Near-infrared spectroscopy prediction of southern pine No. 2 lumber physical and mechanical properties

This study investigated near-infrared spectroscopy (NIRS) to rapidly estimate physical and mechanical properties of No. 2 2 × 4 southern pine lumber. A total of 718 lumber samples were acquired from six mills across the Southeast and destructively tested in bending. From each piece of lumber, a 25-mm-length block was cut and diffuse reflectance NIR spectra were collected from the transverse face using a FOSS 5000 scanning spectrometer. Calibrations were created using partial least squares (PLS) regression and their performance checked with a prediction set. Overall moderate predictive ability was found between NIRS and the properties for the calibration and prediction sets: block specific gravity (SG) (R ² = 0.66 and R _p ²  = 0.63), lumber SG (0.54 and 0.53), modulus of elasticity (MOE) (0.54 and 0.58), and modulus of rupture (MOR) (0.5 and 0.4). Model performance for MOE (R _p ²  = 0.70) and MOR (R _p ²  = 0.50) improved when performing PLS regression on a matrix containing lumber SG and NIR spectra. Overall NIRS predicted MOE better than linear models using lumber SG (R ² = 0.46), whereas lumber SG (R ² = 0.51) predicted MOR better than NIRS. Overall NIRS has reasonably good predictive ability considering the small volume of wood that is scanned with the instrument.     

Nondestructive evaluation of drying stress level on wood surface using near-infrared spectroscopy

A nondestructive technique for swiftly measuring the stress level of the surface of wood is proposed, which is important for process control in timber drying. Partial least squares (PLS) regression models for predicting surface-released strain (ε) were developed using NIR spectra obtained from Sugi (Cryptomeria japonica D. Don) samples during drying. The predictive ability of the models was evaluated by PLS analysis and by comparing NIR-predicted ε with laboratory-measured values. The PLS regression model using the NIR spectra pre-processed by MSC and second derivatives with a wavelength range of 2,000–2,220 nm showed good agreement with the measurement (R ² = 0.72). PLS analysis identified the wavelengths around 2,035 nm as making significant contributions to the prediction of ε. Orthogonal signal correction (OSC) was an effective pre-processing technique to reduce the number of factors required for the model using the wavelength range 1,300–2,500 nm. However, the predictive ability of the OSC-corrected model was not improved. Elapsed times to reach the maximum tensile stress (T _max) and the stress reversal point (T _rev) at the wood surface during drying were detected correctly for 75 % of the samples. The results show that NIR spectroscopy has potential to predict the drying stress level of the timber surface and to detect critical periods in drying, such as T _max and T _rev.     

Near-infrared spectroscopy and wavelength selection for estimating basic density in Mimosa tenuiflora [Willd.] Poiret wood

The aim of the present work was to estimate the basic wood density of Mimosa tenuiflora by using near-infrared spectroscopy (NIRS). Fifty-eight wood samples representing sapwood, heartwood and pith were evaluated by gravimetric method and NIRS together with wavelength selection methods. A comparison was made among several multivariate calibration techniques and algorithms for preprocessing and variable selection of data, including full-spectrum partial least squares (PLS), interval PLS, backward interval PLS, synergy interval PLS, genetic algorithm-PLS and successive projections algorithm for interval partial least squares (iSPA–PLS). Finally, the results obtained using iSPA–PLS model for the root mean square error of calibration and prediction were 0.0383 and 0.0166 g/cm³, respectively. A t-test was performed to compare the results of the models with each other and with a reference method. NIRS and iSPA–PLS can be used to predict basic density of Mimosa tenuiflora [Willd.] Poiret wood samples rapidly. In addition, the basic density could also be predicted with only 17 wavelengths in the range from 2,090 to 2,208 nm that should allow for measurement of this parameter using handheld NIR spectrometer.     

Comparative studies on microstructures and chemical compositions of cell walls of two solid wood floorings

Two common wood flooring materials, taun (Pometia spp.) and cumaru (Dipteryx odorata), were used as investigated objects and comparison was made between the two wood species for their density, microstructure, microfibril angle (MFA), cellulose crystallinity and the main chemical composition. Results showed that the density of cumaru was 0.941 g·cm^?3, significantly larger than that of taun, 0.737 g·cm^?3. The biggest difference of two wood species in microstructures was fiber cells. Fiber cells of cumaru had dense cell walls, almost no cell lumens; while fiber cells of taun had relatively thin cell walls, with apparent cell lumens. The thickness of fiber cell wall of cumaru and taun were 6.80 and 2.82 µm, respectively, and the former is about 2.5 times thicker than the latter. Measured data of MFA indicated that the average MFA of cumaru was 11.7°, smaller than that of taun, 13.4°. The relative crystallinity of cumaru and taun were 54.0 and 50.8%, respectively. The two wood species had the similar holocellulose contents, but the lignin content of cumaru was higher than that of taun, especially that the content of extractive of cumaru was as twice as that of taun.     

In situ measurement of tensile elastic moduli of individual component polymers with a 3D assembly mode in wood cell walls

We attempted to measure in situ the tensile elastic moduli of individual component polymers with a three-dimensional (3D) assembly mode in the cell walls of Sugi (Cryptomeria japonica D. Don) without isolating the polymers. To prepare wood tangential slices [50 × 6 × 0.2 mm (L × T × R)] consisting of lignin with a 3D assembly mode in the cell walls, cellulose and hemicellulose were removed using the method of Terashima and Yoshida (2006) to obtain methylated periodate lignin slices. To prepare wood slices consisting of polysaccharide with a 3D assembly mode in the cell walls, lignin was removed using the method of Maekawa and Koshijima (1983) to obtain holocellulose slices. Static tensile test was applied to determine the elastic moduli of 3D lignin and 3D polysaccharide slices. The followings were revealed. The elastic modulus of the 3D lignin slices was 2.8 GPa, regardless of the microfibril angle (MFA) in the slices. The elastic moduli of the 3D polysaccharide slices with MFAs of 14°, 23°, 34°, and 42° were 18, 12, 9, and 4 GPa, respectively. The former shows that the lignin with a 3D assembly mode behaves as an isotropic substance in the cell walls, while the latter suggests that the 3D polysaccharide slice shows marked anisotropic structure in the cell wall. Despite the fact that cellulose content increased after lignin removal, values of substantial elastic modulus of the cell wall slightly decreased regardless of MFA. Following two possible reasons were pointed out for explaining this phenomenon. First, lignin removal caused an artifactual deterioration in the polysaccharide slices at the level of macromolecular aggregate. Second, rigid and fusiform-shaped cellulose crystallites are dispersed in the soft matrix of amorphous polysaccharide, and those are loosely connected to each other by the intermediary of matrix polysaccharide. Those suggest that the rigid cellulose crystallite can optimize its strong mechanical performance in the polysaccharide framework of the wood cell wall in combination with the ligninification.     

Colorimetric and vibrational spectroscopic characterization of weathered surfaces of wood and rigid polyvinyl chloride–wood flour composite lumber

Rigid polyvinyl chloride–wood flour composite lumber containing either pine or maple wood flour and pine and maple lumber was subjected to accelerated weathering according to the ASTM Standard G 53 protocol. Non-weathered and weathered surfaces of all specimens were analyzed using colorimetric methods, reflectance infrared Fourier transform and Raman spectroscopic techniques. In the FT-IR spectra, conjugated ketones (1,744 cm^?1) of lignin as evidenced by their skeletal vibrations (1,560–1,500 cm^?1) and stretching (1,440–1,500 cm^?1) were reduced in weathered specimens. Cellulose was largely unaffected by weathering. C–O bending vibrations at 1,040 cm^?1 from holocellulose in pine specimens and intensity bands at 1,125–1,090 and 1,360 cm^?1 (C–O stretching and O–H bending from cellulose) in the maple and wood–plastic composite (WPC)-maple specimens were unaffected. A band at 1,650 cm^?1 became prominent after weathering of both pine and maple WPC specimens which is due to C=C–C=C stretching vibration of weathered PVC portion of the specimen. Raman shifts at 530 and 840–900 cm^?1 are attributed to C–O and C–C–O stretching in cellulose (remain unchanged). The role of extractives in weathering of pine is shown by the disappearance of Raman shifts at 392 and 434 cm^?1 (C=C deformations in pine extractives) in weathered pine. One-Way ANOVA, between-group designs showed significant effect on brightness (L*), redness (a*) and yellowness (b*) for all treatments.     

Changes of chemical properties and the water vapour sorption of <Emphasis Type="Italic">Eucalyptus pellita</Emphasis> wood thermally modified in vacuum

The aim of this study was to evaluate the chemical composition and the dynamic water vapour sorption properties of Eucalyptus pellita wood thermally modified in vacuum. For this purpose, wood samples were thermally modified in a vacuum oven at 160–240 °C for 4 h. Chemical composition were investigated by wet chemical analysis, elemental analysis, as well as Fourier transform infrared (FTIR) analysis, and dynamic water vapour sorption properties were evaluated by dynamic vapour sorption apparatus. The results showed that holocellulose and alpha-cellulose contents decreased and lignin and extractives contents relatively increased during the heat process. Elemental analysis showed a reduction in hydrogen content and an increase in carbon content. FTIR analysis indicated that the degradation of hemicellulose and condensation reactions of lignin occurred. In addition, the thermo-vacuum resulted in a reduction in the equilibrium moisture content of wood during the adsorption or desorption process. And the sorption hysteresis had a decreasing trend with increasing treatment temperature. The development of the hygroscopicity was related to the increase in the relative content of lignin, the degradation of the carbonyl groups in xylan and the loss of carbonyl group linked to the aromatic skeleton in lignin after heat treatment.     

Enzymatic hydrolysis of wood with alkaline treatment

Pulverized samples of wood, cedar and eucalyptus were treated with 5 N NaOH solutions at 25–150 °C. Hemicellulose and lignin content in the samples decreased with increasing treatment temperatures, while the recovery of glucose was maintained at nearly 90 %. X-ray diffraction analysis showed that the content of the original cellulose I structure in the samples decreased with increasing temperature, and most of the cellulose in the sample treated at 150 °C was converted to cellulose II by mercerization. Enzymatic hydrolysis of the alkaline-treated samples was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The samples treated at higher temperatures showed better enzymatic degradability. Treatment with an alkaline solution of lower concentration (1 N NaOH) at 150 °C was also used. Despite significant quantities of hemicellulose and lignin being removed, mercerization was not induced. The enzymatic degradability was much lower than that of the sample treated with a 5 N NaOH solution at 150 °C. Thus, treatment with concentrated alkaline solution at high temperature led to not only the removal of hemicellulose and lignin, but also to modification of the cellulose structure, which resulted in high efficiency of enzymatic saccharification of the wood samples.     

Variation analyses of growth and wood properties of <Emphasis Type="Italic">Larix olgensis</Emphasis> clones in China

The growth traits (tree height, diameter at breast height, and stem straightness degree) and wood properties [wood density (WD), fiber length, fiber width, ash content (AC), lignin content, cellulose content, hemicellulose content (HEC), and holocellulose content] of 208 26-year-old Larix olgensis clones were analyzed. Except for WD and AC, there were significant differences (p < 0.01) for all traits among clones. The phenotypic coefficient of variation and repeatability of all traits were 9.34–35.33% and 0.218–0.930, respectively. Tree height and diameter at breast height showed significant positive correlation; however, the correlation coefficients among growth characteristics and wood properties were mostly not significant. Ten clones (L70, L56, L82, L90, L59, L91, L61, L92, L86, and L64) were selected as excellent clones under a selection rate of 5%, using tree height, diameter at breast height, and stem straightness degree as evaluation indexes, providing genetic gains of 28.69, 17.96, and 0.67%, respectively. Ten clones (L88, L305, L59, L66, L253, L304, L277, L298, L248, and L293) were selected as excellent clones using wood properties as an evaluation index, with a selection rate of 5%, providing genetic gains in WD, fiber length, fiber width, cellulose content, and HEC of 4.14, 3.64, 9.28, 6.77, and 9.61%, respectively. This study provides a theoretical basis for selecting excellent L. olgensis clones.     

Development and activity of early saproxylic fungal communities in harvested and unmanaged boreal mixedwood stands

Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.     

Chemical reactivity of heat-treated wood

Chemical reactivity of heat-treated wood was compared with that of untreated wood. For this purpose, heat-treated pine or beech sawdust was reacted with different carboxylic acid anhydrides in pyridine or with phenyl isocyanate in dimethyl formamide. Compared to controls, weight gains obtained with heat-treated sawdust are smaller showing a lower chemical reactivity. FTIR analyses of lignin and holocellulose fractions, isolated after acidic hydrolysis of polysaccharides or delignification with sodium chlorite, indicate that both components are involved in the reactions. Compared to lignin, holocellulose exhibits important infrared absorptions of about 1,730 cm⁻¹, characteristic of ester or urethane linkages formed. Lower reactivity of heat-treated sawdust is explained by the decrease in free reactive hydroxyl groups in holocellulose due to the thermal degradation of hemicelluloses, considered more reactive than cellulose.     

Recycled ionic liquid 1-ethyl-3-methylimidazolium acetate pretreatment for enhancing enzymatic saccharification of softwood without cellulose regeneration

In this work, pretreatment of wood meals using a recycled ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), enhanced glucose liberation by enzymatic saccharification, without dissolution of cellulose and lignin. In contrast, previous studies on IL pretreatment have mostly focused on lignocellulosic dissolution to regenerate cellulose and removing lignin. Softwood (Cryptomeria japonica) was pretreated with [Emim]Ac at 60–100 °C for 2–8 h without collecting regenerated cellulose. The pretreatment did not have a strong effect on wood component dissolution (weight of residues: 91.7–98.8%). The residues contained relatively high amounts of lignin (26.6–32.6%) with low adsorption of [Emim]Ac (0.9–2.7%). Meanwhile, the crystallinity index (C _r I) of cellulose in the wood was significantly reduced by pretreatment, from 50.9% to 28.4–37.1%. In spite of the high lignin contents in the residues, their glucose liberation values by enzymatic saccharification using a cellulase mixture were 3–16 times greater than that of untreated wood. A good correlation was found between the saccharification effectiveness of pretreated samples and the C _r I. Although lignin dissolved in [Emim]Ac continued to accumulate after repeated use of [Emim]Ac, the pretreatment was found to be effective for three consecutive cycles without the need to remove the dissolved materials.     

Liquefaction and product identification of main chemical compositions of wood in phenol

To clarify liquefaction ratios and their construction variations of the main chemical compositions of wood in phenol using phosphoric acid as a catalyst, the chemical ingredients of wood such as holocellulose, cellulose and lignin, were measured and extracted according to GB methods. With Fourier transform infrared （FTIR）, the product identification of reactant before and after liquefaction in phenol was investigated. The molecular weights and their distributions of the liquefaction results （acetone soluble parts） were studied by gel permeation chromatography （GPC）. Results show that the molecular weights and their distributions of poplar and Chinese fir are almost the same. In poplar, the distribution of cellulose is the largest, and that ofholocellulose the smallest after liquefaction. For Chinese fir, the distribution of holocellulose is the largest, and that of cellulose the smallest. After liquefaction of poplar cellulose, the change bands of FTIR spectrum observed below 1 600 cm^-1, can be attributed to new substitute groups. The same is true for poplar lignin. For Chinese fir, the spectra of liquefaction results of all chemical compositions differ from that of wood meal. This reveals the more activity groups were produced because of the reactions between Chinese fir and phenol. The research shows that the liquefaction ratios of poplar decrease in the following order： holocellulose 〉 lignin 〉 cellulose, and those of Chinese fir in the order： lignin 〉 cellulose 〉 holocellulose.     

Spectral image database for observing the quality of Nordic sawn timbers

In this study, a comprehensive spectral image database of Nordic sawn timbers for public use was measured. Economically significant Finnish wood species birch (Betula sp.), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) were chosen for inclusion in the database. The total of samples was 107 containing heartwood, sapwood, decayed wood, blue stain, mold, resin, early wood, late wood, knots, cracks, pith, reaction wood and bark. Board and crosscut samples were measured in frozen, melted and room-dried conditions. The reflectance of samples was measured over a 300- to 2,500-nm wavelength range. Additionally, the photoluminescence of samples excited by an ultraviolet B light source was measured. The spot size used was 250 μm with an 80 mm \(\times \) 200 mm imaging area, and produced all in all 44 million spectra. In this paper, examples of the possibilities of this spectral image database as a means of detection of the spatial distribution of aromatic lignin and the moisture content (MC) of nonfrozen timber were introduced and provided. From the results, it was found that it was possible to detect the lignin distribution from spectral images, and simple and robust methods for wood MC estimations were also introduced.     

Impact of thermal modification on color and chemical changes of spruce and oak wood

Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and chemical changes in spruce (Picea abies L.) and oak wood (Quercus robur F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the L*a*b* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-O-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.     

马尾松木材化学组分的遗传控制及对木材育种的意义

本文利用 1 3年生马尾松子代测定林的 2 0个自由授粉家系的木材试样 ,着重研究木材化学组分的遗传学问题。研究结果表明 ,木材化学组分、基本密度和生长性状在家系间的差异都达到了极显著水平 ,并受中等至强度的遗传控制。在 6个木材化学组分中 ,灰分、戊聚糖和 1 %NaOH抽出物含量的遗传力较高 ,木质素、综纤维素和热水抽出物含量的遗传力稍低。生长性状与木材密度呈显著的负相关 ,而与木材化学组分相关性很小 ,似相互独立。遗传相关认为灰分和热水抽出物含量可分别作为综纤维素和木质素的间接选择指标。由于综纤维素和木质素含量在家系间的绝对差异较小 ,仅为 2 %～ 3% ,对选育的实际意义不大。可选择综纤维素含量高的优株进行无性繁殖加以利用     

人工林米老排木材化学成分及其在树干高度上的变异

采用我国木材化学成分分析国家标准,对人工林米老排木材化学成分进行了测定和研究分析.结果表明:人工林米老排木材冷水抽提物含量和热水抽提物含量分别为2.67%和3.12%,1%NaOH抽提物含量为17.08%,纤维素含量为47.49%,综纤维素含量为80.42%,木素含量为28.80%,pH值为5.44;木材冷水抽提物和综纤维素含量在树干的不同高度上略有差异,但方差分析检验,差异不显著,热水抽提物、1%NaOH抽提物、纤维素和木素含量在树干的不同高度上差异显著,达到1%显著性水平;由树基往上,热水抽提物含量略呈两端高、中间低的趋势,冷水抽提物、1%NaOH抽提物和木素的含量逐渐降低,综纤维素含量和木材pH值逐渐升高;纤维素含量在树干上的分布规律为中间高、两端低,而且从树干中部往上的降低幅度较大.     

Longitudinal shrinkage behaviour of compression wood in radiata pine

The behaviour of longitudinal shrinkage was investigated in the corewood of a swept, 17-year-old New Zealand radiata pine stem. Wood categories in terms of normal wood, mild compression wood and severe compression wood were identified microscopically using autofluorescence of lignin. Average longitudinal shrinkage was collated according to corewood location and wood category within corewood in the leaning and the vertical parts of the stem, and then maximum radial difference of longitudinal shrinkage within growth ring was examined. The results show that the average longitudinal shrinkage is significant (2.4%) in the corewood of the leaning part of the stem. Among wood categories, severer compression wood displays the highest (2.9%) average longitudinal shrinkage. In the context of this study, growth rings may consist of one of three types of wood: (1) only normal wood; (2) a single compression wood type; and (3) mixed-type wood. Where multiple compression woods co-existed with normal wood, the maximum radial difference of longitudinal shrinkage within the growth ring was found to be 4.0%. A strong correlation (R ² = 0.90) between average MFA and average longitudinal shrinkage suggests a significant influence of the average MFA on average longitudinal shrinkage across the three growth ring types.     

Application of VIS/NIR spectroscopy for estimating chemical,physical and mechanical properties of cork stoppers

The aim of this study was to evaluate the potential of visible and near infrared spectroscopy (Vis/NIRS) in predicting the chemical, physical and mechanical behavior of single-piece natural corks stoppers used for sealing wine bottles. Two training sets of 90 and 150 cork stoppers were used to obtain four spectra per sample in different positions: two of the stopper bases (transversal section) and two of the stopper sides (tangential section and radial section). The samples were scanned in the range of 400–2,500 nm using a Foss-NIRSystems 6500 SY II spectrophotometer equipped with a remote reflectance fiber-optic probe. On each training set, two-thirds of the samples were used to develop modified partial least square (MPLS) calibration equations, and the remaining one-third of the sample for the external validation of these MPLS equations. The best equations were obtained for the transversal section, which is the recommended one when applying Vis/NIRS technology to cork. The best results for the chemical composition were obtained for waxes and total polyphenols, showing coefficient of determination of the cross validation (r _cv ² ) values of 0.64 and 0.56 and coefficient of determination of the external validation (r _EV ² ) values of 0.53 and 0.55, respectively. The best equation for the physical and mechanical parameters was obtained for moisture content (r _cv ²  = 0.86 and r _EV ²  = 0.85), with somewhat lower results for density, compression force and extraction force (r _cv ²  = 0.66, 0.72, 0.52 and r _EV ²  = 0.52, 0.49, 0.51, respectively). The SECV (standard error of cross validation) and SEP (standard error of external validation) were similar for all the physical and mechanical parameters, thus confirming the robustness of the equations. MPLS model for moisture content fulfills the requirements for screening (RPD >2.5), but MPLS models obtained for waxes, total polyphenols, density, compression force and extraction force are not good enough for routine analysis or quality control. The results obtained from the MPLS models based on Vis/NIRS technology would permit the continuous quality control of humidity in the production line as well as obtaining information about certain chemical components (extractives contents) and some physical and mechanical parameters (density, extraction force and compression force).     

Evaluation of intra-ring wood density profiles using NIRS: comparison with the X-ray method

Key message

Pith-to-bark wood density profiling is interesting in forestry science. By comparing it with the X-ray method, this study proved that a fiber optic NIR spectrometer with a high-precision displacement system could accurately measure intra-ring wood density with a spatial resolution of 0.5 mm.

Context

Most near-infrared spectroscopy (NIRS) studies for wood density determination use samples that have been pulverized beforehand. Attenuation of ionizing radiation is still the standard method to determine wood density with high spatial resolution. However, there is evidence that NIRS could be an accurate and affordable method for determining intra-ring density in solid wood strips.

Aims

In this study, we research whether the results published for intra-ring density predictions in wood can be improved when calibrated with X-ray microdensitometry.

Methods

The measurements were made using a fiber optic probe with a separation between measurement points of 0.508 mm in a range between 1200 and 2200 nm. A total of 4520 density points were used to create partial least squares regression (PLSR). X-ray densitometry data were used as reference values. Twenty PLSR calibrations were randomly executed on 31 samples collected from 28 Pinus radiata D. Don trees.

Results

Upon selecting 20 latent variables, the R ² value was 0.873 for the training group and 0.895 for the validation group, while RMSEP values are 43.1 × 10^?3 and 47.1 × 10^?3 g cm^?3 for the training and validation groups, respectively. The range error ratio (RER) was 13.7.

Conclusion

The RER was high and almost in the range suggested for quantification purposes. Results are superior to wood density studies in the literature which do not employ spatial resolution and to those found in studies using hyperspectral imaging.