The Impact of Internal Checking on the Log and Timber Value of Fire Salvage Ash Type Sawlogs

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1 ` PROCESSING PROJECT NUMBER: PNB DECEMBER 2012 The Impact of Internal Checking on the Log and Timber Value of Fire Salvage Ash Type Sawlogs This report can also be viewed on the FWPA website FWPA Level 4, Queen Street, Melbourne VIC 3000, Australia T +61 (0) F +61 (0) E info@fwpa.com.au W

2 THE IMPACT OF INTERNAL CHECKING ON THE LOG AND TIMBER VALUE OF FIRE SALVAGE ASH TYPE SAWLOGS Prepared for Forest & Wood Products Australia by Greg Barnes and Alan McGreevy of QA Pty Ltd, on behalf of VicForests

3 Publication: The Impact of Internal Checking on the Log and Timber Value of Fire Salvage Ash Type Sawlogs Project No: PNB This work is supported by funding provided to FWPA by the Australian Government Department of Agriculture, Fisheries and Forestry (DAFF) Forest & Wood Products Australia Limited. All rights reserved. Whilst all care has been taken to ensure the accuracy of the information contained in this publication, Forest and Wood Products Australia Limited and all persons associated with them (FWPA) as well as any other contributors make no representations or give any warranty regarding the use, suitability, validity, accuracy, completeness, currency or reliability of the information, including any opinion or advice, contained in this publication. To the maximum extent permitted by law, FWPA disclaims all warranties of any kind, whether express or implied, including but not limited to any warranty that the information is up-to-date, complete, true, legally compliant, accurate, non-misleading or suitable. To the maximum extent permitted by law, FWPA excludes all liability in contract, tort (including negligence), or otherwise for any injury, loss or damage whatsoever (whether direct, indirect, special or consequential) arising out of or in connection with use or reliance on this publication (and any information, opinions or advice therein) and whether caused by any errors, defects, omissions or misrepresentations in this publication. Individual requirements may vary from those discussed in this publication and you are advised to check with State authorities to ensure building compliance as well as make your own professional assessment of the relevant applicable laws and Standards. The work is copyright and protected under the terms of the Copyright Act 1968 (Cwth). All material may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest & Wood Products Australia Limited) is acknowledged and the above disclaimer is included. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of FWPA. ISBN: Researcher: VicForests Level 7, 473 Bourke Street MELBOURNE 3000, Prepared by Greg Barnes and Alan McGreevy QA Pty Ltd Level 2, 2 Market Street MELBOURNE 3000 Forest & Wood Products Australia Limited Level 4, Queen St, Melbourne, Victoria, 3000 T F E info@fwpa.com.au W

4 Executive Summary Following the Victorian wildfires of 2005/06 and 2009, sawmillers reported abnormally high levels of internal checking in the timber from Victorian Ash fire salvage logs, causing a loss in timber value due to the reduced yield of appearance quality products. This project was established by VicForests to examine the patterns of internal check development and severity throughout the air seasoning period, in slabs sawn from fire salvage sawlogs compared with slabs cut from normal green logs. After final processing into dry skip-dressed timber, the product/grade yield and timber value achieved for both samples have been compared, with the extent of downgrade caused solely by internal checking separately identified. Factors that could be used to schedule and manage fire salvage harvesting to minimise the impact of any wildfire induced abnormal internal checking were investigated. Four air drying methods were tested to determine whether it would be possible to significantly reduce the loss of timber value caused by internal checking through altered air drying methods. Until the final stages of air drying, the research did not uncover any significant difference in the spatial pattern, timing and severity of checking between the salvage and the green samples that would have identified an additional wildfire effect either heat induced anatomical changes, or the progressive outcome of moisture loss or moisture gradient stress in the standing, fire-killed trees. In both samples the variability in the development and extent of checking appeared to be dominated by the normal range of genetic and environmental factors that govern tree growth and wood properties, with no obvious overlay fire effect. Although the phenomenon of abnormal internal checking that had previously been reported by sawmillers did not appear to exist, internal checking did cause a clear and measurable difference between the timber grade yields and values from the two samples. The difference was due to the fact that a very large proportion of the checks in the green timber samples closed up, firstly in the last stages of air drying and particularly during reconditioning. This trend was also observed in the fire salvage samples, but to a much lesser extent. This points to the possibility that the ability for internal checks to recover is inhibited or damaged in timber sawn from fire killed trees. Further research to investigate the effectiveness of different reconditioning treatments steam saturation, temperature and duration may yield commercial benefits. More fundamental research to examine heat induced changes at the cellular level, which would make the salvage timber less responsive to steam treatment of collapse, checking and shrinkage, may also provide a guide to commercial solutions. The potential for reducing internal checks in fire salvage timber during reconditioning would add to the gains that can be made through modified air drying practices. The research has shown that an initial two month period of block stacking and plastic wrapping to retain and equalise moisture content significantly reduced the incidence of internal checking, compared with normal open yard air drying. If the cost of this double handling and the additional stock holding time can be kept under $100/m 3 then the increased value of the timber should outweigh the cost. Even without the initial time in plastic wrap, air drying in more controlled conditions such as a hessian sided shed would increase the value of the finished timber by $48/m 3. i

5 The application of the same four air drying treatments in the green control did not create any significant difference in grade yield or timber value, mainly because the reconditioning process effectively eliminated any variation in the extent and severity of internal checks that had developed during air seasoning. The research indicates that under the particular circumstances of this research, and without applying any modified air drying or reconditioning practices, there is a 12% reduction in the value of the sawn timber directly attributable to internal checking, using the green control as the reference base. This difference can be reduced to 3% (at an additional cost) if modified air drying practices are implemented. These results must be considered in light of the experimental limitations described in the body of the report. The only tree or coupe based predictive measure of the comparative risk of value loss due to internal checking that proved to be of any relevance was moisture gradient. It may be possible to predict the severity of internal checking in timber sawn from fire killed trees by measuring the moisture gradient from the sapwood and outer heartwood towards the heart of the tree. The most effective measure is the moisture gradient at the head end of the millable trunk, which would therefore necessitate the felling of sample trees. Before this could be adopted as an operational tool in scheduling fire salvage coupes, more data is needed to examine the changes in moisture gradient with stem height, and with the time elapsed since the fire. The small number of logs taken from the Toolangi log dump was not sufficient to conclusively demonstrate whether a period of storage under water spray has any significant effect in reducing internal checking by wetting the sapwood and reducing the moisture gradient. However, the results do suggest that this may be the case regardless of whether the logs are from fire killed or green coupes. A further trial to assess the cost:benefit of the effect of various periods under water spray on internal checking and final product value could be worthwhile. The study did not provide any evidence that either of the Victorian Ash species Alpine Ash or Mountain Ash is more or less prone to internal checking, either in the green or the salvage samples. More internal checking occurred in the butt logs than in the head logs, for both the salvage and green control samples. The impact of this difference was more significant in the salvage logs because the closure of checks during reconditioning was far less effective. The fact that the salvage head logs did not check as much as the butt logs shows that the heat of the crown fire did not change the general rule that the timber from butt logs tends to check more than head log timber because growth ring width and wood density differentials are greatest in the early years of growth. ii

6 Table of Contents Executive Summary... i Introduction... 1 Methodology... 3 Sawlog Selection... 3 Assessing Fire Intensity and Measuring Tree Moisture Content... 4 Sawmilling... 5 Racking Out and Air Drying... 7 Monitoring Internal Check Development During Air Drying... 7 Final Drying and Dry Milling Experimental Limitations Results and Discussion Moisture Content Loss and Internal Checking During Air Drying Abnormal Internal Checking in Timber from Fire-killed Trees The Impact of Internal Checking on Final Grade Yield and Value of Seasoned Skip-Dressed Timber Comparison of Air Drying Methods Variation Between and Within Coupes Genetic and Environmental Factors Variation Between Butt and Head Logs Anatomical Factors Scheduling Fire Salvage Harvesting - Tree & Coupe Predictors of Internal Check Severity Conclusions Recommendations Acknowledgements Appendix 1 Green Coupe and Sawlog Record 35 Appendix 2 - Coupe Location Maps 37 Appendix 3 - Tree Moisture Profile & Fire Intensity 39 Appendix 4 Slab Allocation by Drying Treatment 45 Appendix 5 Internal Check Development and Impact 47 Appendix 6 Timber Value Comparisons 64

7 Introduction Internal checking in Ash type Eucalypts has always been a fact of life for Victorian and Tasmanian sawmillers. Internal checks, caused by differential shrinkage across growth rings, significantly reduce the yield of appearance grade timber, with a corresponding major loss in timber value. While the severity of internal checking can be reduced by careful initial drying (air drying or pre-drying), and by closing checks during reconditioning, it cannot be prevented. The occurrence and intensity of internal checks is influenced by a range of genetic and environmental factors. There are wide variations in the nature and extent of internal checking in different trees growing in the same location, while the concentration of internal checks in individual growth rings reflects the environmental conditions that influenced tree growth and growth stresses during that year such as drought, fire etc. In general, internal checks tend to occur in low density early wood, particularly where it is encased by bands of high density late wood, which restricts the ability of the early wood to shrink. For this reason checking and collapse are most prevalent in the faster grown juvenile wood near the heart, at or close to the base of the tree. Ash sawmillers have developed a relatively fatalistic attitude to the random and unpredictable occurrence of internal checking in sawn timber. Steam reconditioning is used to recover collapse and shrinkage, but also to reduce the appearance and value impact of open internal checks. Along with restricting the air flow around seasoning racks in the early stages of air drying, or the application of mild pre-drying schedules in controlled environment sheds, reconditioning is a vital process in minimising the negative effect of internal checks on the yield of appearance grade products from Ash type sawlogs. The progressive development of internal checks during air drying, their location across the tree cross-section and along the length of the bole has not been objectively studied, so the remedial effects of reconditioning have not been quantified by comparing internal checking before and after. In 2009, Forest & Wood Products Australia (FWPA) published a comprehensive research review, looking at the causes of checking, identifying check prone material, and methods for preventing or ameliorating checking 1. This report which provides a consolidated reference on the science of internal checking and its commercial impact includes the following statement in the Executive Summary....a topical question at the moment is whether or not bushfires have any effect on the collapse and checking propensity of fire salvage logs? This current research project was commissioned by VicForests, and subsequently supported by FWPA, to investigate that question. Internal checking in fire salvage logs had already become a commercial issue for VicForests and its customers following the 2006/07 fires, when abnormal checks were observed by the seasoning manager at the ITC Alexandra sawmill, located in the outer growth rings of quarter sawn slabs, rather than in or near the juvenile wood near the heart. This supposedly abnormal internal checking occurred within 1 Blakemore, P. and Northway, R. (2009) Review of, and recommendations for, research into preventing or ameliorating drying related internal and surface checking in commercially important hardwood species in south-eastern Australia (PNB ) Forest and Wood Products Australia., Melbourne Australia. 75pp. 1

8 days after sawing, as it was found after three weeks when drying racks were removed from an initial corral air seasoning treatment. This treatment involves the close stacking of racks of appearance quality slab, protected by a perimeter of structural quality racks; with the aim of reducing air flow and maintaining a cooler, more humid micro-environment. Once identified, this report of excessive checking led to negotiations about the value of fire salvage logs. This increased risk of checking potentially precluded the production of 25 mm nominal thickness slabs for appearance products and significantly reduced the recovery of appearance grades from 38 mm and 50 mm material. Decisions on product targets start with the selection of the green mill cutting pattern and as the increased risk of checking in fire salvage logs could not be predicted, the safest strategy was to cut for F17, despite its lower price and market demand compared with appearance products. The potential for higher levels of internal checking again became a commercial issue when salvage harvesting commenced following the February 2009 fires. VicForests recognised the need to obtain more substantive and independent evidence of the nature and extent of the effect of wildfire on the increased occurrence of internal checking in fire-killed sawlogs. By tracking the development of internal checks in a sample of fire salvage logs, as moisture content is lost during air drying, and by comparing this with a control sample of logs from green coupes; the aims were to:- 1. Determine whether the heat effects of wildfire caused a significant increase in the occurrence of internal checks. 2. Determine whether different air drying techniques could be effective in reducing the severity of internal checking. 3. Determine whether internal check severity was correlated with any indicators that could be used to assist coupe planning and scheduling and the sequencing of salvage harvesting, to reduce the impact of internal checking on timber value, consequently on log value. As well as monitoring internal check development during air drying, the actual grade yield of seasoned timber products was determined for the fire salvage logs and for the control, so that the actual difference in timber value could be quantified. Because the normal range of genetic and environmental variability in Ash forests represents the main cause for the difference in timber value, the overall proportion of production that had to be downgraded to structural grade solely because of internal checking has been used as the most appropriate identifier of any additional wildfire effect. 2

9 Methodology Sawlog Selection VicForests staff selected the coupes that would be sampled, and assisted with contractor liaison, log identification and transport to mill. Twenty four fire salvage sawlogs were harvested in November 2009, from standing trees that were chosen according to visual indicators of the fire intensity they had suffered, without regard to sawlog size or quality. Four logs were taken from each of six coupes with an additional four logs taken from the VicForests Toolangi log dump. As it was not possible to obtain the green control logs until after fire salvage harvesting was completed, it was decided to harvest the control sample twelve months after the salvage sample, so that air drying would again commence in midsummer. While it was not possible to season each sample under the same weather conditions, this decision gave the best chance of similar drying conditions. For the control green log sample four logs were taken at random from each of six coupes, plus four Mountain Ash and four Alpine Ash logs from the Toolangi dump. Each sawlog was numbered and coded to identify the source coupe. See Appendix 1 for a record of sawlog sources, log grade and log volume. See Appendix 2 for a coupe location map overlaid with the 2009 bushfire boundaries. The first tree selected from Tricep TR1 The Woollybutt coupe (Armstrong) Black Range Handprint coupe Handprint log HP1 3

10 Green coupe Hathor Western Cym green coupe Assessing Fire Intensity and Measuring Tree Moisture Content Four possible predictors of abnormal internal checking were examined during log selection in the 2009 fire damaged coupes. Firstly, each standing tree was visually examined and given a Fire Intensity Score, using the following criteria:- 0 = green tree, no visible fire damage, 1 = light crown damage, some green leaf, no bark damage, 2 = moderate damage, some dead leaf, bark splits confined to smooth barked top log, 3 = heavy crown damage, no leaf or small twigs, butt log bark split but not loose, 4 = severe crown damage, butt log bark loose, barrel checks started. Where possible, trees were selected in each coupe to cover the range of fire intensities that were apparent see Appendix 3. A full cross section sample (approximately 125x125 mm) was taken from the butt and head of each log. Each section was immediately wrapped in plastic to avoid any moisture loss, before the preparation of oven dry samples at Timber Training Creswick. To provide a full moisture profile from wane to wane across the butt and head end sections, 20 mm wide samples were taken at 20 mm intervals and the core moisture content of each sample determined using the oven dry method. For large sections over 500 mm long the gap between samples was increased to 40 mm, and for a few small head sections it was reduced to 3 mm (the width of a saw cut). 4

11 Sawing and Preparing the Moisture Content Profile Oven Dry Samples The following oven dry measurements for Handprint log HP4 provide an example of the moisture profiles obtained from the butt and head samples. Table 1 Typical Moisture Content Profile Measurements 0-2 cm 4-6 cm 8-10 cm cm cm cm Heart cm cm cm cm cm Butt 107% 106% 104% 104% 107% 117% 138% 132% 110% 96% 100% 100% 0-2 cm 4-6 cm 8-10 cm cm Heart cm cm cm cm Head 84% 88% 91% 94% 98% 97% 95% 93% 86% This raw data was then amalgamated to provide average moisture contents for the outer, middle and inner third of each radial section a total of six moisture levels see Appendix 3. This information provides three possible means of identifying the potential for increased internal checking the average moisture content level through the cross section, the moisture level in the outer third of the cross section and the severity of the moisture gradient, calculated as the moisture differential per centimetre, between middle and outer third. Sawmilling The fire salvage logs were sawn into 38 mm slabs (overcut to 44 mm for seasoning) at Reid Bros. Timber, Yarra Junction on 19 November 2009, 3-9 days after harvesting, with the exception of the Toolangi Dump logs, which had been stored under water sprays before delivery to Reids. These logs were selected with a view to obtaining some indication of the effect of time under water, which ranged from eight days up to 108 days before milling. 5

12 A total of 54 mill logs were sawn from the 28 fire salvage bush logs. The length and centre diameter of each mill log was recorded, as well as observations of fire damage. The log number was marked on each slab and the number of slabs per mill log tallied. Slabs were block stacked and fully plastic wrapped, before being transported to Timber Training Creswick six days later. The cutting pattern used by Reids resulted in a mix of quartersawn and backsawn slabs. After removing a substantial wing on the twin Canadian saw breakdown carriage, the log was turned onto the flat and sawn through and through, with the wings transferred to the resaw bench. Unless the log was small, the first flitch was returned to the carriage and also sawn through and through. A small proportion of the slabs were cut on the bench, these were mostly backsawn. The 32 green logs were cross-cut into 63 mill logs and sawn into oversize 38 mm quarter sawn slabs at Gunns Timber Heyfield on the 29 th of November 2010, 6 to 13 days after harvesting. The eight logs sourced from the Toolangi Dump were harvested in mid-july 2010, giving them approximately 135 days storage under water sprays before milling. The ends of each mill log were painted with a sequence of colours, and the colour code was cross-referenced with a sequential log number, so that the slabs from each log could be identified. The same procedures that were used for measurement of the salvage mill logs were also used at Gunns for the green logs. The slabs were also block stacked, but not plastic wrapped, before delivery to Creswick fourteen days after milling. The Gunns mill layout allows for more complete quarter sawing than was possible at Reids. Basically, each log is quartered and the slabs are cut alternating between the faces of each quarter. All of the slabs were sawn on the secondary bandsaw after initial breaking down. Log Preparation and Milling the Green Logs at Gunns Heyfield 6

13 Racking Out and Air Drying The salvage slabs were sorted into four different drying treatments at Timber Training Creswick in early December 2009, two weeks after milling. Treatments 1 and 2 were immediately racked out - treatment 1 (T1) for open air drying, while treatment 2 (T2) was placed in a shade cloth sided drying shed, surrounded by other timber racks. Treatments 3 and 4 were block stacked and fully wrapped in plastic for a period of nine weeks, before being racked out in early February Treatment 3 (T3) was placed next to treatment 1 and treatment 4 (T4) placed in the drying shed. Drying treatments were defined by the Manager, Timber Training Creswick. The green log slabs were sorted into the same four drying treatments and racked out or block stacked in December 2010, three weeks after milling. Treatments 3 and 4 were racked out after nine weeks in plastic wrap. The number of slabs from each log in each drying treatment is given in Appendix 4. T1 and T3 open air drying T2 and T4 drying in hessian sided shed Monitoring Internal Check Development During Air Drying A single slab from each mill log was randomly selected for each treatment and kept in a separate pack, or drying rack. Two sample biscuits were cut from each sample slab at approximately three weekly intervals, one for oven drying to determine moisture content, the other for assessment of the location and severity of internal checks. The actual sampling dates were:- Table 2 Biscuit Sampling Dates FIRE SALVAGE SLABS GREEN SLABS Date Days Since Milling Date Days Since Milling 07/12/ (T3 only) 1 22/12/ (T2 only) 1 22/12/ (T1, T2 & T4) 2 18/01/ (T1, T2 & T4) 2 13/01/ /02/ /02/ /03/ /02/ /03/ /03/ /04/ /04/ (T3 & T4) 3 17/05/ /06/ (T3 & T4) 08/07/ (T3 & T4) 4 11/11/ /11/ /12/

14 1 The first set of sample biscuits was taken from one treatment only, on the basis that it was representative of all treatments at this time. 2 Treatment 4 was also regarded as representative of T3 as both were block stacked and plastic wrapped at this time. 3 T1 and T2 were not sampled as they were already below fibre saturation point on 18/3/ T1 and T2 were not sampled as the previous tests showed that they were not losing any more moisture under the prevailing winter weather conditions. 5 These samples were taken to examine the effectiveness of reconditioning in closing up internal checks and reducing their visual impact. The small sub-sample of fire salvage biscuits taken after reconditioning and before final drying showed that a significant proportion of checks had closed up as a result of this process. This raised the question as to whether the effect of wildfire on internal checking was related to increased occurrence, or alternatively to a reduction in the effectiveness of reconditioning. The fire salvage samples had also demonstrated some tendency for checks to close up in the final stages of air drying, at or near fibre saturation point. A full set of green samples was taken prior to reconditioning and at the completion of kiln drying to investigate these changes more thoroughly. For these three samples, only one set of biscuits was taken, as there was no need to measure moisture content. The visual assessment of the timing, location and severity of internal check development involved the following steps:- 1. A colour photocopy or photograph was taken to compare the four biscuits from each log (treatments 1 to 4), (see below for examples for one salvage log and a green log). 2. Each biscuit was divided into an inner, middle and outer third. Any heart was excluded as well as the outer sapwood. 3. Using backlight from a 50 W halogen lamp, as well as a magnifying glass, all internal checks were identified and marked on each biscuit. 4. Within each one third section, the severity of internal checking was coded as follows:- - 0=no checks, - 1=slight, 1 growth ring only, - 2=severe, 1 growth ring only, - 3=slight, 2-3 growth rings, - 4=severe, 2-3 growth rings, - 5=slight more than 3 growth rings, - 6=severe, more than 3 growth rings. 5. The average grain angle in each third was measured so that the section could be classified as backsawn (< 45 o ) or quartersawn ( 45 o ). Appendix 5 shows the average grain angle of each sample slab. 6. The aggregate length affected by internal checks in each third was measured (in 5 mm increments) and converted to a percentage of the total length of the backsawn or quartersawn sections (IC%). 7. From this data an Internal Check (IC) Score was calculated for each biscuit, giving a reduced weighting to the backsawn sections (the more backsawn the section, the more that checking is likely to occur, and the wider they spread across the length of the biscuit section). An increased weighting was given to checks occurring in the outer third, because this (along with the early occurrence of checks) had been regarded as a symptom of the abnormal internal checking found in timber from fire killed trees. The weightings used were:- Table 3 Internal Check Score Weightings INNER THIRD MIDDLE THIRD OUTER THIRD QUARTERSAWN BACKSAWN

15 The reduced weightings for the backsawn sections are based on the 3:1 ratio between the average quarter sawn angle of 67.5 o and the average backsawn angle of 22.5 o. Table 4 Example of Internal Check Data for a Single Sample Biscuit. INTERNAL CHECK SEVERITY & GRAIN IC% ORIENTN. HEART INNER MIDDLE OUTER QS BS IC SCORE Refer to points 4 & 5 above Refer to point 6 Refer to point 7 6 BS 3 QS 1 QS 22% 77% (22*(0.67+1)/2+77*.11) = 20 Appendix 5 presents the progressive moisture content and internal check development data collected for each mill log and drying treatment. Finally a photograph and photocopy record was taken of the time series of samples taken from each slab to capture the progressive development of internal checks over the drying period. This primary recording of internal check development, both spatially within the sample slab profile, and over time as drying progressed, provides both visual and numerical options for identifying internal check severity, as an early predictor of timber grade yield and value; and hence sawlog value, including any differentials between coupes. Salvage Log 17 (the head log from Toolangi Dump Log 4), biscuit samples taken from treatments 1-4, by date. The typing on each biscuit represents the moisture content at the time of sampling. The red numbers indicate the Internal Check Score. 9

16 Green Log 17 (the head log from Toolangi Dump Log 3), biscuit samples taken from treatments 1-4, by date. The typing on each biscuit represents the moisture content at the time of sampling. The red numbers indicate the Internal Check Score. 10

17 Salvage Log 17 (the head log from Toolangi Dump Log 4), time sequence of the biscuit samples taken for each air drying treatment. The typing on each biscuit represents the moisture content at the time of sampling. The red numbers indicate the Internal Check Score. The circled areas enclose internal checks. 11

18 Green Log 17 (the head log from Toolangi Dump Log 3), time sequence of the biscuit samples taken for each air drying treatment. The typing on each biscuit represents the moisture content at the time of sampling. The red number indicate the Internal Check Score. The circled areas enclose internal checks. Final Drying and Dry Milling In July 2010 the slabs from each salvage drying treatment were de-sticked and sorted numerically into block stacks for transport to Gunns Timber Products Heyfield, where they were re-racked for final drying. Reconditioning and kiln drying occurred in October 2010, but due to a number of operational scheduling difficulties, the final processing and grading of the finished (skip dressed) timber was not completed until 3 February Due to the milder and wetter weather in 2011, the air dried slabs from the green log were not transported to Gunns Heyfield (in stick) until October and November 2011, for reconditioning and kiln drying in December. The slabs were skip dressed on the 3 rd of February 2012, before the final product was sawn and graded on the 22 nd of February In each case, the timber was graded and sorted by Gunns personnel in accordance with their normal operating procedures, including use of their ultrasonic void detector. For each piece, the treatment and log number, the width, the grade and the reason for downgrade from appearance to structural (grade defect, backsawn, or internal check) was recorded. The grade tally system used for this project meant that a piece with identified internal check was only recorded in that category if it did not have any other grade limiting defect. Likewise, F17 backsawn was only recorded as such if it had neither grade defect nor internal checking. Finished product piece length was recorded for a substantial sub-sample. Regardless of grade, the average piece length for the salvage slab was 3.5 metres, and 3.7 for the green slab. The average piece length in each Treatment was used to calculate the timber volume tallies for each treatment. The appearance timber was graded as Select and Standard Gunns do not produce High Feature grade from 38 mm stock. The falldown to F17 included a small proportion of nonstructural Merch grade, but this was not differentiated. As noted in the Introduction, the volume of falldown due solely to internal checking, expressed as a percentage of the total timber volume, has been used as the best indicator of the severity of internal checking. This percentage (F17 IC%) is included with the full set of grade yield results given in Appendix 5. 12

19 Experimental Limitations VicForests salvage logging operations in 2009 effectively prevented the simultaneous harvesting of trees from unburnt coupes for the control samples. The twelve month delay in obtaining the control sample logs had several ramifications:- The cutting patterns for each set of samples were different, as they were sawn at different sawmills, leading to a need to adjust for average grain angle and the relative proportions of backsawn material. Grain angle is correlated with the risk of internal checking, as it is known that the more the timber tends towards being truly backsawn, the more it will check. Backsawn timber also has a greater tendency to surface check, which again reduces the yield of appearance grade products. The method of determining the Internal Check Score from the biscuits sampled during air drying is also sensitive to the average grain angle of the quarter sawn and backsawn samples, as the lesser the average angle, the greater the affected surface area. These differences are analysed in the Results section. The green control slabs were air dried under generally wetter and cooler conditions, leading to a longer air drying timeframe. The final skip dressed product yields depend on the consistency and accuracy of the commercial grading at Gunns Heyfield, along with the associated void scanner that is used by Gunns to identify (and downgrade) timber with internal checks. The twelve month gap between the two final grading runs meant that different grading personnel were involved. Product targets and procedures should have been the same. The salvage slabs were less truly quarter sawn, and were therefore wider, giving the opportunity for the operator in charge of the multi-saw to saw for maximum dimension rather than grade maximisation. This possibility is examined in the Results section by comparing average product widths by grade for the two samples. In an operational sense, log quality is specified through the designation of log grade (D grade being VicForests lowest quality sawlog to B grade being highest). Ideally, the log grades and also log dimension, especially diameter which affects product recovery, should have been as consistent as possible between the fire salvage sample and the control sample. There was considerable difference in the log quality between the two samples as indicated by the log grades with the fire salvage sample comprising around 23% less B grade (by volume), and 14% more D grade. Table 5 Log Grade Proportions and Average Diameters Salvage sample Control sample B grade m3 (41.5%); av diam 63 cm m3 (64.8%); av diam 61 cm C grade m3 (44.3%); av diam 59 cm m3 (35.2%); av diam 68 cm D grade m3 (14.2%); av diam 59 cm Another significant limiting factor was the sample size of 28 fire salvage trees, which proved to be insufficient to identify the effects of any predictor of increased internal checking, over and above the normal range of checking that is the result of genetic and environmental conditions. Also, as the sample trees were harvested nine months after the February 2009 fires (6-9 months for the four Toolangi Dump logs) this project did not provide any insight into the possible increase in the severity of internal checking as standing dead trees dry out 13

20 before harvesting. Progressive sampling of trees from a fire killed coupe would be needed to investigate whether (for example) any of the following possible patterns actually occurs. Figure: Theoretical examples of progression of IC development Finally, a key difference between the level of internal checking in the salvage and green samples may be the relative effectiveness of reconditioning in closing up checks. A subsample of biscuits (39 biscuits in salvage compared to 252 in the control) was taken after the salvage slabs were reconditioned to assess this. However, in hindsight a full set of biscuit samples should have been taken, to compare with the full set that was subsequently taken from the green sample slabs. Finally it has not been possible to confirm that the observed closure of internal checks in the finished (skip-dressed) timber will continue to be the case if the timber is dressed or moulded for appearance applications. 14

21 Results and Discussion Moisture Content Loss and Internal Checking During Air Drying While the same four air drying treatments were accurately applied to the salvage and green slabs, the cooler and wetter weather in the summer, autumn and winter of 2011, compared with 2010, meant that the green control timber experienced significantly milder drying conditions. Graphs 1-4 compare the different moisture loss rates in the salvage and green samples for each drying treatment, from the date of racking out. Graph 1-4 Moisture Loss Comparison by Treatment Tmt Drying tmt after milling Final air drying tmt T1 Racked out, open air No change T2 Racked out, shade cloth sided shed No change T3 Block stacked in plastic Racked out, open air T4 Block stacked in plastic Racked out, shade cloth sided shed Despite the (unexpected) higher initial moisture content in the salvage slabs, each graph shows that the salvage slabs dried much more rapidly than the green slabs. Whether this may have caused even more severe internal checking in the salvage timber compared with the green control is examined in the next Section. Graphs 5 and 6 compare the four treatments moisture loss patterns separately for the salvage and green air drying treatments. These graphs illustrate the drying time differential due to the time in plastic wrap for T3 and T4. 15

22 Graph 5 & 6 Moisture Loss Comparison by Treatment These graphs show that the only differences between the two pairs of drying treatments occurred in T3 and T4. In the Salvage graphs the dip in the T4 line was due to the plastic wrap blowing off one end of the sample pack (and some other T4 packs). As the graph shows, the two lines came back together after the plastic was replaced. After racking out T3 and T4 lost moisture at approximately the same rate as T1 and T2 until winter conditions slowed the drying down after 100 days and kept the final moisture content above 20%. The T3 curve finished slightly higher in moisture content probably due to direct exposure to winter rain. In the Green treatments, T3 lost moisture at a greater rate than did T4 after they were racked out, until the lines re-joined between 150 and 200 days. There is no apparent reason for this, as a similar variation did not occur between T1 and T2. Abnormal Internal Checking in Timber from Fire-killed Trees This project provided no evidence to support the assertion that abnormally severe internal checking occurred in fire salvage timber - specifically early in the air drying process and in the outer growth rings. This is demonstrated by the following graphs. Graph 7 Internal Check Score Over Air Drying Period Before reconditioning After reconditioning 16

23 The graph shows a similar pattern of internal check development in both the green and salvage timber during the first 125 days of seasoning. Over the next 75 days, checking developed more severely in the green slabs. In the final air drying stage (below 25% moisture content in the salvage samples and below 30% moisture content in the green samples the sections to the left of the first arrows) there was a slight decline in internal check severity in the salvage slabs, compared with a far more dramatic reduction in the green slabs. Perhaps the most significant finding indicated by the graph is the relative difference in the effectiveness of reconditioning in closing up internal checks, as shown by the difference between the slope of the lines between the arrows. Graph 8 Internal Checking in the Outer Growth Rings Before reconditioning After reconditioning Unlike Graph 1, in this case checking in the outer growth rings was marginally higher in the salvage slabs, in the first 150 days of air drying. As the temperature effects of wildfire are presumably confined to the cambium, the sapwood, and possibly to the outer growth rings of the heartwood, this could be interpreted as a sign of abnormal internal checking. However, after this time the level of checking was higher in the green slabs. As with the first graph, far more internal checks closed up in the green slabs during the final stages of air drying and particularly during reconditioning. This may have been influenced by the milder drying conditions experienced by the green control, but it again highlights the likelihood that the timing, duration and conditions of reconditioning may hold the key to improving the closure of internal checks in the timber from fire killed trees. Note that for the salvage logs, the post-reconditioning results are based on only 39 biscuit samples, not the normal full set of 216 (54 logs by 4 treatments). For the green logs a full set of 252 sample biscuits was taken after reconditioning and kiln drying. An examination of the various stresses and causative influences that operate at the cellular level, which could impede the closure of internal checks in fire salvage timber, could provide valuable information, but it is beyond the scope of this project. These causes may relate to immediate changes caused by high fire temperatures, or the time related stresses associated with moisture loss in the standing dead trees before harvesting. 17

24 The variation in these two indicator measures of internal check development (IC Score and IC Severity), between drying treatments, species, coupes, and trees within coupes is examined later in this Section, along with the correlation between these measures and the impact of internal checking on final dry sawn grade yield. The source for this information, as well as for graphs 1 and 2 and Table 5 below, is the full set of data provided in Appendix 5. The Impact of Internal Checking on Final Grade Yield and Value of Seasoned Skip-Dressed Timber See page 12 for a description of the grade marking and tallying system. Table 6 Timber Grade Yield Seasoned Appearance F17 by Cause 1 Select Standard Total Defect Backsawn Internal Check Total Salvage 18.2% 10.5% 28.7% 17.0% 20.6% 33.7% 71.3% Green 29.7% 17.3% 47.0% 47.6% 2.5% 2.9% 53.0% 1 - Includes a small proportion of non-structural merch grade. The results in this Table are in line with the analysis of checking in biscuit samples as given in Graphs 7 and 8, as each of these measures of the severity of internal checking predicted a much higher occurrence of internal checks in the dry sawn timber from the fire salvage logs. As the graphs showed that there was no significant difference in the development of checks, the relative effectiveness of reconditioning in closing checks was the main indicator of this result. As the final yields are based on skip dressed product, a question that remains unanswered is whether the closed checks would re-open and reappear on the surfaces of moulded or dressed products. As noted in the Introduction, the occurrence and intensity of internal checks is influenced by a range of genetic and environmental factors, of which wildfire is just one. Nevertheless, Table 6 demonstrates that it has had an impact. As the overall yield of appearance grade timber is also a reflection of the same range of genetic and environmental factors, the difference in the Total Seasoned Appearance percentage given in the Table cannot be solely attributed to the increased effect of internal checking due to wildfire. The more appropriate measure would be the proportion of timber yield that was downgraded to F17 solely because of internal checking (33.7% vs. 2.9%). Table 6 shows that downgrade due solely to internal checking was significantly greater in the salvage timber (more than ten times the percentage in the green control) with a consequent major fall in the yield of appearance grade timber (18.3% less than in the green control). As the yield of appearance timber is critical to both sales revenue and profitability, the immediate and obvious conclusion to be drawn from Table 6 is that these salvage logs, which were harvested six to nine months after the fire, were of lower value than the green control logs. 18

25 The values given in Table 7 are based on comparative timber prices provided by Gunns - $1,400/m 3 for Select, Standard $1,100/m 3 and F17 $838/m 3. Table 7 Comparative Timber Value by treatment Timber Value ($/m 3 of timber) T1 T2 T3 T4 Overall Salvage $ 919 $ 966 $ 1,019 $ 969 $ 968 Green $ 1,050 $ 1,049 $ 1,051 $ 1,052 $ 1,051 Reduction in value 12 % 8 % 3 % 8 % 8 % Based on these calculations, the salvage timber is worth 8% less than the green timber. However, the comparative timber values for air drying treatment T1 provide a more representative reflection of the actual commercial outcome achieved when sawmillers processed the 2009 fire salvage sawlogs (other than the absence of corralling). The reduction in timber value in this case is 12%. If the salvage timber had been air dried using the more costly T3 process, the loss of value would have been just 3% per cubic metre of timber. For more comparative information on estimated timber values see Appendix 6. There are a number of reasons why it was not possible to take a full timber tally and determine actual log recoveries during this study such as the loss of timber from the sample slabs from which biscuits were sawn, and the use of sub-samples to determine average timber lengths. Neither is it possible to determine comparative (rather than absolute) recoveries that are not impacted by extraneous factors. It is worth noting that comparing average timber length with average log length shows that there was a significantly larger amount of docking loss in the salvage timber. The average length loss for the salvage timber was 31.7%, compared with 20.9% for the green. A number of factors, other than Internal Check contribute to this difference including the tendency for backsawn timber to split more than quartersawn and increased taper in longer lengths (salvage logs cut at Reids were sawn to maximum 6m lengths compared to 5.4m in the control logs at Heyfield). Despite these conclusions on the effect of internal checking on relative timber value, there are some aspects of the Table 6 figures that bear closer evaluation. The proportions of appearance and F17 timber yielded by the green sample are reasonably close to the long running averages achieved by Gunns and therefore they represent a sound base for comparison with the salvage logs. Comparing the relative proportions of the timber that was downgraded solely because it was backsawn, indicates that a substantial amount of the salvage slab material (sawn at Reids to the cutting pattern described on page 6) would have been capable of yielding appearance grade timber. Table 6 shows that there is almost a tenfold difference in the respective yield percentages for F17 Backsawn. 19

26 The slabs that were selected at random to provide the biscuit samples during air drying also support this conservative adjustment to the yield proportions. Eighty seven percent of the green sample slabs were quarter sawn, with an average grain angle of 66 o. The average grain angle for the green backsawn slabs was 39 o. The corresponding figures for the salvage sample slabs are 56% quarter sawn with an average grain angle of 67 o, 44% backsawn with an average angle of only 27 o. These figures confirm that the salvage slabs would have included a much higher proportion of obviously backsawn material than the green slabs. Another possible indicator of the effect of the backsawn proportions is average board width. As the multi-saw operator is able to observe the presence of internal checks from the spray marks left by the void detector, as well as the presence of surface checks, it is logical to saw for greatest dimension whenever appearance grades are no longer possible. Table 8 shows that this occurred in both the green and salvage samples, but that the wider backsawn salvage slabs yielded a significantly higher average width. Table 8 Average Timber Width By Grade Select Standard F17 (Defect) F17 (Backsawn) F17 (Internal Check) Overall Average Salvage 99 mm 98 mm 98 mm 114 mm 124 mm 114 mm Green 100 mm 95 mm 97 mm 105 mm 108 mm 101 mm Based on all of this evidence it can be assumed that the slabbing of the salvage logs at Gunns green mill would have resulted in a much higher yield of the appearance grades, up to 18% higher based on the comparative yields given in Table 6. The next step in further analysis of the yield results in Table 6 is to consider what the grade yields would have been if the logs had been harvested before the fire occurred. As the fire salvage logs had not developed any significant barrel checks, it is reasonable to assume that increased internal checking is the only effect that the fire would have had on timber grade yield and value. While genetic and environmental influences mean that the green control and the salvage samples cannot be considered as equivalent in quality, the proportions that were downgraded only because of internal checking (33.7% vs. 2.9%), indicate that the yield of appearance grades in the salvage sample could have been up to 30% higher. As noted above, genetic and environmental factors can cause wide variations in appearance grade yields, but this analysis of the comparative Table 6 figures suggest that the salvage logs selected for the study must have been of far better quality than the green logs. But, as noted in the discussion of Experimental Limitations, the log grade mix and average log diameter of the green logs was superior to the salvage logs (see Table 5). It must be accepted that log grade and log diameter are both imperfect predictors of timber yield and quality, but this data does not support the possibility that the green logs were of lower quality and size than the salvage logs. Consideration of the above observations, specifically (i) that in the absence of both fire effects and the increased proportion of backsawing, the appearance grade recovery from the salvage logs could have been unprecedently high at up to 77% (28.7% + 18% + 30%), and (ii) the very low percentage of defect in the lower quality salvage logs (17.0% compared to 47.6% in the control) raises some questions over the grade yields recorded. 20

27 As a final observation, both the examination of internal check development during air drying particularly the closure of checks during reconditioning and the final grade yield data demonstrate that internal checking is a significant problem in fire killed trees that have been left standing for some months after being burnt. As noted on page 14, the effect of time delay between the date of the fire and the date of harvesting needs further study, as it was not part of the experimental design for this study. The next step is to examine the various factors and causes that may suggest management strategies that will minimise value loss due to internal checking. Comparison of Air Drying Methods The four air drying methods described on page 7 under the heading Racking Out and Air Drying were tested to compare their usefulness in reducing the occurrence and severity of internal checking. The following graphs and Tables examine the differences between the treatments in relation to three measures the IC Score, IC severity in the outer third, and the F17 IC% Yield. Graph 9 & 10 Average Internal Check Development Over Air Drying Period Salvage Slabs Green Slabs In the salvage slabs, the development of internal checks in the early stages of air drying was similar (allowing for the time delay in the racking out of T3 and T4), with the exception that T3 peaked at a lower level than the internal check severity found in T1, T2 and T4. The phenomenon of internal check closure during the final stages of air drying and during reconditioning, as demonstrated by the slope of the curve, was greater in T4. This graph suggests that T2 and T3 would be the most affected by internal check downgrade in the final product yields (F17 IC%) and this is examined later in this Section. In the green slabs, the development of internal checks in the early stages of air drying was again similar, with the only exception being that T2 developed more checks than T1. Although each of the green slab drying treatments had a higher peak IC Score than their equivalent salvage treatments, the steep final slope of each graph shows that this was overcome by the extent of internal check closure during the final stages of air drying and reconditioning. 21

28 Graphs 11 & 12 Internal Check Severity in the Outer Growth Rings Salvage Slabs Green Slabs Internal checking near and under the sapwood was thought to be an indicator of abnormally severe checks in fire salvage timber. These graphs show that very different patterns of checking occurred in the various fire salvage treatments, whereas the green treatments show a more consistent pattern. The peaks of each curve in the green graph indicate that T3 and T4 reduced the extent of checking compared with T1 and T2. However, at the end of reconditioning there was little difference between the four treatments, although T1 and T3 (in the open yard) ended at a slightly lower point than T2 and T4. The salvage graph shows that T1 and T4 developed far more checks in the outer third of the cross section than did T2 or T3. But at the end of air drying and after reconditioning these positions were reversed. In fact T3 did not show any decline in the number of observable, open checks, which has otherwise been a feature of both measures of internal checking, in all of the treatments. However, sample size was not robust for the post reconditioning data point. As noted in the previous Section, the two measures of internal check development during air drying (IC Score and IC Severity in the Outer Third) both provided a reasonable prediction of the impact of internal checking on grade yield and falldown, and this is supported by the similarities between the lines for each treatment in the respective graphs (with salvage T3 an exception to some extent). If this correlation does exist at the level of each drying treatment, then the endpoint of each curve in Graphs 9 and 11 indicates that the T2 and T3 salvage treatments will have higher proportions of F17 falldown due to internal checks than will T1 and T4 Table 8 below shows that the reverse is the case but that there is a possible link with the high point of the curves, rather than the endpoint. As T1 and T4 had the highest Peak IC Score and Quarter Sawn Outer Third Severity, the effectiveness of these measures as a predictor of F17 IC% falldown is examined later. Graphs 10 and 12 do not indicate any significant difference between the green treatments. If anything, T3 may have a marginally better (lower) F17 IC% falldown. 22

29 Table 9 Timber Grade Yield by Drying Treatment Drying Seasoned Appearance F17 by Cause Treatment Select Standard Total Defect Backsawn Internal Check Total Salvage T1 10.5% 8.1% 18.6% 15.5% 19.5% 46.4% 81.4% T2 17.2% 12.0% 29.2% 16.9% 24.6% 29.3% 70.8% T3 25.9% 13.5% 39.4% 15.8% 23.0% 21.8% 60.6% T4 19.7% 7.8% 27.5% 20.3% 13.9% 38.3% 72.5% Green T1 30.3% 15.9% 46.2% 46.3% 3.8% 3.7% 53.8% T2 28.7% 19.0% 47.7% 45.2% 3.3% 3.8% 52.3% T3 29.2% 18.8% 48.0% 46.7% 2.3% 3.1% 52.1% T4 31.0% 15.3% 46.3% 52.6% 0.4% 0.7% 53.7% Chart 1 Effect of Drying Treatment on Seasoned Appearance Grade Yield and Internal Checking Falldown The four drying treatments made no difference to the grade yields from the green logs, although Treatments 3 and 4 did achieve a marginal reduction in internal checking. In the salvage logs, the influence of internal checking on grade yield reduces significantly from T1 to T2 and then to T3. The increased F17 IC% that then occurs in T4 is perhaps partly explained by the fact that the wind blew the plastic wrapping from one end of some of the T4 packs during the time when they were meant to be fully plastic wrapped this was noted earlier in relation to the pack of T4 sample slabs. Given the fact that T2 was better than T1, it may still be that the T4 procedure will be the best option for minimising the development of checks. The possible cost:benefit of an initial period of moisture equalisation by block stacking and plastic wrapping fire salvage slabs can be estimated by comparing the average product values for T1 and T3. The average value per cubic metre of timber for T1 is $918.50, $ for T2 and for T3 it is $1,018.75/m 3. This means that the double handling and delay associated with T3 must cost less than $100/m 3 to break even, or to make a marginal gain. 23

30 Variation Between and Within Coupes Genetic and Environmental Factors Table 10 summarises the variation between both the green and salvage coupes by ranking them in relation to their peak IC Score, cross-referenced with rankings for their final Internal Check Score at the end of air drying and for the yield of F17 falldown that was due solely to internal checking. Table 10 Variation in Internal Checking Between Coupes Coupe Name Species Type IC Score F17 IC% Peak Final 1 Score Rank % Rank Shona Alpine Ash Salvage % 9 Toolangi Dump 2 Mountain Ash Salvage % 12 Ping Pong Mountain Ash Green % 1 Hathor Mountain Ash Green % 3 Toolangi Dump 3 Alpine Ash Green % 2 Woollybutt Mountain Ash Salvage % 10 Blackbeard Mountain Ash Salvage % 13 Toolangi Dump 4 Mountain Ash Green % 6 Handprint Mountain Ash Salvage % 14 Opposite Phasmid Mountain Ash Salvage % 15 Marney Creek Mountain Ash Green % 7 East Bennies Mountain Ash Green % 8 Tricep Mountain Ash Salvage % 11 Western Cym Mountain Ash Green % 4 Hannibal Alpine Ash Green % 5 1 Prior to reconditioning. 2 These logs were originally sourced from Black Range coupes. 3 These logs were originally sourced from Maverick coupe. 4 - These logs were originally sourced from Big Bull Fiddle coupe. The ranking according to peak IC Score shows an even spread of green and salvage coupes, indicating that the same range of internal check development and severity occurs in both fire salvage and green logs. Although the green coupes show a much greater reduction from the peak to the final IC Score, the same conclusion applies to the rankings according to the final IC Score three green coupes and two salvage coupes make up the best five, while the worst five includes three salvage and two green coupes. These results again show that the level of internal checking found in the biscuit samples does not appear to correlate strongly with the level of internal checking that was found in the finished product by Gunns Void Detector and subsequently downgraded by their grader. For the green coupes F17 IC percentages range from 0.9% to 11.5%, for the salvage coupes the range is from 19.7% to 42.3%. As discussed earlier, the extent to which internal checks close up during reconditioning, and to a lesser extent at the end of air drying, appears to be a major cause for the difference. The experimental limitations due to the twelve month delay in the final processing of the green slabs are also a likely factor. However, if the salvage and green coupes are examined separately a correlation between the internal checking found in the biscuit samples and in the dry sawn product does emerge (see Table 11 below). 24

31 Table 10 does not provide any evidence to support a conclusion that one species Alpine Ash or Mountain Ash is more check prone than the other. Nor is there any real indication that log storage under water has any positive benefit. Nevertheless, the IC Scores for all three sets of Toolangi Dump logs are relatively low. To properly test the potential benefit of time under water, logs from a small number of both salvage and green coupes should be broken into three sub-sets one sawn and processed immediately, one sawn after 2-3 months under water, and the last after 4-6 months. Additional field and map work would be needed to investigate any common factors in coupe location, elevation, fire history and site conditions that may correlate with the propensity for internal checking. A cursory examination of the two coupe maps in Appendix 2 does give some geographic link between coupes in relation to their peak IC Score. The three Powelltown area coupes Marney Creek, East Bennies and Opposite Phasmid - all had high peak IC Scores (22-25). The three Acheron coupes Hathor, Ping Pong and Shona had the lowest IC scores (5-12). Table 11 Variation in Internal Checking Between Salvage Coupes Coupe Name Species IC Score F17 IC% Peak Final 1 Score Rank % Rank Shona Alpine Ash % 1 Toolangi Dump 2 Mountain Ash % 4 Woollybutt Mountain Ash % 2 Blackbeard Mountain Ash % =5 Handprint Mountain Ash % =5 Opposite Phasmid Mountain Ash % 7 Tricep Mountain Ash % 3 1 Prior to reconditioning. 2 These logs were originally sourced from Black Range coupes. Table 11 demonstrates that either the peak or final IC Score could be used as a predictor of the effect of internal checking on final grade yields, because (unlike the green coupes) there is only a marginal decline from the peak score to the final IC Score. Only the Tricep and Toolangi Dump F17 IC percentages are major exceptions to the trendline suggested by the IC Score rankings. Linear regression analysis provides an r 2 of for the following graph. Graph 13 Correlation of Salvage Log Peak IC Score and F17 IC% Falldown Tricep Toolangi Dump 25

32 Table 12 Variation in Internal Checking Between Green Coupes Coupe Name Species IC Score F17 IC% Peak Final 1 Score Rank % Rank Ping Pong Mountain Ash % 1 Hathor Mountain Ash % 3 Toolangi Dump Alpine Ash % 2 Toolangi Dump Mountain Ash % 6 Marney Creek Mountain Ash % 7 East Bennies Mountain Ash % 8 Western Cym Mountain Ash % 4 Hannibal Alpine Ash % 5 1 Prior to reconditioning. Although the respective rankings in Table 12 are not as obviously linked as was the case in the salvage coupes, regression analysis does indicate a slight predictive relationship between the Peak IC Score and the impact of internal checking on final yield, with an r 2 of Western Cym and Hannibal are significant outliers to the trendline, because the much higher F17 IC % for East Bennies has tended to flatten the trendline away from these two coupes. Graph 14 Correlation of Green Log Peak IC Score and F17 IC% Falldown Western Cym Hannibal East Bennies These findings support the view that the propensity for internal checking does vary from coupe to coupe, especially for fire killed coupes being salvaged. Whether this propensity can be predicted by indicators that can be observed or measured in standing trees, to provide a guide for scheduling coupe harvesting to minimise checking is addressed later in this paper. The individual tree data in this study (see Appendix 5), supports the reasonable assumption that the genetic and environmental variation of trees within a coupe will be less than between coupes. While this can inferred from the coupe average data given in Tables 11 and 12, Tables 13 and 14 summarise the within coupe variation using the same three measures of internal checking. 26

33 Table 13 Variation in Internal Checking Within Salvage Coupes Peak IC Score Final IC Score F17 IC% Tree Coupe Shona % 13.7% 2.5% 10.3% Toolangi Dump % 27.9% 49.0% 35.4% Woollybutt % 26.7% 42.5% 24.1% Blackbeard % 51.3% 32.1% 23.2% Handprint % 51.4% 27.5% 26.5% Opp. Phasmid % 45.7% 37.0% 44.9% Tricep % 29.6% 45.2% 25.5% The cells highlighted in red in both Table 13 and Table 14 indicate trees where at least one of the measures of internal checking varies widely from the same measure for other trees in the same coupe. While there is a level of environmental variation within coupes, along with genetic variation, it is not as obvious or significant as the between coupe variation. Table 14 Variation in Internal Checking Within Green Coupes Peak IC Score Final IC Score F17 IC% Tree Coupe Ping Pong % 0.0% 0.0% 0.0% Hathor % 0.0% 1.8% 0.9% Toolangi Dump % 1.7% 0.0% 3.3% Toolangi Dump % 1.9% 6.1% 6.0% Marney Creek % 2.8% 0.0% 19.7% East Bennies % 11.1% 18.8% 13.8% Western Cym % 3.2% 2.9% 2.7% Hannibal % 0.0% 4.6% 2.4% 1 Alpine Ash ex Maverick 2 Mountain Ash ex Big Bull Fiddle Variation Between Butt and Head Logs Anatomical Factors Graphs 15 & 16 Internal Checking in Butt and Head Logs 27

34 As all of the salvage coupes suffered crown fires, and the thinner bark of the head logs split and peeled more quickly and more completely than did the thicker butt log bark; any abnormal fire induced internal checking should have been more prevalent in the head logs. Graph 15 shows that this was not the case. Generally, the timber from butt logs tends to check more than head log timber because growth ring width and wood density differentials are greatest in the early years of growth. In the green slabs the reconditioning process closed up many of the butt log checks, bringing the two lines in graph 16 much closer together at the endpoint. This indicates that the impact of checking on final grade yield will be more significant in the salvage sample than in the green control and this is confirmed by the following Table. Table 15 Butt and Head Log Timber Grade Yield Seasoned Appearance F17 by Cause Select Standard Total Defect Backsawn Internal Check Total Salvage Butt 18.6% 9.3% 27.9% 11.9% 23.4% 36.8% 72.1% Head 17.8% 12.0% 29.8% 23.3% 17.1% 29.8% 70.2% Green Butt 31.3% 16.1% 47.4% 46.3% 2.6% 3.7% 52.6% Head 29.2% 18.3% 47.5% 48.3% 2.3% 1.9% 52.5% The salvage head log F17 grade yields show a significant reduction in the downgrade percentage due to internal check compared with the butt logs (7%), but the doubling of the F17 due to defect percentage counteracts this, so that there is only a marginal increase in the yield of appearance grades. This is expected because the top end of head logs is likely to carry more knots and associated faults. In the green logs, the head log F17 IC% is half the butt log percentage (a difference of 1.8%), but again this transfers across to the F17 by defect category, not to the appearance grades. Excluding the short logs that were not crosscut before milling, only twelve of the fifty four logs (22%) were more affected by internal checks in the head log than the butt. Six of these were salvage logs and six were green. Appendix 6 shows that there is virtually no difference between the comparative timber values from butt and head logs. For the green logs the comparative values are butt $1,056.29/m 3, head $1,050.23/m 3. The salvage logs have slightly lower values butt $966.60/m 3, head $969.46/m 3. Scheduling Fire Salvage Harvesting - Tree and Coupe Predictors of Internal Check Severity Four possible predictors of internal check severity were recorded when the salvage sawlogs were selected. The first is based on observation of indicators of the fire intensity experienced by each tree (see page 4). The remaining three are based on the moisture content measurements taken across the butt and head cross section of each bush log (see page 5). Appendix 3 gives the fire intensity number for each tree, as well as the moisture profile data for the head and butt end of each salvage sawlog. This data allows comparisons to be drawn between each coupe, and also between the butt and head see Table 16 below. In this latter case, it might be expected that the effect of a crown fire may be more severe at the head end of the log, where the thinner, smooth bark provides less protection, allowing both a greater initial heat effect and subsequently more rapid moisture loss from the outer growth rings. 28

35 It is also possible to examine the extent of any correlation between the fire intensity indicator and the moisture content levels and gradients, to check the possibility that the visual signs of fire intensity (as a predictor of internal checking severity) simply reflect the increased drying stresses within the tree as shown by either reduced moisture content or increased moisture gradient. The same butt and head moisture profile measurements were also made for the green logs, so that the extent of the expected changes in moisture profiles caused either directly by the fire or by the subsequent months as standing dead trees, could be compared with living tree data. If there is little difference between the moisture content conditions within the fire-killed trees and the living trees, then it is unlikely that any tree moisture content measurements (obtained from drill core samples, or by falling test trees) would be useful as indicators of susceptibility to severe internal checking and hence assist with the scheduling of fire salvage operations. The graphs below compare the average moisture content profiles across the log cross-section for the living and fire killed trees, excluding all the Toolangi Dump logs. Graphs 17 & 18 Moisture Profiles of Living and Dead Trees These graphs demonstrate some unexpected findings. Firstly, the fire killed salvage logs had higher overall moisture levels at both ends of the harvested log, despite the nine months since the fire with the consequent cracking and loss of bark, and the drying and barrel checking of the cambium and sapwood. The average moisture content levels across each profile were Green Butt 127.2%, Salvage Butt 131.0% and Green Head 107.7%, Salvage Head 113.1%. Secondly, this difference in moisture content is even greater in the outer third of the butt cross sections - Green Butt 115.2%, Salvage Butt 121.0%. However, it is less in the head cross section - Green Head 98.8%, Salvage Head 100.4% - indicating the expected moisture evaporation from the outer growth rings, possibly migration of moisture down the tree, and (questionably) migration of moisture into the heartwood. The ends of each green graph tend to flatten out, indicating that the moisture gradient becomes progressively lower approaching the outer surface of the living tree. This does not occur to the same extent in the Salvage Butt graph and is not apparent at all in the Salvage Head curve. The steepness of the moisture gradient between the outer third and the middle third is an indicator of moisture stress, which may correlate with the severity of internal checking. Having shown that there are differences between the salvage and green trees, do these measures provide any indication of internal checking and timber grade yield? 29

36 Table 16 Salvage Coupe Averages of Tree Moisture Profiles and Gradients Coupe Ave. Fire Intensity Average Moisture Content Average MC Outer Third Moisture Gradient (Δ MC%/cm) Outer Middle Third Butt Head Butt Head Butt Head Shona % 109.2% 118.3% 99.6% 0.2% 1.7% Blackbeard % 124.0% 135.9% 108.4% 0.6% 2.1% Opp. Phasmid % 117.6% 118.4% 103.5% 3.0% 4.4% Tricep % 114.9% 126.4% 100.8% 0.5% 2.9% Woollybutt % 110.5% 114.4% 97.9% 3.0% 2.7% Handprint % 102.6% 112.8% 92.1% 0.4% 2.3% All Coupes % 113.1% 121.0% 100.4% 1.3% 2.7% Apart from the Alpine Ash coupe (Shona), the increasing average fire intensity correlates directly with declining average moisture content. The same correlation exists with the average moisture content in the outer third of the cross section, with Tricep s butt moisture content the sole exception. There is no apparent link between the average fire intensity scores and either of the moisture gradient measures. Linear regression analyses of the combined coupe data in Table 16 against the three measures of internal checking in Table 10 demonstrate that the moisture gradient in the head cross section is potentially the most useful predictor of the impact of internal checking on timber grade yield. The r 2 values for each regression are given in Table 17. Table 17 Correlation of Salvage Coupe Indicators With Internal Checking Severity Internal Check Measure Average Fire Intensity Average Moisture Content Average MC Outer Third Average Moisture Gradient (Δ MC%/cm) Outer Middle Third Butt Head Butt Head Butt Head Peak IC Score Final IC Score F17 IC% This table indicates that the only measures that are of any possible use in predicting internal checking are the moisture gradient at the upper end of the trunk and the moisture content level in the butt where (as with all of the moisture content correlations) the higher the moisture content, the greater the likelihood of severe checking. Nevertheless, given the limited number of trees and coupes that could be included in this study, and the inherent genetic and environmental variation between trees, the significance of these correlations deserves further investigation. The head end moisture gradient measure suggests that moisture evaporates more rapidly from the outside of the dead tree as height increases, while the butt average moisture content indicates that it also drains down the tree under the force of gravity. Before these measures could be put to use in salvage coupe planning and scheduling, more data collection and hypothesis testing is essential. The collection of quantitative data on the movement and loss of moisture over time in fire killed standing trees, would require the progressive felling and sampling of a number of test trees. Any further investigation could be carried out in any firekilled Ash area, if not a wildfire then possibly a regeneration burn escape, or any intensely burnt location within a fuel reduced area. 30

37 The regression correlations given in Table 17 were also calculated for the green control, to confirm that they were different to the salvage data. Table 18 Correlation of Green Coupe Indicators With Internal Checking Severity Internal Check Measure Average Moisture Content Average MC Outer Third Average Moisture Gradient (Δ MC%/cm) Outer Middle Third Butt Head Butt Head Butt Head Peak IC Score Final IC Score F17 IC% Table 18 demonstrates that there is virtually no relationship between the moisture content measures and internal check development. Unlike the salvage logs, where the trend lines all show that the higher the moisture content the greater the likelihood of checking, the slope of the weak trend lines for the green control varied randomly from flat to slightly positive or negative. As may be expected the only possible correlations were between the moisture gradient measures and the internal check scores. The successful closure of internal checks during reconditioning means that there is no correlation with the dry product F17 IC%. 31

38 Conclusions It may be possible to predict the severity of internal checking in timber sawn from fire killed trees by measuring the moisture gradient from the sapwood and outer heartwood towards the centre of the tree. The most effective measure is the moisture gradient at the head end of the millable trunk, which would necessitate the felling of sample trees. Before this could be adopted as an operational tool in scheduling fire salvage coupes, more data is needed to examine the changes in moisture gradient with stem height, and with the time elapsed since the fire. The pattern of development of internal checks over the air drying period, and the severity of checks, demonstrated that the supposed phenomenon of abnormal internal checking does not exist in fire salvage timber. The fact that the internal checks closed up to a far greater extent in the green control during the latter stages of air drying and particularly during reconditioning, suggests that further research in two areas could be commercially beneficial. Firstly in trialling a range of reconditioning treatments steam saturation, temperature and duration - and secondly in examining differences at the cellular level that would make the salvage timber less responsive to steam treatment of collapse, checking and shrinkage. This research provides an indicative reduction of 12% in the value of sawn timber recovered from salvage logs compared with green logs, when harvested six to nine months after the fire event and seasoned by conventional air drying methods and under the particular circumstances prevailing at the time. This result must be considered in light of the experimental limitations described in the body of the report. Initial moisture content retention through block stacking and plastic wrapping of salvage slabs significantly reduced the incidence of internal checking, compared with normal open yard air drying. If the cost of this double handling and the additional stock holding time can be kept under $100/m 3 the increased value of the timber should outweigh the cost. The research showed that air drying in more controlled conditions such as a hessian sided shed would increase the value of the finished timber by $48/m 3. The small number of logs taken from the Toolangi log dump was insufficient to conclusively demonstrate whether it has any significant effect in reducing internal checking by wetting the sapwood and reducing the moisture gradient. However, the results do indicate that this may be the case regardless of whether the logs are from fire killed or green coupes. A further trial to assess the cost:benefit of the effect of various periods under water spray on internal checking and final product value could be worthwhile. The study did not provide any evidence that either Ash species Alpine Ash or Mountain Ash is more or less prone to internal checking. More internal checking occurred in the butt logs than in the head logs, for both the salvage and green control samples. The effect of this difference was more significant in the salvage logs because the closure of checks during reconditioning was far less effective. 32

39 Recommendations There are no specific recommendations apart from the suggestions for further research, investigation or commercial trials in the Conclusions. 33

40 Acknowledgements Reid Bros. Timber for assistance with the green milling of the fire salvage sawlogs. Timber Training Creswick, and specifically Rob Rule, Manager and Ivan Porter, for assistance with racking out, air drying, biscuit sampling and moisture content testing. Staff and Management at Gunns Timber Heyfield for slabbing the green sawlog sample, slab transport, final air drying, reconditioning, kiln drying and dry milling. Staff and management have continued their involvement since the 29 May 2012, when the Gunns Timber Products Heyfield mill was sold to Australian Sustainable Hardwoods Pty Ltd. In addition to the overall project sponsorship and oversight, the assistance of VicForests staff and logging contractors in the selection and transport of sawlogs is gratefully acknowledged. 34

41 Appendix 1 Fire Salvage Coupe and Sawlog Record Coupe Location Harvest Date Species Log Code Log Diameter (cm) Log Length (m) Log Volume (m 3 ) Tricep Armstrong 10/11/09 Mtn. Ash TR D TR C TR C TR C Woollybutt Armstrong 10/11/09 Mtn. Ash WB B D WB C D WB C D WB B C Shona Acheron 10/11/09 Alp. Ash S C S B S B S B Handprint Black Range 12/11/09 Mtn. Ash HP B HP B C HP B C HP B Toolangi Dump Opposite Phasmid Log Grade ex Black Range 03/08/09 Mtn. Ash TL C 03/09/09 TL B C ~ 15/10/09 TL C ~ 10/11/09 TL B Bunyip 13/11/09 Mtn. Ash OP C OP C OP C OP C Blackbeard Mt Disappointment 16/11/09 Mtn. Ash BB B C BB B BB C BB D Average/Total B Grade m 3, (41.5%), average diameter 63 cm C Grade m 3, (44.3%), average diameter 59 cm D Grade m 3, (14.2%), average diameter 59 cm 35

42 Coupe Location Harvest Date Appendix 1 Green Coupe and Sawlog Record Species Log Code Log Diameter (cm) Log Length (m) Log Volume (m 3 ) Hathor 16/11/10 Mtn. Ash H B H B C H C H C Hannibal 16/11/10 Alp. Ash HB B HB B HB B C HB B Toolangi Dump Toolangi Dump Log Grade ex Maverick 13/07/11 Alp. Ash TD B TD B TD B C TD B ex Big Bull Fiddle 19/07/11 Mtn. Ash TL B TL B TL B TL B Ping Pong 18/11/10 Mtn. Ash PP C PP C PP C PP C Western Cym 18/11/10 Mtn. Ash WC B WC B WC B WC C East Bennies 18/11/10 Mtn. Ash EB B C EB B EB B EB B C Marney Ck. 18/11/10 Mtn. Ash MK B MK C MK B MK B Average/Total B Grade m 3, (64.8%), average diameter 61 cm C Grade m 3, (35.2%), average diameter 68 cm 36

43 Appendix 2 Salvage Coupe Map 37

44 Appendix 2 Green Coupe Map 38