Southern Pine Research Articles

Successional dynamics of carbon sequestration in forests of the eastern United States

AbstractCarbon sequestration in the forests of the eastern United States is an important offset to the country's CO2 emissions. Much of the eastern forestland is the product of reforestation of abandoned agricultural land or recovery following clear‐cutting over a century ago. This has led to concerns that eastern forests are even‐aged and that rates of carbon sequestration will decline as forests increase in carbon. Our objective was to examine the successional dynamics of forest carbon sequestration—using live tree carbon stocks as a proxy for successional status—for the six broadly defined forest types present in the region. We used datasets from the National Forest Inventory (NFI) for the 31 US states from Minnesota south to Louisiana and eastward and analyzed live tree net carbon increment for 2007–2021, the period for which NFI plot remeasurement data were available for all 31 states. Spruce–fir and southern pines were the only forest types for which carbon increment declined even modestly over a significant fraction of the range of live tree carbon observed in the region, and southern pine–hardwood forests were the only forests in which predicted sequestration in live tree carbon declined to zero within the range of carbon stocks observed in the region. Northern hardwood–conifer forests, oak–hickory forests, and lowland forests experienced either no decline or a slight increase in sequestration in live tree carbon across the range of successional status observed in the region. Thus, the average stocks of live tree carbon per unit area increased steadily over the study period. At some point in succession, rates of mortality are expected to increase and balance gross growth, leading to zero net sequestration in live tree carbon. Mature and old‐growth stands, however, are rare in all six forest types, and mortality as a fraction of live tree carbon for all six forest types declined across the range of successional status present in the region. Our results thus provide no support for the hypothesis that the successional dynamics of forests in this region can be expected to lead to near‐term declines in net carbon sequestration.

Predicting Wood Density Using Resistance Drilling: The Effect of Varying Feed Speed and RPM

The IML PD series Resi is a device used to assess the drilling resistance of wood. The IML PD series Resi instrument is being widely adopted for commercial wood quality assessment due to its speed, cost-effectiveness, and precision when combined with web-based trace processing. Collecting Resi data with fixed feed speed and RPM settings is challenging due to inherent basic density variations within and between tree species. Altering these settings affects the drilling resistance amplitude of the Resi data, impacting basic density predictions. This study introduces the concept of chip thickness to combine feed speed and RPM into a single parameter to minimise the effects of different sampling conditions on the basic density predictions. Regression models, with chip thickness as the regressor variable, account for 97% to 99% of variance in mean Resi outerwood amplitude across six species. The demonstrated adaptability of chip thickness for adjusting feed speed and RPM settings, along with species-specific functions correlating it with Resi amplitude, holds promise for standardizing amplitude values across diverse feed speeds and RPM settings. Optimal sampling conditions needed to predict basic density lie within the 30%–40% amplitude range. To drill a ~30 cm diameter tree, the recommended fastest settings were 200 cm/min and 3500 RPM for Southern Pine (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Sénéclauze)) and Radiata Pine (Pinus radiata (D. Don.)), 200 cm/min and 2500 RPM for Hoop Pine (Araucaria cunninghamii (Mudie)), 50 cm/min and 5000 RPM for Spotted Gum (Corymbia citriodora subsp. variegata (F. Muell.)), 200 cm/min and 4500 RPM for White Cypress (Callitris glaucophylla (Thompson & Johnson)), and 150 cm/min and 3500 RPM for Shining Gum (Eucalyptus nitens (H. Deane & Maiden) Maiden) based on the billets sampled.

Utilization of Synthetic Near-Infrared Spectra via Generative Adversarial Network to Improve Wood Stiffness Prediction.

Near-infrared (NIR) spectroscopy is widely used as a nondestructive evaluation (NDE) tool for predicting wood properties. When deploying NIR models, one faces challenges in ensuring representative training data, which large datasets can mitigate but often at a significant cost. Machine learning and deep learning NIR models are at an even greater disadvantage because they typically require higher sample sizes for training. In this study, NIR spectra were collected to predict the modulus of elasticity (MOE) of southern pine lumber (training set = 573 samples, testing set = 145 samples). To account for the limited size of the training data, this study employed a generative adversarial network (GAN) to generate synthetic NIR spectra. The training dataset was fed into a GAN to generate 313, 573, and 1000 synthetic spectra. The original and enhanced datasets were used to train artificial neural networks (ANNs), convolutional neural networks (CNNs), and light gradient boosting machines (LGBMs) for MOE prediction. Overall, results showed that data augmentation using GAN improved the coefficient of determination (R2) by up to 7.02% and reduced the error of predictions by up to 4.29%. ANNs and CNNs benefited more from synthetic spectra than LGBMs, which only yielded slight improvement. All models showed optimal performance when 313 synthetic spectra were added to the original training data; further additions did not improve model performance because the quality of the datapoints generated by GAN beyond a certain threshold is poor, and one of the main reasons for this can be the size of the initial training data fed into the GAN. LGBMs showed superior performances than ANNs and CNNs on both the original and enhanced training datasets, which highlights the significance of selecting an appropriate machine learning or deep learning model for NIR spectral-data analysis. The results highlighted the positive impact of GAN on the predictive performance of models utilizing NIR spectroscopy as an NDE technique and monitoring tool for wood mechanical-property evaluation. Further studies should investigate the impact of the initial size of training data, the optimal number of generated synthetic spectra, and machine learning or deep learning models that could benefit more from data augmentation using GANs.

Experimental investigation on withdrawal resistance performance of nails in southern pine

The objective of this study is to evaluate the structural performance and withdrawal capacity of three types of nails embedded in southern pine (SP) framing members. Pull-out tests on 430 specimens were conducted until complete withdrawal occurred. Representative variables derived from practical wall-to-wall or wall-to-floor connections were considered, including nail type, nail diameter, embedment length, and nail direction. Results reveal that the failure modes of specimens depend on nail shank roughness. Smooth shank nails (SSNs) and concrete nails (CNs) mainly experience nail-wood interface sliding and wood fiber tearing failures, while zinc-coated helically threaded nails (ZHTNs) exhibit wood fiber shearing and tearing failures. As expected, the ultimate withdrawal capacity increased with greater embedment length, with the highest capacity of nails in the perpendicular-to-grain direction, followed by parallel-to-grain. The withdrawal load-slip relationships of nails in SP consist of three stages: linear-elastic rise, plunge, and failure stage for SSNs and CNs, while ZHTNs exhibit elastic-plastic behavior during the second phase. The modified Rafi model suggested in this study can be used to translate the withdrawal bond-slip relationships of nails in SP. Finally, a withdrawal resistance calculation equation for SP was put forward and validated, showing an average difference of 10.33% between theoretical and experimental values.

Comparison of microscopy and quality control testing to examine the durability of adhesive bondline in cross-laminated timber

Adhesive bonding quality significantly contributes to the integrity and quality of cross-laminated timber (CLT). There are several factors affecting bonding quality in glued-layered wood products such as CLT that are generally categorized as the properties of wood, adhesive type and curing conditions. The adhesive bonding performance of five different types of CLTs made from yellow-poplar and southern pine lumber using phenol-resorcinol formaldehyde and polyurethane structural adhesives were studied using light microscopy and ANSI/APA PRG-320 mechanical evaluation tests. The results show that CLTs with a thin bondline and the highest effective penetration had the highest shear strength, and with least face delamination. The effect of wood anatomy on bonding quality was demonstrated in mixed species CLT with different penetrations into different species. The effect of adhesive curing was observed through the presence of generating gaps and microbubbles in adhesive lines.

Modeling wood product carbon flows in southern us pine plantations: implications for carbon storage

BackgroundWood products continue to store carbon sequestered in forests after harvest and therefore play an important role in the total carbon storage associated with the forest sector. Trade-offs between carbon sequestration/storage in wood product pools and managed forest systems exist, and in order for forest sector carbon modeling to be meaningful, it must link wood product carbon with the specific forest system from which the products originate and have the ability to incorporate in situ and ex situ carbon synchronously over time.ResultsThis study uses elements of a life cycle assessment approach, tracing carbon from US southern pine timber harvests to emission, to create a decision support tool that practitioners can use to inform policy design around land- and bioproduct-based mitigation strategies. We estimate that wood products from annual loblolly and shortleaf pine timber harvests across the southern US store 29.7 MtC in the year they enter the market, and 11.4 MtC remain stored after 120 years. We estimate fossil fuel emissions from the procurement, transportation, and manufacturing of these wood products to be 43.3 MtCO2e year−1. We found that composite logs, used to manufacture oriented strand board (OSB), were the most efficient log type for storing carbon, storing around 1.8 times as much carbon as saw logs per tonne of log over 120 years.ConclusionsResults from our analysis suggest that adjusting rotation length based on individual site productivity, reducing methane emissions from landfills, and extending the storage of carbon in key products, such as corrugated boxes, through longer lifespans, higher recycling rates, and less landfill decomposition could result in significant carbon gains. Our results also highlight the benefits of high site productivity to store more carbon in both in situ and ex situ pools and suggest that shorter rotations could be used to optimize carbon storage on sites when productivity is high.

Variation in RNA interference sensitivity in the southern pine beetle, Dendroctonus frontalis (Coleoptera: Curculionidae)

Abstract Intraspecific genetic variation underpins many evolutionary processes and phenomena. For species considered pests, the dynamics of how genetic variation is distributed geographically take on a greater importance, because they can impact pest-management strategies directly. This is particularly true when management strategies are genetic in nature, such as population manipulation via RNA interference (RNAi; a naturally occurring antiviral response that disrupts translation of messenger RNAs into proteins to silence genes). Using RNAi for gene silencing is highly species specific; however, the efficacy of this approach in geographically distinct populations of widespread pest species has not been evaluated comprehensively. Here, we present a preliminary study evaluating differential susceptibility of geographically disparate populations of southern pine beetle, Dendroctonus frontalis, to RNAi. Although the efficacy of RNAi has been demonstrated in localized populations, D. frontalis has a broad distribution across North and Central America and is expanding its range owing to climate change. We observe differences in response between and within geographically distinct populations from its core range and recently expanded range. Our findings have broad implications for the use of RNAi as a management tool in widely distributed species and highlight the need for a deeper understanding of intraspecific genetic variation in this species and others.

Assessing the potential impact of retaining native off‐site tree species in woodland restoration

Reestablishing appropriate tree species is an important step in converting off‐site monocultures into woodlands. Species conversion is often necessary, as off‐site exotic species rarely function like woodland species. However, when off‐site tree species are native, and functionally redundant to woodland species, conversion may be unnecessary. To explore this possibility in the southeastern United States, we reviewed the literature on trait differences among the primary southern pines and qualitatively assessed the effect of their identity at the species and stand‐levels. In this region, woodland restoration focuses on removing loblolly (Pinus taeda) and slash pine (P. elliottii) to reestablish longleaf (P. palustris) or shortleaf pine (P. echinata). Our review found minimal variation among species in understory flammability, fire resistance at maturity, and Red‐cockaded Woodpecker (Leuconotopicus borealis) habitat at the stand‐level. Longleaf and shortleaf pine were generally more resistant to abiotic and pest disturbance at the tree‐level; however, stand‐level differences in wind, drought, and boring insect resistance among southern pines growing in open forests were considered minimal. Retaining loblolly and slash pine will improve stand‐level productivity in the short term, but creates regeneration problems due to low juvenile fire resistance and resilience. Ice resistance and long‐term carbon sequestration will also likely be reduced by retaining loblolly and slash pine. Collectively, these results suggest that southern pine species are generally interchangeable at the stand‐level in woodlands; although woodlands featuring loblolly and slash pine may be less stable in the face of disturbance than those dominated by shortleaf and longleaf pine.

The Use of High-Resolution Satellite Imagery to Determine the Status of a Large-Scale Outbreak of Southern Pine Beetle

Timely detection of insect infestation (or other disturbance) in a forest is vital for an adequate response plan to be developed. To determine the status of an active infestation of southern pine beetle (Dendroctonus frontalis) in the Bienville National Forest, WorldView-2 imagery was utilized. Principal components analysis (PCA) was performed and correlated with spectral reflectance bands to assess differences between the classification of spectral reflectance bands and principal components. Unsupervised classification of combinations of principal components (e.g., combining principal components 1 and 2, principal component 1 alone, and principal component 2 alone) was performed and compared with combinations of principal component correlations with spectral reflectance bands (e.g., all bands, bands 1–5, bands 6–8, and bands 2, 4, and 5). Combining principal components 1 and 2 was more accurate than other methods, closely followed by spectral bands 1–5. Employing PCA will aid resource managers in quickly detecting areas of active insect infestation and allow them to deploy adequate response measures to prevent or mitigate continued outbreaks.

Decay resistance of southern pine wood containing varying amounts of resin against Fomitopsis ostreiformis (Berk.) T. Hatt.

Abstract Resin production in wood tissues is a regular feature of pine wood species, including southern pine. High resin contents of southern pine wood may increase wood resistance against decay fungi. The current study investigated the effect of resin contents in southern pine wood on decay resistance by exposing non-extracted heartwood, mixed wood (sapwood + heartwood), and sapwood blocks with varying resin content to brown rot, Fomitopsis ostreiformis in a laboratory decay test. Matching blocks of each wood type were successively extracted in a Soxhlet using three solvents to determine resin content and were exposed to decay fungus in parallel. Results showed that mass losses in non-extracted heartwood and mixed wood depended on resin content levels, and very shallow or no mass losses were observed in blocks containing more than 31 % resin content. Sapwood experienced high mass losses, but the presence of resinous extractives significantly increased the decay resistance. All solvent-extracted blocks experienced high mass loss (53–55 %). Scanning electron microscopy showed that penetration of brown rot hyphae and cell damage depended on the resin contents of blocks. Most of the identified compounds through GC-MS belonged to oleoresins, among which monoterpene hydrocarbons, oxygenated monoterpenoids, and sesquiterpenes were more abundant in heartwood than sapwood.

Predicting Wood Density Using Resistance Drilling: The Effect of Instrument and Operator

The IML PD series Resi is an instrument designed to measure the drilling resistance of wood. Use of the IML PD series Resi instrument is rapidly becoming a routine method among Australian forest plantation growers for wood quality assessments. The major driver in the commercial uptake of the IML Resi is that it is fast, cheap, and sufficiently precise for commercial use, particularly when the data are processed through a user-friendly, web-based processor. This study examined whether the accuracy of wood density predictions was impacted by the use of different Resi tools and different operators, which has never been examined before. Seven Resi instruments were evaluated across six sites with two operators on plantation-grown Southern Pine (Pinus caribaea var. hondurensis (Sénéclauze) or hybrids between Pinus elliottii var. elliottii (Engelm) × P. caribaea var. hondurensis) trees. Two types of Resi instruments were used (IML Resi PD-400 and IML Resi PD-500), and all had been recently serviced or were new. The instruments were operated by experienced operators. Constant sampling conditions of feed speed 200 cm/min and 3500 RPM were used. The order of instrument use, and hence the order of operator assessment at each site, was randomized. The variance between Resi instruments was small. The measured mean basic density of 50 mm outerwood cores across all plots was 542 kg/m3, while Resi-predicted basic density varied among instruments between 535 and 547 kg/m3. One Resi instrument underpredicted basic density by 9 kg/m3 and another overpredicted by 5 kg/m3. The operator had no effect on the basic density prediction. Resi PD400 or PD500 instruments gave similar basic density predictions.

Wood properties of mature loblolly pine grown in Hawaii, North Carolina, and Mississippi: impacts of climate conditions on specific gravity and chemical composition

Higher productivities for loblolly pine (Pinus taeda L.) growing at exotic locations (e.g., Hawaii, Brazil) indicate that the full growth potential of this southern pine species has yet to be reached in plantations across the southeastern United States (US). The higher productivity of Hawaii-grown loblolly pine has been attributed to more favorable climate conditions. To date, physical, anatomical, and chemical property data for loblolly pine wood from exotic locations are scarce. Mid-infrared spectroscopy coupled with multivariate analysis was used to screen for chemical differences between wood samples from Hawaii (HI), North Carolina (NC), and Mississippi (MS). The principal component analysis scores plot showed that the MS samples formed a distinct cluster apart from overlapping clusters for the other two sites. Using standard wet chemistry procedures, we found that the mean lignin content for the MS site (30.1%) was significantly lower than that determined for the NC (34.5%) and HI (33.9%) sites; said lower lignin value was offset by significantly higher glucose and mannose contents. Results on the US mainland were seemingly consistent with the greater formation of latewood at sites with longer growing seasons, and the lower lignin content of latewood relative to earlywood shown for pines. Given the low percent latewood for the HI site (37.2%) relative to both mainland sites (MS, 54.8%; NC, 53.1%), yet similar lignin contents between the NC and HI sites, it appears that the relative lignin value for these exotically-grown loblolly pine trees cannot be solely attributed to the proportion of latewood.

Southern pine beetle (Coleoptera: Curculionidae) and its associated insect community: similarities and key differences between northeastern and southeastern pine forests.

We examine consequences of climate-induced range expansion on community composition and diversity within trees attacked by the southern pine beetle (Dendroctonus frontalis Zimmermann). At the northernmost limit of the southern pine beetle range where populations have persisted for multiple years (currently Long Island, NY), we collected and reared bark samples and placed emergence traps on southern pine beetle-attacked pitch pine, Pinus rigida Mill. (Pinales: Pinaceae). From these samples, we quantified southern pine beetle gallery length and emergence as well as the diversity and abundance of all associated insects including known and suspected competitors, predators, and parasitoids. We compared our results to that of historic sampling data (1975-1997) in the core of southern pine beetle's range in the southern United States. Key community members were present in both the northern and southern regions; composition and relative abundances differed markedly. A key predator, the clerid beetle Thanasimus dubius (Fabricius) (Coleoptera: Cleridae), was present in similar densities in both regions. Southern pine beetle infested a greater proportion of the length of the tree bole in the North. This increased tree utilization may be a consequence of a lack of resource competition by Ips De Geer (Coleoptera: Curculionidae) engraver beetles, which we found only in very low abundance in the northern sites. We discuss the implications of these results in the context of southern pine beetle range expansion. Continued study of the southern pine beetle community and temporal southern pine beetle dynamics in the North will add to our current knowledge base and aid preservation of rare and ecologically valuable pine barrens of New England.

Impact of Growth Characteristics on Properties of 2 by 8 Southern Yellow Pine Structural Lumber

Abstract Southern pine is one of the most important softwood resources in the United States, and the majority of southern pine is for lumber production, more specifically for construction. The lumber used for construction is required to meet strength-specifications as a method of ensuring the strength values within different classes. Most of the southern pine lumber is visually graded, which is based on knot, slope of grain, and wane. However, the presence of pith is not included in the visual grading system. The presence of pith indicates presence of juvenile wood, which has a negative effect on mechanical properties. The objective of this study was to evaluate the effect of pith on rings per inch, percentage of latewood, modulus of elasticity (MOE), and modulus of rupture (MOR) in 292 samples of southern pine No. 2 2 by 8 lumber. Lumber without pith had significantly greater MOE (11.1 vs. 10.0 GPa), MOR (39.7 vs. 36.4 MPa), and specific gravity (12% moisture content [MC]; 0.55 vs. 0.52) than did lumber with pith. The results show that the presence of pith is an important factor that can improve lumber grading, and it could be included in the visual grade system.

Comparing the Effects of Prescribed Burning on Soil Chemical Properties in East Texas Forests with Longleaf and Other Southern Pines in the Overstory

Little has been reported on the effects of repeated prescribed burning on southern United States’ forest soils, especially when site preparation is not the prescribed fire objective. This study was aimed at identifying any correlations between the soil chemical properties among differing burn intervals and the effects prescribed burning has on them. Sampling was performed in 36 plots at three sites with two different burn intervals (2–3 years and biannually) and measured properties: (1) pre-burn (before the fire), (2) post-burn (one month after the fire), and (3) at vegetation green-up (three months after the fire). Sites varied by overstory species with longleaf pine (Pinus palustris) and shortleaf pine (Pinus echinata Mill.) in the overstory on one site, a mix of loblolly pine (P taeda L.) and shortleaf pine on another, and longleaf and loblolly pines on the third. SAS was used to determine the effects of prescribed burning between different time spans (pre-burn to post-burn, post-burn to green-up, and pre-burn to green-up) and between the two different burn intervals. We found that there could be short-term responses in soil chemical properties from repeated burning treatments including nitrogen in the forms of ammonium and nitrate, the carbon-to-nitrogen ratio, and electrical conductivity, all of which decreased following fire regardless of overstory species.

A new look at the kinetics of oxygen delignification of softwood kraft pulp

Abstract Using a Berty-type CSTR reactor, Ji (2007. Kinetics and mechanism of oxygen delignification, Ph.D. thesis. The University of Maine) obtained oxygen delignification kinetics first order in lignin when neglecting the higher initial delignification phase. In the present study the same Berty/CSTR reactor with an improved temperature control was used to determine the oxygen delignification kinetics of Southern Pine kraft pulp, with the kinetics now corrected for lignin removed by oxygen-free alkaline leaching. This removes the initial high delignification rate peak so that the kinetics over the entire lignin range can be modelled as first order in “reactive” lignin, which is lignin corrected for a small amount of unreactive lignin. It suggests that softwood pulp oxygen delignification consists of two contributions; phenolic delignification and alkaline leaching. The initial alkaline leaching phase is mathematically described by semi-infinite alkaline diffusion of dissolved lignin trapped in the cell wall after pulp washing. For phenolic delignification, the reaction orders in alkali concentration and oxygen of the power law delignification equation are 0.3 and 0.44 respectively, while the activation energy is 63 kJ/mol. Taking into account the unreactive HexA, the small amount of unreactive lignin, and the lignin removed by alkaline leaching, the kappa number is well predicted by the new delignification kinetics.

The profitability of artificial and natural regeneration: A forest investment comparison of Poland and the U.S. South

The historical development of silviculture has been closely related to an increasing need for timber, which resulted in more planted forests and artificial regeneration over time. The idea of natural regeneration through shelterwood cutting was often not accepted by forest owners as a management practice because of inadequate financial returns and less certain outcomes. Despite the evolving dominance of planted forests, questions remain if the lower costs of natural regeneration may still provide sufficient profitability of forest investments. In this paper, the profitability of planted versus natural forest management in Poland and the U.S. South was examined. A discounted cash flow model was developed to evaluate the profitability of artificial and natural regeneration in hypothetical Scots and loblolly pine stands in Poland and the U.S. South, respectively, and hardwood stands (dominated by oak spp.) in both countries. The results have shown that for both countries and species, natural regeneration regimes produce higher internal rates of return (IRR), largely due to less expensive establishment costs. The largest difference in returns is observed for hardwood in the US South (97 basis points, bps, or almost 1 percentage point), followed by pine in the US South (84 bps) and pine and hardwood in Poland (both ca. 70 bps).  Southern pines in the U.S. South may have larger net present values (NPV) at moderate discount rates, as well as provide more certain wood production outcomes, which have contributed to their pervasive adoption.  We conclude that natural stand forest management, in addition to better rates of return, may bring other non-financial benefits (e.g., genetic diversity, resilience), which may support forest owners and the environment, especially under changing climate conditions. Nevertheless, the regeneration method and its feasibility and profitability should be carefully considered on a case-by-case basis for each forest investment.

Influence of wet-dry cycles on the withdrawal capacity and corrosion of zinc electroplated self-tapping screws in CCA-treated and untreated Southern pine

Fastener products are commonly exported to different continents, and it is important to understand their performance in local timber species and construction practices. This paper investigates the effects of cyclic moisture changes on the withdrawal performance of yellow-zinc and nickel-zinc coated European screws in Australian copper chrome arsenate (CCA) treated Southern Pine, up to a maximum of 24 cycles. A 68–78% loss of the initial withdrawal strength was observed after three cycles, but this was recovered after twelve cycles. Overall, screws lost at least 50% of their initial strength after 24 cycles, regardless of the treatment or fastener coating. The corrosion resistance of nickel-zinc screws in CCA-treated timber was superior to that of yellow-zinc screws in the first three cycles, but the difference disappeared as the moisture cycle number increased. In CCA-treated timber, the corrosion rates of yellow-zinc screws were 40% higher than those in untreated timber. Although nickel-zinc screws were relatively more corrosion-resistant than yellow-zinc screws, the strength loss caused by corrosion confirms that the selected screws are best suited for indoor use. Finally, following a comparative analysis of test results, some recommendations were made in this paper for future research.

Study of mass transfer and hygroscopic properties of Australian mass-timber panels and species in hot and humid conditions- moisture sorption and desorption

ABSTRACT Wood is a commonly used building material with numerous advantages over other construction products. However, in engineered wood products such as cross-laminated-timber and laminated veneer lumber moisture absorption can lead to decay, swelling, deformation, and glue line failures, diminishing their properties. Understanding moisture intrusion processes in these materials can aid manufacturers, engineers, and architects in developing effective moisture management strategies during and after construction. The porosity of CLT 3P sections was 56.5%, higher than CLT 2P sections at 36.8%. True density varied among species, with radiata pine, southern pine, and shining gum measuring 1358, 1411, and 1031 kg/m3, respectively. True density values for CLT 3P, CLT 2P, and LVL were 1202, 837, and 1406 kg/m3, respectively. The species and sample type significantly influenced porosity and density values, crucial for future moisture modelling and predicting moisture gain/loss during wetting and drying processes. Moisture sorption and desorption properties were examined for Australian timber species, CLT, and LVL at different temperatures. LVL samples exhibited higher moisture content and dimensional changes, possibly due to improved moisture transfer facilitated by lathe checks. CLT samples demonstrated greater anisotropic behaviours than those of LVL samples. The product type and sample type had significant effects on equilibrium moisture content values.

Study of the hygroscopic properties of three Australian wood species used as solid wood and composite products

The use of engineered wood products and mass timber panels such as cross laminated timber (CLT), glued laminated timber (glulam) and laminated veneer lumber (LVL) is becoming more common, as these products have benefits in terms of environmental credentials and resource utilisation and have the potential to provide faster and more economical construction processes. However, timber exposed to moisture for prolonged periods can degrade biologically, leading to a loss of appearance and decreased mechanical properties. Southern pine, radiata pine and shining gum timber are important forest resources for the Australian timber industry. To date, no in-depth studies on the hygroscopic properties of these species have been carried out from a timber wetting point of view. Consequently, existing literature has a knowledge gap regarding the determination of moisture movement properties in these species that are applicable to numerical modelling when used as solid wood or in the production of engineered wood products (EWPs). The work presented herein will help develop a better understanding of moisture ingress and egress in solid timber and EWPs and provide data for future predictive tools (such as numerical modelling) for moisture management in timber buildings. Samples were prepared from solid timber as well as EWP’s to examine the relationships between glue lines and edge gaps in CLT and multiple glue lines in LVL on moisture movement. As expected, longitudinal permeability was higher than radial and tangential permeability for the species tested. Southern pine samples had higher gas and liquid permeability values than radiata pine and shining gum. CLT with end grain sections including an edge gap had higher gas and liquid permeability than similar sections with glue lines only. LVL sections with 1 glue line had slightly lower permeability values than in samples with 2 glue lines. Gas and liquid permeabilities were lower for LVL samples than a two-layered veneer section without a glue line illustrating the barrier posed by the glue line. The moisture loss parameter during the diffusion testing was higher for LVL ends and CLT ends with edge gaps than face and edge sample sections. The results will be used to develop numerical models for moisture behaviour in solid and composite timber panels when exposed to humidity and free water. It is recommended to conduct additional studies to examine the impact of the adhesive layer and its properties on impeding moisture migration or functioning as a moisture barrier.