Floristic Composition and Community Structure of Epiphytic Angiosperms in an Urban Forest Fragment in the Eastern Amazon

Vascular epiphytes are one of the most important forest components, contributing to microclimatic maintenance. These plants find ideal conditions for development in the Amazon due to the spatial heterogeneity and high temperature and humidity typical of this biome. In recent years, the Brazilian Amazon has undergone dramatic changes in its landscape, mainly due to the increase in deforestation and fire rates. We present here the floristic composition and analyze the community structure of epiphytic angiosperms of an urban forest fragment in Eastern Amazon. A total of 71 epiphytic individuals were recorded belonging to eight species and four families. Orchidaceae was the most representative family, corroborating the pattern for surveys of epiphytic diversity in the Neotropical region. Epiphytic species were found on 24 individuals of 10 tree species. The epiphytic importance value (IVe) was low for all species, except for Aechmea tocantina and Rhipsalis baccifera. Cactaceae was the family with the highest IVe. Most epiphytes were found in the crown of trees (83.1%). The diversity index of the fragment was H’ = 1.80 and the equity index was J= 0.87, reflecting the absence of highly dominant species. Conservation of urban forest fragments is necessary for the maintenance of epiphytic flora and ecosystem services.

Structuring Interaction Networks Between Epiphytic Bryophytes and Their Hosts in Yunnan, SW China

Ecological networks are commonly applied to depict general patterns of biotic interactions, which provide tools to understand the mechanism of community assembly. Commensal interactions between epiphytes and their hosts are a major component of species interactions in forest canopies; however, few studies have investigated species assemblage patterns and network structures of epiphyte–host interactions, particularly non-vascular epiphytes in different types of forest. To analyze the characteristics of network structures between epiphytes and their hosts, composition and distribution of epiphytic bryophytes were investigated from 138 host individuals using canopy cranes in a tropical lowland seasonal rain forest (TRF) and a subtropical montane moist evergreen broad-leaved forest (STF), in Southwest China. We structured binary networks between epiphytic bryophytes and their hosts in these two forests, which presented 329 interactions in the TRF and 545 interactions in the STF. Compared to TRF, the bryophyte–host plant networks were more nested but less modular in the STF. However, both forests generally exhibited a significantly nested structure with low levels of specialization and modularity. The relatively high nestedness may stabilize the ecological networks between epiphytic bryophytes and their hosts. Nevertheless, the low modularity in epiphyte–host networks could be attributed to the lack of co-evolutionary processes, and the low degree of specialization suggests that epiphytes are less likely to colonize specific host species. Vertical distribution of the bryophyte species showed structured modules in the tree basal and crown zones, probably attributing to the adaptation to microclimates within a host individual. This study highlights the nested structure of commensal interaction between epiphytic bryophytes and host trees, and provides a scientific basis to identify key host tree species for conservation and management of biodiversity in forest ecosystems.

Vascular epiphyte assemblage structure and distribution patterns in the south-temperate zone

<p>Vascular epiphytes, which are specialised to spend their entire life cycle within trees, are significant contributors to local ecosystem services. However, our current understanding of epiphyte distributions, co-occurrences, and general ecology lags far behind that of terrestrial plants. Furthermore, the majority of epiphyte research is undertaken in tropical forests, with comparatively few studies extending into temperate climates. As such, whether epiphytic plant assemblage structure varies geographically, or is influenced by area and isolation effects needs further scrutiny. In addition, how epiphytes are distributed in relation to host tree ontogeny and microclimates specific to south-temperate forests is poorly understood. Here, I attempt to bridge this gap by researching epiphyte distributions and assemblage structure in New Zealand, southern Chile, and Australia. In the first biogeographic study of epiphyte-host interactions, I determined if epiphyte-host network structure (i.e. nestedness, species co-occurrences, species specialisation) varied among New Zealand and Chilean temperate forests (Chapter 2). At the forest stand level, network structure was consistent with stochastic structuring, which suggests that dispersal and disturbances are important drivers of epiphyte distributions at a biogeographic scale. However, deterministic structure was observed in New Zealand networks with regards to nestedness (i.e. when specialists interact with generalists), which suggests that positive species interactions influence epiphyte distributions at a within-tree scale. Second, I determined whether the composition of plant communities residing in epiphytic birds’ nest ferns (Asplenium goudeyi) on Lord Howe Island, Australia, are influenced by fern size, isolation from a major propagule source and resident plant community richness (Chapter 3). Results suggest that plant communities are structured by dispersal. For one, there was a significant isolation effect on resident plant community richness. Additionally, wind-dispersed taxa were well represented in isolated ferns, while animal-dispersed taxa and taxa with no specific dispersal strategies were absent. This is the first study to test the combined effects of area, isolation and resident plant richness on epiphytic plant assemblage structure. Third, using Darwin’s geological theory of island ontogeny as a theoretical construct, I explored changes in epiphyte species richness throughout tree ontogeny (Chapter 4). Theoretical frameworks have helped bridge the gap between our understanding of vascular epiphytes and terrestrial plants, however, none have been implemented to guide investigations on epiphyte assemblage development. Based on the general features of island ontogeny, I found three stages of epiphyte assemblage development: (i) an initial stage where host trees are devoid of epiphytes, (ii) a second stage where trees acquire epiphytes into maturity, and (iii) a hypothetical stage where epiphyte assemblages follow a period of species decline following host tree mortality. In addition to these results, I found interspecific variation in the ontogenetic stage at which host trees become favourable for epiphyte establishment and the rate at which epiphyte assemblages develop. Lastly, I explored the systematic distribution of epiphytes and mistletoes in relation to microclimate gradients around the trunks of trees (Chapter 5). In addition, I tested the physiological responses of epiphytes and mistletoes to reductions in their most limiting resources to determine if the responses were consistent with their distribution patterns. The radial distributions of epiphytes and mistletoes were highly directional, and paralleled gradients of humidity, light and water. Additionally, the photochemical efficiency of epiphytes and CO₂ assimilation in mistletoe leaves decreased in plants growing in environments with lower water and light availability, respectively. However, mistletoe leaves still assimilated CO₂ in lower light conditions, which suggests a high plasticity of mistletoes to growing in a canopy environment. Despite over 120 years of recognising the importance of vertical microclimates on epiphyte distributions, this is the first systematic study of epiphytic plant distributions in relation to microclimate gradients around the trunks of trees. This thesis has increased our understanding of epiphytic plant assemblage structure, and how it is influenced by host tree species, isolation, area and resident plant species richness. In addition, this thesis has increased our understanding of the effect of host tree ontogeny and microclimate on epiphyte distribution patterns. Together, these studies may be built upon more broadly to further elucidate drivers of epiphyte assembly and distribution patterns.</p>

Vascular epiphyte assemblage structure and distribution patterns in the south-temperate zone

<p>Vascular epiphytes, which are specialised to spend their entire life cycle within trees, are significant contributors to local ecosystem services. However, our current understanding of epiphyte distributions, co-occurrences, and general ecology lags far behind that of terrestrial plants. Furthermore, the majority of epiphyte research is undertaken in tropical forests, with comparatively few studies extending into temperate climates. As such, whether epiphytic plant assemblage structure varies geographically, or is influenced by area and isolation effects needs further scrutiny. In addition, how epiphytes are distributed in relation to host tree ontogeny and microclimates specific to south-temperate forests is poorly understood. Here, I attempt to bridge this gap by researching epiphyte distributions and assemblage structure in New Zealand, southern Chile, and Australia. In the first biogeographic study of epiphyte-host interactions, I determined if epiphyte-host network structure (i.e. nestedness, species co-occurrences, species specialisation) varied among New Zealand and Chilean temperate forests (Chapter 2). At the forest stand level, network structure was consistent with stochastic structuring, which suggests that dispersal and disturbances are important drivers of epiphyte distributions at a biogeographic scale. However, deterministic structure was observed in New Zealand networks with regards to nestedness (i.e. when specialists interact with generalists), which suggests that positive species interactions influence epiphyte distributions at a within-tree scale. Second, I determined whether the composition of plant communities residing in epiphytic birds’ nest ferns (Asplenium goudeyi) on Lord Howe Island, Australia, are influenced by fern size, isolation from a major propagule source and resident plant community richness (Chapter 3). Results suggest that plant communities are structured by dispersal. For one, there was a significant isolation effect on resident plant community richness. Additionally, wind-dispersed taxa were well represented in isolated ferns, while animal-dispersed taxa and taxa with no specific dispersal strategies were absent. This is the first study to test the combined effects of area, isolation and resident plant richness on epiphytic plant assemblage structure. Third, using Darwin’s geological theory of island ontogeny as a theoretical construct, I explored changes in epiphyte species richness throughout tree ontogeny (Chapter 4). Theoretical frameworks have helped bridge the gap between our understanding of vascular epiphytes and terrestrial plants, however, none have been implemented to guide investigations on epiphyte assemblage development. Based on the general features of island ontogeny, I found three stages of epiphyte assemblage development: (i) an initial stage where host trees are devoid of epiphytes, (ii) a second stage where trees acquire epiphytes into maturity, and (iii) a hypothetical stage where epiphyte assemblages follow a period of species decline following host tree mortality. In addition to these results, I found interspecific variation in the ontogenetic stage at which host trees become favourable for epiphyte establishment and the rate at which epiphyte assemblages develop. Lastly, I explored the systematic distribution of epiphytes and mistletoes in relation to microclimate gradients around the trunks of trees (Chapter 5). In addition, I tested the physiological responses of epiphytes and mistletoes to reductions in their most limiting resources to determine if the responses were consistent with their distribution patterns. The radial distributions of epiphytes and mistletoes were highly directional, and paralleled gradients of humidity, light and water. Additionally, the photochemical efficiency of epiphytes and CO₂ assimilation in mistletoe leaves decreased in plants growing in environments with lower water and light availability, respectively. However, mistletoe leaves still assimilated CO₂ in lower light conditions, which suggests a high plasticity of mistletoes to growing in a canopy environment. Despite over 120 years of recognising the importance of vertical microclimates on epiphyte distributions, this is the first systematic study of epiphytic plant distributions in relation to microclimate gradients around the trunks of trees. This thesis has increased our understanding of epiphytic plant assemblage structure, and how it is influenced by host tree species, isolation, area and resident plant species richness. In addition, this thesis has increased our understanding of the effect of host tree ontogeny and microclimate on epiphyte distribution patterns. Together, these studies may be built upon more broadly to further elucidate drivers of epiphyte assembly and distribution patterns.</p>

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

Plants and animals evolve different attachment structures and strategies for reversible or permanent adhesion to different substrate types. For vascular epiphytes, having the ability to permanently attach to their host plants is essential for establishment and survival. Unlike mistletoe roots, roots of vascular epiphytes do not penetrate the host tissues but instead achieve attachment by growing in close contact to the surface of the substrate. However, the fundamental understanding of the attachment functions of epiphytic roots remains scarce, where majority of studies focused on the general root morphology, their functional properties and the descriptions of associated microbial endophytes. To date, research on attachment strategies in plants is almost entirely limited to climbers. Therefore, this study aims to fill the knowledge gap and elucidate the attachment functions of roots of epiphytic orchids. With the use of histology and high-resolution cryo-scanning electron microscopy (cryo-SEM) technique with freeze fracturing, the intimate root-bark substrate interface of epiphytic orchid Epidendrum nocturnum Jacq was investigated. Results showed a flattened underside of the root upon contact with the substrate surface, and the velamen layer appeared to behave like a soft foam, closely following the contours of the substrate. Root hairs emerged from the outermost velamen layer and entered into the crevices in the substrate, whenever possible. A layer of amorphous substance (glue-like substance) was observed on the surface of the root hairs. Combining the observations from this study and knowledge from previous studies, we hypothesised that epiphytic orchid roots produced a layer of glue-like substance to adhere the root to the substrate. Then root hairs are produced and enter into the voids and crevices of the substrate. This further generates a mechanical interlocking mechanism between root and substrate, thus reinforcing the attachment of the root (and hence the whole plant) to its substrate.

Persistent Effects of Historical Selective Logging on a Vascular Epiphyte Assemblage in the Forest Canopy of the Western Ghats, India

Forest canopies have been dubbed the last biological frontier and continue to remain underexplored. Vascular epiphytes form a rich assemblage of plants within the forest canopy and apart from sustaining diverse taxa, they also fulfill critical ecological functions. Vascular epiphytes are particularly sensitive to perturbations of microclimate and microhabitat within the canopy, especially from anthropogenic changes such as logging. The forests of the megadiverse Western Ghats in India harbor a rich assemblage of vascular epiphytes, but their ecology has not been examined systematically. We compared the diversity, abundance, and composition of a vascular epiphyte assemblage between an unlogged and a historically selectively logged forest in the southern Western Ghats, India, and identified factors affecting the epiphyte assemblage. Canopies of 100 trees each in selectively logged and unlogged forests were accessed using the single-rope technique. We found 20 species of vascular epiphytes with the assemblage dominated by members of Orchidaceae. The diversity and abundance of epiphytes were significantly greater in the selectively logged forest. One host tree, Cullenia exarillata, supported the greatest number of epiphytes in both forest stands. The niche widths of epiphyte species, computed with host tree species as a resource, were similar between the two stands but a greater number of species pairs overlapped in the selectively logged forest. Overall, epiphyte abundance was negatively associated with unlogged forests. Host tree species, tree height, and presence of moss on branches were positively associated with the abundance of epiphytes. Despite being ecologically important, no study has thus far examined the impact of selective logging on the epiphyte assemblage in the Western Ghats. Our findings contribute to the knowledge of vascular epiphytes from South and Southeast Asia and set the stage for future research and conservation.

Biovera-Epi: A new database on species diversity, community composition and leaf functional traits of vascular epiphytes along gradients of elevation and forest-use intensity in Mexico

This data paper describes a new, comprehensive database (BIOVERA-Epi) on species distributions and leaf functional traits of vascular epiphytes, a poorly studied plant group, along gradients of elevation and forest-use intensity in the central part of Veracruz State, Mexico. The distribution data include frequencies of 271 vascular epiphyte species belonging to 92 genera and 23 families across 120 20 m × 20 m forest plots at eight study sites along an elevational gradient from sea level to 3500 m a.s.l. In addition, BIOVERA-Epi provides information on 1595 measurements of nine morphological and chemical leaf traits from 474 individuals and 102 species. For morphological leaf traits, we provide data on each sampled leaf. For chemical leaf traits, we provide data at the species level per site and land-use type. We also provide complementary information for each of the sampled plots and host trees. BIOVERA-Epi contributes to an emerging body of synthetic epiphytes studies combining functional traits and community composition. BIOVERA-Epi includes data on species frequency and leaf traits from 120 forest plots distributed along an elevational gradient, including six different forest types and three levels of forest-use intensity. It will expand the breadth of studies on epiphyte diversity, conservation and functional plant ecology in the Neotropics and will contribute to future synthetic studies on the ecology and diversity of tropical epiphyte assemblages.