Size characteristics of mature cones (berries) and seed quality were studied at the individual berry level in three Juniperus taxa indigenous to Slovakia. The globose berries were characteristic of J. communis subsp. communis and J. communis nothovar. intermedia and ovoid berries of J. communis subsp. nana. All three taxa had smaller berries than those of the corresponding species in other countries. In five populations of the studied taxa, three-seeded berries were the most frequent, with one population of J. communis subsp. communis being exceptional, producing predominantly two-seeded berries. The average number of seeds per berry has ranged from 2.06 to 2.94 in J. communis subsp. communis depending on locality. In J. communis nothovar. intermedia it was 2.40 seeds per berry, whereas in J. communis subsp. nana 2.81 seeds per berry. Of these, the fraction ranging between 0.033 and 0.67 represented filled seeds, and the fraction between 1.35 and 1.88 aborted seeds. Cytological study of seed development dynamics revealed an abrupt decline of the viability seed potential at the prezygotic stage of fertilization process in J. communis subsp. communis and a smaller extent of deterioration of morphologically differentiated embryos and encompassing gametophyte of mature seeds. Cytological illustrations of these disturbances in fertilization process are presented and discussed in the paper.

Forest restoration and afforestation across Europe are accelerating, yet the decision-making processes governing forest establishment remain unevenly examined, especially from a biodiversity perspective. Considering this and the global environmental changes of climate shifts, land-use transitions, and biological invasions, the present review provides guidance for planning and establishment of multifunctional forests that enhance biodiversity outcomes without compromising long-term forest productivity or resilience. Aiming to assist both practitioners and researchers, we have particularly focused on tree species selection, plant production and management of forest reproductive material, and on-field establishment practices. Literature revision and expert observations indicate that tree species selection must integrate functional traits, provenance performance, and ecological impact assessments alongside species distribution models, since climatic suitability alone does not predict performance under future conditions. Genetic diversity remains severely underutilized in operational forestry but can be advanced through assisted migration, provenance mixing, and traceable seed sources as practices that need to be better supported and monitored. Concurrently, the plant production chain contains multiple points where genetic diversity is eroded, along with advancement opportunities explored through pan-European projects focusing on diversity standards, regional seed-exchange networks, and low-cost molecular monitoring. On-field, the choice between direct seeding and planting needs to link better genetic diversity targets and site conditions rather than biased preference. And finally, urban forests, increasingly recognized as components of the restoration continuum, require context-specific species selection and a transition from isolated specimen planting to more complex and inclusive design (similar to stand level in natural forests) to deliver meaningful biodiversity and multifunctionality outcomes.

Needle structure was analyzed in three Juniperus communis taxa from different localities in central Slovakia. The main aim was to test the hybrid origin hypothesis of J. communis nothovar. intermedia (Schur) Nyman, defined as a cross between J. communis L. ssp. communis and J. communis ssp. nana (Hook.) Syme. While DNA-based analyses remain the most reliable tool for inferring evolutionary history, comparative needle morphology can provide complementary evidence, including diagnostic traits for taxonomic delimitation. In this study, we evaluated three morphometric and sixteen anatomical needle traits, measured via microscopy in ten shrubs per taxon. The analyses indicated that most traits in nothovar. intermedia matched one of the parents, with only two traits proving strongly diagnostic, separating all three taxa: needle length, which showed an intermediate mean phenotype in nothovar. intermedia (R2 = 0.824, p = 0.011; between parents), and vascular bundle height, which displayed a transgressive pattern (R2 = 0.552, p = 0.031; between parents). Although the diagnostic value of individual traits for hybrid detection was generally weak, a phylogenetic network analysis based on six diagnostic traits that separated individuals of the parental taxa provided evidence for reticulate evolution. These results support the hybrid origin of J. communis nothovar. intermedia and highlight needle traits with potential value for distinguishing ssp. communis and ssp. nana in natural populations, which may assist in taxonomic delimitation and inform future conservation assessments.

Pollen viability in three Juniperus taxa native to Slovakia was investigated using in vitro germination test. The highest germination percentage and longest pollen tubes were surprisingly found in J. communis var. intermedia which is believed to be a putative hybrid between J. communis var. communis and J. sibirica . Germination rate of the hybrid averaged at 78.70% as compared with 64.96% and 60.83% of the pollen germination in the corresponding parental species. The same tendency holds for the pollen tube length reaching 38.68 µm in the putative hybrids, 31.39 µm in J. communis var. communis and 28.08 µm in J. sibirica . At the taxa level, the above given data were statistically highly significant in both pollen viability characteristics. Highest viability of J. communis var. intermedia pollen does not corroborate the widespread notion on reduced fertility of the plant interspecific hybrids. Additional tests are suggested to verify the hybrid nature of the putative hybrid population using DNA based population study and artificial crossing experiments involving the putative parental species J. communis var. communis and J. sibirica .

River corridors are among the most important natural pathways for invasive species to spread into landscapes. Nevertheless, the ecological processes underlying invasions of riparian habitats are poorly understood for many taxonomic groups. We sampled bryophytes, vascular plants, and molluscs along three West Carpathian rivers (Central Europe) to identify spatial trends and drivers of native and alien species diversity across multiple taxa. Generalised additive models revealed decreasing downstream diversity patterns across all studied rivers and taxonomic groups. In contrast, alien diversity showed the opposite trend, displaying a high degree of idiosyncrasy among the rivers. Random forest analysis revealed that climate-induced variables (altitude and related temperature) played a more pronounced role in the diversity of alien species than in the diversity of native species. The diversity of native species was more influenced by local land use and habitat alternations (molluscs) or by source-to-mouth river interactions along the longitudinal gradient (plants). Dispersal limitation and temperature constrain alien species distributions along river corridors, while a multitude of natural and anthropic influences drive native species diversity. The climate-driven distribution of alien plants and molluscs suggests future altitudinal and longitudinal shifts in non-native species along river corridors, which will be exacerbated by ongoing climate warming and associated environmental changes.

Background and Aims Invasive species are a threat to the conservation of biological systems. In Central Europe, riparian ecosystems are especially susceptible to plant invasions, as waterflow mediates the spread of plant propagules, while invasive species may then affect soil including soil microbial communities. As waterflow also enhances connectivity among different segments of a river, spatial continuity of abiotic as well as biotic components of riparian ecosystems is expected. Methods We studied activity and functional diversity of microbial communities in three headwater streams in Central Europe. Plant diversity, soil properties and soil microbiota were assessed on 20 sample plots per river regularly distributed along the streams. Soil microbial activity and community-level physiological profiling were used to study the soil microbial community. Results Although the α-diversity of plants and soil microbiota was comparable, plant communities were substantially more differentiated than microbial communities. Richness in alien and invasive plants significantly differed among rivers, which was reflected in different spatial patterns and trends of microbial activity and diversity. A high level of spatial continuity and clearest longitudinal trends were observed in the Kysuca river with straightened riverbed and a high occurrence of artificial surfaces in the adjacent areas. The number of both alien and invasive plants significantly affects the composition of microbial functional groups of riverbed soils. Conclusion Continuity of processes in riparian ecosystems was confirmed also for headwater streams. However, the extent to which it applies to a particular stream strongly depends on particular environmental setting and stream characteristics.

Pollen viability, dispersion ability and longevity during deep-freezer storage were studied in three Juniperus taxa distributed in Slovakia. All these characteristics of pollen are closely related to the pollination and/or fertilization success of the junipers in nature. Pollen viability varied considerably between the three populations of J. communis and one population of each, J. sibirica and J. communis var. intermedia. Pollen germination rate ranged between 40.75% and 75.06%, and pollen tube length between 30.32 and 40.41 µm. A clear tendency indicates a higher germination rate of J. communis pollen from lower altitudes and reduced germination of J. sibirica and J. communis var. intermedia pollen from higher altitudes. The dispersion potential of the J. communis pollen during its shedding seems relatively low. In 2021, pollen cloud density was diluted at 68.1% at the 4 m distance from the test shrub, in 2022 of 52.1% at the 17 m distance from the pollen source. A deep-freezer storage of juniper pollen in a double-walled polyethylene bag with silica gel was not efficient enough, as indicated by the drop of pollen germination rate of 31.2% in J. communis and of 79.4% in J. sibirica during a 1-year storage period at − 81 °C.

European beech is an ecologically and commercially important species, which is expected to decline in several regions because of heat and drought stress associated with climate change. Knowledge of the genetic basis of the adaptation to climate is needed to guide assisted migration. Genetic variation at 1704 single-nucleotide polymorphisms (SNPs) resulting from ddRAD sequencing, primarily located in gene exons, was studied in 181 specimens representing 123 populations distributed over most of the whole range. Bayesian analysis of population structure yielded two clusters exhibiting a clear longitudinal cline and correlated with indicators of low temperatures and temperature fluctuation. Five SNPs were significantly associated with climatic variables related primarily to heat and temperature ranges. Two alternative explanations are offered for the observed response patterns: (i) differential sensitivity to heat and (ii) response mediated by vegetative phenology.

Pedunculate oak is an economically and ecologically very valuable species at the European level and for Bosnia and Hercegovina, and research into variation of this species is very important. In 2007, pedunculate oak leaf material was collected in 27 populations in Bosnia and Herzegovina along with seeds, which were used to establish a provenance trial. In the trial, leaves were collected in 2021, and 14 morphological traits were measured in both types of material. Analysis of variance showed generally non-significant differences between generations, but significant variation among populations and population-by-generation interactions. However, the correlations between generations were non-significant for most traits, and neither were the correlations with climatic parameters. The results indicate both genetic and environmental effects on leaf morphology. The utility of leaf morphology for gene conservation is shortly discussed.

Local adaptation is key for ecotypic differentiation and species evolution. Understanding underlying genomic patterns can allow the prediction of future maladaptation and ecosystem stability. Here, we report the whole-genome resequencing of 874 individuals from 100 range-wide populations of European beech (Fagus sylvatica L.), an important forest tree species in Europe. We show that genetic variation closely mirrors geography with a clear pattern of isolation-by-distance. Genome-wide analyses for genotype-environment associations (GEAs) identify relatively few potentially adaptive variants after correcting for an overwhelming signal of statistically significant but non-causal GEAs. We characterize the single high confidence genomic region and pinpoint a candidate gene possibly involved in winter temperature adaptation via modulation of spring phenology. Surprisingly, allelic variation at this locus does not result in any apparent fitness differences in a common garden. More generally, reciprocal transplant experiments across large climate distances suggest extensive phenotypic plasticity. Nevertheless, we find indications of polygenic adaptation which may be essential in natural ecosystems. This polygenic signal exhibits broad- and fine-scale variation across the landscape, highlighting the relevance of spatial resolution. In summary, our results emphasize the importance, but also exemplify the complexity, of employing natural genetic variation for forest conservation under climate change. The genomic basis of local adaptation can contribute to predicting species' future maladaptation. This study shows that local adaptation in European beech is genetically complex, with current analyses only skimming the surface of the encoded information, highlighting the need for bigger data.

Key message Seven European beech provenances differing largely in growth performance were grown at two common garden sites in Germany and Slovakia. The intra-specific variability of most traits was explained more by phenotypic plasticity than inter-provenance variability, and efficiency-related traits showed a higher phenotypic plasticity than safety-related traits. Context To maintain climate-resilient future forests, replicated common-garden experiments are suited for developing assisted migration strategies for key tree species. Aims We analysed the magnitude of inter-provenance variability and phenotypic plasticity for 12 functional traits of European beech ( Fagus sylvatica L.) and analysed whether the climate at the place of origin left an imprint. Moreover, we asked whether growth is unrelated to xylem safety and to what extent the foliar, xylem and growth-related traits are coordinated. Methods Terminal branches were collected from 19-year-old and 22-year-old trees of seven European beech provenances planted at two common garden sites in Germany and Slovakia, respectively. Three hydraulic, three wood anatomical and four foliar traits were measured and related to two growth-related variables. Results At the two sites, the same pair of provenances showed the highest and lowest growth. Nevertheless, a high degree of phenotypic plasticity was observed, as all traits differed significantly between sites after accounting for provenance effects, with hydraulic safety-related traits showing the lowest and efficiency-related traits the highest plasticity. There was no evidence for inter-provenance variability in xylem embolism resistance ( P 50 ) or the foliar carbon isotope signature (δ 13 C), a proxy for intrinsic water use efficiency (iWUE), and both were unrelated to growth. P 50 was positively correlated with the lumen-to-sapwood area ratio and vessel density. Conclusions Because of the lacking trade-off between embolism resistance and growth, highly productive provenances can be selected without reducing the drought tolerance of the branch xylem. However, as xylem safety is only one element of a trees’ drought response, it may be beneficial to select provenances with other more conservative drought adaptations such as smaller vessel lumen areas for increasing xylem safety and small supported total leaf areas for reduction of total transpiration.

Norway spruce is expected to suffer from drought stress and other manifestations of climate change. This study relies on a manipulative experiment with drought-stressed and well-watered (control) seedlings, comprising five provenances of Norway spruce distributed along a steep elevational transect from 550 to 1,280 m a.s.l. within the natural range. Seedlings were subjected to measurement of physiological traits (content of phytohormones and monoterpenes, slow and fast chlorophyll a fluorescence kinetics, gas exchange, hyperspectral indices), and genotyping at 8 nuclear microsatellite loci. Comparison of the coefficient of differentiation at neutral loci (FST) vs. differentiation at phenotypic traits (PST) was used to identify traits underlying divergent selection. In total, 18 traits exhibited a significant PST – FST difference. However, the consistency in differentiation patterns between drought-stressed and control plants was limited, only three traits exhibited signals of selection under both treatments. This outcome indicates that the identified differentiation patterns can only be interpreted in the context of environmental setup of the experiment, and highlights the importance of common gardens in adaptation research, as they allow both elimination of environment-induced phenotypic variation and studying genotype-by-environment interaction in physiological responses to environmental stresses.

Studies in community genetics have often revealed a relationship between genetic diversity of the focal species and species diversity of the associated biotic communities. This relationship was studied in forest communities dominated by black alder (Alnus glutinosa Gaertn.), one of the few tree species tolerating an anoxic environment of waterlogged soils. It is a dominant species of tree overstory in two types of communities: alder carrs, forest swamps with stagnating water, and riparian forests occurring along smaller waterflows, periodically flooded with a considerable water level fluctuation during the vegetation period. Plant community composition and genetic variation of alder populations were studied in 218 black alder communities of both types distributed along a broad latitudinal transect from the Pannonian lowland to the Western Carpathians (Hungary, Slovakia, Poland). Species diversity was significantly higher in riparian stands than in alder carrs, while no difference was observed in the genetic diversity. The analysis of population structure revealed differentiation between Pannonian and Carpathian populations, which may be attributed to different migration pathways during the Holocene. No correlation was observed between genetic diversity of alder and species diversity of the associated vascular plant communities. On the other hand, using the ddRAD-sequencing approach applied to 96 trees, we identified 19 single-nucleotide polymorphisms significantly associated with climatic and soil variables. However, the hypothesized bioindication function of the plant community composition on the genetic variation of black alder as a focal species was not confirmed.

European beech is one of the most common tree species in Europe and is generally suggested to play even more of a prominent role in forestry in the future. It seems to have the potential to partially replace Norway spruce, as it is less sensitive to expected warmer and drier conditions. It is, however, not well known in which regions these new plantings would be particularly favourable and if specific provenances may be better adapted to the new conditions than others. Therefore, we estimated the potential early height growth under climate conditions in 2040–2060 for 20 beech provenances across a region covering the Czech Republic and Slovakia. This Central European region is expected to experience considerably drier and warmer conditions in the future. For this exercise, we implemented a new neural network model developed from height growth information obtained from the open-access BeechCOSTe52 database. The simulations are driven by past and future climate data obtained from the WorldClim database of historical climate data and future climate projections. Simulations revealed that provenances originating from drier regions performed on average significantly better than those from regions with good water supply. Moreover, provenances originating from drier regions had a particularly large advantage in the relatively arid regions of Central Czechia and Southern Slovakia. We can also confirm that all provenances showed a high phenotypic plasticity of height growth across the whole investigated region.

Local adaptation is a key concept in biology: shift of genetic structures of populations due to differential survival of genotypes is expected to lead to phenotypes providing an advantage in the local environment. Variation of sequences of twelve candidate genes was investigated in 13 Norway spruce (Picea abies (L.) Karst.) provenances originating from sites distributed along an altitudinal gradient from 550 to 1300 m a.s.l. Signals of selection were assessed in 103 single nucleotide polymorphisms (SNP). The Bayesian F-ST outlier identification methods as Implemented in the programs BayeScan and Arlequin did not identify any SNP with a clear evidence of selection. The approaches relying on SNP-climate associations (spatial analysis method based on logistic regression of allele frequencies with environmental variables. Bayesian method applied in BayEnv2) identified several relationships but none of them remained significant after correction for multiple testing. Gene flow, epigenetic inheritance and former management of the studied populations are discussed as potential reasons for this weak evidence of selection signals.

The complex of beech taxa in western Eurasia ( Fagus sylvatica L. s.l. ) represents one of the most widespread broad-leaved trees in the temperate forests of the northern hemisphere. Two subspecies are generally recognized, F. sylvatica ssp. sylvatica in Europe and F. sylvatica ssp. orientalis in southwestern Asia, but several strongly differentiated regional populations were identified within this complex. To reveal geographical and genomic patterns of hybridization and introgression, genetic variation at 6789 single-nucleotide polymorphisms (SNP) resulting from ddRAD sequencing was studied in 288 specimens representing 207 populations distributed across the whole range. Two clusters resulting from a Bayesian analysis of population Structure well coincided with the subspecies, while increasing the number of clusters allowed to distinguish divergent lineages within subspecies. Two zones of potential hybridization between such lineages were analyzed: western Balkans at the contact of both subspecies and the Alpine area at the contact of populations coming from different glacial refugia. Geographical distribution of hybrid indices in the Balkan hybrid zone indicates asymmetric gene flow preferentially directed from F. orientalis to F. sylvatica . Eight SNPs showed a significant shift of genomic cline centers, seven of them toward excess F. orientalis ancestry, suggesting that introgression irregularly affects different regions of the beech genome. On the other hand, no genomic cline outliers were found in the Alpine hybrid zone. Implications for assisted gene flow are shortly discussed.

The benefits and risks of human-aided translocation of individuals within the species range, assisted gene flow (AGF), depend on the genetic divergence, on the rate and direction of hybridization, and on the climate transfer distance between the host and donor populations. In this study, we explored the use of Oriental beech (Fagus sylvatica subsp. orientalis), growing from Iran to the Balkans, for AGF into European beech populations (F. sylvatica subsp. sylvatica) that increasingly suffer from climate warming. Using samples from natural populations of Oriental and European beech and microsatellite loci, we identified 5 distinct genetic clusters in Oriental beech with a divergence (FST) of 0.15 to 0.25 from European beech. Using this knowledge, we traced the origin of 11 Oriental beech stands in Western Europe established during the 20th century. In two stands of Greater Caucasus origin, we found evidence for extensive hybridization, with 18% and 41% of the offspring having hybrid status. Climate data revealed higher seasonality with warmer and drier summers across the native Oriental beech sites in comparison to the planting sites in Western Europe. Accordingly, we found that bud burst of Oriental beech occurred four days earlier than in European beech. Overall, our results suggest that AGF of Oriental beech could increase the genetic diversity of European beech stands and may foster introgression of variants adapted to expected future climatic conditions. Our study showcases the evaluation of the benefits and risks of AGF and call for similar studies on other native tree species.