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.

Abandoned agricultural lands carry a legacy of soils contaminated with heavy metals from previous land use practices. Phytoremediation using fast-growing trees is widely used method for ecosystem restoration by accumulating heavy metals in aboveground biomass. In Northern Europe, where 1.8 to 2.6 million hectares of abandoned agricultural land can be afforested, the knowledge of fast-growing tree species' phytoremediation capacity is still poorly studied. This study examines the phytoremediation capacity after 20 years of afforestation of former agricultural lands with hybrid aspen plantations in hemiboreal Estonia, with a particular focus on the effects of different forest site type (Aegopodium, Dryopteris, Hepatica, and Oxalis) on heavy metal concentrations in topsoil and on bark and wood bioaccumulation factors. Soil, wood, and bark samples were collected from 24 sample plots to assess the allocation and accumulation of heavy metals in soil and biomass. The concentration of heavy metals in soil varied by site type, with waterlogged (Dryopteris) sites showing significantly higher levels of Cu, Fe, Ni, and Zn, whereas Cd and Mn were more concentrated in alkaline and dry (Hepatica) sites. The concentration of heavy metals in wood varied with tree size and age; smaller trees had significantly lower Cd, Cu, Fe, and Zn levels, while wood formed in the first decade of stand development showed higher concentrations of Cd, Cu, Mn, and Zn. Soil physical and chemical characteristics showed strong correlations with heavy metal bioaccumulation factors, particularly in bark. Soil pH negatively affected Mn bioaccumulation in all tree parts and Ni, Zn, and Cd in specific tissues, while soil P and available water content positively influenced metal uptake of trees. We found that the phytoremediation capacity of hybrid aspen plantations on former agricultural lands is controlled by soil properties and depends on tree size and age.

Afforestation of former agricultural lands is promoted to mitigate climate change. Yet, long-term effects of afforestation on soil quality remain insufficiently studied in Northern Europe. We evaluated changes in soil organic carbon (SOC), total nitrogen (Ntot), pH, and plant-available macro- and micronutrient (P, K, Ca, Mg, Cu, Mn) concentration in a 20-year period from early (5-year) to late (25-year) stand development period in hybrid aspen (Populus tremula & times; P. tremuloides) plantations on abandoned agricultural lands in Estonia. Soil samples were collected from 49 permanent plots when stands were 5, 15, and 25 years old in the A- and B-horizons. Linear mixed-effects models were applied to identify key stand- and soil-related predictors of change. Between 5 and 25 years, the A-horizon acidified by 0.3 pH units, while SOC (13.7%), Ntot (10.1%), Mg (17.0%), Cu (92%), and Mn (16.6%) increased. In the B-horizon, pH declined by 0.2 units, while Ntot (86%), Cu (192%), and Mn (35%) increased. Most changes occurred during early stand development (5-15 years), while pH, SOC, and Ntot stabilized between 15 and 25 years. Although A-horizon P remained stable, its decline with increasing height growth suggests faster-growing stands drew more heavily on this reserve. Initial soil property values dominated long-term trajectories in both horizons. Repeated soil monitoring over 20 years in hybrid aspen plantations revealed stabilization of SOC and nutrients.

Afforestation of former agricultural land with silver birch (Betula pendula Roth) is increasingly promoted in Northern and Eastern Europe, yet its long-term effects on soil–plant heavy metal dynamics remain insufficiently understood. We assessed heavy metal accumulation in soil and woody biomass (stemwood and bark) 20 years after afforestation of former agricultural land at 11 plantations. Eleven elements (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn) were initially determined, but subsequent analyses focused on five elements (Cr, Cu, Fe, Mn, and Zn) consistently detected above the limit of quantification. Metal allocation between stemwood and bark and the influence of soil physicochemical properties (pH, P, K, Corg, Ntot, bulk density and available water content) were analyzed. We also examined relationships between soil metal concentrations, tree growth, and the distribution of metals between stemwood formed at early-age (1–10 years) and late-age (11–23 years). Heavy metal accumulation was primarily governed by soil properties, with pH, P, and K showing important relationships with bioaccumulation patterns, while the role of Corg varied among elements and substrates. No statistically significant evidence was found that elevated soil metal concentrations inhibited tree growth. Within stems, metal concentrations varied with wood age, with higher levels observed in early-age wood. Overall, the findings highlight the importance of soil properties in shaping heavy metal dynamics in birch plantations and provide insight into long-term trace metal allocation in forest ecosystems established on former agricultural soils, supporting sustainable afforestation and the evaluation of woody biomass for potential bioenergy use.

Lichens are key components of forest ecosystems, contributing to biodiversity and serving as sensitive indicators of environmental change. Their post-fire dynamics can provide valuable insights into habitat resilience, succession processes, and the ecological impacts of fire. Understanding lichen responses to fire is therefore essential for informing conservation and management in fire-affected forests. This study addresses a key knowledge gap by investigating the recovery dynamics of lichen communities across a post-fire chronosequence in Scots pine-dominated forests in hemiboreal Estonia. Using a space-for-time substitution approach, we examined lichen community composition and richness in stands that experienced stand-replacing fires at different points in time-specifically 16, 27, 42, 73, 84 and 187 years since fire. Lichen communities were surveyed across different substrate types in 18 study plots (each 100 m2), alongside measurements of stand structure and soil characteristics. In total, 96 lichenized taxa (lichens) were recorded in post-fire forest stands, including 10 of high conservation value. The time since the fire was associated with shifts in lichen species composition, however it was not a significant predictor of community-level species richness or Shannon diversity, according to linear mixed models. Richness, diversity, and composition of lichens were significantly influenced by several stand characteristics. In particular, our results highlight the importance of substrate heterogeneity, particularly the availability of deadwood and tree species diversity, in maintaining lichen richness in fire-affected forests. To conserve lichen diversity across landscapes, it is crucial to retain a mosaic of successional stages, as different species thrive at different points along the post-disturbance gradient.

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.

In silviculture, tree species mixing is seen as a potential measure to increase ecosystem carbon (C) sequestration due to higher resulting productivity compared to monocultures. Currently, there is a lack of studies on how monocultures and mixtures of the two main boreal tree species, Norway spruce and silver birch, compare regarding C sequestration and storage in planted stands. We evaluated ecosystem C stocks, stand productivity and soil nutritional status in spruce and birch monocultures as well as mixed stands with 50/50 mixing proportion two decades after afforestation of abandoned agricultural lands with homogeneous soil fertility. We found that Norway spruce monocultures had the highest mean annual increment (MAI), highest ecosystem C stock, and the highest periodic annual increment (PAI). In silver birch stands, C was mostly stored in the stems of the trees, whereas Norway spruce monocultures had a significantly higher share of C stored in the canopy. While the growth of individual silver birches was not influenced by the stand type, Norway spruce was suppressed by the inter-specific competition in the mixtures, where the average tree stem MAI was 56% lower than in the monocultures. In general, the SOC and soil nutrient concentrations were similar in the mixed-species stands and monocultures. Spruce monocultures had a higher SOC stock in the forest floor. In conclusion, we did not confirm a higher productivity of mixed stands compared to monocultures, but different patterns of C allocations indicate the need for longer observations to identify the silvicultural system with the best climate benefit.

Coppice plantations have gained a high interest for biofuel production and carbon uptake in short rotation cycles. There is a limited knowledge how such intensive coppice management affects soil fertility and nutrients supply to maintain carbon sink. We studied ecosystem carbon and nutrients balance and allocation during a 5-year period in hybrid aspen coppice under different thinning methods in hemiboreal Estonia. The benchmark value for the changes was defined before the coppice emerged after the clear-cut of the previously planted hybrid aspen plantation. The studied systematical thinning treatments were as follows: corridor thinning with removal of 67% of the trees (CT), cross-corridor thinning with removal of 89% of the trees (CCT), and unthinned (UT) coppice. The UT and CT treatments resulted in a positive carbon balance at the ecosystem level. In all treatments, a decrease of soil acidity, organic C, total N, K, Mg and Mn contents, and an increase of soil Cu and B contents were observed in the 0–20-cm deep layer. The concentrations of leaf N, P, and K were higher in UT than in the two thinning treatments, indicating that the aspens had not entirely recovered from the changed root to shoot ratio 2 years after thinning, whereas the leaf mass fraction of medium- and small-sized trees had already increased. Bioenergy harvest from the UT site in a 5-year rotation would cause 5–18% removal of NPK from the total ecosystem pool. Overall, hybrid aspen coppice showed positive ecosystem carbon balance after the first 5-year period; however, further monitoring of soil properties is needed as we found decrease of soil organic C and nutrients concentrations in short term. Graphical Abstract

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.

Climate change accompanied by altered natural disturbance regimes threatens the resilience of boreal and hemiboreal forests. Bryophytes, an important part of plant biomass and diversity, fulfill numerous important functions in forests, thus markedly contributing to the resilience of these ecosystems. We studied abundance, richness, diversity and community composition of bryophyte species 20–21 years after wind disturbance in moderately damaged, heavily damaged and heavily damaged and subsequently salvage-logged stands; overmature forest stands with similar tree species composition were included in the study as a reference group. The community characteristics were linked with treatment and accompanying environmental variables. Altogether, 108 bryophyte taxa (81 mosses and 27 liverworts) were identified in study plots. We found that bryophytes responded to windthrow severity level and salvage logging in terms of species richness, diversity, and composition; diversity of microhabitats was the most important environmental variable explaining the variation in diversity metrics. Besides exhibiting greater overall species richness, uncleared wind-disturbed plots contained more bryophyte species with high conservational value as well, compared to salvage-logged and control plots. The largest number of bryophyte taxa was associated with deadwood substrates. Ordination analysis further emphasized the importance of deadwood substrate for liverworts. In order to fulfill the objective of biodiversity conservation, wind-disturbed forests should be left to recover naturally, to ensure a favorable status of all naturally occurring species and to improve the status of endangered and rare species. Retaining a proportion of surviving and/or wind-damaged trees while salvaging might also alleviate the unfavorable environmental conditions for bryophyte species while “lifeboating” some species through the following successional stages.

Fast-growing Populus spp. are well-acknowledged to restore contaminated soils from heavy metals in industrial areas. Thus far, there is no knowledge about the phytoremediation capacity of Populus spp. plantations in hemiboreal Estonia conditions to restore industrially polluted areas. The objective of this study was to assess the soil contamination rate of heavy metals (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb and Zn) and their uptake by mature hybrid aspen (Populus tremula × Populus tremuloides Michx.) in plantations in different industrial pollution areas (e.g. cement factory, oil shale mining). For the reference, industrially polluted plantations were compared with the low pollution area hybrid aspen plantation on former agricultural soil, which was influenced by fertilization and liming before afforestation. Twenty-one years after afforestation, soil samples were collected from the 0–10 cm topsoil layer. Aboveground biomass sampling was performed for bark and stem wood by ingrowth cores to separate wood formed during early (1–10 years) and late (11–21 years) stand development. Two decades after the afforestation of industrially polluted areas, the heavy metal concentrations in the soil were higher than the reference plantation and the standard reference for unpolluted soils in most cases. The highest concentrations of heavy metals in woody biomass were in the oil shale quarry spoil; because of poor growth, the accumulated pools in aboveground biomass were low. Cd differed from other metals and accumulated less in wood and more in bark. The concentration of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni and Zn) was higher in the first decade of stand formation (1–10 years) than in the last 10 years (11–21 years). High pools of heavy metals were accumulated in aboveground biomass in the reference plantation, indicating the considerable removal of heavy metal residues from the previous fertilization and liming source with harvest. Two decades of afforestation with hybrid aspen is too short for complete ecosystem restoration from heavy metals in industrially polluted areas.

Treating peat with nutrient-rich ash significantly increases the content of different nutrients in the substrate. Such ash treatment promotes the revegetation of abandoned extracted peatlands. The aim of this study is to analyze the effect of wood ash (WA15 = 15 t ha−1 and WA10 = 10 t ha−1), oil shale ash (OSA8 = 8 t ha−1), and a mixture of wood ash and oil shale ash (WA10 + OSA8) on the revegetation (vascular plants and bryophytes) of the Puhatu abandoned extracted peatland in NE Estonia. The following results were obtained: (1) The MRPP tests indicate that there are compositional differences between the treatments. (2) Altogether, 23 vascular plant and 3 bryophyte species were recorded in the treatment areas. (3) Nine years after these ash treatments, the highest mean vascular plant species richness was recorded for WA15 (3.8 ± 0.3) and the lowest for OSA8 (2.0 ± 0.3). (4) A greater number of vascular plant species was observed in the WA15 area. (5) Mixed ash and wood ash had a significant effect on the amount of biomass in vascular plants. Treating with either wood ash or a mixture of ash ensured the rapid formation of vascular plants and bryophyte layers, contributing to the restoration of the abandoned peatland ecosystem.

Background The cultivation of short-rotation tree species on non-forest land is increasing due to the growing demand for woody biomass for the future bioeconomy and to mitigate climate change impacts. However, forest plantations are often seen as a trade-off between climate benefits and low biodiversity. The diversity and composition of soil fungal biota in plantations of hybrid aspen, one of the most planted tree species for short-rotation forestry in Northern Europe, are poorly studied. Methods The goal of this study was to obtain baseline knowledge about the soil fungal biota and the edaphic, floristic and management factors that drive fungal richness and communities in 18-year-old hybrid aspen plantations on former agricultural soils and compare the fungal biota with those of European aspen stands on native forest land in a 130-year chronosequence. Sites were categorized as hybrid aspen (17-18-year-old plantations) and native aspen stands of three age classes (8-29, 30-55, and 65-131-year-old stands). High-throughput sequencing was applied to soil samples to investigate fungal diversity and assemblages. Results Native aspen forests showed a higher ectomycorrhizal (EcM) fungal OTU richness than plantations, regardless of forest age. Short-distance type EcM genera dominated in both plantations and forests. The richness of saprotrophic fungi was similar between native forest and plantation sites and was highest in the middle-aged class (30-55-year-old stands) in the native aspen stands. The fungal communities of native forests and plantations were significantly different. Community composition varied more, and the natural forest sites were more diverse than the relatively homogeneous plantations. Soil pH was the best explanatory variable to describe soil fungal communities in hybrid aspen stands. Soil fungal community composition did not show any clear patterns between the age classes of native aspen stands. Conclusion We conclude that edaphic factors are more important in describing fungal communities in both native aspen forest sites and hybrid aspen plantation sites than forest thinning, age, or former land use for plantations. Although first-generation hybrid aspen plantations and native forests are similar in overall fungal diversity, their taxonomic and functional composition is strikingly different. Therefore, hybrid aspen plantations can be used to reduce felling pressure on native forests; however, our knowledge is still insufficient to conclude that plantations could replace native aspen forests from the soil biodiversity perspective.

New forests on former agricultural land originate either from natural regeneration or active restoration. Previous research has compared biodiversity of naturally regenerated stands (NR) and plantations (PL), however, whether understory succession towards natural forests depends on stand type remains unknown. In this study, we used data from two monitorings on permanent plots (2011 and 2019) in PL (n = 11) and NR (n = 11) birch stands in Estonia to highlight successional changes in herb and bryophyte communities together with environmental changes. We further evaluated whether stand type influenced the recovery of forest specialists. We found an increase in tree growth characteristics, soil phosphorus and nitrogen content, no change in light conditions and a decrease in soil pH in both stand types. The amount of litter and deadwood was higher in NR in 2011. Herb richness increased from 123 to 130 and the number of bryophytes from 43 to 62. Stand types shared 50

Short-rotation forestry on former agricultural soils is a novel silvicultural system for producing woody biomass and mitigating climate change through CO2 uptake. However, tree plantations are often criticized for their low biodiversity and are sometimes referred to as "green deserts". We hypothesize that regarding biodiversity, the spontaneous natural regeneration of birch on former agricultural lands may be preferable to plantations. In this study, we compared soil fungal diversity and composition of fast-growing silver birch (Betula pendula Roth) plantations on former agricultural lands (n = 11) with naturally regenerated birch stands on former agricultural lands (n = 11) and native forest birch stands (n = 11) at the age of 21-28 years in hemiboreal Estonia. PacBio third-generation sequencing was carried out to analyse fungal species richness and composition in the soil samples. Sequencing of the fungal ITS region from 33 birch stand soil samples yielded 2830 fungal OTUs. We found that the total fungal species richness, per sample species richness, Shannon diversity index, and Pielou's evenness index did not differ significantly between the studied stand types. However, fungal community composition of both plantations and naturally regenerated stands on former agricultural lands differed significantly from the native forest stands, indicating that previous land use (agriculture vs. forest) had a stronger effect on fungal assemblages than the used regeneration method (planting vs. natural regeneration). The relative abundance of ectomycorrhizal and arbuscular mycorrhizal fungi was higher, and the relative abundance of saprotrophic fungi was lower in plantations than in native birch dominated forest stands. Soil chemical properties were found to be weak explanatory variables for describing soil fungal richness and composition. We identified historical surrounding forest cover, stand age, stand distance from a native forest, and soil Mg content as the factors significantly affecting soil fungal communities. These results indicate that fast-growing birch plantations established on former agricultural soils or naturally regenerated stands on such soils in the Northern Europe region harbour soil fungal diversity levels similar to those of same-aged native birch forests.

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.

Since fire frequency is expected to increase globally due to climate change, it is important to understand its effects on forest ecosystems. We studied the long-term patterns in species diversity, cover and composition of vascular plants and bryophytes after forest fire and the site-related factors behind them. Research was carried out in northwestern Estonia, using a chronosequence of Scots pine ( L.) stands, located on nutrient poor sandy soils, where fires had occurred 12, 23, 38, 69, 80 and 183 years ago. In every stand three 100 m vegetation plots were established to collect floristic and environmental information. The effects on floristic characteristics of time since fire, light, and soil variables were evaluated with linear mixed models, followed by backward variable selection. Compositional variation was analysed with non-metric multidimensional scaling, Multi-response Permutation Procedures, and Indicator Species Analysis. Altogether, 31 vascular plant and 39 bryophyte species were found in vegetation plots. The cover of the vascular plant and bryophyte layers increased with a longer time since fire. Soil and light variables impacted the richness of several vascular plant and bryophyte groups, whereas only the richness of liverworts and dwarf-shrubs correlated with time since fire. Considerable compositional differences were observed in vascular plant and bryophyte assemblages between recently vs. long-time ago burned stands. To conclude, time since fire significantly impacted compositional patterns of vascular plants and bryophytes in pine forests on nutrient poor soils, although time-related trends in species richness were less evident.Pinus sylvestris2

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 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 herbaceous understory is a key component of forest biodiversity. Moreover, it holds the capability to alter the dynamics and composition of the overstory. Severe wind disturbance changes the conditions in a forest ecosystem radically, causing alteration of understory characteristics as well. In this paper we analyze impacts of different storm damage levels and post-storm management on understory vegetation richness, diversity and composition in mixed spruce-hardwood forest stands located in hemiboreal Estonia. We examined understory vegetation in moderately damaged (n = 4), heavily damaged (n = 4) and post-storm salvage-logged stands (n = 4) 19-20 years after storm disturbance. Mature mixed spruce-hardwood forests were included as a reference group (n = 4). Study plots were also assessed regarding canopy openness, richness of microhabitats and coverage of woody species. A total of 98 herbaceous and 2 dwarf shrub taxa were found on 208 vegetation quadrats (1 m2 square each). Total coverage of the herb layer and species richness were greatest at salvage-logged plots when compared to other treatments. However, we found no significant effect of treatment on diversity (Shannon's H') nor evenness (Pielou's index) of herbaceous species. Our results indicate that approximately-two decades after wind disturbance, the understory communities differ from each other as a response to different storm damage levels and post-storm management. Compared to control plots, salvage-logged plots demonstrated greatest contrast regarding species composition. Salvage-logged plots had greatest light levels, but lowest estimates for microsite richness and woody species coverage. Moderately damaged plots demonstrated greatest within-group variation regarding light conditions and species composition. Our findings suggest that salvage logging after severe wind disturbance might induce delayed succession toward a closed canopy due to intense understory competition and lack of opportunity-providing microhabitats for tree regeneration.