Effect of Host Tree Traits on Epiphyte Diversity in Natural and Anthropogenic Habitats in Ecuador

Vascular epiphytes represent a highly diverse element of tropical rain forests, but they depend strongly on the structure and taxonomic composition of their tree communities. For conservation planning, it is therefore critical to understand the effect of host tree characteristics on epiphyte species richness in natural and anthropogenically transformed vegetation. Our study compares the effect of human land‐use on epiphyte diversity based on 220 study plots in a lowland rain forest and an Andean cloud forest in western Ecuador. We evaluate the relevance of host tree size and taxonomic identity for epiphyte species richness in contiguous primary forests, forest fragments, isolated remnant trees (IRTs), and secondary forests. At both study sites, epiphyte diversity was highest in primary forests, and it was lowest on IRTs and in secondary forests. Epiphyte species numbers of forest fragments were significantly reduced compared with the contiguous primary forest at the lowland study site, but not in the cloud forest area. Host tree size was a core predictor among secondary forests, but it had less significance within other habitat types. Taxonomic identity of the host trees also explained up to 61 percent of the variation in epiphyte diversity, especially for IRTs. The structural and taxonomic composition of the tree community in anthropogenically transformed habitat types proved to be fundamental to epiphyte diversity. This highlights the importance of deliberate selection of tree species for reforestation in conservation programs and the possible negative effects of selective logging in primary forests. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

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.     

Elevational changes in the avian community of a Mesoamerican cloud forest park

Harboring many range‐restricted and specialized species, high elevation tropical cloud forests are diverse habitats represented in many protected areas. Despite this, many such areas receive little practical protection from deforestation and land conversion. Moreover, montane species may be more sensitive to climate change owing to various factors affecting community assembly across elevational gradients. Few studies have used annual monitoring to assess how biological communities in cloud forests may be shifting in response to habitat or climate change or assessed the efficacy of protected areas in buffering these effects. We analyzed avifaunal community trends in a 10‐yr dataset of constant‐effort bird point‐count data in a cloud forest national park in Honduras, Central America. We found that species richness and diversity increased at higher elevations, but decreased at lower elevations. Abundances of most dietary and forest‐dependency groups exhibited similar trends, and many key cloud forest species shifted upslope and/or increased in abundance. Taken together, our results suggest that the avian community is moving upslope and species composition is changing. Results for species richness and diversity were similar when only nondegraded transects were considered, suggesting the role of climate change as an important driver. At lower elevations, however, many species may be negatively affected by increased habitat degradation, favoring species with low forest dependency. Continued habitat conversion and climate change could push the cloud forest bird community further upslope, potentially resulting in increased competition, mortality, and even extirpation of some species. Increased protection is unlikely to mitigate the effects of climate change.     

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.     

Carbon pools recover more quickly than plant biodiversity in tropical secondary forests

Although increasing efforts are being made to restore tropical forests, little information is available regarding the time scales required for carbon and plant biodiversity to recover to the values associated with undisturbed forests. To address this knowledge gap, we carried out a meta-analysis comparing data from more than 600 secondary tropical forest sites with nearby undisturbed reference forests. Above-ground biomass approached equivalence to reference values within 80 years since last disturbance, whereas below-ground biomass took longer to recover. Soil carbon content showed little relationship with time since disturbance. Tree species richness recovered after about 50 years. By contrast, epiphyte richness did not reach equivalence to undisturbed forests. The proportion of undisturbed forest trees and epiphyte species found in secondary forests was low and changed little over time. Our results indicate that carbon pools and biodiversity show different recovery rates under passive, secondary succession and that colonization by undisturbed forest plant species is slow. Initiatives such as the Convention on Biological Diversity and REDD+ should therefore encourage active management to help to achieve their aims of restoring both carbon and biodiversity in tropical forests.     

Microclimatic factors associated with elevational changes in army ant density in tropical montane forest

Abstract.  1. The density (rate of encountering foraging raids) and species richness of army ants (Formicidae: Ecitoninae, and behaviourally convergent Ponerinae) was measured in montane tropical forest. Above-ground and subterranean army ant raids were sampled using standard protocols at four sites across an elevational gradient (1200–1650 m above mean sea level) in and near cloud forest in the area of Monteverde, Costa Rica.
2. Mean ambient temperature differed among sites, and decreased with elevation. For the above-ground foraging army ant species, raid rates also declined with elevation. Surface army ant raid rates, however, were not affected by day to day weather variation within sites (temperature, cloud cover, or precipitation).
3. For the underground foraging army ant species, raid rates did not vary directionally with elevation, and subterranean raid rates were not affected by day to day weather variation within sites.
4. Army ant species richness was not directionally related to elevation, and species sharing among sites was generally high.
5. Army ant community structure changes with elevation in Neotropical montane forest, and the results suggest that the strongest effects are of temperature regimes on the density of raids. These findings provide a baseline against which to detect changes in army ant communities that may accompany directional climate change in tropical cloud forests.     

Structure of the Epiphyte Community in a Tropical Montane Forest in SW China

Vascular epiphytes are an understudied and particularly important component of tropical forest ecosystems. However, owing to the difficulties of access, little is known about the properties of epiphyte-host tree communities and the factors structuring them, especially in Asia. We investigated factors structuring the vascular epiphyte-host community and its network properties in a tropical montane forest in Xishuangbanna, SW China. Vascular epiphytes were surveyed in six plots located in mature forests. Six host and four micro-site environmental factors were investigated. Epiphyte diversity was strongly correlated with host size (DBH, diameter at breast height), while within hosts the highest epiphyte diversity was in the middle canopy and epiphyte diversity was significantly higher in sites with canopy soil or a moss mat than on bare bark. DBH, elevation and stem height explained 22% of the total variation in the epiphyte species assemblage among hosts, and DBH was the most important factor which alone explained 6% of the variation. Within hosts, 51% of the variation in epiphyte assemblage composition was explained by canopy position and substrate, and the most important single factor was substrate which accounted for 16% of the variation. Analysis of network properties indicated that the epiphyte host community was highly nested, with a low level of epiphyte specialization, and an almost even interaction strength between epiphytes and host trees. Together, these results indicate that large trees harbor a substantial proportion of the epiphyte community in this forest.     

Assessing the effects of selective logging on birds in Neotropical piedmont and cloud montane forests

In tropical and subtropical forests there is limited information about how to integrate sustainable timber management with the conservation of biodiversity. We examined the effect of selective logging on the bird community to help develop management guidelines to assure the conservation of biodiversity in forests managed for timber production. The study design consisted of control and harvested plots in piedmont and cloud forests of the subtropical montane forests of the Andes in northwestern Argentina. We conducted bird point-count surveys combined with distance estimation. Breeding season bird community composition was more similar between control and logged forest in both the cloud forest and piedmont, than between the two elevations, probably because Neotropical bird communities change dramatically along elevational gradients. Within each elevation zone, community composition changed significantly between harvested and control forests. Both between and within each elevation zone no significant differences in bird density were detected. Similarly, when we analyzed bird density according to diet guilds no general pattern could be extracted. However, we found a significantly greater density of cavity nesters and lower of non-cavity nesters in control plots, probably because most trees that can develop suitable cavities were extracted in logged plots and these plots had a greater structural diversity enabling more nesting resources. Grouping species according to their nesting habitat requirements has rarely been used in the neotropics and other tropical and subtropical forests, but focusing management attention on cavity nesters might address the most sensitive portion of the avian community as well as other species dependent on trees likely to hold cavities.     

Diversity of dung and carrion beetles in a disturbed Mexican tropical montane cloud forest and on shade coffee plantations

This paper analyzes the diversity of dung and carrion beetles (Scarabaeinae and Silphidae) in four human-induced habitats of a disturbed tropical montane cloud forest: polyspecific shade coffee plantations, monospecific shade coffee plantations, tropical montane cloud forest fragments, and clear cuts. The four habitats had similar richness, species composition, and assemblage structure of dung and carrion beetles. Differences were found in abundance and biomass levels for the four dominant species in the landscape. Dung beetles were more abundant than carrion beetles, but the biomass was higher for the latter. Carrion beetles were seasonal, while dung beetles were clearly not. When forest fragments and shade coffee plantations were compared to other similar habitats in the region, the same general pattern was observed. However, forests with high disturbance and monospecific shade coffee plantations had lower species richness than forests with low and medium disturbance and polyspecific shade coffee plantations. Thus shade coffee plantations maintain connectivity between patches of cloud forest in a landscape that is strongly affected by human activities. Protecting landscape diversity appears to ensure high species richness.     

Climate and microhabitat shape the prevalence of endozoochory in the seed rain of tropical montane forests

Endozoochory, the dispersal of seeds by animal ingestion, is the most dominant mode of seed dispersal in tropical forests and is a key process shaping current and future forest dynamics. However, it remains largely unknown how endozoochory is associated with environmental conditions at regional and local scales. Here, we investigated the effects of elevation, climate, and microhabitat conditions on the proportion of endozoochorous plant species in the seed rain of the tropical Andes of southern Ecuador. Over 1 year, we measured seed rain in 162 seed traps on nine 1-ha forest plots located at 1000, 2000, and 3000 m a.s.l. We recorded climatic conditions (mean annual temperature and rainfall) in each plot and microhabitat conditions (leaf area index and soil moisture) adjacent to each seed trap. In total, we recorded 331,838 seeds belonging to 323 morphospecies. Overall, the proportion of endozoochorous species in the seed rain decreased with elevation. The relative biomass of endozoochorous species decreased with increasing rainfall, whereas the relative seed richness of endozoochorous species increased with increasing temperature and leaf area index. These findings suggest an interplay between climate factors and microhabitat conditions in shaping the importance of endozoochorous plant species in the seed rain of tropical montane forests. We conclude that changing climatic and microhabitat conditions are likely to cause changes in the dominant dispersal modes of plant communities which may trigger changes in the current and future dynamics of tropical forests.     

Cryptogamic epiphytes in primary and recovering upper montane oak forests of Costa Rica – species richness,community composition and ecology

Species richness, community composition and ecology of cryptogamic epiphytes (bryophytes, macrolichens) were studied in upper montane primary, early secondary and late secondary oak forests of the Cordillera de Talamanca, Costa Rica. Canopy trees of Quercus copeyensis were sampled with the aim of getting insight in patterns and processes of epiphyte succession and recovery of diversity in secondary forest following forest clearing. Species richness of cryptogamic epiphytes in secondary and primary forests were nearly the same, showing that primary forests are not necessarily more diverse than secondary forests. High species richness of secondary forests was presumed due to the closed canopy, resulting in permanently high atmospheric humidity in these forests. Similarity in species composition of secondary and primary forests increases with forest age, but after 40 years of succession one third (46 species) of primary forest species had not re-established in the secondary forest. Community composition in primary and secondary forests differed markedly and indicates that a long time is needed for the re-establishment of microhabitats and re-invasion of species and communities adapted to differentiated niches. Genera and species exclusive to primary forests are relevant as indicator taxa and conservation targets. Forty percent (68 species) of all species recorded are restricted to secondary forests, indicating the important contribution of secondary forest diversity to total species richness of the oak forests of Costa Rica.     

Small montane cloud forest fragments are important for conserving tree diversity in the Ecuadorian Andes

Montane tropical cloud forests, with their complex topography, biodiversity, high numbers of endemic species, and rapid rates of clearing, are a top global conservation priority. However, species distributions at local and landscape scales in cloud forests are still poorly understood, in part because few regions have been surveyed. Empirical work has focused on species distributions along elevation gradients, but spatial variation among forests at the same elevation is less commonly investigated. In this study, the first to compare tree communities across multiple Andean cloud forests at similar elevations, we surveyed trees in five ridge‐top forest reserves at the upper end of the ‘mid‐elevation diversity bulge’ (1900–2250 masl) in the Intag Valley, a heavily deforested region in the Ecuadorian Andes. We found that tree communities were distinct in reserves located as close as 10 to 35 km apart, and that spatially closer forests were not more similar to one another. Although larger (1500 to 6880 ha), more intact forests contained significantly more tree species (108–120 species/0.1 ha) than smaller (30 to 780 ha) ones (56–87 species/0.1 ha), each reserve had unique combinations of more common species, and contained high proportions of species not found in the others. Results thus suggest that protecting multiple cloud forest patches within this narrow elevational band is essential to conserve landscape‐level tree diversity, and that even small forest reserves contribute significantly to biodiversity conservation. These findings can be applied to create management plans to conserve and restore cloud forests in the Andes and tropical montane cloud forests elsewhere.     

The Conservation Value of Secondary Forests for Vascular Epiphytes in Central Panama

Secondary forests that develop following land abandonment could compensate for the losses of diversity and structure that accompany deforestation of old‐growth forests in tropical regions. Whether secondary forests can harbor similar species richness, density, and composition of old‐growth forests for vascular epiphytes remains largely unknown for secondary forests older than 50 yr. We examined community structure (species richness, density, and species composition) of vascular epiphytes in older secondary forests between 35 and 115 yr after land abandonment and nearby old‐growth forests to determine if the community structure of epiphytes in secondary forests approaches that of old‐growth forests over time. The recovery of epiphyte species richness was rapid with 55‐year‐old forests containing 65 percent of old‐growth epiphyte species richness. Secondary forest epiphyte communities were found to be statistically nested within secondary forests older in age and within old‐growth forests. Similarity of epiphyte communities to old‐growth forests increased to 75 percent, 115 yr after abandonment. This study suggests that secondary forests will likely recover old‐growth epiphyte richness and composition given enough time. Epiphyte densities did not recover quickly with 55‐year‐old forests having 14 percent and 115‐year‐old forests having only 49 percent of the density of old‐growth forest epiphytes. The low density of epiphytes in secondary forests could impact rainforest diversity and function. We conclude that in less than 115 yr, although secondary moist forests have high conservation value for some aspects of community structure, they are unlikely to compensate biologically for the loss of diversity and ecosystem function that high epiphyte densities provide.     

Exploring the effect of host tree identity on epiphyte bryophyte communities in different Canarian subtropical cloud forests

This study explores the host tree preferences of epiphyte bryophyte communities in two key types of evergreen cloud forests on La Gomera (Canary Islands, Spain): ericaceous versus broadleaved laurel forest. By comparing two pairs of tree species (Erica arborea and Myrica faya vs. Ilex canariensis and Laurus novocanariensis) that occur in both forest types, we quantitatively examined whether epiphyte-host relationships change with the type of forest. In 51 ancient forest stands, the low-trunk bryophyte composition on the two host tree groups was analysed with both non-parametric procedures and ordination analyses. Our results highlight that the influence of local environmental conditions on the structuring of epiphyte communities may be different depending on the host tree identity. Whilst the epiphyte composition of the host tree group formed by I. canariensis and L. novocanariensis differed significantly between forest types depending on solar exposure, we failed to find variations for the other host tree group, excepting in those localities wherein mist precipitation was extremely high. Our findings highlight the importance of the natural diversity of tree species along environmental gradients, as well as of water availability at different spatial scales for epiphytic bryophytes in montane cloud forests.     

Large‐scale fungal diversity assessment in the Andean Yungas forests reveals strong community turnover among forest types along an altitudinal gradient

The Yungas, a system of tropical and subtropical montane forests on the eastern slopes of the Andes, are extremely diverse and severely threatened by anthropogenic pressure and climate change. Previous mycological works focused on macrofungi (e.g. agarics, polypores) and mycorrhizae in Alnus acuminata forests, while fungal diversity in other parts of the Yungas has remained mostly unexplored. We carried out Ion Torrent sequencing of ITS2 rDNA from soil samples taken at 24 sites along the entire latitudinal extent of the Yungas in Argentina. The sampled sites represent the three altitudinal forest types: the piedmont (400–700 m a.s.l.), montane (700–1500 m a.s.l.) and montane cloud (1500–3000 m a.s.l.) forests. The deep sequence data presented here (i.e. 4 108 126 quality‐filtered sequences) indicate that fungal community composition correlates most strongly with elevation, with many fungi showing preference for a certain altitudinal forest type. For example, ectomycorrhizal and root endophytic fungi were most diverse in the montane cloud forests, particularly at sites dominated by Alnus acuminata, while the diversity values of various saprobic groups were highest at lower elevations. Despite the strong altitudinal community turnover, fungal diversity was comparable across the different zonal forest types. Besides elevation, soil pH, N, P, and organic matter contents correlated with fungal community structure as well, although most of these variables were co‐correlated with elevation. Our data provide an unprecedented insight into the high diversity and spatial distribution of fungi in the Yungas forests.     

Big‐sized trees overrule remaining trees' attributes and species richness as determinants of aboveground biomass in tropical forests

Large‐diameter, tall‐stature, and big‐crown trees are the main stand structures of forests, generally contributing a large fraction of aboveground biomass, and hence play an important role in climate change mitigation strategies. Here, we hypothesized that the effects of large‐diameter, tall‐stature, and big‐crown trees overrule the effects of species richness and remaining trees attributes on aboveground biomass in tropical forests (i.e., we term the “big‐sized trees hypothesis”). Specifically, we assessed the importance of: (a) the “top 1% big‐sized trees effect” relative to species richness; (b) the “99% remaining trees effect” relative to species richness; and (c) the “top 1% big‐sized trees effect” relative to the “99% remaining trees effect” and species richness on aboveground biomass. Using environmental factor and forest inventory datasets from 712 tropical forest plots in Hainan Island of southern China, we tested several structural equation models for disentangling the relative effects of big‐sized trees, remaining trees attributes, and species richness on aboveground biomass, while considering for the full (indirect effects only) and partial (direct and indirect effects) mediation effects of climatic and soil conditions, as well as interactions between species richness and trees attributes. We found that top 1% big‐sized trees attributes strongly increased aboveground biomass (i.e., explained 55%–70% of the accounted variation) compared to species richness (2%–18%) and 99% remaining trees attributes (6%–10%). In addition, species richness increased aboveground biomass indirectly via increasing big‐sized trees but via decreasing remaining trees. Hence, we show that the “big‐sized trees effect” overrides the effects of remaining trees attributes and species richness on aboveground biomass in tropical forests. This study also indicates that big‐sized trees may be more susceptible to atmospheric drought. We argue that the effects of big‐sized trees on species richness and aboveground biomass should be tested for better understanding of the ecological mechanisms underlying forest functioning.     

Altitudinal Change in LAI and Stand Leaf Biomass in Tropical Montane Forests: a Transect Study in Ecuador and a Pan-Tropical Meta-Analysis

Abstract Leaf area index (LAI) is a key parameter controlling plant productivity and biogeochemical fluxes between vegetation and the atmosphere. Tropical forests are thought to have comparably high LAIs; however, precise data are scarce and environmental controls of leaf area in tropical forests are not understood. We studied LAI and stand leaf biomass by optical and leaf mass-related approaches in five tropical montane forests along an elevational transect (1,050–3,060 m a.s.l.) in South Ecuador, and conducted a meta-analysis of LAI and leaf biomass data from tropical montane forests around the globe. Study aims were (1) to assess the applicability of indirect and direct approaches of LAI determination in tropical montane forests, (2) to analyze elevation effects on leaf area, leaf mass, SLA, and leaf lifespan, and (3) to assess the possible consequences of leaf area change with elevation for montane forest productivity. Indirect optical methods of LAI determination appeared to be less reliable in the complex canopies than direct leaf mass-related approaches based on litter trapping and a thorough analysis of leaf lifespan. LAI decreased by 40–60% between 1,000 and 3,000 m in the Ecuador transect and also in the pan-tropical data set. This decrease indicates that canopy carbon gain, that is, carbon source strength, decreases with elevation in tropical montane forests. Average SLA decreased from 88 to 61 cm² g⁻¹ whereas leaf lifespan increased from 16 to 25 mo between 1,050 and 3,060 m in the Ecuador transect. In contrast, stand leaf biomass was much less influenced by elevation. We conclude that elevation has a large influence not only on the leaf traits of trees but also on the LAI of tropical montane forests with soil N (nitrogen) supply presumably being the main controlling factor.     

Low modularity and specialization in a commensalistic epiphyte–phorophyte network in a tropical cloud forest

Species interactions can shape the structure of natural communities. Such sets of interactions have been described as complex ecological networks, an example of which is the commensal network formed by epiphyte–phorophyte interactions. Vascular epiphytes germinate and grow on phorophytes (support trees), assuming a horizontal distribution (among the phorophyte species) and a vertical distribution (from the base of the tree trunk to the crown of phorophytes, i.e., through ecological zones). Here, we investigated the organization of these structural dimensions of the epiphyte–phorophyte network in a Brazilian tropical montane cloud forest. The analyzed network, comprising 66 epiphyte species and 22 phorophyte species, exhibited a nested structure with a low degree of specialization, a typical pattern for epiphyte–phorophyte networks in forests. The network was slightly modular, with 65% of the species common to three modules, and had vertical structure corresponding to the vertical organization of the phorophytes. The size (diameter at breast height) of phorophyte individuals influenced the network structure, possibly due to the increase in habitat area, the time available for colonization by epiphytes, and a greater number of microenvironments. We found that the distribution of the epiphyte species differed between the phorophyte ecological zones, with greater richness in the lower portions and greater abundance in the upper portions of the phorophytes. The results provide relevant guidance for future research on the characteristics and the vertical and horizontal organization of vascular epiphyte and phorophyte networks. Abstract in Portuguese is available with online material.     

The incidence and implications of clouds for cloud forest plant water relations

Although clouds are the most recognisable and defining feature of tropical montane cloud forests, little research has focussed on how clouds affect plant functioning. We used satellite and ground‐based observations to study cloud and leaf wetting patterns in contrasting tropical montane and pre‐montane cloud forests. We then studied the consequences of leaf wetting for the direct uptake of water accumulated on leaf surfaces into the leaves themselves. During the dry season, the montane forest experienced higher precipitation, cloud cover and leaf wetting events of longer duration than the pre‐montane forest. Leaf wetting events resulted in foliar water uptake in all species studied. The capacity for foliar water uptake differed significantly between the montane and pre‐montane forest plant communities, as well as among species within a forest. Our results indicate that foliar water uptake is common in these forest plants and improves plant water status during the dry season.     

Optimal climate for large trees at high elevations drives patterns of biomass in remote forests of Papua New Guinea

Our ability to model global carbon fluxes depends on understanding how terrestrial carbon stocks respond to varying environmental conditions. Tropical forests contain the bulk of the biosphere's carbon. However, there is a lack of consensus as to how gradients in environmental conditions affect tropical forest carbon. Papua New Guinea (PNG) lies within one of the largest areas of contiguous tropical forest and is characterized by environmental gradients driven by altitude; yet, the region has been grossly understudied. Here, we present the first field assessment of aboveground biomass (AGB) across three main forest types of PNG using 193 plots stratified across 3,100‐m elevation gradient. Unexpectedly, AGB had no direct relationship to rainfall, temperature, soil, or topography. Instead, natural disturbances explained most variation in AGB. While large trees (diameter at breast height > 50 cm) drove altitudinal patterns of AGB, resulting in a major peak in AGB (2,200–3,100 m) and some of the most carbon‐rich forests at these altitudes anywhere. Large trees were correlated to a set of climatic variables following a hump‐shaped curve. The set of “optimal” climatic conditions found in montane cloud forests is similar to that of maritime temperate areas that harbor the largest trees in the world: high ratio of precipitation to evapotranspiration (2.8), moderate mean annual temperature (13.7°C), and low intra‐annual temperature range (7.5°C). At extreme altitudes (2,800–3,100 m), where tree diversity elsewhere is usually low and large trees are generally rare or absent, specimens from 18 families had girths >70 cm diameter and maximum heights 20–41 m. These findings indicate that simple AGB‐climate‐edaphic models may not be suitable for estimating carbon storage in forests where optimal climate niches exist. Our study, conducted in a very remote area, suggests that tropical montane forests may contain greater AGB than previously thought and the importance of securing their future under a changing climate is therefore enhanced.