Ponderosa Pine Research Articles

Opportunities for winter prescribed burning in mixed conifer plantations of the Sierra Nevada

BackgroundYoung, planted forests are particularly vulnerable to wildfire. High severity effects in planted forests translate to the loss of previous reforestation investments and the loss of future ecosystem service gains. We conducted prescribed burns in three ~35-year-old mixed conifer plantations that had previously been masticated and thinned during February in order to demonstrate the effectiveness of winter burning, which is not common in the Sierra Nevada, California.ResultsOn average, 59% of fine fuels were consumed and the fires reduced shrub cover by 94%. The average percent of crown volume that was damaged was 25%, with no mortality observed in overstory trees 1 year following the fires. A plot level analysis of the factors of fire effects did not find strong predictors of fuel consumption. Shrub cover was reduced dramatically, regardless of the specific structure that existed in plots. We found a positive relationship between crown damage and the two variables of Pinus ponderosa relative basal area and shrub cover. But these were not particularly strong predictors. An analysis of the weather conditions that have occurred at this site over the past 20 years indicated that there have consistently been opportunities to conduct winter burns. On average, 12 days per winter were feasible for burning using our criteria. Windows of time are short, typically 1 or 2 days, and may occur at any time during the winter season.ConclusionsThis study demonstrates that winter burning can be an important piece of broader strategies to reduce wildfire severity in the Sierra Nevada. Preparing forest structures so that they can be more feasible to burn and also preparing burn programs so that they can be nimble enough to burn opportunistically during short windows are key strategies. Both small landowners and large agencies may be able to explore winter burning opportunities to reduce wildfire severity.

Trends of forest and ecosystem services changes in the Mescalero Apache Tribal Lands

Forests are critically important for the provision of ecosystem services. The Sacramento Mountains of New Mexico, USA, are a hotspot for conservation management and the Mescalero Apache Tribe's homeland. The multiple ecosystem services and functions and its high vulnerability to changes in climate conditions make their forests of ecological, cultural, and social importance. We used data from the Mescalero Apache Tribal Lands (MATL) Continuous Forest Inventory over 30 yr to analyze changes in the structure and composition of ecosystems as well as trends in ecosystem services. Many provisioning, regulating, cultural, and supporting services were shared among the MATL ecosystems and were tied to foundational species dominance, which could serve as a reliable indicator of ecosystem functioning. Our analysis indicates that the MATL are in an ongoing transition from conifer forests to woodlands with declines in two foundation species, quaking aspen and ponderosa pine, linked to past forest management and changing climate. In addition, we detected a decrease in species richness and tree size variability, amplifying the risk of forest loss in a rapid climatic change. Continuous permanent plots located on a dense grid (1 × 1 km) such as the ones monitored by the Bureau of Indian Affairs are the most detailed data available to estimate forests multiresource transitions over time. Native lands across the USA could serve as the leading edge of detecting decadal-scale forest changes and tracking climate impacts.

The aboveground and belowground growth characteristics of juvenile conifers in the southwestern United States

AbstractJuvenile tree survival will play an important role in the persistence of coniferous forests and woodlands in the southwestern United States (SWUS). Vulnerability to climatic and environmental stress declines as trees grow, such that larger, more deeply rooted juveniles are less likely to experience mortality. It is unclear how juvenile conifers partition the aboveground and belowground components of early growth, if growth differs between species and ecosystem types, and what environmental factors influence juvenile carbon allocation above‐ or belowground. We developed a novel data set for four juvenile conifer groups (junipers, piñon pines, ponderosa pines, firs; 1121 juveniles sampled, 221 destructively) in three height classes (<150 mm, 150–300 mm, and 300+ mm), across 25 SWUS sites. We compared growth characteristics across groups and height classes and related differences to climatic and environmental factors. As tree height increased from <150 mm to 300+ mm, belowground growth increased, root:shoot ratio declined, and specific leaf area declined for all conifers except firs. Maximum rooting depth was shallower than previous estimates (<˜400 mm). Lower elevation juveniles were frequently located in sheltered microsites that provided high shading, whereas mid‐ and higher elevation juveniles were frequently unsheltered. Across all forest and woodland sites, herbaceous cover was positively correlated with aboveground growth. At study locations comprised of multiple sites, differences in aboveground growth were best explained by ecosystem type (piñon pine‐juniper woodland, ponderosa pine forest, mixed‐conifer forest) and local environmental variation. Our results indicate generally more belowground early growth and more aboveground later growth, but specific allocation patterns varied among ecosystem (greater proportional shoot growth at lower and mid‐elevations compared with higher elevations). Juvenile conifers had similar magnitudes of proportional growth across conifer groups, displaying limited capacity to acclimate growth to differences in climate that control ecosystem type. If juvenile conifers also do not acclimate physiologically to their environment, our findings suggest that local environmental variation will play a primary role in regulating forest and woodland persistence and modify the effects of climate change in the SWUS.

Vegetation structure controls on snow and soil moisture in restored ponderosa pine forests

AbstractThinning of semi‐arid forests to reduce wildfire risk is believed to improve forest health by increasing soil moisture. Increased snowpack, reduced transpiration and reduced rainfall interception are frequently cited mechanisms by which reduced canopy density may increase soil moisture. However, the relative importance of these factors has not been rigorously evaluated in field studies. We measured snow depth, snow water equivalent (SWE) and the spatial and temporal variation in soil moisture at four experimental paired treatment‐control thinning sites in high elevation ponderosa pine forest northern Arizona, USA. We compared snow and soil moisture measurements with forest structure metrics derived from aerial imagery and 3‐dimensional lidar data to determine the relationship between vegetation structure, snow and soil moisture throughout the annual hydrologic cycle. Soil moisture was consistently and significantly higher in thinned forest plots, even though the treatments were performed 8–11 years before this study. However, we did not find evidence that SWE was higher in thinned forests across a range of snow conditions. Regression tree analysis of soil moisture and vegetation structure data provided some evidence that localized differences in transpiration and interception of precipitation influence the spatial pattern of soil moisture at points in the annual hydrologic cycle when the system is becoming increasingly water limited. However, vegetation structure explained a relatively low amount of the spatial variance (R2 < 0.23) in soil moisture. Continuous measurements of soil moisture in depth profiles showed stronger attenuation of soil moisture peaks in thinned sites, suggesting differences in infiltration dynamics may explain the difference in soil moisture between treatments as opposed to overlying vegetation alone. Our results show limited support for commonly cited relationships between vegetation structure, snow and soil moisture and indicate that future research is needed to understand how reduction in tree density alters soil hydraulic properties.

Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California.

Quantifying the responses of forest disturbances to climate warming is critical to our understanding of carbon cycles and energy balances of the Earth system. The impact of warming on bark beetle outbreaks is complex as multiple drivers of these events may respond differently to warming. Using a novel model of bark beetle biology and host tree interactions, we assessed how contemporary warming affected western pine beetle (Dendroctonus brevicomis) populations and mortality of its host, ponderosa pine (Pinus ponderosa), during an extreme drought in the Sierra Nevada, California, United States. When compared with the field data, our model captured the western pine beetle flight timing and rates of ponderosa pine mortality observed during the drought. In assessing the influence of temperature on western pine beetles, we found that contemporary warming increased the development rate of the western pine beetle and decreased the overwinter mortality rate of western pine beetle larvae leading to increased population growth during periods of lowered tree defense. We attribute a 29.9% (95% CI: 29.4%-30.2%) increase in ponderosa pine mortality during drought directly to increases in western pine beetle voltinism (i.e., associated with increased development rates of western pine beetle) and, to a much lesser extent, reductions in overwintering mortality. These findings, along with other studies, suggest each degree (°C) increase in temperature may have increased the number of ponderosa pine killed by upwards of 35%-40% °C-1 if the effects of compromised tree defenses (15%-20%) and increased western pine beetle populations (20%) are additive. Due to the warming ability to considerably increase mortality through the mechanism of bark beetle populations, models need to consider climate's influence on both host tree stress and the bark beetle population dynamics when determining future levels of tree mortality.

Phylogenomics in the Hard Pines (Pinus subsection Ponderosae; Pinaceae) Confirms Paraphyly in Pinus ponderosa, and Places Pinus jeffreyi with the California Big Cone Pines

Abstract— We sampled 130 individuals (2 to 25 per taxon) of Pinus subsections Ponderosae and Sabinianae. Nucleotide sequences were obtained by targeting 703 low copy nuclear genes. From the unenriched portion of the short reads, we assembled nearly complete plastome nucleotide sequences. We used 600 nuclear genes and the plastome sequences to create phylogenies and species trees that we compared to evaluate cytonuclear concordance and reticulation. We found that Pinus jeffreyi belongs with Pinus subsect. Sabinianae based on morphological synapomorphies as well as strong molecular phylogenetic support. Pinus ponderosa sensu lato is paraphyletic, and we suggest treatment as three species: P. ponderosa sensu stricto (with P. ponderosa var. ponderosa, P. ponderosa var. benthamiana, and P. ponderosa var. washoensis), P. scopulorum, and P. brachyptera. The persistence of lineages with the footprints of ancient nuclear introgression (labeled bpw in clade N4) and chloroplast capture (labeled bpw in clade P1) should caution species identification in Pinus subsection Ponderosae based on limited molecular data. The hybrid frequency was low based on cytonuclear discordance, and the persistence of an ancient P1 plastid clade is a better explanation than hybridization between P. ponderosa and P. jeffreyi for unexpected plastid associations in the western Sierra Nevada, USA. We identified a new potential zone of ancient admixture between P. ponderosa and P. scopulorum in Idaho, USA. Some populations of P. arizonica, P. brachyptera, P. engelmannii, and P. scopulorum in the USA are more closely related to taxa with distributions limited to Mexico than they are to each other. To integrate phylogeny and taxonomy, future work should sample widely in Mexico and the USA, score morphological characters (including seedling characters from the known seed parent), on the same individual as used for molecular data, and use methods that are based on individuals rather than population frequencies.

Environmental Influences on Density and Height Growth of Natural Ponderosa Pine Regeneration following Wildfires

Over the past century the size and severity of wildfires, as well as post-fire recovery processes (e.g., seedling establishment), have been altered from historical levels due to management policies and changing climate. Tree seedling establishment and growth drive future overstory tree dynamics after wildfire. Post-fire tree regeneration can be highly variable depending on burn severity, pre-fire forest condition, tree regeneration strategies, and climate; however, few studies have examined how different abiotic and biotic factors impact seedling density and growth and the interactions among those factors. We measured seedling density and height growth in the period 2015–2016 on three wildfires that burned in ponderosa pine (Pinus ponderosa) forests in the period 2000–2007 across broad environmental and burn severity gradients. Using a non-parametric multiplicative regression model, we found that downed woody fuel load, duff depth, and fall precipitation best explained variation in seedling density, while the distance to nearest seed tree, a soil productivity index, duff depth, and spring precipitation as snow best explained seedling height growth. Overall, results highlight the importance of burn severity and post-fire climate in tree regeneration, although the primary factors influencing seedling density and height growth vary. Drier conditions and changes to precipitation seasonality have the potential to influence tree establishment, survival, and growth in post-fire environments, which could lead to significant impacts for long-term forest recovery.

Combined drought and bark beetle attacks deplete non-structural carbohydrates and promote death of mature pine trees.

How carbohydrate reserves in conifers respond to drought and bark beetle attacks are poorly understood. We investigated changes in carbohydrate reserves and carbon-dependent diterpene defences in ponderosa pine trees that were experimentally subjected to two levels of drought stress (via root trenching) and two types of biotic challenge treatments (pheromone-induced bark beetle attacks or inoculations with crushed beetles that include beetle-associated fungi) for two consecutive years. Our results showed that trenching did not influence carbohydrates, whereas both biotic challenges reduced amounts of starch and sugars of trees. However, only the combined trenched-bark beetle attacked trees depleted carbohydrates and died during the first year of attacks. While live trees contained higher carbohydrates than dying trees, amounts of constitutive and induced diterpenes produced did not vary between live and beetle-attacked dying trees, respectively. Based on these results we propose that reallocation of carbohydrates to diterpenes during the early stages of beetle attacks is limited in drought-stricken trees, and that the combination of biotic and abiotic stress leads to tree death. The process of tree death is subsequently aggravated by beetle girdling of phloem, occlusion of vascular tissue by bark beetle-vectored fungi, and potential exploitation of host carbohydrates by bark beetle symbionts as nutrients.

Influence of soil properties on millipede (Diplopoda) communities in forest stands of various tree species

Although millipedes are faunistically among the best studied groups of edaphon in Europe, there is still a lack of available information on the ecological requirements of particular species. Habitat preferences that determine the distribution of species are largely controlled by soil properties, habitat structure and microclimate. In forests, habitat features are predominantly driven by the properties of woody tree species. Millipedes, like other saprophages, are influenced by the characteristics of litter and soil. However, the effect of tree species on millipede communities has not been investigated in forest stands consisting of several autochthonous or allochthonous tree species. Our study examines the effect of soil properties related to several autochthonous and allochthonous tree species on millipede communities. The research was carried out at 9 stands in the Arboretum Mlyňany (western Slovakia). Each stand represents a monoculture of one of 9 tree species: 4 autochthonous species (Picea abies, Taxus baccata, Quercus cerris, and Carpinus betulus) and 5 allochthonous species (Picea orientalis, Pinus nigra, Pinus ponderosa, Thuja occidentalis, and Castanea sativa). The results of this research confirmed relationships between (1) the soil pH and the total activity-density of millipedes, (2) the soil pH and the structure of the millipede communities, (3) the soil conductivity and the structure of the millipede communities, and (4) the leaf litter pH and the equitability of the millipede communities. In terms of the total activity-density and species richness of the millipedes, forest stands with autochthonous tree species provided more favourable conditions for millipedes than forest stands with allochthonous tree species. Millipedes achieved high abundance and diversity in these stands and can therefore contribute to the faster decomposition of dead organic matter and nutrient recycling in forest ecosystems.

Ventenata (Ventenata dubia) Response to Grazing and Prescribed Fire on the Pacific Northwest Bunchgrass Prairie

The exotic annual grass ventenata (Ventenata dubia L.) is raising concern as it rapidly invades multiple ecosystem types within the United States, including sagebrush steppe, ponderosa pine forests, woodlands, and much of the Palouse and Pacific Northwest Bunchgrass Prairie (PNB). Despite increasing attention, little is known about the invasion dynamics of ventenata, especially its response to disturbances such as grazing and fire. In this study, we examined how cattle grazing and prescribed fire affect the abundance (standing crop, cover, frequency, and density) of ventenata and other plant groups on the PNB over time using two separate long-term studies established in 2004. The first study (Cattle Grazing) looked at the 14-yr effect of cattle grazing exclusion on ventenata aboveground biomass and cover. Our second study (Grazing and Prescribed Fire) examined main and interactive effects of cattle exclusion and prescribed fire on ventenata over three sampling periods (2008, 2016, and 2018). We documented a 30% increase in ventenata cover and 55% increase in frequency on the PNB over the past 15 yr, including areas that were not disturbed by fire or cattle grazing. We found only weak evidence that cattle grazing increased ventenata standing crop when compared with cattle-excluded paddocks, something that could be related to timing of use. There was no evidence that prescribed burning impacted the response of ventenata on its own. However, we found some evidence of interactions between cattle grazing and prescribed fire that suggests prescribed burning could help reduce the abundance of ventenata in areas grazed by livestock. These studies reinforce the important differences between ventenata and other invasive winter annuals in grasslands and clarify a need for research that focuses primarily on the dynamics between this relatively new exotic species in grasslands and the many ecosystems it now inhabits.

The effects of ENSO and the North American monsoon on mast seeding in two Rocky Mountain conifer species.

We aimed to disentangle the patterns of synchronous and variable cone production (i.e. masting) and its relationship to climate in two conifer species native to dry forests of western North America. We used cone abscission scars to reconstruct ca 15 years of recent cone production in Pinus edulis and Pinus ponderosa, and used redundancy analysis to relate time series of annual cone production to climate indices describing the North American monsoon and the El Niño Southern Oscillation (ENSO). We show that the sensitivity to climate and resulting synchrony in cone production varies substantially between species. Cone production among populations of P. edulis was much more spatially synchronous and more closely related to large-scale modes of climate variability than among populations of P. ponderosa. Large-scale synchrony in P. edulis cone production was associated with the North American monsoon and we identified a dipole pattern of regional cone production associated with ENSO phase. In P. ponderosa, these climate indices were not strongly associated with cone production, resulting in asynchronous masting patterns among populations. This study helps frame our understanding of mast seeding as a life-history strategy and has implications for our ability to forecast mast years in these species. This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.

Substrate stoichiometric regulation of microbial respiration and community dynamics across four different ecosystems

Microbes decompose soil organic matter (SOM), yet it is unclear how substrate inputs (i.e., stoichiometry) directly mediate microbial activities and community dynamics. We hypothesized that C+N input has the largest effect on microbial respiration and community structure, followed by C input and N input. Soils were collected from four ecosystems (grassland, piñon-juniper, ponderosa pine, mixed conifer) and amended with NH4NO3 (N only; 100 μg g−1 wk−1), 13C-glucose (C only; 1000 μg g−1 wk−1), or C+N in a five-week laboratory incubation. We found that C+N input induced the greatest total respiration while C input induced the greatest SOM-derived respiration (i.e., priming effect) across ecosystems. Shifts in community composition were the largest with C+N input, followed by C input, and showed little response to N input. C only and C+N inputs increased both of the relative and absolute abundances of Actinobacteria and Proteobacteria (α, β, γ), but reduced the relative abundances of Verrucomicrobia and δ-Proteobacteria. C+N input increased the relative abundances of Bacillales, Rhizobiales, Burkholderiales and of 9 families, and reduced the relative abundances of Myxococcales and of 12 families, but showed little effect on the absolute abundances of these bacterial taxa. N input reduced the absolute abundances of Actinobacteria, Proteobacteria, and Verrucomicrobia but did not affect their relative abundances in the mixed conifer soil; by contrast, N input reduced relative abundances of δ-Proteobacteria and increased the relative abundances of γ-Proteobacteria but did not affect their absolute abundances in the ponderosa pine soil. We also found that substrate inputs were the main driver of SOM decomposition, microbial respiration and diversity, while soil ecosystem was the main driver of community composition and abundances of most bacterial phyla. Our work suggests that substrate stoichiometry has predictable effects on soil C cycling, microbial diversity and community composition, but has variable effects on microbial abundances, and that incorporating bacterial gene copies in abundance calculations can help more accurately estimate microbial responses across taxonomic levels and ecosystems.

Relationships among forest structure, solar radiation, and plant community in ponderosa pine plantations in the Patagonian steppe

In Patagonia, Argentina, forest management in plantations with exotic pines usually focus on timber production, without considering the plant community of their understory. However, there is growing interest in conserving the biodiversity in these productive systems, due to the important role of biodiversity in the stability and functions of newly created ecosystems. Since solar radiation is one of the main limiting factors for vegetation development in forest plantations established in treeless steppes, we carried out this study with the objectives of analyzing and establishing relationships among variables of the forest structure, the solar radiation transmitted through different forest structures, and attributes of the plant community in ponderosa pine plantations in northwestern Patagonia. We selected three plantations located in the steppe that were managed traditionally and presented a wide range of forest structures. We assessed relationships between variables of the forest structure and variables of the light environment, as well as the relationship of variables of the forest structure and the light environment with the richness and cover of the plant community, using generalized linear mixed-effects models. We also assessed the relationship of diffuse radiation with the presence and cover of species grouped by their growth-form, nativity, and the most frequent species, using generalized linear mixed-effects models and Kendall correlations. Canopy cover and basal area were the forest structural variables that explained most of the diffuse radiation variability, which was the best variable characterizing the light environment. Diffuse radiation decreased linearly as canopy cover and basal area increased, and the understory plant community responded to that gradient, decreasing both total species richness and cover. Besides, different responses of the presence and cover of the most frequent species and species grouped by their growth-form and nativity in response to the available solar radiation in the understory were detected. Whereas some species or groups did not show a significant response, those that did were, in general, positively related to diffuse radiation, although to a different extent. These results indicate that ponderosa pine plantations in Patagonia affect their understory plant community. However, they also suggest that promoting forest management guidelines that lower basal area, raises canopy height and manages residual slash would enhance plant community attributes, balancing timber production and biodiversity conservation.

First Report of Diplodia Shoot Blight and Canker Disease caused by Diplodia sapinea on Ponderosa Pine in Wyoming, USA.

Diplodia sapinea is a common fungal pathogen that causes shoot blight and canker of naturally occurring and planted pines and other conifers throughout the world. Damage can be severe severe, affectingand affect needles, new shoots, branches, and main stems, often leading to mortality. In August 2018, aerial surveys revealed 1,659 ha of ponderosa pine (Pinus ponderosa) displaying varying degrees of crown necrosis in Crook County, Wyoming (WY). In May 2019, ground surveys of this area, which was previously affected by hail the previous spring, identified typical Diplodia shoot blight and canker signs and symptoms (e.g., pycnidia, crooked shoots, discolored needles, resinous cankers). Symptoms were observed in thousands of seedlings, saplings, and mature ponderosa pine trees over the large area. Because D. sapinea had not been previously reported in WY, this study was conducted to confirm the presence and aggressiveness of D. sapinea isolates from WY on this commercially and ecologically important host tree. Pycnidia and conidia (size 34 to 39 μm × 12 to 13 μm) consistent with D. sapinea were confirmed in 19 trees from three locations in the county. Three isolates were confirmed as D. sapinea using species-specific PCR (Smith and Stanosz 2006) and are retained at the Rocky Mountain Research Station, Moscow, ID and Colorado State University, Fort Collins, CO. To confirm isolate aggressiveness, 3-year-old potted ponderosa pine seedlings were inoculated in greenhouses from March to April 2020 at the Charles E. Bessey Nursery, Halsey, NE using similar methods as previously described (Blodgett and Stanosz 1997). Wounding was conducted using a scalpel to excise a single needle fascicle from a recently expanded shoot. Cuts were made flush to the stem at 2 to 2.5 cm below an apical bud-tip. A 1.5% water-agar plug with cultured mycelia of one of the three DNA-confirmed isolates was placed over the stem wound, or sterile water-agar plugs were used as negative controls. Parafilm® (4-cm wide) was wrapped around the inoculated stems, centered at the wound for 4 weeks. Two independent trials were conducted consecutively, 3 hrs apart, in different greenhouses with five seedlings per isolate or control. Symptoms first appeared 5 days post-inoculation. All seedlings inoculated with the three isolates developed typical D. sapinea symptoms, including cankers (mean length 5.98.7 ± 1.13.0 cm standard error and 5.5 ± 0.8 cm standard error, trial 1 and 2 respectively) at 4-weeks post-inoculation, while mock-inoculated seedlings developed no symptoms. Stem segments (2-cm long) were excised, centered at canker margins (or centered 3 cm below wounds for controls), and surface disinfested for 30 sec in 70% ethanol and 5 min in 1.05% sodium hypochlorite, then placed in Petri plates containing tannic acid agar (Blodgett et al. 2003). After 3 weeks, isolates were subcultured from colony margins to Petri plates containing 1.5% water agar and autoclaved ponderosa pine needles. Pycnidia and conidia consistent with D. sapinea were confirmed after another month from all seedlings inoculated with each isolate, but not from control seedlings. This report confirms that D. sapinea is present in WY, and WY isolates can be aggressive pathogens of ponderosa pine. Reducing host water stress (Blodgett et al. 1997a, Blodgett et al. 1997b) may be the best option to manage Diplodia shoot blight and canker disease in forested sites. This can be accomplished by stand thinning and/or managing competing vegetation. Favoring non-host species might be an alternative management option in areas with severe disease.

Mechanical thinning without prescribed fire moderates wildfire behavior in an Eastern Oregon, USA ponderosa pine forest

Reducing fuels to better manage risk of high severity wildfire in seasonally dry, fire-prone forests of the western U.S. is an important goal of forest managers, including private landowners, non-governmental organizations, tribal, state, and local governments, and federal agencies. Managing fire risk is a critical objective of the U.S. Forest Service, which emphasizes the use of thinning to reduce tree density and ladder fuels followed by prescribed fire to reduce surface fuel. But the area of Forest Service land treated with thinning and prescribed fire is lagging far behind the area treated only with mechanical thinning due to regulatory and logistical challenges in prescribed fire implementation. Determining if mechanical thinning alone (without prescribed fire) can achieve adequate fire risk reduction has important implications for addressing the fire and fuel management goals set by Congress and the Administration, as well as the management objectives set by non-federal actors. In this study, we report on the effects of mechanical thinning and standard post-thinning fuels management but without prescribed fire on modeled fire behavior and changes in fuel loading over time in a ponderosa pine forest in Eastern Oregon. Thinning without prescribed fire significantly reduced potential crown fire immediately following thinning and also moderated surface modeled fire behavior beginning 2–3 years following thinning. Although small (<7.6 cm diameter) woody surface fuel loading increased following thinning, other ground and surface fuels (i.e., litter and duff) declined substantially, which we attribute to surface disturbance from ground-based logging, decreased deposition of litter, and increased decomposition. These results suggest that fuel reduction and fire risk management objectives can be met with mechanical thinning alone for a number of years. Prescribed fire is likely necessary to extend the effectiveness of mechanical thinning after significant tree or shrub regeneration. Continued monitoring will allow managers to use prescribed fire most efficiently to achieve fire and fuel management objectives.

Red turpentine beetle primary attraction increases linearly with (−)‐β‐pinene+ethanol dose regardless of component ratios, and no change in response with addition of high‐release frontalin

Abstract Lure efficacy for primary attraction of red turpentine beetle, Dendroctonus valens (Coleoptera: Curculionidae: Scolytinae) observed previously in US Pacific Northwest ponderosa pine forests is (−)‐β‐pinene+ethanol &gt; (+)‐3‐carene+ethanol &gt; (+)‐α‐pinene+ethanol. Influence of (−)‐β‐pinene+ethanol release rates was tested with nine lures representing all combinations of three release levels for each compound in a 3 × 3 factorial design field test in Oregon. Beetle catch had a positive, linear relationship with the combined (−)‐β‐pinene+ethanol total release (or dose), resulting from higher release of either one or both compounds. Reversing component ratios, that is, 1 : 2 versus 2 : 1 with similar total doses, produced minimal changes in beetle response. Females produce frontalin with dual aggregation and sex‐pheromone functions. In another test, high‐release frontalin, defined as &gt;1.0 mg/day release, was tested at 1.4 to 1.5 mg/day in combination with each monoterpene+ethanol lure above and their trap catch compared with (−)‐β‐pinene+ethanol lures. Presence of high‐release frontalin produced minimal changes in beetle responses.

Preference and Performance of the Pine-Tree Lappet Dendrolimus pini on Various Pine Species

Global commercial and recreational transport may lead to the unintentional invasion of insect species, which in turn may pose a threat to native organisms. In this study, we aimed to assess whether the economically important pest of Pinus sylvestris L., moth Dendrolimus pini L. (DP), is able to feed on nine other pine species, and how this will affect its survival, performance, growth, and development. We carried out food choice tests and a no-choice laboratory feeding experiment. We found that this insect mostly preferred its prime host, but also Pinus cembra L., Pinus contorta Douglas ex Loudon, Pinus nigra J.F.Arnold, and Pinus ponderosa Douglas ex C.Lawson. The performance test revealed a host-specific response of DP to the host plant. This response was manifested in a large variation in body mass as well as in a decrease or increase in life-history traits, such as fecundity, and wing morphology parameters. However, the larvae’s choice of particular hosts corresponded to the results of the performance test. Larvae more willingly selected food allowing better results in their performance. Larvae achieved better values of growth and development when fed on European and North American pine species or on species with two- and three-needle fascicles. In addition, attractants and repellents in needles of different pine species were chemically analyzed. Variations in the secondary metabolite composition as well as the specific leaf area of different pine species effectively explained the results found in the insects, but the content of sugars and nitrogen remains to be elucidated. We speculate that DP poses a serious threat to large areas of pine forests, if transferred, as it can survive and develop on many economically important tree species in North America and Europe.

Forest Resistance to Extended Drought Enhanced by Prescribed Fire in Low Elevation Forests of the Sierra Nevada

Prescribed fire reduces fire hazards by removing dead and live fuels (small trees and shrubs). Reductions in forest density following prescribed fire treatments (often in concert with mechanical treatments) may also lessen competition so that residual trees might be more likely to survive when confronted with additional stressors, such as drought. The current evidence for these effects is mixed and additional study is needed. Previous work found increased tree survivorship in low elevation forests with a recent history of fire during the early years of an intense drought (2012 to 2014) in national parks in the southern Sierra Nevada. We extend these observations through additional years of intense drought and continuing elevated tree mortality through 2017 at Sequoia and Kings Canyon National Parks. Relative to unburned sites, we found that burned sites had lower stem density and had lower proportions of recently dead trees (for stems ≤47.5 cm dbh) that presumably died during the drought. Differences in recent tree mortality among burned and unburned sites held for both fir (white fir and red fir) and pine (sugar pine and ponderosa pine) species. Unlike earlier results, models of individual tree mortality probability supported an interaction between plot burn status and tree size, suggesting the effect of prescribed fire was limited to small trees. We consider differences with other recent results and discuss potential management implications including trade-offs between large tree mortality following prescribed fire and increased drought resistance.

Assessment of Pyrolytic Biochar as a Solar Absorber Material for Cost-Effective Water Evaporation Enhancement

Enhancement of water evaporation using carbon-based solar absorbers has been gaining acceptance for its potential use in solar-driven water desalination. The evaporation rate can be increased by using these materials as either a floating suspension or as particles dispersed in water. Although several materials have been proposed for the purpose of increasing the rate of water evaporation, there is still a need to develop low-cost materials that exhibit strong solar absorbance with the purpose of providing freshwater to rural and low-income communities. Biochar is a carbon-rich material, obtained from the thermochemical conversion of biomass. Although it is mainly used as an organic amendment for soil, in this study, its potential utilization as a low-cost solar absorber is analyzed. Two pyrolytic biochars are investigated, that is, Ponderosa pine from forest waste, and walnut shell from the agricultural sector. Measured solar absorptivity values were >92% at 1 g/L dispersion concentration, whereas the transmittance of light was <1% for a 10 mm path length. Controlled indoor experiments with a solar simulator resulted in evaporation rates between 1 and 1.1 kg/m2-h, which are significantly higher than for pure water. Biochar was found to be more economical than some of the other carbon materials analyzed in the literature, thus, opening an opportunity for feasible use in low-cost solar stills.

Ecophysio-optical traits of semiarid Nebraska grasslands under different Juniperus virginiana and Pinus ponderosa canopy covers

Despite conservation efforts in the U.S. Great Plains, woody species have continued to expand at an unprecedented rate, threatening key ecosystem services and resilience. Cross-scale monitoring of these grasslands is key to successful integrative management strategies. In this study we measured plant optical traits derived from hyperspectral proximal sensing techniques with a field spectrometer, coupled with field-based measurements, including fluorescence and chlorophyll content, to determine the impacts of Juniperus virginiana and Pinus ponderosa expansion on grasslands health in Nebraska Sandhills, and investigated the use of optical-based approaches as indicators of successful monitoring of grasslands. Our results showed that higher woody species cover in grasslands was associated with lower soil moisture, decline in forbs, shrubs, and grasses cover and productivity, as well as herbaceous chlorophyll content and fluorescence, compared to non-invaded grasslands. We derived 13 vegetation indices (VIs) from optical-based methods and validated them against traditional handheld measurements of plant ecophysiological traits and vegetation biomass and composition. VIs, including Normalized Difference Vegetation Index (NDVI), Water Index (WI) and Chlorophyll Index at red edge (CIred edge) performed best when tested against biomass, and chlorophyll content and fluorescence (Fv/Fm), suggesting their potential use for assessing grasslands vegetation health. We demonstrate that optical-based approaches can serve as efficient non-invasive tools that can be part of multi-scale successful integrative management strategies.