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The western United States is projected to experience more frequent and severe wildfires in the future due to drier and hotter climate conditions, exacerbating destructive wildfire impacts on forest ecosystems such as tree mortality and unsuccessful post‐fire regeneration. While empirical studies have revealed strong relationships between topographical information and plant regeneration, ecological processes in ecosystem models have either not fully addressed topography‐mediated effects on the probability of plant regeneration, or the probability is only controlled by climate‐related factors, for example, water and light stresses. In this study, we incorporated seedling survival data based on a planting experiment in the footprint of the 2011 Las Conchas Fire into the Photosynthesis and EvapoTranspiration (PnET) extension of the LANDIS‐II model by adding topographic and an additional climatic variable to the probability of regeneration. The modified algorithm included topographic parameters such as heat load index and ground slope and spring precipitation. We ran simulations on the Las Conchas Fire landscape for 2012–2099 using observed and projected climate data (i.e., Representative Concentration Pathway 4.5 and 8.5). Our modification significantly reduced the number of regeneration events of three common southwestern conifer tree species (piñon, ponderosa pine, and Douglas‐fir), leading to decreases in aboveground biomass, regardless of climate scenario. The modified algorithm decreased regeneration at higher elevations and increased regeneration at lower elevations relative to the original algorithm. Regenerations of three species also decreased in eastern aspects. Our findings suggest that ecosystem models may overestimate post‐fire regeneration events in the southwest United States. To better represent regeneration processes following wildfire, ecosystem models need refinement to better account for the range of factors that influence tree seedling establishment. This will improve model utility for projecting the combined effects of climate and wildfire on tree species distributions. [ABSTRACT FROM AUTHOR]

Analysis of functional traits is a cornerstone of ecology, yet individual traits seldom explain useful amounts of variation in species distribution or climatic tolerance, and their functional significance is rarely validated experimentally. Multivariate suites of interacting traits could build an understanding of ecological processes and improve our ability to make sound predictions of species success in our rapidly changing world. We use foliar water uptake capacity as a case study because it is increasingly considered to be a key functional trait in plant ecology due to its importance for stress‐tolerance physiology. However, the traits behind the trait, that is, the features of leaves that determine variation in foliar water uptake rates, have not been assembled into a widely applicable framework for uptake prediction. Focusing on trees, we investigated relationships among 25 structural traits, leaf osmotic potential (a source of free energy to draw water into leaves), and foliar water uptake in 10 diverse angiosperm and conifer species. We identified consistent, multitrait "uptake syndromes" for both angiosperm and conifer trees, with differences in key traits revealing suspected differences in the water entry route between these two clades and an evolutionarily significant divergence in the function of homologous structures. A literature review of uptake‐associated functional traits, which largely documents similar univariate relationships, provides additional support for our proposed "uptake syndrome." Importantly, more than half of shared traits had opposite‐direction influences on the capacity of leaves to absorb water in angiosperms and conifers. Taxonomically targeted multivariate trait syndromes provide a useful tool for trait selection in ecological research, while highlighting the importance of micro‐traits and the physiological verification of their function for advancing trait‐based ecology. [ABSTRACT FROM AUTHOR]

Summary: Traditional phenological models use chilling and thermal forcing (temperature sum or degree‐days) to predict budbreak. Because of the heightening impact of climate and other related biotic or abiotic stressors, a model with greater biological support is needed to better predict budbreak.Here, we present an original mechanistic model based on the physiological processes taking place before and during budbreak of conifers. As a general principle, we assume that phenology is driven by the carbon status of the plant, which is closely related to environmental variables and the annual cycle of dormancy–activity. The carbon balance of a branch was modelled from autumn to winter with cold acclimation and dormancy and from winter to spring when deacclimation and growth resumption occur.After being calibrated in a field experiment, the model was validated across a large area (> 34 000 km2), covering multiple conifers stands in Québec (Canada) and across heated plots for the SPRUCE experiment in Minnesota (USA). The model accurately predicted the observed dates of budbreak in both Québec (±3.98 d) and Minnesota (±7.98 d).The site‐independent calibration provides interesting insights on the physiological mechanisms underlying the dynamics of dormancy break and the resumption of vegetative growth in spring. [ABSTRACT FROM AUTHOR]

The benefits of early detection of biological invasions are widely recognized, especially for protected areas (PAs). However, research on incipient invasive plant species is scarce compared to species with a recognized history of invasion. Here, we characterized the invasion status of the non-native conifer Juniperus communis in PAs and interface areas of Andean Patagonia, Argentina. We mapped its distribution and described both the invasion and the environments this species inhabits through field studies, a literature review, and a citizen science initiative. We also modeled the species' potential distribution by comparing the climatic characteristics of its native range with those of the introduced ranges studied. The results show that J. communis is now widely distributed in the region, occurring naturally in diverse habitats, and frequently within and close to PAs. This species can be considered an incipient invader with a high potential for expansion in its regional distribution range, largely due to its high reproductive potential and the high habitat suitability of this environment. Early detection of a plant invasion affords a valuable opportunity to inform citizens of the potential risks to high conservation value ecosystems before the invader is perceived as a natural component of the landscape. [ABSTRACT FROM AUTHOR]

Fossil wood is a significant proxy for terrestrial palaeoclimate and palaeogeography. Abundant and diversified Mesozoic fossil wood has been documented in China. However, there are limited reports of Jurassic fossil wood records from northwest China. Herein, several calcified wood fossils are described in anatomical detail, from the Middle Jurassic (Bajocian to Callovian) Xinhe Formation in Gansu Province. They were identified as two species of the fossil wood genus Xenoxylon Gothan of Coniferales, namely X. latiporosum (Cramer) Gothan and X. peidense Zheng et Zhang. The newly collected material represents the first record of Jurassic petrified wood from Gansu Province. Based on the palaeoclimatic implication of Xenoxylon, we propose that the Baojishan Basin may have experienced a distinct short-term cooling during the Middle Jurassic. We analysed the fossil diversity and spatial-temporal distribution of Xenoxylon species in China. A total of 15 Xenoxylon species have been documented in China. These occurred from the Late Triassic to Late Cretaceous, but flourished from the Jurassic to Cretaceous intervals. Geographically, they are distributed across 13 provinces, mainly in northeast China. Significantly, this record expands the distribution of this important climate indicator taxon. [ABSTRACT FROM AUTHOR]

Lichens, a symbiotic association of fungi and algae, are suitable to serve as a bio-indicator of air pollution due to their ability to absorb toxic materials into their thallus. The photobiont performs photosynthesis; it belongs to blue-green algae, i.e. cyanobacteria and/or green algae; a mycobiont is a fungus from the Ascomycetes, Basidiomycetes or Deuteromycetes group. Biodiversity Index (LBI) which was used to determine the effect of phytotoxic gases released from pollutants on the diversity of lichens, especially on Level II Sample Plots with conifers. One of the goals of the study is to determine which species of lichen are the most tolerant and the most sensitive to air pollution. This is one of several different methods that have been developed to monitor the environmental quality. One of them, which was used as basis for obtaining the basic statistical parameters, with the subsequently used T-test that confirmed some of the basic initial assumptions, is the significance of sample surface coverage by lichens. The percentages of lichen coverage of the recordings were obtained with basic photo processing programs, most simply viewed in black and white technique. The results are represented graphically through maps. Different aspects of the current biomonitoring should be compared to the results obtained in practice to date, in order to increase the number of the related studies in the years to come. Lastly, the current studies, progress, and challenges of biomonitoring using lichen as a biological indicator were discussed, and relevant recommendations were formulated. [ABSTRACT FROM AUTHOR]

Allopolyploidy is considered as a principal driver that shaped angiosperms' evolution in terms of diversification and speciation. Despite the unexpected high frequency of polyploidy that was recently discovered in the coniferous genus Juniperus, little is known about the origin of these polyploid taxa. Here, we conducted the first study devoted to deciphering the origin of the only hexaploid taxon in Juniperus along with four of its closely related tetraploid taxa using AFLP markers with four primers combinations. Phylogenetic analysis revealed that the 10 studied species belong to 2 major clusters. J. foetidissima appeared to be more related to J. thurifera, J. sabina, and J. chinensis. The Bayesian clustering analysis showing a slight variation in genetic admixture between the studied populations of J. foetidissima, suggesting an allopolyploid origin of this species involving J. thurifera and J. sabina lineages, although a purely autopolyploidy origin of both J. thurifera and J. foetidissima cannot be ruled out. The admixed genetic pattern revealed for J. seravschanica showed that the tetraploid cytotypes of this species originated from allopolyploidy, whereas no clear evidence of hybridization in the origin of the tetraploid J. thurifera and J. chinensis was detected. This study provides first insights into the polyploidy origin of the Sabina section and highlights the potential implication of allopolyploidy in the evolution of the genus Juniperus. Further analyses are needed for a more in-depth understanding of the evolutionary scenarios that produced the observed genetic patterns. [ABSTRACT FROM AUTHOR]

Amber and plant remains were discovered in the lower Cenomanian lignitic clay from La Gripperie-Saint-Symphorien (Charente-Maritime, western France). The amber mainly consists of scarce and infracentimetric pieces showing a wide range of sizes and colours. The shape of the amber grains greatly varies, including more or less cylindrical fragments of flows and spherical drops. Plants consist of foliar remains corresponding to isolated pinnae and pinnules of ferns (Matonia sp., Weichselia reticulata (Stokes & Webb, 1824) Fontaine emend. Alvin, 1971), leafy axes of conifers (Geinitzia reichenbachii (Geinitz, 1842) Hollick & Jeffrey, 1909, Pagiophyllum sp.) and leaves of angiosperms (including cf. Eucalyptolaurus depreii Coiffard, B.Gomez, Thiébaut & J.Kvaček and three morphotypes of undeterminable leaves). They are preserved as isolated cuticles, charcoalified compressions without cuticle, and external casts. Angiosperms are clearly the most abundant and diverse remains of the plant assemblage. This latter contrasts with most of Albian-Cenomanian coastal floras from the Aquitaine Basin, which are dominated by gymnosperms characterised by xeromorphic adaptations and tolerating halophytic conditions. Similar to the coeval sites of Puy-Puy (Charente-Maritime) and Jaunay-Clan (Vienne), the plant-rich clay from La Gripperie-Saint-Symphorien was probably deposited in innermost coastal environments heavily influenced by inland/continental freshwater. [ABSTRACT FROM AUTHOR]

The allometry of the pipe model quantifies the approximate proportionality between the tree leaf amount and the stem cross-sectional area at the crown base (ACB). It is useful for estimating and modeling carbon fixation abilities of trees but requires climbing the tree and is thus unsuitable for large-scale studies. Here, we adopted a previously proposed allometry (hereafter the quasi-pipe (qPipe) model allometry) formulating the relationship between the tree leaf amount and a surrogate of ACB, ACB_Est, calculated from tree dimensions measurable from the ground. Using published/unpublished data for 962 trees of 159 species collected between tropical rainforests and boreal forests, we established pipe and qPipe model allometries for evergreen-conifer, deciduous-conifer, evergreen-broadleaf, and deciduous-broadleaf plant functional types (PFTs). For the leaf area per tree (LA), allometric lines on a log–log plane were almost identical among the four PFTs in both models, with slopes of ~ 1. For the leaf mass per tree (LM), however, the allometric lines separated among the four PFTs in both models and had slopes greater than 1, indicating that the proportionality assumed in the pipe model held for LA but not LM. The applicability of the qPipe model in estimating the stand-scale leaf amount was further examined. [ABSTRACT FROM AUTHOR]

The benefits of early detection of biological invasions are widely recognized, especially for protected areas (PAs). However, research on incipient invasive plant species is scarce compared to species with a recognized history of invasion. Here, we characterized the invasion status of the non-native conifer Juniperus communis in PAs and interface areas of Andean Patagonia, Argentina. We mapped its distribution and described both the invasion and the environments this species inhabits through field studies, a literature review, and a citizen science initiative. We also modeled the species' potential distribution by comparing the climatic characteristics of its native range with those of the introduced ranges studied. The results show that J. communis is now widely distributed in the region, occurring naturally in diverse habitats, and frequently within and close to PAs. This species can be considered an incipient invader with a high potential for expansion in its regional distribution range, largely due to its high reproductive potential and the high habitat suitability of this environment. Early detection of a plant invasion affords a valuable opportunity to inform citizens of the potential risks to high conservation value ecosystems before the invader is perceived as a natural component of the landscape. [ABSTRACT FROM AUTHOR]

Forests are threatened globally by increased recurrence and intensity of hot droughts. Functionally close coexisting species may exhibit differences in drought vulnerability large enough to cause niche differentiation and affect forest dynamics. The effect of rising atmospheric [CO2], which could partly alleviate the negative effects of drought, may also differ between species. We analysed functional plasticity in seedlings of two taxonomically close pine species (Pinus pinaster Ait. Pinus pinea L.) under different [CO2] and water stress levels. The multidimensional functional trait variability was more influenced by water stress (preferentially xylem traits) and [CO2] (mostly leaf traits) than by differences between species. However, we observed differences between species in the strategies followed to coordinate their hydraulic and structural traits under stress. Leaf 13C discrimination decreased with water stress and increased under elevated [CO2]. Under water stress both species increased their sapwood area to leaf area ratios, tracheid density and xylem cavitation, whereas they reduced tracheid lumen area and xylem conductivity. Pinus pinea was more anisohydric than P. pinaster. Pinus pinaster produced larger conduits under well-watered conditions than P. pinea. Pinus pinea was more tolerant to water stress and more resistant to xylem cavitation under low water potentials. The higher xylem plasticity in P. pinea , particularly in tracheid lumen area, expressed a higher capacity of acclimation to water stress than P. pinaster. In contrast, P. pinaster coped with water stress comparatively more by increasing plasticity of leaf hydraulic traits. Despite the small differences observed in the functional response to water stress and drought tolerance between species, these interspecific differences agreed with ongoing substitution of P. pinaster by P. pinea in forests where both species co-occur. Increased [CO2] had little effect on the species-specific relative performance. Thus, a competitive advantage under moderate water stress of P. pinea compared with P. pinaster is expected to continue in the future. [ABSTRACT FROM AUTHOR]

There is an increasing interest in mixed conifer-broadleaf stands as a way to increase the diversity and productivity of managed forests. This study examined the impacts of varying densities of planted broadleaf trees on conifer performance, total stand productivity, and understory plant cover 20 years after stand establishment. The study took place in the Malcolm Knapp Research Forest in Maple Ridge, British Columbia. It used a randomized complete block design to compare treatments containing low, moderate, or high broadleaf densities added to a constant conifer density. Each block contained a conifer-only plot as a control. Conifers were composed of equal amounts of western hemlock, western redcedar, and Douglas-fir. Broadleaves were composed of either red alder or paper birch. We found that conifer volume was significantly lower in most broadleaf treatments relative to the control, due to lower hemlock and redcedar volumes. Douglas-fir, on the other hand, had a higher volume—albeit not significant—in the broadleaf treatments. There were no significant differences in total stand volume between any of the treatments and the control. Shrub cover was significantly higher in the low and high alder treatments relative to the control, but there were no differences in shrub cover between birch treatments and the control. The results suggest that low alder density provides a good balance of conifer yield and understory development. [ABSTRACT FROM AUTHOR]

Drought legacies in radial tree growth are an important feature of variability in biomass accumulation and are widely used to characterize forest resilience to climate change. Defined as a deviation from normal growth, the statistical significance of legacy effects depends on the definition of "normal"—expected growth under average conditions—which has not received sufficient scrutiny.We re‐examined legacy effect analyses using the International Tree‐Ring Data Bank (ITRDB) and then produced synthetic tree‐ring data to disentangle four key variables influencing the magnitude of legacy effects. We hypothesized that legacy effects (i) are mainly influenced by the auto‐correlation of the radial growth time series (phi), (ii) depend on climate‐growth cross‐correlation (rho), (iii) are directly proportional to the inherent variability of the growth time series (standard deviation, SD), and (iv) scale with the chosen extreme event threshold.Using a data simulation approach, we were able to reproduce observed lag patterns, demonstrating that legacy effects are a direct outcome of ubiquitous biological memory. We found that stronger legacy effects for conifers compared to angiosperms is a consequence of their higher auto‐correlation, and that the detectability of legacy effects following rare drought events at individual sites is compromised by strong background stochasticity.Synthesis. We propose two pathways forward to improve the assessment and interpretation of legacy effects: First, we highlight the need to account for auto‐correlated residuals of climate‐growth regression models a posteriori, thereby retrospectively adjusting expectations for "normal" growth variability. Alternatively, we recommend including lagged climate variables in regression models a priori. By doing so, the magnitude of detected legacy effects is greatly reduced and biological memory is directly attributed to antecedent climatic drivers. We argue that future analyses should focus on understanding the functional reasons for how and why key statistical parameters describing this biological memory differ across species and sites. These two pathways should also stimulate improved process‐based representation of vegetation carbon dynamics in mechanistic models. [ABSTRACT FROM AUTHOR]

The assembly and function of the phyllosphere microbiome is important to the overall fitness of plants and, thereby, the ecosystems they inhabit. Presently, model systems for tree phyllosphere microbiome studies are lacking, yet forests resilient to pests, diseases, and climate change are important to support a myriad of ecosystem services impacting from local to global levels. In this study, we extend the development of model microbiome systems for trees species, particularly coniferous gymnosperms, by undertaking a structured approach assessing the phyllosphere microbiome of Pinus radiata. Canopy sampling height was the single most important factor influencing both alpha- and beta-diversity of bacterial and fungal communities (p < 0.005). Bacterial and fungal phyllosphere microbiome richness was lowest in samples from the top of the canopy, subsequently increasing in the middle and then bottom canopy samples. These differences maybe driven by either by (1) exchange of microbiomes with the forest floor and soil with the lower foliage, (2) strong ecological filtering in the upper canopy via environmental exposure (e.g., UV), (3) canopy density, (4) or combinations of factors. Most taxa present in the top canopy were also present lower in tree; as such, sampling strategies focussing on lower canopy sampling should provide good overall phyllosphere microbiome coverage for the tree. The dominant phyllosphere bacteria were Alpha-proteobacteria (Rhizobiales and Sphingomonas) along with Acidobacteria Gp1. However, the P. radiata phyllosphere microbiome samples were fungal dominated. From the top canopy samples, Arthoniomycetes and Dothideomycetes were highly represented, with abundances of Arthoniomycetes then reducing in lower canopy samples whilst abundances of Ascomycota increased. The most abundant fungal taxa were Phaeococcomyces (14.4% of total reads) and Phaeotheca spp. (10.38%). A second-order effect of canopy sampling direction was evident in bacterial community composition (p = 0.01); these directional influences were not evident for fungal communities. However, sterilisation of needles did impact fungal community composition (p = 0.025), indicating potential for community differences in the endosphere versus leaf surface compartments. Needle age was only important in relation to bacterial communities, but was canopy height dependant (interaction p = 0.008). By building an understanding of the primary and secondary factors related to intra-canopy phyllosphere microbiome variation, we provide a sampling framework to either explicitly minimise or capture variation in needle collection to enable ongoing ecological studies targeted at inter-canopy or other experimental levels. [ABSTRACT FROM AUTHOR]

Ongoing climate change increasingly affects growth conditions of native conifers such as Picea abies (Norway spruce) and Pinus sylvestris (Scots pine) in Central Europe. These conifers are primarily cultivated for wood production. To obtain ecologically and economically stable forests, forestry seeks alternative species that might be less prone to novel climatic conditions, such as Cedrus libani (Lebanon cedar). We aim at investigating growth responses to climatic factors of C. libani compared to native P. abies and P. sylvestris in Central Europe for 25 years (1994–2019). Growth responses were used as a proxy for tolerance towards climatic stress events, such as heat and drought. Height, diameter at breast height (DBH) and radial increment were measured for 40-year-old tree stands of C. libani and native conifers. Radial growth responses to selected climate parameters were analysed using bootstrapped correlations with detrended growth index chronologies and growth response indices for drought years (2003, 2012, 2015, 2018). For C. libani, radial growth was positively correlated with high water availability in late winter and spring, while for P. abies, February and summer and for P. sylvestris, July showed such a relationship. Cedrus libani exhibited the highest resistance, recovery, and resilience in response to climatic extremes. Against the background of climate change, C. libani could serve as an alternative conifer species to establish climate-resistant viable forests in Central Europe. [ABSTRACT FROM AUTHOR]

Many tropical species live close to their thermal limits within a narrow niche. Here, we investigate the ecophysiological limits of the tropical tree Podocarpus trinitensis , which is endemic to Trinidad and Tobago where most populations exist as isolated stands on hilltops. Five wild stands from a range of elevations were compared in the field with measurements of leaf temperature, canopy cover, stomatal conductance (gs), chlorophyll content and several chlorophyll fluorescence parameters. A parallel greenhouse experiment was used to acclimate seedlings to 'CONTROL' and 'HEAT' treatments (with mid-day air temperatures of 34.5 and 37 °C respectively), after which the above parameters were measured along with photosynthetic light and temperature response curves, leaf morphology and in vitro Fv/Fm thermostability. There was a positive association between improved physiological performance and elevation. In the high elevation sites, leaf temperatures were significantly lower while most of the physiological parameters were higher (gs , chlorophyll content, ɸ PSII, ETR max and I sat90). In the greenhouse, HEAT and CONTROL plants were similar for most parameters, except leaf temperature (which was coupled with air temperature) and leaf mass per unit area (which was higher in HEAT plants). Temperature response curves showed an optimum temperature for photosynthesis of 30 ± 0.5 °C (T Opt) and in vitro Fv/Fm indicated a critical temperature of 47.4 ± 0.38 °C for HEAT and 48.2 ± 0.24 °C for CONTROL (T 50), with no indication of heat acclimation. Podocarpus trinitensis was found to be shade tolerant. In the field, seedlings established under a close canopy (>95% canopy cover) and had a low light saturation point (LCP). In the greenhouse, where more light was available, seedlings retained a low light compensation point, light saturation point (LSP) and maximum photosynthetic rate (A max). The results suggest that P. trinitensis is moderately heat tolerant with the higher elevation sites being more habitable, but stands are also able to survive near sea level under a closed canopy. The narrow niche, along with the 30 ± 0.5 °C optimum temperature for photosynthesis and the lack of thermal plasticity in critical temperature, suggests that P. trinitensis has little room to acclimate to temperatures higher than those currently experienced. [ABSTRACT FROM AUTHOR]

There is increasing interest in using natural enemies to control pests in urban green spaces, but this is often hampered by a lack of information on enemies of particular pest groups. Here we provide an assessment for the first time of seasonal population of coccid species and its natural enemies on Chamaecyparis lawsoniana (A. Murray) Parl, 1864. The main coccid pest, Planococcus vovae (Nasonov, 1909), is attacked by parasitoids and predators. According to the gathered data, the peak population of both coccids and their natural enemies was observed in spring. The most common species in natural enemies was, Scymnus syriacus Marseul, 1868. Biodiversity indexes of the natural enemies community in the selected stations demonstrated the highest and lowest amounts for both Shanon winner and Margalef index in S3 and S1 before and after for the Simpson index in S1 and S4,5. This study suggests that the natural enemies of coccids on conifer trees may be more complex and diverse than what was observed in the present study. [ABSTRACT FROM AUTHOR]

Eurasian red squirrels Sciurus vulgaris have unusually high δ13C values compared to other forest rodents, which is seemingly related to the consumption of 13C-enriched conifer seeds. To test this hypothesis, we analyzed the hair of wild and zoo-kept red squirrels, seeds of pine and spruce, and feathers of specialized and opportunistic consumers of conifer seeds, crossbills Loxia spp., and woodpeckers Dendrocopos major. Data on the isotopic composition (δ13C and δ15N values) of hair or feathers of other species of forest rodents and birds were obtained from published studies. The range of mean δ13C values of hair of wild forest rodents (19 species) exceeded 10 ‰. All squirrel species had high 13C content, S. vulgaris having maximum δ13C values. In contrast, S. vulgaris kept in captivity had an isotopic composition similar to other captive rodents. The feathers of crossbills were enriched in 13C compared to other forest birds (15 species), while seeds of coniferous trees often had higher δ13C values compared to seeds of other woody plants. Distinctiveness of the isotopic composition of mammals and birds feeding on the seeds of coniferous trees suggests that this resource can be traced through the entire forest food web. [ABSTRACT FROM AUTHOR]

A dynamic vegetation model was adapted to a mixed forest of deciduous broad‐leaved trees and evergreen conifers in Hokkaido, the northernmost main island of Japan, located within a transition zone between cool‐temperate and sub‐boreal forest ecosystems. In this forest, elevation and a terrestrial‐wetness index affect tree biomass and the percentage of conifers. We maximized agreement between this observed pattern and model output by calibrating parameters that control drought and excessive soil‐moisture tolerance, establishment rate, and background mortality rate. In the simulation, biomass increased as a single peak curve with simulation year, while the percentage of conifers increased until the end of 200 simulation years. The 75‐year simulated forest was most comparable to the adapted forest, consistent with the average frequency of catastrophic storm disturbances in Hokkaido. The model also reconstructed a reasonable succession pattern based on temperature and soil moisture. Therefore, the model mechanistically reconstructed the mixed forest via spatial niche segregation and succession after catastrophic disturbances. However, the model did not reconstruct the percentages of broad‐leaved trees and conifers of forests prior to the disturbance in independent validation plots, demonstrating that additional processes should be considered in future models. [ABSTRACT FROM AUTHOR]

DNA barcode databases are increasingly available for a range of organisms, facilitating the wide application of DNA barcode‐based studies. Here we announce the development of a comprehensive DNA barcode reference library of Japanese native woody seed plants representing 43 orders, 99 families, 303 genera and 834 species, and comprising 77.3% of the genera and 72.2% of the species of native woody seed plants in Japan. A total of 6216 plant specimens were collected from 223 sites across the subtropical, temperate, boreal and alpine biomes in Japan with most species represented by multiple accessions. This reference library utilized three chloroplast DNA regions (rbcL, trnH‐psbA and matK) and consists of 14,403 barcode sequences. Individual regions varied in their identification rates, with species‐level and genus‐level rates for rbcL, trnH‐psbA and matK based on blast being 57.4%/96.2%, 78.5%/99.1% and 67.8%/98.1%, respectively. Identification rates were higher using region combinations, with total species‐level rates for two region combinations (rbcL & trnH‐psbA, rbcL & matK and trnH‐psbA & matK) ranging between 90.6% and 95.8%, and for all three regions being equal to 98.6%. Genus‐level identification rates were even higher, ranging between 99.7% and 100% for two region combinations and being 100% for the three regions. These results indicate that this DNA barcode reference library is an effective resource for investigations of native woody seed plants in Japan using DNA barcodes and provides a useful template for the development of libraries for other components of the Japanese flora. [ABSTRACT FROM AUTHOR]

Understanding the physiological and molecular adjustments occurring during tree stress response is of great importance for forest management and breeding programs. Somatic embryogenesis has been used as a model system to analyze various processes occurring during embryo development, including stress response mechanisms. In addition, "priming" plants with heat stress during somatic embryogenesis seems to favor the acquisition of plant resilience to extreme temperature conditions. In this sense, Pinus halepensis somatic embryogenesis was induced under different heat stress treatments (40 °C for 4 h, 50 °C for 30 min, and 60 °C for 5 min) and its effects on the proteome and the relative concentration of soluble sugars, sugar alcohols and amino acids of the embryonal masses obtained were assessed. Heat severely affected the production of proteins, and 27 proteins related to heat stress response were identified; the majority of the proteins with increased amounts in embryonal masses induced at higher temperatures consisted of enzymes involved in the regulation of metabolism (glycolysis, the tricarboxylic acid cycle, amino acid biosynthesis and flavonoids formation), DNA binding, cell division, transcription regulation and the life-cycle of proteins. Finally, significant differences in the concentrations of sucrose and amino acids, such as glutamine, glycine and cysteine, were found. [ABSTRACT FROM AUTHOR]

The article presents the results of the search for microsatellite or simple sequence repeat (SSR) loci with tri-, tetra-, penta- and hexanucleotide tandem repeat motifs in the draft de novo assembly of the Siberian fir (Abies sibirica Ledeb.) genome and the development of convenient relatively highly and moderately polymorphic markers that can be easily genotyped even by simple gel electrophoresis. In total, 64 pairs of oligonucleotide polymerase chain reaction (PCR) primers for 32 detected microsatellite loci were designed and tested. Based on the testing results, 10 most promising polymorphic loci were selected and genotyped in eight natural populations of Siberian fir. Homologous microsatellite loci in the genome of European silver fir (Abies alba Mill.) were also identified by mapping Siberian fir contigs, containing SSR loci to the European silver fir genome assembly. A multiplex panel of 14 universal microsatellite loci was developed and genotyped in samples from four natural populations of A. alba and a small sample of eight Nordmann fir (Abies nordmanniana (Steven) Spach) trees. [ABSTRACT FROM AUTHOR]

Simple Summary: In the dry and hot climates of Central Asia, forested areas are small and vulnerable to climate change. Therefore, it is important to understand the reactions of tree growth to climatic factors there. We studied several habitats of Scots pine, Schrenk spruce, and Zeravschan juniper near the semiarid limits of the respective forest types across Kazakhstan, the largest country in Central Asia. Standardized chronologies of tree-ring width were obtained for each site from wood samples, and then compared among themselves with a series for temperature and precipitation. Large distances and differences between species and habitats limited similarity in the dynamics of conifer growth. However, a common pattern was found in their reactions to climate. Maximal temperatures of the current and previous growing seasons were found to be crucial factors limiting the growth of all considered forest stands. Reactions to the precipitation and drought index are positive, but their strength depends on the species and aridity of a particular habitat. Temporal intervals of climatic impact on tree growth also vary across the country. The forests of Central Asia are biodiversity hotspots at risk from rapid climate change, but they are understudied in terms of the climate–growth relationships of trees. This classical dendroclimatic case study was performed for six conifer forest stands near their semiarid boundaries across Kazakhstan: (1–3) Pinus sylvestris L., temperate forest steppes; (4–5) Picea schrenkiana Fisch. & C.A. Mey, foothills, the Western Tien Shan, southeast; (6) Juniperus seravschanica Kom., montane zone, the Western Tien Shan, southern subtropics. Due to large distances, correlations between local tree-ring width (TRW) chronologies are significant only within species (pine, 0.19–0.50; spruce, 0.55). The most stable climatic response is negative correlations of TRW with maximum temperatures of the previous (from −0.37 to −0.50) and current (from −0.17 to −0.44) growing season. The strength of the positive response to annual precipitation (0.10–0.48) and Standardized Precipitation Evapotranspiration Index (0.15–0.49) depends on local aridity. The timeframe of climatic responses shifts to earlier months north-to-south. For years with maximum and minimum TRW, differences in seasonal maximal temperatures (by ~1–3 °C) and precipitation (by ~12–83%) were also found. Heat stress being the primary factor limiting conifer growth across Kazakhstan, we suggest experiments there on heat protection measures in plantations and for urban trees, alongside broadening the coverage of the dendroclimatic net with accents on the impact of habitat conditions and climate-induced long-term growth dynamics. [ABSTRACT FROM AUTHOR]

Summary: Identification of wood formation, cell wall deposition, lignification, and the maturation process contribute to a better understanding of biomass accumulation processes. Traditional methods for studying xylem development are limited by dyeing effects and discrimination experience, are non-quantitative for the degree of cell wall deposition and lignification, or are unsuitable for broad-leaved trees. In this study, we integrated several already existing methods to improve the discriminative accuracy of the cell development stage and to quantitatively describe the cell wall deposition and lignification degree for both softwood and hardwood tree species. To do this, we collected tree microcores every 7–14 days during a growing season for two species, one conifer (Platycladus orientalis) and one broad-leaved tree (Acer truncatum), in the mountainous areas in Beijing, China. We tracked the xylem development using semi-thin section technology combined with polarization microscopy. This integrated approach allows a quantitative description of the xylem cell wall deposition and lignification process of both hardwood and softwood tree species. This approach can be applied to demonstrate the dynamic process between the cambium layer and the production of wood cells and to describe the cell wall deposition and lignification process of wood cells from generation to maturation. This approach has certain application prospects for exploring scientific issues related to wood formation and accumulation processes in forestry and ecological studies. [ABSTRACT FROM AUTHOR]

Aims: Shifts in xylem phenology directly determine the forest capacity for carbon sequestration. However, a systematic understanding of the spatial patterns and the underpinning drivers in determining the cessation of wood formation (Ccw) is lacking at a pan‐continental scale. Here, we addressed this knowledge gap by compiling a new dataset of multiple xylem phenology timings for northern conifers. Locations: Sixty‐two study sites, Northern Hemisphere (25–55° N). Time period: 2003–2018 (16 years). Taxa: Thirty‐three conifer species. Methods: A generalized additive model was fitted to characterize the latitudinal pattern in Ccw. Structural equation modelling and a linear mixed‐effects model were applied to determine the main drivers underlying the latitudinal pattern in Ccw. Results: The Ccw followed a flat S‐shaped pattern with increasing latitude. Photoperiod was the dominant determinant of the latitudinal pattern of Ccw, and a longer photoperiod was associated with an earlier Ccw. Both mean growing‐season temperature and total growing‐season precipitation exhibited significantly positive relationships to the cessation of cell elongation and thus the Ccw across all study sites. In arid regions, the pre‐growing‐season temperature had a significantly negative effect on Ccw. In humid regions, Ccw was positively affected by the mean growing‐season temperature. The onset of wood formation showed significantly positive coupling with Ccw at arid sites but not at humid sites. Early successional species were sensitive to hydrothermal variations during the pre‐growing season. Main conclusions: We reveal the dominant role of photoperiod in determining the cessation of wood formation for northern conifers and highlight differentiated interactive effects between photoperiod and seasonal climatic factors and the preceding xylem phenophases in determining Ccw among ecoregions and tree species. These insights provide evidence to reduce uncertainty in prediction of the forest carbon uptake potential and the consequent biophysical feedbacks of northern forests. [ABSTRACT FROM AUTHOR]

SUMMARY: The enzyme glutamine synthetase (EC 6.3.1.2) is mainly responsible for the incorporation of inorganic nitrogen into organic molecules in plants. In the present work, a pine (Pinus pinaster) GS1 (PpGS1b.2) gene was identified, showing a high sequence identity with the GS1b.1 gene previously characterized in conifers. Phylogenetic analysis revealed that the presence of PpGS1b.2 is restricted to the genera Pinus and Picea and is not found in other conifers. Gene expression data suggest a putative role of PpGS1b.2 in plant development, similar to other GS1b genes from angiosperms, suggesting evolutionary convergence. The characterization of GS1b.1 and GS1b.2 at the structural, physicochemical, and kinetic levels has shown differences even though they have high sequence homology. GS1b.2 had a lower optimum pH (6 vs. 6.5) and was less thermally stable than GS1b.1. GS1b.2 exhibited positive cooperativity for glutamate and substrate inhibition for ammonium. However, GS1b.1 exhibited substrate inhibition behavior for glutamate and ATP. Alterations in the kinetic characteristics produced by site‐directed mutagenesis carried out in this work strongly suggest an implication of amino acids at positions 264 and 267 in the active center of pine GS1b.1 and GS1b.2 being involved in affinity toward ammonium. Therefore, the amino acid differences between GS1b.1 and GS1b.2 would support the functioning of both enzymes to meet distinct plant needs. Significance Statement: A GS1b paralog (GS1b.2) expressed in developing tissues has been identified in pine (Pinus pinaster). The kinetic properties of the enzyme differ from those of the previously studied GS1b.1, despite their high sequence identity. [ABSTRACT FROM AUTHOR]

Despite growing interest in predicting plant phenological shifts, advanced spring phenology by global climate change remains debated. Evidence documenting either small or large advancement of spring phenology to rising temperature over the spatio‐temporal scales implies a potential existence of a thermal threshold in the responses of forests to global warming. We collected a unique data set of xylem cell‐wall‐thickening onset dates in 20 coniferous species covering a broad mean annual temperature (MAT) gradient (−3.05 to 22.9°C) across the Northern Hemisphere (latitudes 23°–66° N). Along the MAT gradient, we identified a threshold temperature (using segmented regression) of 4.9 ± 1.1°C, above which the response of xylem phenology to rising temperatures significantly decline. This threshold separates the Northern Hemisphere conifers into cold and warm thermal niches, with MAT and spring forcing being the primary drivers for the onset dates (estimated by linear and Bayesian mixed‐effect models), respectively. The identified thermal threshold should be integrated into the Earth‐System‐Models for a better understanding of spring phenology in response to global warming and an improved prediction of global climate‐carbon feedbacks. [ABSTRACT FROM AUTHOR]

Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration. [ABSTRACT FROM AUTHOR]

Most species of the family Cupressaceae are widely distributed throughout China, but Sabina przewalskii f. pendula and Juniperus przewalskii are endemic to the Qinghai-Tibet Plateau region. Therefore, they are of great significance to the plateau ecosystem. Sabina przewalskii and J. przewalskii have similar characteristics, but they be distinguished by the presence or absence of drooping branchlets. However, this feature can be difficult to distinguish with the naked eye. In this study, the complete chloroplast (CP) genomes of S. przewalskii and J. przewalskii were determined by highthroughput sequencing, aiming to unveil their differences at the molecular level. The sizes of the CP genomes of J. przewalskii and S. przewalskii are 128,748 bp and 127,315 bp, respectively, sharing the typical structure of conifer species. The GC content of the S. przewalskii plastome is 35.08%, encoding 84 proteins, 32 tRNAs and 4 rRNAs. The GC content of the J. przewalskii CP genome is 34.98%, and one additional rpl32 gene was detected. Phylogenetic analysis proved that J. przewalskii showed a close relationship to Juniperus tibetica and S. przewalskii, both of which belong to the family Cupressaceae. Our results of the plastome of J. przewalskii and S. przewalskii further clarify the evolution of Cupressaceae species. The divergent regions and the repetitive sequences identified could be developed as molecular markers that would benefit breeding and species discrimination. [ABSTRACT FROM AUTHOR]

Background and Aims: Free living, non-symbiotic nitrogen-fixing bacteria (diazotrophs) that inhabit plant rhizosphere substantially contribute to nitrogen input in forest ecosystems. Different plant species provide heterogeneous habitats for rhizosphere diazotrophs by releasing root exudates containing potential resources for microbial utilization, but the ecological processes of diazotrophic community assembly and association with plant species are not fully understood. Methods: We investigated the diazotrophic abundance (as assessed by real-time quantitative PCR), diversity, and composition of rhizosphere diazotrophic communities (based on nifH-amplicon sequencing) for four non-leguminous broadleaf tree species and three conifer tree species in a forest ecosystem. Results: The analysis revealed that the rhizosphere of four broadleaf tree species harbored higher diazotrophic abundance and diversity by 239% and 50.0% respectively, as compared to the conifer tree species. Further, phylogenetic distance between the seven tree species was positively correlated (Mantel r = 0.482, P < 0.001) with the dissimilarity of diazotrophic community assembly, thus determining rhizosphere potential nitrogen fixation indicated by nifH gene abundance. Of the top 20 genera (ranked by percentage increase in Mean Squared Error) that contribute to potential nitrogen fixation, 11 rare genera were at low relative abundances (< 1%). Network analysis further showed the central position of rare genera in the diazotrophic co-occurrence network of four broadleaf tree species, as the closeness centrality of rare genera was significantly higher than that of abundant genera. Conclusion: Overall, the study suggested that the identity of tree species impresses the assembly of diazotrophic communities in its rhizosphere. Possible implication of our findings for forest management is discussed for maintaining nitrogen sustainability in forest ecosystems. [ABSTRACT FROM AUTHOR]

Many plants undergo adaptation to fire. Yet, as global change is increasing fire frequency worldwide, our understanding of the genetics of adaptation to fire is still limited. We studied the genetic basis of serotiny (the ability to disseminate seeds exclusively after fire) in the widespread, pioneer Mediterranean conifer Pinus halepensis Mill., by linking individual variation in serotiny presence and level to fire frequency and to genetic polymorphism in natural populations. After filtering steps, 885 single nucleotide polymorphisms (SNPs) out of 8000 SNPs used for genotyping were implemented to perform an in situ association study between genotypes and serotiny presence and level. To identify serotiny‐associated loci, we performed random forest analyses of the effect of SNPs on serotiny levels, while controlling for tree size, frequency of wildfires, and background environmental parameters. Serotiny showed a bimodal distribution, with serotinous trees more frequent in populations exposed to fire in their recent history. Twenty‐two SNPs found in genes involved in stress tolerance were associated with the presence‐absence of serotiny while 37 found in genes controlling for flowering were associated with continuous serotiny variation. This study shows the high potential of P. halepensis to adapt to changing fire regimes, benefiting from a large and flexible genetic basis of trait variation. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) panels are an innovative wooden product that has gained popularity in recent years because it has a high strength-to-weight ratio, improves construction efficiency, and it is a natural and renewable material. Therefore, the recently released 2021 International Building Code (IBC) include guidelines for CLT panels for the construction of buildings of up to 18 stories. The construction applications of CLT panels as well as the research initiatives have largely centered on softwood tree species such as laminates, and the application of hardwood species has yet to be investigated. This paper documents the structural behavior of several hardwood species abundant in the Appalachian region and demonstrates the promising feasibility of using these species in the construction industry with CLT panels considering the architectural and structural behavior and economic aspects. The hardwood tree species selected are abundant in the Appalachian region and this paper highlights their potential as a construction material and provides an insight for future development. Three hardwood species including red maple, sweetgum, and sycamore are considered for this study, and three- and five-ply panels are fabricated to evaluate their behavior. The samples are tested in three directions for compression to understand the orthotropic behavior. Considering the softwood species including southern yellow pine and Douglas fir as a baseline for comparison, a total of 120 samples are tested and evaluated based on ASTM standards. The results show an average higher compressive strength from sweetgum panels followed by red maple, sycamore, Douglas fir, and southern yellow pine in the main directions used for structural walls. The findings imply a potential market for the underutilized hardwood species in Appalachia, which may lead to future economic development in the region. [ABSTRACT FROM AUTHOR]

Two nests of Hoplitis curvipes are described from Apulia (Italy) and Dagestan (Russia). Both nests consisted of two brood cells placed side by side under a stone. The cells were neither attached to each other nor to the substrate. They were constructed from leaf fragments, which were imbricately arranged, forming a cone-like structure; each leaf fragment consisted of a basal part that was masticated to leaf pulp and an apical part that protruded freely from the cell wall. The cell wall was formed by the fusion of the masticated basal parts of the leaf fragments and thus entirely consisted of leaf pulp. The cell was sealed with a closing plug made of pure leaf pulp; a few leaf fragments were glued to its outer surface. The cocoon consisted of two layers: the outer layer was restricted to the anterior portion of the cell and had several longitudinal air-exchange slits on its lateral surface, while the inner layer had an air-exchange orifice in its most anterior dome-shaped top. Results of measurements of brood cell dimensions and contents are provided. The nesting biology of species of the H. curvipes group is discussed. [ABSTRACT FROM AUTHOR]

The EFSA Panel on Plant Health performed a pest categorisation of Urocerus albicornis (Hymenoptera: Siricidae), the black horntail sawfly, for the territory of the EU. U. albicornis is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. U. albicornis occurs throughout Canada and continental USA and has established in northern Spain, and probably in southern France (based on two specimens caught in two sites) and Japan (based on one individual caught in one site). It attacks mostly stumps or fallen or weakened trees of at least 20 species of Pinaceae (Abies spp., Larix spp., Picea spp., Pinus spp., Pseudotsuga menziesii, Tsuga spp.) and of Cupressaceae (Thuja plicata). In Spain, the females fly between May and September with a peak in August and September. The eggs are deposited into the sapwood, together with mucus containing a venom and a white‐rot wood‐decay basidiomycete, either Amylostereum chailletii or A. areolatum. Each fungus is symbiotic with the insect. The larvae feed on wood infected by the fungus. All immature stages live in the host sapwood. In British Columbia, the lifecycle of the pest lasts 2 years but has not been fully characterised elsewhere. The wood of the host trees is impacted by decay due to the fungus, and structurally impaired by the larval galleries. U. albicornis can be carried in conifer wood, solid wood packaging material (SWPM) or plants for planting. Wood from North America is regulated by 2019/2072 (Annex VII) while SWPM is managed according to ISPM 15. The pathway plants for planting is largely closed by prohibition, with the exception of Thuja spp. Climatic conditions in several EU member states are conducive for establishment and the main host plants are widespread in those areas. Further spread and introduction of U. albicornis is likely to decrease the quality of host wood and may influence forest diversity by selectively affecting conifers. Phytosanitary measures are available to reduce the likelihood of additional entry and further spread, and there is a potential for biological control. Despite uncertainty regarding potential damage, U. albicornis satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. [ABSTRACT FROM AUTHOR]

Summary: Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire‐induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the impact of a lethal fire dose on nonstructural carbohydrates (NSCs) and xylem hydraulics in Pinus ponderosa saplings.Saplings were burned with a known lethal fire dose. Nonstructural carbohydrates were assessed in needles, main stems, roots and whole plants, and xylem hydraulic conductivity was measured in the main stems up to 29 d postfire.Photosynthesis and whole plant NSCs declined postfire. Additionally, all burned saplings showed 100% phloem/cambium necrosis, and roots of burned saplings had reduced NSCs compared to unburned and defoliated saplings. We further show that, contrary to patterns observed with NSCs, water transport was unchanged by fire and there was no evidence of xylem deformation in saplings that experienced a lethal dose of heat from fire.We conclude that phloem and cambium mortality, and not hydraulic failure, were probably the causes of death in these saplings. These findings advance our understanding of the physiological response to fire‐induced injuries in conifer trees. [ABSTRACT FROM AUTHOR]

Adapting forests to climate change is a critical issue for forest management. It requires an understanding of climate effects on forest systems and the ability to forecast how these effects may change over time. We used Spanish Second National Forest Inventory data and the SIMANFOR platform to simulate the evolution of CO2 stock (CO2 Mg · ha−1) and accumulation rates (CO2 Mg · ha−1 · year−1) for the 2000–2100 period in pure and mixed stands managed under different Shared Socioeconomic Pathways (SSPs) in Spain. We hypothesized that (1) the more optimistic climate scenarios (SSP1 > > SSP5) would have higher CO2 stock and accumulation rates; (2) mixed stands would have higher CO2 stock and accumulation rates than pure stands; and (3) the behavior of both variables would vary based on forest composition (conifer–conifer vs. conifer–broadleaf). We focused on Pinus sylvestris L., and its main mixtures with Pinus nigra, Pinus pinaster, Fagus sylvatica and Quercus pyrenaica. The SSP scenarios had correlating CO2 stock values in which SSP1 > SSP2 > SSP3 > SSP5, ranging from the most optimistic (SSP1) to the most pessimistic (SSP5). Though pure stands had higher CO2 stock at the beginning, differences with regard to mixed stands were drastically reduced at the end of the simulation period. We also found an increase in the aboveground CO2 proportion compared to belowground in conifer–broadleaf mixtures, while the opposite trend occurred in conifer–conifer mixtures. Overall CO2 accumulation rates decreased significantly from the beginning to the end of the simulation period, but our results indicated that this decline would be less drastic in mixed stands than in pure ones. At the end of the simulation period, CO2 accumulation rates were higher in mixed stands than in pure stands for all mixtures, fractions (aboveground and belowground) and SSPs. Knowing the evolution of mixed forests in different climate scenarios is relevant for developing useful silvicultural guidelines in the Mediterranean region and optimizing forestry adaptation strategies. Better understanding can also inform the design of management measures for transitioning from pure stands to more resource efficient, resistant and resilient mixed stands, in efforts to reduce forest vulnerability in the face of climate change. This work highlights the importance and benefits of mixed stands in terms of CO2 accumulation, stand productivity and species diversity. [ABSTRACT FROM AUTHOR]

Climate change is increasing the severity and duration of drought events experienced by forest ecosystems. Because water is essential for tree physiological processes, the ability of trees to survive prolonged droughts will largely depend on whether they have access to reliable water sources. While many woody plant species exhibit the ability to shift water sources between different depths of soil and rock water in response to changes in climate and water availability, it is unclear if Sierra Nevada conifers exhibit this plasticity. Here we analysed the δ18O and δ13C values of annual tree rings to determine the water-use patterns of large Sierra Nevada conifers during the 2012–16 California drought and 4 years before this drought event (2004–07). We analysed four species (Pinus jeffreyi Grev. & Balf. (Jeffrey pine), Pinus lambertiana Dougl. (sugar pine), Abies concolor (Gord. & Glend.) Lindl. Ex Hilderbr (white fir) and Calocedrus decurrens (Torr.) Florin (incense-cedar)) across a range of topographic positions to investigate differences in water-use patterns by species and position on the landscape. We found no significant differences in δ18O and δ13C values for the pre-drought and drought periods. This stability in δ18O values suggests that trees did not shift their water-use patterns in response to the 2012–16 drought. We did find species-specific differences in water-use patterns, with incense-cedar exhibiting more depleted δ18O values than all other species. We also found trends that suggest the water source used by a tree may depend on topographic and growing environment attributes such as topographic wetness and the surrounding basal area. Overall, our results suggest that the water source used by trees varies by the species and topographic position, but that Sierra Nevada conifers do not switch their water-use patterns in response to the drought. This lack of plasticity could make Sierra Nevada conifers particularly vulnerable to drought mortality as their historically reliable water sources begin to dry out with climate change. [ABSTRACT FROM AUTHOR]

Climate change challenges the adaptive capacity of several forest tree species in the face of increasing drought and rising temperatures. Therefore, understanding the mechanistic connections between genetic diversity and drought resilience is highly valuable for conserving drought-sensitive forests. Nonetheless, the post-drought recovery in trees from a transcriptomic perspective has not yet been studied by comparing contrasting phenotypes. Here, experimental drought treatments, gas-exchange dynamics and transcriptomic analysis (RNA-seq) were performed in the relict and drought-sensitive fir Abies pinsapo Boiss. to identify gene expression differences over immediate (24 h) and extended drought (20 days). Post-drought responses were investigated to define resilient and sensitive phenotypes. Single nucleotide polymorphisms (SNPs) were also studied to characterize the genomic basis of A. pinsapo drought resilience. Weighted gene co-expression network analysis showed an activation of stomatal closing and an inhibition of plant growth-related genes during the immediate drought, consistent with an isohydric dynamic. During the extended drought, transcription factors, as well as cellular damage and homeostasis protection-related genes prevailed. Resilient individuals activate photosynthesis-related genes and inhibit aerial growth-related genes, suggesting a shifting shoot/root biomass allocation to improve water uptake and whole-plant carbon balance. About, 152 fixed SNPs were found between resilient and sensitive seedlings, which were mostly located in RNA-activity-related genes, including epigenetic regulation. Contrasting gene expression and SNPs were found between different post-drought resilience phenotypes for the first time in a forest tree, suggesting a transcriptomic and genomic basis for drought resilience. The obtained drought-related transcriptomic profile and drought-resilience candidate genes may guide conservation programs for this threatened tree species. [ABSTRACT FROM AUTHOR]

Airborne light detection and ranging (LiDAR) data are increasingly used to inform sustainable forest management practices. Information about species composition is needed for a range of applications; however, commonly used area-based summaries of LiDAR data are limited to accurately differentiate tree species. The objective of this study was to map dominant species groups across a large (>580,000 ha) boreal forest by combining area-based and individual tree metrics derived from single photon LiDAR data with multispectral information derived from Sentinel-2 imagery. Classification of the forest into jack pine (Pinus banksiana), black spruce (Picea mariana), mixed conifer, mixedwood, and hardwood species groups resulted in an overall accuracy of 67.8% compared with field data. A more generalized classification into softwood, hardwood, and mixedwood had an overall accuracy of 83.2%. The reflectance in the red edge region of the electromagnetic spectrum (λ = 740 nm), the area and volume of tree crowns, and the cumulative distribution of LiDAR returns in the canopy were particularly important variables to discriminate between species groups. Wall-to-wall predictions of species groups based on remotely sensed data—as derived herein—could provide a spatially-detailed alternative to stand-level species composition information traditionally derived from photo-interpreted aerial imagery. [ABSTRACT FROM AUTHOR]

Premise: Understanding mechanisms fostering long‐term persistence of marginal populations should provide key insights about species resilience facing climate change. Cone serotiny is a key adaptive trait in Pinus banksiana (jack pine), which shows phenotypic variation according to the fire regime. Compared to range‐core populations within the fire‐prone boreal forest, low and variable serotiny in rear‐edge populations suggest local adaptation to uncommon and unpredictable wildfire regime. We assessed environmental/physiological factors that might modulate intraspecific variation in cone serotiny. Methods: We experimentally subjected closed cones to incrementing temperatures, then tested seed germination to determine whether and how various ecological factors (cone age, branch height, tree size, tree age) are related to cone dehiscence and seed viability in jack pines from rear‐edge and range‐core populations in eastern Canada. Results: Cones from rear‐edge populations dehisce at a lower opening temperature, which increases with cone age. Cones from range‐core stands open at a more constant, yet higher temperature. Cones from rear‐edge stands take between 13 and 27 years to reach the level of serotiny achieved at the range core. At the rear edge, seed viability is steady (51%), whereas it decreases from 70% to 30% in 20 years at the range core. Conclusions: We inferred the mechanisms of a bet‐hedging strategy in rear‐edge populations, which ensures steady recruitment during fire‐free intervals and successful postfire regeneration. This capacity to cope with infrequent and unpredictable fire regime should increase the resilience of jack pine populations as global changes alter fire dynamics of the boreal forest. [ABSTRACT FROM AUTHOR]

Two new species of Blattisociidae mites, Lasioseius triplax sp. nov. and Lasioseius verruciger sp. nov., are described from females found in phoretic association with the mycophagous erotylid beetle Triplax russica (Linnaeus) and under the bark of dying conifers, respectively, both from southwestern Slovakia. The new species are unusual in having reduced sclerotization of the posterior part of the sternal shield. Only a few species of Lasioseius Berlese have this character state, the purpose and possible function of which are unknown. An identification key for species with reduced sclerotization of the sternal shield is presented. Lasioseius allii Chant is firstly reported from Slovakia, and some notes on the morphology of this and related species are given. for publication: for Lasioseius triplax: for Lasioseius verruciger: [ABSTRACT FROM AUTHOR]

Background and aims Foliar water uptake (FWU) has been documented in many species and is increasingly recognized as a non-trivial factor in plant–water relationships. However, it remains unknown whether FWU is a widespread phenomenon in Pinus species, and how it may relate to needle traits such as the form and structure of stomatal wax plugs. In this contribution, these questions were addressed by studying FWU in current-year and 1-year-old needles of seven Pinus species. Methods We monitored FWU gravimetrically and analysed the needle surface via cryo-scanning electron microscopy. Additionally, we considered the effect of artificial wax erosion by application of the surfactant Triton X-100, which is able to alter wax crystals. Key results The results show for all species that (1) FWU occurred, (2) FWU is higher in old needles compared to young needles and (3) there is substantial erosion of stomatal wax plugs in old needles. FWU was highest in Pinus canariensis , which has a thin stomatal wax plug. Surfactant treatment enhanced FWU. Conclusions The results of this study provide evidence for (1) widespread FWU in Pinus , (2) the influence of stomatal wax plugs on FWU and (3) age-related needle surface erosion. [ABSTRACT FROM AUTHOR]

Aim: Well‐managed semi‐arid forests help offset global change by storing significant amounts of carbon above‐ and belowground and maintaining hydrological cycles. Larger trees have been the focus of many studies due to their carbon storage and habitat quality, yet recruitment and small trees are important components of ecosystem resilience and recovery. Here, we study the impacts of disturbances (including harvesting) on recruitment, mortality and growth for a mixed conifer‐broadleaf semi‐arid forest type using long‐term data. Location: Pilliga Forest in New South Wales, inland eastern Australia. Taxon: Callitris‐Eucalyptus forests. Methods: We used data from permanent sample plots (PSPs) spanning 55 years, calculated stand structure, gains and losses and determined reasons for tree death (harvesting, fire, wind, drought and other effects). We extracted climate and fire data for the PSP locations using spatial analysis. Results: Stocking of studied forests remained stable (modest increase in basal area and stem density), despite harvesting and wildfires over 6 decades. Compared to stands in the 1940s and prior to European settlement, current forests are composed of more trees per unit area, and these trees have smaller diameters. Recruitment and sustained presence of small trees have buffered impacts of recurring drought, fire and harvesting. Fires are a common feature of the studied ecosystems and fire impacts have increased in the past 20 years, especially in unmanaged stands, where fires have reduced tree carbon by >50%. Main conclusions Recruitment and growth of small trees are critical to offset carbon losses due to fire, drought and harvesting. All size classes have important ecological values in semi‐arid forests and must be included in long‐term monitoring programmes. Long‐term data offer unique insights into combined effects of climate change, management and disturbances, especially for fire‐prone ecosystems, where small trees are often susceptible to fire. [ABSTRACT FROM AUTHOR]

Cephalotaxines harbor great medical potential, but their natural source, the endemic conifer Cephalotaxus is highly endangered, creating a conflict between biotechnological valorization and preservation of biodiversity. Here, we construct the whole biosynthetic pathway to the 1-phenethylisoquinoline scaffold, as first committed compound for phenylethylisoquinoline alkaloids (PIAs), combining metabolic modeling, and transcriptome mining of Cephalotaxus hainanensis to infer the biosynthesis for PIA precursor. We identify a novel protein, ChPSS, driving the Pictet-Spengler condensation and show that this enzyme represents the branching point where PIA biosynthesis diverges from the concurrent benzylisoquinoline-alkaloids pathway. We also pinpoint ChDBR as crucial step to form 4-hydroxydihydrocinnamaldehyde diverging from lignin biosynthesis. The elucidation of the early PIA pathway represents an important step toward microbe-based production of these pharmaceutically important alkaloids resolving the conflict between biotechnology and preservation of biodiversity. [ABSTRACT FROM AUTHOR]

Height-diameter models are fundamental for the inventory of timber, biomass and carbon. Located in the central region of Mexico, Abies religiosa is a conifer with high timber value that lacks models to estimate its height as a function of diameter. The objective of this study was to determine a local height-diameter model for A. religiosa trees under a mixed-effects model approach in the region of Tlaxco, Tlaxcala, Mexico. The first step consisted in evaluating the quality of fit of three growth models and one power model. We used height-diameter data of 1,539 trees measured in 197 circular plots of 1,000 m². The selected model was the Weibull, which was adjusted in a second step under the mixed-effects modelling approach. Our results showed that the most accurate predictive capacity was obtained when using the sub-basin covariate as a clustering factor and the random effect in the parameter corresponding to the asymptote. Under this approach, the goodness of fit of the model was superior to the traditional one adjusted by nonlinear least square. Comparatively the gains in fit statistics R², RSME and AIC were of 12.19 %, 47.99 % and 8.46 %, respectively. The proposed model is robust, reliable, and biologically coherent for its operational application in the forest management of A. religiosa in the study region. [ABSTRACT FROM AUTHOR]

Conifers inhabit some of the most challenging landscapes where multiple abiotic stressors (e.g. aridity, freezing temperatures) often co-occur. Physiological tolerance to multiple stressors ('poly-tolerance') is thought to be rare because exposure to one stress generally limits responses to another through functional trade-offs. However, the capacity to exhibit poly-tolerance may be greater when combined abiotic stressors have similar physiological impacts, such as the disruption of hydraulic function imposed by drought or freezing. Here, we reviewed empirical data in light of theoretical expectations for conifer adaptations to drought and freeze–thaw cycles with particular attention to hydraulic traits of the stem and leaf. Additionally, we examined the commonality and spatial distribution of poly-stress along indices of these combined stressors. We found that locations with the highest values of our poly-stress index (PSi) are characterized by moderate drought and moderate freeze–thaw, and most of the global conifer distribution occupies areas of moderate poly-stress. Among traits examined, we found diverse responses to the stressors. Turgor loss point did not correlate with freeze–thaw or drought stress individually, but did with the PSi, albeit inverse to what was hypothesized. Leaf mass per area was more strongly linked with drought stress than the poly-stress and not at all with freeze–thaw stress. In stems, the water potential causing 50% loss of hydraulic conductivity became more negative with increasing drought stress and poly-stress but did not correlate with freeze–thaw stress. For these traits, we identified a striking lack of coverage for substantial portions of species ranges, particularly at the upper boundaries of their respective PSis, demonstrating a critical gap in our understanding of trait prevalence and plasticity along these stress gradients. Future research should investigate traits that confer tolerance to both freeze–thaw and drought stress in a wide range of species across broad geographic scales. [ABSTRACT FROM AUTHOR]

The Western conifer seed bug, Leptoglossus occidentalis, is native to North America and has already been considered a significant pest in several European countries since its first observation in Italy in 1999. In Spain and Portugal, it was recorded for the first time in 2003 and 2010, respectively, and its impact on Stone Pine (Pinus pinea) is of major concern. Before developing control measures for this insect pest, it is paramount to clarify its spatiotemporal dynamics of invasion. Therefore, in this study, we aimed to (a) characterise the genetic structure and diversity and (b) invasion pathways of L. occidentalis populations in the Iberian Peninsula. To do so, specimens of L. occidentalis were collected at fourteen sites widely distributed within the Iberian Peninsula. We used mtDNA sequences of Cytochrome b and eleven microsatellite markers to characterise the genetic diversity and the population structure in the Iberian Peninsula. Our genetic results combined with the observational dates strongly support a stratified expansion of L. occidentalis invasion in the Iberian Peninsula proceeding from multiple introductions, including at least one in Barcelona, one in Valencia, and one in the west coast or in the Southeastern region. [ABSTRACT FROM AUTHOR]

The EFSA Panel on Plant Health performed a pest categorisation of Urocerus japonicus (Hymenoptera: Siricidae), the Japanese horntail, for the territory of the EU. U. japonicus is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072 but was identified as an actionable pest in a commodity risk assessment of Pinus thunbergii artificially dwarfed plants from Japan. U. japonicus occurs across Japan and on the Korean Peninsula. It attacks fallen or weakened Japanese cedars, Cryptomeria japonica and Japanese cypresses, Chamaecyparis obtusa. It has also been observed attacking Pinus spp., Abies spp., Larix kaempferi and Picea jezoensis. The females oviposit into the sapwood. Eggs are deposited together with a symbiotic basidiomycete fungus, Amylostereum laevigatum. The larvae feed on wood infected by the fungus. All immature stages live in the hosts sapwood. The lifecycle of the pest lasts 1 year, sometimes 2 years. The wood of the host trees is discoloured by the fungus and therefore loses much of its economic value. U. japonicus can be carried in conifer wood, solid wood packaging material (SWPM) or plants for planting. Wood from Japan is regulated by 2019/2072 (Annexes VII and XI) whilst SWPM is managed by ISPM 15. The pathway plants for planting is largely closed by prohibition, with the exception of Cryptomeria spp. and specified bonsai plants for planting. Climatic conditions in several EU Member States are conducive for establishment, but the main host plants are not very common in those areas, being only amenity trees, although the other hosts mentioned in the literature, Pinus spp., Abies spp., Picea spp. and Larix spp., are widespread. The introduction of U. japonicus is likely to decrease the quality of host wood, as in Japan. Phytosanitary measures are available to reduce the likelihood of entry and further spread, and there is a potential for biological control. U. japonicus satisfies all the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. [ABSTRACT FROM AUTHOR]

Non‐native tree species are widely used in forest plantations. This may have negative consequences for biodiversity. Hitherto, most studies have compared species diversity between native and non‐native forest stands, which makes it difficult to separate the impact of tree species per se from stand characteristics. Our study, conducted in the south of Sweden, compares saproxylic beetle diversity across different nutritional groups, in dead wood of two native and four non‐native tree species in a block design after one and three seasons. Such an approach allows analysis of the impact of non‐native tree species per se.Mean species richness (± SD) per log was lower in non‐native than in native tree species (non‐native trees: lodgepole pine: 10.7 (± 5.3); Sitka spruce: 8.5 (± 4.3), Douglas fir: 7.1 (± 4.3), Japanese larch 9.4 (± 4.6); native trees: Norway spruce: 12.0 (± 6.0), Scots pine: 12.3 (± 5.2)). Sample‐based rarefaction revealed that when only native tree species were pooled, the species richness was higher than for all tree species combined. The difference in species composition among tree species was strongly driven by bark and wood consumers in the first season, while for predators and fungivores, the differences were smaller. Species composition differed most in the first season.Dissimilarity in beetle species composition was positively correlated with phylogenetic distances of the tree species. Species richness was lower in non‐native tree species that are only remotely related to native trees species. Of the studied non‐native tree species, lodgepole pine was more closely related to native tree species and consistently harboured higher species richness.Synthesis and applications. Although non‐native tree species also harbour saproxylic beetle communities, the use of non‐native tree species, especially those only remotely related to native tree species, reduces local diversity of saproxylic beetles. Thus, for biodiversity conservation, an extensive use of non‐native tree species is not recommended as this increases the risk of losing forest biodiversity, especially when they are only distantly related to native tree species. [ABSTRACT FROM AUTHOR]

Plant-associated microbes including dark septate endophytes (DSEs) of forest trees play diverse functional roles in host fitness including growth promotion and increased defence. However, little is known about the impact on the fungal transcriptome and metabolites during tripartite interaction involving plant host, endophyte and pathogen. To understand the transcriptional regulation of endophyte and pathogen during co-infection, Norway spruce (Picea abies) seedlings were infected with DSE Phialocephala sphaeroides , or conifer root-rot pathogen Heterobasidion parviporum , or both. Phialocephala sphaeroides showed low but stable transcripts abundance (a decrease of 40%) during interaction with Norway spruce and conifer pathogen. By contrast, H. parviporum transcripts were significantly reduced (92%) during co-infection. With RNA sequencing analysis, P. sphaeroides experienced a shift from cell growth to anti-stress and antagonistic responses, while it repressed the ability of H. parviporum to access carbohydrate nutrients by suppressing its carbohydrate/polysaccharide-degrading enzyme machinery. The pathogen on the other hand secreted cysteine peptidase to restrict free growth of P. sphaeroides. The expression of both DSE P. sphaeroides and pathogen H. parviporum genes encoding plant growth promotion products were equally detected in both dual and tripartite interaction systems. This was further supported by the presence of tryptophan-dependent indolic compound in liquid culture of P. sphaeroides. Norway spruce and Arabidopsis seedlings treated with P. sphaeroides culture filtrate exhibited auxin-like phenotypes, such as enhanced root hairs, and primary root elongation at low concentration but shortened primary root at high concentration. The results suggested that the presence of the endophyte had strong repressive or suppressive effect on H. parviporum transcripts encoding genes involved in nutrient acquisition. [ABSTRACT FROM AUTHOR]