Pankaj K. AGGARWAL

Pankaj K. AGGARWAL IUFRO Division 5 Conference 5.01.01 Biological control of wood quality

Variation in growth strains in five clones of Eucalyptus tereticornis Pankaj K. Aggarwal and Shakti S. Chauhan • Institute of Wood Science & Technology(Indian Council of Forestry Research & Education) • Bangalore, India

Background India has 2.5% of the geographical area and 1.5% of the world forest area and support 16% population of the world. Gap between demand and supply of timber is widening and therefore shortage of conventional preferred species, high cost, lengthy production period of Conventional species has necessitated the need to utilize man made forests which is available. Conventional technology for Processing is not appropriate for fast grown species as they are inherently characterized by growth stresses due to which they are prone to have processing problems. Also wood is juvenile and liable to cause distortions during sawing and seasoning.

What are growth stresses ? • Growth stresses are generated in the cambial layers of woody stems during the cell maturation. • Growth stresses are generally resolved in the longitudinal, radial and tangential directions following the natural geometry of the trees. • These are common to all species however their magnitudes differ from species to species. Contd…

In general, these stresses are reported to be less in softwood as compared to hardwood. Most emphasis is paid to longitudinal (axial) growth stresses. They largely determine distortion on sawing. High magnitude of growth stresses results in Brittleheart in standing trees {Low value corewood} End-splitting in logs {Low recovery of sawn timber} Warping, twisting in sawn boards – {Excessive planning wastes and low productivity}

Defects due to high growth stresses Growth stresses causes severe sawing problems in plantation timber and that’s the reason we need to study this very important parameter.

Pattern and distribution • The distribution of longitudinal growth stress has been observed to vary progressively from tensile at the periphery to compressive at the centre. • The change from tension to compression is considered to occur at about one third to halfway along the radius from the periphery.

How do growth stresses originate in trees?? • Several theories and hypothesis have been postulated: - Weight of the tree (Martley,1928) - Longitudinal cell shortening (Jacobs,1938) - Lignin swelling (Boyd,1985) - Cellulose tension (Bamber, 1979,1987) - Combination of LS and CT (Okuyama, 1993, 2000)

Why this study ? • Eucalyptus - planted extensively mainly for pulp and paper and fuel wood • Utilization of this species is limited due to growth stresses • Improvement in both breeding and processing of the plantation grown species is gaining importance. • With the clonal forestry gaining significant thrust for quality production, it is desirable to study the variation in growth stresses in different clones. • Selection of appropriate clones provide an opportunity to grow trees with pre-defined wood characteristics for future production.

Objectives Utilization of clonal material of eucalypts and propagation of low stresses clones through evaluation of : • Variation in growth strains in clones raised by Indian Tobacco company (ITC). • Variation of strains with diameter.

Materials • 6 logs of each of five clones obtained from ITC Bhadrachalam in Andhra Pradesh (a southern state in India.) • Diameter of the logs- 9 cm to 17 cm. • Age at the time of measurements- 8 years

Measuring growth stresses • It is not possible to measure growth stresses directly. • Growth strains can be measured with greater ease by relieving the stresses. • The magnitude of released growth strains can be considered an indicator of growth stresses, as stresses are proportional to strains within the elastic region. Contd…

Growth stresses are evaluated by growth strain and modulus of elasticity. For measurement of growth strain there are several techniques: (a) Plank stripping method (b) Nicholson’s Method (c)The French method (d) The strain gauge method We have measured growth strain using strain gauge method. Contd…. Measuring growth stresses ….

Strain gauge Eucalypt log Measuring growth stresses……… • Longitudinal strains were measured in logs using strain gauges. • Strain gauges were glued to the wood surface. • Wood fibres were cut above and below the strain gauge to release the growth stresses. • Strains were recorded. Contd…

Measuring growth stresses……… • Hole diameter (30 mm) • Hole depth (20 mm) • Distance between hole edge and strain gauge (10 mm) Contd…

Measuring growth stresses……… Strain measuring indicator

It is less destructive method as compared to other available methods. It is more suitable for measuring longitudinal strain in a very thin layer of wood. Instantaneous recording of the strain value. Compact and suitable for repeated measurement. Measurement can be made at several points simultaneously However, it is expensive. Advantages of strain gauge method

Variability between different clones

Analysis ANOVA indicates a significant difference in growth strains between different clones.

Difference in strain on two sides Significant association between strain measured on one side with the strain on opposite side in logs

Relationship between log diameter and growth strains No strong association between log diameter and growth strains

Conclusions Growth stresses is one of the most important wood quality criteria The study revealed a significant variation in growth strains between different clones providing an opportunity to select low stress clone for sawn timber production. There was a significant association between strain measured on one side with the strain on opposite side in logs. These suggests that a single measurement of strain on a log could indicate magnitude of stresses for screening purpose. Tree growth as represented by the log diameter does not appear to have any significant association with growth strains.

Acknowledgement: • IUFRO for SAP • FAO for partial funding • ICFRE for supporting my work • MoEF, Govt. of India • Authorities at my institute • Dr Andrew wong • Dr Susan Siau

THANK YOU

Pankaj K. AGGARWAL