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The Neotropical realm hosts some of the Earth’s most species-rich biodiversity hotspots, with vascular epiphytes significantly contributing to this diversity. However, many regions of the Neotropics where epiphytic species of restricted distribution are reported coincide with threatened ecosystems, such as the tropical montane cloud forest. Moreover, epiphytes may be especially vulnerable to land use and climate change impacts due to their dependence on host trees. We assessed the conservation status of vascular epiphytes in the Neotropics for the families that represent over 80% of the global epiphyte diversity (Araceae, Bromeliaceae, Orchidaceae, Piperaceae, and Polypodiaceae) and identified geographical centers of accumulation of threatened epiphyte species. We gathered information from free-access web repositories, specific epiphytic plant databases, and scientific and grey literature. We assessed the extinction risk of 11,446 epiphyte species following IUCN Red List guidelines, using Criterion B (geographic range size). We found nearly 60% (6,721 species) to be threatened, with 1,766 critically endangered (CR), 3,537 endangered (EN), and 1,418 vulnerable (VU). The threatened species are mainly found in the centers of endemism of vascular epiphytes in Central America, the northern Andes, and the Atlantic Forest. Our study emphasises that the centers of threatened species largely coincide with diversity hotspots, highlighting epiphytes as an especially vulnerable group that requires urgent conservation actions.

We investigated the physiological responses of two epiphytic orchids under three light regimes of 20, 50, and 70% of total daily radiation under drought and rewatering conditions. Stanhopea tigrina was the one more affected because it exhibited strong photoinhibition and reduction of both electron transport rate and nocturnal acidity under drought and high radiation. However, this species maintained relatively high relative water content (RWC) values and underwent osmotic adjustment during the drought period and recovered photosynthetic variables during watered period. Prosthechea cochleata maintained similar water and photosynthetic responses to light conditions during the drought period and was more tolerant than S. tigrina. Principal component analysis provided evidence that water variables, such as RWC and succulence of both leaf and pseudobulb, were the most important variables for both species. Our results suggest that S. tigrina is more sensitive to drought than P. cochleata, and could be more affected by global warming.

Introduction. Tropical montane forests support a high abundance and diversity of bryophytes and lichens on different substrates. However, quantitative information about how their biomass and water-...

Epiphytes are structurally-dependent plants which grow on other plants without taking nourishment from them. Phylogenetic and ecophysiological differences divide them into non-vascular epiphytes (e.g. mosses and lichens), which are distributed worldwide, and vascular epiphytes (e.g. orchids and bromeliads), which are restricted to the tropics and subtropics. Within their distributional ranges, their abundance is strongly influenced by atmospheric water availability, since they have no access to soil water and are strongly coupled to the atmosphere. Epiphytes are most conspicuous in the tropics, in particular in cloud forests, but they can also be very abundant in cool-temperate wet forests. Their importance for precipitation partitioning rises from their widespread distribution, their location at the atmosphere-biosphere interface, and their adaptations specifically aimed at capturing and retaining atmospheric inputs. The interaction of epiphytes and precipitation partitioning is bidirectional: they deliberately contribute to partitioning and they depend on this partitioning (capture and retention of water and nutrients) for their survival. Additionally, they may be affected by partitioning by other canopy elements, taking advantage of throughfall and stemflow. Stemflow has been shown to be particularly important for non-vascular epiphytes on tree trunks, providing both water and nutrients. The presence of epiphytes increases the effect of forest canopy structure on the vertical and horizontal redistribution of precipitation by diversifying and changing nutrient pathways and by modifying water availability spatially and temporally. These functions are more pronounced in epiphytes than in the rest of the canopy, as epiphytes have developed a diverse array of strategies and mechanisms to cope with intermittent water supplies. Although quantitative information is scarce, it is clear that interception can be substantially increased by epiphytes, in particular by bryophytes and tank-forming bromeliads. In continuously wet environments, however, the potential water-uptake capacity of these groups may not be fully used because of low desiccation rates. Overall, much quantitative and process-oriented research into epiphyte interactions with precipitation interception is still needed to better understand the role of this functionally diverse group of plants in global climate and hydrological cycles. Mutual influence of epiphytes and precipitation redistribution will occur anywhere where epiphytes occur. However, the magnitude and exact mechanisms of the interactions will differ across climate zones and ecosystem types, based on epiphyte abundance, functional composition, and spatial distribution, as well as the frequency and intensity of precipitation as rain, fog and snow.

The interception of precipitation by vegetation has important consequences for climate and water resources. Although canopy interception has been studied for centuries, many fundamental unknowns remain. We present persistent questions that reflect challenges in measuring, representing, and understanding how terrestrial ecosystems intercept, partition, and transport precipitation—down to soils or back to the atmosphere. In summary of this book, we outline future needs and simultaneously provide a primer for those interested in precipitation interception processes.

Prosopis pallida (algarrobo) is a highly adapted species to extremely dry and wet conditions. Its geographic distribution at both sides of the Pacific Ocean is associated with its plastic response to El Nino event, an extreme climate event that changes precipitation regimes. In this review, we summarized the current knowledge of this versatile species based on scientific literature. Our analysis conducted identify three main research topics: geographical distribution, ecophysiology and population plasticity, and ecosystem services provision to guide the review in a methodological and unbiased way. In the geographical distribution section, we describe the origin, history, and native distribution of algarrobo, as well as the current distribution and the degree of invasiveness in some countries. In the ecophysiology and population plasticity section, we focus on the mechanisms used by algarrobo to avoid water stress during drought and maximize plant growth during El Nino. We discuss how this is reflected in the most important leaf functional traits, such as leaf mass per area (LMA) or gas exchange-related traits. We analyse the importance of phenotypic plasticity and intraspecific variability as adaptive ways to resist extreme rainfall and prolonged droughts on P. pallida growth during the last 50 years. Finally, we summarized the main ecosystem services and ecological benefits provided by P. pallida as well as its potential industrial uses. With this review, we wish to consolidate the current scientific knowledge of this species, to point out gaps of knowledge and suggest future research directions. As the world becomes a warmer place, P. pallida can be a key species to understand plant resilience to extreme events in dryland ecosystems.

We assessed the diversity, vertical distribution, and the effect of structural and geographical factors on the diversity of vascular epiphyte assemblages (VEAs) in two forest types in the “El Cielo” Biosphere Reserve. We found 2839 epiphyte individuals from 15 species on 240 host trees (27 species) in the semideciduous forest and 5085 individuals from 8 species on 215 host trees (12 species) in the pine–oak forest. Epiphytes showed a preference for the middle zone of the host trees. The diversity of VEAs was uneven in both forest types, although the VEA in the semideciduous forest was the most diverse. VEAs across forests were slightly similar in their composition (30% mean overlap), but very different in their structure (i.e., they did not share very abundant species). The variation in species richness among VEAs was influenced by forest structure, independently of forest type. Compositional differences of VEAs among forest types were explained by geographic distance and host-tree identity (31% and 28% variation explained, respectively). By characterizing the diversity of VEAs we provide a basic understanding of the factors influencing epiphyte diversity in these understudied ecosystems.

Despite their ecological importance, particularly in tropical rainforests, vascular epiphytes are among the least studied plant groups. Theoretical knowledge about the composition, structure and dynamics of epiphyte assemblages is strikingly scarce; in contrast to soil-rooted plants for which major insights have been gained in the last decades. These insights cannot be simply transferred to epiphytes, because structurally-dependent vascular epiphytes are fundamentally different in several aspects from non-structurally-dependent plants, as well as from other epiphyte types (e.g. mosses). Apart from the difficulty of accessing the canopy, we largely attribute the lack of development in the field to terminological issues and the lack of standardized sampling, both of which stem from the lack of a conceptual framework. We develop such a framework for future studies and illustrate the potential of this suggested approach. Our analysis is based on a review of studies of vascular epiphyte assemblages that have data on abundance, since diversity comprises two aspects: species richness and relative abundance. We found 62 studies of very idiosyncratic character over the last 30 years, of which 18% included a temporal component ranging from 4 months to 8 years. Surprisingly, over 80% of the studies collected data at the tree level, but few analyzed the data at that level (34%) and none has made their data available for meta-analyses. We argue that this represents a problem in the development of the field and we urge researchers to make this wealth of data available. We suggest explicitly using the host individual as the sampling unit when studying vascular epiphyte assemblages. Moreover, the ecological scales (zone, tree and stand scales) i.e. relating to the three-dimensional nature of vascular epiphytes assemblages (VEAs), can be used to scale up or down from the host individual. The importance of scaling, and availability of data at the tree level, was assessed by comparing diversity patterns of vascular epiphytes at the tree and stand scales, which revealed clear and consistently different patterns. More general questions on the diversity patterns of vascular epiphytes could be answered if the wealth of data already collected were made accessible and if future sampling were to be standardized.

Earlier snowmelt changes spring stress exposure and growing-season length, possibly causing shifts in plant species dominance. If such shifts involve trees, this may lead to changes in treeline position. We hypothesized that earlier snowmelt would negatively affect the performance of tree seedlings near the treeline due to higher spring stress levels, but less so if seedlings were protected from the main stress factors of night frosts and excess solar radiation. We exposed seedlings of five European treeline tree species: Larix decidua, Picea abies, Pinus cembra, Pinus uncinata, and Sorbus aucuparia to two snow-cover treatments (early and late melting, with about two weeks difference) combined with reduced sky exposure during the day (shading) or night (night warming), repeated in two years, at a site about 200 m below the regional treeline elevation. Physiological stress levels (as indicated by lower Fv/Fm) in the first weeks after emergence from snow were higher in early-emerging seedlings. As expected, shade reduced stress, but contrary to expectation, night warming did not. However, early- and late-emerging seedlings did not differ overall in their growth or survival, and the interaction with shading was inconsistent between years. Overall, shading had the strongest effect, decreasing stress levels and mortality (in the early-emerging seedlings only), but also growth. A two-week difference in snow-cover duration did not strongly affect the seedlings, although even smaller differences have been shown to affect productivity in alpine and arctic tundra vegetation. Still, snowmelt timing cannot be discarded as important for regeneration in subalpine conditions, because (1) it is likely more critical in very snow-rich or snow-poor mountains or landscape positions; and (2) it can change (sub)alpine vegetation phenology and productivity, thereby affecting plant interactions, an aspect that should be considered in future studies.

Do epiphytes drop out above the treeline because of climatic reasons or due to lack of appropriate substrate? We set out to address this question by studying various key aspects of their biology at a natural treeline on a tropical mountain top in Panama: species composition of assemblages, host preferences, population structure and dynamics, individual growth and reproductive investment. Lack of relevant climate data caused us to monitor microclimatic conditions in tree crowns for 12 months. At our study site we found 15 epiphyte species, mostly ferns, although in terms of abundance orchids were highly dominant. Compared to lowland vegetation of similar stature, the epiphyte assemblages were less species-rich and abundances lower. Some species may only be present at this treeline because of continuous immigration from lower elevations (i.e. represent sink populations). Many species, however, were rather abundant with many reproductive individuals, arguably forming viable local populations. The results of a detailed demographic study with the orchid Pachyphyllum hispidulum over three years also support this notion, being comparable to studies from lowland habitats. Our descriptive study does not allow unambiguous conclusions on mechanisms, but our findings suggest that lack of suitable substrate (=trees) rather than climatic reasons are responsible for the disappearance of epiphytes immediately above the treeline. This notion needs rigorous verification by experimental physiological studies.

Vascular epiphytes contribute significantly to tropical diversity. Research on the factors that determine vascular epiphytic diversity and composition in tropical areas is flourishing. However, these factors are entirely unknown in tropical-temperate transition zones, which represent the distribution limit of several epiphytic species. We assessed the degree to which climatic and structural variables determine the diversity of vascular epiphytic assemblages (VEAs) in a transition zone in Mexico: the El Cielo Biosphere Reserve. We found 12,103 epiphytic individuals belonging to 30 species and 15 genera along a climatic gradient from 300 to 2,000 m a.s.l. Bromeliaceae and Orchidaceae were the most species-rich families. Forests along the windward slope of the Sierra Madre Oriental (semideciduous forest and tropical montane cloud forest) had higher species richness than forests along the leeward slope (pine-oak forest and submontane scrub). Species richness was largely determined by seasonality and, to a lesser degree, by forest structure, whereas abundance was mainly determined by host tree size. Variation in VEAs composition was largely explained by climatic variables, whereas forest structure was not as important. VEAs differed among forest types and slopes in terms of taxonomic and functional composition. For example, certain bromeliad indicator species reflected differences between slopes. Although within-tree epiphytic species richness (alpha diversity) was low in this transition zone relative to other habitats, species turnover among forest types (beta diversity) was high. These findings suggest that each forest type makes a unique and important contribution to epiphytic diversity in this transition zone.

The taxonomic composition of the vascular epiphyte flora at the Rio Changuinola, Panama, was examined and complemented with an analysis of biogeographic affinities and physiological parameters related to plant water and nutrient relations. In an area of ca. 1000 ha, we found a total of 476 species of vascular epiphytes. This marks a new diversity record among lowland rainforest sites. Species composition was closely related to nearby lowland forest sites but not to montane sites. The floristic similarity with lowland sites decreased with distance and relative position towards the Andes. On basis of isotope discrimination, the proportion of species with Crassulacean Acid Metabolism (CAM) was found to be low compared to other studies, and many of these species showed a rather weak expression of this photosynthetic pathway. This observation and distributional shifts in 15% of the species in the study area towards lower elevations suggest that local water availability is high which in turn is arguably responsible for the high species richness.

Hardly any molecular studies have been done on euendoliths of marine coastal environments, especially along the supratidal ranges of carbonate coasts. In our study, we provide a comparative sequence analysis using 454 pyrosequencing of the 16S ribosomal RNA (rRNA) gene combined with extensive microscopy of the endolithic community from rock pools of the Croatian Adria. Molecular diversity indices and richness estimates showed high level of diversity, particularly in high-salinity samples. The most common cyanobacteria belong to the order Pleurocapsales, similar to observations on limestone coasts in other parts of the world. Using single-cell amplification sequences of Hormathonema spp., Hyella caespitosa, and Kyrtuthrix dalmatica was for the first time introduced to the public GenBank. Microscopic investigations did not show qualitative variances in diversity among sites with different salinity but clear differences in prevalent organisms from similar environments suggesting that most of them are adapted to inhabit extreme, marine endolithic habitats and that similar species inhabit geographically separated but ecologically similar environments. This is a remarkable concordance rather seldom seen in molecular community studies in support of the hypothesis that endolithic ecosystems are seeded from a global meta-community. The relative diversity of the community is greater than those described from harsh endolithic habitats of cold and hot deserts. The maximum likelihood phylogenetic tree consisting of 166 operational taxonomic units (OTUs) at 96 % sequence similarity revealed 11 distinct clusters. Three clusters contained only epilithic or endolithic taxa, and five clusters contained mixed epilithic and endolithic taxa. Organisms clustered according to their taxonomic affiliations and not to their preferences to salt concentrations.

A considerable number of plants depend on structural support of other plants. To understand their diversity and ecology, it is essential to know how strongly potential host species differ in their suitability as hosts. This review focuses on vascular epiphytes, i.e. structurally dependent plants that do not parasitize their hosts. Despite a longstanding interest in the topic, our knowledge on the strength of their host specificity is still scanty. This is arguably due to conceptual confusion, but also because of the large complexity of the study system, which turns quantifying host specificity in the field into a challenge., Information on the degree of host specificity is fundamental for an understanding of the ecology of structurally dependent plants such as vascular epiphytes. Starting with the seminal paper of A.F.W. Schimper on epiphyte ecology in the late 19th century over 200 publications have dealt with the issue of host specificity in vascular epiphytes. We review and critically discuss this extensive literature. The available evidence indicates that host ranges of vascular epiphytes are largely unrestricted while a certain host bias is ubiquitous. However, tree size and age and spatial autocorrelation of tree and epiphyte species have not been adequately considered in most statistical analyses. More refined null expectations and adequate replication are needed to allow more rigorous conclusions. Host specificity could be caused by a large number of tree traits (e.g. bark characteristics and architectural traits), which influence epiphyte performance. After reviewing the empirical evidence for their relevance, we conclude that future research should use a more comprehensive approach by determining the relative importance of various potential mechanisms acting locally and by testing several proposed hypotheses regarding the relative strength of host specificity in different habitats and among different groups of structurally dependent flora.