Community dynamics of lignicolous lichens on standing deadwood in a 275‐year chronosequence

The loss of pristine old-growth boreal forest landscapes due to the intensive management for timber production has caused both a severe decline of forest biodiversity in Northern Europe as well as significantly altered their carbon stocks and dynamics. Understanding of the dynamics of old-growth forests is needed to evaluate the consequences of different forest management and conservation strategies on climate change mitigation and biodiversity conservation. It is increasingly suggested that integrated forest management and conservation planning is required to secure both biodiversity and carbon storage values. However, it is insufficiently known how closely these values coincide at the local level, i.e., whether the same structural and quality features in old-growth forests support both high biodiversity and carbon stock.The objectives of this study were, first, to explore the dynamics of stand growth and carbon sequestration in boreal old-growth forests and second, to investigate whether the occurrence of red-listed epiphytic forest lichens coincides with high carbon stock and structural features related to it. The study was based on an extensive repeated forest inventory dataset collected between 1990 and 2019 in southern Finland and a lichen inventory conducted during 2020 – 2021 at the same sites.The estimated volume of standing trees and deadwood were higher in the studied forest stands than in managed forests on average. Estimates of net primary production showed varying trends of carbon sequestration among the study plots. Stand gross growth increased by 50% during the study period. The standing volume remained stable because a large proportion of the biomass increment was allocated to deadwood. The study sites showed a high occurrence of red-listed epiphytic lichens. No relationship was found between the species richness of red-listed lichens and the aboveground carbon stock. However, a significant negative relationship was found between the number of red-listed lichen occurrences and carbon stock.  The species richness of red-listed lichens showed a strong unimodal response to the aboveground carbon stock change: the highest species richness was associated with intermediate carbon sinks.Our results highlight the major role of tree mortality driving the carbon dynamics of old-growth forests, with simultaneous benefits for deadwood-associated species. However, more research is needed on the stability of carbon stocks of forests in the face of shifting disturbance regimes due to climate change. While the species richness of red-listed epiphytic lichens had a neutral relationship with the aboveground carbon stock size, we observed fewer occurrences in carbon-rich forests, and lower species richness and occurrences in plots with large carbon sinks. Therefore, if climate benefits are sought with methods that increase stand density, negative impacts may be expected on lichen species that fare poorly in dense stands with low light. Additionally, high carbon sequestration in fast-growing stands may come at the expense of reduced biodiversity.In summary, this study supports the idea that old-growth forests provide considerable benefits regarding both climate change mitigation and biodiversity. Therefore, increasing the area of old-growth forests would simultaneously support these key goals.

Modern forestry has created stands with even age distribution of trees and fragmentation of the habitat. In boreal forests, the effects on biodiversity within many taxa need to be examined. We tested the hypothesis that species richness of foliose and fruticose lichens and spiders is positively related in the lower canopy of spruce (Picea abies) in forests with, or without, management in central Sweden. High species richness of lichens may increase the structural complexity of the microhabitat on spruce branches, and bring a higher species richness also in the spider community. In six areas, spruce branches were sampled in old-growth and managed boreal forest stands, respectively. Forest management did not affect the species richness of spiders or lichens, but an effect due to sampling area was found in the latter taxon. There was a significant covariation between species richness of lichens and spiders, and the hypothesised positive correlation was confirmed by separate analyses for each area and combining the probabilities. Moreover, regression analysis on mean values from each site revealed a positive relationship. We conclude that species richness of lichens and spiders covary on spruce branches for functional reasons, i.e. more lichen species promotes a more diverse spider community by increasing the structural heterogeneity. Our results might provide a ‘shortcut’ for assessing biodiversity in boreal forests.

Summary
\nConflicting evidence exists with respect to the putative effect of forest management on plant species diversity. Various published studies have concluded that primeval forests are not that species-rich and that forest management may increase species richness in certain cases. Yet, it appears that such conclusions have often been drawn from the comparison of production forests to reference forests with a management legacy, i.e. stands in which forest management ceased only a few decades ago. 
\nThe present study explores the impact of forest management on the diversity of vascular plants, bryophytes and lichens in Fagus sylvatica production forests in comparison to untouched primeval forests without any detectable management legacy in the western Carpathian Mountains, eastern Slovakia. This study in three production and three primeval forests also assesses the role of natural forest dynamics for species diversity and highlights the importance of height in the crown for the diversity and composition of epiphytic bryophyte and lichen communities. 
\nThe results demonstrate that forest management-related disturbances do not increase landscape-level vascular plant species richness in comparison to untouched primeval forests. Even though mean plot-level diversity (alpha-diversity) was higher in the production forests, rarefaction/extrapolation showed a similarly high landscape-level vascular plant diversity (gamma-diversity) in the primeval forests. Comparing the gamma-diversity of vascular plants in the initial, optimal and terminal stages with the production forests showed no significant differences between the three stages, and to the managed stands. In contrast, mean plot-level species richness of epiphytic cryptogams tended to be higher in the primeval forests. Rarefaction/extrapolation revealed an about 30 and 100 % higher bryophyte and lichen species richness (gamma-diversity) in the primeval forests, respectively. Comparing the epiphyte species diversity of the three stages with the production forests provided a significantly higher species richness in any stage of the forest development. Species turnover between plots (beta-diversity) was in the three systematic groups generally higher in the primeval forests, indicating a greater habitat heterogeneity and spatially more variable species composition of the communities. In addition to habitat diversity, habitat continuity is playing an essential role for maintaining a high higher species richness in the primeval forests. This is visible when comparing the epiphyte species richness on stems of a given stem diameter class between production und primeval forests. Epiphytic bryophyte and lichen diversity per stem size class was significantly higher in the primeval forests. This was attributed to the fact that trees with large diameters in the production stands rarely were older than 100 years, whereas the maximum age of large-sized beeches in the primeval forest was over 400 years. 
\nNatural forest dynamics affected the composition, but not the species richness, of the forest floor vegetation. Certain species showed a strong preference for either the initial, optimal or terminal stage, reflecting a high species turnover in primeval forests. Vascular species richness, however, did not differ between the three stages. In contrast to vascular plants, bryophyte and lichen species composition and richness on living trees and standing deadwood was strongly affected by natural forest dynamics. In general, epiphyte diversity increased from the initial to the terminal stage. Several bryophytes and lichens showed a distinct preference for one of the three stages, showing a close association with the ageing of trees and diameter growth. Of the detected bryophytes and lichens, 50 and 22 %, respectively, were significantly associated with large-diameter stems (≥70 cm). Bryophytes and lichens on lying deadwood were not affected by natural forest development, as no stage differences in the species richness were detectable.
\nThe analysis of the epiphytic bryophyte and lichen vegetation from the tree base to the crown demonstrated that sampling only the lowermost 2 m results in a marked underestimation of total epiphyte species richness in temperate broadleaf forests. More specifically, about 10 % of the overall bryophyte and 48 % of the lichen species pool would have been missed. The vertical change in the epiphytic bryophyte and lichen flora reflects the increase in light intensity, decrease in atmospheric moisture and the growing input of acids and nitrogen compounds when moving from the trunk base to the canopy. The vertical change in microclimate and microsite conditions also leads to distinct compositional variations of both studied groups along the height gradient. 
\nThis study clearly shows that forest management markedly reduces overall plant diversity and strongly impacts on the species composition in managed forests in comparison to untouched primeval forests. The higher plant species richness in primeval forests is mainly due to the much longer habitat continuity and greater habitat heterogeneity in horizontal and vertical direction, as generated by the processes of natural forest development. The disappearance of the terminal stage of forest development and a principal reduction in forest structural heterogeneity in production forests promote the loss of many plant species with close association to primeval forest attributes. Protecting the last remaining temperate primeval forests is thus an important element of a global strategy to conserve the biodiversity on earth.

Bryophytes and lichens are two main components of the forest floor vegetation. They provide essential ecosystem services, including nutrient recycling and water regulation. Here, we contrast the species richness, cover and community composition of forest floor bryophytes and lichens in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) dominated production forests. The study sites were located in the hemiboreal zone of southern Sweden, and represented early-, mid- and late rotation stands. Our aim was to examine the potential consequences for forest floor biodiversity from the decreasing use of Scots pine production forests in this region.Whereas Scots pine and Norway spruce stands did not differ in bryophyte cover, we found a higher cover of lichens in Scots pine stands, and highest in the intermediate aged stands. Also the species richness of lichens was higher in the Scots pine stands, while bryophyte species richness was higher in the Norway spruce stands. Differences in canopy cover and associated light transmittance to the forest floor appears to be important drivers for distinctive different forest floor communities in the Scots pine and Norway spruce stands, as revealed by Non-Metric Multidimensional Scaling (NMDS). Mean Ellenberg indicator values for bryophytes and lichens showed that species associated with Scots pine stands were characterized by their tolerance of brighter conditions, higher insolation, and better adaptation to a continental climate. Norway spruce stands instead had a comparably larger proportion of species tolerating lower light, but also indicators of higher available nutrient levels, humidity, and pH. The outcome of the Ellenberg indicator species analysis, as well as the larger cover of lichens,and adaptations to drought found among some mosses, revealed that forest floor communities are shaped by different environmental factors in Scots pine and Norway spruce production stands. These environmental differences, and the quantified shifts in forest floor communities identified in this study, indicate the large shifts in understory bryophyte and lichen species composition and abundance that is likely to occur if Scots pine stands are converted to Norway spruce.

Tree and stand level variables affecting the species richness, cover and composition of epiphytic lichens on temperate broad-leaved trees (Fraxinus excelsior, Quercus robur, Tilia cordata, Ulmus glabra, and U. laevis) were analysed in floodplain forest stands in Estonia. The effect of tree species, substrate characteristics, and stand and regional variables were tested by partial canonical correspondence analysis (pCCA) and by general linear mixed models (GLMM). The most pronounced factors affecting the species richness, cover and composition of epiphytic lichens are acidity of tree bark, bryophyte cover and circumference of tree stems. Stand level characteristics have less effects on the species richness of epiphytic lichens, however, lichen cover and composition was influenced by stand age and light availability. The boreo-nemoral floodplain forests represent valuable habitats for epiphytic lichens. As substrate-related factors influence the species diversity of lichens on temperate broad-leaved trees differently, it is important to consider the effect of each tree species in biodiversity and conservation studies of lichens.

Tree hollows often harbor animals and microorganisms, thereby storing nutritive resources derived from their biological activities. The outflows from tree hollows can create unique microenvironments, which may affect communities of epiphytic organisms on trunk surfaces below the hollows. In this study, we tested whether the species richness and composition of epiphytic bryophytes (liverworts and mosses) and lichens differ above and below tree hollows of Aria japonica and Cercidiphyllum japonicum in a Japanese temperate forest. The species richness of epiphytic bryophytes and lichens did not differ above and below hollows; however, the species composition of bryophytes differed significantly above and below hollows. Indicator species analyses showed that the moss species Anomodon tristis and the liverwort species Porella vernicosa were significantly more common below than above hollows, while the liverwort species Radula japonica and four lichen species, including Leptogium cyanescens, occurred more frequently above than below hollows. Our results highlight that tree hollows can produce unique microenvironments on trunk surfaces that potentially contribute to the maintenance of epiphytic diversity on a local scale.

Tree hollows often harbor animals and microorganisms, thereby storing nutritive resources derived from their biological activities. The outflows from tree hollows can create unique microenvironments, which may affect communities of epiphytic organisms on trunk surfaces below the hollows. In this study, we tested whether the species richness and composition of epiphytic bryophytes (liverworts and mosses) and lichens differ above and below tree hollows of Aria japonica and Cercidiphyllum japonicum in a Japanese temperate forest. The species richness of epiphytic bryophytes and lichens did not differ above and below hollows; however, the species composition of bryophytes differed significantly above and below hollows. Indicator species analyses showed that the moss species Anomodon tristis and the liverwort species Porella vernicosa were significantly more common below than above hollows, while the liverwort species Radula japonica and four lichen species, including Leptogium cyanescens, occurred more frequently above than below hollows. Our results highlight that tree hollows can produce unique microenvironments on trunk surfaces that potentially contribute to the maintenance of epiphytic diversity on a local scale.

With an increasing demand for forest-based products, there is a growing interest in introducing fast-growing non-native tree species in forest management. Such introductions often have unknown consequences for native forest biodiversity. In this study, we examine epiphytic lichen species richness and species composition on the trunks of non-native Pinus contorta and compare these to the native Pinus sylvestris and Picea abies in managed boreal forests in northern Sweden across a chronosequence of age classes. Overall, we recorded a total of 66,209 lichen occurrences belonging to 57 species in the 96 studied forest stands. We found no difference in species richness of lichens between stands of P. contorta and P. sylvestris, but stands of P. abies had higher total species richness. However, species richness of lichens in stands of P. abies decreased with increasing stand age, while no such age effect was detected for P. contorta and P. sylvestris. Lichen species composition progressively diverged with increasing stand age, and in 30-year-old stands all three tree species showed species-specific assemblages. Epiphytic lichen assemblages in stands of 30-year-old P. contorta were influenced by greater basal area, canopy closure, and average diameter at breast height, P. abies stands by higher branch density and canopy closure, and stands of P. sylvestris by greater bark crevice depth. Differences in lichen species richness and composition were mainly explained by canopy closure and habitat availability, and the greater canopy closure in mature P. abies stands promoted the colonization and growth of calicioid lichen species. Our results indicate that the non-native P. contorta have similar species richness as the native P. sylvestris. The main difference in lichen species richness and composition is between P. abies and Pinus spp. in managed forests of boreal Sweden.

The species richness and composition of lichens was quantified for four temperate broad-leaved tree species (Acer platanoides, Fraxinus excelsior, Tilia cordataandUlmus glabra) in boreo-nemoral forests on the talus slope of the North-Estonian limestone escarpment (North-Estonian Klint). Thirteen study sites were distributed along the klint on a west to east gradient. The effects of tree and stand characteristics and geographical location of a stand on composition and diversity of epiphytic lichens were evaluated by multivariate analyses (DCA, CCA, pCCA) and by general linear mixed models (GLMM). Tree level variables (e.g. bark pH, bryophytes cover and host tree species) explained the largest fraction of the variation in lichen species composition. However, species richness and composition were significantly influenced also by the unique habitat conditions of klint forest (length of the forest fragment, proximity of the stand to the sea and height of the escarpment). A significant correlation between stand locality and lichen diversity on the tree bole was found which is most likely related to local air pollution gradients caused by alkaline cement dust and acid pollutants in the north-eastern part of Estonia.

Comparing the plant diversity of paired beech primeval and production forests: Management reduces cryptogam, but not vascular plant species richness

Tree species traits are the predominant control on the decomposition rate of tree log bark in a mesic old-growth boreal forest

AimNatural disturbances influence forest structure, successional dynamics and consequently, the distribution of species through time and space. We quantified the long‐term impacts of natural disturbances on lichen species richness and composition in primary mountain forests, with a particular focus on the occurrence of endangered species.LocationTen primary mountain spruce forest stands across five mountain chains of the Western Carpathians, a European hotspot of biodiversity.MethodsLiving trees, snags and downed logs were surveyed for epiphytic and epixylic lichens in 57 plots. Using reconstructed disturbance history, we tested how lichen species richness and composition was affected by the current forest structure and disturbance regimes in the past 250 years. We also examined differences in community composition among discrete microhabitats.ResultsDead standing trees as biological legacies of natural disturbances promoted lichen species richness and the occurrence of threatened species at the plot scale, suggesting improved growing conditions for rare and common lichens during the early stages of recovery post disturbance. However, high‐severity disturbances compromised plot‐scale species richness. Both species richness and the number of old‐growth specialists increased with time since disturbance (i.e., long‐term uninterrupted succession). No lichen species was strictly dependent on live trees as a habitat, but numerous species showed specificity to logs, standing objects or an admixture of tree species.ConclusionsLichen species richness was lower in regenerating, young and uniform plots compared with overmature and recently disturbed areas. Natural forest dynamics and its legacies are critical to the diversity and species composition of lichens. Spatio‐temporal consequences of natural dynamics require a sufficient area of protected forests for provisioning continual habitat variability at the landscape scale. Ongoing climatic changes may further accentuate this necessity. Hence, we highlighted the need to protect the last remaining primary forests to ensure the survival of regionally unique species pools of lichens.

Retention forestry is a commonly used approach to include biodiversity conservation in forest management of production forests. Tree-related microhabitat (TreM) assessment is suggested as a good practice for the selection of habitat trees to retain. TreMs are small structures on living or dead trees that provide living substrates, shelter, breeding places, or food sources for various groups of organisms, therefore, they can be a good indicator of the presence of forest-dwelling species. However, the knowledge linking bryophyte and lichen species diversity with TreMs is still scarce. In this study, TreMs and bryophyte and lichen species composition were assessed on living retention trees in 39 young forest stands (10–20 years post-cut) in Latvia to test whether the richness of epiphytes on retention trees up to 2 m height is related to the number of TreM types. There was a strong positive correlation between the total number of TreMs and lichen richness on Betula pendula (Rs = 0.66; p < 0.001), a moderate positive correlation on Alnus glutinosa (Rs = 0.56; p = 0.040), but no such link was found for other evaluated species. Trees with TreMs—foliose and fruticose lichens and dead branches–hosted more lichen species than trees without these TreMs. The number of bryophyte species on a tree was explained mainly by tree species, and bryophyte richness did not significantly correlate with the total number of TreMs. These findings suggest that retention trees of diverse species and with a high number of TreMs can contribute to maintaining greater species richness of epiphytic bryophytes and lichens.

Landscape structure, habitat fragmentation, and the ecology of insects

The article describes the results of studies of the factors affecting lichen diversity in 46 manor parks of the region of Pskov. The investigated parks were founded in the end of XVIII – beginning of XX centuries. Twenty of them are fragmented and currently occupy less than 5 ha, the area of nine parks varies from 5 to 10 ha, those preserved within historical boundaries cover from 11 to 100 ha. Manor parks are situated both within the settlements’ boundaries (31 parks) and outside the settlements either bordering forest (12) or agricultural lands (3). Ten of the former border the forests. During the study 166 lichen species were identified. Statistical methods were performed to investigate the factors affecting lichen diversity in manor parks. Linear regression analysis was used to examine the dependence of the lichens species number on the park age/date of park creation (dispersion pattern), area of the parks (box plot), substrata diversity (dispersion pattern), and the dependence of the epiphytic lichens species number on tree and shrub species diversity (dispersion pattern). With the biserial correlation coefficient the impact of the settlement and the presence of the surrounding natural forests was calculated. Correlation analysis was performed to demonstrate the colligation between lichen species composition of the parks located in different subzones of forest zone in the region of Pskov. Our findings show that the number of lichen species depends on the park area (p = 0,0315), the variety of substrate types (p ˂ 0,001), and the variety of trees and bushes planted (p ˂ 0,001). The date of park creation and the presence of the surrounding natural forests do not influence the species diversity of lichens. We reveal that the location of the parks in a specific subzone of forest zone (southern taiga and mixed coniferous-broad-leaved forest) has no significant effect on the lichen species composition. The species richness of lichens tends to decrease in parks located within the settlements. The data obtained indicate not only the similarity of the species composition of lichens in the studied communities, but also the long-term development of lichen park communities in comparable climatic and landscape conditions.