The effects of stand structure on ground-floor bryophyte assemblages in temperate mixed forests

The effect of tree species composition, stand structure characteristics and substrate availability on ground-floor bryophyte assemblages was studied in mixed deciduous forests of Western Hungary. Species composition, species richness and cover of bryophytes occurring on the soil and logs were analysed as dependent variables. The whole assemblage and functional groups defined on the basis of substrate preference were investigated separately. Substrate availability (open soil, logs) was the most prominent factor in determining species composition, cover and diversity positively, while the litter of deciduous trees had a negative effect on the occurrence of forest floor bryophytes. Besides, bryophyte species richness increased with tree species and stand structural diversity, and for specialist epiphytic and epixylic species log volume was essential. Sapling density and light heterogeneity were influential on bryophyte cover, especially for the dominant terricolous species. Many variables of the forest floor bryophyte community can be estimated efficiently by examining stand structure in the studied region. Selective cutting increasing tree species diversity, stand structural heterogeneity and dead wood volume can maintain higher bryophyte diversity in this region than the shelter-wood system producing even-aged, monodominant, structurally homogenous stands.     

Forest and substrate type drive bryophyte distribution in the Alps

Understanding the main factors driving bryophyte communities in forests is a worthwhile research area as it provides a framework within which to evaluate effective management options. Previous studies elucidated the role of forest structure, substrate, and climate, but their effect in a wide environmental context encompassing several types of forests is still unclear. The aim of this study was to assess the effect of climate, stand structure, substrates (tree trunks, deadwood, forest floor), and different forest types for species richness, species composition, and cover of bryophytes. Seven different types of Alpine forests dominated by spruce, larch-stone pine, silver-fir, Scots pine, oak, beech, and alder were selected. Bryophytes were sampled on tree trunks, deadwood, and forest floor. The importance of forest type, substrate, climate, and forest structure was determined by variance partitioning. Species richness and species composition were best explained by substrate (respectively 13% and 11%) and by forest type (respectively 13% and 11%). The bryophyte cover was primarily explained by the forest type (24%), and to a lesser extent by the climatic factors and stand structure. Overall, these results suggest that in this region ecologically based forest management might focus their efforts in protecting all the forest types and associated substrates. This means that forests of less economic value should also be preserved, and that acceptable silvicultural options should pay attention to the naturally available substrates. Too often, deadwood availability was a limiting substrate for bryophytes.     

Change in the bryophyte diversity and species composition of Central European temperate broad-leaved forests since the late nineteenth century

The diversity and species composition of the bryophyte flora colonizing the forest floor, live trees and deadwood in semi-natural broad-leaved forests of northern Germany was compared between a recent survey in 2013 and historical records from around 1900. The survey was based on the comparison of presence/absence data and their interpretation with help of ecological indicator values. Total species richness has declined in bryophytes growing on the forest floor but not in the other guilds, whereas a dramatic species turnover was found for all three guilds. This turnover was apparently primarily driven by the increased atmospheric load of reactive nitrogen from anthropogenic emissions. Sensitive species were replaced by more eutrophication-tolerant bryophytes; liverworts are overrepresented among the sensitive and thus declining species. Promotion of the competitive strength of vascular plants due to increased nitrogen levels is the likely cause of the reduction of bryophyte species richness on the forest floor. Former acidification by high atmospheric sulfur dioxide loads has left an imprint in the bryophyte vegetation by having favored acidophytic species and discriminating against basiphytic species. An increase in the mean indicator value for temperature suggests a beginning effect of climate warming on the bryophyte vegetation. Change in forest structure had an apparently smaller imprint on the bryophyte diversity of the studied semi-natural forests than atmospheric chemistry and climate. In this respect, bryophytes differ from the ecologically similar lichens, where published studies from the same region showed a dramatic decline of species richness and a stronger susceptibility to forest management.     

Environmental drivers of ectomycorrhizal communities in Europe's temperate oak forests

Ectomycorrhizal fungi are major ecological players in temperate forests, but they are rarely used in measures of forest condition because large‐scale, high‐resolution, standardized and replicated belowground data are scarce. We carried out an analysis of ectomycorrhizas at 22 intensively monitored long‐term oak plots, across nine European countries, covering complex natural and anthropogenic environmental gradients. We found that at large scales, mycorrhizal richness and evenness declined with decreasing soil pH and root density, and with increasing atmospheric nitrogen deposition. Shifts in mycorrhizas with different functional traits were detected; mycorrhizas with structures specialized for long‐distance transport related differently to most environmental variables than those without. The dominant oak‐specialist Lactarius quietus, with limited soil exploration abilities, responds positively to increasing nitrogen inputs and decreasing pH. In contrast, Tricholoma, Cortinarius and Piloderma species, with medium‐distance soil exploration abilities, show a consistently negative response. We also determined nitrogen critical loads for moderate (9.5–13.5 kg N/ha/year) and drastic (17 kg N/ha/year) changes in belowground mycorrhizal root communities in temperate oak forests. Overall, we generated the first baseline data for ectomycorrhizal fungi in the oak forests sampled, identified nitrogen pollution as one of their major drivers at large scales and revealed fungi that individually and/or in combination with others can be used as belowground indicators of environmental characteristics.     

Spatial patterns in seed bank and vegetation of semi-natural mountain meadows

Soil seed bank composition and vegetative spatial patterns were studied in four mountain meadow communities in the Broto Valley (N. Spain), in order to analyse the differences that might exists between the two life forms. Soil and vegetation samples were taken at 1 m intervals from 10 m × 10 m quadrats in each meadow in one-year study. The spatial distribution of species was analysed along with the calculation of an autocorrelation coefficient which takes account of the relative position of samples: (Moran’s I). The results indicate that the abundance of the majority of the species in the seed bank and in the vegetation are randomly distributed, the percentage of species with a clumped distribution only exceeds 35% in the vegetation of one meadow and none of the taxa identified showed a uniform spatial organisation. The species that were distributed in the seed bank in a clumped pattern in more than one meadow were those of the pioneer species (Anagallis arvensis, Centaurium erythraea, Lamium purpureum and Stellaria media). All of these formed long-term persistent seed banks but were absent in the established vegetation in these meadows. According to the results, there exist not only differences between the spatial distribution of the species present in the same community, but also, that some species change their pattern of distribution according to the life form and to the grassland type in which they are found.     

Causes of the large variation in bryophyte species richness and composition among boreal streamside forests

Questions: Boreal forests along small streams are bryophyte diversity hotspots because they are moist, productive and relatively high pH. Do these factors also explain the large differences in species richness and species composition found among streamside sites? Do the species of species‐poor sites represent nested subsets of the species of more species‐rich sites? How do the results apply to conservation? Location: Forests along small streams in mid‐boreal Sweden. Methods: Survey of the flora of liverworts and mosses and habitat properties, including calculation of a pH‐index based on species indicator values, in 37 sites (1000‐m² plots). Results: The number of bryophyte species per plot ranged from 34 to 125. Neither soil moisture nor basal area of trees (a proxy for productivity) correlated significantly with species richness and composition, whereas pH‐index and cover of boulders did. Species richness and composition were more strongly correlated with pH‐index for mosses than for liverworts. The richness and composition of bryophyte species most frequently found on moist ground, stream channel margins and, most unexpected, woody debris were all more strongly associated with the pH‐index than with other habitat properties. Although species composition was significantly nested, there was still some turnover of species along the first ordination axis. Conclusions To attain high numbers of species, streamside forests need to have boulders and at least pockets with higher soil and stream‐water pH. The number of Red list species was weakly correlated with total species richness and the most species‐rich sites contained many species found more in non‐forest habitats. Hence, bryophyte conservation in streamside forests should not focus on species‐rich sites but on the quality and quantity of substrate available for assemblages of forest species that are strongly disfavoured by forestry.     

Plant species diversity in abandoned coppice forests in a temperate deciduous forest area of central Japan

We investigated plant species diversity as it related to stand structure and landscape parameters in abandoned coppice forests in a temperate, deciduous forest area of central Japan, where Fagus crenata was originally dominant. The species occurring in the study plots were classified into habitat types based on a statistical analysis of their occurrence bias in particular habitats (e.g., primary forest, coniferous plantation) in the landscape studied. The relationships between stand structure, which reflected the gradient of management, and forest floor plant species diversity (H and J) and richness (number of species per unit area) were not significant. However, these factors did influence the forest floor plant composition of the different types of habitat. According to the multiple regression analysis, species diversity and the richness of forest floor plants was affected by landscape parameters rather than by stand structure. For trees, species richness was mainly affected by the relative dominance of F. crenata, which is one of the stand structure parameters that decreases with intensive management. This is probably because many of the tree species that are characteristic of coppice forests increase after F. crenata have been eliminated by management; these species are not dominant in the original forest, where they are suppressed by F. crenata, the shade-tolerant dominant species. The species diversity (H and J) of trees was positively correlated with some landscape parameters, including the road density around the study plot, which may be associated with the intensity of management activity. The number of disturbance-tolerant species increased with increasing road density. Stand structure mainly affected disturbance-intolerant forest floor plant species and disturbance-tolerant tree species. Thus, the species diversity responses differed between forest floor plants and trees. The impact of forest management on species diversity was more prominent for forest floor plants.     

Climate and pH as determinants of vegetation succession in Central European man‐made habitats

Questions: (1) What are the most important abiotic environmental variables influencing succession in central European man‐made habitats? (2) How do these variables interact with one another and with variation in community properties? Location: Central, western and southern parts of the Czech Republic. Habitats included old fields, urban sites, spoil heaps after coal mining, sites at water reservoirs, extracted sand pit and peatland and reclaimed sites in areas deforested by air pollution. Methods: We investigated vegetation patterns on 15 succes‐sional seres, sampled by the same methods. Time of succession over which the data were available ranged from 12 to 76 years. The cover of vascular plant species (in %) was estimated in 5 m × 5 m plots. The relationships between vegetation characteristics (species composition, total cover, cover of woody species, species number and rate of dominant species turnover) and 13 abiotic site factors, including climatic and soil variables, were tested using CCA ordination and regression models. Results: Substratum pH, the only substratum characteristic, and climate were the environmental variables significantly affecting the vegetation patterns in the course of succession. The rate of succession, measured as the turnover of dominant species, was significantly more rapid in lowland than in mountain climates. On alkaline soils, species numbers in succession increased towards warmer climates. However, acid soils prevented any increase in species numbers, regardless of the climate. Surprisingly, forms of nitrogen and contents of C, P and cations did not exhibit any significant effect on the vegetation characteristics studied. Conclusions: Our approach, to compare a number of seres, can contribute not only to our understanding of succession, but also to help restoration projects to predict vegetation change because the crucial environmental variables, as identified by this study, are easy to measure.     

Ecological perspectives for the restoration of plant communities in European temperate forests

Simultaneously with increasing afforestation efforts in western Europe, among conservationists the consciousness is growing that protecting areas to conserve biodiversity will not be sufficient in the long term, and that also the ecological restoration of more or less severely altered areas will be necessary. The probability that recently established forest stands develop towards their ecological reference (i.e. ancient forest) depends largely on the possibility of the target species to colonize them. We focused on the colonization ability of forest plant species and particularly on so-called ancient forest plant species. Major constraints for ecological forest restoration are the spatial characteristics of the target site (isolation, shape and area), imposing dispersal limitations, and in the duration and intensity of the historical land use, leading to changes in habitat characteristics influencing recruitment probability. We reviewed the ecological literature with respect to these constraints and conclude that it takes at least a century to restore the understorey layer of recent forests, even when the target stand is adjacent to a well-developed ancient forest. Both recruitment and dispersal limitation of the target species are responsible for this. Newly established forests should therefore be situated at a minimal distance of the ancient forest source. In other cases, forest plant species will not be able to colonize the newly established forest on a measurable time scale and artificial introduction of forest plant species can be taken into consideration. The negative effects of habitat characteristics, and mainly high soil nutrient values in the recent forest stand can be mitigated by soil nutrient lowering measures. Disturbances in the recent forest should be minimized to maintain a high canopy closure level, preventing light demanding, high competitive species from establishing a stable population. An additional negative consequence of soil disturbances is that it stimulates germination of species from the soil seed bank, which is mainly composed of highly competitive or ruderal species.     

The influence of environmental factors and management methods on the vegetation of mesic grasslands in a central European mountain range

We examined how environmental factors combined with the diverse ways of the extensive management of mesic mountain grasslands affect species composition and diversity in the Polish part of Central Sudetes Mts. Based on the data from 100 research plots altitude, organic matter content and exchangeable magnesium in the soil, as well as the maximum soil water capacity and amount of sand fraction significantly affected species composition. Among the management methods, a significant effect on the differentiation of species composition was observed following the cessation of usage and mowing. Mown meadows had the highest share of forbs in the biomass, whereas those abandoned ones were dominated by tall and expansive grasses, mainly Calamagrostis epigejos. The species richest grasslands occurred in areas with soils of high water capacity, containing high concentrations of calcium and low amounts of total nitrogen. No significant effect of management methods on the total number of species as well as on the number of forb species was observed. Mown pastures had the highest mean value of the Shannon–Wiener diversity index.     

Vertical stratification of the termite assemblage in a neotropical rainforest

The importance of termites as decomposers in tropical forests has long been recognized. Studies on the richness and diversity of termite species and their ecological function have flourished in more recent times, but these have been mostly conducted in a thin stratum within a standing man’s reach. Our aims were to evaluate the specific richness and composition of the termite assemblage in the canopy of a tropical rainforest and to determine its originality with respect to the sympatric ground-level fauna. We conducted systematic searches for canopy termites, together with conventional sampling of the sympatric ground-level fauna, in the San Lorenzo forest, Panama. We hypothesized that (1) the canopy accommodates two categories of wood-feeding termites (long-distance foragers and small-colony “one-piece” species) and possibly soil-feeders in suspended soil-like habitats; (2) due to the abundance of soil-feeders, the overall diversity of the ground fauna is higher than that of the canopy; (3) differences in microclimate and resource accessibility favour vertical stratification among wood-feeders. Sixty-three canopy samples yielded ten species of termites, all wood-feeders. Five of these were not found at ground level, although a total of 243 ground samples were collected, representing 29 species. In addition to long-distance foragers (Microcerotermes and Nasutitermes spp.) and small-colony termites (mostly Kalotermitidae), the canopy fauna included Termes hispaniolae, a wood-feeding Termitidae from an allegedly soil-feeding genus, living in large dead branches. Soil-feeders were absent from the canopy, probably because large epiphytes were scarce. As predicted, the ground fauna was much richer than that of the canopy, but the species richness of both habitats was similar when only wood-feeders were considered. Vertical stratification was strongly marked among wood-feeders, as all common species, apart from the arboreal-nesting Microcerotermes arboreus, could unequivocally be assigned to either a ground or a canopy group. The canopy, therefore, contributes significantly to the total species richness of the termite assemblage, and the diversity, abundance and ecological importance of canopy termites in tropical rainforests may be higher than previously recognized.Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at .     

Influence of tree age, tree size and crown structure on lichen communities in mature Alpine spruce forests

Testing the relations between tree parameters and the richness and composition of lichen communities in near-natural stands could be a first step to gather information for forest managers interested in conservation and in biodiversity assessment and monitoring. This work aims at evaluating the influence of tree age and age-related parameters on tree-level richness and community composition of lichens on spruce in an Alpine forest. The lichen survey was carried out in four sites used for long-term monitoring. In each site, tree age, diameter at breast height, tree height, the first branch height, and crown projection area were measured for each tree. Trees were stratified into three age classes: (1) <100 years old, immature trees usually not suitable for felling, (2) 100–200 years old, mature trees suitable for felling, and (3) >200 years old, over-mature trees normally rare or absent in managed stands. In each site, seven trees in each age class were selected randomly. Tree age and related parameters proved to influence both tree-level species richness and composition of lichen communities. Species richness increased with tree age and related parameters indicative of tree size. This relation could be interpreted as the result of different joint effects of age per se and tree size with its area-effect. Species turnover is also suspected to improve species richness on over-mature trees. Similarly to species richness, tree-level species composition can be partially explained by tree-related parameters. Species composition changed from young to old trees, several lichens being associated with over-mature trees. This pool of species, including nationally rare lichens, represents a community which is probably poorly developed in managed forests. In accordance to the general aims of near-to-nature forestry, the presence of over-mature trees should be enhanced in the future forest landscape of the Alps especially in protected areas and Natura 2,000 sites, where conservation purposes are explicitly included in the management guidelines.     

Tree and stand level variables influencing diversity of lichens on temperate broad-leaved trees in boreo-nemoral floodplain forests

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. Nomenclature Randlane et al. (2007) for lichens; Leht (2007) for vascular plants.     

Local and regional trends in the ground vegetation of beech forests

We sampled moss and vascular forest vegetation in five ancient beech forests from northwest France, embracing in each a wide array of environmental conditions. Indirect (PCA) and direct (RDA) gradient analysis were used to discern local and regional ecological factors which explain the observed variation in species composition. Our results point to a global factor encompassing a large array of soil and light conditions, unravelled when local particularities of studied forests are singled out. The humus form, numerically expressed by the Humus Index, explains a large part of the observed variation in ground vegetation. Our study confirmed opposite trends in vascular and moss species richness according to humus condition. Ecological factors to which vascular and moss forest species respond at the regional level can be estimated directly in the field by visually inspecting humus forms and vegetation strata despite of the confounding influence of local factors.