Yellow Pine Research Articles

Influence of incorporating beta-cyclodextrin/essential oil-based wood preservative on the bonding strength of wood composite products

The introduction of additives during the production of wood composites may disrupt the development of bonding strength between wood and adhesive, potentially compromising the structural performance of wood composites. This study investigates the impact of incorporating a natural wood preservative into 3-ply southern yellow pine (SYP) plywood on its bonding strength. The formation of β-cyclodextrin and trans-cinnamaldehyde (βCD-tCN) inclusion complex as a natural wood preservative was confirmed by Fourier transform infrared and X-ray diffraction analyses, with an inclusion yield ranging 78 % to 120 %. The differential scanning calorimetry analysis found the curing of pMDI with wood was not significantly affected by the βCD-based additives. The influence of βCD-tCN addition on the bonding strength of a wood composite was assessed by a shear strength test of the 3-ply plywood, following ASTM D906-20. The average shear strength of all panels ranged 1.53 N/mm2 to 2.07 N/mm2, exceeding the minimum requirement of 1.00 N/mm2 for cross-layer bond lines according to EN 16351-2015. Statistical analysis indicated no significant differences between the bonding strength of pristine pMDI and pMDI containing βCD-tCN complex. The combined results suggest that βCD-tCN could be effectively implemented in the manufacturing of wood composite products.

When do contemporary wildfires restore forest structures in the Sierra Nevada?

BackgroundFollowing a century of fire suppression in western North America, managers use forest restoration treatments to reduce fuel loads and reintroduce key processes like fire. However, annual area burned by wildfire frequently outpaces the application of restoration treatments. As this trend continues under climate change, it is essential that we understand the effects of contemporary wildfires on forest ecosystems and the extent to which post-fire structures are meeting common forest restoration objectives. In this study, we used airborne lidar to evaluate fire effects across yellow pine and mixed conifer (YPMC) forests of California’s Sierra Nevada. We quantified the degree to which forest structures in first-entry burned areas (previously unburned since ~ 1900s) and unburned controls aligned with restoration targets derived from contemporary reference sites. We also identified environmental conditions that contributed to more restorative fire effects.ResultsRelative to unburned controls, structural patterns in first-entry burned areas aligned more closely with reference sites. Yet, across all burn severities, first-entry wildfires were only moderately successful at meeting targets for canopy cover (48% total area) and ladder fuels (54% total area), and achieving these targets while also producing tree clump and opening patterns aligning with reference sites was less common (16% total area). Moderate-severity patches had the highest proportion of restorative fire effects (55–64% total area), while low- and high-severity patches were either too dense or too open, respectively. Our models (and publicly-available mapped predictions) indicated a higher probability of restorative effects within 1 km of previous fires, within the mid-upper climate range of the YPMC zone, and under moderate fire intensities (~ 1–2 m flame lengths).ConclusionsFirst-entry wildfires can sometimes restore structural conditions by reducing canopy cover and ladder fuels and increasing structural heterogeneity, especially within moderate-severity patches. However, these initial fires represent just one step toward restoring dry forest ecosystems. Post-fire landscapes will require additional low- to moderate-intensity fires and/or strategic management interventions to fully restore structural conditions. In yet unburned forests, managers could prioritize mechanical treatments at lower elevations, early-season burning at mid to high elevations, and resource objective wildfires in landscapes with mosaics of past wildfires.

Hydrothermal liquefaction of southern yellow pine with downstream processing for improved fuel grade chemicals production

The hydrothermal liquefaction (HTL) technique for liquefying lignocellulose biomass feedstock is often associated with low biocrude yield and poor fuel properties. This study examined the HTL of southern yellow pine sawdust and the hydrotreatment (HYD) of produced biocrudes in an effort to address these challenges. Pine HTL treatment was performed within water and water–ethanol mixed reaction medium at 250, 300, and 350℃ temperatures using metallic iron (Fe) as a catalyst. The rising reaction temperature in a water medium and increasing ethanol content in a mixed reaction medium were found to be effective in enhancing the biocrude yield from the non-catalytic pine HTL process. Maximum non-catalytic biocrude yield of 18 wt.% was produced in water at 350℃, whereas the ethanol and water (1:1 on mass basis) mixture generated the highest biocrude yield of 34 wt.% at 300℃ without any catalyst. The iron catalyst facilitated a maximum of 29 wt.% of biocrude yield as opposed to 18 wt.% without the catalyst at 350℃ in water. The use of an iron catalyst also raised the calorific value of produced biocrudes by 2.5–14 % within 250-350℃ in both water and water–ethanol media. The catalytic and non-catalytic biocrude products were chosen to undergo HYD treatment at 400 °C under high hydrogen pressure (initial 1000 psi) using an alumina-supported cobalt-molybdenum catalyst. The HYD treatment reduced the oxygen content of upgraded oils by 36–60 % compared to the parent HTL biocrudes with 35–37 MJ/kg calorific values. The simulated distillation detected the maximum gasoline range compounds in upgraded oil from catalyst and water–ethanol conditions, whereas the GC–MS analysis revealed the production of increased aromatic hydrocarbons in all upgraded HYD oils. This work has demonstrated the potential of ethanol and inexpensive iron catalyst in enhancing the biocrude production from pine, which could be upgraded to better fuel using the HYD process.

The Effect of Different Densification Levels on the Mechanical Properties of Southern Yellow Pine

Plantations, typically involving the cultivation of fast-growing trees like southern yellow pine, offer avenues to enhance sustainability and manage limited resources more effectively. However, fast-growing trees suffer from low mechanical properties due to less dense wood. Densification and the development of engineered wood products represent approaches to developing high-performance products from fast-growing tree species. In this study, the correlation between the densification levels and mechanical properties of a fast-growing species, loblolly pine (Pinus taeda L.), was established to improve resource utilization. Wood specimens were densified at three compression ratios: 16.67%, 33.33%, and 50.00%. The impact of densification levels on bending strength, bending stiffness, shear strength, and hardness was studied. The findings highlighted the positive impact of densification on structural integrity, as bending stiffness consistently improved, eventually reaching a 42% enhancement at a compression ratio of 50.00%. However, bending strength showed an initial increasing trend but reached a plateau at higher densification levels. Densification levels showed minimal changes in shear strength parallel to the grain. Notably, densification significantly enhanced hardness properties, particularly on the tangential surface, where a fourfold increase was observed at a 50% compression ratio. Overall, these findings reveal the relation between the compression ratio and the mechanical properties of lumber and are beneficial for utilizing lower-quality wood species in construction and engineering applications.

Determining the Extent of damage in Snapped Southern Yellow Pine Trees with Acoustic Testing

Abstract Salvage of downed timber following a windstorm allows recovery of management options for landowners and wood products for industry. Because wood volumes are large and logging, transportation, mill storage, and processing capacities are limited, avoiding the selection of logs with damage can conserve those resources. Visual damage indicators are typically used to select and differentiate products, but damaged logs are still delivered to mills. Following experimental tree winching in 2021 and a tornado in 2023, we assessed lengths of broken trees with a Fakopp microsecond timer. Using a recognized defect limit (10% deviation from the maximum acoustic velocity) about 80 percent of volume in broken tops could be recovered. Standard rules of thumb applied from the end of visible damage resulted in the recovery of about 50 percent of the volume with a relatively low defect rate (<10%). Applying bucking rules developed from acoustic measurements based on distance from snap might be easier to apply and increase recovery rates to over 70 percent of broken top volume.

Mechanical Properties of Underutilized Hardwood Species and Potential for Use in Fabrication of Cross-Laminated Timber Industrial Mats

Abstract This research evaluated the mechanical and physical properties of three underutilized hardwood species according to visual lumber grades. Findings are discussed in relation to the requirements recommended such as density, modulus of rupture (MOR), and modulus of elasticity (MOE) for the manufacture of cross-laminated timber (CLT) industrial mats, which is a potential end use of low-valued hardwood species. Results showed that all species tested had an average MOE greater than that required for CLT lumber. Visual grading was an important component in strength determinations as evidenced by the correlation between MOE and MOR. All grades of red oak (Quercus rubra L.) had higher densities than those of southern yellow pine, which is the traditional wood used in manufacturing CLT industrial mats, with a density of 616 kg/m3 at 12 percent moisture; the average density of the red oak tested was 770 kg/m3 at 13.98 percent moisture. All grades of red oak also had MOE and MOR values that met the requirements for lumber used in the manufacture of CLT industrial mats. For sweetgum (Liquidambar styraciflua L.), all grades met the required values for MOE and MOR, but only Grades 3 and 4 met the required density. All grades of yellow poplar (Liriodendron tulipifera L.) met the required MOE and MOR, but none met the required density.

Post-fire resurveys reveal predictability of long-term conifer recruitment in severely burned California dry forests

High severity fire is far outpacing post-fire reforestation capacity across the American West, highlighting the need to better understand when and where natural regeneration is sufficient to meet short- and long-term reforestation goals. The vast majority of available post-fire data represents regeneration in the first few years following a fire, raising the question of how well recovery trajectories can be predicted from early post-fire snapshots. We utilize a unique dataset from seven wildfires and 78 plots surveyed twice following stand-replacing fire in two California ecoregions, the northern Sierra Nevada and Klamath Mountains, to ask (1) how are post-fire vegetation and conifer densities changing over time and (2) how well do relatively early post-fire sampling efforts and biophysical factors (availability of seed source, shrub competition, and microclimate) explain longer-term (12–23 year) conifer recovery in California dry forests. Change in conifer seedling density between survey periods was highly variable. Overall, densities of all conifer species during the first decade after fire provided reliable estimates of longer-term conifer recovery in northern California dry forests, though in different ways for different species. Early post-fire seedling density readily explained longer-term densities for less shade-tolerant species, yellow pine (Pinus ponderosa and Pinus jeffreyi) and Douglas-fir (Pseudotsuga menziesii). In contrast, early seedling density was a poor predictor for shade-tolerant species, predominantly white fir (Abies concolor), with site conditions better explaining longer-term density. In general, the probability of a site experiencing net seedling mortality between surveys was highest in sites with high shrub cover and the probability of net recruitment increased with decreasing heat load, suggesting a continued role of microclimate and competition in forest recovery long after the initial post-fire period. Our results lend support to the use of relatively early post-fire surveys to infer longer-term forest recovery trajectories for forest management planning and can help refine reforestation prioritization tools.

Altitude-dependent variations in some morphological and anatomical features of Anatolian chestnut

Morphological measurements of Anatolian chestnut (Castanea sativa Mill.) leaves were done within the borders of Abana district of Kastamonu province. The study was conducted using mixed (oak, beech, hornbeam, black pine, and yellow pine) medium (41% to 70%) and fully closed (71% to 100%) stands. Some leaf parameters, such as leaf blade width, petiole length, leaf blade length, leaf length, distance between lateral veins, teeth width, teeth length, the angle between the leaf base and the petiole, and the angle between the midrib and lateral veins, were measured. Moreover, stomata of the leaves picked up from precise altitudes were observed under a scanning electron microscope. The differences between fibre elevation, fibre wall thickness, elasticity coefficient, rigidity coefficient, Muhlstep rate, and Runkel ratio were found in the wood samples taken from different altitude zones. It was found that altitude did not affect leaf blade width, fibre length, fibre width, felting ratio, and lumen width. However, it was determined that altitude affected other studied characteristics.

Wood dimensional stability enhancement by multivalent metal-cation-induced lignocellulosic microfibrils crosslinking

Wood is a hygroscopic material that responds to the moisture changes of the surrounding environment through swelling and shrinkage, making it dimensionally unstable. Here, we introduce a facile metal-ion-modification (MIM) approach to enhance the dimensional stability of wood. The MIM process involved swelling the wood samples with aqueous metal ion solutions and drying. The high valent metal cations, such as Fe3+, Al3+, and Zr4+, interacted with the hydrophilic groups (e.g., OH, COOH) present in the wood fibers, limiting their access to water and moisture, thereby enhancing the wood's hydrophobicity and dimensional stability. Evaluation of three wood species, southern yellow pine, poplar, and red oak, revealed water contact angles of 120–130° after MIM, indicative of enhanced surface hydrophobicity. Fe3+ treatment decreased southern yellow pine's swelling ratio from 6 % to 4 %. Fe3+-treated wood exhibited tangential anti-swelling efficiencies ranging from 39.83 % to 57.14 % and radial anti-swelling efficiencies from 34.74 % to 48.33 %, varying across wood species. The enhancement of wood dimensional stability can be attributed to the formation of irreversible coordination bonds between metal cations and lignocellulosic microfibrils in the wood cell wall. These bonds prevent the microfibrils from slipping in response to moisture absorption and desorption.

Physical and mechanical properties of mycelium-based fiberboards

Mycelium-based fiberboards were evaluated as potential environmentally friendly substitutes for conventional wood-based composites. The goal of this study was to produce and test fiberboards out of yellow pine and poplar fiber mixtures without using any extra adhesive. Pleurotus ostreatus and Ganoderma lucidum fungi were used. The physical and mechanical characteristics of the fiberboards were tested under the influence of two different types of fungi and two different incubation periods. The key findings indicated that the mycelium-based fiberboards had higher water absorption and thickness swelling percentages compared to control boards produced with adhesives. The fiberboards produced from fibers inoculated with Ganoderma lucidum and incubated for 30 days had higher mechanical properties compared to other test fiberboards. This indicated the possibility of utilizing them in specific applications. Although the mycelium-based fiberboards did not fully meet all the EN 622-5 (2009) standard requirements for dry-condition use, the results highlighted their potential in sustainable material development. This study provided useful insights into the utilization of mycelium for the development of mycelium-based fiberboards.

Timing of Hydrothermal Alteration and Au-Sb-W Mineralization, Stibnite-Yellow Pine District, Idaho

Abstract The Stibnite-Yellow Pine district of central Idaho was mined from the early 1900s until the 1990s, extracting gold, antimony, tungsten, and mercury from veins and disseminated and replacement ores in mountainous terrain along the headwaters of the Salmon River. Mining during the two World Wars supplied critical antimony and tungsten to the war efforts. Recent exploration has delineated mineral resources of over 187 metric tons Au, 274 metric tons Ag, and 93,000 metric tons Sb. Mineralization is hosted in Cretaceous Idaho batholith granitic rocks and a sequence of Neoproterozoic to Paleozoic metasedimentary strata of carbonate and siliciclastic compositions. Historic studies outlined some of the complex paragenesis but debated the absolute age of mineralization. New petrographic and geochronologic work documents a sequence of five hydrothermal events in the Stibnite-Yellow Pine district. Event 1 is related to Cretaceous magmatic and hydrothermal activity and includes events ranging in age from 86 to 75 Ma, including sparse quartz-molybdenite veins dated at 86 Ma. Disseminated gold mineralization of Event 2 is associated with sericitic alteration and sulfidation of igneous biotite and replacement of plagioclase by potassium feldspar, largely in granodiorite. Gold is present in zoned arsenian pyrite in both disseminated ores and in crosscutting carbonate-quartz veins containing pyrite and arsenopyrite. The large Yellow Pine deposit, localized at a dilatant bend in the Meadow Creek fault, hosts such disseminated and vein gold. Event 2 is interpreted as the major gold-forming event; 40Ar/39Ar ages of sericite and potassium feldspar alteration range, respectively, from 70 to 59 and 66 to 56 Ma. The long span is interpreted to reflect the age of gold mineralization and local overprinting by Event 3. A narrower range from 66 to 61 Ma is interpreted to date the peak of gold mineralization and alteration. Event 3, tungsten mineralization with scheelite, is texturally later than Event 2 gold and localized along the Meadow Creek structure. Event 3 scheelite has been dated by isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb methods at 57 Ma. Event 4, best developed in the West End area, includes gold-silver–bearing quartz-carbonate-pyrite veins and breccias with epithermal textures and potassium feldspar alteration envelopes. Adularia from Event 4 yields 40Ar/39Ar plateau ages of 52 to 51 Ma. Event 5 antimony and mercury mineralization consists of stibnite veins and breccia cements at the Yellow Pine and Hangar Flat deposits as well as cinnabar veins and replacements at the peripheral Fern and Hermes deposits; it is constrained by an LA-ICP-MS U-Pb date on scheelite (ca. 47 Ma) intergrown with stibnite. Minor propylitic and argillic alteration is evident in 47 Ma igneous dikes, which do not contain economic mineralization. The Au-Sb-W ores in the Stibnite-Yellow Pine mining district formed over an extended time period from about 70 to 45 Ma in multiple pulses that were localized along the Meadow Creek fault zone. Each event corresponds to episodes of magmatism and/or hydrothermal activity in the region. Insignificant Event 1 skarn and molybdenum mineralization is similar in age to the Thompson Creek porphyry molybdenum deposit in central Idaho. Event 2 gold mineralization occurred during a magmatic gap in central Idaho but was synchronous with magmatism in the Bitterroot lobe further north; Event 2 is similar in age to orogenic gold-arsenic mineralization at the Beartrack mine in eastern Idaho. Event 3 scheelite mineralization coincides with tungsten mineralization at the Quartz Creek deposit, late magmatism in the Bitterroot lobe, and rapid exhumation of the Atlanta lobe of the Idaho batholith. Event 4 gold mineralization is coincident with the onset of regional Challis magmatism and extension. Event 5 antimony and mercury mineralization is time-equivalent to epithermal gold mineralization in the nearby Thunder Mountain volcanic field and the peak of Challis magmatism.

Enhanced cross laminated timber (ECLT) for ballistic resistant design

Cross-laminated timber (CLT), an engineered wood product, has grown in popularity in the United States over the last decade due to its ease of assembly, aesthetic appeal, and potential to serve as a sustainable and renewable alternative building material. The improved robustness of CLT over light-frame timber structures has increased its potential in force-protected infrastructure that must resist blast waves and ballistic projectile penetration, but softwood CLT is typically not sufficient to fulfill standard criteria for ballistic threats. To address these threats, enhanced CLT (ECLT) composite panels were manufactured with layers of various reinforcing materials (e.g., steel, FRP) placed between wood laminations. These panels were tested against various ballistic threats during two sets of laboratory tests in order to provide a basis for future research. The first set of testing subjected laboratory-produced Southern Yellow Pine (SYP) ECLT to 84 shots of 0.50-inch (1.27 cm) steel sphere projectiles to evaluate the performance of various reinforcing materials, layups, and fastening methods. A subsequent set of tests subjected commercially produced ECLT of steel-reinforced Spruce-Pine-Fir (South) (SPF-S) to 36 shots of NATO ammunition projectiles traveling at realistic, standard striking velocities. Except for a panel using four layers of a thin and finely woven steel hardware cloth, steel reinforcement was effective in stopping projectiles from all three types of NATO ammunition fired. Ultimately considering the results of these two sets of tests, an initial cost-benefit structure was developed and discussed to compare ECLT configurations holistically, a multi-material wood analytical model framework was established and compared to experimental results, and the first ballistic experimental database for ECLT was created.

FOREST SEMANTIC SEGMENTATION BASED ON DEEP LEARNING USING SENTINEL-2 IMAGES

Abstract. Forests are invaluable for maintaining biodiversity, watersheds, rainfall levels, bioclimatic stability, carbon sequestration and climate change mitigation, and the sustainability of large-scale climate regimes. In other words, forests provide a wide range of ecosystem services and livelihoods for the people and play a critical role in influencing global atmospheric cycles. Providing sustainable, reliable, and accurate information on forest cover change is essential for an holistic forest management, efficient use of resources, neutralizing the effects of global warming and better monitoring of deforestation activities. Within the scope of this study, it is aimed to perform semantic segmentation of 5 different tree species (larch, red pine, yellow pine, oak, spruce) from Sentinel-2 satellite images. For this purpose, the regions where these tree species are densely populated in Turkey (Marmara, Aegean, Eastern Black Sea) were selected as pilot regions. A unique data set was created using the data of the selected pilot regions. As a result of the study, it was possible to determine the forest types temporally for the selected classes with more than 90% Intersection over Union score for all classes. The developed deep learning model with the created forest data set can be implemented to the other forests areas with same species in other parts of the world.

Environmental Marine Degradation of PLA/Wood Composite as an Alternative Sustainable Boat Building Material

Abstract IIn this study, which can be considered a contribution to the global effort to produce sustainable materials and to search new manufacturing methods for the boat building industry, the performance of a 3D printable polylactic acid and recycled wood (PLAW) composite was investigated under the simulated operational conditions of a boat. The wood used in the composite was yellow pine (Pinus sylvestris), a local wood widely used in boat building and 8% by weight in the composite. For the study, tensile and compressive strength tests were performed in both atmospheric and post-aging conditions, using composite samples produced by the additive manufacturing method. The durations of the accelerated aging before the experiments were one, two and four weeks. During these aging periods, water spraying, a salty fog environment and a drying cycle were applied at elevated temperatures and at equal time intervals, daily. The effect of wood additive on the composite and the joining efficiency of the components were also examined with scanning and optical microscopes. The performance of the obtained composite and the effects of aging on performance were measured using two different thermal analyses: differential scanning calorimetry and thermogravimetric analysis. From the results obtained, it can be seen that PLAW composite can be used in the manufacture of structural elements subjected to relatively low loads in boats. It is an option that will provide integrity in the future interior design of wooden boats.

Improved engineering model for water absorption in softwoods

Modeling of moisture transfer in porous materials is typically partitioned into liquid transport and vapor diffusion. Coefficients for liquid transport are often derived from laboratory measurements of water absorption by partial immersion. Although the assumption that capillary liquid transport is dominant while vapor diffusion is negligible is a reasonable assumption for mineral-based materials, recent work indicates that it is not representative of water absorption in wood across the grain. This article builds on earlier work and develops an improved engineering model for liquid water transport in softwoods. The approach uses a constant liquid diffusivity value, relies primarily on ordinary hygrothermal property measurements, and partitions vapor and liquid transport in a practical way that is informed by current understanding of wood–water interactions. The model is optimized using one-dimensional simulations calibrated against measured water uptake across a range of softwood species. Laboratory measurements were conducted to investigate key properties of eastern white cedar, which had the highest relative error in a previous version of the model, and to examine the practicality and relevance of vacuum saturation and free saturation for southern yellow pine. The model accuracy is improved by paying closer attention to the moisture storage function and capillary saturation value.

Design and Evaluation of a Shear Analogy Tool for Custom Cross-Laminated Timber (CLT) Panels Made from Various Wood Species

Abstract A user-friendly cross-laminated timber (CLT) design tool called SAM-CLT was developed to calculate the minimum design values for custom CLT panels. Custom panels are those made from different species not currently included in APA PRG 320 and include the use of multiple species in a panel. The tool uses the design value of hardwood and softwood lumber published in the national design specification book to design custom CLTs and the standard CLT grade lumber specification values published in PRG 320 standard. SAM-CLT was designed based on the shear analogy model and is intended to assist CLT manufacturers, construction and design companies, and researchers in designing and evaluating CLTs’ deformation when using different lumber types and thicknesses. This project included the calibration and validation of the tool, followed by examples of its use by computing the design value of the softwood, hardwood, and softwood–hardwood hybrid CLTs. The SAM-CLT tool was adjusted to match the published standard design values on PRG 320 and validated by comparing output for standard CLT layups. In the next step, SAM-CLT tool was used to calculate the minimum design value of custom CLTs made from hardwood–yellow poplar lumber and softwood–southern yellow pine lumber. Based on observed validation results of the tool and its application results to determine the design values for various CLT layups, this project concludes that SAM-CLT can be a valuable tool for designing custom CLTs, evaluating CLTs’ strength properties, and promoting heterogeneous lumber types in CLT manufacturing.

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.

Snag dynamics and surface fuel loads in the Sierra Nevada: Predicting the impact of the 2012–2016 drought

Forest die-backs linked to extreme droughts are expected to increase as the climate dries and warms. An example is the 2012–2016 hotter drought in California that induced widespread tree mortality in the Sierra Nevada, California. The sudden increase in snags (i.e., standing dead trees) raised immediate concerns about their impact on wildfire hazard and longer-term questions about their effect on ecosystem structure and function. We quantified the likely progression of snag fall and fuel succession following the recent extensive mortality event in the southern Sierra Nevada mixed conifer forest. Our results used data from a long-term demography study to project trends in surface fuel loads at three study sites in Yosemite, Sequoia and Kings Canyon national parks. In the short term (2017–2021), fine woody debris and litter + duff significantly increased across all three sites (>145 % and >55 %, respectively); coarse woody debris increased significantly at one site (48.6 %); and total fuel loads increased significantly at two of the three sites (38 % and 69 %). Snag longevity increased with size, with the relationship varying by species. Yellow pine was a notable outlier: size played a small role in influencing its fall rates. Overall, species-specific snag fall rates in the southern Sierra Nevada were 20 % to 40 % slower than previously reported. By 2040, projected median cumulative inputs of biomass from future snag fall range from 49.4 Mg ha−1 to 136.1 Mg ha-1across our three sites, which exceeds the amounts currently present (47.17–89.97 Mg ha−1) and is well above estimates of historical coarse woody debris amounts in the Sierra Nevada (17.7 Mg ha -1). These results provide a robust empirical basis to refine the snag fall algorithm in vegetation simulation models. Options to manage the impact of extreme number of snags and their large surface combustible biomass include salvage operations and prescribed burning, with both methods having operational, financial, and legal limitations that need to be considered.

Consistently heterogeneous structures observed at multiple spatial scales across fire-intact reference sites

Yellow pine and mixed-conifer (YPMC) forests of California’s Sierra Nevada have experienced widespread fire suppression for over a century, resulting in ingrowth and densification of trees, heavy fuel accumulation, and shifts in species composition. Under warmer and drier climates, these forests are primed for stand-replacing fires and severe drought mortality, requiring management interventions to improve their resilience and mitigate future impacts. Observations from functioning frequent-fire systems (e.g., contemporary reference sites) can provide key insights about pattern-process relationships in fire-intact systems, which can be used to inform regional management efforts. In this study, we used airborne lidar data to quantify and compare forest structure at multiple spatial scales between contemporary reference sites (i.e., forests with a restored frequent, low-intensity fire regime) and control sites (i.e., typical fire-suppressed forests). We evaluated structures at the neighborhood- (∼1 ha), site- (∼100–1,000 ha), and among-site- (∼10,000–100,000 ha) levels. In reference sites, high proportions of individual trees, small clumps of 2–4 trees, and open space formed mostly open canopy structures at the neighborhood-level, and patches of these neighborhood-level structures were arranged in heterogeneous spatial patterns within sites. We observed low variability in site-level structures among reference sites, indicating a stabilizing effect of frequent, low-intensity fire across broad, ecosystem scales. In fire-suppressed control sites, edaphic factors and other non-fire disturbances occasionally produced heterogeneity at the neighborhood- and site-level, but the degree of heterogeneity was not consistent across sites. Structural patterns in contemporary reference sites suggest improved resilience to future disturbances and climate change, and increased provisioning of ecosystem services relative to control sites. We suggest applying these metrics to help inform multi-scale and multi-resource management in Sierra Nevada forests.

Mechanical, physical and compositional effects of Meruliporia incrassata on Southern Yellow Pine

Abstract With the growing risk of fungal degradation in timber-framed structures from significant moisture intrusion events due to climate change, it is increasingly critical to develop mechanistic relationships between fungal degradation mechanisms and the strength of untreated wood components. While extensive work has been performed characterizing wood decay, no study has yet addressed the effects of Meruliporia incrassata on untreated Southern Yellow Pine. This seeks to address this knowledge gap by evaluating the effects of the common brown rot fungus on an ubiquitous building material in the southeast United States – Southern Yellow Pine. Properties of Southern Yellow Pine were evaluated at seven decay stages over the course of 12 weeks of exposure to M. incrassata. Changes in physical properties – mass, density, and moisture content – were measured at each stage. Changes in stiffness were characterized via ultrasonic pulse velocity testing, and thermogravimetric analysis was utilized to assess compositional changes. The study found rapid and significant losses in stiffness at decay stages as early as four-weeks. Hemicellulose and cellulose degradation occurred steadily throughout the decay period. These results can be utilized to develop a stronger understanding of the mechanical behavior of timber-framed structures in the United States degraded by brown rot.