Fast-growing hybrid aspen has been widely planted on former agricultural lands in Northern and Eastern Europe to produce pulpwood and sequester carbon into woody biomass. The biodiversity of mature hybrid aspen plantations has so far been rarely analysed. Moreover, the potential of hybrid aspen plantations to host flora typical of European aspen stands – recognised as biodiversity hotspots in Eurasian boreal forests – has not been evaluated. This study focused on two organism groups with contrasting habitat preferences – ground-dwelling herbs and epiphytic lichens. We sought to clarify how environmental and landscape factors influenced the diversity of herbs, lichens, and species characteristic of European aspen stands (EA species). Data were collected across 42 study plots within 20 hybrid aspen plantations in Estonia. Altogether, 162 herb species and 65 lichens were recorded, including 92 species also found in European aspen stands. The proportion of EA species was higher among lichens (86.2%) than among herbs (22.2%), reflecting a stronger legacy effect of former agricultural land-use on ground-dwelling species than on epiphytes. Responses of herb and lichen diversity to environmental variables differed. Richness of herbs was related to litter and stand characteristics. Compositional analyses also highlighted the role of soil-litter variables and stand structure in herb composition. Lichens responded to landscape-related variables. A greater extent of older forests around the study plots increased the richness of EA species. In conclusion, mature hybrid aspen plantations are relatively species-rich and can enhance landscape connectivity for forest species, particularly epiphytes, in agricultural landscapes.

Silver birch (Betula pendula) and hybrid aspen (Populus tremula × P. tremuloides) are widely planted tree species on former agricultural lands in Northern and Eastern Europe due to their fast growth, high biomass production and CO2 sequestration. As few comparative studies on the biodiversity of silver birch and hybrid aspen plantations have been carried out, we aimed to evaluate above- and below-ground diversity in silver birch plantations (SBs) and hybrid aspen plantations (HAs) and associate the trends with environmental variables. For this, we collected data on herbs, ground-dwelling bryophytes, epiphytic bryophytes, lichens, closed forest species and soil fungi from 10 SBs and 10 HAs (< 25 years of age) in Estonia. The richness and composition of herbs was similar in SBs and HAs, whereas all other groups differed either in species richness, composition or both. Overall, HAs hosted higher richness of ground-dwelling bryophytes and epiphytic lichens and lower richness of epiphytic bryophytes than SBs, which was associated with differences in litter and light conditions. The richness of closed forest species was similar between HAs and SBs and increased in correlation with the area of surrounding forests, whereas the compositions differed. The HAs hosted higher fungal richness of all soil fungi, as well as ectomycorrhizal, saprotrophic and plant pathogenic fungi and differed compositionally from SBs. Based on our findings, both birch and hybrid aspen plantations provide benefits with respect to biodiversity, as they support compositionally different assemblages of bryophytes, lichens, closed forest species and soil fungi.

National Red Lists are useful tools in establishing local conservation priorities. The threat status of Estonian lichens based on the IUCN system has been assessed twice, in 2008 and 2023. In the latest Red List, the proportion of species of elevated conservation concern, that is taxa belonging to the Near Threatened and threatened categories or having become regionally extinct in Estonia, was high (58%) while Least Concern (LC) species represented one-third (36%) of all taxa. Macrolichens were more threatened than microlichens. The Red List Index (RLI), illustrating the trends of species in their projected extinction risk, was calculated. The values were low (< 0.7 in 2023), thus indicating a heightened risk both for the set of all species and for macrolichens. More than half of all Estonian lichens are associated with woodlands and 54% of these species are of elevated conservation concern. Lichens preferring broad-leaved deciduous trees included more threatened than LC species, while among lichens preferring other deciduous or coniferous trees the proportion of LC species was higher than that of threatened taxa. Lichens inhabiting calcareous grasslands had the highest share (69%) of taxa of elevated conservation concern. Comparisons of national red-listed data with four selected countries (Czech Republic, Denmark, Finland and Sweden) revealed that the biggest overlaps of Estonian taxa of elevated conservation concern were with the Czech Republic and Finland.

The loss of ancient forests threatens many species. Effective nature conservation needs information on how forest availability in the surrounding landscape in space and time determines the diversity of multiple taxa. We explored the relationship between forest availability at different spatiotemporal scales and the diversity of various groups: vascular plants (woody species, ground layer), epiphytes (bryophytes and lichens), fungi (ectomycorrhizal, arbuscular mycorrhizal, pathogenic, saprotrophic), and carabid beetles. Besides the observed diversity, we also estimated dark diversity, i.e. suitable but absent species. Dark diversity is theoretically a sensitive metric in detecting ecosystem conditions as it is typically relatively large and contains susceptible species. We recorded the observed diversity by field sampling and soil DNA in 100 temperate ancient old-growth forest sites in southern Estonia; dark diversity was estimated for the same sites using species co-occurrence data. Forest availability estimates were obtained from four topographic maps (1900s-2010s) at the 0.5–5 km radius. The biodiversity of forest specialists was higher at larger historical forest availability at the spatial scale of 2–5 km radius. The diversity of light-demanding forest ecotone taxa mainly had negative relationships with young forests on previous agricultural lands (at 0.5–2 km radius). Dark diversity models were often more strongly associated with forest availability than observed diversity models. Dark diversity enhances our understanding of how current and historical forest availability affects local biodiversity. As young forests cannot provide suitable habitats for many forest-dwelling species, stable forest habitats must be preserved as source areas to enhance biodiversity.

Fragmented natural habitats, such as old-growth forests, have been often considered island-like systems. How-ever, whereas the isolation of real islands is mostly a function of their spatial arrangement, the biodiversity of old-growth forest patches is also affected by how well the surrounding suboptimal habitats, such as younger forests, can support the functional connectivity between the old-forest fragments. The latter topic remains largely unclear due to the lack of mechanistic knowledge about the processes behind species' affinity for old forest. Although in animal ecology, functional connectivity has often been investigated with mechanistic agent-based models, these have rarely been applied for passively dispersing organism groups. We used a pattern-oriented modeling approach by combining a spatially explicit agent-based model and an empirical biodiversity dataset of Estonian old-growth nemoral forest sites, to study how forests of different ages between the old-forest frag-ments are exploited by different passively or slowly dispersing functional groups. We found that the establish-ment of ground layer vegetation, epiphytes, ectomycorrhizal and pathogenic fungi is significantly restricted in the younger forests, whereas no clear difference between forest-age classes emerged for survival. Our results thus suggest that establishment, not survival, is the main process behind the species' affinity for old forest, concurring with studies that have demonstrated the importance of suitable microhabitat availability in older forests. We conclude that young secondary forests do not support the connectivity - and consequently, biodiversity - of many old-forest specific groups.

The dataset includes vascular plant, bryophyte and lichen species data and environmental data collected from 33 birch stands in Estonia representing three stand types with different restoration approach (birch plantations on previous agricultural land, naturally regenerated stands on previous agricultural land and birch stands on native forest land).

The effect of stand age on biodiversity in the stands of Populus tremula, a keystone tree species in boreal forests, has been insufficiently studied, although this knowledge is crucial for maintaining biodiversity in managed forests. We studied the assemblages of vascular plants, bryophytes and lichens from a chronosequence of aspen stands (n = 20) with an age from 8 to 131 years, aiming to identify the main patterns in species richness and composition. Altogether, 72 vascular plant species were found in the field layer and 17 species in the shrub layer. The total numbers of bryophyte and lichen species were 92 and 104, respectively. Overall, 2 vascular plant, 12 bryophyte and 9 lichen species were the taxa with a high conservation value. Sixteen lichens were regarded as management sensitive or focal species based on earlier studies, and 10 vascular plant species were hemeraphobic (severely disturbed by human activities). The effect of stand age on average species richness estimates depended on the studied species groups. Stand age had a negative effect on the average number of vascular plants, field layer species, apophytic vascular plants and epixylic lichens and a positive effect on the number of lichens, the number of epiphytic bryophytes and lichens and on bryophytes and lichens with a high conservation value. The compositional patterns of vascular plants, bryophytes and lichens strongly correlated with stand age. In addition, stand characteristics, soil properties and light conditions influenced the assemblages, although the direct effects were variable for different groups. The largest differences could be observed in vascular plant, bryophyte and lichen communities between young and old stands; for lichens, also mature and old stands differed significantly. Our results indicate that more than 60 years are required for the recovery of some species groups after clear cutting. At the same time, other species groups were either not negatively affected by clear-cutting or showed a higher richness in younger stands. Therefore, we conclude that the management of aspen stands should involve the combination of different management regimes on the landscape scale (variation from short to long rotations in different stands, maintaining retention trees and ceasing of clear-cutting in some stands). Our results also show that as second-storey Tilia cordata played an important role in maintaining biodiversity in the studied stands, this tree species needs to be preserved in forests where lime trees naturally grow as co-dominants.

The threat status of 161 lichenized species that were considered common in Estonia was assessed in 2021. For most of these species, it was the second Red List assessment using the IUCN system (the first such evaluation was performed in 2008). The main data sources for species occurrence were the records reported in 100 study sites located throughout the country during 2020, and the PlutoF biodiversity database. 125 species remained, according to the new assessment, in the category Least Concern (LC) and their populations are not under threat in Estonia at present. Two species were placed in the category Not Applicable (NA) because of systematic revisions while 33 species were assigned to the categories Endangered (EN), Vulnerable (VU) or Near Threatened (NT); one further species received the status Data Deficient (DD). Thus, the threat status has changed for 22% of the studied species that had generally been considered common in Estonia. The reasons for this change are variable but there is clear evidence that 26 species have become more threatened during last 12 years.

Less intensive harvesting methods (e.g., selection cutting, shelterwood cuttings) are recommended as alternatives to clearcutting for maintaining mature forest biodiversity in the process of forest regeneration. However, the long-term impact of low-intensity harvesting methods has rarely been studied. Our aim was to clarify the long-term effects of repeated selective cutting, thinning, and shelterwood cutting on the richness, abundance, and species composition of vascular plants, bryophytes, and lichens in Scots pine forests (Pinus sylvestris L.). Data were collected from 25 mature stands located in dry Podzols in southwestern Estonia with a known management history for the last 70 years. Altogether, 35 vascular plant, 41 bryophyte, and 78 lichen species were recorded, including five species with conservational value. Generally, the management history was not related to species richness, except a negative correlation with the species number of epiphytic lichens on conifer trees. In addition, the abundance of two lichen species from the genus Chaenotheca was lower in more frequently managed stands. Species richness and composition were most strongly affected by soil pH and light conditions. We conclude that long-term, low-intensity harvesting of Scots pine forests on nutrient-poor Podzols maintains suitable habitats for vascular plants, bryophytes, and lichens, confirming its suitability for sustainable forest regeneration.

Understanding the distribution of genetic patterns and structure is an essential target in population genetics and, thereby, important for conservation genetics. The main aim of our study was to investigate the population genetics of Usnea subfloridana, a widespread lichenised fungus, focusing on a comparison of genetic variation of its populations amongst three geographically remote and disconnected regions, in order to determine relationships amongst environmental data, variation in lichen secondary chemistry and microsatellite data in genotyped populations. In all, 928 Usnea thalli from 17 populations were genotyped using seven specific fungal microsatellite markers. Different measures of genetic diversity (allelic richness, private allelic richness, Nei's unbiased genetic diversity and clonal diversity) were calculated and compared between lichen populations. Our results revealed a low genetic differentiation of U. subfloridana populations amongst three distant areas in Estonia and also a high level of gene flow. The results support suggestion of the long-range vegetative dispersal of subpendulous U. subfloridana via symbiotic propagules (soralia, isidia or fragments of thalli). Our study has also provided evidence that environmental variables, including mean annual temperature and geographical longitude, shape the genetic structure of U. subfloridana populations in Estonia. Additionally, a weak but statistically significant correlation between lichen chemotypes and microsatellite allele distribution was found in genotyped specimens.

Ecosystem biomass, soil conditions and the diversity of different taxa are often interrelated. These relationships could originate from biogeographic affinity (varying species pools) or from direct ecological effects within local communities. Disentangling regional and local causes is challenging as the former might mask the latter in natural ecosystems with varying habitat conditions. However, when the species pool contribution is considered in statistics, local ecological effects might be detected.In this study we disentangle the indirect effects of the species pool and direct ecological effects on the complex relationships among wood volume, soil conditions and diversities of different plant and fungal groups in 100 old‐growth forest sites (10 × 10 m) at the border of boreal and nemoral zones in northern Europe.We recorded all species for different vegetation groups: woody and herbaceous vascular plants, terricolous and epiphytic bryophytes and lichens. Fungal communities were detected by DNA‐based analyses from soil samples. Above‐ground wood volume was used as a proxy of biomass. We measured soil pH and nutrient content and obtained modelled climate parameters for each site. Species pool effect was considered by dividing sites into boreal and nemoral groups based on community composition. In order to disentangle direct and indirect effects, we applied variation partitioning, and raw and partial correlations.We found many significant positive relationships among studied variables. Many of these relationships were associated to boreal and nemoral species pools, thus indicating that biogeographic affinity of interacting plants and fungi largely defines forest diversity and functioning. At the same time, several relationships were significant also after considering biogeography: woody plant and ectomycorrhizal fungi diversities with wood volume, many plant and fungal groups with each other, or with soil conditions. These direct ecological interactions could be considered in forestry practices to achieve both economic gain and maintenance of biodiversity.

Few studies have investigated the genetic diversity of populations of common and widespread lichenized fungi using microsatellite markers, especially the relationships between different measures of genetic diversity and environmental heterogeneity. The main aim of our study was to investigate the population genetics of a widespread and mainly clonally reproducing Usnea subfloridana at the landscape scale, focusing on the comparison of lichen populations within hemiboreal forest stands. Particular attention has been paid to the genetic differentiation of lichen populations in two geographically distinct regions in Estonia and the relationships between forest characteristics and measures of genetic diversity. We genotyped 578 Usnea thalli from eleven lichen populations using seven specific fungal microsatellite markers. Measures of genetic diversity (allelic richness, Shannon's information index, Nei's unbiased genetic diversity, clonal diversity, the number of multilocus genotypes, the number of private alleles, and the minimum number of colonization events) were calculated and compared between Usnea populations. Shared haplotypes, gene flow and AMOVA analyses suggest that unconstrained gene flow and exchange of multilocus genotypes exist between the two geographically remote regions in Estonia. Stand age, mean circumference of the host tree, size of forest site and tree species composition did not show any significant influence on allelic richness, Shannon's information index, Nei's unbiased genetic diversity, clonal diversity, the number of private alleles, and the minimum number of colonization events of U. subfloridana populations. Therefore it was concluded that other factors of habitat heterogeneity could probably have a more significant effect on population genetics of U. subfloridana populations.

The lichen genus Cetrelia represents a taxonomically interesting case where morphologically almost uniform populations differ considerably from each other chemically. Similar variation is not uncommon among lichenized fungi, but it is disputable whether such populations should be considered entities at the species level. Species boundaries in Cetrelia are traditionally delimited either as solely based on morphology or as combinations of morpho- and chemotypes. A dataset of four nuclear markers (ITS, IGS, Mcm7, RPB1) from 62 specimens, representing ten Cetrelia species, was analysed within Bayesian and maximum likelihood frameworks. Analyses recovered a well-resolved phylogeny where the traditional species generally were monophyletic, with the exception of Cetrelia chicitae and Cetrelia pseudolivetorum. Species delimitation analyses supported the distinction of 15 groups within the studied Cetrelia taxa, dividing three traditionally identified species into some species candidates. Chemotypes, distinguished according to the major medullary substance, clearly correlated with clades recovered within Cetrelia, while samples with the same reproductive mode were dispersed throughout the phylogenetic tree. Consequently, delimiting Cetrelia species based only on reproductive morphology is not supported phylogenetically. Character analyses suggest that chemical characters have been more consistent compared to reproductive mode and indicate that metabolite evolution in Cetrelia towards more complex substances is probable.

Trees are the only or main growth substrate for thousands of lichen species, including many endangered ones. The present study gives an overview of the diversity of red-listed (belonging to the IUCN categories CR, EN, VU and NT) lichens on Estonian trees based on nearly 1300 herbarium samples collected during ca. 150 years. According to the results, altogether 75 threatened and near-threatened lichen species are known from Estonian trees. The highest number of red-listed species are accounted for Fraxinus excelsior (34 red-listed species), followed by Quercus robur, Populus tremula, Betula spp., Picea abies and Acer platanoides (30 to 26 species per each host tree). In addition to the importance of different tree species as host trees for the red-listed lichens, we also discuss, taking into account the frequency of the tree species and predicted changes in the age structure of their stands in Estonia, the future perspectives of the epiphytes associated with them. Populus tremula can be considered as the best possible alternative phorophyte for the greatest part of threatened lichen species that are growing on temperate broadleaved trees.

The importance of single-species forest plantations in sustaining biodiversity could be bigger than expected. We described the diversity of lichens and bryophytes in 15 midterm (16- to 17-year-old) hybrid aspen (Populus tremula x Populus tremuloides) plantations in Estonia. Species richness and composition data were linked with environmental and landscape-scale variables. Altogether, 44 lichen and 37 bryophyte species were recorded from plantations; richnesses of bryophytes and lichens were positively correlated. Lichen species composition was significantly affected by landscape-scale parameters (distance to the nearest present forest, distance to the nearest forest continuously occurring in the same place since the 1930s, and forest area in the study plot vicinity in the 1930s). Bryophyte species composition was affected mainly by light conditions and forest area in the 1930s. Among lichens, the sexual crustose species functional group dominated in midterm plantations; appearance of asexual lichens of different growth forms is expected during the next years. Our results indicate the importance of long-term availability of good-quality forests as sources of propagules. Short-rotation hybrid aspen plantations can provide temporary habitats for forest species and thus in part contribute to preserving landscape-scale biodiversity, if they are close to possible colonization sources. Green-tree retention in plantations will probably raise the biodiversity value of those short-term communities.

Suomen Rupijäkälät. Edited by Soili Stenroos, Saara Velmala, Juha Pykälä and Teuvo Ahti. 2015. Norrlinia 28. Helsinki: Luonnontieteellinen Keskusmuseo Luomus. Pp. 454. Page size 260×180 mm. ISSN 0780-3214, ISBN 978-951-51-0837-1. Hard cover. Price: €96.00. - Volume 48 Issue 1

Recent taxonomic and DNA sequence-based studies in several groups of lichen-forming fungi have revealed incongruence between the morphological and molecule-based circumscriptions of species. While the cosmopolitan genus Usnea is well-known and easily recognized by the yellowish beard-like thallus with central cord, delimitation of many Usnea species is difficult due to the high variation and complexity of diagnostic characters. In this study, we assessed the monophyly of 18 species from section Usnea occurring in North America and Europe, including sorediate and sexually reproducing taxa with both pendent and shrubby thalli. Six nuclear markers (ribosomal internal transcribed spacer (ITS) and intergenic spacer (IGS), and protein-coding beta-tubulin, MCM7, RPB1 and RPB2) were sequenced for 144 samples. All analyzed loci show weak genetic structure and short branch lengths in single-locus topologies, suggesting recent diversification history of the sampled taxa. Concatenated, multi-locus analyses conducted in Bayesian and maximum likelihood frameworks, as well as coalescent-based species delimitation and species tree methods, recover several distinct clades, some represent traditional morphology-based species (Usnea cavernosa, U. praetervisa, U. silesiaca, U. wasmuthii), while others form clusters of two or more species (Usnea florida–U. subfloridana, U. fulvoreagens–U. glabrescens, U. barbata–U. chaetophora–U. dasopoga–U. diplotypus, U. barbata–U. intermedia–U. lapponica–U. substerilis). We propose synonymization of U. substerilis under U. lapponica. The status of several other species within intermixed clusters requires further evaluation with more extensive sampling and the inclusion of more variable markers before taxonomic consequences can be considered. A new species, Usnea parafloridana is described from Wisconsin, USA.

17 18 Very little is known whether and how air pollution impacts genetic diversity of 19 lichenized fungi that are well-known indicators of environmental quality. We studied 20 the genetic variation of eight Usnea subfloridana populations in Pinus sylvestris21 dominated boreal forest stands in southern Estonia, Northern Europe; four of these 22 populations were exposed to long-term dust pollutio n released from unpaved road. 23 The mean bark pH of lichen-phorophyte differed cons iderably between polluted and 24 unpolluted forest stands. We genotyped 274 Usnea thalli using nine specific fungal 25 microsatellite markers. Genetic variation measures w re calculated and compared 26 between populations from different habitats. Alleli c richness, Shannon's information 27 index, and genetic diversity of lichen populations were significantly higher in 28 unpolluted forest sites than in polluted forest sit es. We conclude that environmental 29 disturbances caused by alkaline dust pollution had negative impact on the genetic 30 variation of U. subfloridana, a common species of lichenized fungi. 31 32

Very little is known whether and how air pollution impacts genetic diversity of lichenized fungi that are well-known indicators of environmental quality. We studied the genetic variation of eight Usnea subfloridana populations in Pinus sylvestris-dominated boreal forest stands in southern Estonia, Northern Europe; four of these populations were exposed to long-term dust pollution released from unpaved road. The mean bark pH of lichen phorophyte differed considerably between polluted and unpolluted forest stands. We genotyped 274 Usnea thalli using nine specific fungal microsatellite markers. Genetic variation measures were calculated and compared between populations from different habitats. Allelic richness, Shannon's information index, and genetic diversity of lichen populations were significantly higher in unpolluted forest sites than in polluted forest sites. We conclude that environmental disturbances caused by alkaline dust pollution had negative impact on the genetic variation of U. subfloridana, a common species of lichenized fungi.