The relationship between tree size and epiphyte species richness: testing four different hypotheses

Aim For epiphytic plants trees are habitat units, and tree size determines epiphyte species richness. While growing, trees generate vertical microhabitats that are exploited by epiphytes. One would expect to find four different types of relationship between tree size and epiphyte species richness: positive linear (young trees), neutral (old trees), negative (old decaying trees) and positive asymptotic (trees of mixed size class in a mature forest). We tested these relationships in plots of colonizing sweetgum trees in pastureland, isolated remnant trees in pastureland (old oaks) and sweetgum and oaks in a pristine forest. Location The study was carried out in a landscape shaped by the fragmentation of lower montane cloud forest in San Andrés Tlalnelhuayocan (19°30′56′′ N and 96°59′50′′ W; 1500–1600 m a.s.l.) in central Veracruz, Mexico. Methods We measured the d.b.h. of all oaks and sweetgum trees (d.b.h. ≥ 5 cm) present in pastureland and in three 100 m² plots of a lower montane cloud forest. All trees were climbed and species richness of the epiphytes recorded. Results As expected, colonizer trees in pastureland showed a linear positive relationship. Although we found evidence that remnant oaks in pastureland had a neutral relationship between tree size and epiphyte species richness, the low power of the test did not allow us to make conclusions about the kind of relationship. Mixed size‐class pristine forest trees showed a positive linear relationship between tree size and epiphyte species richness instead of a positive asymptotic one. Main conclusions Our results suggest that in the study area epiphyte communities are unsaturated, as the number of species increases with tree size and does not reach a ceiling. This evidence supports the idea that the species–area relationship is not asymptotic. However, the epiphyte community on remnant pastureland oaks may be saturated as epiphyte species richness did not increase with tree size, but a larger sample size is needed to confirm the neutral pattern. Neutral, asymptotic and negative patterns in the relationship between tree size and epiphyte species richness depend on the saturation of the trees by epiphytes. Other studies have suggested tree saturation, but further research is necessary in order to confirm or rule out these patterns.     

Vascular Epiphytes on Isolated Pasture Trees Along a Rainfall Gradient in the Lowlands of Panama

Secondary habitats are increasing in importance in tropical countries due to ongoing destruction of pristine vegetation. In spite of the magnitude of current changes, our understanding of their effects on nontrees (e.g., nonvascular or vascular epiphytes) is still very patchy, particularly in lowland habitats. Here, we report a study with isolated pasture trees in southwest Panama. The >800 studied trees, which belonged to >100 different species, harbored almost 27,000 epiphytes of 83 species. Orchidaceae was the most species‐rich family, with almost 60 percent of all species, while Bromeliaceae were most abundant. A rainfall gradient in the study region from ca 1000 to >3000 mm explained more of the variation in species abundance and richness than host characteristics (e.g., species identity, tree size). The unexpectedly large number of epiphytes in these pastures still represents a substantial change relative to a natural setting, which is suggested by a comparison with a forest inventory under similar climatic conditions. In pastures, species richness was lower as deduced from individual‐based rarefaction curves, a larger proportion of species and individuals showed crassulacean acid metabolism, and the relationship of epiphyte abundance/species richness and tree diameter was much less steep. Even the already reduced diversity, however, may be only transient in secondary habitats—the long‐term persistence of epiphyte populations in pastures is an open question and has to be addressed by repeated monitoring to fully evaluate the significance of pasture trees for the conservation of vascular epiphytes in tropical lowlands.     

Habitat isolation changes the beta diversity of the vascular epiphyte community in lower montane forest,Veracruz, Mexico

Habitat isolation is one of the most important factors endangering the biodiversity, but little research has been done with vascular epiphytes. In order to understand the effect of isolation on the epiphyte community, we studied epiphyte diversity on three plots in a forest fragment, two riparian forest fragments, and in isolated pastureland trees. We found 118 vascular epiphyte species. On forest plots, both epiphyte richness per tree (S_tree) and species turnover rate within trees (β_tree) registered the highest values, although the lowest S_tree diversity was also found there; additionally inside the forest were host species with clearly different epiphyte community. S_tree and β_tree diversities of riparian fragments behaved similarly to those of the forest. Isolated trees had the second highest S_tree diversity, although their β_tree diversity was the lowest. In the forest plots were both, the highest and lowest expected accumulated richness (α diversity); on riparian fragments it was intermediate, and the second lowest α diversity was registered for isolated trees. Species turnover rate among plots (β) was high and was associated with both, isolation and a distance gradient from permanent water sources. The epiphyte community on isolated trees was clearly different to the other habitats. Results suggest that deforestation eliminated dry areas and specific hosts that were important for the maintenance of epiphyte species richness. In pastureland trees the epiphyte β_tree diversity diminished, suggesting a simplification of the environment for epiphytes and causing a low α diversity.     

Role of dominant tree species on diversity of herbivorous insect community in temperate forests

Oak (Quercus spp.) and hornbeam (Carpinus spp.) are one of dominant tree species in East Asian temperate broad leaf deciduous forests and many insect species, including more than 65% of Lepidoptera species, feed on these trees. We sampled lepidopteran caterpillars from two 0.1 ha plots in a temperate forest to investigate the role of dominant trees (oaks and hornbeams) in herbivore community. In total, we identified 738 caterpillars from 223 Lepidopteran species on 34 tree species. Most caterpillar species were from species-rich families such as Geometridae 25% (56 spp.), Noctuidae, and Tortricidae. After excluding dominant trees, plant-herbivore network analyses showed increased network specialization and nestedness and decreased generality and vulnerability. These results suggest that oaks and hornbeams support a large Lepidopteran herbivore community, and co-occurring plant species support diverse but specific herbivores. Geographical distribution and plant community are closely related to diversity of the herbivore community. Future work is needed to investigate the likelihood that specialist herbivores become relatively more abundant in the forest as oaks are succeeded by hornbeams.     

Organic matter transformations and soil fertility in a treed pasture in semiarid NE Brazil

Planted silvo-pastoral systems are formed by sparing selected native trees when land is cleared for pasture establishment, or by planting selected species – often known agroforestry species – into the establishing pasture. Isolated trees within pastures and savannas are often associated with `resource islands', characterized by higher fertility and organic matter levels under the tree canopies. We here examine the processes underlying the differences in fertility and organic matter in a buffel grass (Cenchrus ciliaris L.) pasture that contained two tree species (Ziziphus joazeiro Mart., Spondias tuberosa Arruda Cam.) preserved from the native thorn forest and a planted agroforestry species (Prospois juliflora Swartz D.C). The objective is to distinguish effects of soil variability from those induced by the presence of trees or the planting of pasture. The ¹³C signatures of the original (largely C3) vegetation, the preserved and planted trees, and the planted C4 grass were used to distinguish the provenance of organic matter in the top soil (0–15 cm). This allowed the conclusion that all trees maintained C3 derived C at the original thorn forest level, while lower levels under pasture were due to mineralisation of organic matter. The net rates of forest-derived C loss under pasture varied with soil type amounting to between 25 and 50% in 13 years after pasture establishment. Only on Alfisol, C inputs from the pasture compensated for the C3-C losses. Analysis of organic and inorganic P fractions indicated Z. joazeiro and P. juliflora enriched the soil under their canopy with P, whereas S. tuberosa had no positive effect on fertility. A combination of ANOVA and spatial analysis and mapping was used to show vegetation effects.     

Contribution of peeling host for epiphyte abundance in two tropical dry forests in the “El Cielo Biosphere Reserve”, Mexico

Host traits partly determine the abundance and species richness of epiphytes in tropical forests. It has been proposed that older trees with rough bark and evergreens often house more individuals and more epiphytic species than those with thin, smooth, and peeling bark, which harbor few epiphytes. We hypothesize (i) that epiphytes are more abundant and species-rich in the more shaded forest, which is related to bark roughness, and (ii) that epiphytes are distributed in the middle of the host, where microenvironmental conditions are more favorable to survival. We evaluated abundance, species richness, and vertical distribution of epiphytes in two tropical dry forests, according to the deciduousness and basal area of the trees. Moreover, we selected the most abundant epiphytes to test whether their distribution is related to a specific bark type and examine their vertical distribution in two dry forests. We distinguished a high abundance and species richness of epiphytes in the deciduous forest, although basal area and host species richness were higher in the semi-deciduous forest. In both forests, we found a positive relationship between epiphyte abundance and basal area. Higher abundance of epiphytes was related to the predominance of Tillandsia schiedeana, a drought-adapted species, in both forests. Unexpectedly, epiphytes abundantly colonized Bursera simaruba, a host with peeling bark and a very branched crown, where small individuals of T. schiedeana colonized abundantly toward the top of the crown. Our results show the importance of the tropical dry forest, particularly, B. simaruba, in maintaining epiphyte diversity in terms of T. schiedeana colonization.     

Isolated Pasture Trees and the Vegetation under their Canopies in the Chiapas Coastal Plain,Mexico1

The Coastal Plain of Chiapas (southern Mexico) was formerly covered by large tracts of subhumid tropical forests but is heavily deforested at present. In this region, 15 pastures were selected to characterize species composition of isolated trees, as well as to describe species composition, growth form patterns, and patterns of dispersal units in the vegetation growing under their canopies. The 65 recorded pasture trees belonged to 20 species and 11 families, of which Fabaceae and Moraceae were the most species-rich. Coccoloba barbadensis (Polygonaceae) and Enterolobium cyclocarpum (Fabaceae) were the most abundant and frequent trees in the studied pastures. More than half (55%) of isolated tree species were fleshy-fruited. In the vegetation sampled under pasture trees, 134 species and 45 families were found. Fabaceae and Poaceae had the largest numbers of species. Herbs were the predominant growth form (46.3%), followed by shrubs (23.9%), trees (23.1%), and lianas (2.2%); 6 species could nor be placed in any growth form category. Most species of this flora were fleshy-fruited (43.3%), followed by heavy, gravity-dispersed fruits (17.9%). The analysis of dispersal units by growth form category confirmed the prevalence of fleshy fruits, although their predominance was not so obvious among herb species. Almost half (49.2%) of the flora under pasture trees was typical of secondary vegetation; this pattern was true for herbs but not for most woody species, which were typical of primary vegetation. A numeric classification of the vegetation samples taken under pasture trees produced eight floristic groups, all of which were independent of the specific identity of pasture trees. No significant effect of dispersal unit type of pasture tree on the characteristics of the vegetation growing under them was found. Future attempts to re-create the original forest cover using isolated trees in pastures as regeneration foci should pay more attention to the maintenance of a large specific diversity independently of the dispersal types among these components of tropical landscapes.     

Can spatial variation in epiphyte diversity and community structure be predicted from sampling vascular epiphytes alone?

Aim Non‐vascular epiphytes have been largely ignored in studies examining the biotic and abiotic determinants of spatial variation in epiphyte diversity. Our aim was to test whether the spatial patterning of species richness, biomass and community composition across geographic regions, among trees within regions, and among branches within trees is consistent between the vascular and non‐vascular components of the temperate rain forest flora. Location Coastal lowland podocarp‐broadleaved forests on the west coast of the South Island of New Zealand. Methods We collected single samples (30 × 25 cm) from 96 epiphyte assemblages located on the inner branches of 40 northern rata (Metrosideros robusta) trees. For each sample, branch characteristics such as branch height, branch diameter, branch angle, branch aspect, and minimum and maximum epiphyte mat depth were recorded. The biomass for each individual epiphyte species was determined. Results Northern rata was host to a total of 157 species, comprising 32 vascular and 125 non‐vascular species, with liverworts representing 41% of all species. Within epiphyte mats, the average total organic biomass of 3.5 kg m^?2 of branch surface area consisted largely of non‐living biomass and roots. Vascular and non‐vascular epiphytes showed strikingly different spatial patterns in species richness, biomass and composition between sites, among trees within sites, and among branches within trees, which could not be explained by the branch structural characteristics we measured. The two plant groups had no significant association in community composition (r = 0.04, P = 0.08). However, the species richness of vascular plant seedlings was strongly linked to the presence/absence of lichens. Main conclusions Non‐vascular plants contributed substantially to the high species richness and biomass recorded in this study, which was comparable to that of some tropical rain forests. High variability in community composition among epiphyte mats, and very low correlation with any of the environmental factors measured possibly indicate high levels of stochasticity in seed or spore colonization, establishment success or community assembly among branches in these canopy communities. Although we found some evidence that vascular plant seedling establishment was linked to the presence of lichens and the biomass of non‐living components in the epiphyte mats, there was no correlation in the spatial patterning or determinants of species richness between non‐vascular and vascular plants. Consequently, variation in total epiphyte biodiversity could not be predicted from the measurement of vascular plant diversity alone, which highlights the crucial importance of sampling non‐vascular plants when undertaking epiphyte community studies.     

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.     

Differences in epiphyte biomass and community composition along landscape and within-crown spatial scales

Vascular epiphytes contribute to the structural, compositional, and functional complexity of tropical montane cloud forests because of their high biomass, diversity, and ability to intercept and retain water and nutrients from atmospheric sources. However, human-caused climate change and forest-to-pasture conversion are rapidly altering tropical montane cloud forests. Epiphyte communities may be particularly vulnerable to these changes because of their dependence on direct atmospheric inputs and host trees for survival. In Monteverde, Costa Rica, we measured vascular epiphyte biomass, community composition, and richness at two spatial scales: (1) along an elevation gradient spanning premontane forests to montane cloud forests and (2) within trees along branches from inner to outer crown positions. We also compared epiphyte biomass and distribution at these scales between two different land-cover types, comparing trees in closed canopy forest to isolated trees in pastures. An ordination of epiphyte communities at the level of trees grouped forested sites above versus below the cloud base, and separated forest versus pasture trees. Species richness increased with increasing elevation and decreased from inner to outer branch positions. Although richness did not differ between land-cover types, there were significant differences in community composition. The variability in epiphyte community organization between the two spatial scales and between land-cover types underscores the potential complexity of epiphyte responses to climate and land-cover changes.     

Epiphytic (including hemiepiphytes) diversity in three timber species in the southwestern Amazon, Brazil

Forestry managers have been searching for ways to reduce the impacts of logging on Amazonian biodiversity, but some basic factors are still not considered in native forestry operations, among them the diversity of epiphytes associated with the logged trees. Our goals in this study were to determine the floristic composition, quantify the species richness, and characterize the species diversity of the vascular epiphytic community present in three timber tree species in Acre State, Brazil. We collected and identified all epiphytes in 30 randomly selected trees ≥35 cm DBH of each of three important timber species, Tabebuia serratifolia, Manilkara inundata and Couratari macrosperma. We also documented the epiphyte diversity in 120 randomly selected trees ≥35 cm DBH of 56 other species to determine whether the three timber species have different epiphyte diversity than the tree community at large. The epiphyte samples in the three timber species showed 77 species, 13 of which were new records for the flora of Acre state. The epiphyte community in the randomly selected trees presented a total of 56 species. The timber species phorophytes hosted on average three times more epiphyte species per tree than the other 120 randomly selected trees. These results show that a substantial portion of local floristic richness can be lost during logging activity due if not properly managed by rescuing epiphytes after felling the trees. Although these epiphytes could contribute positively to forestry sustainability due to their ornamental value, increasing the economic yield per hectare, there are no local initiatives for economic use of epiphytes.     

Influence of wildfire on diversity of culturable soil microfungal communities in the Mount Carmel forest,Israel

The fire-related variations in culturable microfungal communities in the soil of the Mount Carmel forest, Israel, were examined by comparing the communities from burned and adjacent unburned soil plots under pine and oak trees – collected 6, 18, and 26 months after the fire. A total of 82 species representing 44 genera were isolated using the soil dilution plate method. The results showed that the fire had strongly influenced the composition and structure of microfungal communities. The fire remarkably changed physical and chemical properties of the environment, decreasing water holding capacity, organic matter and total nitrogen content in the burned soil. These changes supported abundant development of fast-growing mycoparasitic species (Clonostachys rosea and Trichoderma spp.) and caused significant decrease in species richness. The variations in community composition were much more expressed in the burned soils under oak vegetation as compared with the pine trees. In the oak burned soils, the contribution of the “mesic” component, Penicillium spp., was markedly lower, whereas the contribution of the “xeric”, stress-selected component, melanin-containing species, was higher than in the unburned communities. Such variations can be also considered as a community response to the fire-related decrease in water and nutrient content in the burned soils.     

A metapopulation approach to the analysis of long‐term changes in the epiphyte vegetation on the host tree Annona glabra

Question: Do vascular epiphyte species have a metapopulation structure? What are the qualitative and quantitative long‐term changes of the complete vascular epiphyte vegetation in a particular host tree species? Location: Lowland forest on Barro Colorado Island (9° 10’ N, 79°51’ W), Republic of Panama. Methods: In 1994 and 2002 we conducted a census of all vascular epiphytes growing on more than 1000 Annona glabra trees (= patches). Epiphyte species abundances were recorded at the tree level in each census. Results: The number of epiphyte individuals increased from ca. 15 000 to ca. 23 700 individuals during the census interval while the species composition on Annona glabra as a whole was rather stable. There was a strong positive relationship between occurrence in patches and local abundance of the species, and between species richness and host tree stand size. The dynamics of local populations of a given species were uncorrelated to each other; small and large local populations of most species had the same probability to go extinct. The frequency distribution of species on all host trees was not bimodal, but on a subset of heavily colonized host tree stands it was. Numbers of species and individuals were correlated with tree size which was not due to a correlation of tree size and tree age. Conclusions: As far as the most abundant epiphyte species with metapopulation structures are concerned, these species belong to diverse families, e. g. Orchidaceae, Bromeliaceae and Polypodiaceae. Even ca. 80 years after the initial establishment of the host tree species in the study area epiphytes are still in the stage of initial colonization and have not reached a steady state as indicated by the strong increase in individuals and the ongoing colonization of empty trees.     

Nest site selection in middle and great spotted woodpeckers <Emphasis Type="Italic">Dendrocopos medius</Emphasis> &; <Emphasis Type="Italic">D. major</Emphasis>: implications for forest management and conservation

Success of species conservation depends to a large extent on comprehensive management that considers all critical aspects of a species’ niche. Many studies have examined habitat factors in relation to occurrence, abundance or foraging behaviour of European woodpecker species, while relatively little is known about nest site selection. I compared habitat structures used for nesting by middle and great spotted woodpeckers Dendrocopos medius and D. major with available structures in an oak forest in the Swiss lowlands. I first tested if nest trees were randomly selected among available trees by focusing on species, condition and diameter of nest trees, and on the presence of the fruiting body (hereafter sporophore) of polypores (wood-decomposing fungi). Second, I examined if the nesting niches of the two species were differentiated. Both species showed strong preferences for oaks, large trees, dead trees and for trees with sporophores. Nest sites of the two species differed most strongly with respect to the presence of sporophores, cavity age and tree condition, pointing towards interspecific competition for nest sites. Old living or dead trees with sporophores are central components of the nesting niche of middle and great spotted woodpeckers. Conservation plans for the threatened middle spotted woodpecker have so far mostly focused on the needs in terms of distribution and foraging; future conservation strategies and forest management must take into account the preference for dead and decaying trees with sporophores as another vital resource. This will also provide benefits for other woodpecker species as well as for the community of secondary cavity nesters.     

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.     

Pollination and phenology of flowers in the canopy of two contrasting rain forest types in Amazonia,Colombia

The main objective of this investigation was to study the pollination characteristics of two types of Amazonian rain forest at plant community level. Seasonally inundated forest was compared with upland (tierra firme) forest. The study focused on plant species in the canopy. The pollination spectra show that in both forests most canopy trees and lianas are pollinated by small bees, large bees, butterflies or by small, relatively unspecialized insects. In the upland forest small bees are the most important pollinators (32% of all species of trees and lianas are pollinated by them), whereas large bees are predominant in the floodplain (22%). Other pollinators, like hummingbirds, bats, moths, and beetles are less common (>10%), but always somewhat more important in the flood plain than in the upland forest. Bees are the most common pollinators of epiphytes. In the flood plain forest, flies are also important as epiphyte pollinators (19%), whereas in the upland forest hummingbirds pollinate more epiphytes. The phenological patterns are quite similar in both the upland and the flood plain. We found a peak in flowering in the transition period between the wet and the dry season. Flowering activity was lowest during the wet season. Differentiation in sexual systems was correlated with life form. Dioecy and monoecy were found mostly among tree species. Most species of all life forms though were hermaphroditic. No difference with respect to the relative importance of sexual systems was found between the two forest types.     

Primary ecological succession in vascular epiphytes: The species accumulation model

Epiphytes are integral to tropical forests yet little is understood about how succession proceeds in these communities. As trees increase in size they create microhabitats for late‐colonizing species in both small and large branches while maintaining small tree microhabitats for early colonizing species in the small and young branches. Thus, epiphyte succession may follow different models depending on the scale: at the scale of the entire tree, epiphytes may follow a species accumulation model where species are continuously added to the tree as trees increase in size but at the scale of one zone on a branch (e.g., inner crown: 0–2 m from the trunk), they may follow the replacement model of succession seen in terrestrial ecosystems. Assuming tree size as an indicator of tree age, I surveyed 61 Virola koschnyi trees of varying size (2.5–103.3 cm diameter at breast height) in lowland wet tropical forest in Costa Rica to examine how epiphyte communities change through succession. Epiphyte communities in small trees were nested subsets of those in large trees and epiphyte communities became more similar to the largest trees as trees increased in size. Furthermore, epiphyte species in small trees were replaced by mid‐ and late‐successional species in the oldest parts of the tree crown but dispersed toward the younger branches as trees increased in size. Thus, epiphyte succession followed a replacement model in particular zones within treecrowns but a species accumulation model at the scale of the entire tree crown.     

The epiphyte vegetation of Annona glabra on Barro Colorado Island, Panama

Aim Information on the community composition, structure, and dynamics of epiphyte vegetation is scarce. A survey of the epiphytes occurring on all individuals of one particular host tree species in a well-studied neotropical research site allowed us a comparison of the epiphyte flora of this tree with the local epiphyte flora, the analysis of spatial distribution patterns and the use of these patterns as indications for changes in time. In the future, our results can be used as a baseline data-set for the direct observation of the long-term dynamics in epiphyte communities. Location The study was conducted on Barro Colorado Island (BCI), Panama. Methods We recorded all individuals of the vascular epiphytes growing on Annona glabra L., a flood-tolerant, multiple-stemmed tree, which is restricted to the shoreline of BCI. Data on tree biometrics, epiphyte species, and epiphyte abundances were collected for more than 1200 trees. Results In total, we encountered almost 15,000 epiphytic individuals in sixty-eight species, corresponding to more than one third of the entire epiphyte flora of Barro Colorado Island. The component species differed strongly in abundance: the four most important species accounted for >75% of all individuals. In most cases, the same four species were also the first to colonize a tree (=phorophyte). Colonization patterns indicated no replacement of early colonizers by late arrivals. Species richness and epiphyte abundances showed a positive correlation with the size and the density of the host trees. All species showed a highly clumped distribution and the physiognomy of epiphyte communities of individual trees was dominated either by one or several of the four most common species or by a set of frequently co-occurring tank bromeliads. Other species were dominant only in exceptional cases. Most species were always rare. A distance effect on community composition was mostly confined to a local scale with an increased similarity in the species assemblage of stems of a tree v. neighbouring trees. Main conclusions The epiphytes on a single small phorophyte species may encompass a surprisingly large proportion of the local epiphyte flora. The observations that most tree crowns are inhabited by a single or only very few species, and that all epiphyte species show highly clumped distributions suggest a predominance of very local dispersal within a tree crown, which is only infrequently interrupted by successful long-distance dispersal between crowns.     

Intraspecific variation in epiphyte functional traits reveals limited effects of microclimate on community assembly in temperate deciduous oak canopies

Forest canopies are heterogeneous environments where changes in microclimate over short distances create an opportunity for niche‐based filtering of canopy‐dwelling species assemblages. This environmental filtering may not occur if species' physiological capacities are flexible or if rapid dispersal alleviates compositional differences. I assess the role of humidity, light and temperature gradients in structuring epiphyte communities in temperate deciduous oak (Quercus) canopies and determine whether gradients filter species with fixed traits or whether environmental constraints act primarily to alter individual phenotypes. I measured environmental conditions and seven functional traits related to water and light acquisition on individual macrolichens at 60 sample locations in northern red oaks Quercus rubra in two Piedmont forests in North Carolina, USA. The effects of environmental variables on individual‐level traits and community composition were evaluated using linear mixed models and constrained ordination (RDA). In general, traits and community composition responded weakly to environmental variables and trait variation within taxa was high. Cortex thickness exhibited the strongest response, such that individuals with thicker cortices were found in samples experiencing lower humidity and higher light levels. Overall, gradients of humidity, light and temperature were not strong environmental filters that caused large changes in community composition. This was probably due to phenotypic variability within taxa that enabled species to persist across the full range of environmental conditions measured. Thus, humidity affected the phenotype of individuals, but did not limit species distributions or alter community composition at the scale of branches within trees. Community and trait responses were primarily associated with site‐level differences in humidity, suggesting that in these forests landscape‐scale climatic gradients may be stronger drivers of epiphyte community assembly than intra‐canopy environmental gradients.     

Floristic composition and structure of vegetation under isolated trees in neotropical pastures

Abstract. Large isolated trees are a common feature of the agricultural landscape in humid tropical regions originally covered by rain forest. These isolated trees are primarily used as a source of shade for cattle and people. 13 pastures (totalling ca. 80 ha) currently used as cattle pasture were studied. In them, we registered 265 isolated trees belonging to 57 species. 50 trees of the most frequent species (Ficus spp. n = 30 and Nectandra ambigens n = 20) were selected to examine the influence of isolated trees on floristic composition and vegetation structure in the pastures. At each tree, three 4–m² quadrats were sampled: under the canopy, directly under the canopy perimeter, and beyond the canopy in the open pasture. Under-canopy vegetation was structurally and floristically different from the other two sampling sites. Mean species richness per quadrat was significantly higher under the canopy (17.8 ± 4.3 SD) than at the canopy perimeter (11.2 ± 3.4) and in the open pasture (10.6 ± 3.6) sites. Stem density was higher at under-canopy sites, where greater proportions of endozoochorous and rain-forest species were found. Isolated trees function as nursery plants for rain-forest species by facilitating the establishment of zoochorous species whose seeds are deposited under the tree canopies by frugivorous birds or bats. Our results imply that isolated trees may play a major role in seed dispersal and establishment of native species, which is of consequence for the preservation of rain-forest species in these fragmented landscapes.