Ponderosa Pine Research Articles

Long-term efficacy of fuel reduction and restoration treatments in Northern Rockies dry forests.

Fuel and restoration treatments seeking to mitigate the likelihood of uncharacteristic high-severity wildfires in forests with historically frequent, low-severity fire regimes are increasingly common, but long-term treatment effects on fuels, aboveground carbon, plant community structure, ecosystem resilience, and other ecosystem attributes are understudied. We present 20-year responses to thinning and prescribed burning treatments commonly used in dry, low-elevation forests of the western United States from a long-term study site in the Northern Rockies that is part of the National Fire and Fire Surrogate Study. We provide a comprehensive synthesis of short-term (<4 years) and mid-term (<14 years) results from previous findings. We then place these results in the context of a mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak that impacted the site 5-10 years post-treatment and describe 20-year responses to assess the longevity of restoration and fuel reduction treatments in light of the MPB outbreak. Thinning treatments had persistently lower forest density and higher tree growth, but effects were more pronounced when thinning was combined with prescribed fire. The thinning+prescribed fire treatment had the additional benefit of maintaining the highest proportion of ponderosa pine (Pinus ponderosa) for overstory and regeneration. No differences in understory native plant cover and richness or exotic species cover remained after 20 years, but exotic species richness, while low relative to native species, was still higher in the thinning+prescribed fire treatment than the control. Aboveground live carbon stocks in thinning treatments recovered to near control and prescribed fire treatment levels by 20 years. The prescribed fire treatment and control had higher fuel loads than thinning treatments due to interactions with the MPB outbreak. The MPB-induced changes to forest structure and fuels increased the fire hazard 20 years post-treatment in the control and prescribed fire treatment. Should a wildfire occur now, the thinning+prescribed fire treatment would likely have the lowest intensity fire and highest tree survival and stable carbon stocks. Our findings show broad support that thinning and prescribed fire increase ponderosa pine forest resilience to both wildfire and bark beetles for up to 20 years, but efficacy is waning and additional fuel treatments are needed to maintain resilience.

Early treatment effects on plantation growth and biodiversity in mature ponderosa pine forest

We address the concerns that managed forest plantations may cause reductions of diversity of understory vegetation. We performed inventories of two mature ponderosa pine plantations in which multiple treatments were applied during plantation establishment. At stand age 35, we measured tree heights and diameters, understory plant cover and diversity, soil nutrients and chemical properties, and soil microbial biomass and diversity with phospholipid fatty acid. We found a significant, positive effect from both herbicide (H) and fertilizer (F) applications on subsequent overstory tree growth and development ( P &lt; 0.05); insecticide (I) effect was minimal. We observed negative effects on understory plant diversity decades later when herbicide was applied during stand establishment. However, lower plant diversity and ground cover appeared to have been caused primarily from overstory canopy closure, supported by the increased understory cover and diversity observed in the HI and HFI plots that had been thinned at age 12. Similarly, while fertilizer increased tree growth at both sites, it only negatively affected understory plants at the higher quality site. We did not find significant influence of treatment effects on soil nutrients and microbial communities. Therefore, to mitigate the potential loss of understory biodiversity in plantations, foresters can manage overstory trees with traditional pre-commercial thinning techniques and early tending.

Bending Characteristics of Custom CLT Layups Laminated with Ponderosa Pine Harvested from Restoration Programs

Bending Characteristics of Custom CLT Layups Laminated with Ponderosa Pine Harvested from Restoration Programs

Investigate on the physical and mechanical properties of wood-polymer composition materials made on the premise of neighborhood wood flours

This study aims to demonstrate the feasibility of obtaining wood-polymer composites, which focus on materials that are difficult to recycle. For this purpose, local poplar and pavloniya wood samples, the density of which corresponds to this process, were impregnated with polyvinyl chloride and CaCO3, which form free radicals. Samples were taken using a hot press. Physico-mechanical parameters of the samples were analyzed. Due to the low permeability of the poplar wood showed only increasing values of stiffness parallel and perpendicular to the grain. Undebarked ponderosa pine chips were treated by hot water extraction to modify the chemical composition. In the treated pine (TP), the mass was reduced by approximately 20%, and the extract was composed mainly of degradation products of hemicelluloses. Wood flour produced from TP and unextracted chips (untreated pine, UP) was blended with high-density polyethylene (HDPE) and polypropylene (PP) and was extruded into wood plastic composites (WPCs).

Molecular composition and the impact of fuel moisture content on fresh primary organic aerosol emissions during laboratory combustion of ponderosa pine needles

Environmental context Wildland fire smoke and its impacts on air quality and human health are increasing globally. However, uncertainties in organic emissions from these fires hinder our understanding of downwind atmospheric photochemical processes driving the formation of hazardous air pollutants. In this study, we investigated the impact of fuel moisture content on organic species emission during the combustion of ponderosa pine needles, an important fuel source in the western United States. Rationale Pine needles represent an important fuel source in coniferous forest systems in the western United States. During forest fires, they can be easily ignited and help sustain flame on the ground. Methodology In this study, a comprehensive chemical analysis was conducted to examine oxygenated organic compounds (OOCs) present in PM2.5 (particles ≤ 2.5 µm in aerodynamic diameter) formed from burning dry and moist ponderosa pine (Pinus ponderosa) needles (PPN) in the presence and absence of fine woody debris (FWD). The effect of fuel moisture content (FMC), a key parameter that influences smoke formation, has not received much attention. Therefore, we also investigated the effect of FMC on PM2.5 formation and its composition. Thirty three experiments were conducted at the US Forest Service Fire Science Laboratory. PM2.5 was collected onto 47-mm Teflon filters, and silylated extracts were analysed by gas chromatography–mass spectrometry. Results More than 50 OOCs were identified, including levoglucosan and mannosan; n-dodecanoic acid and n-hexadecanoic acid; dihydroabietic acid, and dehydroabietic acid; and a series of intermediate volatile and semivolatile organic compounds. Mass spectra of a wide variety of compounds in electron and chemical ionisation mode are provided. Most of these OOCs were identified in this study for the first time in PPN aerosol, although some were previously reported in pine wood and other biomass burning aerosol. Our results show significant changes in the composition and abundance of particles depending on the amount and type of PPN burned. When compared with dry PPN, moist PPN showed decreased emissions of PM2.5 and OOCs, due likely to the presence of water in the system that partially suppressed the production of OOCs. Discussion Incorporating pine needles in atmospheric models as a contributor to smoke particles generated during forest fires is an essential step towards reducing the current uncertainties regarding the influence of these aerosols on chemical/air mass characteristics, regional meteorology, and the climate.

Nonstructural carbohydrates explain post-fire tree mortality and recovery patterns.

Trees use nonstructural carbohydrates (NSCs) to support many functions, including recovery from disturbances. However, NSC's importance for recovery following fire and whether NSC depletion contributes to post-fire delayed mortality are largely unknown. We investigated how fire affects NSCs based on fire-caused injury from a prescribed fire in a young Pinus ponderosa (Lawson & C. Lawson) stand. We assessed crown injury (needle scorch and bud kill) and measured NSCs of needles and inner bark (i.e., secondary phloem) of branches and main stems of trees subject to fire and at an adjacent unburned site. We measured NSCs pre-fire and at six timesteps post-fire (4days-16months). While all trees initially survived the fire, NSC concentrations declined quickly in burned trees relative to unburned controls over the same post-fire period. This decline was strongest for trees that eventually died, but those that survived recovered to unburned levels within 14months post-fire. Two months post-fire, the relationship between crown scorch and NSCs of the main stem inner bark was strongly negative (Adj-R2=0.83). Our results support the importance of NSCs for tree survival and recovery post-fire and suggest that post-fire NSC depletion is in part related to reduced photosynthetic leaf area that subsequently limits carbohydrate availability for maintaining tree function. Crown scorch is a commonly measured metric of tree-level fire severity and is often linked to post-fire tree outcome (i.e., recovery or mortality). Thus, our finding that NSC depletion may be the mechanistic link between the fire-caused injury and tree outcome will help improve models of post-fire tree mortality and forest recovery.

Wind-induced torsional vibration in a ponderosa pine tree

The overall response of above-ground tree parts to wind loading consists of torsional and bending vibrations. While bending vibrations have been frequently measured in previous studies, measurements of torsional vibrations are scarce. Therefore, three-dimensional tree response measurements were conducted along the stem and on several branches of a ponderosa pine (Pinus ponderosa) tree. The measurements reveal that tree parts respond to external forces with torsional and bending vibrations even at low wind loads. As wind loading intensifies, the contribution of torsional vibration to the overall tree response rapidly diminishes, stabilizing at a lower level Concurrently, the share of bending vibrations becomes more prominent, accounting for nearly the entire tree response. Torsional vibrations are most pronounced in the crown space and more localized than bending vibrations. Under the wind loading conditions during the study period, they were hardly measurable in the lower stem parts. If one aims to quantify torsion in above-ground tree parts, multiple measurements are necessary depending on the research objectives. The results also indicate that depending on the wind load, one- and two-dimensional measurements of the wind-induced tree response made in lower stem parts are only sometimes suitable to capture the overall tree response to wind loads.

A species' response to spatial climatic variation does not predict its response to climate change.

The dominant paradigm for assessing ecological responses to climate change assumes that future states of individuals and populations can be predicted by current, species-wide performance variation across spatial climatic gradients. However, if the fates of ecological systems are better predicted by past responses to in situ climatic variation through time, this current analytical paradigm may be severely misleading. Empirically testing whether spatial or temporal climate responses better predict how species respond to climate change has been elusive, largely due to restrictive data requirements. Here, we leverage a newly collected network of ponderosa pine tree-ring time series to test whether statistically inferred responses to spatial versus temporal climatic variation better predict how trees have responded to recent climate change. When compared to observed tree growth responses to climate change since 1980, predictions derived from spatial climatic variation were wrong in both magnitude and direction. This was not the case for predictions derived from climatic variation through time, which were able to replicate observed responses well. Future climate scenarios through the end of the 21st century exacerbated these disparities. These results suggest that the currently dominant paradigm of forecasting the ecological impacts of climate change based on spatial climatic variation may be severely misleading over decadal to centennial timescales.

Canopy-mediated microclimate refugia do not match narrow regeneration niches in a managed dry conifer forest

Structurally heterogeneous forest conditions provide diverse microclimates which can support juvenile tree regeneration, survival, and growth. However, the extent to which juvenile trees depend on moderated microclimates depends on their physical maturity and species-specific tolerances for environmental stresses related to variables like soil moisture, heat, and shade. Linking juvenile responses to microclimates for different life-stages and species facilitates more nuanced understanding of regeneration niches and is especially important in dry conifer forests where structurally heterogeneous conditions are a frequent objective of forest restoration treatments. In this study, we sampled microclimate conditions and planted seeds and greenhouse-grown seedlings across a range of overstory structure and microclimate conditions in a heterogeneous forest restoration treatment in Colorado, USA. We assessed how fine-scale (∼1–20 m) spatial variation in overstory structure and topography related to variability in microclimate conditions and, collectively, how these biophysical conditions influenced survival and growth of ponderosa pine (Pinus ponderosa var. scopulorum) and Douglas-fir (Pseudotsuga menziesii var. glauca) over 3 years. We found evidence of strong canopy buffering of mean daily vapor pressure deficit (VPD), but buffering of daily maximum VPD was moderate, and buffering of soil moisture was weak except in the hottest and driest month of our 3-year study. Although canopy cover provided refuge from hot and dry conditions, survival and growth of juvenile trees across life-stages and species were greatest in above-average canopy openness, with warm and dry microclimate conditions in May. The spatial patterns of seedling establishment relative to canopy cover, driven by early-season microclimate conditions, did not match canopy-mediated, moderate microclimates later in growing seasons when weather conditions were most limiting. Importantly, our results reflect a specific regeneration trajectory initiated by favorable early-growing season conditions in the first year of study, which promoted survival and growth resilience through subsequent limiting conditions, most notably a hot and dry second year of study. The patterns observed in this study are consistent with drivers of landscape-scale regeneration previously identified for dry conifer forests and show that overstory structure and microclimate variation can mediate these patterns at very fine spatial scales. The narrow spatial and temporal ranges of conditions which supported survival and growth in this study highlight opportunities for restoration treatment planning in similar forests, but also underscore the susceptibility of these dominant dry forest species to potential future changes in the timing and intensity of abiotic conditions which limit regeneration success.

Damage reduction of Acromyrmex lobicornis in Pinus ponderosa using mixed pine species in combination with push–pull tools

Abstract Leaf‐cutting ants (LCAs) cause significant damage to forest plantations and are mainly managed by broad‐spectrum synthetic insecticides. In Patagonia, Pinus ponderosa (Pinales: Pinaceae) (Douglas 1836) and Pinus contorta (Pinales: Pinaceae) (Dluglas 1838) are the predominant pine species in forest plantations. Previous research has shown that dehydrated citrus pulp is an LCAs attractant, and tea tree essential oil acts as an LCAs repellent. We evaluated the use of dehydrated citrus pulp and tea tree oil to manage LCAs behaviour in a push–pull setting, using mixed pine species in small plot fields, to reduce the LCA Acromyrmex lobicornis (Hymenoptera: Formicidae) (Emery, 1888) damage in young P. ponderosa plants. We combined the treatment with attractant and repellent in a mono‐specific plantation design (three ponderosa plants surrounded with pulp and three sprayed with tea tree extract) or mixed plantation designs (three contorta plants with pulp and three ponderosa plants with tea tree). The combination of both mono‐specific and mixed plantations with push–pull stimuli delayed discovery and decreased the damage in pines sprayed with the repellent. Mono‐specific as well as mixed species designs were equally effective, reducing ant damage and increasing ~50% the survival probability of P. ponderosa when push–pull stimuli were applied. The use of a push–pull strategy with plant‐based compounds provides potential as a management tool that reduces and delays LCA damage in pine trees.

Increases in understory plant cover and richness persist following restoration treatments in Pinus ponderosa forests

Abstract A combination of forest thinning followed by prescribed burning is widely applied in the western United States to increase ecosystem resistance and resilience to disturbances. Understory plant community responses may be driven by both management treatments and climatic factors. Thus, responses to treatments during a 20‐year megadrought have implications for the role of management in fostering adaptive capacity to climate change. We used a network of five sites (600 plots) spanning an environmental gradient in ponderosa pine (Pinus ponderosa) forests of the American Southwest, an ecosystem that is broadly distributed and actively managed throughout the western United States. We used repeated long‐term monitoring data to quantify plant community responses to treatment 1–5‐, 6–10‐ and &gt;10‐year post‐implementation. Specifically, we focussed on the effects of treatment and abiotic conditions on native and non‐native plant cover and species richness and the proportion of native species with northern (cool‐mesic) biogeographic affinities. Overall, thinning and prescribed burning nearly doubled native cover and increased native species richness by about 50% relative to untreated controls. These effects persisted for over a decade after treatment, even under the influence of significant and persistent drought. Cover and richness were also greater on intermediate to wet sites. Finally, native species with northern biogeographic affinities were reduced for up to 5 years after treatment relative to those with southern (warm‐xeric) affinities, and in dry years, indicating that both management and interannual climate variability may foster shifts to plant communities that are more resilient to a warming climate. Synthesis and applications. In ponderosa pine forests of the American Southwest, tree thinning followed by prescribed burning will generally promote restoration goals of increasing resilience to climate change by enhancing the diversity and abundance of native understory plant species, even during a persistent 20‐year megadrought.

Metal cation concentrations improve understanding of controls on soil organic carbon across a precipitation by vegetation gradient in the Patagonian Andes

Tephra-derived soils retain more organic carbon (C) than soils formed from any other parent material, but this C may be sensitive to changes in climate and land use. Here we evaluate the effects of precipitation, temperature, and afforestation on extractable metals and organic C storage in young tephra-derived soils in a temperate climate. We conducted our investigation across five sites in the Patagonian Andes that vary from 250 mm to 2200 mm mean annual precipitation, and 12 to 9.7 ℃ mean annual temperature from east to west. At each of the five sites are paired plots of natural vegetation, varying from grasses and shrubs at the dry sites to closed-canopy forest at the wet, and stands of Pinus ponderosa planted in monocultures 35 years prior to sampling. Previous research at these sites showed that aboveground net primary production and soil organic C increased with rainfall, but total soil organic C content was lower in pine plantations than natural vegetation. Here we assess whether variation in precipitation and vegetation type also affect soil mineral properties that promote soil C stabilization. Soils were collected to the depth of auger refusal and extracted with 0.5 M HCl for 24 h to target the combined exchangeable and adsorbed metals, including secondary short-range-ordered mineral phases and the plant available pools of Mg, Ca, and K. Pine afforestation lowered concentrations of HCl-extractable K (p < 0.1) and Ca (p < 0.01) within the top 0 – 30 cm. Other elements, while not affected by vegetation type, did respond to the rainfall gradient. Al, Si, P, and Mn all increased in the surface soils with increasing rainfall (p < 0.01), suggesting the development of short-range-order volcanic mineral phases that retain nutrients such as P and Mn. The addition of Al and Ca in the linear model to describe soil organic C explained more of the total variance than rainfall and vegetation type alone, indicating the importance of Al complexes and cation (Ca) bridging with secondary minerals to soil C retention. Importantly, the lower concentration of Ca in planted pine soils may signal a long-term decrease in the potential soil C stored in afforested soils due to a lower capacity for cation bridging. Our results show that the chemistry of these young tephra soils is dynamic, responding to both precipitation and afforestation in distinct ways with potential long-term impacts on nutrient cycling and C storage.

Holy Shit: Lutheran Carnality and Thinking like a Tree

This article begins with my experience of a Ponderosa pine and centers on an ecological reading of Dietrich Bonhoeffer’s vision of God and the world as “one reality” in his Ethics. A non-dualistic spirituality embraces aspects of reality Christians typically shun, such as the scatological dimension of our animal lives. I engage these questions through attention to the literal, ethical, socio-economic, and symbolic realities of shit, drawing on the work of Donna Haraway and tracing Martin Luther’s carnal sacramentality as well as his scatological repudiation of capitalism. The article honors Bonhoeffer’s vision of one reality in attempting to think like a tree: to value the holy plant food our bodies produce and to inhabit ritual practices that make such interspecies valuing and shared life possible.

Forest restoration treatments indirectly diversify pollination networks via floral- and temperature-mediated effects.

In North American conifer forests, a variety of federally initiated thinning programs are implemented to restore pre-European settlement forest structures, but these changes may impact ecosystem function via impacts on sensitive biotic communities. Across the wildland-urban interface of the Front Range region of Colorado, agencies associated with the Collaborative Forest Landscape Restoration Program (CFLRP) have implemented thinning treatments across thousands of hectares of ponderosa pine forest; here we leverage these treatments as an experimental framework to examine thinning effects on a pollinator community. We measured variation in forest structure and sampled bee community assemblages using multiple methods (trapping and netting) to compare bee biodiversity and patterns of floral visitation by bees (bee-flower networks) between mechanically thinned stands that were 3-10 years after treatment and nonthinned stands. Three key findings emerged: (1) Native bee abundance, richness, and diversity were 120%, 53%, and 37% greater, respectively, in thinned stands. In addition, nestedness, richness, and abundance of bee-flower interactions were all substantially higher in thinned stands, and there was increased functional redundancy in bee assemblages after thinning. (2) Structural equation modeling indicated that variation in temperature and floral abundance were mediated by canopy openness and correlated with bee richness and abundance, thereby indirectly driving variation in bee-flower interactions. (3) Four floral species (Penstemon virens, Cerastium arvense, Erysimum capitatum, and Geranium caespitosum) were identified as key connectors in bee-flower interaction networks, though these were not necessarily the most abundant flowering plants. Our analyses indicate that native bee α-diversity and bee-flower interactions positively responded to thinning treatments, and these effects were indirectly driven by canopy removal. We conclude that CFLRP treatments have conservation value for native bee communities. Further monitoring is warranted to evaluate the longevity of these effects.

Can the inter-rotational productivity in ponderosa pine plantations be sustained in the face of climatic change?

Inter-rotational productivity (i.e., productivity of successive rotations) of ponderosa pine plantation was measured on experimentally treated plots with a common design at three diverse sites in northern California. The objectives were to examine the carryover effects of fertilization (F) and understory control by herbicide (H) applied in the first rotation of plantation, on growth in the second rotation and to determine the sustainability of plantation productivity between rotations. Carryover effects varied among the three sites. There was a significant and positive H and F effect (P < 0.03) on tree height and aboveground biomass at Whitmore, a site of intermediate quality; only an H effect at Elkhorn (P < 0.01), the site of low quality; and an F effect at Feather Falls (P = 0.05), the site of high quality. Genetically improved seeds resulted in slightly taller height than the original seed sources, but the difference was not statistically significant. While annual precipitation was similar, growing season precipitation was 6–42 % lesser and air temperature was about 0.9–1.4 °C higher during the second rotation than in the first rotation. Due to the warmer air temperature, the sites likely endured drier air, greater evapotranspiration, and lesser soil water availability. These environmental changes appear to have caused the observed growth reduction in these ponderosa pine plantations. This was despite the management techniques we applied for improved pine growth during the second rotation: genetically improved seeds and control of competing vegetation. It is believed that these are the first reported observations of growth decline in managed ponderosa pine plantations associated with warming climate. If these results are representative of a larger region and a future trend, use of ponderosa pine plantation forestry as a method of increasing forest carbon sequestration, may be overestimated for future rotations.

Thinning Combined with Prescribed Burn Created Spatially Heterogeneous Overstory Structures in Contemporary Dry Forests: A Comparison Using LiDAR (2016) and Field Inventory (1934) Data

Restoring current ponderosa pine (Pinus ponderosa Dougl. Ex P. and C. Laws)-dominated forests (also known as “dry forests”) to spatially resilient stand structures requires an adequate understanding of the overstory spatial variation of forests least impacted by Euro-American settlers (also known as “reference conditions”) and how much contemporary forests (2016) deviate from reference conditions. Because of increased tree density, dry forests are more spatially homogeneous in contemporary conditions compared to reference conditions, forests minimally impacted by Euro-American settlers. Little information is available that can be used by managers to accurately depict the spatial variation of reference conditions and the differences between reference and contemporary conditions. Especially, forest managers need this information as they are continuously designing management treatments to promote contemporary dry forest resiliency against fire, disease, and insects. To fill this knowledge gap, our study utilized field inventory data from reference conditions (1934) along with light detection and ranging and ground-truthing data from contemporary conditions (2016) associated with various research units of Blacks Mountain Experimental Forest, California, USA. Our results showed that in reference conditions, above-ground biomass—a component of overstory stand structure—was more spatially heterogeneous compared to contemporary forests. Based on semivariogram analyses, the 1934 conditions exhibited spatial variation at a spatial scale &lt; 50 m and showed spatial autocorrelation at shorter ranges (150–200 m) compared to those observed in contemporary conditions (&gt;250 m). In contemporary conditions, prescribed burn with high structural diversity treatment enhanced spatial heterogeneity as indicated by a greater number of peaks in the correlograms compared to the low structural diversity treatment. High structural diversity treatment units exhibited small patches of above-ground biomass at shorter ranges (~120 to 440 m) compared to the low structural diversity treatment units (~165 to 599 m). Understanding how spatial variation in contemporary conditions deviates from reference conditions and identifying specific management treatments that can be used to restore spatial variation observed in reference conditions will help managers to promote spatial variation in stand structure that has been resilient to wildfire, insects, and disease.

Mortality thresholds of juvenile trees to drought and heatwaves: implications for forest regeneration across a landscape gradient

Tree loss is increasing rapidly due to drought- and heat-related mortality and intensifying fire activity. Consequently, the fate of many forests depends on the ability of juvenile trees to withstand heightened climate and disturbance anomalies. Extreme climatic events, such as droughts and heatwaves, are increasing in frequency and severity, and trees in mountainous regions must contend with these landscape-level climate episodes. Recent research focuses on how mortality of individual tree species may be driven by drought and heatwaves, but how juvenile mortality under these conditions would vary among species spanning an elevational gradient—given concurrent variation in climate, ecohydrology, and physiology–remains unclear. We address this knowledge gap by implementing a growth chamber study, imposing extreme drought with and without a compounding heatwave, for juveniles of five species that span a forested life zones in the Southwestern United States. Overall, the length of a progressive drought required to trigger mortality differed by up to 20 weeks among species. Inclusion of a heatwave hastened mean time to mortality for all species by about 1 week. Lower-elevation species that grow in warmer ambient conditions died earlier (Pinus ponderosa in 10 weeks, Pinus edulis in 14 weeks) than did higher-elevation species from cooler ambient conditions (Picea engelmannii and Pseudotsuga menziesii in 19 weeks, and Pinus flexilis in 30 weeks). When exposed to a heatwave in conjunction with drought, mortality advanced significantly only for species from cooler ambient conditions (Pinus flexilis: 2.7 weeks earlier; Pseudotsuga menziesii: 2.0 weeks earlier). Cooler ambient temperatures may have buffered against moisture loss during drought, resulting in longer survival of higher-elevation species despite expected drought tolerance of lower-elevation species due to tree physiology. Our study suggests that droughts will play a leading role in juvenile tree mortality and will most directly impact species at warmer climate thresholds, with heatwaves in tandem with drought potentially exacerbating mortality especially of high elevation species. These responses are relevant for assessing the potential success of both natural and managed reforestation, as differential juvenile survival following episodic extreme events will determine future landscape-scale vegetation trajectories under changing climate.

Evaluating Close-Range Photogrammetry for 3D Understory Fuel Characterization and Biomass Prediction in Pine Forests

Understory biomass plays an important role in forests, and explicit characterizations of live and dead understory vegetation are critical for wildland fuel characterization and to link understory vegetation to ecosystem processes. Current methods to accurately model understory fuel complexity in 3D rely on expensive and often inaccessible technologies. Structure-from-motion close-range photogrammetry, in which ordinary photographs or video stills are overlaid to generate point clouds, is promising as an alternative method to generate 3D models of fuels at a fraction of the cost of more traditional field surveys. In this study, we compared the performance of close-range photogrammetry with field sampling surveys to assess the utility of this alternative technique for quantifying understory fuel structure. Using a commercially available GoPro camera, we generated 3D point cloud models from video-derived image stills of 138 sampling plots across two western ponderosa pine and two southeastern slash pine sites. We directly compared structural metrics derived from the photogrammetry to those derived from field sampling, then evaluated predictive models of biomass calibrated by means of destructive sampling. Photogrammetry-derived measures of occupied volume and fuel height showed strong agreements with field sampling (Pearson’s R = 0.81 and 0.86, respectively). While we found weak relationships between photogrammetry metrics and biomass 0 to 10 cm in height, occupied volume and a novel metric to characterize the vertical profile of vegetation produced the strongest relationships with biomass above the litter layer (i.e., &gt;10 cm) across different fuel types (R2 = 0.55–0.76). The application of this technique has the potential to provide managers with an accessible option for inexpensive data collection and can lay the groundwork for the rapid collection of input datasets to train landscape-scale fuel models.

The influence of wildfire on invasive plant abundance and spatial structure in eastern ponderosa pine savanna

The influence of wildfire on invasive plant abundance and spatial structure in eastern ponderosa pine savanna

Numerical assessment of In-plane behavior of multi-panel CLT shear walls for modular structures

Ponderosa pine (Pinus ponderosa) harvested from restoration forests in the Pacific Northwest region of the United States is being considered for use in cross laminated timber (CLT). A prototype modular building was designed and constructed to assess the feasibility of using such CLT panels in emergency housing that can be rapidly assembled, disassembled, and reused. The modular building uses narrow-width CLT panels connected with intra-modular connections (butt joints with inclined screws) that develop the wall modules, which are connected to each other at the corners with point-type inter-modular connections. To accurately predict the behavior of this modular structure under seismic loading, it is necessary to be able to simulate the connections and wall modules under lateral loading. These selected intra- and inter-modular connections in PP CLT have been mechanically characterized in previous experiments. This paper presents the methodology and results from benchmarking the selected in-plane CLT connections against the experimental data in OpenSees. Further, the impacts of the selected connections on the in-plane monotonic and cyclic behavior of multi-panel CLT shear wall modules are also presented. The results show that the Pinching4 material model in OpenSees, when benchmarked using the simulated annealing algorithm, was able to successfully simulate the selected connections. Simulations of multi-panel wall modules indicate that modules with closely spaced screws in the butt joint behave as a single wall panel, while those with widely spaced screws behave as coupled walls. Recommendations on the spacing of intra-modular connections and the applicability of the modular system using the selected connections are provided based on the finite element analysis.