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Testing and modeling of CLT-to-CLT joints made using hardwood dowels and screws with varying spacing
With the increasing popularity of mass timber, utilizing large-diameter wood screws and hardwood dowels can offer an easy and cost-efficient way to join structural elements. However, the existing research on hardwood dowels is limited to single fastener joints under monotonic loading. No research is available on the group effects of joints with multiple hardwood dowels. Here, this paper presents the results of 96 monotonic and cyclic single-shear plane CLT-to-CLT joint tests with hardwood dowels (Red Oak and Yellow Birch, 25.4 mm diameter) and self-tapping wood screws (8 mm diameter) in Grand-Fir CLT, where screws were inserted both perpendicular and at a 45-degree angle to the grain for comparison to hardwood dowels. The study evaluated the mechanical properties of the joints by changing fastener spacing. Mechanical properties such as yielding and peak strength, displacement, elastic and yielding stiffness, and ductility were evaluated. The results showed equal strength and stiffness properties for hardwood dowels comparable with large-diameter screws. Additionally, the hardwood dowel joints demonstrated moderate ductility properties. The strength and stiffness of the tested joints were compared with analytical equations found in the literature by considering the group action factor of the fasteners. Lastly, a nonlinear force-displacement model was presented and compared to the experimental results and analytical calculations, which gives the possibility to predict and optimize the mechanical behavior of hardwood dowel and screw joints with varying numbers and spacing between fasteners.
Initial plant community responses to hardwood control treatments in restoration of remnant longleaf pine (Pinus palustris) woodlands
Changes in land use over the past century have contributed to substantial losses of longleaf pine (Pinus palustris) woodlands in the southeastern USA and replacement with higher density, mixed pine and hardwood stands that suppress understory development and limit application of prescribed fire. To increase understanding of limiting factors and identify potential approaches for restoring longleaf pine woodlands, we studied in this work initial availability of light and soil water and 2-year (2018–2019) plant community responses after controlling overstory hardwoods in five remnant longleaf pine woodlands having no evidence of previous agriculture at the Savannah River Site near Aiken, SC, USA. Seven hardwood control treatments and a non-treated check were compared in a randomized compete block experiment: cutting, cutting + shredding of logging residues, stem injection with imazapyr herbicide, cutting + basal spray with imazapyr herbicide, cutting + basal spray with triclopyr herbicide, cutting + directed foliar spray with a mixture of glyphosate and imazapyr herbicides, and cutting + broadcast foliar spray with the same herbicide mixture. In the year prior to hardwood cutting (2016), understory light availability averaged 23% of full sun. Throughout the year of treatment installation (2017), average soil water content (SWC) was below permanent wilting point (5.5% SWC) where overstory hardwoods were retained; whereas, it was above wilting point (7.5%) where they had been cut. Thus, combined effects of shade and root competition from overstory hardwoods probably limited cover of herbaceous species in the non-treated check. In the 2 years following treatment, hardwood survival averaged > 99%, 62%, 42% and < 1% for the non-treated check, cutting, shredding, and herbicide treatments, respectively. Relative to the non-treated check, herbaceous species richness was increased by shredding, stem injection, basal spray, or directed foliar treatments; herbaceous cover was increased by basal spray or directed foliar treatments; and woody cover was decreased by directed or broadcast foliar treatments. The directed foliar spray was the most effective treatment for achieving many of the desired understory characteristics of a longleaf pine woodland, including a diverse understory dominated by herbaceous vegetation capable of supporting periodic prescribed fires. Although the imazapyr basal spray treatment increased cover of remnant woodland indicator species, none of the treatments increased richness of this species group, suggesting that restoration of native species composition will be expedited by enrichment seedings or plantings.
AmeriFlux FLUXNET-1F US-Wi1 Intermediate hardwood (IHW)
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-Wi1 Intermediate hardwood (IHW). This is the FLUXNET version of the carbon flux data for the site US-Wi1 Intermediate hardwood (IHW) produced by applying the standard ONEFlux (1F) software. Site Description - The Wisconsin Intermediate Hardwoods site is located in the Washburn Ranger District of the Chequamegon National Forest. A member of the northern coniferous-deciduous biome, surveys from the mid-19th century indicate the region consisted of a mixed stand of red, white, and jack pines. After extensive timber harvesting, wildfires, and farming activity, the region turned into a fragmented mosaic of stands of various ages and composition. The intermediate hardwoods site is one of ten sites that collectively represent the successional stages of development in the predominant stand types of a physically homogeneous landscape. In 2001, northern hardwood stands of all ages occupied 45% of the region.
AmeriFlux FLUXNET-1F US-Wi8 Young hardwood clearcut (YHW)
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-Wi8 Young hardwood clearcut (YHW). This is the FLUXNET version of the carbon flux data for the site US-Wi8 Young hardwood clearcut (YHW) produced by applying the standard ONEFlux (1F) software. Site Description - The Wisconsin Clearcut Young Hardwood site is located in the Washburn Ranger District of the northeastern section of Chequamegon National Forest. A member of the northern coniferous-deciduous biome, surveys from the mid-19th century indicate the region consisted of a mixed stand of red, white, and jack pines. After extensive timber harvesting, wildfires, and farming activity, the region turned into a fragmented mosaic of stands of various ages and composition. The young hardwood clearcut site is one of ten sites that collectively represent the successional stages of development in the predominant stand types of a physically homogeneous landscape. In 2001, northern hardwood stands of all ages occupied 45% of the region.
Monotonic testing of single shear-plane CLT-to-CLT joint with hardwood dowels
Reducing embodied carbon emissions in buildings and striving for carbon neutrality through sustainable design has become a primary goal in the construction industry. The industry is expanding its use of wood-engineered products, such as cross-laminated timber (CLT) to achieve those sustainability goals. Furthermore, replacing steel fasteners with lower embodied carbon alternatives is gaining increased attention in timber engineering. This paper aims to quantify the mechanical behavior of single shear-plane CLT-to-CLT joints using hardwood dowels. The study includes 154 single shear-plane experimental tests with four different CLT species, two hardwood dowel species, and two dowel diameters. Further, the test specimens were subjected to cyclic and monotonic loading until failure, and mechanical properties such as yielding and ultimate strength, serviceability and yielding stiffness, and ductility were quantified. The hardwood dowel CLT-to-CLT joints demonstrated high strength with up to 10.3 kN (2.3 kips) capacity per dowel and lateral stiffness of up to 5.2 kN/mm (30.8 k/in) per dowel. This strength and stiffness are roughly equivalent to or exceed values for mass timber wood screws, making hardwood dowels a good alternative. In addition, the observed mean ductility of joints ranged from 2.4 to 4.5. Finally, analytical equations for the joints' yielding strength, lateral serviceability stiffness, and yielding stiffness were derived with non-linear regression analysis and validated using the experimental test results.
AmeriFlux FLUXNET-1F US-Wi3 Mature hardwood (MHW)
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-Wi3 Mature hardwood (MHW). This is the FLUXNET version of the carbon flux data for the site US-Wi3 Mature hardwood (MHW) produced by applying the standard ONEFlux (1F) software. Site Description - The Wisconsin Mature Hardwood site is located in the Washburn Ranger District of the northeastern section of Chequamegon National Forest. A member of the northern coniferous-deciduous biome, surveys from the mid-19th century indicate the region consisted of a mixed stand of red, white, and jack pines. After extensive timber harvesting, wildfires, and farming activity, the region turned into a fragmented mosaic of stands of various ages and composition. As an assemblage, the ten Wisconsin sites are indicative of the successional stages of development in the predominant stand types of a physically homogeneous landscape. The mature hardwood stand represents a typical naturally regenerated second-growth forest, free of anthropogenic disturbances for at least 70 years.
AmeriFlux FLUXNET-1F US-PFn SW4 Hardwood-3 CHEESEHEAD 2019
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-PFn SW4 Hardwood-3 CHEESEHEAD 2019. This is the FLUXNET version of the carbon flux data for the site US-PFn SW4 Hardwood-3 CHEESEHEAD 2019 produced by applying the standard ONEFlux (1F) software. Site Description - This tower (32m, trailer-based, telescoping) is located in the southwestern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest - aspen, oak, birch, some pines (canopy height: 20 - 26 m).
AmeriFlux FLUXNET-1F US-PFp SE2 Hardwood-4 CHEESEHEAD 2019
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-PFp SE2 Hardwood-4 CHEESEHEAD 2019. This is the FLUXNET version of the carbon flux data for the site US-PFp SE2 Hardwood-4 CHEESEHEAD 2019 produced by applying the standard ONEFlux (1F) software. Site Description - This tower (32m, trailer-based, telescoping) is located in the southeastern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest - black ash and red maple (canopy height: 20 - 24.4 m).
AmeriFlux FLUXNET-1F US-PFi NE3 Hardwood-1 CHEESEHEAD 2019
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-PFi NE3 Hardwood-1 CHEESEHEAD 2019. This is the FLUXNET version of the carbon flux data for the site US-PFi NE3 Hardwood-1 CHEESEHEAD 2019 produced by applying the standard ONEFlux (1F) software. Site Description - This tower (32m, trailer-based, telescoping) is located in the northeastern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest (canopy height: 18 - 20m).
Hot Water Extraction: Short Rotation Willow, Mixed Hardwoods, and Process Considerations
Short rotation woody crops (SRWC) like shrub willow are highly productive biomass resources of interest for energy and fuel applications. Hot water extraction (HWE) as an upgrading tool to enable the use of willow biomass in pellet applications has been proposed, and is of increasing interest. This study treats willow and mixes of willow and conventional mixed hardwood feedstock with HWE in a tumbling laboratory reactor to elucidate the effects of time, temperature, feedstock mixes, and other process considerations (water:biomass ratio, presteaming, counter-current processing) on mass removals and other extraction outcomes (e.g., sugar, acetate, and furan yields). Results demonstrated alignment of extraction outcomes with P-factor from 155 °C to 175 °C, with a good compromise of removed mass and co-product potential in the range from 575–800 P-factor. The preferred condition was chosen as 575 P-factor. HWE of mixes of willow and hardwood feedstocks showed a linear response of extraction outcomes to willow:hardwood ratios. Testing of water:biomass ratios demonstrated that this is a significant consideration, with each outcome being affected somewhat differently, and indicating that HWE is more diffusion dependent than expected. Presteaming shows little to no effect on extraction outcomes, while multi-stage cooks simulating counter-current operation indicate a significant potential value in counter-current extraction.
Linking habitat suitability with a longleaf pine-hardwood model: Building a species-predictive fire-land management framework
Active management of fire-dependent ecosystems for specific species leads to complex tradeoffs, which affect conservation outcomes to other species. Therefore a multi-species evaluation of management actions is required. Habitat Suitability Models (HSMs) can help in predicting the likelihood of species occurrence using corresponding environmental variables and empirical relationships that link occurrence with specific environmental conditions. Incorporating multiple species into HSMs and relating them to habitat dynamics is crucial for ecosystems that require active management with prescribed fire. To address this issue, we developed multi-species HSM driven within an existing population model of the longleaf pine-hardwood ecosystem to assess the suitability of an ecosystem given different fire management strategies and environmental conditions. The population model used in this study provides spatial and temporal changes of longleaf pine-hardwood habitat structure in response to fire. These habitat values are used by the HSM to calculate habitat suitability for three threatened and endangered faunal species of this ecosystem, which all thrive with frequent fire, but have unique habitat requirements. Transient habitat conditions are traced to predict longleaf pine ecosystem trajectories under various management strategies, thereby evaluating current land management actions, such as thinning or prescribed fire frequencies. We tested a suite of environmental conditions to emphasize the sensitivity of the species to different fire management actions. The results of our modeling suggest that maximum suitable habitat for all three species can be achieved with fire frequency occurring at approximately once every three years. The modeling results support current management actions and provide a new habitat assessment tool that incorporates ecological factors for multiple species, thus providing for habitat optimization.
Variation in hyphal production rather than turnover regulates standing fungal biomass in temperate hardwood forests
Abstract Soil fungi link above‐ and belowground carbon (C) fluxes through their interactions with plants and contribute to C and nutrient dynamics through the production, turnover, and activity of fungal hyphae. Despite their importance to ecosystem processes, estimates of hyphal production and turnover rates are relatively uncommon, especially in temperate hardwood forests. We sequentially harvested hyphal ingrowth bags to quantify the rates of Dikarya (Ascomycota and Basidiomycota) hyphal production and turnover in three hardwood forests in the Midwestern United States, where plots differed in their abundance of arbuscular (AM)‐ vs. ectomycorrhizal (ECM)‐associated trees. Hyphal production rates increased linearly with the percentage of ECM trees and annual production rates were 66% higher in ECM‐ than AM‐dominated plots. Hyphal turnover rates did not differ across the mycorrhizal gradient (plots varying in their abundance of AM vs. ECM trees), suggesting that the greater fungal biomass in ECM‐dominated plots relates to greater fungal production rather than slower fungal turnover. Differences in hyphal production across the gradient aligned with distinctly different fungal communities and activities. As ECM trees increased in dominance, fungi inside ingrowth bags produced more extracellular enzymes involved in degrading nitrogen (N)‐bearing relative to C‐bearing compounds, suggesting greater fungal (and possibly plant) N demand in ECM‐dominated soils. Collectively, our results demonstrate that shifts in temperate tree species composition that result in changes in the dominant type of mycorrhizal association may have strong impacts on Dikarya hyphal production, fungal community composition and extracellular enzyme activity, with important consequences for soil C and N cycling.
Profiling overstory survival trends following varying thinning and burning disturbance regimes in a mixed pine-hardwood forest in the US South
Prescribed burning as a silvicultural tool may be effective for achieving various management objectives, yet some practitioners have concerns about inadvertently increasing overstory tree mortality. Using extensive data from a long-term, ongoing study in northcentral Alabama, USA, that systematically applies a variety of thinning and prescribed burning disturbances on mixed pine-hardwood stands, we assess survival trends for different groups of trees. The primary research question is whether more frequent prescribed burns adversely affects overstory survival versus infrequent or no burns; secondary questions explore whether overstory survival trends differ based on thinning level, species group, or size class. Interest is in broad groups of trees, not individual tree survival or mortality; consequently, survival analysis methods are used, including nonparametric Kaplan-Meier (KM) techniques for examining single grouping factors, and parametric accelerated failure time models for analyzing simultaneous effects of multiple covariates. Leveraging relatively recent methodological advances, the statistical techniques are adjusted for interval censored data. KM survival curves showed that more frequent prescribed fires did not result in differing survival trends. Also, trees in unthinned stands had the lowest 14-year survival compared to thinned stands, oaks had the highest survival compared to pines and the others species group, and the smallest size class of overstory trees had the lowest survival. In conclusion, these results support managing transitional mixed pine-hardwoods using thinning and multiple prescribed fires to restore specific species composition and structure.
AmeriFlux US-PFi NE3 Hardwood-1 CHEESEHEAD 2019
This is the AmeriFlux version of the carbon flux data for the site US-PFi NE3 Hardwood-1 CHEESEHEAD 2019. Site Description - This tower (32m, trailer-based, telescoping) is located in the northeastern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest (canopy height: 18 - 20m).
AmeriFlux US-PFn SW4 Hardwood-3 CHEESEHEAD 2019
This is the AmeriFlux version of the carbon flux data for the site US-PFn SW4 Hardwood-3 CHEESEHEAD 2019. Site Description - This tower (32m, trailer-based, telescoping) is located in the southwestern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest - aspen, oak, birch, some pines (canopy height: 20 - 26 m).
AmeriFlux US-PFp SE2 Hardwood-4 CHEESEHEAD 2019
This is the AmeriFlux version of the carbon flux data for the site US-PFp SE2 Hardwood-4 CHEESEHEAD 2019. Site Description - This tower (32m, trailer-based, telescoping) is located in the southeastern quadrant of the 10 x 10km study domain. It is located in a mixed hardwood forest - black ash and red maple (canopy height: 20 - 24.4 m).
AmeriFlux FLUXNET-1F US-PFm SW3 Hardwood-2 CHEESEHEAD 2019
This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-PFm SW3 Hardwood-2 CHEESEHEAD 2019. This is the FLUXNET version of the carbon flux data for the site US-PFm SW3 Hardwood-2 CHEESEHEAD 2019 produced by applying the standard ONEFlux (1F) software. Site Description - This tower (32m, trailer-based, telescoping) is located in the southwestern quadrant of the 10 x 10km study domain. It is located in an aspen and maple forest (canopy height: 15 m).