Trees (2005) 19: 654–660DOI 10.1007/s00468-005-0429-0

ORIGINAL ARTICLE

K. M. Bhat · P. K. Thulasidas · E. J. Maria Florence ·K. Jayaraman

Wood durability of home-garden teak against brown-rotand white-rot fungi

Received: 9 December 2004 / Accepted: 9 March 2005 / Published online: 26 April 2005C© Springer-Verlag 2005

Abstract Natural decay resistance of teak wood grown inhome-garden forestry and the factors influencing decay re-sistance were determined in comparison with that of a typi-cal forest plantation. Accelerated laboratory tests were con-ducted on 1800 wood samples drawn from 15 trees of threeplanted sites. Analysis of variance based on a univariatemixed model showed that planted site, fungal species, andtheir interaction terms were important sources of variationin decay resistance. With increasing decay resistance fromcentre to periphery of the heartwood, radial position was acritical factor and the interaction effect of fungal species ×radial position was significant in influencing the durabil-ity. No significant differences were found in decay resis-tance either between the opposite radii or due to the vari-ous possible interaction terms of radii with the site, fungalspecies and radial position. There were significant differ-ences in decay resistance against brown-rot fungi betweenwet and dry sites of home-garden teak although differ-ences against white-rot fungi were non-significant amongthe three planted sites. Polyporus palustris was the moreaggressive brown-rot fungus than Gloeophyllum trabeum.The higher susceptibility of wet site home-garden teak tobrown-rot decay was associated with a paler colour of thewood and lower extractive content.

K. M. Bhat (�) · P. K. ThulasidasDivision of Forest Utilisation, Kerala Forest Research Institute,Peechi, 680 653 Kerala, Indiae-mail: kmbhat@kfri.orgTel.: +91-487-2699037Fax: +91-487-2699249

E. J. Maria FlorenceDivision of Extension and Training, Kerala Forest ResearchInstitute,Peechi, 680 653 Kerala, India

K. JayaramanDivision of Forest Information Management System, KeralaForest Research Institute,Peechi, 680 653 Kerala, India

Keywords Tectona grandis . Decay resistance .Extractive content . Wood colour . Mixed effectsmodel . Trees outside forest

Introduction

Home-garden forestry with teak (Tectona grandis L. f.) isincreasingly becoming a practice of growing trees outsideforests (ToF) as one of the sustainable options in tropicalcountries. In India, especially Kerala State, it accounts formore than 50% of the industrial round wood supply. Theterm home-garden forestry is used in the present study torefer to the practice of growing trees in combination withvarious crops around the homesteads, as a kind of agro-forestry (Nair 1989). It is prevalent in India with a fellingcycle of 35 years as against the traditional teak planta-tion rotation of 50 years or more in the tropics. Although,wood density, dimensional stability and strength propertiesare not significantly different, the world wide reputation ofteakwood for natural durability is being questioned whensupplied from trees outside the forests (Bhat et al. 2004).Home-garden teak generally fetches a lower price with thenotion that the wood is less durable and paler in colour thanthat of natural and plantation forests.

The main objective of the present study was to assess thenatural decay resistance of home-garden teak in compari-son with teak grown in a typical forest plantation site andto determine the influencing factors.

Materials and methods

Field sampling

Trees were felled in order to compare the 35-year-old teakfrom homesteads with that grown in a typical forest planta-tion of Nilambur (Karulai Range). The field sampling wasdone from both dry (Nemmara, Palghat district) and wet(Muvattupuzha, Ernakulam district) localities of Kerala torepresent the diverse conditions of home-garden forestry

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Table 1 Environmental conditions and size of sampled teak trees from wet and dry localities as compared to forest plantation at Nilambur,Kerala

Factor Wet (Muvattupuzha, Ernakulam) Dry (Nemmara, Palghat) Forest plantation(Karulai, Nilambur)

Altitude (m.a.s.l) 20 40 60North latitude 9◦ 59′ 10◦ 35′ 11◦ 15′

East longitude 76◦ 34′ 76◦ 35′ 76◦ 13′

Soil type Loamy sand Loamy sand Loamy sandAnnual rainfall–range (mm) 2500–3500 1500–2300 2500–3000Temperature range ◦C 17–34 26–37 17–37Relative humidity % Above 80 70 70Tree age (year) 35 35 35Mean tree height (m) 17.0 14.0 21.0Mean diameter at breast-height(cm)

39.6 24.0 31.0

with respect to moisture/rainfall, which is known to influ-ence teak growth (Priya and Bhat 1999). The Nilamburplantation, with its well-drained alluvial soil, was chosenfor comparison because teak from this geographic locationin India is known to display the best growth with larger logdimensions and golden yellowish-brown wood. This teakis widely reputed as Malabar teak in the trade for superiorquality timber. The three site conditions and tree charac-teristics are given in Table 1. For laboratory investigations,five defect-free dominant teak trees from each of the home-steads representing wet and dry localities of Kerala weresampled in addition to five trees of the same age from atypical forest plantation of Nilambur.

Decay resistance

To test the natural decay resistance, the billet (30 cmlong) taken immediately above breast height (1.37 m aboveground) was used. The outer sapwood portion was removed,and inner heartwood was sawn into 2 cm×2 cm battens ra-dially from the centre to the periphery of the heartwoodcylinder, excluding pith, for preparing test blocks (Fig. 1).Decay resistance in teak is known to vary from the cen-tre outwards (Bhat and Florence 2003). From each tree,inner, middle and outer samples representing three radialpositions from the centre to the peripheral boundary ofheartwood from two opposite radii were selected (with fourreplicates) to cover the variation between the radial posi-

Sapwood

Outer

Middle

Inner

Pith

Heartwood

Fig. 1 Schematic illustration of test blocks from two opposite radiiof the heartwood cylinder removed immediately above the breastheight (BH) level

tions and between the radii, if any (Fig. 1). Test blocks of2 cm×2 cm×1 cm size were prepared according to the pro-cedure described by Bakshi et al. (1967). Altogether, 1800test blocks (600 each representing wet and dry planted sitesof home garden as well as the typical forest plantation site)were prepared so as to allow two test blocks each in 900test bottles (500 g capacity). From each tree, three blocks(outer, middle and inner) were used as adjustment blocks(control samples). Highly perishable timber, Bombax ceibaLinn., was selected as a feeder strip for the test fungi andblocks were prepared from the quarter sawn sample (size2 cm×2 cm×1 cm). Reference blocks, similar to test blocksin size were also prepared from the same mature tree ofB. ceiba.

The test fungi included two brown-rot fungi, Gloeophyl-lum trabeum (Pers. ex Fr.) Murr. (FRI 90) and Polyporuspalustris Berk. and Curt. (FRI 422), and three white-rotfungi, Pycnoporus sanguineus (Linn. ex Fr.) Murr. (FRI1135), Trametes hirsuta (Wulf. ex Fr.) Lloyd. (FRI 715)and T. versicolor (Linn. ex Fr.) Pilat. (FRI 684) obtainedfrom the Forest Research Institute, Dehra Dun, India. Theprocedure described in ASTM Standard D2017-71 (1981)for accelerated laboratory testing was followed. The testfungi were sub-cultured and grown in 2% potato dextroseagar (PDA) in Petri dishes to prepare adequate inoculumfor the 1800 blocks.

A soil block method was used for the decay test. One-third of the test bottles were filled with loam soil (pH 5.9)with a water holding capacity of 20–40%. In each testbottle, two feeder strips were kept and the bottles weresterilized at 121◦C for 30 min on two succeeding days.An 8 mm diameter PDA disc cut from the margin of theactively growing colony of the test fungi was placed asep-tically near the feeder strips on the soil. The inoculatedbottles were kept in the incubation room at 28◦C and 70%relative humidity. After 2–3 weeks, when the feeder stripwas almost covered with the fungus, the surface steril-ized (at 100◦C for 30 min) test blocks and reference blockswere transferred aseptically and placed on the feeder strips.Adjustment blocks were kept on the un-inoculated feederstrips.

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After 8 week exposure to the test fungi, two referenceblocks were taken out, the surface mycelium was removed,and the blocks were oven dried and weighed to determinethe percentage weight loss. Additional pairs of blocks weretaken out at weekly intervals until a weight loss of 60%based on oven dry weight was reached. At that stage, testblocks and adjustment blocks were removed from the bottleand their oven dry weight determined. If the adjustmentblocks had suffered any weight loss due to any other causes,necessary corrections were made in the oven dry weightof test blocks. The relative resistance of each test blockto decay was measured as the percentage loss in oven dryweight during 8 week exposure to attack by the five selectedwood decay fungi.

Extractive content

The total extractive content was analysed to ascertain the ef-fect of extractives on the natural durability of home-gardenteak. The ASTM Standard D1107-56 (1984) for the deter-mination of alcohol–benzene solubility of wood was fol-lowed. Whole heartwood samples from pith to peripheryin each radial direction were selected and powdered in aWiley mill. The powder was allowed to pass through a No.40 (420 µm) sieve and retained on a No. 60 (250 µm)sieve. Test specimens consisting of 2 g air-dried sawdustplaced in extraction thimbles (30 mm × 100 ml) wereplaced in Soxhlet extraction apparatus (capacity 100 ml)and extracted with 150 ml of ethyl alcohol and benzene(1:2 ratio) in the extraction flask continuously for 8 hkeeping the liquid boiling briskly. After evaporating thesolvent from the extraction flask, the contents (extractive

content) of the flask were dried in an oven at 105◦C for1 h, cooled in a desiccator and weighed to determine thepercentage of ethanol-benzene soluble extractive contentbased on moisture-free sawdust.

Colour measurement

A 5 cm thick cross-sectional disc was removed from eachtree at BH level and air-dried. A radial strip of 3 cm widthwas cut from inner to outer heartwood in both radii ex-cluding the pith. Two samples from the opposite radii wereground in a Wiley mill separately. The powder was passedthrough a No. 40 (420 µm) sieve and retained on a No. 60(250 µm) sieve. The colour of these samples was deter-mined by the CIE (1976) (L* a* b*) system within 24 hafter sample preparation to avoid colour changes causedby oxidation or light. The procedure of colour measure-ment using a UV Spectrophotometer (Shimadzu 3100PC)was described by Thulasidas et al. (2004) in an earlierstudy.

Statistical analysis

Analysis of variance (ANOVA) was carried out using a uni-variate mixed model with three levels of errors to explainthe variation in durability (Table 2). Location (planted site),fungus type and position within radius were taken as fixedeffects. Variation between trees (random effect) within lo-cation by fungus type acted as error for comparing thevariation due to location, fungus type and their interac-tions. Different radii and their interaction with location and

Table 2 Results of the ANOVA on weight loss (logarithmic scale)

Source of variation df Type III SS Mean square F value P>F

Location 2 11.49 5.74 5.93 0.0045**Fungus type 4 449.18 112.29 115.87 <0.0001**Location × fungus type 8 19.84 2.48 2.56 0.0180**Tree number (location × fungustype)

60 58.15 0.97 8.62 <0.0001**

Radii 1 1.05 E-6 1.05 E-6 0.00 0.9981ns

Location × radii 2 0.92 0.46 2.51 0.0900ns

Fungus type × radii 4 5.02 E-2 1.26 E-2 0.07 0.9913ns

Location × fungus type × radii 8 2.03 0.25 1.38 0.2258ns

Tree × radii (location × fungus) 60 11.06 0.18 1.64 0.0051**Position 2 33.39 16.69 148.52 <0.0001**Location × position 4 1.04 0.26 2.31 0.0582ns

Fungus type × position 8 12.69 1.59 14.12 <0.0001**Location × fungus type ×position

16 1.92 0.12 1.07 0.3893ns

Radii × position 2 5.76 E-2 2.88 E-2 0.26 0.7743ns

Location × radii × position 4 3.02 E-2 7.55 E-3 0.07 0.9917ns

Fungus type × radii × position 8 0.44 5.44 E-2 0.48 0.8669ns

Location × radii × position 16 0.47 2.69 E-2 0.26 0.9983ns

Error 233 26.19 0.11

**Significant at P=0.01; ns non-significant; small values in the table are indicated in scientific notation

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Table 3 Mean values ofweight loss percentage causedby different fungi on35-year-old home-garden teakfrom wet and dry sites comparedto a forest plantation location

Location Weight loss (%)Brown-rot White-rotP. palustris G. trabeum P. sanguineus T. hirsuta T. versicolor

Wet 43.30a 7.05b 1.86c 2.76c 1.94c

Dry 18.41d 4.28e 1.70cf 3.02cf 1.73cf

Plantation 26.88g 2.34cfh 2.06cfh 2.16cfh 1.65cfh

Note. Cell values differing by a letter in the superscript are significantly different at P=0.05

Table 4 Mean values ofweight loss percentage causedby different fungi on35-year-old home-garden teakat different radial positionswithin the stem

Fungus type Weight loss (%)Inner Middle Outer

Brown-rotP. palustris 40.81a 29.10b 18.04c

G. trabeum 9.01a 3.36b 2.33c

White-rotP. sanguineus 2.29a 1.86b 1.52c

T. hirsuta 3.09a 2.63b 2.21c

T. versicolor 2.17a 1.78b 1.44c

Note. Cell values differing by aletter in the superscript withineach row are significantlydifferent at P=0.05

fungus type formed another set of factors for which tree byradius level within location by fungus type formed the error.Position and all related effects formed a third set of effects,which were compared against the residual error. Since thedata were non-orthogonal due to missing values, Type IIIsums of squares were computed. The analysis was doneusing PROC GLM of SAS. Probability level of 0.05 wasused for testing the significance of effects. The residuals ofANOVA in the original scale showed a diverging patternwhen plotted against the corresponding predicted values.This showed that low weight loss values varied less whencompared to large weight loss values. In order to correctfor this heteroscedastic pattern, logarithmic transformationwas applied to the original values. All the statistical testsand comparisons of means were carried out in the trans-formed scale. The adjusted means were compared usingleast significant difference admitting only planned com-parisons. Bias correction was applied while transformingthe means back to the original scale by adding half of themean square error to the adjusted means before taking theantilogarithm.

One-way analysis of variance followed by Duncan’s mul-tiple range test (P=0.05) was used to test the significanceof extractive content percentage and colour differences be-tween the home-garden and plantation grown teak.

Results and discussion

Weight loss

The percentage weight losses in the test blocks providea measure of the relative decay resistance. The ANOVAon weight loss showed significant location × fungusinteraction (Table 2), implying that the effect of fungustype varied with the locations (planted sites) (P=0.018).The mean weight losses of the test blocks exposed to theselected decay fungi are given in Table 3. The analysis

revealed larger differences between the three sites in thepercentage of weight loss caused by brown-rot fungi thanthe white-rot fungi. While the two brown-rot fungi causedmore severe weight loss in wood samples from the wet sitethan the dry and plantation sites, the weight loss due to thethree white-rot fungi did not vary significantly among thethree sites and the mean weight loss was less than 10%. Theextent of differences between fungi over the locations ismore evident from Table 3. The relative weight loss causedby P. palustris was higher in the wet location than in otherlocations.

The fungus type × position interaction was also signifi-cant implying that the effect of position within radius alsochanged with the fungus. The two-way table of weightloss corresponding to different fungi and positions is givenin Table 4. The weight loss caused by different fungi atthe inner position was uniformly higher than at periph-eral positions but the extent differed by fungi. The differ-ences in weight loss caused by brown-rot fungi at differ-ent positions were larger than those caused by the white-rot fungi. The weight loss caused by P. palustris at in-ner positions was more than any other fungus or at anyother position. The effect of cardinal direction (two op-posite radii) in the stem cross section was non-significanton weight loss and so were its interactions with any otherfactor like site or fungal type as seen from the ANOVA(Table 2).

The overall coefficient of determination of the modelwas 0.96 indicating that the model used for the analysiswas highly effective leaving only 4% of the total variationin weight loss unexplained.

Extractive content

The results of the total extractive content as determinedby ethanol–benzene solubility of wood are presented inTable 5. The ANOVA showed significant differences in

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Table 5 Mean values of totalextractive content and basicwood specific gravity ofhome-garden teak from wet anddry localities and forestplantation teak (n=5 each)

Parameter Wet Dry PlantationSolvent Mean SD Mean SD Mean SD

Total extractivecontent (%)

ethanol-benzene(1:2 ratio)

12.4a 2.2 15.98b 1.4 13.3a 2.8

Wood specificgravity

0.600a 0.005 0.640a 0.001 0.597a 0.002

Note. Cell values differing by a letter in the superscript are significantly different at P=0.05

total extractive content over sites. The total extractivecontent differed significantly between wet and dry sites(P=0.05) with the lowest value for the wet site (12%). Incontrast, although the dry site showed higher values for totalextractive content (16%), the difference from the plantationspecimen was non-significant (P>0.05).

Wood colour

The one-way ANOVA revealed significant differences inthe L* a*b* values between wet, dry and plantation sites.The chromaticness index a* (redness) and b* (yellowness)together contribute to the chroma or saturation of colourin the L* a* b* system. The percentage luminance, light-ness/brightness index is represented by the symbol L*. Thethree factors L* a* and b* are highly saturated in plantationspecimens of teak from Nilambur (Fig. 2a–c). Wood fromthe dry site home-garden also exhibited a similar pattern ofhigh luminance and chroma. The yellowness value b* ofthe wet site sample was lower, hence the low luminance in-dex L* (Fig. 2a and c). The wet site sample being paler (lessyellow) also differed significantly (P<0.05) from the drysite and plantation specimens with more yellowish colour.

Factors influencing decay resistance

By and large, teak wood belongs to Durability Class I(Highly Resistant Timbers) of the general classificationsystem (Bakshi et al. 1967; ASTM 1981). The weight lossin wet site samples due to the attack of brown-rot fungi, viz.,P. palustris, to the extent of 43% brings the teak wood downto Class III (Moderately Resistant Timbers). The dry andplantation site samples belong to the same durability class;they were more resistant than wet site samples (Table 3).White-rot fungi did not cause any damage to the timberas the percentage weight loss was in the range of 1.7–3.0,which is much less than the threshold value of 10% fordurability Class I as reported by Bhat and Florence (2003)for 5-year-old juvenile teak from high input plantations.Similarly, the negligible effect of white-rot fungi on de-cay resistance was reported in Bolivian tropical hardwoods(Miller et al. 2003). Our findings are also in agreementwith the results of Balasundaran et al. (1985) that P. palus-tris was the most aggressive fungus causing decay in fivecommercially important timbers of Kerala.

Although the extent of decay differs between fungi, decayresistance consistently increased from the centre to the pe-

47

51

55

59

L*

brig

htne

ss

a

5

6

7

8

a* r

edne

ss

b

20

22

24

wet dry plantation

wet dry plantation

wet dry plantation

b* y

ello

wne

ss

c

Fig. 2 a–c Lightness index (L*) and chromaticness a* and b* (CIEL* a* b* system) in relation to wet, dry sites of home-garden teakand forest plantation

riphery of the heartwood. This is attributed to lower extrac-tive content in the juvenile wood near the pith and its radialincrease towards the outer heartwood region as reported inteak and softwoods like larch (Narayanamurthi et al. 1962;Simatupang and Yamamoto, unpublished document; Gier-linger and Wimmer 2004). The dependence of durabilityagainst brown-rot fungi on the amount and nature of ex-tractives has been reported in teak as well as in softwoodslike Pinus sylvestris and Larix sp. (Da Costa et al. 1958,Rudman and Da Costa 1959; Narayanamurthi et al. 1962;Bakshi et al. 1967; Da Costa and Osborne 1967; Hillis1987; Simatupang and Yamamoto 1996; Harju et al. 2003;Geirlinger et al. 2004). The quantity of total extractives asan indicator of natural durability and dimensional stabilityof teak has been established by several studies (Sandermannand Simatupang 1966; Simatupang et al. 1996; Yamamotoet al. 1998). The differences in relationship between

659

durability and extractive content over the different sitesand due to fungus type observed in the present study (Ta-bles 3 and 5) support the view that individual compoundslike tectoquinons play a more crucial role in determiningdecay resistance than the total extractive content (Haupt etal. 2003).

Often, wood specific gravity is considered as an indicatorof decay resistance in both angiosperms and gymnosperms(Panshin and de Zeeuw 1980). The data presented in Table 5suggest that it is not a criterion of wood durability of home-garden teak as the specific gravity differences among thethree sites were non-significant despite the marked diam-eter growth differences. It was also shown that fast grownteak wood is not necessarily less dense and lighter (Bhat1998).

The colour of wood is associated with extractive con-tent, and is a useful parameter to estimate the durability oflarch heartwood (Geirlinger et al. 2004). The present find-ing of higher susceptibility of wet site home-garden teak tobrown-rot fungi is therefore attributable to the lower extrac-tive content accompanied by paler colour (less yellow) andfaster growth rate (Tables 1 and 2, Fig. 2a and c) than dry siteteak (Thulasidas et al. 2004). However, in Thuja plicata—aspecies with high natural durability, darker colour is as-sociated with lower extractive content with the possibledominant effect of the pigmentation of individual toxiccompounds rather than the amount of total extractive con-tent (MacLean and Gardner 1956). It deserves mention thatresistance to the most aggressive pathogen, P. palustris washigher on the dry site home-garden trees than in plantationtrees (Table 3). With the low susceptibility to brown-rotfungi, the dry locality teak displayed characteristic darkerheartwood with decorative black streaks, probably due to aparticular pattern of distribution and higher amount of ex-tractives. These characteristics are probably more relatedto site/edaphic factors than to diameter growth rate and age(Nelson et al. 1969; Nelson and Heather 1972; Wilkins andStamp 1990; Thulasidas and Bhat 2003). The smaller ef-fect of diameter growth rate on natural durability of teakwas also reported by Da Costa et al. (1961). However, itdeserves mention that different species of fungi have dif-ferent relationships of decay resistance with annual growthas observed in white spruce (Yu et al. 2003). Although theL* a* b* values are highly saturated in the plantation teak;durability was lower due to the presence of a lesser amountof extractives than the dry site home-garden teak (Table 5).

In the present study, with the limited sampling of fivetrees from each site and individual trees assumed to haverandom effects, no attempt was made to compare differ-ences between trees. The influence of genetic differencedue to individual trees on extractive content, colour anddecay resistance of wood has already been indicated inteak and other species (Bakshi et al. 1967; Da Costa andOsborne 1967; Hiller et al. 1972; Ericsson et al. 2001; Bhatand Florence 2003). The possible effects of genetic differ-ences on variability of decay resistance among wet, dry andplantation sites also remain unexplained within the scopeof the present study.

The present observation that no significant difference ex-ists in decay resistance between the opposite radii withinthe trees throws light on the required sampling intensity inteak with respect to the cardinal direction. One radius ofthe heartwood should be adequate for evaluating the natu-ral decay resistance of the stem wood at least in dominantstraight trees.

Conclusions

Timber from homesteads on a wet site was more susceptibleto brown-rot fungi than timber from a dry site and a forestplantation. No significant differences existed with respectto the decay resistance against white-rot fungi between thehome-garden and plantation grown teak irrespective of wetor dry site.

Higher decay resistance to brown-rot fungi of wood froma dry site was associated with higher extractive content anddarker colour than wet site home-garden teak, which hadfaster growth, lower extractive content and paler colouredwood.

Natural decay resistance of home-garden teak dependedon planting site, fungal species, radial position from thecentre to the periphery of the heartwood and their inter-action terms. However, no significant difference existedbetween the opposite radii implying that any one radius inthe heartwood should be adequate for evaluating the naturaldecay resistance of the stem wood in teak.

Acknowledgements We are grateful to Dr. J. K. Sharma, Direc-tor (KFRI) for constant encouragement and support. This studywas carried out with the sponsorship of the Kerala Forest Depart-ment. The cooperation received from the Forest Department in tim-ber sample collection from Karulai, Nilambur South Forest Divi-sion, has been very invaluable. We gratefully acknowledge Dr. M.Balasundaran, then Scientist-in-Charge of Pathology Division(KFRI) and Late Prof. Takashi Okuyama for extending the facili-ties to carry out the wood decay studies and colour measurement inthe Department of Bio-material Physics, School of Bio-agriculturalSciences, Nagoya University, Japan, respectively. Our sincere thanksare due to Mr. T. S. Baburaj, Research Fellow for the help renderedin various ways in the pathology laboratory. The able technical as-sistance rendered by Mr. K. K. Suresh and Mr. K. Praveen, ForestUtilisation Division in the laboratory investigation is acknowledged.We are grateful to Prof. Everett Hansen (Oregon State University)and Prof. Adam M. Taylor for their valuable comments in improvingthe manuscript.

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