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Fire-adapted dry forests and nearby communities both need to be sustained as climate changes. Wildfires have increased in the ~25.5 million ha of dry forests in the western US, but are wildfires already more severe than historical (preindustrial) wildfires, warranting suppression, or is more fire needed? Recent research suggests that a higher percentage are more severe, but is this from more high-severity fire (≥70% mortality) or simply less lower-severity fire? To resolve this question, I compared government fire-severity data from 2000–2020 with corresponding government Landfire historical data, representing the last few centuries. The fire rotation (expected time to burn across an area of interest) for high-severity fire was 477 years recently versus 255 years historically, a deficit, not a surplus. High-severity fire would need to increase 1.9 times to equal historical rates. Thus, reducing high-severity fire through fuel reductions is fire suppression, which has significant well-known adverse ecological impacts. These include reductions in (1) natural burn patches, snags, and non-forest openings, that favor diverse fire-adapted species, and (2) landscape heterogeneity that can limit future disturbances and enhance landscape ecological processes. Even larger deficits were in moderate (4.4 times) and low (5.8 times) fire severities. However, if only these lower severities were restored, the high-severity percentage would correspondingly be reduced to low levels. All fire severities are needed to provide a variety of post-fire settings that favor a broad suite of selection pressures and adaptations to emerging climate. This paper shows that to sustain and adapt dry forests and nearby communities to fire and climate change, the billions spent on fuel reductions to reduce high-severity fire can be redirected to protecting the built environment, fostering both safe and sustainable dry forests and human communities. [ABSTRACT FROM AUTHOR]

The current state of dark coniferous forests on Earth is a bio-indicator of global environmental change, in particular, the process of gradual degradation of tree species of the genera Pine, Spruce and Fir, due to the negative impact of anthropogenic activities, abiotic and biotic factors. The purpose of the study is to establish the symptoms, prevalence and harmfulness of the causative agent of ulcerative tumour-like disease on the shoots and trunks of white fir. The research was conducted on the territory of the forest fund of the Pokuttia Carpathians, in particular, within the branch Kutske forestry of the State Specialised Economic Enterprise "Forests of Ukraine" in the Kosivske forest enterprise. The study uses classical phytopathological and mycological methods, which are used to investigate the aetiology of the disease, analyse typical symptoms (starting from the early stages), and perform microscopy of the affected parts of fir. The symptoms, aetiology, and pathogenesis of white fir ulcer-like disease, which tends to spread, were investigated. A new name for the disease is substantiated, in particular, it is proposed to use the name "ulcerative tumour-like disease" of fir instead of the current name "cancer". It is shown that a typical sign of infection is the development of tumours, which eventually transform into ulcers. It was found that the tumour-like type of lesion prevails on the undergrowth of fir, and on plants of the upper tiers - ulcerative. It is noted that a typical sign of ulcerative tumour-like disease of white fir is also the presence of pathologies such as "witches' broom". It is proposed to remove affected trees with typical signs of infection with ulcerative tumour-like disease to reduce the infectious background, especially during lighting and cleaning, since affected trees are not released from infection. Therefore, assessing the risk of infection of white fir trees with ulcerative tumour-like disease at the level of specific stands and ensuring an appropriate response to potential infection risks is an important part of sustainable forest management. [ABSTRACT FROM AUTHOR]

Climate change and disturbance are altering forests and the rates and locations of tree regeneration. In semi-arid forests of the southwestern USA, limitations imposed by hot and dry conditions are likely to influence seedling survival. We examined how the survival of 1-year seedlings of five southwestern US conifer species whose southwestern distributions range from warmer and drier woodlands and forests (Pinus edulis Engelm. Pinus ponderosa Douglas ex C. Lawson) to cooler and wetter subalpine forests (Pseudotsuga menziesii (Mirb.) Franco , Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr. and Picea engelmannii Parry ex Engelm.) changed in response to low moisture availability, high temperatures and high vapor pressure deficit in incubators. We used a Bayesian framework to construct discrete-time proportional hazard models that explained 55–75% of the species-specific survival variability. We applied these to the recent climate (1980–2019) of the southwestern USA as well as 1980–2099 CMIP5 climate projections with the RCP8.5 emissions pathway. We found that the more mesic species (i.e. P. menziesii , A. concolor and P. engelmannii) were more susceptible to the effects of hot and dry periods. However, their existing ranges are not projected to experience the conditions we tested as early in the 21st century as the more xeric P. edulis and P. ponderosa , leading to lower percentages of their existing ranges predicted to experience seedling-killing conditions. By late-century, extensive areas of each species southwestern range could experience climate conditions that increase the likelihood of seedling mortality. These results demonstrate that empirically derived physiological limitations can be used to inform where species composition or vegetation type change are likely to occur in the southwestern USA. [ABSTRACT FROM AUTHOR]

Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plants under water stress alter their normal morphological and physiological processes. However, biomass allocation and nutrient use efficiency remain largely unknown under the interactive effect of irrigation and fertilization for many economically important conifer species. In this study, we compared biomass allocation and resources use efficiency of two-year-old (plug+1) containerized balsam fir [Abies balsamea (L) Mill.] 'Cooks' and concolor fir [Abies concolor (Gord. & Glend.) Lindl. Ex Hildebr.] 'Cibola', and one-year-old bare-root white pine [Pinus strobus L.] transplants grown under variable watering and fertilization conditions. In a controlled greenhouse setting, transplants were submitted to three irrigation levels and two fertilization rates in a factorial experimental design. Fir species, mainly concolor fir, had a greater capacity to utilize water resulting in decreased stem water potential than white pine, leading to increased aboveground growth and shoot-to-root (S/R) ratio. White pine transplants had a higher assimilatory nutrient efficiency, nutrient use efficiency (NUE), root weight ratio, and a lower nitrogen availability index than the two fir species, suggesting a better ability to tolerate water stress. The high rates of fertilization increased nutrient concentration more than growth, suggesting luxury consumption. These results indicate that white pine responds to drought stress by closing their stomata and decreasing their S/R ratio to limit physiological activities, while the two fir species exhibit increased water uptake via expanded fine root networks, increasing the NUE and S/R ratio. However, there was no clear trend for the irrigation and fertilization interaction for NUE for three species, making it difficult to generalize responses. [ABSTRACT FROM AUTHOR]

The mid-elevation forest of California's Sierra Nevada poses a bioclimatic paradox. Mid-elevation trees experience a montane Mediterranean climate, with near-freezing winter days and rain-free summers. The asynchrony between warmth and water input suggests low primary production, limited by photosynthetic dormancy in winter cold, and again in summer and early autumn with drought, yet this forest is characterized by tall trees and high biomass. We used eddy covariance in a mid-elevation Sierra stand to understand how winter cold and summer drought limit canopy photosynthesis and production. The trees exhibited canopy photosynthesis year-round. Trees avoided winter dormancy, and daytime CO2uptake continued despite a deep snowpack and near-freezing temperatures. Photosynthesis on sunny days continued at half of maximum rates when air temperature was 0 °C. Likewise, the vegetation avoided summer drought dormancy, and high rates of daytime CO2uptake and transpiration continued despite a 5-month period with only negligible water input. We attribute this drought avoidance to deep rooting and availability of deep soil water. Year-round photosynthesis helps explain the large biomass observed in the Sierra Nevada, and implies adaptive strategies that may contribute to the resiliency or vulnerability of Sierran vegetation to climate change.

Climate change is shifting forest tree species distributions across elevational and latitudinal gradients, and these changes are often pronounced at ecotones where species meet their climatic bounds and are replaced by other species. Using an extensive ecotone composed of lower‐montane white fir (Abies concolor var. lowiana) and upper‐montane red fir (Abies magnifica var. magnifica) in the central Sierra Nevada range of California, USA, we (1) examined how the demographics of the ecotone have responded to recent climate using a field observational study and a historical dataset, (2) quantified climate drivers across species life stages using contemporary demographic data, and (3) tested the potential impacts of future climate on species‐specific seedling survival and growth in a fully factorial growth chamber experiment that varied temperature, growing season length, and water availability. A re‐examination of the ecotone midpoint after 35 yr suggested a reduction in A. concolor sapling and tree densities and a rise in A. magnifica proportional dominance between surveys. Seedling abundances across the ecotone indicated that A. magnifica tends to dominate the regeneration layer and currently forms an important component of the seedling community at elevations below those where A. magnifica saplings or trees begin to co‐dominate stands. Observational and experimental assessments suggest that temperature and precipitation serve as important drivers, differentiating A. concolor vs. A. magnifica distributions, and are primary stressors at the seedling stage. Seedlings of both species were adversely affected by experimental climate treatments, although A. concolor exhibited greater survival and a more conservative growth strategy under extreme climatic stress than A. magnifica. Projections indicate that historical climate conditions will rise by an amount greater than the ecotone's current elevational extent by the end of the 21st century. Differential drivers of species abundances suggest that the projected climate will expand conditions that promote A. concolor abundance and impede A. magnifica abundance across the ecotone; however, disturbance activity and microclimatic conditions will also influence regeneration and overstory tree dynamics. Our study demonstrates the importance of quantifying species‐specific responses to climate and indicates that widespread regeneration failure may be one possible consequence in which species exhibit strong sensitivity to projected climate conditions. [ABSTRACT FROM AUTHOR]

Ende August 2013 wurden im Bundesland Brandenburg außergewöhnliche, bis dahin unbekannte Krankheits­erscheinungen an Kolorado-Tanne (Abies concolor) festgestellt. Betroffen waren zwei Waldflächen im Raum Potsdam. Das Alter der ca. 0,5 und 1 ha umfassenden Pflanzungen betrug zu diesem Zeitpunkt 27 bzw. 28 Jahre. Im Herbst 2016 trat das gleiche Schadbild 115 km südöstlich des Erstfundes – in der Niederlausitz – an Kolo­rado-Tannen derselben Altersstufe erneut auf. Bei der dortigen Befallsfläche handelte es sich um einen 0,15 ha großen Reinbestand. Das Krankheitsgeschehen war in allen Fällen durch intensives Abwerfen noch grüner Nadeln, massiven Harzfluss an Ästen und Stämmen, rasches Zurücksterben der Kronen und letztendlich vollständiges Absterben der Bäume gekennzeichnet (Heydeck et al., 2015). Da im Nordostdeutschen Tiefland bis zum Jahr 2013 keine vergleichbaren Schadereignisse registriert wurden und auch aus anderen Bundesländern keine Mitteilungen über ähnliche Symptome an Abies concolor vorlagen, war die Ursache der Absterbeprozesse zunächst unklar. Zwecks eingehender Analyse der festgestellten Krankheitserscheinungen wurden von geschädigten Bäumen mehrfach Nadel-, Zweig-, Ast-, Rinden- und Holzproben entnommen. Bei mikromorphologischen Untersuchungen ließen sich an erkrankten Ästen sowie auf der Rinde absterbender Kolorado-Tannen mit hoher Stetigkeit Konidienlager (Sporodochien) eines Kleinpilzes aus der Formgattung Cylindrocarpon nachweisen. Später konnte an frisch abgestorbenen Bäumen in unmittelbarer Nähe des anamorphen Stadiums auch die dazugehörige Teleomorphe (Perithecien einer Neo­nectria-Art) diagnostiziert werden. Der gleiche Pilz wurde mit Labormethoden mehrfach aus dem Bastgewebe noch lebender Kolorado-Tannen isoliert (Merkel, 2018). Die Mikromerkmale stimmten mit der Spezies Neonectria neomacrospora (Ascomycota, Nectriaceae) überein. Mole­kulargenetische Analysen bestätigten, dass es sich bei dem Erreger eindeutig um die Art Neonectria neomacrospora (C. Booth & Samuels) Mantiri & Samuels handelt. Eine nennenswerte Beteiligung von Insekten bei der Entstehung der Schäden konnte ausgeschlossen werden. Berichte aus Skandinavien lassen erkennen, dass der genannte Krankheitserreger in Norwegen bereits seit 2008 schwerwiegende Schäden an mehreren Abies-Arten verursacht hat, vor allem in Weihnachtsbaumkulturen (Talgø et al., 2012). Auch in Dänemark und Schweden kam es durch den Pilz zu Pflanzenausfällen. Offenbar entwickelt Neonectria neomacrospora unter bestimmten Voraussetzungen eine hohe Aggressivität gegenüber verschiedenen Tannen-Arten, darunter Abies concolor. Inzwi­schen wurde der Krankheitserreger in weiteren euro­päischen Ländern nachgewiesen und 2017 in die Frühwarnliste der EPPO aufgenommen (EPPO, 2020a). Die betroffenen Bestände im brandenburgischen Landeswald sind mittlerweile vollständig geräumt, wobei das infizierte Pflanzenmaterial sachgerecht entsorgt wurde. Zurzeit lässt sich noch nicht abschätzen, ob Neonectria neomacrospora im Nordosten Deutschlands künftig an Bedeutung gewinnen wird und dann möglicherweise auch andere Nadelbaumarten infiziert.

Previously unknown disease symptoms were detected for the first time on white fir (Abies concolor) in the federal state of Brandenburg in the end of August 2013. Symptoms were observed at two locations near Potsdam on 27 and 28 years old trees in an area of about 0.5 ha and 1 ha respectively. In autumn 2016 identical symptoms were identified on white firs of similar age in Niederlausitz, 115 km southeast of the first recorded instance. This third observation was made in a planted 0.15 ha pure stand. In each case an intense loss of green needles, a strong resin flow on trunk and branches, rapid dieback of the crown and finally the death of the whole tree was observed (HEYDECK et al., 2015). No instances of similar damage in Abies concolor in the northeast German lowlands or in other federal states of Germany were reported before August 2013. The cause of the disease remained initially unidentified. Samples of needles, twigs, branches, bark and wood from damaged trees were repeatedly collected and analysed. Microscopic morphological investigation provided consistent evidence of conidiomata (sporodochia) on damaged branches and bark of dying white firs of a Cylindrocarpon-like micromycete. The associated teleomorph (perithecia of a species of the genus Neonectria) was subsequently identified close to the anamorphic stage in trees that had recently died. The same fungus has also been isolated repeatedly in the laboratory from phloem tissue of living white firs (MERKEL, 2018). Microscopic characteristics belonging to the species Neonectria neomacrospora (Ascomycota, Nectriaceae) were observed. Molecular genetic methods subsequently confirmed the pathogen was Neonectria neomacrospora (C. Booth & Samuels) Mantiri & Samuels. Insects had not contributed appreciably to the development of damage symptoms. Since 2008 Neonectria neomacrospora has caused serious damage on several species of fir (Abies), especially on Christmas tree farms in Norway, Denmark and Sweden (TALGØ et al., 2012). Infected trees even died as a result of the fungal infection. It appears that Neonectria neomacrospora can develop an intense pathogenicity against various fir species, including Abies concolor, under certain conditions. The pathogen has also recently been detected in additional European countries and has been registered in the EPPO Alert List (EPPO, 2020a) in 2017. The affected tree stands owned by the federal state of Brandenburg have now been completely felled and infected plant material was disposed of appropriately. The future relevance of Neonectria neomacrospora in northeastern Germany and the potential infection of other coniferous tree species remain to be investigated. [ABSTRACT FROM AUTHOR]

Two new subspecies of fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) are described herein: Arceuthobium abietinum subsp. mathiasenii (Mathiasen's dwarf mistletoe) and Arceuthobium abietinum subsp. grandae (grand fir dwarf mistletoe). The former dwarf mistletoe--Mathiasen's dwarf mistletoe--parasitizes Rocky Mountain white fir in Nevada, Utah, and Arizona and Durango fir in northern Mexico; whereas, grand fir dwarf mistletoe parasitizes grand fir as well grand fir × white fir hybrids in California, Oregon, and Washington. The recognition of these subspecies and, hence, their classification is based on morphological discontinuities and host range differences when compared to white fir dwarf mistletoe (Arceuthobium abietinum subsp. abietinum), red fir dwarf mistletoe (A. abietinum subsp. magnificae), and Wiens' dwarf mistletoe (A. abietinum subsp. wiensii). The combined analyses of plant height, third internode length and width, fruit dimensions, staminate spike and petal dimensions, and anther distance to tip, contributed most to the discrimination of subspp. grandae and mathiasenii from subspp. abietinum and magnificae. The flowers of Mathiasen's dwarf mistletoe were larger than all of the other taxa classified under A. abietinum. The shoot color of Mathiasen's dwarf mistletoe was frequently blue-green, brown, yellow-brown, or redbrown, and plants were often highly glaucous, while the shoot color of the other subspecies were typically yellow-green or yellow, except for Wiens' dwarf mistletoe whose shoots are often green-brown or red-brown. Differences in host specificity and geographic distribution also distinguish the new subspecies from the other taxa of A. abietinum. [ABSTRACT FROM AUTHOR]

Oak woodlands are dependent on frequent fire to maintain the low stem density and diverse understories that typify these ecosystems. Without this recurrent disturbance, fire-sensitive conifer competitors encroach on oaks, reducing their vigor, and diminishing habitat quality. In fire-excluded oak woodlands, stand-replacing wildfire can trigger shifts in canopy dominance from seed-generated conifers to oaks, which are capable of vigorous sprouting following topkill. We examined the occurrence and sprouting dynamics of California black oak ( Quercus kelloggii Newb.) following repeated wildfires in the Lassen National Forest, California. We found that following reburn, changes in oak relative stand dominance, as well as oak sprout basal area and height, were each positively related to fire severity (P < 0.0001 for each analysis). While conifer regeneration suffered complete mortality at moderate and high reburn severities, 97% of topkilled oaks resprouted from surviving rootstocks, reinforcing oak dominance. Black oak resprouts that originated following topkill in the first wildfire were frequently topkilled in the second fire, including at lower burn severities survived by advance conifer regeneration. The results of this study indicate that while as individuals, black oaks are resilient to recurring wildfire, restoration of historic woodland structure and function is an unlikely outcome of these repeated disturbances. Management of post-wildfire regenerating oak stands in this region will require supplemental fuel reduction treatments, including prescribed burning. [ABSTRACT FROM AUTHOR]

Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Disturbance severity and snow duration have species-specific effects on seedlings. • Lower substrate burn severity disadvantaged Abies concolor seedlings. • Earlier snowmelt in the germination year decreased Abies concolor survival. • Post-fire compositional shifts toward drought-tolerant Pinus species are possible. Climate change is altering forest composition through species-specific responses to fire and drought. Future forest composition will depend on how the different regeneration niches of co-occurring species align with current environmental conditions, especially after fire, which can promote germination by exposing mineral soil. Few studies, however, have examined the effects of disturbance severity and microclimate on post-fire regeneration to define and compare the regeneration niches of co-occurring tree species. We used seven years of annual demography and microenvironment data from a 25.6-ha fully censused, stem-mapped forest dynamics plot in California, USA, to examine how disturbance severity, snow duration, and temperature extremes affect the survival of Abies concolor and Pinus lambertiana seedlings that germinated naturally after a low- to moderate-severity fire. We defined disturbance severity at the microsite level, based on characteristics of the substrate, and at the neighborhood level, based on tree mortality. Both disturbance severity and snow duration had species-specific effects on seedling survival, but these differed by life stage. During the germination year, later snow disappearance was associated with a 0.5 increase in survival probability for A. concolor but hardly affected P. lambertiana ; in contrast, higher neighborhood disturbance severity increased survival of both species. After the germination year, higher substrate burn severity was associated with a 0.8 increase in survival probability for A. concolor but hardly affected P. lambertiana ; higher neighborhood disturbance severity and later snow disappearance increased annual survival of both species, but maximum summer temperature had minimal effect. Overall, available seed, higher substrate burn severity, higher neighborhood disturbance severity, and later snow disappearance promoted natural regeneration. However, lower substrate burn severity and earlier snow disappearance in the germination year disadvantaged A. concolor seedlings, increasing the relative abundance of P. lambertiana seedlings compared to the local tree population. Our results indicate that natural post-fire compositional shifts toward drought-tolerant Pinus species–and away from less drought-tolerant Abies species–are possible in the Sierra Nevada, with potential benefits for forest persistence under climate change. Broadly, we show that species differences in regeneration niches shape how disturbance severity and microclimate affect forest species composition. [ABSTRACT FROM AUTHOR]

The chemical composition, including the enantiomeric excess of the main terpenes, of essential oils from seeds and cones of Abies concolor was studied by chromatographic (GC) and spectroscopic methods (mass spectrometry, nuclear magnetic resonance), leading to the determination of 98 compounds. Essential oils were mainly composed of monoterpene hydrocarbons. The dominant volatiles of seed essential oil were: limonene (47 g/100 g, almost pure levorotary form) and α-pinene (40 g/100 g), while α-pinene (58 g/100 g), sabinene (11 g/100 g), and β-pinene (4.5 g/100 g) were the predominant components of the cone oil. The seed and cone essential oils exhibited mild antibacterial activity, and the MIC ranged from 26 to 30 μL/mL against all of the tested bacterial standard strains: Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, Escherichia coli, and Klebsiella pneumoniae. The cytotoxic studies have demonstrated that tested essential oils were cytotoxic to human skin fibroblasts and human microvascular endothelial cells at concentrations much lower than the MIC. The essential oils from A. concolor seeds and cones had no toxic effect on human skin fibroblasts and human microvascular endothelial cells, when added to the cells at a low concentration (0-0.075 μL/mL) and (0-1.0 μL/mL), respectively, and cultured for 24 h. [ABSTRACT FROM AUTHOR]

• Density reduction from fire or mechanical damage increased post-fire growth rates. • Density reduction from bark beetle mortality did not affect post-fire growth rates. • Pinus had a stronger post-fire growth response to competitive release than Abies. • Mortality and diameter distribution, not growth, control composition of large trees. Global increases in large-tree mortality and multiple disturbances such as fire, drought, and pestilence increase the importance of understanding how large-tree growth responds to changes in competitive neighborhoods. We used 34,175 spatially mapped trees within 25.6 ha that burned at low to moderate severity in 2013 to investigate how changes to tree neighborhoods affected growth of 3,652 surviving trees of two species, Abies concolor (white fir) and Pinus lambertiana (sugar pine). Using diameter measurements taken in 2014 and 2019, we estimated post-fire radial growth of each surviving tree. We modeled annual basal area increment as a function of diameter and extracted residuals to yield relative growth rate (RGR). We used a multi-model approach and AIC to compare the species-specific effects on RGR of all post-fire tree mortality within a neighborhood radius versus mortality broken down by cause. To represent density reduction around each surviving tree, we computed crowding metrics for neighborhood radii up to 20 m for all tree mortality combined and for each mortality cause. The best-fit model included terms for density reduction within 10 m of the surviving tree due to 1) fire or mechanical damage and 2) bark beetle mortality, as well as their interactions with species and diameter. Density reduction due to fire or mechanical damage had a positive effect on RGR that was nearly twice as strong for P. lambertiana as A. concolor. Tree diameter interacted with density reduction for just P. lambertiana. Small-diameter (10-cm) P. lambertiana had a fourfold larger increase in basal area increment than large-diameter (60-cm) P. lambertiana as density reduction due to fire or mechanical damage ranged from 0 to 100 %. The strong growth response of medium-diameter P. lambertiana to density reductions could eventually increase the abundance of large-diameter (≥60 cm) P. lambertiana. In conjunction with mortality rates, which were lower for large-diameter P. lambertiana (0.97 %) than A. concolor (3.31 %), this could increase the relative abundance of large-diameter P. lambertiana from 51.2 % in 2020 to 62.6 % by 2050. Changes to competitive neighborhoods can have species-specific effects on large-tree growth, an important consideration for long-term management of fire-prone forests. [ABSTRACT FROM AUTHOR]

The achieved results concerning the grafting silver-fir - Abiesconcolor [(Gord. & Glend.) Lindl] scions on white-fir (Abies alba Mill.)rootstocks are reporting in this article. The double-side-veneer grafting method and the plastic tape and the ecological Ceraltin® wax were applied in four experimental variants. The side-veneer-grafting method and the classic materials, such as raffia and the hot wax were used at the two controls involved in this experiment. The grafting success expressed in percents, were transformed in arcsin square root of percent values, and a two-way analysis of variance was performed. Highly significant (p

The chemical composition, including the enantiomeric excess of the main terpenes, of essential oils from seeds and cones of Abies concolor was studied by chromatographic (GC) and spectroscopic methods (mass spectrometry, nuclear magnetic resonance), leading to the determination of 98 compounds. Essential oils were mainly composed of monoterpene hydrocarbons. The dominant volatiles of seed essential oil were: limonene (47 g/100 g, almost pure levorotary form) and α-pinene (40 g/100 g), while α-pinene (58 g/100 g), sabinene (11 g/100 g), and β-pinene (4.5 g/100 g) were the predominant components of the cone oil. The seed and cone essential oils exhibited mild antibacterial activity, and the MIC ranged from 26 to 30 μL/mL against all of the tested bacterial standard strains: Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, Escherichia coli, and Klebsiella pneumoniae. The cytotoxic studies have demonstrated that tested essential oils were cytotoxic to human skin fibroblasts and human microvascular endothelial cells at concentrations much lower than the MIC. The essential oils from A. concolor seeds and cones had no toxic effect on human skin fibroblasts and human microvascular endothelial cells, when added to the cells at a low concentration (0–0.075 μL/mL) and (0–1.0 μL/mL), respectively, and cultured for 24 h.

Understanding temporal forest change across spatial biophysical gradients is fundamental to managing dynamic forests across variable landscapes. This is especially true for identifying how biophysical variation mediates forest development through multi-century changes in climate and eras of forest manipulation by humans. We examined 155 years of forest change across a 13,000-ha mixed conifer landscape in the Spring Mountains, Nevada, USA. We reconstructed forest composition at 31 sites in 1855 (pre-Euro-American settlement, and near the end of the Little Ice Age), 1881 (logging era), 1900 (before establishment of government forest reserve), 1950 (mid-century fire exclusion), and 2009 (present forest). Differing from many other western conifer landscapes, density of large trees (>50 cm in diameter) increased through time. Aside from large trees and one measure of species compositional change, five other measures of forest change (e.g., percent difference in tree density) were spatially variable across the landscape and not well represented by ‘average’ change in the study area. Forest composition in 1855 minimally influenced the next 155 years of forest change. In contrast, the amount, timing, and direction of forest change were linked with topographic gradients. Forests on warm slope aspects incurred the least amount of change, which also was delayed in time, whereas forests on cooler aspects already appreciably changed by 1900. Warm aspects were the only ones to lose trees during the most recent 60-year period (1950–2009), with a decline in median tree density of 13%, compared to continued gains on moister sites. Management applications of this spatio-temporal variation include anchoring fuel treatments around areas of open, little-changed forest to increase effective size of treatments. [ABSTRACT FROM AUTHOR]

Removing all large trees without planning to replace them with either planted or naturally regenerated younger trees (i.e., high-grading) is widely thought to have negative consequences on a forest's productivity and species composition, but no previous studies in California had evaluated this assumption. To make such an evaluation, I measured productivity and canopy species composition shifts following the repeated removal of large trees and compared the results with those from two other basic forest harvest methods: thinning from below and single tree selection. Timber productivity was substantially lower with large-tree removal (0.65 thousand board feet per acre per year) than with the other methods (averaging 1.33 thousand board feet per acre per year), which included the no-harvest control, where yield was zero. Large-tree removal also resulted in more species change, with white fir increasing in the canopy and ponderosa pine decreasing. [ABSTRACT FROM AUTHOR]

• Forests with a restored fire regime had high natural regeneration rates. • Regardless of species, the majority of sampled stems, were found in clumps. • Young trees in clumps had higher diameter and height growth rates than individuals. • There was no significant difference in growth rates among clump sizes. • High shrub cover didn't have a significant negative effect on seedling growth rates. Many dry conifer forests in the western United States were historically adapted to frequent low-to-moderate severity fires, but are increasingly susceptible to large, stand-replacing wildfires due to dramatically altered stand conditions and changing climate. The historic tree spatial patterns of mature stands in fire-adapted forests – individual trees, clumps of trees, and openings (ICO) – are associated with heightened resistance and resilience to fire. How this pattern develops over time, however, is not well understood and could help inform reforestation practices better designed to increase fire resistance in developing stands. We investigated growth rates and spatial patterns among regenerating trees in mixed-conifer forests with restored fire regimes in California's Sierra Nevada. We compared average stocking densities across tree species, size classes, shrub cover, and fire histories. We also examined the effects of microsite topography on spatial patterning of these juvenile trees, and the effects of clump patterning, local stem density and adjacent shrubs on tree growth rates. We found that the majority (75%) of sampled stems were found in clumps. Our mixed-effect models indicated that for trees growing within clumps, increased crowding slowed tree growth, as expected. Surprisingly, however, compared with individual trees growing outside clumps, trees growing within clumps grew significantly faster. Shrub cover in proximity to juvenile trees did not have a consistent impact across our models, but was associated with increased annual height growth. Additionally, plots with high shrub cover had higher stocking rates among the tallest regenerating stems (height > 137 cm). Our findings indicate that clumped spatial patterns of natural tree recruitment may favor the establishment and early growth of regenerating conifers in active-fire forests. While our study focused only on the early stages (<30 years old) of regeneration, our results contrast with common reforestation strategies favoring regular, widely-spaced plantings and aggressive shrub reduction. Our research suggests we need a better understanding of how heterogeneity in the spatial patterns of juvenile trees and shrubs may enhance the resilience of regenerating stands as they mature. [ABSTRACT FROM AUTHOR]

Impacts of drought on tree mortality in high-elevation mixed-conifer forests of southwestern U.S. are poorly understood. A recent extended and severe drought in the region provided an opportunity to investigate the patterns and factors associated with tree mortality in this forest type. Specifically, we quantified mortality that occurred between 1995 and 2008 of four tree species, white fir ( Abies concolor ), limber pine ( Pinus flexilis ), trembling aspen ( Populus tremuloides ), and Douglas-fir ( Pseudotsuga menziesii ), in mixed-conifer forests over three sites in northern Arizona within 84, 0.02 ha plots. We found: (1) varied but substantial tree mortality (4–56% by basal area) in most species between 1996 and 2006 in association with recent severe and prolonged drought; (2) tree mortality differed among sites and species with aspen and white fir having the most mortality (>30% by basal area); (3) relationships between tree mortality and most climatic factors (e.g. temperature, precipitation, Palmer Drought Severity Index) were lagged 1–4 yr; (4) bark beetle attack and intraspecific tree basal area were consistently and positively related to tree mortality for most species and sites, whereas topographic and other stand characteristics were less consistently related to mortality. Results show that aspen, Douglas-fir, and white fir were more vulnerable to recent drought-associated mortality than limber pine. Associations between tree mortality and intraspecific basal area support further evaluation of treatments that reduce intraspecific competition within stands to lower risks of tree mortality in southwestern mixed conifer forests. [ABSTRACT FROM AUTHOR]

Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on bark beetle prevalence in pure, uneven-aged Jeffrey pine (Pinus jeffreyiGrev. & Balf.) interspersed with isolated California white fir (Abies concolorvar.lowiana[Gord.] Lemm.). Based on pitch tube counts in a stand with a moderate bark beetle population in its pine component, the Jeffrey pine beetle (Dendroctonus jeffreyiHopkins) generally preferred larger trees before treatment implementation, but after exhibiting mixed pretreatment tendencies concerning stand density demonstrated a posttreatment proclivity toward higher density. Cut-to-length thinning followed by underburning increased the pine beetle population while whole-tree thinning unaccompanied by burning reduced it. Tree mortality was induced by the bark beetle infestation but was not its sole cause. Pitch tube abundance on white fir far exceeded that on Jeffrey pine, and the greatest influence on the fir engraver (Scolytusventralis LeConte) population was the prevalence of its host tree. The responses presented herein to these thinning and burning practices, which are being increasingly utilized in forest restoration efforts in the western USA, provide natural resource managers insight into potential forest health outcomes when implemented in Jeffrey pine and similar dry site forest types. [ABSTRACT FROM AUTHOR]

Twentieth-century land management has altered the structure and composition of mixed-conifer forests and decreased their resilience to fire, drought, and insects in many parts of the Interior West. These forests occur across a wide range of environmental settings and historical disturbance regimes, so their response to land management is likely to vary across landscapes and among ecoregions. However, this variation has not been well characterized and hampers the development of appropriate management and restoration plans. We identified mixed-conifer types in central Oregon based on historical structure and composition, and successional trajectories following recent changes in land use, and evaluated how these types were distributed across environmental gradients. We used field data from 171 sites sampled across a range of environmental settings in two subregions: the eastern Cascades and the Ochoco Mountains. We identified four forest types in the eastern Cascades and four analogous types with lower densities in the Ochoco Mountains. All types historically contained ponderosa pine, but differed in the historical and modern proportions of shade-tolerant vs. shade-intolerant tree species. The Persistent Ponderosa Pine and Recent Douglas-fir types occupied relatively hot- dry environments compared to Recent Grand Fir and Persistent Shade Tolerant sites, which occupied warm-moist and cold-wet environments, respectively. Twentieth-century selective harvesting halved the density of large trees, with some variation among forest types. In contrast, the density of small trees doubled or tripled early in the 20th century, probably due to land-use change and a relatively cool, wet climate. Contrary to the common perception that dry ponderosa pine forests are the most highly departed from historical conditions, we found a greater departure in the modern composition of small trees in warm-moist environments than in either hot-dry or cold-wet environments. Furthermore, shade-tolerant trees began infilling earlier in cold-wet than in hot-dry environments and also in topographically shaded sites in the Ochoco Mountains. Our new classification could be used to prioritize management that seeks to restore structure and composition or create resilience in mixed-conifer forests of the region. [ABSTRACT FROM AUTHOR]

The Douglas-fir tussock moth (DFTM), Orgyia pseudotsugata McDunnough (Lepidoptera:Erebidae:Lymantriinae), is a native western North American defoliator of true fir, Abies spp. Mill., and Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. We investigated the population genetics and impact associated with the first recorded outbreak of DFTM in southern California (USA), and report the first collection of DFTM in Baja California Norte, Mexico. This latter population is similar genetically to populations from Washington, USA and British Columbia, Canada. We assessed forest stand characteristics, levels of defoliation, and mortality of white fir, Abies concolor Lindl., associated with the DFTM outbreak in the Transverse Mountain Ranges of southern California. We compared these data to those from southern California non-outbreak stands of A. concolor, and from virgin stands with an A. concolor component in the Sierra San Pedro Martir National Park (Mexico). Total stand density (ha-1) was significantly higher (22%) in non-outbreak stands than in outbreak stands. However, outbreak stands had significantly higher mortality of A. concolor than non-outbreak stands [whether expressed as density (70%) or basal area (m² ha-1) (32%)]. Total stand and A. concolor density and basal area for living and dead trees were significantly lower in the Sierra San Pedro Martir National Park than in southern California. Dead A. concolor comprised >95% of all tree mortality in both outbreak and non-outbreak areas in southern California, which corresponded to a mean 20% basal area loss of A. concolor associated with DFTM feeding injury within the outbreak area. The mean level of defoliation of A. concolor by DFTM was 39%, and 62% of all dead A. concolor were associated with DFTM defoliation. In stands with high levels of defoliation, larval feeding and tree mortality were also noted in Jeffrey pine, Pinus jeffreyi Grev. & Balf. The amount of dead A. concolor basal area associated with the fir engraver, Scolytus ventralis LeConte (Coleoptera: Scolytidae), in non-outbreak stands was 96% greater than in outbreak stands. Using the U.S.D.A. National Insect and Disease Risk Map software, a total of 13,534 ha were predicted to be at risk to basal area loss from future DFTM outbreaks on national forest lands in southern California. Changes in forest management practices and fire suppression policies likely led to an increase in the density and continuity of DFTM's preferred host in southern California and to a southward shift in the historic range of DFTM outbreaks. [ABSTRACT FROM AUTHOR]

Mosaics of tree clumps and openings are characteristic of forests dominated by frequent, low- and moderate-severity fires. When restoring these fire-suppressed forests, managers often try to reproduce these structures to increase ecosystem resilience. We examined unburned and burned forest structures for 1937 0.81 ha sample areas in Yosemite National Park, USA. We estimated severity for fires from 1984 to 2010 using the Landsat-derived Relativized differenced Normalized Burn Ratio (RdNBR) and measured openings and canopy clumps in five height strata using airborne LiDAR data. Because our study area lacked concurrent field data, we identified methods to allow structural analysis using LiDAR data alone. We found three spatial structures, canopy-gap, clump-open, and open, that differed in spatial arrangement and proportion of canopy and openings. As fire severity increased, the total area in canopy decreased while the number of clumps increased, creating a patchwork of openings and multistory tree clumps. The presence of openings > 0.3 ha, an approximate minimum gap size needed to favor shade-intolerant pine regeneration, increased rapidly with loss of canopy area. The range and variation of structures for a given fire severity were specific to each forest type. Low- to moderate-severity fires best replicated the historic clump-opening patterns that were common in forests with frequent fire regimes. Our results suggest that managers consider the following goals for their forest restoration: 1) reduce total canopy cover by breaking up large contiguous areas into variable-sized tree clumps and scattered large individual trees; 2) create a range of opening sizes and shapes, including ~ 50% of the open area in gaps > 0.3 ha; 3) create multistory clumps in addition to single story clumps; 4) retain historic densities of large trees; and 5) vary treatments to include canopy-gap, clump-open, and open mosaics across project areas to mimic the range of patterns found for each forest type in our study. [ABSTRACT FROM AUTHOR]

An investigation of wildfire effects on mineral nutrition of Jeffrey pine (Pinus jeffreyiGrev. & Balf.) along with species comparisons of the nutrition of unburned specimens of this pine to those of unburned California white fir (Abies concolorvar.lowiana[Gord.] Lemm.) were conducted in an eastern Sierran mixed conifer stand. Foliar Fe and Mn concentrations were frequently higher and Al was consistently so in burned than in the unburned pine as assessed in six sampling periods distributed over more than two postfire growing seasons while base cation/metallic element molar ratios consisting of Ca/Al, K/Al, K/Mn, Ca/Fe, Mg/Fe, K/Fe, and Ca/Zn were often lower in the former. Foliar N, P, Fe, Zn, and Cu were frequently higher in unburned pine than unburned fir while the reverse proved true concerning K, Ca, Mn, B, and Al; and likewise several molar ratios involving Al and Mn were higher in the former while several involving Fe, Zn, and Cu were higher in the latter. At midstudy, mineral soil in the burned stand portion had lower K but higher S, Mn, and Zn than that in the unburned portion, and the former had several molar ratios that were lower as well. [ABSTRACT FROM AUTHOR]

In the spring of 2008, Dothistroma septosporum, a damaging quarantine pathogen of pine foliage, was documented in Järvselja (southeastern Estonia), apparently for the first time, on white fir ( Abies concolor). Thus, a new host species and genus for the fungus were recorded. Infection of white fir by D. septosporum, and also of some other fir species, was monitored annually on a transect proceeding from southeastern Estonia to northern Latvia. As a result, D. septosporum was detected also on silver fir ( Abies alba). It is not clear why this fungus with a worldwide distribution appeared on this new host genus definitely in northern Europe. [ABSTRACT FROM AUTHOR]

An investigation of wildfire effects on water relations of Jeffrey pine (Pinus jeffreyiGrev. & Balf.) along with species comparisons of the water relations of unburned specimens of this pine to those of unburned white fir (Abies concolorvar.lowiana[Gord.] Lemm.) were conducted in a mixed conifer stand located in the Lake Tahoe Basin. Xylem water potentials were significantly lower in burned than in the unburned Jeffrey pine as measured in predawn, midday, and evening periods distributed over more than two postfire growing seasons, while soil water potentials were lower in burned than in unburned stand portions during the drier parts of the growing season, but the reverse proved true during the wetter part. Diurnal fluctuation in bole diameter, a measure of stored water recharge capacity, was largely unaffected by wildfire, however. Xylem water potentials were consistently lower in unburned white fir than in unburned Jeffrey pine and DBH fluctuation was often lower in the fir than in the pine as well, but soil water potentials associated with unburned subject trees did not differ significantly between the two species. Demonstrated here are ecophysiological alterations that occur in Sierra Nevada mixed conifer due to wildfire and shifting species composition. [ABSTRACT FROM PUBLISHER]

We studied vegetation composition and structure in a mixed conifer-oak ecosystem across a range of fire severity 10 years following wildfire. Sample plots centered on focal California black oaks (Quercus kelloggii) were established to evaluate oak and neighboring tree and shrub recovery across a gradient of fire severity in the southern Cascade Range, USA. Shrub and oak resprouting was strongest around focal oaks where conifer mortality was greatest. Linear modeling revealed negative relationships between California black oak sprout height or basal area and residual overstory tree survival, primarily white fir {Abies concolor). The two dominant competing species, California black oak and white fir, showed opposite responses to fire severity. Sprouting California black oak and associated shrubs dominated in severely burned areas, while surviving, non-sprouting white fir maintained dominance by its height advantage and shading effects in areas that burned with low fire severity. Our results indicate that high-severity fire promotes persistence and restoration of ecosystems containing resprouting species, such as California black oak, that are increasingly rare due to widespread fire exclusion in landscapes that historically experienced more frequent fire. We present a conceptual model based on our results and supported by a synthesis of postfire resprouting dynamics literature. Our results and conceptual model help illuminate long-term postfire vegetation responses and the potential ability of fire to catalyze formation of alternate vegetation community structures that may not be apparent in studies that evaluate postfire effects at shorter time-since-fire intervals or at coarser scales. [ABSTRACT FROM AUTHOR]

Mechanical thinning and the application of prescribed fire are commonly used to restore fire-adapted forest ecosystems in the Western United States. During a 10-year period, we monitored the effects of fuel-reduction and forest-restoration treatments on levels of tree mortality in an interior ponderosa pine, Pinus ponderosa Dougl. ex Laws., forest in California. Twelve experimental plots, ranging in size from 77-144 ha, were established to create two distinct forest structural types: mid-seral stage (low structural diversity; LoD) and late-seral stage (high structural diversity; HiD). Following harvesting, half of each plot was treated with prescribed fire (B). A total of 16,473 trees (8.7% of all trees) died during the 10-year period. Mortality was primarily attributed to bark beetles (Coleoptera: Curculionidae, Scolytinae) (10,655 trees), specifically fir engraver, Scolytus ventralis LeConte, mountain pine beetle, Dendroctonus ponderosae Hopkins, western pine beetle, D. brevicomis LeConte, pine engraver, Ips pini (Say), and, to a much lesser extent, Jeffrey pine beetle, D. jeffreyi Hopkins. Trees of all ages and size classes were killed, but mortality was concentrated in the smaller-diameter classes (19-29.2 and 29.3-39.3 cm at 1.37 m in height). Most mortality occurred three to five years following prescribed burns. Higher levels of bark beetle-caused tree mortality were observed on LoD + B (8.7%) than LoD (4.2%). The application of these and other results to the management of interior P. ponderosa forests are discussed, with an emphasis on the maintenance of large trees. [ABSTRACT FROM AUTHOR]