Beech versus spruce deadwood as forest microhabitat: does it make any difference to bryophytes?

The presence data of 153 bryophyte species, recorded on beech (BDW) and spruce (SDW) deadwood in the managed forests within a montane watershed, were analysed by controlling for different plot size, substrate pH and elevation. Only three pleurocarpous species, which were probably remnant epiphytes from live wood, showed relative specificity for BDW, but none to SDW. The few species displaying preference for BDW or SDW were generally true epixylic, mosses and hepatics, respectively. The chances of occurrence of epiphytic (early successional) and epixylic (mid-late successional) taxa on either deadwood species increased and respectively, decreased with the substrate pH. There was no consistent relationship between bryophyte preference to BDW/SDW and elevation. Neither total nor threatened species richness was related to deadwood species identity. However, at 100 cm² resolution and within certain extension range, the cumulative number of bryophyte species was significantly higher on BDW than on SDW, despite no significant difference in species pool size. Threatened species richness increased monotonically towards lower elevations, suggesting that valley bottoms might act as refugia with high air humidity. The number of threatened species and in particular, the presence of Lophozia ascendens, were good predictors of total bryophyte richness regardless of deadwood species identity.     

The significance of deadwood for total bryophyte,lichen, and vascular plant diversity in an old-growth spruce forest

Modern silviculture has led to a reduction in deadwood, especially that of large diameter, and thus the loss of an important habitat niche in most European forests. We analyzed the significance of deadwood for the total species diversity in three plant groups (bryophytes, lichens, and vascular plants) in one of Central Europe’s few remnants of unmanaged old-growth forest. The site is a montane forest of Picea abies on Mt. Brocken, Harz Mountains, Germany, which has not been managed for at least several centuries, undergoes natural forest dynamics, and thus harbors large amounts of standing and downed deadwood. Epiphyte vegetation of live trees and the ground vegetation were studied for comparison. We did not find any obligate deadwood species. Nevertheless, 84 % (70 species) of the total species were found on standing or downed deadwood. One-third of these species, or 28 % of the total species in the forest, were only sampled on deadwood, whereas the remaining species were also found on live trees and/or the ground. Bryophytes were the largest group of species on deadwood (47 % of the deadwood-inhabiting species), followed by lichens (37 %) and vascular plants (16 %). Large-diameter deadwood in an advanced stage of decay harbored more species than smaller fragments in the early stages of decay. Despite the lack of obligate deadwood colonizers, deadwood apparently plays a key role for forest plant diversity, mainly by providing an environment with low competition and thus facilitating the establishment of species.     

Transient trade‐off between climate benefit and biodiversity loss of harvesting stumps for bioenergy

To replace fossil fuel and thereby mitigate climate change, harvesting of wood such as stumps for bioenergy will likely increase. Coarse deadwood is an important resource for biodiversity and stumps comprise the main part of the coarse deadwood in managed forests. We provide the first integrated analysis of the long‐term climate and biodiversity impacts of a whole landscape. We simultaneously project climate and biodiversity impacts of harvesting stumps to substitute for fossil coal, assuming scenarios with different proportions of the landscape with stump harvest (10, 50, 80%) the coming 50 years. A life cycle approach was used to calculate future global temperature changes and future metapopulation changes in six epixylic lichens. Metapopulation dynamics were projected using colonization and extinction models based on times series data. Harvesting stumps from ≥50% of the clear‐cut forest land benefits climate with a net global temperature reduction >0.5·10^?9 K ha^?1 after 50 years if assuming substitution of fossil coal. For all scenarios, using stump bioenergy leads to immediate (within 1 year) reductions in temperature of 50% compared to using fossil coal, increasing to 70% reduction after 50 years. However, large‐scale stump harvest inflicted substantial metapopulation declines for five of six lichens. High stump harvest levels (≥50%) put common lichens at risk of becoming red‐listed following the IUCN criteria. The net temperature reduction (cooling effect) from substituting fossil coal with stumps harvested for bioenergy increased over time, while lichen metapopulations stabilized at lower equilibria after two to three decades. This indicates that trade‐offs between climate and metapopulations of commons species are transient, where climate benefits become more prevalent in the long term. As both objectives are important for meeting (inter‐)national climate and biodiversity targets, integrated analyses such as this should be encouraged and urged to guide policymaking about large‐scale implementation of stump harvest.     

Colonization–extinction dynamics of epixylic lichens along a decay gradient in a dynamic landscape

Metapopulation models are often used for understanding and predicting species dynamics in fragmented landscapes. Several models have been proposed depending on e.g. the relative importance of patch dynamics on the metapopulation dynamics. Dead wood is a dynamic substrate patch, and species that are confined to such patches have experienced a high degree of habitat loss in managed forests. Little is, however, known about how the population dynamics of epixylic species are affected by the fast dynamics of their substrate patches. We quantified the effect of local patch conditions and metapopulation processes on colonizations and extinctions of epixylic lichen species in a managed boreal forest landscape. This was done by twice surveying seven lichen metapopulations on 293 stumps in 30 stands of ages covering the duration of the dynamic patches (stumps). We also investigated the relative importance of local stochastic extinctions from stumps that remained available, and deterministic extinctions due to stump surface disappearance. We found importance of a decay gradient, surrounding metapopulation size, and local population sizes, in driving the colonization–extinction dynamics of epixylic lichens. The species were sorted along the stump decay gradient. Increasing surrounding metapopulation size was associated with increased colonization rates, and increasing local population size decreased lichen extinction rates. Finally, both local stochastic extinctions and deterministic extinctions due to patch disappearance occur, confirming that the long‐term persistence of epixylic lichens depends on colonization rates that compensate for stochastic population extinctions as well as deterministic extinctions.     

Carbon flux from decomposing wood and its dependency on temperature,wood N2 fixation rate,moisture and fungal composition in a Norway spruce forest

Globally 40–70 Pg of carbon (C) are stored in coarse woody debris on the forest floor. Climate change may reduce the function of this stock as a C sink in the future due to increasing temperature. However, current knowledge on the drivers of wood decomposition is inadequate for detailed predictions. To define the factors that control wood respiration rate of Norway spruce and to produce a model that adequately describes the decomposition process of this species as a function of time, we used an unprecedentedly diverse analytical approach, which included measurements of respiration, fungal community sequencing, N₂ fixation rate, nifH copy number, ¹⁴C‐dating as well as N%, δ¹³C and C% values of wood. Our results suggest that climate change will accelerate C flux from deadwood in boreal conditions, due to the observed strong temperature dependency of deadwood respiration. At the research site, the annual C flux from deadwood would increase by 27% from the current 117 g C/kg wood with the projected climate warming (RCP4.5). The second most important control on respiration rate was the stage of wood decomposition; at early stages of decomposition low nitrogen content and low wood moisture limited fungal activity while reduced wood resource quality decreased the respiration rate at the final stages of decomposition. Wood decomposition process was best described by a Sigmoidal model, where after 116 years of wood decomposition mass loss of 95% was reached. Our results on deadwood decomposition are important for C budget calculations in ecosystem and climate change models. We observed for the first time that the temperature dependency of N₂ fixation, which has a major role at providing N for wood‐inhabiting fungi, was not constant but varied between wood density classes due to source supply and wood quality. This has significant consequences on projecting N₂ fixation rates for deadwood in changing climate.     

森林生态系统中木腐真菌群落形成机理及生态功能

在森林生态系统中,枯死木是一个重要的组成部分,为很多生物提供栖息地,有助于养分循环以及碳和水的储存.木材分解是森林生态系统养分循环、土壤形成和碳收支的决定性过程,越来越受到森林生态学家、病理学家和管理者的重视.在此过程中,木腐真菌通过分泌多种酶降解木材主要成分,实现生态系统中的物质循环,具有极为关键和重要的作用.木腐真...     

Epiphytic lichen diversity in old-growth and managed Picea abies stands in southern Finland

Abstract. Epiphytic and epixylic lichens were surveyed on 15 1-ha plots in mature Picea abies-dominated boreal forests in southern Finland. The sample plots were classified into three groups according to the age of the dominant tree stand and recent signs of cutting: (1) early mature managed, ‘EM’ (95 -109 yr), (2) late mature managed, ‘LM’ (126 - 145 yr) and (3) old-growth, ‘OG’ (129 - 198 yr). Two data sets on epiphytic and epixylic lichens were recorded from each plot: (1) species on basal trunks and branches of Picea abies and (2) species on all available woody substrates, including basal parts of all tree species, saplings, snags, logs and stumps. 142 epiphytic and epixylic lichen species were found, of which 83 (58%) occurred on P. abies. Mean total numbers of species per sample plot were 69 in EM, 78 in LM and 88 in OG plots, species number on P. abies were 47, 56, and 54 respectively. The LM plots had lower species numbers than OG plots, mainly due to the lack of old Populus tremula trees, but they had higher species number than the EM plots mainly due to the higher age of Picea abies. Differences in species composition, both within and between the three groups, were small. The results suggest that the epiphytic and epixylic lichen diversity in a managed stand can be increased by prolonging the rotation of the stand to >120 yr and by increasing the diversity of habitats in the stand.     

Positive edge effects on forest-interior cryptogams in clear-cuts

Biological edge effects are often assessed in high quality focal habitats that are negatively influenced by human-modified low quality matrix habitats. A deeper understanding of the possibilities for positive edge effects in matrix habitats bordering focal habitats (e.g. spillover effects) is, however, essential for enhancing landscape-level resilience to human alterations. We surveyed epixylic (dead wood inhabiting) forest-interior cryptogams (lichens, bryophytes, and fungi) associated with mature old-growth forests in 30 young managed Swedish boreal forest stands bordering a mature forest of high conservation value. In each young stand we registered species occurrences on coarse dead wood in transects 0-50 m from the border between stand types. We quantified the effect of distance from the mature forest on the occurrence of forest-interior species in the young stands, while accounting for local environment and propagule sources. For comparison we also surveyed epixylic open-habitat (associated with open forests) and generalist cryptogams. Species composition of epixylic cryptogams in young stands differed with distance from the mature forest: the frequency of occurrence of forest-interior species decreased with increasing distance whereas it increased for open-habitat species. Generalists were unaffected by distance. Epixylic, boreal forest-interior cryptogams do occur in matrix habitats such as clear-cuts. In addition, they are associated with the matrix edge because of a favourable microclimate closer to the mature forest on southern matrix edges. Retention and creation of dead wood in clear-cuts along the edges to focal habitats is a feasible way to enhance the long-term persistence of epixylic habitat specialists in fragmented landscapes. The proposed management measures should be performed in the whole stand as it matures, since microclimatic edge effects diminish as the matrix habitat matures. We argue that management that aims to increase habitat quality in matrix habitats bordering focal habitats should increase the probability of long-term persistence of habitat specialists.     

Preferences of dead wood inhabiting bryophytes for decay stage,log size and habitat types in Hungarian beech forests

Abstract

This study describes the quantitative preferences of epixylic bryophytes for decay stages, log size and habitat type. The two habitats investigated were zonal (situated on plateaux without extreme microclimatic conditions) and ravine-like near-natural beech stands. Preferences of 30 bryophyte species are described using logistic regression modelling. The species pool differed between habitat types. In the ravine-like forests more species are found. Regionally rare epixylic species (mainly liverworts) were limited to these forests. The species richness of individual logs was also higher in the ravine-like than in the zonal forests and the proportion of logs of all sizes colonized by bryophytes was higher in the former. The species were classified into four categories on the basis of their preference for decay stages: strict epixylics, indifferent species, preferential epixylics and epiphytes. The epixylics and preferential epixylics prefer advanced decay stages while the latter extend further into earlier decay stages than strict epixylics. Common epixylic species have a wider tolerance to decay stage than rare ones. Probabilities of species occurrence increase with log size, more strongly in zonal stands than in ravines. A simple successional scheme for bryophyte succession on dead wood is proposed on the basis of the observed species responses.     

茂兰喀斯特森林退化区凋落物的分解动态

为了解亚热带气候型的茂兰喀斯特森林退化区次生林和灌木林的凋落物分解动态过程,该研究采用分解袋法,对茂兰喀斯特森林退化区不同类型的凋落物在不同坡位的分解状况进行了为期18个月的观测,并通过分析凋落物分解时的失重量和失重率的动态变化,比较了次生林和灌木林的凋落叶的失重率变化,探讨了不同坡位对凋落物分解的影响。结果表明:各种类型凋落物的分解速率和失重率在退化区内存在明显的差异,落叶>常绿叶>枯枝(P<0.05),三种凋落物整体变化趋势在分解过程中大致相同,它们在早期都快速分解,中期分解变慢,后期开始加速;落叶在次生林与灌木林中的前期分解速率基本同步,后期为灌木林落叶>次生林落叶,而常绿叶在灌木林与次生林中的分解速率则表现为基本同步;利用回归方程对凋落叶分解50%和95%所需时间进行估测,得出落叶和常绿叶在灌木林中分解50%和95%所需时间少于次生林的;在不同坡位,三种凋落物分解速率的总体趋势为中坡>上坡;三种凋落物的C含量波动性较大,但总体变化趋势是随分解时间的增加而减少,随着分解时间增加,N含量增加,而C/N比则降低。     

Effect of deadwood of different tree species in various stages of decomposition on biochemical soil properties and carbon storage

The primary objective of this paper was to estimate how the mass of Silver fir (Abies alba Mill.) and Scots pine (Pinus sylvestris L.) deadwood in two decay classes affected biochemical processes and the accumulation of soil organic matter, as well as the extent of this impact. We evaluated deadwood mass, as well as the biological activity and influence of the distance from deadwood on biological activity and carbon (C) storage. The investigation was carried out in Magurski National Park, southern Poland, in four randomly selected study plots. The organic C and nitrogen contents and soil pH and texture were analysed. The study also included the determination of enzyme activities. The results obtained demonstrated that soil C storage and the biological activity of the soil were influenced by deadwood form, tree species and decay class. Significant differences in the C content in the soil between the logs of fir and pine trees were noted. With the advancement of the deadwood decomposition process, the C concentration and enzyme activity increased slightly. Lower C accumulation occurred further away from the deadwood. At a 100-cm distance from the deadwood, the influence of the logs was not evident. Higher C storage was found in the soil around the stumps than in the decaying logs. This study confirmed an important role of deadwood in forest ecosystems, i.e., maintaining species biodiversity and increasing C accumulation in the soil environment with a simultaneous increase in the biological activity of the soil.     

Combined observational and experimental data provide limited support for facilitation in lichens

It is increasingly recognized that facilitative interactions can shape communities. One of the mechanisms through which facilitation may operate is when one species facilitates the colonization of another through the exchange of shared symbionts. Lichens are symbiotic associations composed of a mycobiont (lichenised‐fungus) and one or two photobionts (algae or cyanobacteria). Different lichen species may have overlapping specificity for photobionts, creating the possibility that facilitation drives lichen community assembly. To investigate whether facilitation occurs in lichens, we combined an observational study (a) with a manipulative field experiment (b). For (a), we quantified the effect of local patch conditions, facilitation and the size of the surrounding metapopulation on colonizations of an epixylic lichen species (Cladonia botrytes) in an area of managed boreal forest. This was done by twice surveying lichens on 293 stumps, located in stands of three age classes. For (b), we treated unoccupied surfaces of 56 cut stumps with algal mixtures of an Asterochloris photobiont and recorded C. botrytes colonizations over three years. In (a), colonization rates of C. botrytes increased with increasing abundance of other lichen species with specificity for Asterochloris photobionts, consistent with an effect of facilitation. However, in the field experiment (b), colonizations of the focal species did not provide support for facilitation. We conclude that our study provides limited support for facilitation in green‐algal lichens, underscoring the importance of combining observational studies with experiments when studying species interactions.     

Wood-inhabiting fungi on fallen logs of Norway spruce: relations to forest management and substrate quality

A survey of the patterns of wood decaying fungi as to occurrence of sporocarps on naturally fallen logs of Norway spruce ( Picea abies ) was undertaken in two nearby forest stands with different histories of management. One stand was an old-growth forest with few signs of logging, and the other stand was selectively logged 60–80 years ago. Altogether 118 species were found. Forest management had a negative impact on the species diversity. Newly fallen and weakly decayed logs in a natural forest had a higher species richness, more red-listed species, as well as more indicator species compared to similar logs in a managed forest. The importance of dead wood for species diversity of wood inhabiting fungi was clearly demonstrated. Presence of logs in later stages of decomposition increased the total species number in a natural forest stand with 42 (63 %), compared to a survey of only newly fallen and weakly decayed logs. Presence of logs in later stages of decomposition also increased the diversity of the species pool colonising newly fallen and weakly decayed logs. The highest number of fruiting species was found on intermediately decayed logs and on logs lying in contact with the ground. The fungal gradient as revealed in a DCA ordination was primarily related to decay. A successional pathway based on the primary decayer Fomitopsis pinicola was not detected.     

红松阔叶林倒木贮量动态的研究

在森林倒木研究的基础上探讨长白山红松阔叶林倒木贮量的动态,涉及红松阔叶林倒木分解及其贮量的动态规律。研究表明,倒木分解,除心腐木外,均由表及里进行;倒木分解速率在其它生态条件相同时因树种、直径和部位而异。红松阔叶林倒木贮量动态包括现有倒木贮量和倒木年输入量两个分解动态过程,现有倒木贮量在头100年其干重迅速减少,其中椴树比红松尤速,前者分解91%,后者为72%.林地倒木贮量动态与倒木年输入量分解动态相似,但前者在分解初期贮量增加较大,因为部分现有倒木未完全分解;100年后趋于一致,并恒定于16～17t·hm^-2,直至群落的顶极阶段结束.     

Restoring volume,diversity and continuity of deadwood in boreal forests

Restoration of boreal forests by emulating natural disturbances is used to bring back typical components of natural forests that are reduced by silvicultural management. The volume, diversity and continuity of deadwood are the most important factors determining the diversity of deadwood-dependent species. In a large-scale experiment consisting of 43 experimental stands and 15 controls we assessed how alternative restoration methods enhancing deadwood availability (felling and felling + burning with two levels of felling: 20 and 40 % of initial volume of living trees, and a storm treatment) would affect short- and long-term deadwood volume and diversity using 7-year deadwood measurements and simulation modelling. In short-term, restoration by felling + burning increased both the volume and diversity of deadwood, whereas felling only increased merely the volume of deadwood. The simulations of tree growth, mortality and wood decomposition indicated that in comparison to controls, felled and storm-treated stands have greater deadwood volumes up to 40 years and felled + burned stands more than 60 years after restoration. Our results suggest that felling with 20 % of initial tree volume does not harm the future deadwood continuity, whereas intensive burning may imperil the deadwood continuity in a stand level. In conclusion, restoration clearly speeds up the development of the deadwood volumes needed to host large portions of biodiversity, and burning is the most effective restoration method in short- and long term. In practice, several restoration methods could be used concurrently in the landscape to obtain the best results.     

Deadwood as a surrogate for forest biodiversity: Meta-analysis of correlations between deadwood volume and species richness of saproxylic organisms

Deadwood is an important component of forest ecosystems on which many forest dwelling species depend. Deadwood volume is therefore widely used as an indicator of forest biodiversity, notably throughout Europe. However, using deadwood as an indicator has mostly been based on boreal references, and published references for temperate forests are scarce. As a result, the magnitude of the relationship between deadwood volume and species richness remains unclear for saproxylic species. We used meta-analysis to study the correlation between deadwood volume and the species richness of saproxylic beetles and fungi relative to several predictors at the forest stand level: biome, type of deadwood (log, snag, and stump) and decay class (fresh vs. decayed). We showed that the correlation between deadwood volume and species richness of saproxylic organisms was significant but moderate (r = 0.31), and that it varied only slightly between logs and snags or between decay stages. However, we found a strong biome effect: deadwood volume and species richness were more correlated in boreal forests than in temperate forests. This could be attributed both to differences in the history of forest management between biomes and to varying landscape patterns. Finally, we conclude that total deadwood volume is probably not a sufficient indicator of saproxylic biodiversity, and those additional variables (notably at the landscape level) such as type of deadwood or decay class should be integrated in deadwood monitoring. In addition, further forest research is needed to better assess the quantitative relationship between deadwood and saproxylic biodiversity, and in order to build indicators adapted to different biome contexts.     

长白山北坡暗针叶林倒木贮量和分解的研究

对长白山北坡海拔 12 6 0m和 16 2 0m暗针叶林中倒木蓄积、生物量和倒木的分解进行了比较研究 ,结果表明 ,暗针叶林中倒木的蓄积为 180 .87m3·hm-2 ,占林分蓄积的 2 1.83 % .低海拔的倒木蓄积和生物量均比高海拔的低 ,海拔 12 6 0m的倒木蓄积为 5 2 .5 7m3·hm-2 ,生物量为 2 6 .2 1t·hm-2 ;海拔 16 2 0m的倒木蓄积为 193.85m3·hm-2 ,生物量为 5 3 .33t·hm-2 .用单项指数衰减模型对倒木的分解进行模拟可知 ,倒木的分解常数随树种和海拔高度的不同而不同 .冷杉倒木的分解常数比云杉倒木大 ;倒木在低海拔的分解常数比在高海拔的大 ,表明云杉倒木完全分解需要较长的时间 .     

Presence of bark influences the succession of cryptogamic wood-inhabiting communities on conifer fallen logs

Predictors of cryptogamic wood-inhabiting communities need to be examined to understand the drivers of forest biodiversity. We estimated the influence of bark cover on the wood-inhabiting vegetation on conifer logs in early stages of epixylic succession in mature European boreal and hemi-boreal forests. Abundance of substrate groups with respect to log attributes was estimated with generalized linear and generalized linear mixed models. The structure and composition of epixylic communities was analysed using non-metric multidimensional scaling with subsequent environmental fitting. The abundance of true epixylics was inversely related to bark cover. In the first stage, bark cover did not influence the abundance of epiphytes and epigeous species; positively influenced the abundance of facultative epixylics on spruce logs and negatively influenced it on pine logs. In the second stage, the effect of bark cover was positive for epiphytes and epigeous species on spruce logs and for facultative epixylics independent of log species identity and negative for epigeous species on pine logs. Generalist species did not depend on bark cover. Total cover of wood-inhabiting vegetation was marginally influenced by bark cover. The effect of bark cover on epixylic vegetation at community level was negligible. In general, bark cover favours the establishment and growth of species with low substrate specificity. This preference may lead to either burial of logs by epigeous bryophytes, or facilitation of succession towards the dominance of ground vegetation.     

Bryophytes and decaying wood– a comparison between managed and natural forest

A comparative study was made of one managed forest and one natural forest regarding the supply of decaying wood on the ground and the occurrence of bryophytes on the wood, especially epixylic specialists.
The total substrate surface of wood is larger in the primeval forest. The larger quantity of decaying wood increases the probability of wood occurring in ail decay stages. Logs of Populus tremula occurred only in the natural forest. An important proportion of the wood substrate in the natural forest consisted of logs of large diameter class; these logs were missing in the managed forest. Fiftyfour bryophyte species were found on decaying wood. They were separated into four different groups. Facultative epiphytes first colonized decaying wood, followed by epixylic specialists and finally by competitive epigeics. Opportunistic generalists showed a more irregular pattern of occurrence. The bryophyte flora on decaying wood was most species rich in the natural forest. Sixteen epixylic specialists occurred here, several considered to be threatened by forest management, while only 5 of these species occurred in the managed forest.
The higher frequency of epixylic specialists in the natural forest is related to the greater frequency of favourable habitats, specifically: logs of large diameter, decayed wood, Populus tremula and (to a lesser extent) Picea abies.     

Demographic population structure of a leafy epixylic hepatic Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust

Understanding the population processes is central when assessing proper conservation acts, especially in the case of species which inhabit temporal and patchy substrates, such as decaying wood. In epixylic bryophytes, however, only little is known of the demographic population structure and within-population dynamics. In this study on a leafy epixylic hepatic, Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust., a set of demographic traits is investigated, including colony area and size, proportions of the sterile, gemmiparous or sexual developmental stages, the shoot size class distribution among the developmental stages, and numbers of asexual propagules present on the shoots. The estimates of mortality are assessed on the basis of the proportions of dead shoots found in the colonies. The size distribution within the developmental stages of this species shows that a certain threshold size is required for both asexual and sexual reproduction. The shoot size is negatively correlated with density, whereas the numbers of asexual gemmae and the proportions of developmental stages are not affected by shoot density. Furthermore, provisional estimates are calculated for the transitions from early developmental stages to reproductively mature stages. The results indicate that the initial phases of the gametophyte development are the most vulnerable.