Forest Floor Bryophytes Research Articles

Nest building in titmice Paridae: Selectivity in bryophyte use.

In many bird species, reproductive success is dependent on nest quality. However, detailed data on nest composition are scarce, and quantitative analyses have generally used only rough categories, without species identification. Bryophytes dominate the nests of many passerine bird species, but little is known about whether birds have preferences for certain species. In this study, we determined the bryophyte species composition in nests of blue tits Cyanistes caeruleus and great tits Parus major in a forest near Oslo, Norway. We also sampled the abundance of the bryophyte species in plots on the forest floor surrounding a subset of the great tit nests. Blue tits and great tits both used 15 bryophyte species as nest materials, mainly the same pleurocarpous species but in different proportions. The tits preferred highly branched bryophyte species, i.e., Pleurozium schreberi, Rhytidiadelphus squarrosus, and Sanionia uncinata but avoided common forest floor bryophyte species that are sparsely branched. Great tits clearly collected bryophyte species selectively. We also found that bryophyte species content in great tit nests in the same nest box in different years was very similar. Our results also indicated that the great tits collected bryophyte nest materials close to their nests, mostly within 5m, supporting the view that collecting nest materials is costly. We review several hypotheses to explain why the tits prefer certain species of bryophytes as nest materials. These include handling costs and their suitability as structural materials. We recommend field experiments to test specific hypotheses and to study whether preferences are heritable.

Biogeographical patterns of community-level content of N and P and their stoichiometric ratios in subtropical forest floor bryophytes

• Biogeographical patterns of nutrients for bryophytes remain largely unknown. • Relationships between bryophyte nutrients and environmental factors were calculated. • Bryophyte N and P content increased with increasing elevations and decreasing MAT. • Nutrient content of bryophytes and those of soil were positively associated. • Soil nutrient content and MAT were more important determinants of bryophyte N and P. With special phylogenetic status, life history, morphology, adaptations, and ecophysiological strategies, bryophytes differ from vascular plants in terms of the requirement, uptake, allocation, and releasing rate of nutrients. However, biogeographical patterns of nutrients for bryophytes remain largely unknown. The present study determined and calculated the community-level carbon (C), nitrogen (N), and phosphorus (P) content and their stoichiometric ratios of the photosynthetic tissues of the subtropical forest-floor bryophytes collected from 295 sites in Sichuan province, China. We aimed to find out: 1) the geographical patterns in the content of N and P and the stoichiometric ratio of N to P for bryophytes; 2) the effects of environmental factors (climate, soil nutrient content, and stand attributes); and 3) the driving factors. We found that the bryophytes collected from the western plateau had a higher P content and a lower N:P than those from the eastern basin. The bryophytes’ N and P content generally increased with increasing elevations and decreasing mean annual temperature (MAT) and potential evaporation, while the N:P ratio decreased with decreasing elevations. But these patterns were scale-dependent. Nutrient content of bryophytes and those of soil were positively associated. Bryophyte N content was unrelated to mean annual precipitation (MAP) and stand attributes, while P content was negatively related to MAP and shrub and herb cover. Among the environmental factors at play, soil nutrient content and MAT were more important determinants of bryophyte N and P content than MAP and stand attributes. This study contributes to a better understanding of the relationships among environmental factors and bryophyte N and P at a basin-mountain transition zone and provides evidence to quantitatively assess the ecological role of bryophytes in nutrient cycling in the ecosystem.

Central European forest floor bryophytes: Richness, species composition, coexistence and diagnostic significance across environmental gradients of forest habitats

Bryophytes are good indicators of habitat conditions and show associations with different types of forests. In this study we assessed the diversity and distribution of forest floor bryophytes across a wide gradient of Central European forests using vegetation records from the Polish Vegetation Database (PVD). We identified forest types using the Habitat Classification of the European Nature Information System (EUNIS) – the main comprehensive pan-European hierarchical classification of habitats. Based on 9258 plots containing bryophyte species and representing 20 forest types, we assessed the species number and cover, species composition of the bryophyte layer, species tendency for coexistence, and bryophyte diagnostic value for forest types. We explained the observed trends by environmental variables and bryophyte species traits to understand how bryophytes function in forest habitats.Bryophyte species number and cover were high in forest types on moist sites, both with deciduous and coniferous tree stands. The richness and abundance of bryophyte species, as well as the species composition of the bryophyte layer depended mainly on substrate moisture, fertility and pH, as well as on the percentage cover of coniferous and deciduous tree species in the stand. Species traits which responded to environmental factors were, first of all, requirements for substrate moisture, fertility and pH. Bryophytes of closed forests and short-lived shuttle species preferred deciduous stands, while bryophytes occurring in forests as well as on open land and perennial species were associated with coniferous stands.Bryophyte species showed a clear preference for forest types, but their fidelity was usually not high. Based on the fidelity of species, we also identified 10 groups of coexisting species which were also indicators of forest types and were dependent on environmental variables.Forest floor bryophytes respond to environmental gradients by species number, cover and composition, and they play a diagnostic role in forest types. Our research shows the importance of databases in learning about bryophyte ecology. However, the use of vegetation data has some limitations.

Understory vegetation response to alternative silvicultural systems in coastal British Columbia montane forests

This study is one of several investigating the biological effects of silvicultural systems at the Montane Alternative Silvicultural Systems (MASS) project located on Vancouver Island in British Columbia (BC). We compared understory vegetation cover and diversity under four silvicultural systems (clearcutting, patch cutting, dispersed retention, and shelterwood) to an adjacent old-growth forest. Long-term plots were measured pre-harvest and at intervals up to 26 years post-harvest. We also compared vegetation response to fertilization and vegetation control treatments. All harvesting resulted in a short-term reduction in understory cover from logging debris and ground disturbance. Recovery from disturbance varied by species, life-form and system. Understory tree species returned to pre-harvest cover after 15 years and significantly exceeded initial cover after 26 years. Shrubs returned to pre-harvest cover after 5–10 years and continued to increase in most systems. Herb cover was low in the pre-harvest forest but increased rapidly in years three through 10 due to herbaceous colonizers; this was least pronounced in the shelterwood. Herbs have declined rapidly since year fifteen. Forest floor bryophytes were reduced to less than 5% cover in all systems except the shelterwood and they remain at one-third or less of their pre-harvest cover. The shelterwood retained more stand structure and plant species from the original old-growth forest than other systems immediately after logging, except for the retained patches. All the harvesting treatments increased species richness and diversity compared to the pre-harvest forest. The increase in total species and abundance was highest for year 15 when early-seral colonizers were still present, and many pre-harvest species had returned. By year 26, richness and diversity began to decrease as early-seral species were lost. For overall species diversity of vascular plants and forest floor bryophytes, silvicultural system did not have an effect after 26 years. All the late-seral herbs that occur at MASS were present after harvesting but several were locally eliminated or had reduced abundance in cut areas. We found no significant edge effects into retention patches, which had comparable species richness and diversity to the pre-harvest old growth—suggesting that aggregated retention can be effective for maintaining late-seral species. Silvicultural system had more significant long-term effects on shrubs and bryophytes than early vegetation control.

Forest floor bryophyte and lichen diversity in Scots pine and Norway spruce production forests

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.

Long-term responses of forest-floor bryophytes buried by tephra in the 1980 eruption of Mount St. Helens

Responses in bryophyte communities following volcanic disturbance are not well understood. The eruption of Mount St. Helens on 18 May 1980 deposited large amounts of tephra (aerially transported volcanic ejecta) on nearby forests in southwestern Washington and presented an opportunity to examine bryophyte succession, with a focus on mosses. We examined changes in moss community over 36 years following this disturbance, using permanent plots located in old-growth conifer forests. We used an experimental design where we removed the tephra from some of the plots shortly after the eruption. Initial dramatic decreases in total bryophyte cover, moss species richness, and diversity in plots with intact tephra were followed by increases by 2016. Community profiles also shifted through time but were somewhat site-specific. Moss community change was related to changes in vascular plant species and was driven by changes in a few key moss species with distinct growth strategies. Bryophyte change through time was most pronounced in the plots buried by tephra, but differed among sites. Overall, total bryophyte cover had recovered, reaching our estimate of pre-disturbance levels at all sites after 36 years, but trajectories of change differed among sites, demonstrating the importance of idiosyncratic site factors and the dynamics of the vascular plant species.

Field sampling methods for investigating forest-floor bryophytes: Microcoenose vs. random sampling

Because of the high importance of bryophytes in forest ecosystems, it is necessary to develop standardized field sampling methodologies. The quadrat method is commonly used for bryophyte diversity and distribution pattern surveys. Quadrat size and the position of quadrats within the studied area have a significant influence on different analyses. The aim of the present study was to define the minimum quadrat size appropriate for sampling ground bryophytes in temperate beech forests, to compare two different field sampling methods for research on ground bryophytes, the random and microcoenose methods; and to test the adequacy of the microcoenose sampling method in temperate beech forests. Research was carried out on Fruska Gora mountain (Serbia) at four different sites. All sites contained temperate broadleaf forest vegetation, predominantly Fagus sylvatica, but also included various other tree species. Systematic sampling based on nested quadrats was used to determine the minimum sampling area. Random sampling was performed using 10 or 20 microplots (minimum area quadrat), randomly located within 10x10 m plots. Microcoenose sampling is a systematic sampling method based on the fact that every bryophyte fragment on the forest floor is a separate microcoenose. These methods were compared using the following criteria: species richness; Shannon?s diversity index and evenness measure; coverage of dominant species, and the time needed for sampling. The microcoenose sampling method has proven to be highly applicable in temperate beech forests in terms of species richness and diversity, in contrast to random sampling, which was not suitable for bryophyte flora with a patchy distribution.

Modeling and Mapping Forest Floor Distributions of Common Bryophytes Using a LiDAR-Derived Depth-to-Water Index

This article describes how the cartographic depth-to-water (DTW) index in combination with other variables can be used to quantify, model and map the distribution of common forest floor bryophytes, at 1 m resolution. This was done by way of a case study, using 12 terrain and climate representative locations across New Brunswick, Canada. The presence/absence by moss species was determined at each location along upland-to-wetland transects within >10-m spaced 1-m2 forest floor plots. It was found that Bazzania trilobata, Dicranum polysetum, Polytrichum commune, Hylocomium splendens, and Pleurozium schreberi had greater probabilities of occurrence in well-drained forested areas, whereas Sphagnum fuscum and Sphagnum girgensohnii dominated in low-lying wet areas. The presence/absence of each species was quantified by way of logistic regression analyses, using DTW, slope, canopy closure, forest litter depth, ecosite type (8 classes), nutrient regime (4 classes, poor to rich); vegetation type (deciduous, coniferous, mixed, and shrubs), and macro- and micro-topography (upland, wetland; mounds, pits) as predictor variables. Among these, log10DTW and forest litter depth were the most consistent predictor variables, followed by mound versus pit. For the mapping purpose, only log10DTW and already mapped classifications for upland versus wetland and vegetation type were used to predict the probability of occurrences for the most frequent moss species, namely, D. polysetum, P. schreberi and Sphagnum spp. The overall accuracy for doing this ranged from 67% to 83%, with false positives and negatives amounting to 18% to 42%. The overall classification accuracy exceeded the probability by chance alone at 76.8%, with the significance level reached at 75.3%. The average level of probability by chance alone was 60.3%.

Environmental drivers of the bryophyte propagule bank and its comparison with forest-floor assemblage in Central European temperate mixed forests

Species richness, composition and abundance of the bryophyte diaspore bank of Central European temperate mixed forests were compared with the forest-floor bryophyte assemblage. The impact of environmental variables and anthropogenic disturbances, including tree species composition, stand structure, microclimate, light conditions, soil and litter properties, management history, and landscape properties, potentially influencing bryophyte diaspore bank assemblages were explored. Thirty-four, 70–100 years old mixed stands with differing tree species composition were examined in the Őrség National Park, Western Hungary. The diaspore bank was studied by soil collection and cultivation, and data were analysed by multivariate methods. Contrary to the forest-floor bryophyte assemblage, where substrate availability, tree species composition and stand structure were the most influential environmental variables, the composition and abundance of the diaspore bank was mainly affected by site conditions (microclimate, litter and soil properties). Species richness of the bryophyte diaspore bank was lower than that of the forest-floor bryophyte assemblage. Short-lived mosses (colonists, short-lived shuttles) were dominant in the diaspore bank, as opposed to the forest-floor bryophyte community, where perennial mosses dominated. In the studied forests, the importance of the bryophyte diaspore bank was relatively low in the regeneration and maintenance of the forest-floor bryophyte vegetation.

Stochastic processes dominate during boreal bryophyte community assembly

Why are plant species found in certain locations and not in others? The study of community assembly rules has attempted to answer this question, and many studies articulate the historic dichotomy of deterministic (predictable niches) vs. stochastic (random or semi-random processes). The study of successional sequences to determine whether they converge, as would be expected by deterministic theory, or diverge, as stochastic theory would suggest, has been one method used to investigate this question. In this article we ask the question: Do similar boreal bryophyte communities develop in the similar habitat created by convergent succession after fires of different severities? Or do the stochastic processes generated by fires of different severity lead to different communities? Specifically we predict that deterministic structure will be more important for large forest-floor species than stochastic processes, and that the inverse will be true for small bryophyte species. We used multivariate regression trees and model selection to determine the relative weight of structure (forest structure, substrates, soil structure) and processes (fire severity) for two groups of bryophyte species sampled in 12 sites (seven high-severity and five low-severity fires). Contrary to our first hypothesis, processes were as important for large forest-floor bryophytes as for small pocket species. Fire severity, its interaction with the quality of available habitat, and its impact on the creation of biological legacies played dominant roles in determining community structure. In this study, sites with nearly identical forest structure, generated via convergent succession after high- and low-severity fire, were compared to see whether these sites supported similar bryophyte communities. While similar to some degree, both the large forest-floor species and the pocket species differed after high-severity fire compared to low-severity fire. This result suggests that the "how," or process of habitat generation, influences community composition in this system and that a snapshot of habitat conditions taken at only one point in time is insufficient to explain species distribution.

Level and pattern of overstory retention interact to shape long‐term responses of understories to timber harvest

In many regions of the world, variable retention has replaced clear-cutlogging as the principal method of regeneration harvest. Partial retention of the overstory is thought to ensure greater continuity of the species and ecological processes that characterize older forests. Level (amount) and spatial pattern of overstory retention are two basic elements of forest structure that can be manipulated to achieve specific ecological or silvicultural objectives. However, experiments that elucidate the relative importance of retention level and pattern (or their interaction) are rare. Here we assess long-term (> 10 yr) responses of forest understories to experimental harvests of mature coniferous forests replicated at five sites in the Pacific Northwest (PNW). Treatments contrast both the level of retention (40% vs. 15% of original basal area) and its spatial distribution (dispersed vs. aggregated in 1-ha patches). For most vascular plant groups (early seral, forest generalist, and late seral), postharvest changes in cover and richness were reduced at higher levels of retention and in dispersed relative to aggregated treatments. Although retained forest patches were stable, changes in adjacent harvested (cleared) areas were significantly greater than in dispersed treatments. Late-seral herbs were highly sensitive to level and pattern of retention, with extirpations most frequent in the cleared areas of aggregated treatments and at low levels of dispersed retention. In contrast, early-seral species were most abundant in these environments. Forest-floor bryophytes exhibited large and persistent declines regardless of treatment, suggesting that threshold levels of disturbance or stress were exceeded. Our results indicate that 15% retention (the minimum standard on federal forestlands in the PNW) is insufficient to retain the abundance or diversity of species characteristic of late-seral forests. Although 1-ha aggregates provide refugia, they are susceptible to edge effects or stochastic processes; thus, smaller aggregates are unlikely to serve this function. The ability to achieve multiple ecological or silvicultural objectives with variable retention will require the spatial partitioning of habitats to include dispersed retention and larger undisturbed aggregates along with cleared areas.

The contributions of forest structure and substrate to bryophyte diversity and abundance in mature coniferous forests of the Pacific Northwest

Many aspects of forest structure are thought to contribute to the presence, abundance, and diversity of forest-floor bryophytes. To what extent easily measured characteristics of local environment (overstory structure or substrate availability) explain patterns of abundance and diversity remains unclear in most forest ecosystems. We explore these relationships in four mature, Douglas-fir dominated forests in southwestern Washington (U.S.A.). At each site, six 13-ha stands were sampled systematically (787 total plots) to capture variation in physical environment, forest overstory and understory vegetation, substrates, and forest-floor bryophytes. We compared bryophyte species composition, richness, and rank abundance among sites. We used multiple linear regression to model local cover and richness as functions of the physical environment, overstory and understory vegetation, and substrate availability. We compared the contributions of substrates to bryophyte abundance and richness and measured the strength and consistency of associations between individual species and particular substrates. Bryophyte composition differed significantly among sites, but patterns of richness and rank abundance were surprisingly similar, despite differences in stand structure and climate. Regression models explained only 18-23% of the variation in bryophyte cover or richness, likely due to weak relationships between vegetation structure and microclimate, disparity in the spatial scales of measurement, and temporal lags in bryophyte responses to structure. Most non-litter substrates (mineral soil, rock, fresh or decayed wood, stumps, shrub and tree bases) contributed minimally to available growing space, but disproportionately to species richness, particularly at the stand scale. Individual species were most often associated with decayed wood, although few species showed strong substrate specificity. In general, however, substrates contributed to ecological redundancy, with most species occupying multiple substrates and most substrates supporting a diversity of species.

Microtopography creates small-scale refugia for boreal forest floor bryophytes during clear-cut logging

The biotic response of ecological systems to disturbances has traditionally been explained by attributes of the disturbance event itself, such as its intensity, the distribution of traits within a community related to resistance (e. g. physiological, morphological or life-history) or their interaction. Another less investigated mechanism explaining variation in response to disturbance is microtopographic heterogeneity, which might modify survival rates unevenly. We tested the hypothesis that forest floor microtopography creates small-scale refugia for bryophytes following conventional clear-cut logging by comparing a) survival of transplanted bryophytes and b) compositional changes of forest floor bryophytes among three different positions: on the northern side of boulders and stumps and on unsheltered forest floor. The investigation was carried out as a before-and-after study in 12 Swedish boreal forests (eight stands subjected to clear-cutting and four reference stands). Significantly more bryophyte transplants survived where they were sheltered by boulders and stumps (30 and 29% respectively) compared to on level forest floor (10%) and less compositional changes occurred in sheltered microtopographic positions than on level forest floor. Shelter from boulders and stumps increased survival from both microclimatic stress and mechanical disturbance but not from burial by logging residues. Our findings provide evidence that microtopography can modify initial responses to disturbances by creating small-scale refugia. Further studies are needed to determine whether this phenomenon is commonly occurring among other organisms and in other ecosystems and to what extent scattered in-situ survivors can increase the recovery rate following disturbances.

Bryophyte species richness and composition in young forests regenerated after clear-cut logging versus after wildfire and spruce budworm outbreak

The disturbance regime in mixed-wood forests of eastern Canada is characterized by both natural disturbances including wildfires and insect outbreaks as well as forestry. The understanding of how understorey plant assemblages respond to different disturbances is mostly limited to short-term wildfire-logging comparisons of vascular plants. Here, we compare patterns of species richness and composition of four bryophyte guilds in young forests (approx. 40 years old) regenerating after clear-cut logging, wildfire, and spruce budworm outbreak. In addition, young forests were compared with mature spruce-fir dominated stands (approx. 90 years old). Although similar in overall species richness at the scale of 1,000 m2 all young forest types were compositionally distinct with fewer species than mature forests. Stands developed after spruce budworm outbreaks had the highest canopy cover values and the highest surface area of coarse woody debris. These stands had similar numbers of woody debris species as mature forests and were closest to mature forests in species composition. Wildfire-disturbed sites were dominated by deciduous trees and a high number of treebase species. Finally, young managed forest had the highest number of forest floor bryophytes at the scale of 100 m2 among the three young forest types, but was compositionally far from mature forests in their woody debris flora. In conclusion, young forests regenerating after natural disturbances are distinctly different from young forests regenerated after clear-cutting and if natural disturbances are eliminated certain species (e.g., epixylic and treebase species) might become more restricted to older stands in the landscape.

Boulders increase resistance to clear-cut logging but not subsequent recolonization rates of boreal bryophytes

The extent to which a plant assemblage might recolonize a disturbed system is in general related to the availability of propagule sources and sites with appropriate conditions for establishment. Both these factors might be sensitive to aspects of spatial heterogeneity. Microtopographic variation may enhance initial resistance by reducing the impact of the disturbance and facilitating establishment of incoming propagules by providing shaded "safe-sites". This study explores the influence of microtopographic heterogeneity (caused by variation in surface boulder cover) on the recolonization of closed-canopy forest floor bryophytes using a chronosequence of 75 spruce-dominated forests in south-central Sweden (2-163 years after clear-cutting). We found that high boulder cover did increase survival and subsequent persistence in young forests at both investigated scales (i.e. 1,000 and 100 m(2)), although this pattern became less evident on the smaller spatial scale. Species accumulation in boulder-poor subplots was not different when surrounded by boulder-rich compared with boulder-poor subplots suggesting short-distance recolonization from boulder-created refugia to be of little importance during recolonization. To conclude, it seems that boulders increase initial resistance to clear-cutting for this bryophyte guild, but that the subsequent recolonization process is more likely to depend on external propagule sources and factors affecting establishment such as the microclimate in the developing stand.

Old trees contribute bio-available nitrogen through canopy bryophytes

Symbiotic cyanobacteria—bryophyte associations on the forest floor are shown to contribute significantly to stand-level nitrogen budgets through the process of biological nitrogen fixation (BNF), but few studies have considered the role of canopy bryophytes. Given the high biomass of epiphytic bryophytes in many tree species of the North American temperate rain forest, we suggest that canopy bryophytes may contribute substantially to stand-level N dynamics. We confirm the presence of cyanobacteria and measure rates of BNF at three heights (0, 15 and 30 m) in Sitka spruce trees across three watershed estuaries of Clayoquot Sound, British Columbia, Canada. This study is the first to report BNF by cyanobacteria associated with epiphytic and forest floor bryophytes in the coastal temperate rain forest of North America. Cyanobacteria density was significantly greater in epiphytic bryophytes compared to mosses on the forest floor, and rates of BNF were highest at 30 m in the canopy. The majority of total stand-level BNF (0.76 kg N · ha-1 · yr-1) occurs in the canopy, rather than on the forest floor (0.26 kg N · ha-1 · yr-1). We suggest that BNF by cyanobacterial-bryophyte associations in the canopy of coastal temperate rain forests is a unique source of ecosystem N, which is dependent on large, old trees with high epiphytic bryophyte biomass.

Forest floor lichen and bryophyte communities in thinned Pseudotsuga menziesii - Tsuga heterophylla forests

While a great deal of research has illustrated the importance of late-successional forests for maintaining biodiversity in the Pacific Northwest of North America, over 76% of the forests in the region are less than 100 years old. To preserve landscape-level biodiversity, forest managers are increasingly interested in how young stands can be manipulated to favor late-successional species. We sought to understand how stand-level gradients in canopy structure, particularly those affected by thinning, relate to dominant forest floor bryophyte and lichen species composition and abundance. We sampled forest floor lichen and bryophytes ten years after alternative thinning treatments at two sites in western Oregon. Relationships of forest floor communities to canopy structure were site-specific. At the first site, moss and lichen abundance had small-scale geographic patterns and mosses were negatively associated with epiphytic cyanolichen species richness, however, we found no strong associations between forest floor communities and stand structural characteristics. At the second site, lichens, particularly Cladonia, was negatively associated with canopy cover and was most in thinned plots. Bryophyte abundance was positively associated with Tsuga basal area. This relationship was stronger in the thinned stands, which had a different community composition than those left unthinned. Overall, the forest floor communities were fairly homogeneous at both sites and relationships with stand structural variables were subtle, indicating that thinning did not have a strong impact.

Decomposition rates of bryophytes in managed boreal forests: influence of bryophyte species and forest harvesting

The slow decomposition rate of boreal forest floor bryophytes contributes both to maintaining high soil C reserves as well as affecting conditions for tree growth by maintaining excessively high soil water content, cooling the soil and slowing nutrient cycles. In this study, mass loss of three bryophyte species (Pleurozium schreberi, Sphagnum capillifolium, S. fuscum) was measured in unharvested, partial cut and low-retention cut forest blocks. Mesh decomposition bags containing the three species and wood sticks were placed at two depths in colonies of either P. schreberi or S. capillifolium (environment) in the three harvest treatments and retrieved after two growing seasons. Mass loss was primarily related to substrate type (P. schreberi > S. capillifolium > wood sticks > S. fuscum) and secondarily to depth. Harvest treatment and environment (P. schreberi or S. capillifolium) only weakly affected sphagna mass loss. The weak effect of harvest treatment suggests that conditions created by low retention cuts do not to stimulate decomposition in this system and are not important enough to stimulate carbon loss, or to counteract paludification. On the other hand, the strong effect of bryophyte type indicates that conditions affecting bryophyte colonization and succession are of great importance in driving carbon and nutrient cycles.

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.

Nitrogen uptake by Hylocomium splendens during snowmelt in a boreal forest

In most boreal regions snow composes a large portion of the annual precipitation. Although many boreal forest floor bryophytes depend largely on precipitation for their nitrogen (N) supply, bryophyte uptake of snow N is little explored. We studied chemical forms of plant-accessible N in snowmelt, as well as the temporal dynamics of their release. In conjunction we performed a N uptake experiment using the common boreal bryophyte Hylocomium splendens. The results demonstrated that the snowmelt N pool was dominated by NO3− (86%), followed by NH4+ (11%) and amino acid N (3%), in total providing ca 0.3 kg N·ha−1 to the forest floor vegetation. Hylocomium splendens was able to access both inorganic and organic 15N labelled N forms (NO3−, NH4+, and glycine) applied in situ to the snow covering the moss prior to snowmelt. Across all the N forms H. splendens took up ca 24% of the snow-deposited N. Nitrate uptake exceeded that of glycine, while NH4+ uptake was intermediate, reflecting the ambient distribution of the snowmelt N pool between plant-accessible N forms.