Epiphytic macrolichen communities along regional gradients in northern Norway

Abstract. Question: What are the relative influences of human impact, macroclimate, geographic location and habitat related environmental differences on species composition of boreal epiphytic macrolichen communities? Location: Troms county in northern Norway. Methods: Detrended Correspondence Analysis revealed the main gradient structure in lists of epiphytic macrolichen species from deciduous forests. By Canonical Correspondence Analysis with variance partitioning, the relative amount of variance in macrolichen species composition attributable to human impact, macroclimate, spatial context and environmental differences was quantified. Results: There was no significant effect of human impact on species composition of epiphytic macrolichens of deciduous forests. Macroclimate was the most important factor determining epiphytic macrolichen communities, which were also strongly influenced by ecological differences such as forest stand properties. Conclusions: Epiphytic macrolichen communities are determined by a macroclimatic gradient from the coastline to the interior of central north Norway. In marked contrast, the species composition of epiphytic macrolichen communities seems to be unaffected by human impact in the study area, where air pollution was marginal.     

Diversity and succession of epiphytic macrolichen communities in low‐elevation managed conifer forests in Western Oregon

Abstract. We examined epiphytic macrolichen communities in Pseudotsuga menziesii (Douglas‐fir) forests across the western Oregon landscape for relationships to environmental gradients, stand age and structure, and commercial thinning. We used a retrospective, blocked design through the Coast and the western Cascade ranges of Oregon. Each of our 17 blocks consisted of a young, unthinned stand (age 50–110 yr); an adjacent, thinned stand of equivalent age; and an old‐growth stand (age > 200 yr). We found 110 epiphytic macrolichen taxa in the stands. Forage‐providing alectorioid lichens and the nitrogen‐fixing cyanolichen Lobaria oregana associated strongly with old‐growth stands and remnant old trees in younger stands (unthinned + thinned). Relative to unthinned stands, thinned stands had a slightly higher abundance of alectorioid lichens and a greater presence of Hypogymnia imshaugii. However, thinned stands hosted a lower landscape‐level (γ) diversity, lacking many species that occurred infrequently in the unthinned stands. Patterns in the lichen community composition correlated strongly with climatic gradients; the greatest variation in composition was between the Coast and Cascade ranges. The difference in communities between mountain ranges was greatest among stands 70–110 yr old, suggesting a difference in lichen successional dynamics between the ranges.     

Diversity of bryophyte vegetation in some forest types in Estonia: a comparison of old unmanaged and managed forests

The bryophyte vegetation of 3 pairs of unmanaged and managed forest stands, representing Oxalis drained peatland, Aegopodium and Oxalis forest site type, were compared. The total number of bryophyte species in unmanaged stands was 74 and that in managed stands 54. Out of the 20 species occurring only in unmanaged forests, 9 grow on decaying wood, and 3 on trunks or bases of big trees; 13 of them were hepatics. In unmanaged forests 11 hemerophobic species were recorded altogether. Although the difference in substrate and species diversity between unmanaged and managed stands is not statistically significant, in unmanaged forests more substrates characteristic for an old-growth stand are available, and the percentage of species preferring dryer habitats or prolonged humidity is a bit higher than in managed forests; the percentage of species associated with better illuminated habitats is higher in managed forests. Analysis of classification structure of the bryophyte layer synusia shows that the number of societies is also higher in unmanaged forests. This is associated with more numerous microhabitats; the average light and humidity indices calculated for every society, confirm this conclusion. The large discrepancy in bryophyte layer classification structure in old-growth and managed forests of the same forest site type is manifested not so much by species content in synusia as by their abundance proportions. The larger diversity of classification units in unmanaged forests is also seen at the synusia facies level; four of nine facies are confined exclusively to unmanaged stands. This is a strong argument for the informativeness of bryophyte layer classification structure for purposes of indication and monitoring as well.     

Litterfall of epiphytic macrolichens in Nothofagus forests of northern Patagonia,Argentina: Relation to stand age and precipitation

Abstract: The objective of this study was to analyse how stand age and precipitation influence abundance and diversity of epiphytic macrolichens in southern beech Nothofagus forests, estimated by lichen litter sampling. Five sites of Nothofagus dombeyi (Mirbel) Oersted were selected in Nahuel Huapi National Park, Argentina. At each site, lichen fragments from the forest floor were collected at 12.5 m² plots in pairs of young and mature N. dombeyi forest. Additionally, two sites with multi‐aged subalpine Nothofagus pumilio (Poepp. et Endl.) Krasser forest were investigated in a similar manner. Average litterfall biomass per stand varied from less than 1 kg ha^?1 in a young low‐precipitation stand to a maximum of 20 kg ha^?1 in a mature high‐precipitation stand. In places with higher precipitation, litterfall biomass in N. dombeyi forest was considerably higher in old stands as compared with young ones. In places with less than 2000 mm of precipitation, differences in biomass were less pronounced. Old humid stands contained about twice as many taxa in the litter as old low‐precipitation stands and young stands in general. Mature stands in low‐precipitation sites only contained 17% of the litter biomass as compared with mature stands in high‐precipitation sites. Epiphytic lichen composition changed from predominating fruticose lichens (Usnea spp. and Protousnea spp.) in low‐precipitation stands to Pseudocyphellaria spp., Nephroma spp. and other foliose lichens, in the high‐precipitation stands. There were no clear differences in the proportion of fruticose and foliose lichens between young and old stands. Fruticose lichens dominated litter biomass in both N. pumilio sites.     

Forest recovery after swidden cultivation across a 40-year chronosequence in the Atlantic forest of southern Bahia, Brazil

Tree species composition and structure of a 40-year chronosequence of secondary forests was compared with old-growth forests in southern Bahia, Brazil. Twelve stands were randomly selected that represented three age classes: 10, 25, and 40 year old with four replications in each class. All stands selected had been established after abandonment from swidden cultivation and were surrounded by old-growth forests. In every stand, ten 0.01-ha transects were established and all stems (≥5 cm diameter at breast height) were measured and identified. Results were compared with the dataset of two neighboring old-growth sites. Mean diameter, total height, and stand basal area increased with age. Number of trees/ha peaked in 40 year old stands. The results showed that secondary forests in this region take much more than 40 years to recover the structure of old-growth forests. In contrast, species richness recovery was rapid with a continuous accumulation of species with age in secondary forests. Species richness and diversity increased with age as did similarity between secondary stands and old-growth stands. More than half of the species found in the 40 year old stands were shared with the neighboring old-growth forests. However, species richness and diversity were higher in old growth sites.     

Richness of Lichen Species,Especially of Threatened Ones,Is Promoted by Management Methods Furthering Stand Continuity

Lichens are a key component of forest biodiversity. However, a comprehensive study analyzing lichen species richness in relation to several management types, extending over different regions and forest stages and including information on site conditions is missing for temperate European forests. In three German regions (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin), the so-called Biodiversity Exploratories, we studied lichen species richness in 631 forest plots of 400 m² comprising different management types (unmanaged, selection cutting, deciduous and coniferous age-class forests resulting from clear cutting or shelterwood logging), various stand ages, and site conditions, typical for large parts of temperate Europe. We analyzed how lichen species richness responds to management and habitat variables (standing biomass, cover of deadwood, cover of rocks). We found strong regional differences with highest lichen species richness in the Schwäbische Alb, probably driven by regional differences in former air pollution, and in precipitation and habitat variables. Overall, unmanaged forests harbored 22% more threatened lichen species than managed age-class forests. In general, total, corticolous, and threatened lichen species richness did not differ among management types of deciduous forests. However, in the Schwäbische-Alb region, deciduous forests had 61% more lichen species than coniferous forests and they had 279% more threatened and 76% more corticolous lichen species. Old deciduous age classes were richer in corticolous lichen species than young ones, while old coniferous age-classes were poorer than young ones. Overall, our findings highlight the importance of stand continuity for conservation. To increase total and threatened lichen species richness we suggest (1) conserving unmanaged forests, (2) promoting silvicultural methods assuring stand continuity, (3) conserving old trees in managed forests, (4) promoting stands of native deciduous tree species instead of coniferous plantations, and (5) increasing the amount of deadwood in forests.     

Lichenological evidence for the recognition of inland rain forests in western North America

Aim The coastal temperate rain forests of north‐western North America are internationally renowned as the archetypal expression of the temperate rain forest biome. Less well documented is the existence of somewhat similar forests 500–700 km inland on the windward slopes of the Columbia and Rocky Mountains. Here we attempt to show that these inland ‘wetbelt’ forests warrant rain forest status. Location North‐western North America. Methods We use tree‐dwelling macrolichens to assess the degree of environmental congruence between the coastal temperate rain forests and their inland counterparts. Results We report three key findings: (1) 40% of oceanic, epiphytic macrolichens found in Pacific coastal rain forests occur also in inland regions; (2) epiphytic species richness decreases with decreasing latitude, such that roughly 70% of disjunct oceanic species are restricted to regions north of 51° N; and (3) the southward decline in lichen diversity is correlated with a parallel decrease in summer precipitation, but not with mean annual precipitation. Main conclusions These observations are consistent with the recognition of an inland rain forest formation between 50 and 54° N. Inland rain forests represent a small, biologically significant ecosystem whose continued fragmentation and conversion to tree plantations warrant close scrutiny.     

Microfungal diversity associated with Kindbergia oregana in successional forests of British Columbia

Species richness and species composition of microfungi associated with Oregon beaked moss (Kindbergia oregana) were studied at two forest chronosequences on southeast Vancouver Island, British Columbia, Canada. The purposes were to investigate the effects of clear-cutting and the transformation of old-growth forests into secondary forests on microfungi and the succession of microfungi in relation to long-term stand development. Green and brown parts of moss were collected from the forest floor of Douglas-fir (Pseudotsuga menziesii) stands of four age classes: post-harvest regeneration (13–14 years), immature (50–51 years), and mature (85–101 years) stands, and a control old-growth (296–324 years) stand, and used for the isolation of microfungi. A total of 49 microfungal species were recorded. Study site, stand age, and moss parts significantly affected the species richness and species composition of microfungi. The species richness of microfungi was significantly greater on brown than on green moss parts and lower in post-harvest regenerations than in forest stands of the other age classes. The species composition of major microfungal species changed gradually along the seral stages. Possible environmental and biological factors that could account for the succession of microfungi were discussed.     

Insular patterns of calicioid lichens in a boreal old-growth forest-wetland mosaic

Fragmentation of the forested landscape poses a threat to many aspects of biodiversity associated with old-growth forests Studies of the effects of forest fragmentation are often complicated by the variation in composition and age of patches and the matrix This study used a system of isolated stands where patch age and composition were similar and the matrix variability negligible The patches were composed of old-growth Picea abies stands of varying size and shape in a wetland matrix The study organisms were epiphytic crustose calicioid lichens (also known as Caliciales), many of which are very substrate-specific and restricted to old-growth stands The aim of the study was to measure the effect of patch size, patch isolation, habitat and substrate quality on the species riochness and composition of epiphytic calicioids Twenty-four patches ranging from 0 4 to 15 9 ha in size were studied All species of calicioid lichens were registered in 0 1 ha plots in each patch Isolation was measured as the percentage of available habitat within 400 m of a patch Twenty-two species were found with an average of 9 48 ± 0 26 (SE) species per patch and 292 ± 0 18 (SE) species per tree Species richness at patch level correlated with stand structure, primarily tree density, while number of species per tree (reflecting population size) was strongly correlated with island size and several stand variables There was no effect of isolation on species richness Species composition was influenced by both substrate variables and patch size The species composition on the islands showed a significant nestedness, i e species composition on species-poor islands constituted a non-random subset of the species composition on species-rich islands We propose that the explanation for the strong relationship between species richness at tree level and stand size is an edge effect which implies that unaffected interior areas only occur on large islands The different microclimate of the patch edge enables only the hardiest species to establish large populations there whilst shade and moisture demanding species are restricted to the interiors of larger islands     

Plant species diversity in Mediterranean old-growth forests: A case study from central Italy

Abstract

To investigate the differences in understorey composition and diversity between old-growth and managed forests, we analyzed an old-growth and a managed beech stand in the same area displaying similar abiotic features. We considered variations in understorey species composition and richness. The sampled understorey species were characterized in terms of functional traits, Ellenberg's indicator values and taxonomic distinctness; next, we calculated four different pairwise plot-to-plot dissimilarity matrices based on species composition, functional traits, Ellenberg's indices and taxonomic distances. We applied a permutational multivariate extension of ANOVA to test whether the forest stands significantly differ in the considered features. Indicator values of all plant species in managed and old-growth stands were evaluated.

The old-growth forest had a higher species richness; permutational analysis of variance showed significant differences between the two stands in plant species composition, functional traits, Ellenberg indices and taxonomic distances. Indicator species analysis highlighted 14 indicator species for the unmanaged stand, while only 3 indicators were found for the managed one.

The results suggest that forest management determines ecological differences that strongly affect plant species composition.

The knowledge of natural stands dynamics could allow development of new approaches and practices in forest management focusing on biodiversity conservation.     

Slow understory redevelopment after clearcutting in high mountain forests

Besides natural tree regeneration itself, the development of the forest understory community is highly indicative of the ecological recovery of forest stands post-harvesting, and therefore of the sustainability of forest management. High mountain forests might show particularly slow recovery of the understory plant community because of harsh environmental conditions. We compared understory community richness and composition among three age classes of forest stands in the subalpine Engelmann Spruce–Subalpine Fir zone in the interior of British Columbia, Canada. Species composition was found to differ significantly between mature stands (>110 years old and never harvested) and both recent clearcuts (5–8 years old) and the oldest clearcuts present in the study area (second growth: 24–28 years old). A non-metric multidimensional scaling (NMDS) ordination revealed no unidirectional return of species composition in harvested stands towards that of mature forest; indeed, plots in recent clearcuts and second growth stands were similar to one another and clearly separated from the mature stands. Indicator Species Analysis revealed that moss species were particularly indicative of mature forest, with four moss species being common in mature stands but absent from both younger stages. Compared to what has been reported for lower elevation coniferous forests, e.g. in the U.S. Pacific Northwest, redevelopment of the understory appears to be slow after harvesting in these high elevation mountain forests. Rotation intervals that consider the natural temporal pattern of species turnover and the occurrence interval of major natural disturbances (here: fire) should provide effective approaches to sustainable forest management of these forests.     

Edge effects on epiphytic communities in a Mediterranean Quercus pyrenaica forest

Question: What are the edge effect responses of epiphytic lichen communities in Mediterranean Quercus pyrenaica forest? Location: Central Spain. Methods: We established ten transects perpendicular to a road dissecting a well conserved remnant of Q. pyrenaica forest into two sections. Transects extended from the forest/road edge to 100 m into the forest. Data were collected from seven plots in each transect at different distances from the edge. Variables were grouped into stand scale variables (distance to edge, number of trees per plot, mean diameter per plot, irradiance) and tree scale variables (diameter and height of sampled trees, aspect of the sampled square and relative height of the square). We used General Mixed Linear Models and constrained ordination techniques to test the hypothesis that the spatio‐temporal heterogeneity of light and water controls the occurrence of lichens and bryophytes along the edge‐interior gradient in the Q. pyrenaica forest. Results: Microclimatic parameters vary in a non‐linear way; edge and interior stands showed the most divergent and extreme values. Although the micro‐environment within Mediterranean forests is heterogeneous, interior conditions are apparently suitable for the performance of some specific forest epiphytes. Consequently, species richness does not show significant differences along the gradient. Total epiphytic cover increases towards the forest interior, but distance to the edge together with other predictors at the tree scale (aspect and height of the square) are the most relevant predictors for the composition and structure of these communities. Conclusions: Composition and structure of epiphytic communities in a Mediterranean semi‐deciduous forest are affected by the edge between the forest and the road constructed. Since some extremely rare lichens only occur at interior stands, the conservation of these threatened elements requires urgent conservation measures because well preserved and unmanaged forests in the Mediterranean region are very rare.     

Aspen lichens in agricultural and forest landscapes: the importance of habitat quality

The amount of aspen Populus tremula , has declined in the boreal forest landscape. This decline is especially marked in young and intermediate stands due to the lack of regeneration. Aspen regeneration is nowadays mainly restricted to abandoned agricultural land. The decrease of aspen is of particular concern as it has more host-specific species than any other boreal tree species. The main question addressed is whether regenerating aspen stands in agricultural habitats can compensate for the deficiency of young stands in the forest. Data on epiphytic macrolichens show that cyanolichens increased, in number and frequency, with stand age in the forest landscape, and that there was a striking difference in species composition between stands in the two landscapes. Lichens with cyanobacterial and green-algal photobionts dominated in the forest and agricultural stands, respectively. Notably, cyanolichens were not found in stands younger than 50 yr in the forest, and stands younger than 100 yr in the agricultural landscape. This difference between the landscapes cannot be explained by stand age, stand size or isolation. Instead, differences in habitat quality, due to differences in the physical environment associated with the presence of conifers in the older forest stands, appear to be involved. We suggest that in order to conserve cyanolichens that are confined to aspen, active management practices have to be adopted that promote the regeneration of aspen in the forest landscape, and the establishment of conifers in areas where aspen regeneration is confined to the agricultural landscape. In addition, until new aspen stands with appropriate physical environments have been established, these measures must be combined with the preservation of existing old-growth stands, which can provide appropriate source populations.     

Old rural parks support higher biodiversity than forest remnants

One of the main challenges in biodiversity conservation is to curb a further degradation and loss of high-quality habitats. In agricultural matrix landscapes, the detection of alternative habitats for habitat specialists may be a solution. Historic old parks or landscape gardens around manor houses and castles are cultural heritage of nobles, but their value in harbouring biodiversity is poorly acknowledged. Therefore we evaluated the potential of old rural parks to serve as a habitat for nemoral forest species. We recorded stand structure and the presence of forest biodiversity indicators in 74 closed-canopy stands of historic parks and compared them with 93 neighbouring mature forest remnants on ancient forest land. We estimated the importance of stand structure in relation to habitat type on biodiversity indicators. Finally we suggest single-value indicator-complexes for the cost-efficient assessment of the conservation value of forests and forest-like habitats. Park stands outclassed reference forests in several individual structural characteristics, and in combined indicators of habitat quality and biodiversity. Forests had higher estimates for the combined indicator of dead wood, but large-diameter dead wood types were more abundant in parks. Woodpeckers, several old-growth indicator epiphytes and forest herbs had successfully become established in planted forest-like park fragments. Old rural parks resemble high-conservation-value forests more than the best preserved contemporary forest remnants. After the century needed to overcome immigration delay, old parks do provide a refugium for temperate deciduous forest species. Consequently, biodiversity-targeted management should retain and enhance old-growth attributes in forests and on the peripheries of parks: e.g. preserving old trees to provide service for epiphytes, hollow trees and an understorey mosaic for birds and bats; dead wood elements for saproxylic insects and fungi; limited mowing frequency and increased cutting height for forest herbs. Forestry should enhance the recovery of mixed deciduous stands and avoid conifer plantations.     

Epiphytic macrolichens in managed and natural forest landscapes: a comparison at two spatial scales

To maintain biodiversity in managed forests we must understand how forestry affects various organisms across a wide range of spatial and temporal scales. We compared landscape structure, forest structure, and species richness and abundance of epiphytic macrolichens in three pairs of natural and managed boreal forest landscapes. Study landscapes (2500 ha) were located within and adjacent to three of the largest forest reserves in Sweden (Reivo, Muddus, Jelka). The structural heterogeneity within landscapes was higher in managed forests whereas within-stand structural heterogeneity was higher in natural landscapes. Species richness of macrolichens at the stand level (sample plot) was 23% higher in natural forests but there was no difference at the landscape level. Most (86%) of the common species were more frequent in natural landscapes. Lichen abundance (estimated by lichen litter) was two times higher in natural than in managed landscapes, 5.6 and 2.7 kg ha^-1 forest (pooled data), respectively. Both species richness and abundance were negatively related to cutting level (number and basal area of cut stumps) and positively related to stand variables (stand age, stem density and basal area). Lichen-rich forest stands were more numerous but covered a smaller area and were more isolated in managed landscapes. This may in turn have important consequences for dispersal of lichen propagules to second-growth forests. In conclusion, the results suggest that effects of forestry on epiphyte diversity and abundance are strongly related to the spatial scale (stand or landscape). To enhance biodiversity in managed forests we must increase structural heterogeneity at the whole range of spatial and temporal scales.     

Effects of forest management on epiphytic lichen diversity in Mediterranean forests

Question: What are the responses of epiphytic lichens to the intensity of management along a large environmental gradient in Mediterranean Quercus forests? Location: Central Spain. Methods: This study was carried out on 4590 trees located in 306 forest stands dominated by Quercus faginea or Quercus ilex ssp. ballota. The effect of forest management and other predictor variables on several species diversity indicators were studied. Variables modelled were total species richness, cyanolichen richness and community composition. A large number of predictor variables were included: forest fragmentation (patch size, stand variability), climate and topographic (altitude, slope, sun radiation, annual rainfall and mean annual temperature) and intensity of management. General linear models and constrained ordination techniques were used to model community traits and species composition, respectively. Results: Total richness and especially cyanolichens richness were significantly and negatively affected by the intensity of management. Lichen composition was influenced by management intensity, climatic and topographic variables and stand variability. Conclusions: In Mediterranean forests, human activities related to forestry, agricultural and livestock use cause impoverishment of lichen communities, including the local disappearance of the most demanding species. The conservation of unmanaged forests with a dense canopy is crucial for lichen diversity.     

Dispersal ecology of the endangered woodland lichen Lobaria pulmonaria in managed hemiboreal forest landscape

Changes in the forest management practices have strongly influenced the distribution of species inhabiting old-growth forests. The epiphytic woodland lichen Lobaria pulmonaria is frequently used as a model species to study the factors affecting the population biology of lichens. We sampled 252 L. pulmonaria individuals from 12 populations representing three woodland types differing in their ecological continuity and management intensity in Estonia. We used eight mycobiont-specific microsatellite loci to quantify genetic diversity among the populations. We calculated the Sørensen distance to estimate genetic dissimilarity among individuals within populations. We revealed that L. pulmonaria populations have significantly higher genetic diversity in old-growth forests than in managed forests and wooded meadows. We detected a significant woodland-type-specific pattern of genetic dissimilarity among neighbouring L. pulmonaria individuals, which suggests that in wooded meadows and managed forests dominating is vegetative reproduction. The vegetative dispersal distance between the host trees of L. pulmonaria was found to be only 15–30 m. Genetic dissimilarity among individuals was also dependent on tree species and trunk diameter. Lobaria pulmonaria populations in managed forests included less juveniles compared to old-growth forests and wooded meadows, indicating that forest management influences life stage structure within populations. We conclude that as intensive stand management reduces the genetic diversity of threatened species in woodland habitats, particular attention should be paid to the preservation of remnant populations in old-growth habitats. Within managed habitats, conservation management should target on maintenance of the stand’s structural diversity and availability of potential host trees.     

Nuovi reperti di intersessualità nelle Cucurbitacee

Abstract

The aim of this paper is to investigate differences in plant species composition between managed and unmanaged forests, and to assess if these difference give rise to a higher plant diversity in the unmanaged forest. Furthermore our aim is to relate forest structure to differences in plant species composition, identifying the structural attributes more strongly related to the unmanaged forest vegetation. We compared an old-growth forest and a managed highforest in the Abruzzo Lazio and Molise National Park (Central Italy). Plant species composition and diversity, deadwood components and live structure have been analyzed. We used permutational multivariate analysis of variance to test the response of species composition to management factor; furthermore, we compared species richness and beta diversity. Redundancy analysis has been used to relate plant species abundances to structural variables; the importance of dead and living wood components has been compared through variation partitioning. Plant species composition proved to be significantly different in the two sites, and the old-growth stand showed a higher plant diversity. From a structural point of view, we found differences especially in the amount and quality of deadwood, and in the diameter class distribution. These variables are also the most important in determining the old-growth stand plant species composition according to redundancy analysis. Variation partitioning confirmed the greater importance of the deadwood variables. Our results suggest that including deadwood surveys in traditional forest inventories could help in finding forests with both structural and floristic old-growth properties to be considered in conservation programmes. The imitation of natural dynamics, through the creation of gaps avoiding deadwood removal, could be an effective strategy for restoring old-growth conditions, also in terms of plant diversity.     

亚热带常绿阔叶林附生地衣凋落物的物种多样性和生物量的边缘效应

地衣是亚热带山地森林系统附生生物类群的重要组成部分之一,对环境变化极其敏感。为了更好地了解附生地衣对森林边缘效应的响应,我们在云南哀牢山地区原生山地常绿阔叶林中,分别在距林缘5m、25m、50m和 100m处设立样地,收集附生大型地衣的凋落物1年;分析附生地衣凋落物的物种多样性和生物量、功能群特征和组成结构对林缘深度变化的响应特征。研究结果显示,边缘效应能够显著提高林缘附生地衣群落的物种多样性和生物量;其发生的距离最深不超过25m。林缘-林内梯度上,不同地衣功能群的响应模式具有各自的特征。排序分析表明仅在5m样地与其他样地之间存在显著差异,指示种分析则发现仅5m样地具有指示种。哀牢山原生林中边缘效应促进林缘附生地衣生长和分布的现象,可能与当地高湿环境削减了地衣的高光损伤以及以叶状和灌状类群为主的地衣个体受到风力破坏的程度相对较低有关。     

Separating forest continuity from tree age effects on plant diversity in the ground and epiphyte vegetation of a Central European mountain spruce forest

Forest continuity has been identified as an important factor influencing the structure and diversity of forest vegetation. Primary forests with centuries of continuity are usually more diverse than young secondary forests as forest are colonized only slowly and because the former are richer in old tree individuals. In the present study, performed in unmanaged high-elevation spruce forests of the Harz Mountains, Germany, we had the unique opportunity to separate the effects of forest continuity and tree age on plant diversity. We compared an old-growth spruce forest with century-long habitat continuity with an adjacent secondary spruce forest, which had naturally established on a former bog after 1796 when peat exploitation halted. Comparative analysis of the ground and epiphyte vegetation showed that the plant diversity of the old-growth forest was not higher than that of the secondary forest with a similar tree age of >200 years. Our results suggest that a period of >200 years was sufficient for the secondary forest to be colonized by the whole regional species pool of herbaceous and cryptogam forest plants and epiphytes. Therefore, it is likely that habitat structure, including the presence of old and decaying trees, was more important for determining plant diversity than the independent effect of forest continuity. Our results are probably not transferrable to spruce forests younger than 200 years and highly fragmented woodlands with long distances between new stands and old-growth forests that serve as diaspore sources. In addition, our results might be not transferable to remote areas without notable air pollution, as the epiphyte vegetation of the study area was influenced by SO₂ pollution in the second half of the 20th century.