Fraxinus Excelsior Research Articles

Neighbours matter and the weak succumb: Ash dieback infection is more severe in ash trees with fewer conspecific neighbours and lower prior growth rate

Abstract The epidemiology and severity of ash dieback (ADB), the disease caused by the ascomycete fungus Hymenoscyphus fraxineus, has been linked to a variety of site conditions; however, there has been a lack of analysis at an individual tree scale. Symptoms of ADB were scored on ca. 400 trees of Fraxinus excelsior (ash) in permanent sample plots during two successive years in a UK natural woodland reserve. Using comprehensive plot records maintained since 1945, and detailed spatial records updated since 1977, we assembled an array of potential explanatory variables, including site environment factors, ash tree density, previous and present tree condition and near neighbourhood summary statistics (NNSS), such as species mingling and size dominance. Their impact on the severity of ADB of focal ash trees was tested with generalised linear mixed effects models (GLMM). The severity of ADB was much greater in the lower slope parts of the site with moister soils and least in a managed area subject to tree thinning in the previous 35 years. Severity of ADB had a negative association with focal ash tree prior relative growth rate over a period of a decade immediately before the disease was detected at the site. Greater ADB severity was also significantly associated with smaller diameter at breast height of ash trees. Additionally, ADB was significantly positively associated with a greater proportion of heterospecific trees amongst the six nearest neighbours of the focal tree. Synthesis. The relationship of the severity of ADB disease with site environment, tree condition and neighbourhood is complex but nevertheless important in the progression of the disease. The findings suggest some silvicultural interventions, such as thinning to increase the vigour of retained ash trees, might reduce the impact of ADB.

Tree Species Affect Beetle Diversity on the Common Deciduous Dead Wood in Lithuanian Unmanaged Forests

Beetles living in dead wood are species-specific, suggesting that beetle diversity may vary between different deciduous tree species. However, the patterns of diversity variation among deciduous trees are still poorly understood. In this study, we investigated the diversity of beetles associated with dead wood in the second decay stage in four protected areas of Lithuania, using trunk-emergence traps on Alnus glutinosa L., Gaertn. (black alder), Betula sp. L. (birch), Fraxinus excelsior L. (European ash), Populus tremula L. (European aspen), Quercus robur L. (common oak), and Tilia cordata Mill. (small-leaved linden). The findings of our study indicated variation in beetle diversity among the six tree species examined. We identified the greatest diversity of beetles in the decaying trunks of Quercus robur, followed by T. cordata, and F. excelsior. Our cluster analysis suggested a higher similarity in beetle diversity among tree species sharing the same type of bark; however, our db-RDA analysis showed that tree species explained more variance in the data than bark type. Our results support previous research highlighting the importance of dead wood species diversity in maintaining the diversity of beetles in forests. Within the context of current biodiversity decline, understanding the similarities or differences in beetle communities between tree species is key to tackling the loss of insect species.

Pathogenic fungi and oomycetes causing dieback on Fraxinus species in the Mediterranean climate change hotspot region

Environmental changes are occurring on a global scale, but their effects are most pronounced in climate change hotspot zones, such as the Mediterranean basin. Within this area Italy, extending from its southern coasts in the core of the Mediterranean Sea to its northernmost pre-Alpine and Alpine regions, is characterized by a variety of climatic conditions and vegetation types. Surveys conducted in 2018–2022 in forest formations of Central-Northern Italy revealed that the enhanced warming trend and irregular distribution of precipitations are strongly impacting the health of Fraxinus species, with some pathogenic fungi and oomycetes being important contributing factors to the decline of the three main ash species growing there: common ash (Fraxinus excelsior), flowering ash (Fraxinus ornus), and narrow-leaved ash (Fraxinus angustifolia). Isolation from symptomatic plant material collected countrywide under different site conditions and pathogenicity tests revealed a complex phytopathological framework, with several pathogenic species in addition to Hymenoscyphus fraxineus involved with a prominent role in the ash dieback etiology. Key microbial taxa included the fungal and oomycete pathogens Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Phytophthora acerina, and Phytophthora plurivora. The disease impact was higher on sites where ash trees grew under environmental stress (i.e., areas characterized by mild dry winters, hot summers with intense and prolonged drought) and exhibited reduced vigor, also as a consequence of anthropogenic interference (i.e., silvicultural management and fires). The identified causative agents are emerging pathogens that thrive under warmer conditions, their impact in the investigated areas being prevalent compared to H. fraxineus, which appears to be restricted on the Italian peninsula to the cooler and wetter valleys of the Alps and Central-Northern Apennines.

Vegetation responses to pathogen-induced tree loss: Swedish elm and ash forests revisited after 32 years

Invasive fungal pathogens are an increasing problem globally and can cause strong effects on forest ecosystems. In this study, we contrast vegetation surveys in eutrophic elm (Ulmus glabra) and ash (Fraxinus excelsior) forests in southern Sweden, conducted just prior to the arrival of Dutch elm disease (DED) in 1989, and then again in 2021, several years after ash dieback (ADB) began. At the sample plot scale, species richness (α–diversity) of the upper tree layer strongly decreased from 1989 to 2021, and the mean cover of elm decreased from 27 to 1% and of ash from 29 to 13%. In the lower tree and shrub layers, elm and ash were replaced by other, mainly shade-tolerant, tree species. The cover and richness of the shrub layer increased in previously elm-dominated stands but not in ash-dominated stands. The extensive loss of canopy cover in elm stands caused a larger change in upper tree layer species composition and increased compositional variability (β-diversity) between plots when compared to the ash stands. The direction of the changes in tree layer composition between the surveys varied with soil moisture and nutrient availability. While beech increased in less eutrophic plots, more nutrient-rich plots changed toward hornbeam or small-leaved lime, and wetter plots turned toward alder and bird cherry. Hence, our results indicate increased compositional diversity and alternative successional pathways for community reorganization following DED and ADB. Future research will reveal if these pathways will later merge or further split.

Selection of Wood Based on Acoustic Properties for the Solid Body of Electric Guitar

For the purpose of making of a solid body of an electric guitar the acoustic- and mechanical properties of walnut- (Juglans regia L.) and ash wood (Fraxinus excelsior L.) were researched. The acoustic properties were determined in a flexural vibration response of laboratory conditioned wood elements of 430 × 186 × 42.8 mm used for making of a solid body of an electric guitar. The velocity of shear- and compression ultrasonic waves was additionally determined in parallel small oriented samples of 80 × 40 × 40 mm. The research confirmed better mechanical properties of ash wood, that is, the larger modulus of elasticity and shear modules in all anatomical directions and planes. The acoustic quality of ash wood was better only in the basic vibration mode. Walnut was, on the other hand, lighter and more homogenous and had lower acoustic- and mechanic anisotropy. Additionally, reduced damping of walnut at higher vibration modes is assumed to have a positive impact on the vibration response of future modelled and built solid bodies of electric guitars. When choosing walnut wood, better energy transfer is expected at a similar string playing frequency and a structure resonance of the electric guitar.

Wood decomposition, carbon, nitrogen, and pH values in logs of 8 tree species 14 and 15 years after a catastrophic windthrow in a mesic broad-leaved forest in the East European plain

There are limited studies of decomposition of coarse woody debris (CWD) in natural conditions of multi-species mesic broad-leaved forests. We investigated 49 lying logs of 7 angiosperm and 1 gymnosperm species 14 and 15 years after a mass windthrow in an old-growth broad-leaved forest. We observed high heterogeneity of logs in terms of decomposition stages: up to 4 stages in one transverse disk and up to 5 stages in longitudinal fragments of one log. Due to the high heterogeneity of logs, we investigated traits of wood samples rather than individual logs. Bulk density, carbon and nitrogen concentrations, and pH values were examined for 188 CWD samples of 8 species at 5 decomposition stages (from stage 1 least to stage 5 most decayed wood) and 24 control samples of live trees (3 replicates for each species; zero stage of decay). Changes of deadwood volume, carbon and nitrogen stocks over 14 and 15 years after the windthrow were estimated by re-surveying transects established in 2010. From the first to the fifth decay stage, the mean CWD density decreased for all species and averaged 54 ± 16 kg m−3 (SD) at the 5th stage of decay. Regarding decomposition rates, the tree species were arranged in descending rate from diffuse-porous (Populus tremula, Betula pendula, Tilia cordata, and Acer platanoides) to ring-porous (Ulmus glabra, Fraxinus excelsior, and Quercus robur) angiosperms and the coniferous Picea abies was after the diffuse-porous species series and before the ring-porous species. Carbon concentration ranged from 39 to 54 %, but did not change significantly during decomposition (mean value for all species in all decay stages was 45.8 ± 2.5 %). Nitrogen concentration (percentage of dry mass) increased with increasing decay stage and the mean value was 0.2 ± 0.1 % at the zero stage and 0.9 ± 0.5 % at the last decay stage. Despite the increase in N concentration, the mass N per volume decreased during decomposition for all samples considered together due to a significant decrease in wood density. The change in C/N values during deadwood decay reflected the transition of organic matter from the CWD to the SOM (soil organic matter) in forest ecosystems: the ratio C/N varied from 829 (Picea, zero stage) to 16 (Ulmus, last stage) with the mean values 286 ± 149 and 75 ± 45 at the zero and the last stages, respectively. We observed a quadratic trend in the variation of wood pH values by stages: pH mainly decreased from the initial values to the minimum in the middle stages of decay, and then increased in the advanced stages. The mean deadwood volume in the surveyed plots decreased 1.4-fold in the 14–15 years after the windthrow, but the mean stocks of carbon and nitrogen decreased 3 and 2-fold, respectively. Over time, the different decomposition rate of fallen logs leads to a decrease in the proportion of C and N stored in diffuse-porous species at the expense of an increase in this proportion in ring-porous species. This result is worth considering in a carbon management strategy: planting, maintaining stands, and retaining deadwood of ring-porous species, such as Quercus, Ulmus and Fraxinus, promote relatively long-term carbon storage.

Woody Plants Interaction with Aerosol Fine Particulate Matters and Copper in Budapest

Ambient particulate matter pollution is the primary concern as it has a significant impact on human health and the majority of the world's population lives in urban areas. Heavy metals are the most concerning component of particulate matter, and Cu is a highly traffic-related emission element whose overabundance results in toxic effects. Woody plants, on the other hand, contribute to the removal of airborne pollution in urban areas. Our aims are (1) to compare urban woody plants abilities to capture ambient fine particulate matter on leaf surface; and (2) to access the Cu concentration loads on their leaf surfaces. Consequently, our results will provide scientific knowledge for future urban planning concerning air pollution remediation. We investigated the relationship between woody plants and heavy metal pollution in Budapest. Four woody plant species were sampled at different traffic densities. Their Cu contents in the leaf and branch were measured, our results show that Tilia tomentosa and Acer platanoides are better options for ambient Cu accumulation than Fraxinus excelsior and Aesculus hisppocastanus in urban environments. At different traffic densities and sampling times, however, Cu accumulation did not vary across species. This is because, through translocation, woody plants absorb Cu not only from the air but also from the soil. Furthermore, it is also because of the long-distance transportation and long-term suspension of fine particulate matter. From the obtained results, we can conclude that woody plants are important phytoremediation elements in the urban area of Budapest. Planting T. tomentosa and A. platanoides in urban areas of central Europe will be promising for ambient heavy metal pollution phytoremediation. But environmental conditions differ from one place to another. Therefore, a comprehensive study is required in order to apply the results to different locations.

Beetles (Coleoptera) in deciduous dead wood tree species trunks in Lithuania.

We present a list of beetles that emerged from wind-felled tree trunks of several tree species, including European ash (Fraxinusexcelsior), aspen (Populustremula), common oak (Quercusrobur), birch (Betula sp.), small-leaved linden (Tiliacordata) and black alder (Alnusglutinosa). Four hundred and ninety species and 60 families of beetles were collected using trunk-emergence type traps. We found 440 beetle species that had previously been recorded from dead wood; the remaining 50 were newly discovered and all were considered as not directly associated with dead wood. Common oak trunks had the highest diversity of beetles, with approximately 42% of the identified beetle species found in our research. Of all the beetle species identified in the study, about half are saproxylic, while the remaining are considered as not having direct association with dead wood. The results of the study emphasise the importance of dead wood in maintaining beetle diversity in Lithuanian forests. This study provides a valuable baseline for future research on beetles in dead wood in Lithuania and may help to provide information for conservation efforts to protect these important habitats.

Nonlinear kinetic modeling of malachite green adsorption onto green waste bio-adsorbents using CCF- RSM

Malachite Green (MG) adsorption by four different bio-adsorbents: Populus Nigra (PN), Pinus Strobus (PS), Fraxinus Excelsior (FE), and Phragmites Australis (PA) have been investigated. Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analyses were conducted to identify the bio-adsorbents' characterization and study their adsorptive properties. The impact of essential factors, such as adsorbent dosage, initial solution pH, initial MG concentration, and interaction of factors were studied on removal efficiency by face centered design (CCF) as a feature of response surface methodology (RSM). Nonlinear kinetic models including pseudo-first, and pseudo-second order, Elovich, film diffusion, and intra-particle diffusion were evaluated using error functions in order to find the best fitted model. Comparing the obtained results revealed that PA is more effective in decolorization and has an uptake of about 90% in the optimum operating condition. For further investigation, its ashes have been used for MG removal, and as a result, 99.3% dye uptake by PA ash was obtained.

Dead Wood Elements Composition in Different Tree Species and Stages of Decay in the Broad-Leaved Forests of the Kaluzhskie Zaseki Reserve

The content and mass concentration of eight chemical elements Al, Ca, Cu, K, Mg, Mn, P, and Zn were analysed in dead wood of eight tree species at five stages of decomposition. Wood samples were taken at the site of the mass windfall of 2006 in a multispecies broadleaved forest in the Kaluzhskie Zaseki nature reserve. Deadwood of seven deciduous trees species was studied: maple (Acer platanoides), birch (Betula pendula), common ash (Fraxinus excelsior), common aspen (Populus tremula), English oak (Quercus robur), linden (Tilia cordata), rough elm (Ulmus glabra), as well as one coniferous tree species – Norway spruce (Picea abies). A series of one-way analyses of variance was carried out to assess the influence of the species and the stage of deadwood decomposition (including the zero stage for control samples) on the density, content of elements and their mass concentration. Tree species most clearly differed in the content and mass concentration of Mn, Zn, Mg, Ca, and K: R2 varied from 50 to 23% for the content and from 53 to 19% for the mass concentration of elements of the indicated series. The leaders in the content of these elements were the following species: Mn – maple, birch, spruce, linden; Zn – birch and aspen; Mg – maple, elm; Ca – elm; K – linden, elm. The stages of wood decomposition turned out to be a significant factor of variation for the content of Mn, P, Cu, Zn and Ca: R2 varied from 22 to 16%. During the destruction of wood trunks, a significant increase in the content of these elements occurred. Maintenance of cycles of biophilic elements is more successfully implemented in the presence of deadwood of different species at different stages of decomposition.

Assessment of the ecological state of green spaces of Almaty city on the example of Bostandyk district

The article provides an assessment of the ecological state of green spaces on the example of the Bostandyk district of Almaty. The total area of boulevards, squares and green areas of the Bostandyk district of Almaty today is 147.4 hectares. Bostandyk district of Almaty is one of the three greenest districts of Almaty after Medeu and Turksib districts. As our studies have shown, 95 % of green plantations of tree species in the Bostandyk district of Almaty are represented by introducers and a small part of local species — natives. The landscaping of the territory of the city of Almaty is represented by plantings of different types. These include groves, alleys, gardens, parks, boulevards, squares, green areas, intra-district gardening, street gardening. At the same time, a wide variety of species is observed in gardens, parks, boulevards, groves and a very small use of three or four species in landscaping streets. Among the tree plantations, 35 species are massive, which grow along all the streets, boulevards, squares of the Bostandyk district. From hardwoods: Populus nigra, Populus italica, Populus alba, Fraxinus excelsior and others. From the local natural flora grow — Armeniaca vulgaris, Prunus sogdiana, Fraxinus sogdiana, Rhamnus cathartica, Picea schrenkiana.

The phenology and clutch size of UK Blue Tits does not differ with woodland composition

The deciduous tree‐herbivorous caterpillar‐insectivorous bird food chain is a well‐studied system for investigating the impacts of climate change across trophic levels. To date, across Europe, most attention has focused on the impacts of increasing spring temperature on changes to phenology in Oak‐dominated (Quercus spp.) woodlands. Paridae species and Pied Flycatcher Ficedula hypoleuca are the most studied secondary consumers, all of which demonstrate an advancement in reproductive phenology with increases in spring temperature. Shifts in climate and phenology may also impact on reproductive investment in clutch size, and the effects of climate on phenology and clutch size may vary depending on woodland composition. To date, the effects of among‐habitat variation in phenology and reproductive investment have received little attention. Insectivorous birds inhabiting woodlands that differ in tree composition may differ in the timing of breeding, due to local tree leafing phenology acting as a cue for egg‐laying date and/or clutch size. Moreover, for most insectivorous birds, woodland composition within a territory is likely to be the main determinant of food availability for both adults and chicks. Consequently, if warming springs affect the temporal patterns of food availability differently across different woodland compositions, this may affect the optimal average local phenology for nesting birds. Here, using data from 34 long‐term (mean 15 years) nest monitoring sites across the UK, we investigate the effect of woodland tree composition and temperature on Blue Tit Cyanistes caeruleus first egg date (FED) and clutch size. We supplemented the nest monitoring data by quantifying woodland composition, at a site level, through modified point counts. We predict that birds breeding in woodlands with greater proportions of late‐leafing species, such as Oak and Ash Fraxinus excelsior, will breed later than those breeding in woodlands with greater proportions of early‐leafing species, such as Birch Betula spp. and Beech Fagus sylvatica. We found no evidence for differences in Blue Tit FED or clutch size in relation to the proportion of any of the tree species investigated, after controlling for temperature and latitude (FED: −3.4 and 2.2, clutch size: −0.4 and − 0.2 eggs for one‐unit increase in temperature and latitude, respectively). In recent decades and across all sites, clutch size has decreased as spring temperatures have increased, a strategy which could allow birds flexibly to adjust their breeding phenology such that nestling demand coincides with peak food availability. The lack of an effect of woodland composition on Blue Tit phenology suggests Blue Tits do not fine‐tune their reproductive phenology to the local tree composition. Whether this lack of evidence for phenological divergence is due to an absence of divergent selection on breeding phenology and clutch size or to gene flow is not clear.

A glimmer of hope - ash genotypes with increased resistance toash dieback pathogen show cross-resistance to emerald ash borer.

Plants rely on cross-resistance traits to defend against multiple, phylogenetically distinct enemies. These traits are often the result of long co-evolutionary histories. Biological invasions can force naïve plants to cope with novel, coincident pests, and pathogens. For example, European ash (Fraxinus excelsior) is substantially threatened by the emerald ash borer (EAB), Agrilus planipennis, a wood-boring beetle, and the ash dieback (ADB) pathogen, Hymenoscyphus fraxineus. Yet, plant cross-resistance traits against novel enemies are poorly explored and it is unknown whether naïve ash trees can defend against novel enemy complexes via cross-resistance mechanisms. To gain mechanistic insights, we quantified EAB performance on grafted replicates of ash genotypes varying in ADB resistance and characterized ash phloem chemistry with targeted and untargeted metabolomics. Emerald ash borer performed better on ADB-susceptible than on ADB-resistant genotypes. Moreover, changes in EAB performance aligned with differences in phloem chemical profiles between ADB-susceptible and ADB-resistant genotypes. We show that intraspecific variation in phloem chemistry in European ash can confer increased cross-resistance to invasive antagonists from different taxonomic kingdoms. Our study suggests that promotion of ADB-resistant ash genotypes may simultaneously help to control the ADB disease and reduce EAB-caused ash losses, which may be critical for the long-term stability of this keystone tree species.

Comparison of the gaseous benzene adsorption capacity by activated carbons from Fraxinus excelsior L. as a lignocellulosic residual

Comparison of the gaseous benzene adsorption capacity by activated carbons from Fraxinus excelsior L. as a lignocellulosic residual

Fungi associated with stem collar necroses of Fraxinus excelsior affected by ash dieback

In recent decades the vitality and physical stability of European ash trees in Germany have been reduced by European ash dieback, especially when associated with stem collar necroses and rots. This study was carried out to investigate the composition of the fungal communities associated with stem collar necroses. Filamentous fungi were isolated from 58 ash trees out of nine forest stands in northern, eastern, and central Germany. Obtained isolates were identified to a genus or species level by means of morphological and molecular analyses. In total 162 morphotypes including endophytic, saprotrophic, and pathogenic fungi were isolated. For 33 species found no prior reports from Fraxinus excelsior were recognised, including Cryptostroma corticale and Diplodia sapinea. None of the identified species were found at all studied sites, though Diplodia fraxini was the most common fungus with regard to frequency within all isolates, occurring at seven sample sites. This species is followed by Hymenoscyphus fraxineus, Armillaria spp., Neonectria punicea, Diaporthe cf. eres, Fusarium cf. lateritium, and Paracucurbitaria sp. in order of frequency within all isolates. The aforementioned species are characterised and analysed in respect to their occurrence in stem collar necroses and at sample sites. The influence of site conditions on the fungal composition was described for five intensively sampled sites with a minimum of five studied trees (Schwansee, Rhüden, Berggießhübel, Satrup, and Schlangen). The sampling site of Schlangen was further subdivided into four subplots with different positions in the terrain. In the remaining four extensive sample sites, either one or two trees, respectively, were sampled and analysed (Oranienbaumer Heide, Woltershausen, Wolfenbüttel, and Neuhege). Over all sample sites, fungal communities of symptomatic stem tissue are similar concerning the most frequent fungi, but vary greatly according to singularly isolated fungi.

Morphological plasticity of six tree species with different light demands growing in multi-layered deciduous forests in Central Europe

Tree allometry is a plastic feature, and scaling parameters can vary considerably depending on phylogeny, life strategies, growth conditions and ontogeny. We hypothesized that in multi-layered forests growing on rich sites and driven by stand dynamics without stand-replacing disturbances, light is a primary driver of allometric relationships and that the morphological plasticity of tree species is closely associated with their shade tolerance. We quantified and compared the morphological properties of six species that form a shade tolerance gradient: Alnus glutinosa (L.) Gaertner, Quercus robur L., Fraxinus excelsior L., Ulmus laevis Pall., Tilia cordata Miller and Carpinus betulus L. The relationships between tree height and local stand density as predictors and dbh, crown width, crown length and crown volume as response variables were characterized. We found that in the lower stand layer the values of crown parameters increased with tree height at a lower rate in light-adapted than in shade-tolerant species. Conversely, the response of morphological traits on competition was stronger in light-adapted species than in shade-tolerant species. The ratio of crown width-to-crown length was not associated with light demand. Apart from ash, which demonstrated a different allocation pattern, between-species differences in the slenderness ratio were insignificant. Allometry and sensitivity to competition varied in trees growing in the upper and lower stand layers. Our results indicate that the dichotomy of basic growth strategies of stress tolerance versus stress avoidance is overly simplistic and fails to consider social status and species-specific features such as apical control.

Evaluating the Capability of Woody Plants to Capture Atmospheric Heavy Metals in Budapest

Urban green infrastructure planning plays an important role in aspects of pollution reduction, such as heavy metal trapping. However, the reduction effects are both influenced by the different pollution conditions in each city and the species-specific interaction of trees and pollution. Herein, we investigated three common urban woody plants (Acer platanoides L., Fraxinus excelsior L. Westhof’s Glorie, and Tilia tomentosa Moench) in Budapest to compare their heavy metal trapping abilities from the airborne in leaf dust deposits and leaves. All samples were deconstructed by a wet digestion method. Four high traffic-related heavy metal elements (Zn, Cu, Pb, and Ni) were determined by using an atomic absorption spectrometer (AAS). The investigated results showed that the relevant concentration of all measured elements was constant in all species, namely Zn < Cu < Pb < Ni. Although the total heavy metal content in the dust deposit increased towards the end of one vegetation period, the highest percentage of total metal concentration was in the summer season as the particulate matter sources varied in each season. These indicate that woody plants are ideal candidates for pollution monitoring. All of the evaluated elements were loaded highest in the dust deposit of T. tomentosa during all sampling times, followed by A. platanoides, and the least in F. excelsior. A significant correlation between metal contents in the dust deposit and leaf was found in T. tomentosa (0.926 at a p<0.01 level). Therefore, we suggest T. tomentosa, which has better atmospheric trace element capturing capacity than A. platanoides and F. excelsior and thus it is a better option for pollution reduction in the urban area.

Pollination success of Fraxinus excelsior L. in the context of ash dieback

Key messagePaternity analyses show that effective pollination of ash (Fraxinus excelsior L.) in a seed orchard and a floodplain forest affected by ash dieback is more likely to be facilitated by healthier males. Thereby, natural selection can have a positive effect on the health of future generations.ContextOngoing ash dieback and increasing fragmentation of ash populations may result in reduced pollen flow, which can reduce pollination success of future generations of ash trees. Therefore, it is essential to further improve our understanding of gene flow patterns, especially with respect to ash dieback.AimsIn this study, paternity analyses were conducted in a seed orchard and a floodplain forest in Germany in 2018 to explain the relationship between pollination success and the health status of ash trees and distances of effective pollen transport.MethodsCambium samples (i.e., from twigs and stumps) were collected from 251 ash trees (putative father and mother trees) for genotyping, and the health status of each tree was documented using a scoring system to evaluate vitality. Additionally, seeds were harvested from 12 mother trees per site. Genetic analyses using nuclear microsatellites were performed to determine paternal trees. Paternities were assigned based on the likelihood model implemented in the Cervus 3.0.7 software.ResultsOur results showed that the average pollination distance was 76 m in the seed orchard and 166 m in the floodplain forest. In general, pollination success decreased substantially with increasing distance to the mother tree. Despite the dense tree cover in the floodplain forest, pollen were transported over long distances (greater than 550 m), suggesting that non-local sources also play a role in pollination. This is supported by the foreign pollen input identified in the seed orchard (66.5%). Self-pollination was detected only to a very small extent, and thus had no major influence on reproduction. In addition, both healthy and slightly diseased father trees showed similar mating success. However, this was not the case for the severely diseased ash trees (more than 50% of crown damage) because only a few offspring could be assigned to them. Nevertheless, in contrast to the floodplain forest, there was no significant correlation between damage classes and pollination success in the seed orchard.ConclusionLong-distance pollen transport contributes to the connectivity of ash trees in the landscape. Additionally, both healthy and slightly diseased fathers have a greater contribution to pollination, thus potentially improving the health of the next generation of ash trees. Moreover, gene flow between stepping stone populations is necessary to ensure the positive impact on the genetic diversity of ash populations in the future.

Indirect auxiliary organogenesis of Fraxinus excelsior L. as a tool for ash dieback control

The existence of European ash (Fraxinus excelsior L.) is threatened by fungus-induced ash dieback. It is essential to find effective methods to multiply ash genotypes resistant to ash dieback while preserving the genetic diversity of these tree populations. In this paper the efficient method for production of European ash seedlings using indirect auxiliary organogenesis with multi-factor analysis of its effectiveness is presented. Procedures for a dormancy breaking treatment of seeds and effective disinfection of F. excelsior primary explants, as well as appropriate composition of the culture media taking into account impact of growth regulators and physiological gradient on the micropropagation efficiency were developed. As primary explant for micropropagation of F. excelsior, leaf buds, megagametophytes and zygotic embryos were tested. The best-performing type of primary explant for micropropagation of European ash proved to be zygotic embryos, which were successfully used to regenerate seedlings via indirect auxiliary organogenesis. No statistically significant impact of population origin of F. excelsior explant donor trees was observed on the effectiveness of callus initiation. However, such difference was significant in regard to average productivity of acquired callus cultures (number of seedlings produced) and to average root length of regenerated seedlings. Health condition of explant donor trees and their seeds affects the callus initiation rate from zygotic embryos, but does not affect the productivity of callus lines derived from the seeds and the quality of regenerated seedlings. Indirect auxiliary organogenesis of F. excelsior, developed in our study, not only provides the acquisition of ash seedlings of different genotypes, but also enables rapid selection of desired genotypes already at the callus stage. In this way, the presented method benefits not only profit oriented forestry and wood industry, but also provide the effective and fully controllable tool for reintroduction of various resistant to ash-dieback F. excelsior genotypes without loss of variability and genetic identity of its populations.

Study on Single-Tree Extraction Method for Complex RGB Point Cloud Scenes

With the development of sensor technology and point cloud generation techniques, there has been an increasing amount of high-quality forest RGB point cloud data. However, popular clustering-based point cloud segmentation methods are usually only suitable for pure forest scenes and not ideal for scenes with multiple ground features or complex terrain. Therefore, this study proposes a single-tree point cloud extraction method that combines deep semantic segmentation and clustering. This method first uses a deep semantic segmentation network, Improved-RandLA-Net, which is developed based on RandLA-Net, to extract point clouds of specified tree species by adding an attention chain to improve the model’s ability to extract channel and spatial features. Subsequently, clustering is employed to extract single-tree point clouds from the segmented point clouds. The feasibility of the proposed method was verified in the Gingko site, the Lin’an Pecan site, and a Fraxinus excelsior site in a conference center. Finally, semantic segmentation was performed on three sample areas using pre- and postimproved RandLA-Net. The experiments demonstrate that Improved-RandLA-Net had significant improvements in Accuracy, Precision, Recall, and F1 score. At the same time, based on the semantic segmentation results of Improved-RandLA-Net, single-tree point clouds of three sample areas were extracted, and the final single-tree recognition rates for each sample area were 89.80%, 75.00%, and 95.39%, respectively. The results demonstrate that our proposed method can effectively extract single-tree point clouds in complex scenes.