Universitt fr Bodenkultur Wien

Institut fr Botanik

Chemistry, colour and brown-rot decay resistance of larch heartwood and FT-NIR based prediction models

Dissertation

Mag. rer. nat. Notburga Gierlinger

Wien, im Juni 2003

2

Abstract

Extractives and lignin content of a total of 293 larch trees were investigated to understand

the variability existing in larch wood resources in Europe, with respect to species,

provenances, sites and age classes, and to find linkages with brown-rot decay resistance. A

central task was the establishment of new methods for a rapid and non-destructive

determination of chemical and biological parameters in larch heartwood. In this regards the

feasibility of Fourier transform near-infrared spectroscopy (FT-NIR) combined with

multivariate statistics, and of colour measurements (CIEL*a*b* system) to predict these

parameters accurately was explored.

Amounts of different heartwood extractives (acetone solubles, hot water solubles, total

amount of phenols) were shown to be highly variable within the investigated set of larch trees

and strongly influenced by tree age and origin. Old trees (>150 years) from high elevation

sites had significantly higher amounts of extractives compared to young plantation trees (38

years) of the same provenance. A general linear increase of extractives content from pith to

the heartwood-sapwood boundary was observed in the old trees; significant higher amounts

present in the outer part compared to corewood. Phenols content seemed to be species

specific: higher contents were measured in Japanese larch (Larix kaempferi) and hybrid larch

L.x eurolepis), compared to European larch (L. decidua). A strong relationship was observed

between brown-rot decay resistance and the amount of phenols (r = 0.63 to r = 0.88 according

to origins). In addition, the reddishness of heartwood was strongly correlated with the amount

of phenols (r = 0.84) and with decay resistance (r = 0.63). Results on the usability of colour as

an indicator for phenol content and decay resistance were encouraging.

FT-NIR spectroscopy has proven to be accurate and rapid in determining larch heartwood

extractives, lignin and natural durability. Partial Least Squares (PLS) regression models were

established and validated by cross- and test set validation. Applying data pre-processing

methods (e.g, first Derivative and Multiplicative Scatter Correction (MSC)) and selecting

appropriate wavenumbers improved the calibration models. This work demonstrates that a

rapid and accurate prediction of extractives and brown-rot decay resistance through FT-NIR is

possible, which will open new research opportunities as well as new fields of industrial

applications.

Keywords: Larix sp., heartwood extractives, phenolics, lignin, natural durability, brown-rot decay, wood colour, Near Infrared Spectroscopy (NIR), Partial least square regression (PLSR)

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Zusammenfassung

Der Extraktstoff- und Ligningehalt von 293 Lrchen wurde bestimmt, um die in

Europa vorhandene Variabilitt dieser Parameter hinsichtlich Art, Herkunft, Standort und

Alter abzuschtzen, sowie Beziehungen mit der natrlichen Dauerhaftigkeit aufzufinden.

Zentrales Anliegen der Arbeit war die Entwicklung von Methoden zur raschen und przisen

Bestimmung chemischer und biologischer Parameter in Lrchenkernholz. In diesem

Zusammenhang wurde die Fourier-transformierte Nahe-Infratospektroskopie (FT-NIR) in

Kombination mit multivariater statistischer Auswertung sowie die Farbmessung (CIEL*a*b*

system) auf ihre Anwendbarkeit getestet.

Die Extraktstoffgehalte von Lrchenholz sind sehr variabel und werden sehr stark vom

Alter der Bume, der Position im Baum und der genetischen Herkunft beeinflusst. Im

Kernholz alter Bume (>150 Jahre) wurden signifikant hhere Extraktstoffgehalte gemessen

als in jungen Plantagenbumen gleicher Herkunft. Eine betrchtliche Zunahme an

Extraktstoffen vom Mark bis zur Kern- Splintholzgrenze konnte in den alten Bumen

nachgewiesen werden. Der Gehalt an phenolischen Inhaltsstoffen war artspezifisch: das

Kernholz japanischer Lrchen (Larix kaempferi) und Hybridlrchen (L.x eurolepis) enthielt

signifikant hhere Mengen an phenolischen Inhaltsstoffen als jenes europischer Lrchen

Eine hohe Korrelation wurde zwischen dem Gehalt an phenolischen Inhaltsstoffen und

dem Masseabbau durch Braunfulepilze (Poria placenta und Coniophora puteana)

festgestellt (Korrelationskoeffizient innerhalb der untersuchten Herknfte: r = - 0,63 bis r = -

0,88). Farbmessungen zeigten, dass die gemessene Rottnung (a*-Wert) mit dem Gehalt an

Phenolen korreliert und somit auch indirekt mit der Pilzresistenz. Die Ergebnisse der

Farbmessungen zur raschen Beurteilung von Lrchenkernholz hinsichtlich phenolischer

Inhaltsstoffe sowie Pilzresistenz waren vielversprechend.

Die Kombination von FT-NIR Spektroskopie mit multivariater Datenanalyse erwies

sich als zukunftstrchtige Methode zur raschen und sehr przisen Bestimmung von Extrakt-

und Ligningehalten und der natrlicher Dauerhaftigkeit. Mit Datenvorbehandlung der

Spektren (z.B. 1.Ableitung und Streukorrektur) sowie Auswahl geeigneter

Wellenzahlbereiche konnten die Schtzmodelle entscheidend verbessert werden. Diese Arbeit

zeigt, dass die rasche, genaue und zerstrungsfreie Bestimmung mittels FT-NIR

Spektroskopie mglich ist, was sowohl neue Mglichkeiten in der Forschung, als auch neue

industrielle Anwendungsbereiche erffnet

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ORIGINAL PUBLICATIONS

The thesis is based on the following publications, which are referred to in the text by Roman

numerals.

I Gierlinger, N., Schwanninger, M., Hinterstoisser, B.,Wimmer, R., 2002. Rapid

determination of heartwood extractives in Larix sp. by means of Fourier transform near

infrared spectroscopy, Journal of Near Infrared Spectroscopy. 10: 203-214.

II Gierlinger, N., Jacques, D., Schwanninger, M., Wimmer, R., Hinterstoisser, B., Pques,

L.E. 2003. Rapid prediction of natural durability of larch heartwood using FT-NIR

spectroscopy, Canadian Journal of Forest Research (in print).

III Gierlinger, N., Schwanninger, M., Wimmer, R., Hinterstoisser, B., Jacques, D., Pques,

L.E. 2003. Estimation of extractives, lignin and natural durability of larch heartwood

(Larix spp.) by FT-NIR spectroscopy, 12th International Symposium on Wood and

Pulping Chemistry, Madison, USA. Vol. III, 51-54.

IV Gierlinger, N., Jacques, D., Marchal, M., Wimmer, R., Schwanninger, M., Pques, L.E.

2002. Heartwood extractives and natural durability of larch relationships and their

prediction by FT-NIR spectroscopy, In: Proceedings of Improvement of larch (Larix sp.)

for better growth, stem form and wood quality, Gap Auvergne & Limousin. INRA,

Olivet Cedex : 414-421.

V Gierlinger, N., Jacques, D., Grabner, M., Wimmer, R., Schwanninger, M., Rozenberg,

P., Pques, L.E. Colour of larch heartwood and relationships to extractives and brown-

rot decay resistance, Trees (accepted)

VI Gierlinger, N., Jacques, D., Schwanninger, M., Wimmer, R., Pques, L.E. Extractives

and lignin content of different species and origins of Larix sp. and relationships to

brown-rot decay-resistance, Trees (in review)

VII Gierlinger, N., Wimmer, R., Radial distribution of heartwood extractives and lignin in

mature European larch, Wood and Fiber Science (in review)

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CONTENTS

1 INTRODUCTION 7

1.1 THE GENUS LARIX 7

1.2 NATURAL DURABILITY, HEARTWOOD EXTRACTIVES AND WOOD COLOUR 8

1.3 VARIABILITY OF WOOD PROPERTIES AND THE NEED FOR RAPID DETERMINATION 10

1.4 NEAR INFRARED SPECTROSCOPY 11

1.5 AIM OF THE STUDY 13

2 MATERIAL AND METHODS 14

2.1 WOOD MATERIAL 14

2.2 CHEMICAL ANALYSIS 15

2.3 WOOD DECAY TESTS 16

2.4 COLOUR MEASUREMENTS 16

2.5 NIR-SPECTROSCOPY AND MULTIVARIATE CALIBRATION 16

3 RESULTS AND DISCUSSION 17

3.1 RAPID PREDICTION OF CHEMICAL AND BIOLOGICAL PROPERTIES BY MEANS OF FT-

NIR SPECTROSCOPY 17

3.2 COLOUR OF LARCH HEARTWOOD: AN INDICATOR FOR HEARTWOOD EXTRACTIVES AND

BROWN-ROT DECAY RESISTANCE? 18

3.3 VARIATION IN THE CHEMICAL COMPOSITION OF LARCH HEARTWOOD 19

3.4 RELATIONSHIP BETWEEN HEARTWOOD EXTRACTIVES AND BROWN-ROT DECAY

RESISTANCE 23

4 CONCLUSIONS 24

5 ACKNOWLEDGEMENTS 25

6 REFERENCES 26

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PAPER I 29

Rapid determination of heartwood extractives in Larix sp. by means of Fourier transform near

infrared spectroscopy

PAPER II 42

Rapid prediction of natural durability of larch heartwood using FT-NIR spectroscopy

PAPER III 61

Estimation of extractives, lignin and natural durability of larch heartwood (Larix spp.) by FT-

NIR spectroscopy

PAPER IV 68

Heartwood extractives and natural durability of larch relationships and their prediction by

FT-NIR spectroscopy

PAPER V 78

Colour of larch heartwood and relationships to extractives and brown-rot decay resistance

PAPER VI 95

Extractives and lignin content of different species and origins of Larix sp. and relationships to

brown-rot decay-resistance

PAPER VII 114

Radial distribution of heartwood extractives and lignin in mature European larch

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1 Introduction

1.1 The genus Larix

Larix occurs in boreal circumpolar lowlands in Alaska, Canada and Russia, and at

moderate to high altitudes in the mountains of North America, the Alps of Europe, Mongolia,

China, Korea and Japan (Figure 1). The genus comprises a dozen taxa, among them the well-

known species L. decidua (European larch), L. sibirica (Siberian larch), L. occidentalis

(Western larch), L. laricina (Tamarack), L. lyallii (Alpine larch), L. gmelinii and L. kaempferi

(Japanese larch). Larches can grow up to a height of 54meters, may have a diameter of over

1.5meters and their life can exceed 600 years. Larch wood is appreciated for its good

mechanical properties, its colour and texture and also for its high natural durability (Knuchel

1954). It is used for pulp, framing timber, roof tiles, flooring, log houses, posts, poles, railroad

ties, mine props, wharves and pilings.

In Europe, Larix decidua Mill. (European larch) has a scattered natural area and is

present in four geographic zones (Alps, Sudetan Mts, Carpathian, Central Poland ), where

local European larch got sometimes the status of subspecies or varieties (Biswas and Johri

1997). Larix decidua is appreciated for reforestation throughout Europe, southern Canada and

the northeastern United States, because of its fast growth and high quality timber. Beside L.

decidua, Japanese larch (L. kaempferi (Lamb.) Carr). and the hybrids between European and

Japanese larch (L. x eurolepis Henry) play a role (Langner and Reck 1966, Chui and

MacKinnon-Peters 1995). In several international larch provenance experiments the

Figure 1 Geographic distribution of: 1. Larix laricina, 2. Larix occidentalis, 3. L. decidua, 4. L.sibirica, 5. L.

gmelinii, 6. L. kaempferi (from Biswas and Johri 1997)

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performance of different European and Japanese larch provenances was investigated (e.g.

Schober 1985; 1991).

The eastern races from the Sudetan Mts, Tatras and Central Poland and the Japanese

larches, showed on average better height growth performances than the alpine larches. A

reverse trend is usually found for stem straightness. A SW-NE gradient was also found for

some wood properties like heartwood proportion and stiffness, while density parameters

showed more limited variation (Pques and Rozenberg, 1995). Bole canker (Lachnellula

willkommii) was found more often in alpine larches compared to Sudetan, Tatras and Polish

origins (Schober 1985). Japanese larch and hybrid larch were canker resistant. (Sylvestre-

Guinot et al. 1983). Relatively little variation in stem form and growth was found among

Japanese larch origins, which may be due to the five times smaller natural area compared to

the Alpine origins (Schober 1991).

1.2 Natural durability, heartwood extractives and wood colour

Natural durability, or decay resistance, is defined as the ability of wood to resist

biological degradation (Eaton and Hale 1993). Prior to the invention of artificial wood

preservatives people were fully aware of differences in the natural durability between tree

species and different parts of the stem. With the arrival of powerful synthetic biocides, such as

copper-chromium-arsenic (CCA) the importance of natural durability declined (Zabel and

Morrel 1992). Meanwhile, increased public awareness for environmentally friendly products

again led to increased interest in the natural durability of wood.

Knowledge about natural durability comes from experience, from observation and

from systematic field tests with different wood species in ground contact, carried out already

in the 1830s by G.L. Hartig (Eaton and Hale 1993). Later, field tests were supplemented with

laboratory testing by exposing standardized wood blocks to infestation of certain white and

brown rot fungi. Field and laboratory tests have led to a worldwide data collection on

durability of wood species (Willeitner and Peek 1997). Both test types went down to several

European standards (EN 113, EN 350, EN 252) and today natural durability is defined in a

five-class system ranging between 1 (highly durable) and 5 (non-durable).

Decay resistance is restricted to the heartwood of the tree, which is the inner part with

lower moisture content, often a darker colour and a reduced permeability. Heartwood tissues

have ceased to contain living cells and reserve materials have been removed or converted into

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heartwood substances. Heartwood extractives are comprised of a heterogeneous group of

chemical compounds, including terpenoids, tropolones, flavonoids, stilbenes, and other

aromatic compounds (Scheffer and Cowling, 1966). The significance of heartwood

extractives for natural durability was already demonstrated by Hawley et al. (1924). Many

studies about the chemical structure, toxicity and specificity of various heartwood substances

followed (e.g. Rudman 1963, Celimene et al. 1999, DeBell et al. 1997, Schultz et al. 1990,

1995; Scalbert 1991). Compared to commercial biocides, extractives and their isolated

components have poor fungicidal activities (Smith et al. 1989, Rudman et al. 1963, Celimene

et al. 1999). It is proposed that some species with durable heartwood may contain multiple

low-toxicity extractive compounds that interact synergistically, by possessing fungicidal

activity and being excellent free radical scavengers (antioxidants) at the same time (Schultz

and Nicholas 2002). This hypothesis is also supported by the observation that white and

brown rot fungi most likely use some type of free radicals for the initial disruption of cell

walls (Backa et al. 1992, Tanaka et al. 1999). Besides the total extractives content, the micro-

distribution of extractives may also affect the biocidal performance (Hillis 1987; Kleist and

Schmidt 1999). Extractives are located mostly in rays (Hillis 1971), but may also form

coatings on cell walls and pits, and penetrate cell walls. In Larix sp. large amounts (up to

30%) of arabinogalcatan, a heavily branched polysaccharide based on arabinose and galactose

are found in the cell lumens (Ct et al. 1966). Arabinogalactan can be removed easily with

water and may be metabolised by fungi, rather enhancing the decay process than inhibiting it

(Srinivasan et al. 1999). Resin acids are found only in small amounts (0.1%, Viitanen et al.

1997) and flavonoids up to 3.5% (Babkin et al. 2001, Giwa and Swan 1975, Hegnauer 1962).

Srinivasan et al. (1999) found no correlation between hot-water soluble or methylene-chloride

soluble extractive content and mass loss after wood decay of 75 year old tamarack (Larix

laricina) trees, whereas Windeisen et al. (2002) reported a close relationship between

extractives content and weight loss for hybrid larch.

The colour of heartwood depends widely on chemical components interacting with

light i.e. the presence or absence of extractives (Hon and Minemura 2001). Consequently,

heartwood colour has been related to the amount of extractives and to wood decay resistance

in some species (Hiller et al. 1972, Nelson and Heather 1972, Wilcox and Piirto 1976).

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1.3 Variability of wood properties and the need for rapid

determination

Wood is a highly variable material. Parameters differ widely according to species,

geographic origins, sites and positions within trees. Little knowledge exists on the variability

within species, while a great deal is known about chemical properties affecting various

products. Investigations on wood extractives of Pinus sylvestris revealed large variations

between individual trees and a strong genetic control, which consequently provides excellent

opportunities for genetic improvement (Fries et al. 2000, Ericsson et al. 2001). Concerning

heartwood extractives, in Larix a high variability has been observed within and between trees

(e.g. Ct et al. 1966, Dix and Roffael 1997, Gierlinger et al. 2002), but no detailed results

about genetic or environmental influences are available to date.

Decay resistance of larch wood is reported to be highly variable, ranging from non-

durable to moderately durable (class 5 to 3, EN 350-2, Viitanen et al. 1997, Morell and

Freitag 1995, Srinivasan et al. 1999, Nilsson 1997, Jacques et al. 2002). This apparent

variability of results may arise from problems that are linked to differences in test conditions

and to the reliability of the testing method itself, but is primarily linked to the variability

described across sites, species, genetic origins and within and between trees, (Eaton and Hale

1993, Nilsson 1997, Van Acker et al. 1999,2003, Jacques et al. 2002). A higher decay

resistance was reported for older larch trees (Viitanen et al. 1997) and the outer heartwood is

more durable compared to the inner one (Jacques et al. 2002). Venlinen et al. (2001)

showed that the genetic control of decay resistance in Siberian larch is moderate.

Further research about the variations of wood properties, their control, and their effect

on the quality of the end-product is needed. Methods, which allow a rapid and accurate

determination of wood properties are necessary to investigate high numbers of samples and in

several studies non-destructive methods are wished. In industry, rapid methods for wood

classification are required for better utilisation and higher competitiveness.

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1.4 Near Infrared spectroscopy

The history of near infrared (NIR) began in 1800 with Herschel, who found light

radiation beyond the visible spectrum (Barton 2002). But the expansion of NIR spectroscopy

did not start before the 1950s, from the agricultural realm into pharmaceutical, industrial,

process control, food processing and remote imaging spectroscopy. Over the last few years

NIR spectroscopy together with the chemometric approach and multivariate data analysis has

led to numerous applications for different fields of science and industry. There are several

advantages of utilizing the NIR wavelength region: firstly, the rapidity of NIR measurements

facilitates the collection of descriptive data and is a prerequisite for creating control systems

working in real time. Secondly, since there is no need for sample preparation, the technique

should be applicable to virtually any type of sample.

The NIR spectrum extends from 12800 cm-1 (780 nm) to 4000 cm-1 (2500 nm).

Absorption bands observed in reflectance spectra of wood arise from overtones and

combinations of vibrations of C-O, O-H, C-H, and N-H bonds. These absorption signals from

the various constituents are similar and highly overlapping and no distinct absorption bands

can be observed that can be directly related to the chemical abundance of a single wood

constituent. The many overlapping signals result in a spectrum with broad peaks, making it

difficult to interpret compared to the conventional mid-IR spectrum. NIR spectroscopy

therefore must include chemometrics and the reference analysis as part of the comprehensive

set of techniques. Multivariate calibration is a discipline that focuses on finding relationships

between one set of measurements, usually easily or cheaply acquired (as it is the case with

NIR spectra), and other either expensive or laborious measurements. For the establishment of

regression models from multivariate data, Partial Least Squares Projections to Latent

Structures, PLS, is a very suitable projection method (Antti 1999, Geladi 2003). In order to

find out how well the model is performing in making predictions, the model has to be

validated. For internal cross-validation procedures one group at a time is kept out of the

model before the model predicts it, whereas in external test-set validations a number of

samples is kept out of the calibration model to use them solely for validating the predictive

ability. Spectral filtering together with other types of data pre-treatment is often essential for

deriving a properly working multivariate calibration model. Traditional methods of pre-

treatments in order to remove variation in spectra not related to the investigated properties are

base line correction, normalization, first and second order derivatives or Multiplicative Scatter

Correction (MSC), to mention just a few.

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From the early 1990ies several parameters related to wood chemistry, i.e. pulp yield,

cellulose and lignin content (e.g. Wright et al. 1990, Michell 1995, Schimleck et al. 1998,

Schwanninger and Hinterstoisser 2001, Easty et al. 1990) as well as wood extractives

(Schimleck et al. 1997) have been estimated by NIR spectroscopy. Furthermore, studies have

shown that NIR spectroscopy is also capable to determine physico-mechanical properties,

including basic density (Thygesen 1994; Schimleck et al. 1999), mechanical strength

(Hoffmeyer and Pedersen 1995, Gindl et al. 2001) and stiffness (Schimleck et al. 2002).

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1.5 Aim of the study

The aim of this doctoral thesis was to explore the feasibility of FT-NIR spectroscopy

for determining rapidly and accurately biological and chemical parameters of larch heartwood

and to address so far un-answered questions associated with the chemical composition, natural

durability and colour of larch heartwood. In this context the following main hypotheses are

stated as questions:

1. Is it possible to predict heartwood extractives, lignin and natural durability of larch

by means of FT-NIR spectroscopy accurately? The aim was to develop calibration

models based on NIR-spectra of wood meal and solid wood surfaces to predict rapidly and

accurately a large number of samples. (paper I-IV)

2. To what extent can pre-treatment of spectral data and wavenumber selection lead to

enhanced multivariate modelling? Calibration models with different types of data pre-

treatment and wavenumber selection were established and intensively validated and

evaluated to find the most suitable prediction models. (paper I-III)

3. Does the colour of larch heartwood provide information on the extractive content

and natural durability? Heartwood colour is an easy to measure parameter and may be

used as an indicator for extractives and natural durability in larch heartwood (paper V)

4. Are there significant differences in the extractive and lignin contents among different

larch species, origins and age classes ? What is the variability of heartwood

extractives within the genus Larix? With a set of nearly 300 trees grown on six different

sites, which circumvented Larix decidua, L. kaempferi and L. x eurolepis, different origins

of L.decidua, young plantation trees as well as old natural grown trees, the question of

variability was properly addressed. (paper VI, VII)

5. To what extent are extractives and lignin concentrated in wood of old grown trees

from pith to the heartwood-sapwood boundary? A detailed analysis of extractives and

lignin was performed with 25year increment blocks of old-grown trees to find out about

radial trends from pith to the heartwood-sapwood boundary. (paper VII)

6. How strongly is the extractive content correlated with brown-rot decay resistance in

larch heartwood? The widely anticipated relationship between extractives and brown-rot

decay resistance was quantified for larch. In case of a strong linkage, extractives may be

used to predict the decay resistance of larch heartwood. (paper VI, IV)

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2 Material and Methods

2.1 Wood material

A total of 293 larch trees of different species, origins and age classes were available

from 4 plantation sites and 2 natural stands within the framework of the EU-FAIR funded

project CT98-3354 Towards a European Larch Wood Chain (Figure 2, Table 1 and 2).

Table 1 Description of the 6 sampling sites (The two native sites are shaded in grey). (a.s.l. = elevation

above sea level)

Figure 2 Location of the 4 plantation sites (+), the two native stand (*) and origins of the Sudetan (Ruda, Zabreh) and Central Poland provenances (Blizyn) (o).

Most of the trees originated from several replications of a IUFRO (International Union

of Forest Research Organizations) provenance trial in Belgium, Germany and France, with

European larch (Larix decidua Mill.) origins from the Alps (Montgenvre, Langau), the

Sudetan mountains (Ruda, Zabreh) and from Poland (Blizyn) (Table 2, Figure 2). In addition,

1 Japanese larch (Larix kaempferi) origin (Ina) and 2 hybrids (L.x eurolepis) were included. In

summary 13 different groups of larch wood were analysed (Table 2). The Hybrid larch trees

grown in Clanna (Wales, GB) showed the widest growth rings, with mean ring widths almost

twice as wide (7.8mm) compared to the other plantation trees (3.9-4.7mm) (Table 2). The old-

growntrees had significant smaller ring widths: 1.5mm for the trees from Langau, and 0.9mm

for the trees from Montgenvre. All samples were included to study colour, extractives and

natural durability of heartwood (paper V). In the papers I-IV on NIR spectroscopy only

selected samples were chosen to span the whole variability. For paper VI only trees grown on

Site Latitude and

longitude

a.s.l

(m)

Clanna 5143N, 235W 90

Coat an Noz 4831N, 325W 200

Nassogne 5005N, 520E 320

Elm 5200N, 1003E 205

Langau 4749N, 1510E 1050

Montgenevre 4456N, 644E 1800

15

the plantation site in France (Coat an Noz) were selected and for paper VII only a part of the

old trees.

Table 2 Site, origin, species, number of trees, age and ring width (RW, mm) of the sampled groups of

larch trees.

Site Origin Species-variety N Age RW

Clanna GB Hybrid L. x eurolepis 36 39 7.8

Montgenvre L.decidua alpica 18 38 4.3

Ruda L.decidua sudetica 20 38 4.1

Zabreh L.decidua sudetica 19 38 4.0

Ina L. kaempferi 20 38 4.1

Coat an Noz F

Hybrid L. x eurolepis 29 38 4.7

Langau L.decidua alpica 20 38 4.6

Ruda L.decidua sudetica 20 38 4.6

Nassogne B

Zabreh L.decidua sudetica 20 38 4.6

Ruda L.decidua sudetica 29 38 3.9 Elm G

Blizyn L.decidua polonica 20 38 4.1

Langau A Langau L.decidua alpica 26 160 1.5

Mont F Montgenvre L.decidua alpica 27 237 0.9

2.2 Chemical analysis

For the chemical analysis small and clear heartwood samples were dried at 50C and

ground with a cutting mill (Retsch, SM1) to pass a 200m screen. About 3 g air-dried wood

meal (100-200m particle size) was extracted using the fexIKA 200 solid extractor.

Extractions were carried out with acetone (Carl Roth, 5025.2) for 6 hours followed by another

6-hours of hot-water extraction. Extractives were gravimetrically determined according to

TAPPI T204 om-88 standard (% based on dry wood) and water content according to TAPPI T

264 om-88 / 8.2. Total phenols content was determined in the acetone and the hot-water

extracts for 115 trees by a modified Folin-Denis assay (Swain and Hillis, 1959). The

flavonoid taxifolin (3,3',4',5,7-Pentahydroxyflavanone) was used as a standard (Sigma

Aldrich, T4512). Analyses were carried out fourfold on a LKB Biochrom 4060 UV-VIS

spectrophotometer and the mean calculated. The total lignin content (Klason lignin plus acid

16

soluble lignin) was determined according to Schwanninger and Hinterstoisser (2002) and the

moisture contents according to TAPPI T 264 om-88 / 8.2.

2.3 Wood decay tests

Wood decay test were performed at the Centre de Recherche de la Nature des Forts et

du Bois in Gembloux. Detailed description of the method and results is given in Jacques et al.

(2002). The decay resistance data were used in papers II through VI.

2.4 Colour measurements

Colour measurements were performed on dried wood powder (< 100m) with a

Phyma Codec 400 Vis spectrometer. The reflection spectrum was acquired from a measuring

spot of 12mm in the 400-700nm region. The recommended CIE (Commission Internationale

de l` Eclairage) color parameters L* (lightness), a* (along the X axis red (+) to green (-)) and

b* (along the Y axis yellow (+) to blue (-)) were calculated and an average value of three

measurements per sample was used in the further analysis.

2.5 NIR-spectroscopy and multivariate calibration

FT-NIR spectra were recorded on a Bruker FT-IR spectrometer (EQUINOX 55)

equipped with a NIR fibre-optic probe measuring the diffuse reflected light on a 9-10 mm2

spot. A germanium-diode detector with a cut-off wavenumber of 5100 cm-1 was used and the

measurement spectrum ranged between 10000 cm-1 and 5100 cm-1. The thermoplastic resin

Spectralon served as a reference. Each wood powder sample (

17

3 Results and Discussion

3.1 Rapid prediction of chemical and biological properties by

means of FT-NIR spectroscopy

In article I the prediction of heartwood extractives by FT-NIR spectroscopy was

investigated in detail. Besides cross and test-set validation the established models were

subjected to a further evaluation step. Extractives and phenols content of additional samples

were predicted and outliers detected through Mahalanobis distance calculations. Models based

on the whole spectral range and without data pre-processing showed good model statistics in

cross validation and test-set validation, but failed in the evaluation test, which is based on

spectral outlier detection. But selection of data pre-processing methods, manual and automatic

(Martens Uncertainty test) restriction of wavenumber ranges considerably improved the

model predictability. It was possible to reduce the number of principal components by using

the first derivative and Multiplicative Scatter Correction (MSC) without losing predictive

power of the model. With models using maximally four principal components the number of

outliers in the evaluation step remained limited. High coefficients of determination (R2) and

low root-mean-square-errors of cross-validation (RMSECV) were obtained for hot water

extractives (R2 = 0.96, RMSECV = 0.86%, range = 4.9% - 20.4%), acetone extractives (R2 =

0.86, RMSECV = 0.32%, range = 0.8% - 3.6%) and phenolic substances (R2 = 0.98,

RMSECV = 0.21%, range = 0.7% - 4.9%) from wood powder. The models derived from

wood powder spectra were more accurate than those obtained from solid wood surfaces.

From a rapid prediction of extractive contents by FT-NIR spectroscopy predictions on

the decay resistance of larch heartwood are possible, because of the strong correlation

between natural durability and extractives (shown in paper IV and VI). This method is an

attractive, very fast alternative to the estimation of decay resistance and beside models for the

prediction of extractives, calibration models using results from wood decay tests as reference

data can be established (paper II, III and IV). Partial Least Squares regressions between the

data sets of relative decay resistance (x-values) and the FT-NIR spectra were calculated. The

usefulness of Multiplicative Scatter Correction (MSC) was clearly demonstrated in PCA

analysis and also in the improvement of the PLS-model statistics (paper II). High coefficients

of correlation (r) and low root mean square errors of prediction (RMSEP) were obtained for

cross-validation based on wood decay tests with Poria placenta (Fr.) Cooke (r = 0.92,

18

RMSEP = 0.077, range 0.27 1.13) and Coniophora puteana (Schum.: Fr.) Karst. (r = 0.97,

RMSEP = 0.078, range 0.07 1.58).

NIR spectroscopy has proved to be a reliable tool for the prediction of natural

durability (II, III, IV), lignin (III) and extractives (I, III). Larch heartwood quality may be

comprehensively characterized by simultaneous estimation of different parameters using

different calibration models. Although the development of calibration models is labour-

intensive, once established they allow acquiring data non-destructively within minutes and to

process high sample numbers. Since spectra can be taken from small samples it is possible to

measure increment cores. Therefore, this seems to be particularly suitable in forestry and

wood studies, where large numbers of wood samples must be analysed non-destructively. In

tree breeding programmes, often hundreds of genotypes need to be surveyed, and in

silvicultural studies intensive surveys of wood resources may be required to test different

treatment effects. Venlinen (2003) investigated in his thesis genetic parameters for

pinewood and reported encouraging results on the testing of wood durability by electrical

impedance spectroscopy.

3.2 Colour of larch heartwood: an indicator for heartwood extractives and brown-rot decay resistance?

A total of 293 larch trees were included in the analysis about heartwood colour (paper

IV). From the three colour parameters L (lightness), a* (red to blue) and b* (yellow to green)

the a* value revealed to be the most important parameter. Value a* (describing the

reddishness of the samples) turned out to be higher in Japanese larch (Ina-F) and in the

hybrids, compared to the young European larch trees. Moreover, the old-grown trees from

high-elevation European larch stands (Mont-nat, Lang-nat) had higher a*-values than the

young ones of the same origin grown on plantations (Lang-B, Mont-F). Strong relationships

were found between phenolics and reddishness (a*), and also between decay resistance and

reddishness (Table 3). High correlation coefficients were observed throughout, across the

origins as well as within most of the origins (Table 3). The rather high correlation found

between a* and wood decay resistance in larch was clearly indirect, based on the strong

correlation between a* and phenols and the relationship between phenols and decay resistance

(paper VI). Larch heartwood colour differences between origins and sites are associated with

differences in the amount of phenolics and decay resistance, and might therefore be indicative

19

for both. Phenol content and decay resistance predicted with Partial Least Squares regression

models based on colour variable a*, were of lower quality (higher errors) compared to the

prediction by NIR-based models (I- IV). In the colour models the root mean square error of

cross validation has more than doubled to 0.54% (range 0.3-4.7%) for the prediction of the

phenolic content, compared to 0.21% in the NIR-model. Nevertheless, these first results on

the prediction of phenolics and wood decay resistance through colour analysis are most

encouraging. Prediction might be further improved through multivariate calibration models

utilizing the whole visible spectra.

Table 3 Pearson correlation coefficients between reddishness (a*), phenolics (PHE) and relative decay

resistance (x) by analysing all trees, averages of the origins and the origins separately.

PEARSON CORRELATIONS r (a*-phe) r (a*-x)

Trees (n = 293) 0.84** -0.63**

AV of origins (n = 13) 0.93** -0.82**

Ina-F 0.69** -0.62**

Hybrid-F 0.85** -0.70**

Hybrid-GB 0.88** -0.62**

Ruda-D 0.72** -0,27

Ruda-F 0.78** -0.45*

Ruda-B 0.82** -0.27

Zabreh-F 0.79** -0.45

Zabreh-B 0.81** -0.63**

Blizyn-D 0.76** -0.72**

Langau-B 0.81** -0.59**

Montgenvre-F 0.70** -0.66*

Langau-A_nat 0.65** -0.48*

Within origins (n = 18-35)

Montgenvre-F_nat 0.61** -0.34

3.3 Variation in the chemical composition of larch heartwood

A great deal is known about differences between the chemical composition of

different tree species, but only scarce information exists about the degree of variability within

species. In Larix sp. a high variability in the extractive content was observed (Table 4). Hot

water soluble extractives (HWE) ranged from 3.1% to a maximum of 27.0%, the coefficient

20

of variation (CV) was 46% (Table 4). A similar range was reported e.g. by Viitanen et al.

(1997) (3.2 20.5 %) and Srinivasan et al. (1999) (7.3 26.8%). Almost the same coefficient

of variation (CV=45%) was observed for phenols (PHE), with amounts ranging from 0.3% to

4.8%, with a mean of 2.2%. ACE consisting mainly of PHE showed similar values. The

especially high extractive contents present in larch heartwood resulted in considerable

differences between lignin content based on extractive-free dry wood (average = 29.3%) and

lignin content based on non-extracted dry wood (average = 26.1%, Table 4). Lignin (LIGexf)

content was generally less variable (CV = 3.7%) compared to heartwood extractives.

Table 4 Descriptive statistics of chemical properties in larch wood (n= 293 trees, SD = standard deviation,

CV = coefficient of variation, HWE = hot water extractives, ACE = acetone extractives, PHE = total

amount of phenolics, LIGexf = lignin of extractive-free dry wood, LIG = lignin of dry wood)

MEAN SD CV MIN MAX

HWE (% ) 10.2 4.7 46 3.1 27.0

ACE (%) 2.2 0.7 32 0.8 4.3

PHE (%) 2.2 1.0 45 0.3 4.8

LIGexf (%) 29.3 1.1 3.7 26.5 32.3

LIG (%) 26.1 1.2 4.6 22.4 29.6

In paper VI differences between origins and species of even-aged trees grown on the

same plantation site were analysed. No significant differences were found for the hot water

extractives, whereas the total amount of phenols was significantly higher in L. kaempferi

(3.6%) and L. x eurolepis (3.2%), compared to L. decidua (2.1%) (VI).

Besides the comparison of origins, differences between young plantation trees and old

trees from high elevation were of great interest. Figure3A-D shows the same two European

larch origins (Langau and Montgenvre) grown on plantations and at high elevation sites

(native rang). Extractives content of trees from the origin Montgenvre were significantly

higher (p < 0.05) compared to those from the origin Langau. This was observed for both,

young plantation trees and old trees grown at high elevation. For ACE differences between

the two origins were greater than between the young and old trees (Fig. 3A). These results

demonstrate again the origin effect on the extractive content. For HWE and PHE significant

differences between young and old trees were evident, amounts of HWE doubled in the old

trees (Fig. 3B, 3C). The trees of the high elevation site Montgenvre had the highest amount

of extractives of the entire sample set. This may be due to the high age, high elevation and

21

additional stress through periodic infestation of the larch bud moth (Zeriaphera diniana

G.N.). For LIGexf no significant differences were observed between the two origins, but

significant higher amounts were found in the old trees (Fig. 3D).

Figure 3A-D: Comparison of mean values of extractive and lignin contents of old trees grown on high

elevation with young trees from plantations from two European larch origins (Montgenvre = squares,

Langau = triangles)

The radial distribution of extractives and lignin was investigated with blocks of 25

annual rings prepared from the old grown trees (paper VII). A gradual increase was observed

for all extractives from pith to the heartwood-sapwood boundary. The acetone extractives and

the phenolics increased between 1.2% and 2.2% per 100 rings increment, while the hot-water

extractive content rose around 5% per 100 years (paper VII). Calculations showed that within

10 cm radial distance phenol and acetone content doubled, while hot-water extractives took

between 20-30cm to double concentration (paper VII). In Figure 4A-D the amount of

extractives and lignin of the inner part (ring 1 25) is compared with an outer part (ring 75

100). Significant differences were found for extractives, PHE and ACE doubled, and lignin. A

comparison of Figure 3 and 4 clearly shows that the differences observed within the old trees

(inner and outer parts) had similar trends to those observed between old and young trees.

0

1

2

3

4

5

young old

AC

E (%

)

A 0

5

10

15

20

25

young old

HW

E (%

)

B 0

1

2

3

4

young oldPH

E (%

)

C 22

24

26

28

30

32

young old

LIG

exf (

%)

D

22

Figure 4A-D: Comparison of mean values of extractive and lignin contents in the inner (core) part (ring 1-

25) with the outer part (ring 75-100) of old trees from two European larch origins (Montgenvre =

squares, Langau = triangles)

In general, observed variation is the result of a dual and interactive control through

specific environmental and genetic factors. The situation is complex and the effect of

environmental conditions, including silviculture, soil and climate, and of genetic factors

cannot be clearly separated in this study. As mentioned above a huge variation was found

among the investigated larch groups, but to give definite answers on the effect of

environmental and genetic factors, proper experimental designs are needed. In this study

significant differences in the phenol content were found between Japanese and European

larch, suggesting a clear effect of the species. The amount of hot water solubles did not show

such a species-specific behaviour. The strong effect of cambial age on all extractives (ACE,

HWE, PHE) and LIG was clearly visible in the comparison of young plantation trees with

high elevation grown old trees, and in the radial increase from pith to heartwood-sapwood

boundary in the old trees. Posey and Robinson (1969) examined 480 Pinus echinata trees of

different ages growing under a variety of conditions and concluded also that age influences

extractives content more than any other variable.

0

1

2

3

4

5

in out

AC

E (%

)

A 0

5

10

15

20

25

in out

HW

E (%

)B 0

1

2

3

4

5

in out

PHE

(%)

C 22

24

26

28

30

32

in out

LIG

exf (

%)

D

23

3.4 Relationship between heartwood extractives and brown-rot

decay resistance

Heartwood extractives play a key role for natural durability, beside lignification and

growth characteristics (Zabel and Morrell 1992). The influence of extractives on durability

depends on their type, concentration, chemical stability and resistance to microbial

inactivation (Hart 1989). The decay-resistance of tamarack (L. laricina) was not related to

extractives content (hot-water-soluble and methylene-chloride-soluble) according to

Srinivasan et al. (1999). Methylene-chloride-soluble extractives were apparently at too low

concentrations (0.7) was found between extractives contents

(cyclohexane-ethanol (2:1)-soluble together with ethanol-soluble) and natural durability. In

our study the total amount of phenols was strongly linked to decay resistance (paper VI).

Recently, a significant relationship between decay-resistance and the total amount of phenols

was also reported for pine (Harju et al. 2003).

HWE consists mainly of the heavily branched polysaccharide arabinogalactan (Ct et

al. 1967). Srinivasan et al. (1999) suggested that arabinose and galactose sugars might be

easily metabolised by fungi, which should rather enhance than inhibit the decay process.

Opposite to Srinivasan et al. (1999) and in accordance with Viitanen et al. (1997) a

relationship between non-phenolic substances (arabinogalactan, comparable to HWE) and

wood decay was observed (paper IV, VI). Although higher HWE often goes hand in hand

with higher amount of phenolic substances, the high correlations with decay-resistance may

not be due to this fact only. An influence of NOT PHE on decay resistance is suggested, as

correlation coefficients between mass loss and NOT PHE were often similar or even higher

compared to those between PHE, NOT PHE, PHE and mass loss. The possible role of

arabinogalactan in wood decay of larch wood is not understood at this point. Perhaps the

arabinogalactan-filled lumina may not primarily enhance growth by being a nutrient resource,

but act as barriers for hyphal growth in the wood structure. The isolation and characterization

of larch arabinogalactan was the topic of several studies, e.g Odonmazig et al. (1994) or

Ponder and Richards (1997); however, its functionality in the heartwood has been barely

understood and discussed. Ct et al. (1966) concluded that a possible role of arabinogalactan

24

in larch remains entirely obscure and these authors assumed that it might be the product of a

blind alley in plant evolution.

Beside extractives, lignification is often discussed as an additional factor in decay

resistance (Zabel and Morrell 1992). Harju et al. (2003) found no differences in lignin content

between decay resistant and decay-susceptible pine trees. Lignin seems to be of minor

importance in decay resistance of larch wood too (paper VI).

4 Conclusions

The studied material encompassed many contrasting larch wood resources and gave

insight into the great variability for heartwood extractives in larch trees prevalent in Europe.

The amount of phenolic substances revealed to be a key factor in brown-rot decay resistance

and it was strongly influenced by species, origin and age. The reddishness of the heartwood

allowed a rough estimate of the phenolic content and thus of the natural durability; FT-NIR

spectroscopy enabled very rapid and accurate determinations. The contrasting sample set

allowed including a high span of variability in the calibration models, which should therefore

be well suited for the the prediction of new larch samples in future projects. To gain insight

into the possibilities of improving decay resistance of larch heartwood by forest tree breeding,

genetic parameters of decay resistance and of phenolic contents need to be known. FT-NIR

calibration models will be quite useful in such studies. Using a fibre-optic probe, sample

preparation is restricted to grinding or sanding and with the established calibration models

determinations are available within a few minutes, even on increment cores directly extracted

from standing trees. This will lead to a better knowledge of how extractives and natural

durability are controlled by genetics and the environment, as large numbers of samples can be

processed accurately and non-destructively. FT-NIR spectrocopy may break new ground for

optimising wood utilisation: Trees with potentially durable wood may be selected early off-

line in the forest and sawn timber may be graded on-line during the conversion process.

25

5 Acknowledgements

Most of the work reported in the thesis was done within the framework of the EU-project

TOWARDS A EUROPEAN LARCH WOOD CHAIN (FAIR-CT98-3354). Financial support for

almost three years and a unique sample material were the basis, enriched by the continuous

support, valuable comments, discussions and encouragement of the task coordinator Rupert

Wimmer, the coordinator Luc E. Pques (INRA, Orlean), and the co-workers of task 1

(wood quality). I am deeply grateful to my supervisor Rupert Wimmer for his support during

the last four years, especially recently, to finalise the thesis. Thanks to Luc for his

encouragement, his valuable inputs and for correcting most of the manuscripts. Thanks to the

Centre de Recherche de la Nature des Forts et du Bois in Gembloux (Dominique Jacques)

for giving permission to use the data on brown-rot decay resistance.

I would like to thank Michael Grabner and Wolgang Gindl for answering thousands of

questions a biologist asks when beginning to work on wood quality, for the help on wood

processing and many discussions that led to new approaches. Without Barabara

Hinterstoisser and Manfred Schwanninger (Institute of Chemistry, BOKU) the very

interesting work on FT-NIR spectroscopy would not have been that fruitful. Thanks to

Manfred for being available 7 days a week, for helping me acquiring and analysing spectra,

for providing precise lignin data, for valuable inputs, for correcting the manuscripts very

quickly and providing a lot of literature about spectroscopy. My warmest thanks are due to

Sabine Rosner, for scientific help and for brightening up the hours at the institute. I would

like to thank the Institute of Botany, its former head Prof. Hanno Richter, and its acting head

Prof. Karl-Georg Bernhardt, for giving me the opportunity to accomplish the work at the

Institute. Prof. Alfred Teischinger, head of the Institute of Wood Science and Technology at

BOKU, is thanked for his agreement to utilise the colour measuring device.

Financial support from the Austrian Science Foundation (project THE CAUSES OF NATURAL

DURABILITY IN LARCH P15903) during the finishing period of the thesis is acknowledged.

Finally I would like to thank Didi, my family and friends for their support and encouragement

while working on this thesis.

26

6 References Antti H (1999) Multivariate Characterization of Wood Related Materials. Department of Chemistry, Umea University,

Dissertation. pp. 86

Babkin VA, Ostroukhova LA, Malkov YA, Babkin DV, Onuchina NA, Ivanova SZ (2001) Isolation of biologically active compounds from larch wood. 11th ISWPC, International Symposium on Wood and Pulping Chemistry, Nice, France, Vol. II, pp 119-122

Backa S, Gierer J, Reitberger T, Nilson T (1992) Hydroxyl Radical Activity in Brown-Rot Fungi Studied by a New Chemiluminescence Method. Holzforschung 46: 61-67

Barton FE (2002) Theory and principles of near infrared spectroscopy. Spectroscopy Europe 14: 12-18

Biswas C, Mohri BM (1997) The gymnosperms. Springer, Berlin

Celimene C, Micales J, Ferge L, Young R (1999) Efficacy of Pinosylvins against White Rot and Brown Rot fungi. Holzforschung 53: 491-497

Chui YH, MacKinnon-Peters G (1995) Wood properties of exotic larch grown in eastern Canada and north-eastern United States. The Forestry Chronicle 71: 639-646

Cot WA, Day AC, Simson BW, Timell TE (1966) Studies on larch arabinogalactan 1. The distribution of arabionogalactan in larch wood. Holzforschung 20: 178-192

DeBell JD, Morrell JJ, Gartner B (1997) Tropolone content of increment cores as an indicator of decay resistance in western redcedar. Wood and Fiber Science 29: 364-369

Dix B, Roffael E (1994) Extraktstoffgehalt von Lrchensplint- und kernholz. Holz als Roh- und Werkstoff 52: 336

Easty DB, Berben SA, DeThomas FA, Brimmer PJ (1990) Near-infrared spectroscopy for the analysis of wood pulp: quantifying hardwood-softwood mixtures and estimating lignin content. Tappi Journal 73 (4): 257-261

Eaton RA, Hale MDC (1993) Natural durability In:Hall C (eds) Wood: Decay, pests and protection, vol 1. Chapman & Hall, London, pp 311-318

Ericsson T, Fries A, Gref R (2001) Genetic correlations of heartwood extractives in Pinus sylvestris progeny tests. Forest Genetics 8: 73-79

Fries A, Ericsson T, Gref R (2000) High heritability of wood extractives in Pinus sylvestris progeny tests. Can. J. For. Res. 30: 1707-1713

Geladi P (2003) Chemometrics in spectroscopy. Part 1. Classical chemometrics. Spectrochimica Acta Part B 58: 767-782

Gierlinger N, Rosner S, Gindl W, Grabner M, Wimmer R, Schwanninger M, Pques L (2002) Wood anatomical and chemical characteristics of different larch wood resources in Europe. Improvement of larch (Larix sp.) for better growth, stem form and wood quality. INRA, Unit d`Amlioration, de Gntiyue et de Physiologie des Arbres forestiers, Gap - Auverge & Limousin, pp 388-395

Gindl W, Teischinger A, Schwanninger M, Hinterstoisser B (2001) The relationship between near infrared spectra of radial wood surfaces and wood mechanical properties. Journal of Near Infrared Spectroscopy 9: 255-261

Giwa SAO, Swan EP (1975) Heartwood extractives of a western larch tree (Larix occidentalis nutt.). Wood and Fiber 7: 216-221

Harju AM, Venlinen M, Anttonen S, Viitanen H, Kainulainen P, Saranp P, Vapaavuori E (2003) Chemical factors affecting the brown-rot decay resistance of Scots pine heartwood. Trees: 17: 263-268

Hart JH (1989) Role of wood exudates and extractives in protecting wood from decay In:Rowe JW (eds) Natural products of woody plants, vol II. Springer-Verlag, Berlin, pp 861-878

Hawley LF, Fleck LC, Richards CA (1924) The relation between natural durability and chemical composition in wood. Ind. Eng. Chem. 16: 699-706

Hegnauer R (1962) Chemotaxonomie der Pflanzen. Birkhuser Verlag, Basel und Stuttgart

Hiller CH, Freese F, Smith DM (1972) Relationships in black walnut heartwood between colour and other physical and anatomical characteristics. Wood Fiber 4: 38-42

Hillis WE (1971) Distribution, properties and formation of some wood extractives. Wood Science and Technology 5: 272-289

Hillis WE (1987) Heartwood and tree exudates. Springer-Verlag, Berlin Heidelberg New York

Hoffmeyer P, Pedersen JG (1995) Evaluation of density and strength of Norway spruce wood by near infrared reflectance spectroscopy. Holz als Roh- und Werkstoff 53: 165-170

27

Hon DN-S, Minemura N (2001) Color and discoloration In: Hon DN-S, Shiraishi N (eds) Wood and cellulosic chemistry. Marcel Dekker, New York, pp 385-441

Jacques D, Curnel Y, Jourez B, Pques LE (2002) Among and within provenance variability of decay resistance of larch wood to fungi. In: Proceedings of improvement of larch (Larix sp.) for better growth, stem form and wood quality, Gap - Auvergne & Limousin. INRA, Olivet Cedex, pp 405-413

Kleist G, Schmitt U (1999) Evidence of accessory compounds in vessel walls of Sapelli heartwood (Entandropphragma cylindricum) obtained by transmission electon microscopy. Holz als Roh- und Holzstoff 57: 93-95

Knuchel H (1954) Das Holz. H.R. Sauerlnder & Co, Aarau

Langner W, Reck S (1966) Vergleichende Untersuchungen ber das Holz von Larix decidua Mill., Larix leptolepis Gord. und deren Hybriden. Holzforschung 20: 192-199

Michell AJ (1995) Pulpwood quality estimation by near-infrared spectroscopic measurements on eucalypt wood. Appita 48: 425-428

Morrell JJ, Freitag CM (1995) Durability of Dahurian larch. Forest Products Journal 45: 77-78

Nelson ND, Heather WA (1972) Wood color, basic density, and decay resistance in heartwood of fast-grown Eucalyptus grandis Hill ex Maiden. Holzforschung 26: 54-60

Nilsson T (1997) Natural durability of larch heartwood against decay. IRG/WP 97-10201. The International Research Group on Wood Preservation, Stockholm

Odonmazig P, Ebringerova A, Machova E, Alfldi J (1994) Structural and molecular properties of arabinogalactan isolated from Mongolian larchwood (Larix dahurica L.). Carbohydr. Res. 252: 317-324

Pques, L.E. ; Rozenberg, P. (1995) Intraspecific variability of European larch for wood properties: in Proc. 'Larch Genetics and Breeding', IUFRO Working Party S2.02-07. Sweden: 21-33

Ponder GR, Richards GN (1997) Arabinogalactan from Western larch, Part III: alkaline degradation revisited, with novel conclusions on molecular structure. Carbohydrate Polymers 34: 251-261

Posey CE, Robinson DW (1969) Extractives of shortleaf pine: analyses of contributing factors and relations. Tappi 52: 110-115. Tappi 52: 110-115

Rudman P (1963) The causes of natural durability in timber. Part XI. Some tests on the fungi toxicity of wood extractives and related compounds. Holzforschung 17: 54-57

Scalbert A (1991) Antimicrobial properties of tannins. Phytochemistry 30: 3875-3883

Scheffer TC, Cowling EB (1966) Natural resistance to microbial deterioration. A. Rev. Phytopath. 4: 147-170

Schimleck LR, Wright PJ, Michell AJ, Wallis AFA (1997) NIR Infrared spectra and chemical compositions of E.globulus and E.nitens wood. Appita 50: 40-50

Schimleck LR, Michell AJ, Raymond CA, Muneri A (1998) Assessment of the pulpwood quality of standing trees using near infrared spectroscopy. Journal of Near Infrared Spectroscopy 6: A117-A123

Schimleck LR, Michell AJ, Raymond CA, Muneri A (1999) Estimation of basic density of Eucalyptusglobulus using near-infrared spectroscopy. Can. J. For. Res 29: 194201

Schimleck LR, Evans R, Ilic J, Matheson AC (2002) Estimation of wood stiffness of increment coresby near-infrared spectroscopy. Can. J. For. Res. 32: 129-135

Schober R (1985) Neue Ergebnisse des II. Internationalen Lrchenprovenienzversuches von 1958/59 nach Aufnahmen von Teilversuchen in 11 europischen Lndern und den U.S.A. J.D. Sauerlnders Verlag Frankfurt am Main, Gttingen

Schober R (1991) Ergebnisse des I. Internationalen Japanlrchen-Provenienzversuches. J.D. Sauerlnders Verlag Frankfurt am Main, Gttingen

Schultz TP, Hubbard TF, J. L, Fisher TH, Nicholas DD (1990) Role of stilbenes in the natural durability of wood: fungicidal structure-activity relationships. Phytochemistry 29: 1501-1507

Schultz TP, Harms WB, Fisher TH, McMurtrey KD, Minn J, Nicholas DD (1995) Durability of angiosperm heartwood: the importance of extractives. Holzforschung 49: 29-34

Schultz TP, Nicholas DD (2000) Naturally durable heartwood: evidence for a proposed dual defensive function of the extractives. Phytochemistry 54: 47-52

Schwanninger M, Hinterstoisser B (2001) Determination of the lignin content in wood by FT-NIR. 11th ISWPC, International Symposium on Wood and Pulping Chemistry, Nice, France, Vol. III, 641-644

Schwanninger M, Hinterstoisser B (2002) Klason Lignin: Modifications to improve the precision of the standardized determination. Holzforschung 56: 161-166

Smith AL, Campbell CL, Diwakar MP, Hanover JW, Miller RO (1989) Extracts from Black Locust Heartwood as Wood Preservatives: A Comparison of the Methanol Extract with Pentachlorphenol and Chromated Copper Arsenate. Holzforschung 43: 421-423

28

Srinivasan U, Ung T, Taylor A, Cooper PA (1999) Natural durability and waterborne treatability of tamarack. Forest Products Journal 49(1): 82-87

Swain T, Hillis WE (1959) The phenolic constituents of prunus domestica. I. - The quantitative analysis of phenolic constituents. J. Sci. Food Agric. 10: 63-68

Sylvestre-Guinot G., Pques L.E., Delatour C. (1983) Rsistance du mlze hybride inocul par Lachnellula willkommii. Ann.Sc.For. 56: 485-492

Sylvestre-Guinot G., Delatour C. (1983) Possibilits d'apprciation de la sensibilit du genre Larix au Lachnellula willkommii (Hartig) Dennis par inoculations artificielles. Ann.Sc.For. 40: 337-354

Tanaka H, Itakura S, Enoki A (1999) Hydroxyl Radical Generation by an Extracellular Low-Molecular-Weight Substance and Phenol Oxidase Activity During Wood Degradation by the White-Rot Basidiomacete Phanerochaete chrysosporium. Holzforschung 53: 21-28

Thygesen LG (1994) Determination of dry matter content and basic density of Norway spruce by near infrared reflectance and transmittance spectroscopy. Journal of Near Infrared Spectroscopy 2: 127-135

Van Acker J, Militz H, Stevens M (1999) The Signigicance of Accelerated Laboratory Testing Methods Determining the Natural Durability of Wood. Holzforschung 53: 449-458

Van Acker J, Stevens M, Carey J, Sierra-Alvarez R, Militz H, Le Bayon I, Kleist G, Peek RD (2003) Biological durability of wood in relation to end-use Part 1. Towards a European standard for laboratory testing of the biological durability of wood. Holz als Roh- und Holzstoff: 35-45

Venlinen M, Harju AM, Paajanen L, Velling P, Vittanen H (2001) Genetic Variation in the Decay Resistance of Siberian Larch (Larix sibirica Ledeb.) Wood. Holzforschung 55: 1-6

Venlinen M (2003) Decay resistance of heartwood timber as a quality characteristic in Scots pine breeding. Finnish forest research institute Punkaharju, University of Helsinki, Dissertation: pp. 54

Viitanen H, Paajanen L, Saranp P, Viitaniemie P (1997) Durability of larch (Larix spp.) wood against brown-rot fungi. IRG Doc. No: IRG/WP 97-10228. The International Research Group on Wood Preservation, Stockholm

Windeisen E, Wegener G, Lesnino G, Schumacher P (2002) Investigation of the correlation between extractives content and natural durability in 20 cultivated larch trees. Holz als Roh- und Werkstoff 60: 373-374

Wilcox WW, Piirto DD (1976) Decay resistance in redwood (Sequoia sempervirens) heartwood as related to color and extractives. Wood and Fiber Science 7: 240-245

Willeitner H, Peek RD (1997) The natural durability story. 28th Annual meeting of the International research group on wood preservation, Section 1, IRG/WP 97-20119. IRG Secretariat, Whistler, BC, Canada, pp 1-14

Wright JA, Birkett MD, Gambino MJT (1990) Prediction of pulp yield and cellulose content from wood samples using near infrared reflectance spectroscopy. Tappi Journal: 164-166

Zabel RA, Morell JJ (1992) Wood Microbiology, decay and its prevention. Academic Press, Inc, London

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PAPER I

Rapid determination of heartwood extractives in Larix sp. by means of Fourier transform near infrared spectroscopy

Gierlinger, N., Schwanninger, M., Hinterstoisser, B.,Wimmer, R.

J. Near Infrared Spectrosc. 10: 203-214. 2002

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PAPER II

Rapid prediction of natural durability of larch heartwood using FT-NIR spectroscopy

Gierlinger, N., Jacques, D., Schwanninger, M., Wimmer, R., Hinterstoisser, B.,

Pques, L.E.

Canadian Journal of Forest Research: in print.

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Rapid prediction of natural durability of larch heartwood using

FT-NIR spectroscopy

Notburga Gierlinger1, Dominique Jacques2, Manfred Schwanninger3, Rupert

Wimmer1, Barbara Hinterstoisser3, Luc E. Pques4

1 Institute of Botany; BOKU - University of Natural Resources and Applied Life Sciences, Vienna, Gregor-Mendelstr. 33, A-1180 Vienna 2 Centre de Recherche de la Nature des Forts et du Bois, Avenue Marchal Juin 23, B-5030 Gembloux 3 Institute of Chemistry; BOKU - University of Natural Resources and Applied Life Sciences, Vienna, Muthgasse 18, A-1190 Vienna 4 INRA, Unit dAmlioration, de Gntique et de Physiologie des Arbres forestiers, F-45166 Olivet Cedex

Abstract

The feasibility of Fourier-transform near-infrared (FT-NIR) spectroscopy to rapidly

determine natural durability of the heartwood of larch trees (Larix decidua Mill. and L.

kaempferi (Lamb.) Carr.) was investigated. FT-NIR spectra were collected from solid

wood by means of a fibre-optical probe. Basidiomycetes tests (European Standard EN

113) using Coniophora puteana and Poria placenta were carried out on larch

heartwood, with pine sapwood (Pinus sylvestris) used as a reference. The relative

resistance to decay (x-value) was calculated and durability classes estimated according

to European Standard (EN 350-2). Partial Least Squares regressions between the data

sets of wood decay tests (x-values) and the FT-NIR spectra were calculated, it was

found that Multiplicative Scatter Correction (MSC) considerably improved the model

predictability. High coefficients of correlation (r) and low root mean square errors of

prediction (RMSEP) were obtained for cross-validation based on wood decay tests

with P. placenta (r = 0.92, RMSEP = 0.077, range 0.27 1.13) and C. puteana (r =

0.97, RMSEP = 0.078, range 0.07 1.58). Overall, NIR spectroscopy has proven to be

an accurate and fast method for the non-destructive determination of natural

durability, which might be highly relevant for intensive tree breeding programs and for

efforts to optimise wood utilization.

Keywords: Larix sp., heartwood, natural durability, wood decay tests, PLSR, FT-NIR, fibre-optic probe

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Introduction

The ability of tree species heartwood to resist biological degradation is called its

natural durability or decay-resistance (Eaton and Hale 1993) and is an important wood

quality factor essential for environmentally friendly exterior timber uses. Knowledge about

natural durability may come from practical experiences of end-users, from field tests in

ground contact or from standardized laboratory tests (Willeitner and Peek 1997). To compare

natural durability of different wood species a classification based on the computation of a

relative resistance has high practical meaning. This measure is expressed in a five class-

system, with classes ranging from non-durable (class 5) to highly-durable (class 1)

(Bellmann 1988a, European Standard EN 350- 2).

Natural durability of larch (Larix sp.) wood is described as being highly variable,

ranging from non-durable to moderately durable (class 5 to 3, EN 350-2, Viitanen et al. 1997,

Morell and Freitag 1995, Srinivasan et al. 1999, Nilsson 1997). This apparent variability may

arise from problems that are linked to the size of the sample tested and the reliability of the

testing method itself, but is also clearly linked to the large variability within and between

trees, variability across sites, species, genetic origins and with tree age (Bellmann 1988b,

Eaton and Hale 1993, Nilsson 1997, Van Acker et al. 1999, Jacques et al. 2002). Among end-

users larch heartwood is valued for outdoor applications, even though high variability in

timber performance exists. More detailed investigations about the level and variance of larch

heartwood and its natural durability are needed and could be of benefit in tree improvement

programs as well as optimizing wood utilization.

The significance of wood extractives for natural durability was demonstrated as early

as 1924 (Hawley et al.), and it has been a repeatedly discussed topic in the literature (e.g.

Rudman 1963, Reyes-Chilpa et al. 1998, Celimene et al. 1999, Schultz et al. 1990, 1995,

Schultz and Nicholas 2000). Additionally, the wood density, the lignin quantity and its type

may also contribute to the susceptibility of the heartwood against attack and spoilage by

different bio-deteriogens (Eaton and Hale 1993).

Near-infrared (NIR) spectroscopy has shown utility to be a powerful and rapid tool to

estimate parameters related to wood chemistry, i.e. pulp yield, cellulose and lignin content

(Easty et al. 1990, Michell 1995, Schimleck et al. 1998, Schwanninger and Hinterstoisser

2001, Wright et al. 1990) as well as wood extractives (Schimleck et al. 1997, Gierlinger et al.

2002). Furthermore, studies have shown that NIR spectroscopy was also capable to determine

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physico-mechanical properties, including basic density (Thygesen 1994; Schimleck et al.

1999), mechanical strength (Hoffmeyer and Pedersen 1995, Gindl et al. 2001) and stiffness

(Schimleck et al. 2002, Thumm and Meder 2001). It may be concluded therefore, that since

all factors influencing natural durability, i.e. heartwood extractives, lignin and density, may be

successfully determined by NIR spectroscopy, it may also have the potential to rapidly and

non-destructively predict natural durability.

Thus, the purpose of this study was to investigate the feasibility of FT-NIR

spectroscopy as a method to estimate the natural durability of larch heartwood. Durability

classes after inoculation with Coniophora puteana and Poria placenta were determined

according to European standard EN 350-2 using wood from plantation-grown European and

Japanese larch, and the obtained dataset was utilized to establish calibration models with

acquired FT-NIR spectra.

Material and Methods

Forty-year old larch trees, planted on sites in Germany, Belgium and France were

sampled in this study. The trees were part of an European provenance trial with selected larch

provenances planted out across Europe (Table 1). Groups of European larch (Larix decidua

Mill.) trees were selected out of a greater investigated sample pool (described in Jaques et al.

2002) to provide a high variation of decay resistance of even aged plantation trees.

Additionally Japanese larch (L. kaempferi (Lamb.) Carr.), which proved to have higher decay

resistance (Jaques et al. 2003) was added to the sample set (Table 1). From each tree a two-

meter log was cut at breast height upwards and from each a central board was sawn. A set of

24 samples was prepared from each tree, half taken from the inner and the second half from

the outer part of the heartwood. Sixteen samples were submitted to natural durability tests and

8 were used as standards for calculating reference dry matter. Samples (50x25x15mm) were

all planed and placed in a standard climate chamber to equalise at 12 % wood moisture

content prior to fungal inoculation.

Wood decay tests

Natural durability of solid wood was performed according to European Standard EN

350-1. A total of 608 larch samples and reference samples of Pinus sylvestris sapwood were

tested. For each tree, 8 samples were inoculated with Poria placenta (strain FPRL280) and

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another 8 samples with Coniophora puteana (strain FPRL11E). After exposure for sixteen

weeks mycelium was removed from the samples prior to drying at 103 C to a constant

weight. The mass loss was calculated and divided by the mass loss of the pine reference,

resulting in a ratio called x-value as suggested in EN 350-1 (Table 2). Average values were

calculated using 2 in vertical direction adjacent samples (containing the same annual rings),

leading to 4 values per tree and fungi (4x38trees = 152 samples for NIR spectroscopy).

FT-NIR spectroscopy

FT-NIR spectra were recorded on a BRUKER FT-IR spectrometer (EQUINOX 55)

equipped with a NIR fibre-optical probe to measure the diffuse reflected light on a 10 mm2

spot. A germanium-diode detector with a cut-off wavenumber at 5100 cm-1 (1961 nm) was

used and the measurement spectrum ranged between 9970 cm-1 (1003 nm) and 5100 cm-1

(1961 nm). The thermoplastic resin Spectralon served as a reference. With a spectral

resolution of 20 cm-1 (636 data points), one hundred scans per spectrum were acquired and

averaged. Four spectra were acquired of cross sections of 152 samples from freshly cut

surfaces of the oven-dried standard samples, which have been used for calculating the

reference dry matter but not for the decay tests. Spectra were measured equally spaced in

radial direction along the centreline of the transverse plane and the average spectra were used

for calibration.

Data analysis

Chemometric modelling was performed with the UNSCRAMBLER software package

(Version 7.6, CAMO ASA). For pre-processing the algorithms of full multiplicative scatter

correction (MSC, the mean spectrum of the calibration set used as base spectrum), of the first

(1.Der) and second derivative (2.Der) were applied. Spectra were processed (smoothed and

derived) according to Savitzky and Golay (1964) by means of a 9-point smoothing filter and a

second order polynomial. Wavelength selection was done manually as well as automatically

by means of the Martens Uncertainty test (Westad and Martens 2002), to eliminate

unimportant variables to simplify the models and making them more reliable. Calibrations

(CAL) were developed using partial least squares (PLS) regression. The average NIR spectra

were regressed against the natural durability data and by means of full cross-validation (CV)

with one sample omitted a significant number of PC-components (principal components or

factors) were obtained. The root mean square error was calculated for the calibration samples

(RMSEC) and for the predicted samples (RMSEP, %RMSEP = RMSEP/mean).

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Results

Variation of natural durability

Table 2 gives relative frequencies of natural durability classes according to EN350-1.

For P. placenta almost half of the samples were classified as slightly durable, 30% were

moderately durable and the remainder (20%) were non-durable. Mass-losses after exposure to

C. puteana resulted in an even more scattered picture with 10 % being very durable on the

one side, and 12% non-durable on the other side of the scale, while the majority (42%) was

classified as moderately durable.

The relationship between the x-values obtained from the two fungi is shown in Figure

1: a correlation of r = 0.61 and an axis intercept of 0.22 between the two x-values is noticed.

In some cases the two fungi led to a classification differing often in one or two classes, also

seen by the axis intercept. As seen in Figure 1 large variation was found between and also

within each provenance. The provenances Ina (Japanese larch) and Blizyn (European larch)

tended to lower durability classes (meaning higher durability), whereas samples of the

provenance Langau (European larch) had the tendency to be classified as not or slightly

durable (Fig. 1).

Variation of NIR spectra

The NIR diffuse reflectance spectra of the samples from the same durability classes

were averaged. As shown in Figure 2A-B these averaged spectra demonstrated a considerable

baseline shift, especially between 6300 cm-1 (1587 nm) to 5100 cm-1 (1960 nm). For the P.

placenta samples the baseline shifts were more distinctive than for C. puteana and a clear

differentiation of durability classes is shown. After multiplicative scatter correction (MSC)

differences were reduced (Fig. 2C-D), however, closer examination of the 6300 cm-1 (1587

nm) and 5300 cm-1 (1887 nm) region is still indicating a clear association with the durability

classes for the P. placenta group as well as for the C. puteana ones (Fig. 2C-D).

Spectral variability in respect to the durability classes was also investigated through

principal components analysis (PCA) (Fig. 3A, 3B). The scores plot using unmodified spectra

(Fig. 3A) showed no patterns within the samples, whereas after applying MSC to the spectra a

separation according to their durability classes was observed (Fig. 3B). Beside principal

component (PC) 1 vs PC2, where the best separation was seen, also PC2 vs PC3, PC3 vs PC4

and PC1 vs PC3 were investigated.

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Calibration models for the estimation of natural durability

A summary of the calibration models established with the relative mass-loss data from

P. placenta decay tests is found in Table 3. The calibrations were highly acceptable (r = 0.86 -

0.92) and it is shown that data pre-processing, especially MSC significantly improved the

calibrations: r-values increased from 0.84 to 0.92 (CAL), 0.82 to 0.91 (CV) respectively,

whereas root mean square errors improved from 0.098 to 0.073 (CAL), 0.103 to 0.077 (CV)

respectively. The positive effect of MSC as shown in the PCA analysis was confirmed by the

improved model statistics. Automatic wavenumber selection with the Martens uncertainty test

has led to comparably good test statistics, accompanied by a reduction in the number of

principal components (PC) required from 6 to 4. The wavenumber range between 6300 cm-1

(1587nm) and 5100 cm-1 (1960nm), which exhibited the greatest differences between the

average spectra of the durability classes (Fig. 2 A-D), resulted in a poorer calibration than

using wavenumbers selected through the Martens uncertainty test (Table 3). However,

compared to models without data pre-processing with the entire wavenumber region included,

model diagnostics (r, RMSEC, RMSEP) were even better, although only one principal

component was necessary (Table 3). Calibration models established with the mass-loss data

from C. puteana showed similar performance (Table 4). The improvement of the models after

applying MSC was even more drastic: r values increased from 0.79 to 0.97 (CAL), 0.76 to

0.97 (CV) respectively, whereas root mean square errors decreased from 0.191 to 0.072

(CAL), 0.201 to 0.078(CV) respectively.

NIR-predicted versus laboratory-determined x-values are shown in Figs. 4A-B. The

results were obtained from cross-validation models using the entire wavenumber range and

after multiplicative scatter correction (MSC). Figure 4 showed once again the broader range

for x-values obtained from C. puteana tests and the superiority of this model compared to the

model based on P. placenta tests. In most cases, the predicted and true durability classes were

the same and the models fitted very well data for all four provenances over the whole range

(Fig. 4).

Discussion

As Vittanen et al. (1997) demonstrated, natural durability depends among others on

tree species, tree age and the within-tree position (e.g. inner vs. outer heartwood). This was

recently confirmed by Jaques et al. (2002) with a large sample set, who besides the higher

natural durability of Japanese larch compared to European larch, also noted huge variability

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across provenances, among and within trees. The large variation found in this study is due to

different sources including species (European and Japanese larch), provenances (confounded

with sites) and also the variation observed between and within trees (inner and outer part).

The calculated average durability classes, class 4 if based on P. placenta and class 3 if based

on C. puteana, were well in agreement with results from Vittanen et al. (1997). If attacks of

various fungi result in different durability classes, the score obtained for the most aggressive

fungus may be used (Van Acker et al. 1999). In our case, C. puteana was most aggressive and

produced at the same time more variable decay results.

Differences in the average spectra between 6300 cm-1 (1587 nm) and 5300 cm-1 (1887

nm) are associated with the durability classes (Fig. 2C-D). This region includes 1st overtones

from C-H stretch of =CH2, methyl groups, methylen groups and aromatic substances and O-H

stretch/C-O stretch 2nd overtone combinations, present in all main components of wood (e.g

cellulose, extractives and lignin) (Shenk et al. 2001). For natural durability especially

heartwood extractive play a major role and for larch wood a strong correlation between the

total amount of phenols and the x-value was found recently (Gierlinger in preparation). The

flavonoid taxifolin (3,3',4',5,7-Pentahydroxyflavanone), which is known to be a major

phenolic compound in larch heartwood (Hegnauer 1962), shows strong bands within the range

from 6300 to 5300 cm-1 (1587 1887 nm) (Gierlinger et al. 2002).

Statistics for both fungi demonstrate that good calibrations can be obtained to predict

wood decay and confirm the assumption that calibrations can be used to rapidly predict

natural durability. Correlation coefficients were as high as 0.97 and comparable to those

obtained from NIR- models to predict extractive contents (Gierlinger et al. 2002) and wood

density (Thygesen 1994). In this study only two replicated tests were used for the calibration

and improvement may be gained by increasing the replicates for calibration data. The

accuracy of laboratory reference data is a crucial factor for the quality of NIR prediction

models. Although the accuracy of biological wood decay tests is poor compared to chemical

analyses, surprisingly good results were achieved in this work. Coates (2002) demonstrated

that NIR spectroscopic calibration equations might produce predictions at higher accuracy

than laboratory reference values from the calibration set.

In a previous study on NIR-based calibration models for larch heartwood extractives

the restricted wavenumber range below 7500 cm-1 (1333 nm) turned out to be well suited with

no relevant information lost and reduction of number of factors (Gierlinger et al. 2002).

Similar restrictions in the calibration model for natural durability did lead to significant

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information losses resulting in reduced power of prediction. With automatic restriction by

means of the Martens Uncertainty test only few single wavenumbers were removed, which

turned out to be more appropriate.

Multiplicative Scatter Correction (MSC) reduced differences between averaged

spectra and improved the relation to natural durability classes as well as the model statistics

for both fungi. Predicting basic density Thygesen (1994) found that MSC did not provide a

consistent improvement. This may be explained by the influence of wood structure on density

and that scatter in that case is not interfering, but provides additional information. MSC only

slightly improved calibrations developed to predict the extractive contents of larch heartwood

(Gierlinger et al. 2002), because scatter effects on wood powder samples are minor. In this

study the PLS regression calibrations predicting natural durability of solid wood samples were

substantially improved by MSC. As natural durability is strongly influenced by extractives,

the chemical information may be of primary importance and may be improved by removing

scatter effects.

NIR spectroscopy has proved to be a reliable tool for prediction of natural durability.

For a comprehensive prediction of the bioresistance of larch heartwood, NIR models could be

developed by taking into account several test fungi, laboratory and field decay tests. Although

such calibration models will be labor-intensive, once established, they will allow acquiring

data non-destructively within minutes and to process high sample numbers. Since spectra can

be taken from small samples it is possible to estimate natural durability even from standing

trees by taking increment cores. Therefore it seems particularly suitable for several forestry

and wood studies where large numbers of wood samples must be analysed non-destructively.

This is particularly true for tree breeding programmes where hundreds of genotypes need to

be surveyed non-destructively, for silvicultural studies with the necessity to test effects of

different treatments, or for intensive surveys of wood resources.

Conclusions

Partial Least Squares regression calibration, based on FT-NIR-spectra and reference

data of standardized wood decay tests, were successfully applied to estimate the natural

durability classes of larch heartwood. The optimised and verified calibrations could be put

into practice for the forest and forest-products industry to efficiently determine natural

durability. This will lead to a better knowledge on the environmental and genetic control of

natural durability variability by measuring quickly large numbers of samples accurately and

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non-destructively. It may break new ground for selection within tree breeding programs and

for optimized wood utilization. Potentially durable trees may be selected off-line or on-line

during the manufacture process, the latter could become reality with spectral cameras,

operating in the NIR, becoming more readily available.

Acknowledgement

The research was funded by the EU-project "Towards a European Larch Wood Chain

(FAIR 98-3354) and the research project The causes of natural durability in larch (P15903,

Austrian Science Fund). We thank Dr. Wolfgang Gindl (Institute of Wood Science and

Technology) enabling the analysis using the Unscrambler software.

References Bellmann, H. 1988a. Relative Resistenz