Wood Quality Research Articles

Preparation and drying characteristics of poplar wood modified by hexacyclite

In recent decades, wood drying has emerged as an important method to ensure wood quality and improve wood utilization. However, the addition of modifiers to wood can hinder the transfer of moisture, making the drying process difficult. Therefore, the drying of modified wood is challenging. This study focuses on poplar wood and reports the preparation of modified wood capable of releasing health-beneficial negative oxygen ions. In particular, this study examined the effect of hexacyclite on the transfer of internal moisture and heat in wood. Hexacyclite was dispersed using sodium hexametaphosphate as a dispersing agent, and the modified poplar wood was prepared via vacuum pressure impregnation. The process involved six cycles of the following treatments: a vacuum treatment (−0.08 MPa, 20 min), followed by a pressure treatment (1 MPa, 120 min), and a final atmospheric treatment (5 min). The modified wood was dried via kiln drying, during which the overall wood temperature rapidly increased, with the total drying rate also increasing by 1.05%/h. The introduction of hexacyclite potentially altered the way modified wood bound with moisture, leading to permanent changes in the porosity of cell walls and the structure of polymers and thus altering the movement of water molecules. The modified wood continuously emitted far-infrared rays with a wavelength of 8–15 μm. In some large water clusters, after the far-infrared energy was absorbed, the movement of water molecules accelerated, thereby increasing the drying rate in the wood below the fiber saturation point. Ultimately, this resulted in the modified wood drying faster and thus exhibiting a better quality.

Advancements in Wood Quality Assessment: Standing Tree Visual Evaluation—A Review

(1) The early assessment of wood quality, even while trees are standing, provides significant benefits for forest management, sales efficiency, and market diversification. Its definition cannot be in absolute terms but must always be linked to the material’s intended use. (2) In this contribution, a review of the scientific literature is given to discuss the visually evaluable attributes that define wood quality in standing trees, the applicability of the techniques used for their assessment, and the effectiveness of these attributes and technologies in predicting quality, to finally highlight future research needs. (3) The visual characteristics generally used to evaluate wood quality are linked to stem form and dimension, branchiness, and stem damage, but their assessment is challenging due to time and resource constraints. To address these challenges, laser-based and image-based techniques have been applied in field surveys. (4) Laser scanners offer detailed and accurate measurements. Photogrammetry, utilizing images to reconstruct 3D models, provides a cost-effective and user-friendly alternative. Studies have demonstrated the effectiveness of these tools in surveying the visible properties of stems and branches, but further development is necessary for widespread application, particularly in software development, with faster and more effective algorithmic advancements for automatic recognition and subsequent measurement of pertinent characteristics being critical for enhancing tool usability. (5) However, predicting wood quality from these surveys remains challenging, with a limited correlation between the visible tree characteristics assessed and the sawn product quality. Empirical studies evaluating products downstream in the forest-wood supply chain could provide valuable insights. In this sense, the implementation of traceability systems could facilitate the linkage between data on standing trees and the quality of the sawn product. Also, further research is needed to develop models that can accurately predict internal tree characteristics and their impact on product quality.

Control of invasive conifers in temperate Andean forests promotes native vegetation restoration, but requires continuous management

Non-native conifers have been planted widely because of their growth potential and wood quality. However, many of them have become invasive in the introduced ranges. In Chile, the initial introduction of non-native conifers helped the recovery of degraded land, but today some pine species present a high invasion risk when they are not properly managed, leading to detrimental impacts on natural ecosystems and biodiversity. Such is the case of Douglas fir (Pseudotsuga menziesii), a species listed as invasive in south-central Chile, as well as in many other countries, when it establishes beyond the original plantation range. The main goal of this research was to characterize the invasion pattern of P. menziesii within a recently-declared protected area nearby the Conguillío National Park in the Andes Cordillera. We aimed at determining the key factors that promote the invasion of P. menziesii outside the original plantations. We established five 1,000 m2 sampling transects (i.e., 100×10 m), considering two invasion conditions: (i) within the native forest and (ii) far into open scrub areas, both adjacent to P. menziesii plantations. We measured forest structure, soil nutrients, the floristic composition and pine regeneration before and after controlling the invasion within each study conditions. We found that P. menziesii density and soil nutrient availability in the soil decreased with the distance from the plantation. In addition, an increase in native species cover was found after removing pines, but also noted the ability of P. menziesii to readily re-invade the native forest after removal. These results indicate the need for continuous control of P. menziesii, especially inside the native forest at the early stages of invasion. We discuss the need for better plantation management to prevent its spread into natural areas and protect native forests from non-native conifers invasion.

Permafrost melting enhances growth but leads to less intra-annual density fluctuations in boreal Larix gmelinii forests at its southernmost limit in northeast China

Permafrost melting due to climate warming in recent decades has produced significant effects on forest ecosystems, especially the boreal biome at its southernmost limit in Asia. How this warming affects wood formation of trees at intra-annual resolution is unclear, yet is crucial for assessing the impact of permafrost melting on boreal forest growth. In this study, we compared the radial growth and intra-annual wood density fluctuations (IADFs) of Dahurian larch (Larix gmelinii Rupr.) at a permafrost (PF) and a non-permafrost (NPF) site at the southernmost permafrost limit in northeast China and quantified their relationships with climate factors. Drought in early summer was the main factor limiting growth of Dahurian larch. The basal area increment (BAI) of trees at both sites increased initially and then decreased in the 1980s, probably in response to warm-dry climate conditions. Earlywood IADFs (IADF-E) occurred in 14.0% and 9.3% of dated rings at the NPF and PF sites, while the frequency of latewood IADFs (IADF-L) was 6.8% and 2.7% at these two sites. The frequency of IADF-E in trees at both sites was positively and negatively related to June temperatures (and vapor pressure deficit) and precipitation, respectively, suggesting drought stress in June triggered the formation of IADF-E. The IADF-Ls were probably formed in response to warm temperatures in the late growing season. A higher BAI and a lower frequency of IADF-Es of trees at the PF site than at the NPF site indicated that permafrost melting could alleviate drought stress in early summer and promote radial growth of Dahurian larch. This greatly improved forest carbon sequestration and wood quality of some northeastern Asian boreal forests may offset to some extent the adverse effects of warming-drying climates at some sites of northeast Asia. Larch IADF-Es recorded extreme droughts in early summer, giving us a new sight for reconstructing high-frequency extreme climate events. If climate warming continues, the benefits of permafrost melting will gradually disappear and even turn negative due to warmer-dryer climate conditions. Our findings provide valuable information for boreal forest management and conservation under future global warming.

Development of 51 K liquid-phased probe array for Loblolly and Slash pines and its application to GWAS of Slash pine breeding population

Loblolly pine (Pinus taeda) and Slash pine (Pinus elliottii) are important economically and ecologically tree species worldwide. To implement genomic based breeding strategy, genotyping large number of samples is needed. However, huge and complex pines genome make it difficult to obtain abundant and cost-effectively markers. In this study, we designed a SNP array containing 51 K liquid-phased probes based on the published SNPs and probes of the two species, novel Slash pine-specific long-read transcript, and SNPs obtained from a double digest Restriction-Site Associated DNA sequencing (ddRADseq). We performed targeted capture sequencing using the developed SNP array on three pine species of Loblolly, Slash, and Caribbean pine (Pinus caribaea). The probe capture had an efficiency of 68.26% on average. Principal Component Analysis (PCA), phylogenetic analysis, and genetic structure analysis of 28,670 SNPs genotyped for the three pine species demonstrated the transferability of the SNP array for the three pines. Furthermore, we genotyped 221 range-wide Slash pine genotypes, analyzed their genetic diversity and performed a genome-wide association study (GWAS). We identified 95 SNPs significantly associated with growth and wood quality traits of Slash pine. We have identified potential roles of the MYB2 and MYB46 transcription factors in regulating cell cycle and differentiation in Slash pine, while also suggesting that AP2/ERF and Glycosyl hydrolase may play significant roles in wood formation processes. This new SNP array can be widely applied in future molecular breeding research of conifers.

Wood Quality of Young Tectona grandis L. f. Trees and Its Relationship with Genetic Material and Planting Site in Mato Grosso, Brazil

Tectona grandis L. f. (teak) is highly valued in the international market, but its volume and properties vary depending on its genetic material and planting site. Evaluating these factors is crucial for promoting new plantations. Therefore, this study aimed to assess the impact of genetic material (clones TG1 and TG3 and seminal material) and planting site (Nova Maringá and Água Boa, Mato Grosso, Brazil) on morphological parameters (heartwood, sapwood, bark, pith proportions, and pith eccentricity), physical properties (shrinkage and air-dry density), and mechanical properties (static bending strength—fm, compressive strength—fc0, Janka hardness—fH90, and shear strength—fv0). For this purpose, we sampled five trees aged 13 years per genetic material from commercial plantations. In Nova Maringá, trees exhibited, on average, 56.07% heartwood, while in Água Boa, this value was less than 50%. Seminal material showed the lowest percentage of heartwood (49.2%). The pith percentage was significantly greater in Água Boa than in Nova Maringá, regardless of the genetic material. We observed the highest standard deviation (5.61) in pith eccentricity for the seminal material. Both the planting site and genetic material influenced the air-dry density (~12% moisture content), which ranged from 0.535 to 0.618 g·cm−3. Trees grown in Nova Maringá produced wood with higher dimensional stability than those from Água Boa, exhibiting a 14% lower radial shrinkage and a 6% lower volumetric variation. In Nova Maringá, the wood from the seminal material exhibited greater resistance. On the other hand, in Água Boa, that material showed lower resistance (fv0, fm, and fc0), or there was no significant difference (fH90) compared to the clonal materials. When comparing the clonal materials (TG1 and TG3) at each planting site, they demonstrated similar mechanical properties. The variability in physical and mechanical properties among different genetic materials and planting locations highlights the need to select appropriate teak genetic materials for each region. We concluded that more productive teak clones can be selected without compromising the physical and mechanical properties of the wood.

The feasibility of adding wood quality traits as selection criteria in the Galician Pinus pinaster Aiton breeding program: case study

The feasibility of adding wood quality traits as selection criteria in the Galician Pinus pinaster Aiton breeding program: case study

GROUPING OF CLONES OF 4-YEAR-OLD Eucalyptus spp. FOR PULP AND PAPER

As in other countries, In Brazil, new genetic materials of Eucalyptus spp. and their hybrids are multiplied through cloning. These materials, currently in experimental trials, must undergo several stages to select the best ones for pulp and paper production. Therefore, new studies on wood quality are essential. Therefore, this study aimed to group 11 clones of Eucalyptus spp. wood, from a clonal plantation in the municipality of Palmital, São Paulo State, for the production of paper and cellulose. For this purpose, four trees of each clone of 4-year-old Eucalyptus spp. were collected. From each tree, a log of 1 m in length was taken from the base of the tree, for the study of the characterization of the basic density and cellular dimensions of the wood. The results showed that there were significant differences between clones for basic density, fiber length, vessel element length and fiber wall thickness. The Runkel ratio, wall fraction and stiffness coefficient did not show significant differences between the different genotypes. From the results obtained, we can conclude that clones can be differentiated only by basic density, fiber length, vessel element length and fiber wall thickness. The Runkel index, flexibility coefficient and wall fraction of Eucalyptus spp. were more efficient to group the clones into two groups.

Effects of oil heat treatment on poplar wood properties: A pilot scale study

Pilot-scale oil heat treatment was conducted to enhance the quality of poplar wood obtained from a fast-growing plantation. Three target temperatures, namely 180, 190, and 200 ˚C, were chosen for the oil heat treatment process. Clear, small specimens were cut from the lumber, following the prescribed standards for assessing wood quality. Light microscopy revealed the ruptures and deformation of the wood cell wall as the treatment temperature increased. The volumetric swelling of the treated specimen decreased proportionally with the increase in treatment temperature. The impact of oil heat treatment on the mechanical properties of wood varied depending on the specific type of mechanical strength and processing temperature. The modulus of rupture, toughness, and hardness of the treated specimens drastically decreased at 200°C. However, the specimens treated at 200°C exhibited much lower mass loss during the fungal decay test. The results of the analytical test showed an increase in the crystalline cellulose content and thermal stability of the treated wood, due to the thermal degradation of hemicelluloses and amorphous regions of cellulose. Overall, it is concluded that oil heat treatment of poplar wood in the optimal temperature is an efficient approach to upgrade its quality with minimal reduction in mechanical strength.

Evaluating resistance drilling and NIR spectroscopy for quantifying wood quality of young eucalypts grown in Guangxi province in southern China

Cost-effective, non-destructive means of estimating wood properties of eucalypts grown in Guangxi, China, were evaluated using near infrared (NIR) spectroscopy and resistance drilling. For this evaluation, wood samples for NIR analysis and resistance drill measurements were collected from 581 trees, representing eight plantation Eucalyptus taxa across five sites. The near infra-red (NIR) spectra collected from the 581 wood samples were analysed using existing calibrations for kraft pulp yield, cellulose content, hot water extractives and Klason lignin. These spectra and calibrations were effective in predicting over 60% of the variance in total carbohydrates and over 80% of the extractives and lignin values from independent laboratory analysis of a subset of 100 samples. Resistance drilling combined with software developed for processing the drill data proved to be a quick, low cost and effective means of quantifying wood density (as amplitude of the drill torque), stem diameter and bark thickness.

The relationship between branch scar attributes and knot features in birch (Betula pendula and B. pubescens)

There is currently no quality sorting of harvested hardwood timber in Norway on a national scale. Medium- and high-quality logs including those from birch (Betula pubescens Ehrh., B. pendula Roth) are thus not utilized according to their potential monetary value. Increased domestic utilization of quality birch timber requires that the quality of harvested logs be properly assessed for potential end uses. A preferred sorting procedure would use visually detectable external log defects to grade roundwood timber. Knots are an important feature of inner log quality. Thus, the aim of this study was to evaluate whether correlations between branch scar size and knot features could be found in Norwegian birch. Using 168 knots from seven unpruned birch trees, external bark attributes often showed strong correlations with internal wood quality. Both length of the mustache and length of the seal performed well as predictors of stem radius at the time of knot occlusion. The presence of a broken off branch stub as part of an occluded knot significantly increased the knot-effected stem radius, proving that the practice of removing branches and branch stubs along the lower trunk is a crucial measure if quality timber production is the primary management goal.

Development of transgenic Paulownia trees expressing antimicrobial thionin genes for enhanced resistance to fungal infections using chitosan nanoparticles

There is an increasing focus on genetically altering Paulownia trees to enhance their resistance against fungal infections, given their rapid growth and quality wood production. The aim of this research was to establish a technique for incorporating two antimicrobial thionin genes, namely thionin-60 (thio-60) and thionin-63 (thio-63), into Paulownia tomentosa and Paulownia hybrid 9501 through the utilization of chitosan nanoparticles. The outcomes revealed the successful gene transfer into Paulownia trees utilizing chitosan nanoparticles. The effectiveness of thionin proteins against plant pathogens Fusarium and Aspergillus was examined, with a specific focus on Fusarium equiseti due to limited available data. In non-transgenic Paulownia species, the leaf weight inhibition percentage varied from 25 to 36 %, whereas in transgenic species, it ranged from 22 to 7 %. In general, Paulownia species expressing thio-60 displayed increased resistance to F. equiseti, while those expressing thio-63 exhibited heightened resistance to A. niger infection. The thionin proteins displayed a strong affinity for the phospholipid bilayer of the fungal cell membrane, demonstrating their capability to disrupt its structure. The transgenic plants created through this technique showed increased resistance to fungal infections. Thionin-60 demonstrated superior antifungal properties in comparison to thio-63, being more effective at disturbing the fungal cell membrane. These findings indicate that thio-60 holds potential as a novel antifungal agent and presents a promising approach for enhancing the antimicrobial traits of genetically modified Paulownia trees.

The economic evaluation of timber obtained from Norway spruce and scots pine grown under different thinning regimes in Lithuania

ABSTRACT In Lithuania, no studies have determined the relationship between the quality and economic benefits of Norway spruce and Scots pine wood based on age, stand density, and various forest management technologies. This study aims to assess and compare the economic benefits of Norway spruce and Scots pine in stands of different initial densities, depending on different forest management measures. This study calculated different pre-commercial thinning intensities 4 times, 3 times, and 2 times and final thinning profitability by stand volume and wood quality parameters modulus of elasticity and bending strength. Moreover, thinning intensities included three initial stand densities of 3000–3100, 2000–2100, and 1000–1100 trees per hectare, and different thinning regimes when the stand was thinned from below at the age of 8–9, 15, 21, and 35 years. The results showed higher profitability in the pre-commercial thinning of low-intensity with higher frequency − 4 thinning operations over the 40 years. However, the high-thinning intensity − 2 thinning operations over 40 years – applied in young Norway spruce and Scots pine stands will reduce wood quality and profitability in the future. The study found that stand thinning of low intensity tends to improve wood quality and the profitability that depends on it. After assessing the wood quality, it turned out that the 40-year-old Scots pine trees were too young to harvest because of low wood quality. However, the timber from Norway spruce trees could be used profitably if there is a market demand.

Relationship Between Wood Properties and Drying Qualities at Three Age Groups of Mindi (Melia azedarah L) Tree for Furnitur Materials

All wood based products should have been dried to ensure their stable dimension. Indicators of stable dimension can be figured-out from wood physical properties, especially ratio of tangensial shrinkage to radial shrinkage (T/R ratio) and wood drying properties at high temperature. From those two indicators could be predicted the drying quality of wood as a basic to determine minimum – maximum of drying temperature. This research aimed to look-into the relationship between wood properties of wood and drying quality of mindi (Melia azedarach L)wood at their 5, 9, and 13 year-old trees. The preparing of test samples, and testing methods on wood physical properties covered moisture content, air-dry density, and shrinkage in tangential and radial direction, which referred to the BS 1957. Meanwhile, drying properties followed the modified Terazawa’s method. Five classes of wood drying qualities could be derived from the analysis of T/R ratio and drying property at each tree age group. Results revealed that wood density ranged about 0.46 – 0.58 g/cm3. Drying quality of each wood (except the portion near the pith) belong to B (good) for 13 years old, C (fair) for 9 years, and D (poor) for 5 years old. Related to the drying quality, the minimum – maximum temperature for 13 years mindi wood was 55–85 oC; for 9 years was 50–80 oC; and for 5 years was 40–65 oC. Supported by the performance of wood surface, especially at 13 years old, mindi wood was suitable for wooden furniture.

Moisture changes and surface checking development during drying of Masson pine wood

Deformation and surface-checking defects in wood are closely related to the drying stress caused by shrinkage and moisture content (MC) gradients throughout the drying process. In this study, 50-mm-thick Masson pine (Pinus massoniana Lamb.) lumber was used as the research object. The drying stress caused by shrinkage behavior and MC changes was monitored, and the development of surface checks was observed during the drying process. Results showed that when the average MC was 60%, the free water in the surface layer of lumber evaporated completely, causing the MC to decrease below the fiber saturation point (FSP). The surface layer was subjected to tension stresses, resulting in surface checks which primarily distributed in the latewood area and propagated longitudinally. When the average MC was between 30% and 40%, the combined effects of the high MC gradient and anisotropic shrinkage of the wood resulted in further expansion of the checks. As the average MC decreased to less than 20%, the MC of the core layer lumber decreased below the FSP, resulting in the closure or even disappearance of most surface checks. The critical point (average MC of 60%) of drying stress was obtained, which can benefit the fine-tuning of kiln-drying schedules and improve the drying quality of Masson pine wood.

Radial distribution of heartwood extractives in second-growth western redcedar

Western redcedar has high economic value and has been traditionally used for cultural purposes by Indigenous communities. Second-growth redcedar is potentially growing faster due to lower planting densities, fertilization, and tree breeding. Little quantitative information is available about the impact of management practices on wood quality, particularly heartwood extractives. This study evaluated the effects of growth rate and site on heartwood extractives at two locations aged 70–90 years in British Columbia, Canada. A three-parameter sigmoid model was fit to the data using nonlinear mixed effects to analyze the relationship between heartwood extractives relative to cambial age, growth rate, and sampling site. The southern site had significantly higher cumulative extractive concentrations, while all extractive concentrations increased faster. This study shows that smaller trees will reach their peak concentrations earlier than larger trees. Results show that faster growth through active management of western redcedar may lead to increased and more uniformly distributed content of heartwood extractives.

Fenotipos sobresalientes de Pinus chiapensis y Pinus douglasiana en rodales bajo manejo forestal en Oaxaca

In some areas of Oaxaca, Mexico, it is necessary to implement plantations that use seeds of genetic quality, to increase productivity and phenotypic quality. The objective was to select outstanding phenotypes of Pinus chiapensis (Martínez) Andresen and P. douglasiana Martínez, evaluating quantitative and qualitative characteristics. In 2021, 15 superior phenotypes per species were selected to evaluate inventory variables (height, diameter), density (trees ha-1), age and chip increments, recording climate and site data. Crown area (m2), basal area (m2) and total volume with bark (VTcc, m3) were determined for each tree; site index (SI) was determined based on anamorphic curves, density guides and average VTcc. Data were analyzed with Student's t tests, Pearson's correlation (a = 0.05), cluster analysis, and principal component analysis. The species showed significant differences (p ≤ 0.01) in dasometric characteristics. Using the average volume as a selection criterion, six P. chiapensis trees presented volumes above average (≥ 9.76 m3) and seven P. douglasiana trees presented volume above average (> 4.14 m3) and clear stem height (18.7 m), in places with high precipitation; while comparing morphological, of site and climatic characteristics, 10 individuals of P. chiapensis and six of P. douglasiana with excellent quality IS were selected. The selected trees have outstanding characteristics of wood quality and volume, so it is convenient to use them to collect seeds in the study area.

Clonal Evaluation and Genetic Divergence Studies in Mulberry Genotypes

Aims: This study aims to evaluate the wood quality and leaf quality traits of selected mulberry clones and assess the genetic divergence among them, providing valuable insights for the development of superior genotypes with enhanced economic value for the sericulture and agroforestry sectors.
 Study design: Twenty-one genetic resources of mulberry were collected from various regions in India and evaluated through clonal test in a Row Column Design to assess growth attributes and genetic divergence.
 Place and Duration of Study: The study was conducted in India, and the systematic progeny test and clonal evaluation were carried out in Forest College and Research Institute, Mettupalayam during 2018-2022.
 Methodology: The selected clones were evaluated for growth attributes such as plant height, diameter at breast height (DBH), volume, number of branches, leaf length, leaf width, petiole length, number of leaves, and leaf area. Genetic divergence was estimated using D2 statistics, and clustering of clones was performed using the 'GENRES' statistical package.
 Results: The study identified several clones with significantly higher growth attributes, highlighting their potential for selection in breeding and cultivation programs. Variability and heritability studies indicated that volume exhibited the highest heritability, suggesting strong genetic control and potential for improvement.
 Conclusion: Clones MI-0718, MI-0807, and MI-0845 showed superior growth performance and genetic divergence, indicating their suitability for further breeding and improvement programs. The study provides insights into the genetic variability of mulberry clones and emphasizes selecting superior clones for enhancing wood volume and overall productivity.

Methods for kino evaluation and estimates of genetic parameters in Corymbia

Species within the genus Corymbia are regarded as potential alternatives to Eucalyptus. In addition to having superior wood quality, Corymbia spp. are tolerant to most pests, diseases, and abiotic stresses that affecting Eucalyptus plantations, including physiological disorders, water deficit, and wind damage. However, environmental stresses stimulate kino production, which decreases the quality of pulp and sawn wood. This study aimed to develop a method for evaluating kinoand estimate genetic parameters in Corymbia. For this, 16 Corymbia (C. citriodora × C. torelliana) hybrid clones and 5 clones of Eucalyptus were used. Two evaluation methods (M1 and M2) were tested for kino evaluation; M1 consisted of drilling the bark with Pilodyn and M2 consisted of drilling the heartwood with Pilodyn. The following kino parameters were evaluated: exudation incidence, exudate length which flowed over the stem, and exudate weight. Genetic parameters were estimated by a mixed model method (REML/BLUP). The significance of random effects of the statistical model was tested by the likelihood ratio test. Significant clone effects were obtained for all kino parameters, except for exudate length as assessed by M2. Kino parameters determined by M1 exhibited higher heritability and accuracy. Therefore, M1 should be preferred for kino evaluation in Corymbia.

A dual-parameters microwave measurement approach for spruce moisture content

ABSTRACT Moisture content (MC) serves as a pivotal metric for assessing the wood quality, impacting crucial properties such as density, stiffness, and strength. Accurate determination of MC is imperative for ensuring quality and meeting specifications. This study introduces a novel dual-parameters microwave measurement methodology designed for precise MC quantification in spruce. By analyzing the sensitivity and linearity of the S21 with MC across both the S and X bands, we identify the most effective measurement parameters. Experimental work further investigates the correlation between the amplitude and phase of S21 and the MC in spruce, laying the groundwork for a comprehensive understanding of moisture influence on wood properties through microwave techniques. Finally, considering the impact of MC on both the amplitude and phase of S21, we introduce a dual-parameters microwave approach for accurately determining spruce MC. This method has been validated through case studies in both X and S bands. Our discussion extends to the effects of wood material characteristics, moisture distribution within samples, wood texture directions, and specimen dimensions on S21. Experimental results confirm that this approach significantly improves the precision of MC measurements in spruce, achieving an error rate of 0.15% in X band and 0.49% in S band measurements.