Diversity of dry forest epiphytes along a gradient of human disturbance in the tropical Andes

Question: Disturbance effects on dry forest epiphytes are poorly known. How are epiphytic assemblages affected by different degrees of human disturbance, and what are the driving forces? Location: An inter‐Andean dry forest landscape at 2300 m elevation in northern Ecuador. Methods: We sampled epiphytic bryophytes and vascular plants on 100 trees of Acacia macracantha in five habitats: closed‐canopy mixed and pure acacia forest (old secondary), forest edge, young semi‐closed secondary woodland, and isolated trees in grassland. Results: Total species richness in forest edge habitats and on isolated trees was significantly lower than in closed forest types. Species density of vascular epiphytes (species per tree) did not differ significantly between habitat types. Species density of bryophytes, in contrast, was significantly lower in edge habitat and on isolated trees than in closed forest. Forest edge showed greater impoverishment than semi‐closed woodland and similar floristic affinity to isolated trees and to closed forest types. Assemblages were significantly nested; habitat types with major disturbance held only subsets of the closed forest assemblages, indicating a gradual reduction in niche availability. Distance to forest had no effect on species density of epiphytes on isolated trees, but species density was closely correlated with crown closure, a measure of canopy integrity. Main conclusions: Microclimatic changes but not dispersal constraints were key determinants of epiphyte assemblages following disturbance. Epiphytic cryptogams are sensitive indicators of microclimate and human disturbance in montane dry forests. The substantial impoverishment of edge habitat underlines the need for fragmentation studies on epiphytes elsewhere in the Tropics.     

Hydrological properties of the epiphyte mass of a montane tropical rain forest,Colombia

The effect of a well-developed epiphytic vegetation on the interception of rainfall was investigated in an upper montane rain forest at an altitude of 3370 m in the Cordillera Central of the Colombian Andes. Total epiphyte mass was estimated at 12 tonnes dry weight per hectare, most of it being bryophytes and dead organic matter. The hydrological properties of the epiphyte mass were studied using detached branches. Water gain (during rainfall) and water loss (after experimental saturation) were determined gravimetrically in the field.Rain falling on epiphyte-covered branches was efficiently captured. Drainage of water (held temporarily in excess of the retention capacity) was very gradual. Water loss through evaporation was slow. The observations are in accordance with previously reported data for rainfall interception in the forest studied. The potentially large influence of the exceptionally high canopy storage capacity is restricted due to the clumped distribution of epiphytes and associated low turnover rates of water in the epiphyte mass.     

Seedling establishment of vascular epiphytes on isolated and enclosed forest trees in an Andean landscape, Ecuador

The impact of human disturbance on colonisation dynamics of vascular epiphytes is poorly known. We studied abundance, diversity and floristic composition of epiphyte seedling establishing on isolated and adjacent forest trees in a tropical montane landscape. All vascular epiphytes were removed from plots on the trunk bases of Piptocoma discolor. Newly established epiphyte seedlings were recorded after 2 years, and their survival after another year. Seedling density, total richness at family and genus level, and the number of families and genera per plot were significantly reduced on isolated trees relative to forest trees. Seedling assemblages on trunks of forest trees were dominated by hygrophytic understorey ferns, those on isolated trees by xerotolerant canopy taxa. Colonisation probability on isolated trees was significantly higher for plots closer to forest but not for plots with greater canopy or bryophyte cover. Seedling mortality on isolated trees was significantly higher for mesophytic than for xerotolerant taxa. Our results show that altered recruitment can explain the long-term impoverishment of post-juvenile epiphyte assemblages on isolated remnant trees. We attribute these changes to a combination of dispersal constraints and the harsher microclimate documented by measurements of temperature and humidity. Although isolated trees in anthropogenic landscapes are considered key structures for the maintenance of forest biodiversity in many aspects, our results show that their value for the conservation of epiphytes can be limited. We suggest that abiotic seedling requirements will increasingly constitute a bottleneck for the persistence of vascular epiphytes in the face of ongoing habitat alteration and atmospheric warming.     

Functional diversity of epiphytes in two tropical lowland rainforests, French Guiana: using bryophyte life-forms to detect areas of high biodiversity

Recent studies have described a new tropical lowland forest type in the Guianas, the tropical lowland cloud forest. It is characterized by an enriched epiphytic species diversity particularly for bryophytes compared to common lowland rainforest, and is facilitated by frequent early morning fog events in valley locations. While the increase in epiphytic species diversity in lowland cloud forests has been documented, uncertainties remain as to (1) how this small scale variation in water supply is shaping the functional diversity of epiphytic components in lowland forests, and (2) whether information on functional group composition of epiphytes might aid in discerning these cloud forests from the common lowland rainforest. We compare the distribution of functional groups of epiphytes across height zones in lowland cloud forest and lowland rain forest of French Guiana in terms of biomass, cover as well as the composition of bryophyte life-forms. Both forests differed in functional composition of epiphytes in the canopy, in particular in the mid and outer canopy, with the cloud forest having a higher biomass and cover of bryophytes and vascular epiphytes as well as a richer bryophyte life-form composition. Bryophyte life-forms characteristic for cloud forests such as tail, weft and pendants were almost lacking in the canopies of common rain forest whereas they were frequent in lowland cloud forests. We suggest that ground-based evaluation of bryophyte life-form composition is a straightforward approach for identifying lowland cloud forest areas for conservation, which represent biodiversity hotspots in tropical lowland forests.     

苔藓植物对植物天然更新的影响

种子是天然更新的基础,幼苗和幼树的生长是天然更新过程中最敏感的阶段。苔藓植物作为许多生态系统的主要地被物,在维管植物天然更新过程中发挥着不容忽视的作用。在许多植被类型中,都有发育良好的苔藓群落,大量的研究证明它们的存在影响到维管植物的萌发、建成和生长,并且可能进一步影响到物种的共生,有一些种类甚至可能指示树种的更新。本文就苔藓植物对物种更新早期阶段的作用和影响进行了综述。包括苔藓植物的生理特性造成的微气候变化;苔藓群落对种子传播、萌发及幼苗建成的影响。并讨论了苔藓植物与更新物种的种间关系及其对幼苗生长的化感作用。     

Epiphytes of Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis>) plantations in Ireland and the effects of open spaces

The epiphytes of the trunks and branches of mature Sitka spruce (Picea sitchensis) trees were studied in twelve plantations containing open spaces (glades, rides and roads) in the east and southwest of Ireland. A pair of trees was studied at each site: one tree at the south-facing edge of an open space and one in the forest interior. Spruce trees were found to support a moderately diverse range of bryophytes and lichens, including two relatively rare bryophyte species. Clear patterns in vertical distribution were identified, with bryophyte richness and cover decreasing and lichen richness and cover increasing from the tree base to the upper trunk. The open spaces themselves did not appear to affect overall epiphyte diversity, with no significant differences in any of the diversity measures between edge and interior trees. The main effect of open spaces was on the epiphyte cover of the edge trees. This was related to increased light levels combined with the presence of live branches from close to ground level on the south sides of the edge trees, which produced optimum conditions for bryophytes at the tree base and lichens in the upper plots. However, this dense side-canopy negatively affected epiphyte diversity on the north sides of the edge trees. Further research is required to assess the effects of open spaces within forestry plantations on epiphyte diversity.     

Epiphytes of Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis>) plantations in Ireland and the effects of open spaces

The epiphytes of the trunks and branches of mature Sitka spruce (Picea sitchensis) trees were studied in twelve plantations containing open spaces (glades, rides and roads) in the east and southwest of Ireland. A pair of trees was studied at each site: one tree at the south-facing edge of an open space and one in the forest interior. Spruce trees were found to support a moderately diverse range of bryophytes and lichens, including two relatively rare bryophyte species. Clear patterns in vertical distribution were identified, with bryophyte richness and cover decreasing and lichen richness and cover increasing from the tree base to the upper trunk. The open spaces themselves did not appear to affect overall epiphyte diversity, with no significant differences in any of the diversity measures between edge and interior trees. The main effect of open spaces was on the epiphyte cover of the edge trees. This was related to increased light levels combined with the presence of live branches from close to ground level on the south sides of the edge trees, which produced optimum conditions for bryophytes at the tree base and lichens in the upper plots. However, this dense side-canopy negatively affected epiphyte diversity on the north sides of the edge trees. Further research is required to assess the effects of open spaces within forestry plantations on epiphyte diversity.     

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.     

影响广东黑石顶树附生苔藓分布的环境因子

通过对广东省黑石顶自然保护区内5个2500 m2样地内树附生苔藓的调查及有关环境因子的测定,研究了树附生苔藓的分布格局及其与环境因子的关系.树附生苔藓在不同高度的分布存在一定梯度,20 cm高处树附生苔藓的种类数与盖度均大于60 cm及更高处,且其群落优势种的数量组成与后者存在较大差异.不同树种附生苔藓盖度和种数差异较大.基于附生苔藓植物的盖度进行DCA排序及聚类分析将树种分成四组,马尾松(Pinus massoniana)因具有两种特有的网藓(巴西网藓Syrrhopodon prolifer和鞘刺网藓S.armatus)单独一组,福建青冈(Quercus chungii)亦与其余各种的差异均较大,形成一组,其余阔叶树种根据其所处的森林类型分成两组,针阔叶混交林内的阔叶树种和次生阔叶林内的阔叶树种各形成一组.对环境因子及树皮含水量和pH的分析显示,垂直梯度上空气湿度的差异可能是造成附生苔藓在不同高度分布差异的主要影响因子之一,不同树种附生苔藓的差异在一定程度上受树皮pH的影响,而与树皮含水量无关.同一树种上树附生苔藓的分布又在一定程度上受森林类型的影响.     

Vertical distribution of epiphytic bryophytes in an Indonesian rainforest

We studied species richness, composition and vertical distribution of epiphytic bryophytes in submontane rainforest of Central Sulawesi. Bryophytes were sampled on eight canopy trees and on eight trees in the forest understorey. Microclimate was measured at trunk bases and at crown bases. The total recorded number of 146 epiphytic bryophyte species is among the highest ever reported for tropical forests and underlines the importance of the Malesian region as a global biodiversity hotspot. Species composition differed significantly between understorey trees and canopy tree trunks on the one hand, and the forest canopy on the other. Fourty-five percent of the bryophyte species were restricted to canopy tree crowns, 12% to the understorey. Dendroid and fan-like species mainly occurred in the forest understorey whereas tufts were most species rich in the tree crowns. The findings reflect the different microclimatic regimes and substrates found in the understorey and in the forest canopy. The results indicate that assessments of the bryophyte diversity of tropical forests are inadequate when understorey trees and tree crowns are excluded.     

Could the Canopy Structure of Bryophytes Serve as an Indicator of Microbial Biodiversity? A Test for Testate Amoebae and Microcrustaceans from a Subtropical Cloud Forest in Dominican Republic

The mechanisms that ultimately regulate the diversity of microbial eukaryotic communities in bryophyte ecosystems remain a contentious topic in microbial ecology. Although there is robust consensus that abiotic factors, such as water chemistry of the bryophyte and pH, explain a significant proportion of protist and microcrustacean diversity, there is no systematic assessment of the role of bryophyte habitat complexity on such prominent microbial groups. Water-holding capacity is correlated with bryophyte morphology and canopy structure. Similarly, canopy structure explains biodiversity dynamics of the macrobiota suggesting that canopy structure may also be a potential parameter for understanding microbial diversity. Canopy roughness of the dominant bryophyte species within the Bahoruco Cloud Forest, Cachote, Dominican Republic, concomitant with their associated diversity of testate amoebae and microcrustaceans was estimated to determine whether canopy structure could be added to the list of factors explaining microbial biodiversity in bryophytes. We hypothesized that smooth (with high moisture content) canopies will have higher species richness, density, and biomass of testate amoebae and higher richness and density of microcrustaceans than rough (desiccation-prone) canopies. For testate amoebae, we found 83 morphospecies with relative low abundances. Species richness and density differed among bryophytes with different bryophyte canopy structures and based on non-metric multidimensional scaling, canopy roughness explained 25% of the variation in species composition although not as predicted. Acroporium pungens (low roughness, LR) had the lowest species richness (2 ± 0.61 SD per gram dry weight bryophyte), and density (2.1 ± 0.61 SD individual per gram of dry weight bryophyte); whereas Thuidium urceolatum (high roughness) had the highest richness (24 ± 10.82 SD) and density (94 ± 64.30 SD). The fact that the bryophyte with the highest roughness had the highest levels of diversity for testate amoebae suggests that moisture levels at the level of the bryophyte canopy may not represent a biodiversity driver in a cloud forest with high relative humidity; however, high roughness could generate a dynamic and fluctuating moisture environment with concomitant alternating microbial communities. A total of 26 microcrustacean morphospecies were found across 11 bryophytes; however, no bryophyte canopy effect was detected on their richness and density. Microcrustacean mean density was low ranging from less than one individual per 50 cm2 of bryophyte in Leucobryum (LR) to a maximum of 6 ± 3.37 SD individuals/50 cm2 in Monoclea (LR). This lack of pattern suggests that possible explanatory variables may be related to larger scale processes than those examined in this study.     

Branchfall as a Demographic Filter for Epiphyte Communities: Lessons from Forest Floor-Based Sampling

Local variation in the abundance and richness of vascular epiphytes is often attributed to environmental characteristics such as substrate and microclimate. Less is known, however, about the impacts of tree and branch turnover on epiphyte communities. To address this issue, we surveyed branches and epiphytes found on the forest floor in 96 transects in two forests (Atlantic rainforest in Brazil and Caribbean rainforest in Panama). In the Brazilian forest, we additionally distinguished between edge and core study sites. We quantified branch abundance, epiphyte abundance, richness and proportion of adults to investigate the trends of these variables over branch diameter. Branches <2 cm in diameter comprised >90% of all branches on the forest floor. Abundance and richness of fallen epiphytes per transect were highest in the Brazilian core transects and lowest in the Panamanian transects. The majority of epiphytes on the floor (c. 65%) were found attached to branches. At all three study sites, branch abundance and branch diameter were negatively correlated, whereas epiphyte abundance and richness per branch, as well as the proportion of adults were positively correlated with branch diameter. The relationship between branch diameter and absolute epiphyte abundance or richness differed between study sites, which might be explained by differences in forest structure and dynamics. In the Panamanian forest, epiphytes had been previously inventoried, allowing an evaluation of our surveying method by comparing canopy and forest floor samplings. Individuals found on the forest floor corresponded to 13% of all individuals on branches <10 cm in diameter (including crowns), with abundance, richness and composition trends on forest floor reflecting canopy trends. We argue that forest floor surveys provide useful floristic and, most notably, demographic information particularly on epiphytes occurring on the thinnest branches, which are least accessible. Here, branchfall acts as an important demographic filter structuring epiphyte communities.     

Indirect effects of hiking trails on the community structure and diversity of trunk-epiphytic bryophytes in an old-growth fir forest

Abstract

Forest hiking trails may influence local microclimate and biodiversity, but the effects on community structure and diversity of epiphytic bryophytes on trees are currently unknown. Epiphytic bryophytes on 82 Abies faxoniana Rehder & Wilson tree trunks (41 along the hiking trail edge and 41 controls in the forest interior) were investigated at four heights from the ground (10, 50, 120, and 180 cm). At each site, air temperature and humidity were monitored for 1 year. The light radiation levels and air temperature were higher, and the canopy leaf area index and air humidity lower at the trail edge, indicating deterioration in microclimate, resulting from the trail establishment. The epiphytic bryophyte species richness, community cover, and mean cover of dendroid and pendent growth forms on trunks were significantly lower at the trail edge than the control site, suggesting that trail construction caused these reductions. One marked effect of the presence of the trail was the increase in some sun-loving species and decrease in shade-tolerant species. Moreover, the trail also slightly influenced species richness and epiphytic bryophyte cover at both community and species population levels along the height gradient. Comprehensive analyses showed that microclimate deterioration was mainly driven by the trail establishment, and that the change in micro-climate along the trail, rather than any host traits, played an important role in the declining epiphytic bryophyte community structure and diversity at the trail edge, confirming the initial hypothesis that the presence of a raised boardwalk (hiking trail) indirectly influences epiphytic bryophyte community and diversity by altering the microclimate.     

Retention of Inorganic Nitrogen by Epiphytic Bryophytes in a Tropical Montane Forest1

We developed and evaluated a model of the canopy of a tropical montane forest at Monteverde, Costa Rica, to estimate inorganic nitrogen (N) retention by epiphytes from atmospheric deposition. We first estimated net retention of inorganic N by samples of epiphytic bryophytes, epiphyte assemblages, vascular epiphyte foliage, and host tree foliage that we exposed to cloud water and precipitation solutions. Results were then scaled up to the ecosystem level using a multilayered model of the canopy derived from measurements of forest structure and epiphyte mass. The model was driven with hourly meteorological and event‐based atmospheric deposition data, and model predictions were evaluated against measurements of throughfall collected at the site. Model predictions were similar to field measurements for both event‐based and annual hydrologic and inorganic N fluxes in throughfall. Simulation of individual events indicated that epiphytic bryophytes and epiphyte assemblages retained 33–67 percent of the inorganic N deposited in cloud water and precipitation. On an annual basis, the model predicted that epiphytic components retained 3.4 kg N ha/yr, equivalent to 50 percent of the inorganic N in atmospheric deposition (6.8 kg N ha/yr). Our results indicate that epiphytic bryophytes play a major role in N retention and cycling in this canopy by transforming highly mobile inorganic N (ca. 50% of atmospheric deposition is NO^?₃) to less mobile (exchangeable NH⁺₄) and recalcitrant forms in biomass and remaining litter and humus.     

高山森林林窗和生长基质对苔藓植物氮和磷含量的影响

苔藓在森林生态系统养分富集和循环方面有重要作用,苔藓植物在氮磷循环中的作用可能受到森林更新和生长基质的影响.为理解苔藓在森林生态系统养分循环中的作用,研究了高山森林不同位置(林窗中心、林窗边缘、林下)和不同生长基质(活立木、倒木、枯立木、大枯枝、根桩、地表)上的苔藓植物氮磷含量.结果表明:地表苔藓氮含量(3.12 mg·g^-1)显著低于其他生长基质上的苔藓,尽管枯立木附生苔藓氮含量高达17.41 mg·g^-1,但倒木、大枯枝、枯立木和活立木苔藓氮含量差异不显著;最高(1.09 mg·g^-1)和最低(0.61 mg·g^-1)的磷含量分别出现在森林地表和枯立木的苔藓,且森林地表的苔藓磷含量显著高于其他生长基质上的苔藓,但倒木、大枯枝、根桩和活立木上的苔藓磷含量差异不显著.林窗位置显著影响了倒木和大枯枝上的苔藓氮、磷含量,林窗内倒木和大枯枝上的苔藓氮、磷含量显著高于林窗边缘.粗木质残体的类型、腐烂等级对苔藓氮、磷含量的影响存在差异,两者交互作用的影响显著;第Ⅴ腐烂等级倒木上的苔藓氮含量显著高于其他腐烂等级;第Ⅲ腐烂等级大枯枝上的苔藓氮含量显著高于其他腐烂等级;第Ⅱ腐烂等级倒木上的苔藓磷含量显著高于其他腐烂等级;第Ⅳ腐烂等级枯立木上的苔藓磷含量显著高于其他腐烂等级.可见,森林林窗更新和粗木质残体腐解过程会影响苔藓植物的氮、磷含量,同时影响森林生态系统的养分循环过程.     

Tree and stand-scale factors affecting richness and composition of epiphytic bryophytes and lichens in deciduous woodland key habitats

Conservation and sustainable forestry are essential in a multi-functional landscape. In this respect, ecological studies on epiphytes are needed to determine abiotic and biotic factors associated with high diversity. The aim of the present study was to evaluate relative sensitivity of conservation targets (epiphytic bryophytes and lichens) in relation to contrasting environmental variables (tree species, tree diameter at breast height, bark crevice depth, pH, tree inclination, pH, forest stand age, area and type) in boreo-nemoral forests. The study was conducted in Latvian 34 woodland key habitat (WKH) boreo-nemoral forest stands. Generalized linear mixed models and canonical correspondence analysis showed that tree species and tree bark pH were the most important variables explaining epiphytic bryophyte and lichen composition and richness (total, Red-listed, WKH indicator species). Forest stand level factors, such as stand size and habitat type, had only minor influence on epiphytic species composition and richness. The results of the present study indicate a need to maintain the diversity of tree species and large trees, particularly Acer platanoides, Carpinus betulus, Fraxinus excelsior, Populus tremula, Tilia cordata, Ulmus glabra and Ulmus laevis in conservation of epiphytic bryophyte and lichen communities in the future.     

典型喀斯特区不同植被恢复方式苔藓功能性状及其对土壤因子的响应

苔藓功能性状反映了苔藓对生长环境的响应与适应,对其所在土壤表层的功能特性具有重要指示意义。但喀斯特地区植被恢复初期苔藓功能性状与土壤因子关系还缺乏深入认识。以典型喀斯特峰丛洼地人工林、牧草和人工林+牧草3种植被恢复方式下苔藓为研究对象,分析了苔藓功能性状及其与土壤因子的关系。结果表明：(1)苔藓单位面积冠层质量(CMA)、冠层密度(CD)、生物量和饱和吸水量在牧草地有最大值。苔藓冠层高度在牧草地显著低于人工林和人工林+牧草,且牧草地苔藓营养元素含量较低。(2)人工林和人工林+牧草表层土壤(0—2 cm)养分含量和土壤含水量(SWC)较高,牧草地表层土壤养分含量和SWC较低。(3)冗余分析表明,苔藓营养性状(营养元素含量及化学计量比)与土壤因子主要呈正相关关系,而CMA、CD及生物量关联指标与土壤因子主要呈负相关关系,土壤交换性镁和SWC是影响苔藓功能性状的主要土壤因子。研究结果表明,苔藓通过不同的性状组合适应不同植被类型生境,其中牧草地更适宜苔藓拓殖和生长,可考虑将苔藓应用于牧草地对喀斯特退化生态系统进行修复。     

Bole epiphytic bryophytes on <Emphasis Type="Italic">Lithocarpus xylocarpus</Emphasis> (Kurz) Markgr. in the Ailao Mountains,SW China

Epiphytic bryophytes growing on Lithocarpus xylocarpus (Kurz) Markgr. trunks of different diameter classes in primary (132 plots) and secondary (84 plots) Lithocarpus forests in the Ailao Mountains, SW China, were surveyed and analyzed to determine species composition and richness, and to identify environmental variables that may affect it. Among the 65 species (belonging to 32 genera, 19 families) found, 28 occurred in both forests, with Syrrhopodon gardneri (Hook.) Schwaegr. predominanting. Species richness and total coverage in primary forest were significantly higher than in secondary forest. We suggest that a period of perhaps much more than 110 years is necessary for the recovery of epiphytic bryoflora in montane forest of SW China. Fan, turf, and smooth mat are the most important life forms, with high occurrences in both forests. The life form composition of epiphytic bryophytes is determined mainly by microhabitat and host age. Tree age, the presence of primary forest, bark pH, and plot exposure are the environmental variables that have significantly influenced the composition of epiphytic bryophytes. Tree age explained most variations in epiphytic bryoflora. Bark pH is another important parameter that significantly influenced the epiphytic bryophyte community, but seemed indirectly correlated with tree age. Primary forest is a favorable habitat for epiphytes, due mainly to its diversified canopy structure and the presence of large diameter hosts. Moisture-laden southwest trade winds and forest structure could differentiate microclimate and impel a distinct composition of epiphytes in windward and leeward exposures.     

Bryophyte Species Richness on Retention Aspens Recovers in Time but Community Structure Does Not

Green-tree retention is a forest management method in which some living trees are left on a logged area. The aim is to offer ‘lifeboats’ to support species immediately after logging and to provide microhabitats during and after forest re-establishment. Several studies have shown immediate decline in bryophyte diversity after retention logging and thus questioned the effectiveness of this method, but longer term studies are lacking. Here we studied the epiphytic bryophytes on European aspen (Populus tremula L.) retention trees along a 30-year chronosequence. We compared the bryophyte flora of 102 ‘retention aspens’ on 14 differently aged retention sites with 102 ‘conservation aspens’ on 14 differently aged conservation sites. We used a Bayesian community-level modelling approach to estimate the changes in bryophyte species richness, abundance (area covered) and community structure during 30 years after logging. Using the fitted model, we estimated that two years after logging both species richness and abundance of bryophytes declined, but during the following 20–30 years both recovered to the level of conservation aspens. However, logging-induced changes in bryophyte community structure did not fully recover over the same time period. Liverwort species showed some or low potential to benefit from lifeboating and high potential to re-colonise as time since logging increases. Most moss species responded similarly, but two cushion-forming mosses benefited from the logging disturbance while several weft- or mat-forming mosses declined and did not re-colonise in 20–30 years. We conclude that retention trees do not function as equally effective lifeboats for all bryophyte species but are successful in providing suitable habitats for many species in the long-term. To be most effective, retention cuts should be located adjacent to conservation sites, which may function as sources of re-colonisation and support the populations of species that require old-growth forests.     

长白山森林生态系统腐木生苔藓植物生态分布的DCA排序研究

应用除趋势对应分析（ＤＣＡ）对长白山不同森林类型腐木生苔藓植物分布研究表明,长白山红松阔叶混交林、暗针叶林以及两者之间的过渡林林下腐木生苔藓植物组成明显不同．红松阔叶混交林以尖叶匍灯藓、毛尖羽藓、细枝青藓等为主;过渡林以尖叶匍灯藓、鞭枝疣灯藓、羽藓、腐木藓、塔藓等为主;暗针叶林的以塔藓、钩枝镰刀藓、拟垂枝藓、曲背藓、毛梳藓等为主．暗针叶林林下腐木生苔藓植物发生量最大,物种的多样性也最高．海拔高度和林冠郁闭度是影响长白山森林林下腐木生苔藓植物生态分布的主要因素．