Wood Constituents Research Articles

Chemical changes of polysaccharides in heat-treated European beech wood

This work deals with the influence of different heat treatment temperatures (140, 150, 160, 170, 180, 190, 200, and 210 °C) on changes in sapwood and red heartwood of European beech (Fagus sylvatica L.). According to the results of wet chemistry methods, HPLC (high-performance liquid chromatography), FTIR (Fourier transform infrared spectroscopy), SEC (size exclusion chromatography), the wood constituents in sapwood and red heartwood behaved similarly to heat treatment, but the individual proportions were different. The loss of hemicelluloses and the increase in extractives with increasing temperature were more pronounced in sapwood. The amount of cellulose in sapwood and red heartwood showed similar behaviour with increasing temperature. Thermal treatment causes changes in cellulose crystallinity, and the formation of aromatic structures, mainly in beech sapwood. However, the increase in the lignin content of red heartwood was significantly lower than that of sapwood due to its auto condensation, and formation of pseudo-lignin. Among the carbohydrates, the most significant changes were observed in xylose content, which was almost twice as high in red heartwood as in sapwood. Other carbohydrates (glucose, mannose, galactose, and arabinose) reached similar values in sapwood and red heartwood.

Self-Neutralizing Melamine-Urea-Formaldehyde-Citric Acid Resins for Wood Panel Adhesives.

In this study, we used a self-neutralizing system to counteract too acidic a pH, unsuitable for wood adhesives, and tested it on MUF resins augmented by the addition of citric acid or other organic acids, based on the addition of small percentages of hexamine or another suitable organic base to form an acid-base buffer. In this manner, the pH of the adhesive was maintained above the minimum allowed value of 4, and the strength results of wood particleboard and plywood bonded with this adhesive system increased due to the additional cross-linking imparted by the citric acid. Thus, the wood constituents at the wood/adhesive interface were not damaged/degraded by too low a pH, thus avoiding longer-term service failure of the bonded joints. The addition of the buffering system increased the strength of the bondline in both the plywood and particleboard, both when dry and after hot water and boiling water tests. The IB strength of the particleboard was then increased by 15-17% when dry but by 82% after boiling. For the plywood, the shear strengths when dry and after 3 h in hot water at 63 °C were, respectively, 37% and 90% higher than for the control. The improvement in the bonded panel strength is ascribed to multiple reasons: (i) the slower, more regular cross-linking rate due to the action of the buffer; (ii) the shift in the polycondensation-degradation equilibrium to the left induced by the higher pH and the long-term stability of the organic buffer; (iii) the additional cross-linking by citric acid of some of the MUF resin amine groups; (iv) the already known direct linking of citric acid with the carbohydrates and lignin constituents at the interface of the wood substrate; and (v) the likely covalent linking to the interfacial wood constituents of the prelinked MUF-citric acid resin by some of the unreacted citric acid carboxyl groups.

Tenacity of Animal Disease Viruses on Wood Surfaces Relevant to Animal Husbandry

The aim of this study was to analyse the hygienic suitability of wood often used in animal husbandry. To this end, the inactivation of viruses (Enterovirus E as a surrogate for non-enveloped viruses and Newcastle disease virus as a surrogate for enveloped viruses) on germ carriers consisting of various types of wood was studied over an extended period to assess the biosafety of wood as an agricultural building material. The study was designed to assess the intrinsic biocidal activity of the wood itself, without the use of a disinfectant. The laboratory tests were based on German test guidelines and current European standards. Five different types of wood germ carriers, i.e., spruce (Picea abies), pine (Pinus sylvestris), poplar (Populus sp.), beech (Fagus sylvatica) and Douglas fir (Pseudotsuga menziesii), as well as stainless-steel carriers, were inoculated with enveloped and non-enveloped viruses and stored for up to four months, and the remaining infectivity of the viruses was continuously assessed. The results showed that intact, finely sawn timber with a low depth of roughness had an inactivating effect on the viruses up to 7.5 decadal logarithmic levels. For the non-enveloped virus, inactivation was fastest on Douglas fir wood, with the target reduction for effective inactivation (reduction by factor 4.0 log10) being achieved after two weeks, and for the enveloped virus on pine wood, it was already achieved from the day of drying. The hygienic effects of the wood carriers may be due to their hygroscopic properties and wood constituents. These effects offer potential for further investigation, including tests with other wood species rich in extractives.

Characterization of modern and waterlogged archaeological cypress (Glyptostrobus pensilis) wood: An analytical pyrolysis (Py-GC-MS and THM-GC-MS) and infrared spectroscopy (FTIR-ATR) study of within tree (radial) and decay-induced compositional variations

A fundamental understanding of the composition of archaeological wood stored under oxygen-limited environments, such as waterlogged sediments, is needed to inform preservation conditions of remains and to evaluate the validity of sediment and tree core-derived proxies of past environmental conditions. For this purpose, we determined chemical changes along the radial direction of archaeological (∼2000 yrs old) and modern (growth period 1948 to 2018 CE) wood of the Chinese swamp cypress (Glyptostrobus pensilis), an ethnobotanically important species in subtropical China, using conventional analytical pyrolysis (pyrolysis-gas chromatography-mass spectrometry; Py-GC-MS), pyrolysis with in situ methylation (thermally assisted hydrolysis and methylation; THM-GC-MS), and Fourier-transform infrared (FTIR) spectroscopy. The results showed 1) excellent preservation of the archaeological wood expressed by significant contributions of levoglucosan to the polysaccharides fingerprint after Py-GC-MS; 2) considerable chemical differences between archaeological and modern wood, i.e. archaeological wood samples yield relatively small proportions of lignin and large proportions of polysaccharides and terpenoids; 3) major differences in chemical characteristics of sapwood (more polysaccharides) and heartwood (more lignin). Furthermore, some tested decay proxies show large differences between sap- and heartwood (and are therefore of little value), yet the 4-acetylguaiacol/total guaiacol ratio (4AG/G; Py-GC-MS) of heart- and sapwood are similar, implying that this ratio is a more suitable proxy for decay assessment. Data comparison allowed to identify discrepancies and complementarities of Py-GC-MS, THM-GC-MS and FTIR for the characterization of different wood constituents and their preservation during long-term storage under waterlogged conditions. These results expand our understanding of the chemical composition of decomposing trunks of archaeological wood in general, and of G. pensilis in particular.

Impact of a conditioning step during the treatment of wood with melamine-formaldehyde resin on dimensional stabilisation

Abstract The dimensional stabilisation of wood using thermosetting resins relies on the resin uptake into the cell walls. This study tested if a conditioning step after the impregnation and before the final heat-curing enhances the cell wall uptake to improve dimensional stabilisation without increasing the chemical consumption. Small blocks of Scots pine sapwood were vacuum-impregnated with an aqueous melamine formaldehyde solution and conditioned at 33, 70, or 95 % RH for up to 1 week before drying and curing the blocks at 103 °C. However, the conditioning step decreased the cell wall bulking and the moisture exclusion effect compared to the immediate heat curing of the impregnated samples. Analyses of the resin-treated samples by scanning electron microscopy, IR spectroscopy and confocal Raman microspectroscopy provided evidence of wood hydrolysis and polycondensation of the resin within the cell lumen during the conditioning step. Hydrolysis and removal of wood constituents may have counterbalanced the cell wall bulking of the resin. Polycondensation of the resin in the lumen increased its molecule size, which could have hindered the cell wall diffusion of the resin.

Lignin Analysis by HPLC and FTIR: Spectra Deconvolution and S/G Ratio Determination.

Fourier transform infrared spectroscopy (FTIR) is a simple nondestructive technique that allows the user to obtain quick and accurate information about the structure of the constituents of wood. Spectra deconvolution is a computational technique, complementary to FTIR analysis, which improves the resolution of overlapped or unobserved bands in the raw spectra. High performance liquid chromatography (HPLC) is an analytical technique useful to determine the ratio of the lignin monomers obtained by the alkaline nitrobenzene oxidation method. Furthermore, lignin content has been commonly determined by wet chemical methods; Klason lignin determination is a quick and accessible method. Here, we detail the procedures for chemical analysis of the wood lignin using these techniques. Additionally, the deconvolution process of FTIR spectra for the determination of the S/G ratio, in lignin isolated by this or other methods, is explained in detail.

Formulation and characterization of environmentally benign chicken feather-based wood preservatives

This paper develops chicken feather protein-based wood preservatives (CFP-WP). The treatability, leachability and chemical structure of the CFP-WP were analyzed. The crystallinity, thermal properties, micromorphology and decay resistance against fungi of the treated wood samples were investigated to examine their efficacy. The production cost of CFP-WP was also assessed. The results showed that CFP-WP (Cu, B and small molecular amino acids) was able to penetrate into wood cell walls and the active ingredients of preservatives interacted with wood constituents were well fixed onto wood blocks, evidenced by SEM–EDS observation, NMR, FTIR, XRD and TGA/DTG analysis. The morphology analysis elucidated that CFP-WP effectively protected wood against decay fungi. Decay experiments verified that the new preservative prolonged the wood service life, reducing the mass loss up to 10.88% from 51.02% compared to the untreated wood. Further, the production cost of CFP-WP (approx. 130–140 €/tonne) is nearly 30% lower than the commercial price of conventional market preservatives, such as ACQ (approx. 210 €/tonne). The excellent functionalities of this CFP-WP eco-friendly formulation present a great potential to be used as an environmentally benign wood preservative.

Strong, durable and eco-friendly plywood bonded with chemically-upcycled wasted disposable masks

In the post-COVID-19 era, the effective upcycle of wasted disposable medical masks (DMMs) is crucial to minimize negative environmental impacts. This study focuses on the preparation of a strong, durable and eco-friendly three-ply plywood by bonding veneers with chemically-upcycled polypropylene filter (PPF) from DMMs. Alkaline pretreatment was used to enhance the surface polarity and wettability of PPF. Acacia tannin pretreatment cross-lined the phenolic hydroxyl group of acacia tannin with wood constituents and acted as a coupling agent to connect PPF and wood. Electrochemical activation and hot-pressing were applied sequentially (“two-steps”) and simultaneously (“one-step”). Both methods improved mechanical properties compared to the untreated plywood (CK). The “one-step” method showed the highest mechanical properties (bonding strength: 1.2 MPa, modulus of rupture: 65 MPa, and modulus of elasticity: 6.3 GPa). Electrochemical activation magnified acacia tannin’s coupling effect, creating continuous and uniform bond lines among wood-PPF interface. The “one-step” plywood withstood significant deformation in hygro- and thermal-environments, with less strain distribution due to simultaneous electrochemical activation and hot pressing. The formaldehyde emission from both “two-steps” and “one-step” plywoods was as low as 0.07 mg/L, significantly lower than that prepared by the conventional resins. This strong, durable and eco-friendly plywood provides an effective approach to upcycle DMMs and manufacture formaldehyde-free wood-based panels of high-value.

First Description of Non-Enzymatic Radical-Generating Mechanisms Adopted by Fomitiporia mediterranea: An Unexplored Pathway of the White Rot Agent of the Esca Complex of Diseases.

Fomitiporia mediterranea (Fmed) is the primary Basidiomycota species causing white rot in European vineyards affected by the Esca complex of diseases (ECD). In the last few years, an increasing number of studies have highlighted the importance of reconsidering the role of Fmed in ECD etiology, justifying an increase in research interest related to Fmed's biomolecular pathogenetic mechanisms. In the context of the current re-evaluation of the binary distinction (brown vs. white rot) between biomolecular decay pathways induced by Basidiomycota species, our research aims to investigate the potential for non-enzymatic mechanisms adopted by Fmed, which is typically described as a white rot fungus. Our results demonstrate how, in liquid culture reproducing nutrient restriction conditions often found in wood, Fmed can produce low molecular weight compounds, the hallmark of the non-enzymatic "chelator-mediated Fenton" (CMF) reaction, originally described for brown rot fungi. CMF reactions can redox cycle with ferric iron, generating hydrogen peroxide and ferrous iron, necessary reactants leading to hydroxyl radical (•OH) production. These observations led to the conclusion that a non-enzymatic radical-generating CMF-like mechanism may be utilized by Fmed, potentially together with an enzymatic pool, to contribute to degrading wood constituents; moreover, indicating significant variability between strains.

Selectively enzymatic conversion of wood constituents with white and brown rot fungi

Lignocellulosic material is a natural renewable resource and can provide great potential in bioconversion and bioenergy production. This work studied the bioconversion processes of Pinus yunnanensis with white and brown rot fungi treatment, namely T. versicolor, G. trabeum and R. placenta, aiming to clarify the mechanism of enzymatic process and fungi’s intrinsic selectivity in fungal pretreatment during various conversion stages. The results showed that fungi achieved the decomposition and conversion of biomass through the generation of enzymes as well as their action within wood. White rot fungus T. versicolor caused simultaneous rot, which the bioconversion of wood main components occurred uniformly. Brown rot fungi exhibited the ability to depolymerize carbohydrate but degraded polysaccharides with their own bioconversion pathway, and as such caused different conversion of wood chemical components. Morphology observation proved that both white and brown rot fungal pretreatments increased the porosity and improved the accessibility of wood cells. Three kinds of fungi possess the ability to improve the digestibility, but with various situations of the substrate loss. In addition, these three fungi presented their promising potentials in different aspects as well. The research outcomes could provide insight into the mechanism of enzymatic process and role of fungal selectivity on Pinus yunnanensis bioconversion as well as the potential application of fungal pretreatment in future biorefineries and biochemical productions.

Estimasi Cadangan Karbon Dan Serapan Karbon Di Taman Maluku Kota Bandung

The availability of green open space (RTH) in urban areas is very important to mitigate the effects of global warming, especially in reducing CO2 gas levels as a result of human activities. Vegetation with chlorophyll, namely the trees in green open spaces try to absorb carbon dioxide (CO2) using sunlight, water and soil from the atmosphere through the process of photosynthesis. One form of stored photosynthetic results is biomass which makes this vegetation grow bigger and taller . In the carbon cycle and biogeochemical cycle the biomass of green open space vegetation plays an important role, all parts starting from the stems, leaves and roots store biomass. This study aims to determine the estimation of carbon stocks and absorption in Taman Maluku, Bandung City. The method used in this study is a non-destructive method (without harvesting). The research was conducted by collecting tree data and the wet weight of the understorey, then calculating the biomass to obtain estimates of carbon stocks and carbon absorption. From the research it was found that the Maluku Park in Bandung City with an area of 23,633 m2 has carbon reserves of around 179.941 tons from trees and 3.11 tons from undergrowth. Meanwhile, the estimated carbon uptake is 731,422 tonnes by trees and 11,409 tonnes by undergrowth. The high carbon stock can be influenced by several factors including: vegetation density, environment, especially sunlight, volume, specific gravity, wood constituents, water content, and silvicultural measures.

Size- and temperature-dependent oxidative pyrolysis and auto-ignition of spherical beech and spruce wood

Abstract Opposed to piloted ignition, where a substance is ignited by an external flame or spark, the term auto-ignition describes the onset of combustion by spontaneous ignition without an external source. In this study, the influence of the size of spherical wood samples and the temperature surrounding the samples was investigated by performing ignition experiments in a muffle furnace with beech and spruce wood. On a specially constructed rig, spheres with four different diameters (8 mm, 12 mm, 18 mm, and 25 mm) were put into a preheated furnace at five isothermal temperatures (240 °C, 270 °C, 300 °C, 330 °C, and 360 °C). For every temperature, diameter, and wood species, the experiments were repeated eight times, and positions of the spheres on the rig were changed for every measurement. Temperatures inside the samples were recorded with thermocouples (TC) positioned in holes drilled to the middle of the spheres. With rising size and temperature, samples were more prone to auto-ignition in a glowing mode, due to a larger, highly reactive pyrolyzed surface and internal overheating. During heating and oxidative pyrolysis, isothermal phases were present at approximately 360 °C in the recorded temperature curves. The comparison to simultaneous thermal analysis (STA) measurements shows decomposition of hemicelluloses, and cellulose is highest around 360 °C. It is concluded that pyrolysis and disintegration of the main wood constituents use up all arising energy. Due to differences in the composition of the wood polymers, beech wood samples already ignite at lower temperatures compared to spruce wood samples with the same diameter. It can be concluded that the size is a critical factor for auto-ignition at the used temperatures. Larger samples will produce more volatile compounds during pyrolysis and have a larger pyrolyzed, porous surface area where heterogenous oxidation reactions can happen. The influence of the size is already critical at differences on the millimetre scale.

Effect of the interaction between wood constituents and swelling liquid on the creep properties of wood during drying

Abstract This study aimed to clarify the effect of the interactions between the swelling liquid and wood constituents on the creep behavior during drying. Creep tests were conducted during drying of four sample groups (untreated, acetylated, delignified, and hemicellulose-extracted samples) that were swollen using water, one organic liquid, or water-organic mixtures. The largest creep deformation was measured for the hemicellulose-extracted samples, followed by delignified, untreated, and acetylated samples. Apart from the acetylated samples, all treated samples tended to have large creep deformation in water-organic mixtures. For the acetylated samples, the creep deformation was small, except in case of acetone. These differences in the creep deformation behavior are mainly due to the differences in the glass-transition temperature of lignin as a result of the interaction between the wood constituents and the swelling liquid. The considerable increase in creep deformation due to hemicellulose-extraction suggests that hemicellulose, which interacts with lignin and cellulose, reduces the fluidity of the wood due to liquid desorption during creep measurements.

Potential of Wood Hemicelluloses and Their Derivates as Food Ingredients.

A holistic utilization of all lignocellulosic wood biomass, instead of the current approach of using only the cellulose fraction, is crucial for the efficient, ecological, and economical use of the forest resources. Use of wood constituents in the food and feed sector is a potential way of promoting the global economy. However, industrially established food products utilizing such components are still scarce, with the exception of cellulose derivatives. Hemicelluloses that include xylans and mannans are major constituents of wood. The wood hemicelluloses are structurally similar to hemicelluloses from crops, which are included in our diet, for example, as a part of dietary fibers. Hence, structurally similar wood hemicelluloses have the potential for similar uses. We review the current status and future potential of wood hemicelluloses as food ingredients. We include an inventory of the extraction routes of wood hemicelluloses, their physicochemical properties, and some of their gastrointestinal characteristics, and we also consider the regulatory route that research findings need to follow to be approved for food solutions, as well as the current status of the wood hemicellulose applications on that route.

A Study of Chemical Constituents in Platinum Fast-Grown Teak Wood (Tectona grandis) with Age Differences Using Py-GCMS Coupled with Interdependence Multivariate Analysis

Pyrolysis gas chromatography-mass spectrometry (Py-GCMS) is a simple, rapid, and reliable analytical technique to assay lignocellulose biomass. This study aims to analyze the chemical content of various ages of platinum fast-grown teak wood using PyGCMS coupled with interdependence multivariate analysis. Fifty-eight peaks were shown in the pyrogram originating from carbohydrates, lignin, and extractive derivatives. Along with age, platinum fast-grown teak wood showed higher carbohydrate derivatives in heartwood than sapwood. Compared to teak wood grown in conventional (between 36.72-45.69%), platinum fast-grown teak wood has a higher content of carbohydrates (42.82-48.04%). A substantial amount of G-unit lignin was detected in the sapwood, while the S-unit lignin dominated the heartwood. The extractive content of 10-years-old teak wood heartwood was 4.82%, higher than 10- and 20-years-old heartwood from conventional wood (2.23% and 8.88%, respectively). Multivariate analysis of the chemical compound showed that Py-GCMS could be utilized to classify platinum fast-grown and conventional teak wood. 2-methyl anthraquinone (MAQ) content of 10-year-old fast-grown teak wood was 2.5 times higher than 20-year-old conventional teak wood. Based on the study, platinum fast-grown teak wood is promising as alternative wood material to fulfill the market demand for conventional teak wood.

Detailed modeling of hydrogen release and particle shrinkage during pyrolysis of inhomogeneous wood

Hydrogen release during pyrolysis of woody biomass is studied considering anisotropicity and inhomogeneity of wood structure. A new anisotropic shrinkage model is proposed based on the decomposition of main wood constituents, i.e., cellulose, hemicellulose, and lignin. The new shrinkage model can predict the temporal evolution of the wood structure, and the differences between axial and radial shrinkage during pyrolysis. The model agrees very well with several experimental data from the literature. Based on particle temperature during conversion, the pyrolysis is partitioned into four stages, and the hydrogen release and H2 formation from each stage are investigated. Stage (IV) of pyrolysis, from 1000 to 1273 K, is found to be efficient for H2 production owing to the production of considerable mass of H2 with a minimal amount of tar species. Furthermore, the char quality is found to be different at the end of stages (II), (III), and (IV), where around 67.7, 80.5, and 93.4% wt. of solid residue is made of carbon, respectively. The model is also used to explain how the heating rate affects the temperature distribution inside the particle and how it shifts the peak of hydrogen release. Finally, the pyrolysis of two inhomogeneous wood samples — a beech twig with bark and a beech dowel with growth rings — are investigated. The bark can affect the pyrolysis rate, products, and flow pattern inside the particle. The growth rings do not have a considerable effect on the pyrolysis rate and products, but they have a significant impact on the flow pattern. This has an important implication for char conversion studies where the internal surface area and porosity field distribution have a significant effect on the gasification and oxidation rates.

Understanding of cell death induced by the constituents of Taxus yunnanensis wood

The ethanol extract from the wood of Taxus Yunnanensis (TY) induced apoptosis in all cancer cell lines tested, which was mainly due to activation of an extrinsic pathway in human colon cancer DLD-1 cells. The extrinsic pathway was activated by the upregulation of the expression levels of Fas and TRAIL/DR5, which led to the activation of caspase-8. Of note, the machinery of this increase in expression was promoted by the upregulation of MIR32a expression, which silenced MIR34a-targeting E2F3 transcription factor. Furthermore, ectopic expression of MIR32a or siR-E2F3 silencing E2F3 increased Fas and TRAIL/DR5 expression. Thus, the extract activated the extrinsic pathway through the MIR34a/E2F3 axis, resulting in the autocrine and paracrine release of TRAIL, and upregulated expression of death receptors Fas and DR5 in the treated DLD-1 cells, which were functionally validated by Fas immunocytochemistry, and using anti-Fas and anti-TRAIL antibodies, respectively. In vivo, TY showed significant anti-tumor effects on xenografted and syngeneic model mice. The extract may also aid in chemoprevention by selectively making marked tumor cells susceptible to the tumor immunosurveillance system.

A new analytical approach to investigate the influence of wood extracts on the curing properties of phenol-resorcinol\u2013formaldehyde (PRF) adhesives

In this study, the interactions between a phenol–formaldehyde resorcinol (PRF) adhesive and water-extractable wood constituents were investigated using combined in-situ FTIR spectroscopy and rheology analysis for a simultaneous examination of the progress of chemical reactions and coherent changes in rheological properties during adhesive curing. Complementary evolved gas analysis and pyrolysis gas chromatography/mass spectroscopy (Py-GC/MS) were performed to detect differences in the final crosslinking and chemical composition of the cured adhesive, respectively. The rheological and chemical analysis results correlated with the tensile shear strength of wood-PRF assemblies. The results showed that adhesive curing was significantly affected by the presence of acidic wood extractives. In particular, the acidic extractives of chestnut wood led to a delay in the resin curing and less final crosslinking of the cured adhesive. This was most likely caused by a reduction in the catalytic effect of the base-catalyzed curing of the adhesive rather than by direct chemical reactions between the extracts and adhesive. These findings can be useful for adapting the resin formulation to the chemistry of acidic wood species.

Acidic wood extractives accelerate the curing process of emulsion polymer isocyanate adhesives

AbstractEmulsion polymer isocyanate (EPI) adhesive is one of the most widely used structural adhesives in the woodworking industry. However, there has been a lack of knowledge on how the EPI‐adhesive interacts with the chemical constituents of wood, in particular, with the wood extractives that are known to influence the bonding quality. In this study, the interactions of the EPI‐adhesive with the water extracts and selected extractives from European wood species were systematically investigated using different analytical techniques. While the alterations in the curing properties of the pure EPI‐adhesive and EPI‐adhesive‐extract mixtures were revealed by in situ rheology and Fourier‐transform infrared spectroscopy, evolved gas analysis, and pyrolysis‐gas chromatography/mass spectrometry, the solid‐state 13C nuclear magnetic resonance were performed for analyzing the final chemical composition of the cured adhesive. Moreover, the influence of the extraction on the mechanical bonding performance was tested by tensile‐shear tests. The study revealed significant interactions between the EPI‐adhesive and tannin‐rich, acidic wood extracts. The acidic chestnut and oak extracts catalyzed the curing reactions and led to a huge increase in the adhesive viscosity. These interactions might affect the bonding quality, for example, adhesive penetration depth and formation of bonding strength, therefore, careful attention is required when bonding acidic wood surfaces.

Mineralogy of Miocene Petrified Wood from Central Washington State, USA

Silicified wood occurs abundantly in Middle Miocene flows and sedimentary interbeds of the Columbia River Basalt Group (CRBG) in central Washington State, USA. These fossil localities are well-dated based on radiometric ages determined for the host lava. Paleoenvironments include wood transported by lahars (Ginkgo Petrified Forest State Park), fluvial and palludal environments (Saddle Mountain and Yakima Canyon fossil localities), and standing forests engulfed by advancing lava (Yakima Ridge fossil forest). At all of these localities, the mineralogy of fossil wood is diverse, with silica minerals that include opal-A, opal-CT, chalcedony, and macrocrystalline quartz. Some specimens are composed of only a single form of silica; more commonly, specimens contain multiple phases. Opal-A and Opal-CT often coexist. Some woods are mineralized only with chalcedony; however, chalcedony and macrocrystalline quartz are common as minor constituents in opal wood. In these specimens, crystalline silica filling fractures, rot pockets, and cell lumen may occur. These occurrences are evidence that silicification occurred as a sequential process, where changes in the geochemical environment or anatomical structures affected the precipitation of silica. Fossilization typically began with precipitation of amorphous silica within cell walls, leaving cell lumen and conductive vessels open. Diagenetic transformation of opal-A to opal-CT in fossil wood has long been a widely accepted hypothesis; however, in opaline CRBG specimens, the two silica polymorphs usually appear to have formed independently, e.g., woods in which cell walls are mineralized with opal-A but in which lumen contain opal-CT. Similarly, opal-CT has been inferred to sometimes transform to chalcedony; however, in CRBG, these mixed assemblages commonly resulted from multiple mineralization episodes.