exposed street. There is the anecdotal evidence of the
canopies of trees growing at a particular orientation then being transplanted facing
another compass point exhibiting different growth rates (Moore, 1998). For example,
one side of the tree may start its life facing south, with very little conditioning against
solar radiation, then experience being transplanted with that same side facing
northwest. The tree experiences the shock of full sun. To examine this, the four tree
faces (North, East, West, South) that may influence growth stress in eucalypts are
analysed.
53
6.4.2 Materials and Methods
Growth stress at breast height was estimated using the GSM10 method at four
circumferential locations corresponding to the North, East, West and South. Ten trees
were selected randomly from a regrowth forest of Eucalyptus globulus in forest
located at the University of Melbourne (Creswick Campus). The selected trees were at
least 5 m apart from other trees; the trees were standing on an almost even surface,
and were characterised by having very few stem defects. The selected sample had a
range of diameters ranging from 69 to 90 cm. at breast height. A large number of
measurements were made on all trees. Variables measured included tree
characteristics, growth strain, end splitting, and breast height wood properties. The
measurements made and methods used are described in the following section and the
positions on the tree at which these measurements were made are illustrated in Figure
26. The trees were marked as N to show the North direction using a compass (Figure
26a). The other tree faces (East, West and South) were determined just after the North
direction was marked (Figure 27b). Growth stresses were measured using the GSM10
method at a DBHOB of 1.3 m.
54
a) The tree marked with North direction
b) The upper view four tree faces (N, E, S and W)
Figure 26: Growth stress measurement at four difference faces (North, East, West and
South).
55
6.4.3 Results and Discussion
Given the large amount of variation present in the bottom log, the question of how to
sample in a representative manner becomes very important. The growth stresses vary
between tree faces (North, East, West and South), possibly due to the prevailing wind
direction. Figure 27 indicates that the mean growth stresses are higher on the East
face followed by the South, North and West face. Trees on a south-west facing slope
may be more prone to cold injury (southwest trunk damage) than those on other
slopes. Trees on a north-facing slope will bloom a bit later than those on other slopes,
especially a south-to-southwest slope, and are, therefore, less prone to spring frost
damage. Slopes with an eastern exposure receive morning sun earlier than others.
Fruits and foliage on this slope may dry off earlier in the mornings, thus reducing
pressure from certain diseases. Measuring all four tree faces at breast height would
increase the r = 0.95 (Figure 27) but doubles the amount of work required.
Figure 27: Changes in mean growth stress with different tree faces
6.4.4 Conclusion
In this study there is an important theoretical point relating to growth stress that needs
reconsideration. In the higher latitudes (37.403), it is sometimes found that wood
formed on the side of the stem that receives more sunlight or is subject to prevailing
winds is different the wood on shaded or protected sides of the tree. Based on where
the locations of samples were taken, growth stresses depend on the condition of the
R 2 = 0.9463
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
East South North West
Tree Faces (direction)
Growth stress (micron)
56
standing trees. The tree faces that receive more sunlight will affect the percentage of
growth stress compare to the faces of the tree that do not directly reach sunlight. Trees
try to get as much as sunlight as possible to grow and this competition make them
differ from each tree. The spacing between trees also affects the growth stress of
standing trees to get sunlight and wind. Olesen (1973) also found significant
differences in basic density within the tree, the density being highest on the south side
of the tree and lowest on the north. Ring width was less on the south and greater on
the north side, while fibre length was less than on the north side. The wood on the east
side of the tree had some characteristics similar to compression wood but no
excessive longitudinal shrinkage, although it produces low pulp yield with short
fibers. Several of the authors cited remarked that the position of an individual tree
within the forest stand can modify the effects of compass direction.
6.5 Measurement of growth stress at different sites
6.5.1 Introduction
As a result of evolutionary selection, variation occurs within a species range that
grows in different environments (Callaham, 1964; Burley and Wood, 1976). Within
species variation in characteristics are called geographic sources or provenances. For
example, trees from cold climates at higher latitudes or higher elevations usually
develop into slow growing individuals, with straight stems and small limbs with
relatively right-angled branches, making them better adapted to ice and snow.
Geographic growth differences often become “genetically set”, for example, when
selected from high-elevations they often maintain their slow growth and good form
(Langlet, 1967).
To fully understand the effect of provenance variation on wood properties, it is
essential to have a clear understanding of what is meant by environmental and genetic
control of wood. All expression of wood properties is determined by an interaction
between the genetic potential of the tree with the environment in which the tree
grows.
Many provenance studies have been made on the eucalypts, but remarkably few
include wood properties in their assessment. When wood properties have been
considered, they usually relate to pulping qualities of the species. One exhaustive
57
report relating to the wood of Eucalypts as an exotic was made by Barrichelo and
Brito (1976) who analysed the pulping characteristics of the wood of a number of
species of Eucalyptus grown in Brazil.
Eucalyptus globulus is the most widespread eucalypt plantation species in cool
temperate regions. Most plantations have been established to produce pulp wood,
although a growing number of plantations are being managed for solid wood
production (Neilson and Pinkard, 2000). To support the South Australian forest
industry, an experiment was conducted involving 36 species and 88 provenances of
eucalypts at Mount Gambier (Cotterill et al., 1985). This experiment indicated that a
number of eucalypt species could grow at satisfactory rates using prevailing
silviculture regimes which involved complete weed control to maximize water
availability to the tree crop. Apcel (now known as Kimberly Clark, Australia.)
provided support to the National Afforestation Program (NAP) to encourage blue gum
plantation establishment in Australia. This momentum was primarily driven by the
Federal Government‟s support for plantation forestry, the global woodchip market,
and local farmers seeking better economic returns than those obtained from traditional
agricultural pursuits (Yang et al., 2001). This study also determined the relative
importance of genetic and environmental factors on growth stress in Eucalyptus
globulus at two sites in Mount Gambier, South Australia. The study found that the
mean growth stress throughout the stem at the first site (Johnson Block) was higher in
all provenances than the second site (Heath Block).
6.5.2 Materials and Methods
Two sites (forest coupes) of naturally growing Eucalptus globulus were selected for
this study. These two sites are located at the Forest Reserve within The University of
Melbourne, Creswick Campus. Forest Coupe1 was 200 m North East of the Forest
Reserve. The site was characterised by having a mild slope and small gully. Forest
coupe 2 was located 500 m South East of the Forest Reserve. This site was almost flat
and tree distribution was denser compared to site 1, where tree spacing was wider and
the canopy characterised with smaller crowns. Ten trees were randomly selected at
each site to measure growth stress. The stresses were measured at breast height, 1.3 m
from the ground. The growth stress was measured on the surface of each tree using
the GSM10 method (James, 2008). Four readings were taken for each tree. The mean
58
value for each tree was calculated and an analysis carried out to test the significance
of differences between sites and the interaction.
6.5.3 Results and discussion
The analysis of tree means for growth stress is presented in table 8.2 (Appendix A-3).
There was no significant difference between Coupe 1 and Coupe 2. This result
contradicts previous research by Yang et al. (2001) who found that there were
significant differences between sites in Mount Gambier. In their studies, they also
found that there were significant differences between three provenances of E
globulus, (King Island, Jeeralang and SE Tasmania). The Jeeralang provenance may
have had higher growth stress, followed by SE Tasmanian, then King Island
provenances, if the stocking had been similar at both sites. However, there is no
strong evidence to conclude that stocking rates affected the growth stress at different
sites. Wood properties are sometimes under environmental control and vary
considerably with a change in environment. When a wood property is under strong
genetic control, it is not strongly influenced by the environment under which the tree
is grown. In other words the wood properties remain constant despite the trees having
been grown under differing environmental conditions.
Table 6.2: Analysis of tree mean value of growth stress.
Source
Type III Sum of
Squares Df Mean Square F Sig.
Site .800 1 .800 .002 .961
The mean growth strain varied between trees within a single tree at each site. Figure
28 (Forest Coupe 1 and 2) shows the mean growth stress of individual trees for each
tree. The data are presented in ascending order except tree No.8 and No.9 for forest
Coupe 1 and tree no.9 and No.10 for forest Coupe 2. The highest between tree
variations was found in forest coupe 1. The highly significant differences between
individual trees indicate that genetic differences within provenances or environmental
differences relating to planting position are important in determining growth stress.
59
Figure 28: Mean growth stress of 10 individual trees averaged from measurements at
two sites (Forest coupe1 and Forest coupe 2) at 1.3m (breast) height.
6.5.4 Conclusion
From this study, there was no significant difference in mean growth stress between
sites. However, whilst the data suggests that mean growth stress is not affected by
site, a single measurement per tree at breast height 1.3m on ten trees may be sufficient
to detect large variations in growth stress. Larger sample sizes, however, are likely to
be required for detecting or confirming smaller differences.
Coupe 1
0
10 20
30 40
50 60
70
1 2 3 4 5 6 7 8 9 10
Tree
Mean growth stress (micron)
Coupe 2
0 10
20
30 40
50 60
70
1 2 3 4 5 6 7 8 9 10
Tree
Mean Growth Stress (micron)
60
7.0: GENERAL CONCLUSIONS
Eucalypts are renowned for their high growth stress levels. Normally, the growth
stresses occur naturally in trees. The percentage growth stress in trees depends on
either genetic or environmental factors. Maturity of wood is one of the factors that
caused growth stress in trees. When the juvenile wood turns to mature wood, it will
cause tension wood in the cell wall. Growth stress continues to manifest problems
when a tree is felled. These problems comprise end cracks that appear when the tree is
freshly cut. The crack becomes worse when exposed to the sunlight and drying. The
stress causes splitting, warping and dimensional instability during cutting and drying
processes. Due to these problems, a number of factors have been evaluated to identify
whether they influence growth stress with time. Tree variables, such as breast height
(DBH), tree height, slenderness and crown parameter were measured and correlated
with measured growth stress. The results obtained indicate high variability in growth
stress values. It was concluded that growth stress could not be correlated with any
single growth parameter, but with a combination of factors that variously influence
growth stress at different heights and different tree faces (North, East, West and
South) and different sites.
Growth stress in trees is usually measured using the CIRAD Forêt method. A new
technique of measuring stress, GSM10, has been compared to the CIRAD Forêt
method. The CIRAD Forêt method measures the growth stress that is released by
drilling 20 mm hole between two pins while the GSM10 method measures together
with CIRAD Forêt method by attaching the gauge on the CIRAD Forêt method pin.
The growth stress is continuously measured by drilling a 6 mm hole. The absolute
values of the stress released depended on whether the two grooves were sawn inside
or outside the pin targets; the values of the CIRAD Forêt method were approximately
twice those of the GSM10 values. To release most of the surface growth stress and
maximize released strain values, the optimal distance between the ends of the GSM10
and the drill cut to release the growth stress was to 0.5 to 1 cm, and the optimal depth
of the groove was 10 mm deep. Most of the growth stress was released immediately
when the grooves were sawn. In this study, the GSM10 method was potentially more
accurate in measuring growth stress in standing trees. As the average GSM10
readings are about half (0.6291) those of the CIRAD Forêt readings, and the extension
61
stresses can be detected using GSM10 about 10 microns (as shown in Appendix A-1)
and potentially provides an excellent measure of growth stress. Log end splits and
cracks were not severe overall and occurred more often in the large wends of the logs.
GSM10 was developed to quantify the overall severity of log end splitting with split
indices. The quality of wood will enhance if growth stress detected accurately and the
specific milling process will be applied.
Great extension stress (positive value) was detected at the log ends. The growth stress
was measured on the standing trees at 0.5 m from the base and 1.3 m (diameter at
breast height) showed average readings of 22 microns and 64 microns in respectively
(see Appendix A-3 and A-5). In order to reach higher tree heights, trees were felled
and cut into logs for measurement. Log 1: stress measured at 3.0 m, 3.4 m and 3.8 m,
Log 2: stress measured at 4.2 m and 5.0 m heights and Log 3: stress measured at 5.6
m, 6.0 m and 6.3 m heights. Since the 3.0 m, 4.2 m and 5.6 m are at the lower parts or
log ends, they revealed lower growth stresses compared to measurements higher in
the log, for example, 3.8 m, 5.0 m and 6.3 m. To discuss the influence of growth
stresses on wood properties, it is useful to have closer look at the growth stress levels
found in other investigations in hardwood species. There are no studies available that
define the level of growth stresses and their impact on wood quality while processing
the log. Other factors may influence timber quality, for example, drying stresses for
instance. High growth stresses can develop in Eucalyptus globulus, which may have a
severe impact on solid wood utilisation. Some variation is due to the measurement of
trees at different ages and stages of development. Though not tested experimentally, it
is generally believed that growth stress generation in stands can be minimized by
keeping the growth conditions and spatial distribution in the stand as uniform as
possible throughout the life of the stand (Kubler. 1988). This would give the trees no
reason to orient themselves into more favourable positions thus minimizing the levels
of stress generated in tree stems. As a general rule stands should be thinned lightly,
frequently and uniformly, rather than haphazardly and severely after long periods.
Bariska et al. (1987) speculate that the effect of external forces on growth stress
generation in trees should be experimentally verifiable:
a) Supporting trees by means of sway wires to prevent sway over a period of
time. This should result in the generation of lower levels of stress in tree
stems.
62
b) Trees with large slenderness ratios (tree length/diameter), ie. „whippy‟ trees
should develop higher levels of growth stress.
c) Trees of the same species growing in windy areas should develop higher stress
levels than those growing in calm areas.
d) The remaining trees of the same species grown at close spacings should
develop higher levels of growth stresses after severe thinning in order to
provide them with more mechanical support in their new, more exposed
environment.
However, existing evidence suggests that silviculture techniques do not seem to be
effective to control stress levels in trees (Malan, 1988).
A surprising number of studies have been made relative to the position of the tree in
the stand, i.e., whether the tree is dominant, co-dominant, intermediate, or suppressed.
Much of European literature refers to this as the “sociological position” of the tree.
Most researchers state that the crown location does have an effect on wood properties
but many are somewhat vague as to just what the position effect is. Certainly
sociological position affects crown function through light availability and crown size
so it would be expected to have some affect on wood properties (Larson, 1963).
From the results of this study, there is no big difference in the number of growth
stresses obtained at different faces (North, East, West and South). The growth stress
on Eastern faces show the highest growth stress about (35 microns) whilst Western
faces showed the lowest growth stress about (19 microns). The East facing side of a
log showed higher growth stresses because it was exposed more on the sunny side
during the morning compare to West faces. In a study of beech (Fagus sylvatica)
found that the larger amount of light available to the more dominant crown classes
produced larger vessels in the wood along with wider annual rings (Koltzenburg,
1967). On the other hand, fibre length of beech showed no relationship to crown
classes or light availability. The tracheid length of the different tree classes changed
with age; up to 20-30 years, tracheids were longer in the sub-dominant and suppressed
tree, but in later ages they were shorter that in the co-dominant trees (Zobel et al.
1989). Hildebrandt (1960) concluded that the effects of growth conditions on the
properties of beech wood are not important enough to establish rules for silvicultural
treatment of beech stands. It is evident that the tree faces can have an effect on wood
properties. It is of little practical importance in well-managed forests where the
63
intermediate and suppressed trees are removed. Little wood variation occurs between
the dominant and co-dominant trees within a stand.
The areas of the trees used in this study represent a small sample of each site and have
been selected randomly. The growth stresses obtained for each site (Coupe 1 and
Coupe 2) show that there was no significant difference between sites (Table 8.2).
However, a large variation in growth stress readings was obtained for each individual
tree. The error term for this analysis was the variation caused by location in the
circumference of the log and so is not suitable for testing differences between sites.
However, it is suitable for testing differences between sampling heights and between
trees.
7.1 Recommendation
In future studies the following issues should be addressed:
a) The new method GSM10 should be measured on standing trees by drill cut
nearly to the pin target of CIRAD Forêt to get accurate reading.
b) Research into environmental and genetic attributes and their impact on growth
stresses need to assess large numbers of standing trees to give more accurate
results.
c) Wind factors and variables giving rise to potential errors or uncertainty should
be avoided to improve the accuracy of GSM10 during measurement.
64
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APPENDICES
Appendix A-1
C = Creswick (Headhouse)/ Lab 1 Testing method = a) CIRAD + GSM10 + 20 mm drill
b) GSM10 + up the hole + top drill cut (6 mm) c) GSM10 + down the hole + under drill cut (6 mm)
File
Description
a b c CIRAD GSM10 C1 93 58 10 xx C9 45 26 xx xx C10 43 18 18 6 C11 64 25 8 8 C12 95 45 3 xx C13 78 55 36 10 C14 83 40 45 15 C15 36 10 19 xx C16 104 55 10 20 C17 66 35 40 7 C18 82 40 5 25 C19 71 36 21 9 C20 96 40 15 13 C21 87 60 21 Error C22 104 50 25 11 C24 52 12 15 xx
71
Appendix A-2
Location: Headhouse (Creswick)
Height Data Reading
Height Data Reading (NORTH) (microns)
(EAST) (microns)
3.0 m HH3.0NA 65
3.0 m HH3.0EA 48 HH3.0Na 16
HH3.0Ea 18
HH3.0Nb 14
HH3.0Eb 35 HH3.0Nc 10
HH3.0Ec 28
3.4 m HH3.4NA 48
3.4 m HH3.4EA 67 HH3.4Na 33
HH3.4Ea 32
HH3.4Nb 28
HH3.4Eb 14 HH3.4Nc 27
HH3.4Ec 19
3.8 m HH3.8NA 93
3.8 m HH3.8EA 53 HH3.8Na 36
HH3.8Ea 22
HH3.8Nb 15
HH3.8Eb 8 HH3.8Nc 10
HH3.8Ec 17
4.2 m HH4.2NA 68
4.2 m HH4.2EA 49 HH4.2Na 32
HH4.2Ea 13
HH4.2Nb 14
HH4.2Eb 28 HH4.2Nc 10
HH4.2Ec 3
5.0 m HH5.0NA 34
5.0 m HH5.0EA 55 HH5.0Na 11
HH5.0Ea 13
HH5.0Nb 13
HH5.0Eb 9 HH5.0Nc XX
HH5.0Ec 29
5.6 m HH5.6NA 89
5.6 m HH5.6EA 50 HH5.6Na 28
HH5.6Ea 19
HH5.6Nb 47
HH5.6Eb 19 HH5.6Nc 16
HH5.6Ec 20
6.0 m HH6.0NA 79
6.0 m HH6.0EA 74 HH6.0Na 51
HH6.0Ea 35
HH6.0Nb 18
HH6.0Eb 21 HH6.0Nc 38
HH6.0Ec 20
6.3 m HH6.3NA 69
6.3 m HH6.3EA XX HH6.3Na 45
HH6.3Ea XX
HH6.3Nb 13
HH6.3Eb XX HH6.3Nc 71
HH6.3Ec XX
72
Height Data Reading
Height Data Reading
(WEST) (microns)
(SOUTH) (microns)
3.0 m HH3.0WA 20
3.0 m HH3.0SA 53
HH3.0Wa 3
HH3.0Sa 26
HH3.0Wb 52
HH3.0Sb 28
HH3.0Wc 7
HH3.0Sc 14
3.4 m HH3.4WA 56
3.4 m HH3.4SA 74
HH3.4Wa 18
HH3.4Sa 20
HH3.4Wb 22
HH3.4Sb 47
HH3.4Wc 7
HH3.4Sc 3
3.8 m HH3.8WA 80
3.8 m HH3.8SA 44
HH3.8Wa 40
HH3.8Sa 18
HH3.8Wb 18
HH3.8Sb 21
HH3.8Wc 8
HH3.8Sc 14
4.2 m HH4.2WA 73
4.2 m HH4.2SA 17
HH4.2Wa 25
HH4.2Sa 9
HH4.2Wb 15
HH4.2Sb 2
HH4.2Wc 5
HH4.2Sc 19
5.0 m HH5.0WA 67
5.0 m HH5.0SA 69
HH5.0Wa 23
HH5.0Sa 37
HH5.0Wb 12
HH5.0Sb 20
HH5.0Wc 15
HH5.0Sc 37
5.6 m HH5.6WA 59
5.6 m HH5.6SA 65
HH5.6Wa 12
HH5.6Sa 24
HH5.6Wb 72
HH5.6Sb 7
HH5.6Wc 138
HH5.6Sc 2
6.0 m HH6.0WA 56
6.0 m HH6.0SA 62
HH6.0Wa 36
HH6.0Sa 20
HH6.0Wb 22
HH6.0Sb 6
HH6.0Wc 8
HH6.0Sc 9
6.3 m HH6.3WA XX
6.3 m HH6.3SA 71
HH6.3Wa XX
HH6.3Sa 38
HH6.3Wb XX
HH6.3Sb 12
HH6.3Wc XX
HH6.3Sc 32
73
Appendix A-3
Coupe 1 and Coupe 2 (Creswick)
Face 1= North
10 trees (eucalyptus globulus) Face 2= East
Height = 1.3 m
Face 3= West
Face 4= South
Coupe 2
Tree No Height (m) Tree Face
GS (microns)
GSM10a GSM10b
Tree 1 1.3 Face 1 17 25
Tree 1 1.3 Face 2 3 9
Tree 1 1.3 Face 3 10 6
Tree 1 1.3 Face 4 35 8
Tree 2 1.3 Face 1 23 8
Tree 2 1.3 Face 2 26 8
Tree 2 1.3 Face 3 17 3
Tree 2 1.3 Face 4 10 10
Tree 3 1.3 Face 1 10 19
Tree 3 1.3 Face 2 20 6
Tree 3 1.3 Face 3 37 5
Tree 3 1.3 Face 4 20 2
Tree 4 1.3 Face 1 35 20
Tree 4 1.3 Face 2 16 12
Tree 4 1.3 Face 3 22 30
Tree 4 1.3 Face 4 17 21
Tree 5 1.3 Face 1 13 5
Tree 5 1.3 Face 2 11 32
Tree 5 1.3 Face 3 13 4
Tree 5 1.3 Face 4 49 4
74
Coupe 2
Tree No Height Tree Face
GS (microns)
GSM10a GSM10b
Tree 6 1.3 Face 1 18 18
Tree 6 1.3 Face 2 64 26
Tree 6 1.3 Face 3 36 20
Tree 6 1.3 Face 4 63 16
Tree 7 1.3 Face 1 48 14
Tree 7 1.3 Face 2 171 5
Tree 7 1.3 Face 3 10 1
Tree 7 1.3 Face 4 7 1
Tree 8 1.3 Face 1 9 7
Tree 8 1.3 Face 2 166 8
Tree 8 1.3 Face 3 11 7
Tree 8 1.3 Face 4 *** 6
Tree 9 1.3 Face 1 18 31
Tree 9 1.3 Face 2 12 14
Tree 9 1.3 Face 3 23 4
Tree 9 1.3 Face 4 9 5
Tree 10 1.3 Face 1 14 47
Tree 10 1.3 Face 2 18 22
Tree 10 1.3 Face 3 12 37
Tree 10 1.3 Face 4 14 1
75
Appendix A-4
Coupe 1 (height 0.5 m)
Name Result (microns) Comment Hole Cut North East West South
B1Na.txt 9 Reading started at 4388µ and ended at 4397µ (drill hole) 9 /
B1Nb.txt 18 Reset 0, good test, max reading 25µ 18 /
B1Ea.txt Error during testing (no reading) /
B1Eb.txt 9 Reset 0, good test, 9 /
B1Wa.txt 3 Reset 0, good test, max reading =10 3 /
B1Wb.txt 6 Reset 0, good test, max reading =7 6 /
B1Sa.txt 32 Reset 0, good test, max reading =39 32 /
B1Sb.txt 8
Reset 0, when start drill, the graph goes uo and then goes down and goes up again until it releases all the stresses 8 /
B2Na.txt 21 Reset 0, good test 21 /
B2Nb.txt 4 Reset 0, not a good test, graph up and down during testing, do not show accurate reading, max reading = 8 4 /
B2Ea.txt 14 Reset 0. good test, max reading = 26 14 /
B2Eb.txt 3 Reset 5, max =8 3 /
B2Wa.txt 11 Reset 0, good test, max reading =19 11 /
B2Wb.txt 3 Reset 0, good test 3 /
B2Sa.txt 171 Reset 0, not a good test, graph goes up then drop in a large range or reading, max reading = 1942 171 /
B2Sb.txt 4 Reset 4, good test, max reading = -10 4 /
B3Na.txt 10 Reset 5, Good test 10 /
B3Nb.txt 3 Reset 0, a bit strange readings, max reading = 19 3 /
B3Ea.txt 19 Reset 2, good test, max reading = 20 19 /
B3Eb.txt 2 Reset 0, good test, max reading = 6 2 /
B3Wa.txt 36
Reset 0, good test but a bit strange when in the middle of testing it shows range reading where the max reading = 127 36 /
B3Wb.txt 3 Reset 5, good test, max reading = 5 5 /
B3Sa.txt 11 Reset 0, good test, max reading = 20 11 /
B3Sb.txt 1 Reset 0, good test, max reading = 2 1 /
B4Na.txt 30 Reset 0, A bit strange readings at early testing , max reading = 35 30 /
B4Nb.txt undefine Reset 5, not good test. error /
B4Ea.txt undefine Reset 0, not a good test, max reading= 16 error /
76
B4Eb.txt 11 Reset 0, the graph is up and down, max reading = 12 11 /
B4Wa.txt 10 Reset 0. good test, max reading = 22 10 /
B4Wb.txt 13 Reset 0. good test, max reading = 30 13 /
B4Sa.txt 9 Reset -1, good test, max reading = 14 9 /
B4Sb.txt 21 Reset -1, good test 21 /
B5Na.txt 13 Reset 0, good test, max reading = 16 13 /
B5Nb.txt 4 Reset 0, good test 4 /
B5Ea.txt 5 Reset -3, good test, max reading = 10 5 /
B5Eb.txt 7 Reset 0, good test 7 /
B5Wa.txt 13 Reset 0, good test 13 /
B5Wb.txt 2 Reset 0, good test, max reading = 4 2 /
B5Sa.txt 49 Reset 0, good test but a bit strange when some of the readings show too high gs 49 /
B5Sb.txt 4 Reset 92 (forgot to reset at 0), good test 4 /
B6Na.txt 11 Reset 0, good test, max reading = 18 11 /
B6Nb.txt 12 Reset 0, good test, max reading = 18 12 /
B6Ea.txt 22 Reset -2, good test, max reading = 64 22 /
B6Eb.txt 26 Reset 0. good test , 26 /
B6Wa.txt 33 Reset 0, a bit strange at the started but then the testing was ok 33 /
B6Wb.txt 17 Reset, good test 17 /
B6Sa.txt 12 Reset 0, good test 12 /
B6Sb.txt 10 Reset -5, good test 10 /
B7Na.txt 30 Reset -3, good test, max reading = 104 30 /
B7Nb.txt 1 Reset 2, good test, max reading = 13 1 /
B7Ea.txt 10 Reset 1, strange graph 10 /
B7Eb.txt 1 Reset -2, good test, max reading = 5 1 /
B7Wa.txt 6 Reset -2, good test, max reading = 10 6 /
B7Wb.txt 0 Reset 0, good test, max reading = 1 0 /
B7Sa.txt 2 Reset -1. good test , max reading =7 2 /
B7Sb.txt 1 Reset -3, undefined 1 /
B8Na.txt 9 Reset 0, good test, it was windy during testing 9 /
B8Nb.txt 4 Reset 0, good test, it was windy during testing 4 /
B8Ea.txt 6 Reset 0, good test 6 /
B8Eb.txt 7 Reset -1, good test 7 /
B8Wa.txt 3 Reset 0, not really good test, 2 weird readings = 64, 59 3 /
77
B8Wb.txt 4 Reset 0, good test 4 /
B8Sa.txt error error during testing error /
Name Result (microns) Comment Hole Cut North East West South
B8Sb.txt 5 Reset 0, good test 5 /
B9Na.txt 2 Reset 0, good test, max reading = 19 2 /
B9Nb.txt 27 Reset 0, good test, 27 /
B9Ea.txt 3 Reset 0, good test 3 /
B9Eb.txt 3 Reset -1, good test 3 /
B9Wa.txt 18 Reset -2, good test 18 /
B9Wb.txt 2 Reset 0, good test 2 /
B9Sa.txt 10 Reset 0, good test 10 /
B9Sb.txt 5 Reset 3, good test 5 /
B10Na.txt 7 Reset -3, good test, max reading = 13 7 /
B10Nb.txt 32 Reset -5, not sure with the test, weird graph 32 /
B10Ea.txt 17 Reset 0, good test 17
/
B10Eb.txt 17 Reset 0, good test 17 /
B10Wa.txt 12 Reset 0, good test 12
/
B10Wb.txt 36 Reset 0, good test 36 /
B10Sa.txt 7 Reset 0, good test, max reading = 14 7
/
B10Sb.txt 0 Reset 1, not really good test 0 /
78
Appendix A-5
Location: Creswick Bush 1
10 trees of Eucalptus globulus have been randomly selected.
Testing Method: A) CIRAD (20 mm drill hole)
a) GSM10 (20mm drill hole)
b) GSM10 (6mm drill cut at above the 20mm hole)
c) GSM10 (6mm drill cut at below 20mm drill hole)
Height A= 1.3 m; Height B= 0.5 m
Face 1 = North, Face 2 = East, Face 3 = West, Face 4 = South
Appendix A.5.1 – Growth stress of tree 1 (east face) at height 1.3m using 20 mm drill
hole.
79
Appendix A.5.2 – Growth stress of tree 1 (east face) at 1.3m height using 6 mm drill cut.
Appendix A.5.3 – Growth stress of tree 1 (east face) at 1.3m height using 6mm drill cut.
80
Appendix A.5.4 – Growth stress of tree 1 (north face) at 1.3m height using 20mm drill
hole.
Appendix A.5.5 – Growth stress of tree 1 (north face) at 1.3m height using 6mm drill cut.
81
Appendix A.5.6 – Growth stress of tree 1 (north face) at 1.3m height using 6mm drill cut.
Appendix A.5.7 – Growth stress of tree 1 (south face) at 1.3m height using 20mm drill
hole.
82
Appendix A.5.8 – Growth stress of tree 1 (south face) at 1.3m height using 6mm drill cut.
Appendix A.5.9 – Growth stress of tree 1 (north face) at 1.3m height using 6mm drill cut.
.
83
Appendix A.5.10 – Growth stress of tree 1 (west face) at 1.3m height using 20mm drill
hole.
.
Appendix A.5.11 – Growth stress of tree 1 (west face) at 1.3m height using 6mm drill
cut.
84
.
Appendix A.5.12 – Growth stress of tree 1 (west face) at 1.3m height using 6mm drill
cut.
Appendix A.5.13 – Growth stress of tree 1 (east face) at 0.5m height using 20mm drill
hole.
85
Appendix A.5.14 – Growth stress of tree 1 (east face) at 0.5m height using 6mm drill cut.
Appendix A.5.15 – Growth stress of tree 1 (east face) at 0.5m height using 6mm drill cut.
86
Appendix A.5.16 – Growth stress of tree 1 (north face) at 0.5m height using 20mm drill
hole.
Appendix A.5.17 – Growth stress of tree 1 (north face) at 0.5m height using 6mm drill
cut.
87
Appendix A.5.18 – Growth stress of tree 1 (north face) at 0.5m height using 6mm drill
cut.
Appendix A.5.19 – Growth stress of tree 1 (south face) at 0.5m height using 20mm drill
hole.
88
Appendix A.5.20 – Growth stress of tree 1 (south face) at 0.5m height using 6mm drill
cut.
Appendix A.5.21 – Growth stress of tree 1 (south face) at 0.5m height using 6mm drill
cut.
89
Appendix A.5.22 – Growth stress of tree 1 (west face) at 0.5m height using 6mm drill
cut.
Appendix A.5.23 – Growth stress of tree 1 (west face) at 0.5m height using 6mm drill
cut.
90
Appendix A.5.24 – Growth stress of tree 2 (east face) at 1.3m height using 20mm drill
hole.
Appendix A.5.25 – Growth stress of tree 2 (east face) at 1.3m height using 6mm drill cut.
91
Appendix A.5.26 – Growth stress of tree 2 (east face) at 1.3m height using 6mm drill cut.
Appendix A.5.27 – Growth stress of tree 2 (north face) at 1.3m height using 20mm drill
hole.
92
Appendix A.5.28 – Growth stress of tree 2 (north face) at 1.3m height using 6mm drill
cut.
Appendix A.5.29 – Growth stress of tree 2 (north face) at 1.3m height using 6m drill cut.
93
Appendix A.5.30 – Growth stress of tree 2 (south face) at 1.3m height using 20mm drill
hole.
Appendix A.5.31 – Growth stress of tree 2 (south face) at 1.3m height using 6mm drill
cut.
94
Appendix A.5.32 – Growth stress of tree 2 (south face) at 1.3m height using 6mm drill
cut
Appendix A.5.33 – Growth stress of tree 2 (west face) at 1.3m height using 20mm drill
hole.
95
Appendix A.5.34 – Growth stress of tree 2 (west face) at 1.3m height using 6mm drill cut
Appendix A.5.35 – Growth stress of tree 2 (west face) at 1.3m height using 6mm drill cut
96
Appendix A.5.36 – Growth stress of tree 3 (east face) at 1.3m height using 20mm drill
hole.
Appendix A.5.37 – Growth stress of tree 3 (east face) at 1.3m height using 6mm drill cut
97
Appendix A.5.38 – Growth stress of tree 3 (east face) at 1.3m height using 6mm drill cut.
Appendix A.5.39 – Growth stress of tree 3 (north face) at 1.3m height using 20mm drill
hole.
98
Appendix A.5.40– Growth stress of tree 3 (north face) at 1.3m height using 6mm drill
cut.
Appendix A.5.41– Growth stress of tree 3 (north face) at 1.3m height using 6mm drill
cut.
99
Appendix A.5.42– Growth stress of tree 3 (south face) at 1.3m height using 20mm drill
hole.
Appendix A.5.43– Growth stress of tree 3 (south face) at 1.3m height using 6mm drill
cut.
100
Appendix A.5.44– Growth stress of tree 3 (west face) at 1.3m height using 6mm drill cut.
Appendix A.5.45– Growth stress of tree 3 (east face) at 0.5m height using 20mm drill
hole.
101
Appendix A.5.46– Growth stress of tree 3 (east face) at 0.5m height using 6mm drill cut.
Appendix A.5.47–Growth stress of tree 3 (east face) at 0.5m height using 6mm drill cut.
102
Appendix A.5.48– Growth stress of tree 3 (north face) at 0.5m height using 20 drill hole.
Appendix A.5.49– Growth stress of tree 3 (north face) at 0.5m height using 6mm drill
cut.
103
Appendix A.5.50– Growth stress of tree 3 (north face) at 0.5m height using 6mm drill
cut.
Appendix A.5.51– Growth stress of tree 3 (south face) at 0.5m height using 20mm drill
hole.
104
Appendix A.5.52– Growth stress of tree 3 (south face) at 0.5m height using 6mm drill
cut.
Appendix A.5.53– Growth stress of tree 3 (south face) at 0.5m height using 6mm drill
cut.
105
Appendix A.5.54– Growth stress of tree 4 (east face) at 1.3m height using 20mm drill
hole.
Appendix A.5.55– Growth stress of tree 4 (east face) at 1.3m height using 6mm drill cut.
106
Appendix A.5.56– Growth stress of tree 4 (east face) at 1.3m height using 6mm drill cut.
Appendix A.5.57– Growth stress of tree 4 (north face) at 1.3m height using 20mm drill
hole.
107
Appendix A.5.58– Growth stress of tree 4 (north face) at 1.3m height using 6mm drill
cut.
Appendix A.5.59– Growth stress of tree 4 (north face) at 1.3m height using 6mm drill
cut.
108
Appendix A.5.60– Growth stress of tree 4 (south face) at 1.3m height using 20mm drill
hole.
Appendix A.5.61– Growth stress of tree 4 (south face) at 1.3m height using 6mm drill
cut.
109
Appendix A.5.62– Growth stress of tree 4 (south face) at 1.3m height using 6mm drill
cut.
Appendix A.5.63 – Growth stress of tree 4 (west face) at 1.3m height using 20mm drill
hole.
110
Appendix A.5.64 – Growth stress of tree 4 (west face) at 1.3m height using 6mm drill
cut.
Appendix A.5.65 – Growth stress of tree 4 (east face) at 0.5m height using 20mm drill
hole.
111
Appendix A.5.66 – Growth stress of tree 4 (east face) at 0.5m height using 6mm drill cut.
Appendix 8.5.67 – Growth stress of tree 4 (east face) at 0.5m height using 6mm drill cut.
112
Appendix A.5.68 – Growth stress of tree 4 (north face) at 0.5m height using 20mm drill
hole.
Appendix 8.5.69 – Growth stress of tree 4 (north face) at 0.5m height using 6mm drill
cut.
113
Appendix A.5.70 – Growth stress of tree 4 (north face) at 0.5m height using 6mm drill
cut.
Appendix A.5.71 – Growth stress of tree 4 (south face) at 0.5m height using 20mm drill
hole.
114
Appendix A.5.72 – Growth stress of tree 4 (south face) at 0.5m height using 6mm drill
cut.
Appendix A.5.73 – Growth stress of tree 4 (south face) at 0.5m height using 6mm drill
cut.
115
Appendix A.5.74 – Growth stress of tree 4 (west face) at 0.5m height using 20mm drill
hole.
Appendix A.5.75 – Growth stress of tree 4 (west face) at 0.5m height using 6mm drill
cut.
116
Appendix A.5.76 – Growth stress of tree 4 (west face) at 0.5m height using 6mm drill
cut.
Appendix A.5.77 – Growth stress of tree 5 (east face) at 1.3m height using 20mm drill
hole.
117
Appendix A.5.78 – Growth stress of tree 5 (east face) at 1.3m height using 6mm drill cut.
Appendix A.5.79 – Growth stress of tree 5 (east face) at 1.3m height using 6mm drill cut.
118
Appendix A.5.80 – Growth stress of tree 5 (north face) at 1.3m height using 20mm drill
hole.
Appendix A.5.81 – Growth stress of tree 5 (north face) at 1.3m height using 6mm drill
cut.
119
Appendix A.5.82 – Growth stress of tree 5 (north face) at 1.3m height using 6mm drill
cut.
Appendix A.5.83 – Growth stress of tree 5 (south face) at 1.3m height using 20mm drill
hole.
120
Appendix A.5.84 – Growth stress of tree 5 (south face) at 1.3m height using 6mm drill
cut.
Appendix A.5.85 – Growth stress of tree 5 (south face) at 1.3m height using 6mm drill
cut.
121
Appendix A.5.86 – Growth stress of tree 5 (west face) at 1.3m height using 20mm drill
hole
Appendix A.5.87 – Growth stress of tree 5 (west face) at 1.3m height using 6mm drill
cut.
122
Appendix A.5.88 – Growth stress of tree 5 (west face) at 1.3m height using 6mm drill
cut.
Appendix A.5.89 – Growth stress of tree 5 (east face) at 0.5m height using 20mm drill
hole.
123
Appendix A.5.90 – Growth stress of tree 5 (east face) at 0.5m height using 6mm drill cut.
Appendix A.5.91 – Growth stress of tree 5 (east face) at 0.5m height using 6mm drill cut.
124
Appendix A.5.92 – Growth stress of tree 5 (north face) at 0.5m height using 20mm drill
hole.
Appendix A.5.93 – Growth stress of tree 5 (north face) at 0.5m height using 6mm drill
cut.
125
Appendix A.5.94 – Growth stress of tree 5 (north face) at 0.5m height using 6mm drill
cut.
Appendix A.5.95 – Growth stress of tree 5 (south face) at 0.5m height using 20mm drill
hole.
126
Appendix A.5.96 – Growth stress of tree 5 (south face) at 0.5m height using 6mm drill
cut.
.
Appendix A.5.97– Growth stress of tree 5 (south face) at 0.5m height using 6mm drill
cut.
127
Appendix A.5.98– Growth stress of tree 5 (west face) at 0.5m height using 20mm drill
hole.
Appendix A.5.99– Growth stress of tree 5 (west face) at 0.5m height using 6mm drill cut.
128
Appendix A.5.100 – Growth stress of tree 5 (west face) at 0.5m height using 6mm drill
cut.
Appendix A.5.101 – Growth stress of tree 6 (east face) at 1.3m height using 6mm drill
hole.
129
Appendix A.5.102 – Growth stress of tree 6 (east face) at 1.3m height using 6mm drill
cut.
Appendix A.5.103 – Growth stress of tree 6 (east face) at 1.3m height using 6mm drill
cut.
130
Appendix A.5.103 – Growth stress of tree 6 (north face) at 1.3m height using 20mm drill
hole.
Appendix A.5.103 – Growth stress of tree 6 (north face) at 1.3m height using 6mm drill
cut.
131
Appendix A.5.104 – Growth stress of tree 6 (north face) at 1.3m height 6mm microns
drill cut.
Appendix A.5.105 – Growth stress of tree 6 (south face) at 1.3m height using 20mm drill
hole.
132
Appendix A.5.106 – Growth stress of tree 6 (south face) at 1.3m height using 6mm drill
cut.
Appendix A.5.107 – Growth stress of tree 6 (south face) at 1.3m height using 6mm drill
cut.
.
133
Appendix A.5.108 – Growth stress of tree 6 (west face) at 1.3m height using 20mm drill
hole.
Appendix A.5.109 – Growth stress of tree 6 (west face) at 1.3m height using 6mm drill
cut.
134
Appendix A.5.110 – Growth stress of tree 6 (west face) at 1.3m height using 6mm drill
cut.
Appendix A.5.111 – Growth stress of tree 6 (east face) at 0.5m height using 20mm drill
hole.
135
Appendix A.5.112 – Growth stress of tree 6 (east face) at 0.5m height using 6mm drill
cut.
Appendix A.5.113 – Growth stress of tree 6 (east face) at 0.5m height using 6mm drill
cut.
136
Appendix A.5.114 – Growth stress of tree 6 (north face) at 0.5m height using 20mm drill
hole.
Appendix A.5.115 – Growth stress of tree 6 (north face) at 0.5m height using 6mm drill
cut.
137
Appendix A.5.116 – Growth stress of tree 6 (north face) at 0.5m height using 6mm drill
cut.
Appendix A.5.117 – Growth stress of tree 6 (south face) at 0.5m height using 20mm drill
hole.
138
Appendix A.5.118 – Growth stress of tree 6 (south face) at 0.5m height using 6mm drill
cut.
Appendix A.5.119 – Growth stress of tree 6 (south face) at 0.5m height using 6mm drill
cut.
.
139
Appendix A.5.120 – Growth stress of tree 6 (west face) at 0.5m height using 20mm drill
hole.
Appendix A.5.121 – Growth stress of tree 6 (west face) at 0.5m height using 6mm drill
cut.
140
Appendix A.5.122 – Error reading.
Appendix A.5.123 – Growth stress of tree 8 (east face) at 1.3m height using 20mm drill
hole.
141
Appendix A.5.124 - Growth stress of tree 8 (east face) at 1.3m height using 6mm drill
cut.
.
Appendix A.5.125 – Growth stress of tree 8 (north face) at 1.3m height using 20mm drill
hole.
142
Appendix A.5.126 – Growth stress of tree 8 (north face) at 1.3m height using 6mm drill
cut.
Appendix A.5.127 – Growth stress of tree 8 (north face) at 1.3m height using 6mm drill
cut.
143
Appendix A.5.128 – Growth stress of tree 8 (south face) at 1.3m height using 20mm drill
hole.
Appendix A.5.129 – Growth stress of tree 8 (south face) at 1.3m height using 6mm drill
cut.
144
Appendix A.5.130 – Growth stress of tree 8 (south face) at 1.3m height using 6mm drill
cut.
Appendix A.5.131 – Growth stress of tree 8 (west face) at 1.3m height using 20mm drill
hole.
145
Appendix A.5.132 – Growth stress of tree 8 (west face) at 1.3m height using 6mm drill
cut.
Appendix A.5.133 – Growth stress of tree 8 (east face) at 0.5m height using 20mm drill
hole.
146
Appendix A.5.134 – Growth stress of tree 8 (east face) at 0.5m height using 6mm drill
cut.
Appendix A.5.135 – Growth stress of tree 8 (east face) at 0.5m height using 6mm drill
cut.
147
Appendix A.5.136 – Growth stress of tree 8 (north face) at 0.5m height using 20mm drill
hole.
Appendix A.5.137 – Growth stress of tree 8 (north face) at 0.5m height using 6mm drill
cut.
148
Appendix A.5.138 – Growth stress of tree 8 (north face) at 0.5m height using 6mm drill
cut.
.
Appendix A.5.139 – Growth stress of tree 8 (south face) at 0.5m height using 20mm drill
hole.
149
Appendix A.5.140 – Growth stress of tree 8 (south face) at 0.5m height using 6mm drill
cut.
.
Appendix A.5.141 – Growth stress of tree 8 (south face) at 0.5m height using 6mm drill
cut.
150
Appendix A.5.142 – Growth stress of tree 8 (west face) at 0.5m height using 20mm drill
hole.
Appendix A.5.143 – Growth stress of tree 8 (west face) at 0.5m height using 6mm drill
cut.
151
Appendix A.5.144 – Growth stress of tree 8 (west face) at 0.5m height using 6mm drill
cut.
Minerva Access is the Institutional Repository of The University of Melbourne
Author/s:
KAMARUDIN, NORASHIKIN
Title:
A new technology for measuring growth stress in Eucalypts
Date:
2014
Persistent Link:
http://hdl.handle.net/11343/40818
File Description:
A new technology for measuring growth stress in Eucalypts
