However, five trees species were considered as host preferred, while five tree species were limiting hosts. The highest richness was recorded in vertical zone II and the lowest in zones I and V. Conclusions : Larger trees contain greater richness of epiphytic orchids, because they offer better conditions for their establishment, provide a great diversity of microhabitats, greater time and area for epiphytic colonization events.
The texture of the bark is a relevant factor in the host preference, and in the hosts with smooth bark, the presence of epiphytic orchids depends on the accumulation of organic matter.
Species richness and habitat diversification of bryophytes in submontane rain forest and fallows of Bolivia. Journal of Tropical Ecology La Paz, Bolivia. Epiphyte host specificity of Encyclia krugii, a Puerto Rican endemic orchid. Lindleyana 4: Host tree utilization by epiphytic orchids in different land-use intensities in Kathmandu Valley, Nepal. Plant Ecology DOI: Vascular epiphyte vegetation in rocky savannas of southeastern Brazil.
Nordic Journal of Botany Selbyana Barker MG. An update on low-tech methods for forest canopy access and on sampling a forest canopy. Low-tech methods for forest canopy access.
Biotropica Mechanisms regulating epiphytic plant diversity. Critical Reviews in Plant Sciences Bergstrom BJ, Carter R. Host-tree selection by an epiphytic orchid, Epidendrum magnoliae Muhl. Southwest Naturalist 7: Benzing DH. Vascular epiphytes. General biology and related biota. Cambridge: Cambridge University Press. Habitat preference of the epiphyte Tillandsia recurvata Bromeliaceae in a semi-desert environment in Central Mexico. Canadian Journal of Botany Patterns in the distribution of epiphytes and vines in a New Zealand forest.
Austral Ecology Branchfall as a demographic filter for epiphyte communities: lessons from forest floor-based sampling. PLoS One e Epiphyte host preferences and host traits: mechanisms for species-specific interactions. Oecologia The influence of tree species on canopy soil nutrient status in a tropical lowland wet forest in Costa Rica. Plant and Soil Vascular epiphyte distribution patterns: explaining the mid-elevation richness peak. Journal of Ecology Dispersal limitation in epiphytic bromeliad communities in a Costa Rican fragmented montane landscape.
The influence of humidity, nutrients and light on the establishment of the epiphytic bromeliad Tillandsia guatemalensis in the highlands of Chiapas, Mexico. Association of vascular epiphytes in a Guatemalan cloud forest. Epiphytic orchids in a Belizean grapefruit orchard: distribution, colonization, and association.
Lindleyana 1: DNA data and Orchidaceae systematics: a new phylogenetic classification. Orchid conservation. Kota Kinabalu: Natural History Publications, Chase MW. Obligate twig epiphytism in the Oncidiinae and other neotropical orchids. Coextinction and persistence of dependent species in a changing world. Annual Review of Ecology, Evolution, and Systematics Epiphyte diversity and biomass loads of canopy emergent trees in Chilean temperate rain forests: A neglected functional component.
Forest Ecology and Management Habitat isolation changes the beta diversity of the vascular epiphyte community in lower montane forest, Veracruz, Mexico. Biodiversity and Conservation Relationship between tree size and epiphyte species richness: testing four different hypotheses. Journal of Biogeography Freiberg M. Measurements were conducted in isolated trees, teak plantations, and secondary forest patches. Data from months of transition from dry to rainy seasons and vice versa were excluded. Sample size is given as the number of days No.
For statistical treatment see Supporting Information Fig. The pendant loggers measure ambient light in lux within a broad wavelength spectrum ca. Loggers were calibrated against each other before and after the measuring campaign. Readings were taken every 24 min. The V2 loggers measured temperature and relative humidity every 30 min. Although the set-up shielded the V2 loggers from direct rain [see Supporting Information—Figure S4A ], exposure to direct radiation occasionally occurred.
This exposure can lead to recorded temperatures that differ substantially from ambient. Therefore, data points of temperature and relative humidity were removed manually when readings exceeded the mean by more than two times the standard deviation. We regressed the data of our logger against the data of the ESP logger, and then used this logger as the reference for the calibration of all other V2 loggers.
For descriptive stats we kept these values. Statistical analyses were conducted with daily means of the microclimate variables. For the establishment experiment seeds of T. These species were chosen due to their abundance in the study region and the need for a sufficient number of seeds for both the germination and the establishment experiment. The seeds were collected at two T. Infructescences yielded up to 55 capsules containing up to around seeds. The capsules of each species were mixed and kept dry in paper bags until seeds were used.
In , fresh seeds were collected for the germination experiment. In secondary forest patches and plantations, we haphazardly selected one tree for the experiments. For the isolated tree habitat, we selected three tree species that were abundant along the whole rainfall gradient of the study region: Anacardium occidentale , Byrsonima crassifolia and Guazuma ulmifolia. At these sites, individuals of the three tree species grew close to one another mostly within a hectare and on one occasion within 1 km.
As described above, we installed data loggers for light, temperature and relative humidity in Anacardium at each site. All four epiphyte species are xerophytic members of the subfamily Tillandsioideae and use crassulacean acid metabolism CAM Medina , Griffiths and Smith Within the study region of the repeated census Einzmann and Zotz the distribution of the species differed between the precipitation levels defined above.
Tillandsia balbisiana and T. We therefore expected germination and establishment on isolated trees and in areas of low humidity to be lowest in T. In , we set up four germination plots per tree oriented in the four cardinal directions. If necessary, the plots were cleaned of coarse debris, mosses and lichens before the seeds were glued to the bark.
Each plot contained 30 seeds per species. For easier handling, the seeds were tied together in bunches of 10 by their comas. Conspecific seeds were arranged in one line. The relative position of these lines was changed haphazardly in each plot. In January , we revisited all the sites and counted the germinated plantlets that were still alive. Germination success was calculated as percentage of the seeds still present in the tree.
The loss of seeds was analysed separately. Seeds were collected in and were allowed to germinate in Petri dishes lined with cotton wool under constantly wet conditions, under shade cloth in the greenhouse facilities of the Smithsonian Tropical Research Institute STRI in Gamboa, Panama. After 3 months, plantlets were transferred to baskets of fine wire cloth, where they were allowed to grow for about 1 year. During their first month on the wire cloth they were irrigated weekly. Afterwards they received only water through natural rain events.
Between T. The establishment experiment was conducted next to the plots of the germination experiment. To be able to distribute the plantlets more or less evenly between the plots we regrouped them. First, they were detached from the wire mesh. These prepared units were then glued to the bark of the experimental trees, again with silicone [ see Supporting Information—Figure S5B ]. The relative position of the units was changed haphazardly in each plot. In January , all sites were revisited and the surviving plantlets counted.
Similar to the loss of seed packages the complete loss of seedlings was noted and analysed separately for survival. All statistical analyses were performed with R 3. The falling velocity of seeds was related to colonization using a linear model. Normal distribution of the percent data was achieved by angular transformation Dytham Mean percent seed adherence was tested for correlation with bark rugosity applying the Kendall method.
Moreover, for tree species with information on epiphyte abundance Einzmann and Zotz we tested if seed adherence correlated with average relative abundance of epiphytes and the average gain of species and individuals from to as an indicator for new colonizations.
The frequency distribution of seed adherence was strongly skewed. Lacking normal distribution, the microclimate data were analysed with a Kruskal—Wallis test KW , followed by pairwise comparisons using Nemenyi-tests with chi-squared approximation for independent samples NT, Pohlert The data were analysed separately for dry and rainy seasons. As the length of the seasons varied along the rainfall gradient we excluded the transition months between dry and rainy season from the analysis. Thus, for the dry season we only took data from January through March and for the rainy season we used data from June through November.
Similar to the microclimate data, data of germination and establishment experiments were analysed using a KW test. The relationship of V term and colonization success for orchids and bromeliads did not meet expectations Table 2. Seed adherence was tested on 33 tree species belonging to 20 families, one tree species remained undetermined [see Supporting Information—Table S6 ]. Bark rugosity varied from almost zero Eucalyptus sp and Ficus sp to about 9 mm Pinus caribaea. The relationship of seed adherence and bark rugosity was analysed with a segmented regression Fig.
The model estimated the breakpoint at 1. Segmented regression of mean seed adherence and bark rugosity of 33 tree species. Within the first segment there was a significant increase of mean seed adherence with rugosity. For error terms [see Supporting Information—Table S6 ]. We measured microclimate variables within the tree crowns over more than 1. Also, isolated and plantation trees did not show consistent differences in terms of incident light, temperature and relative humidity compared to trees in secondary forest patches Table 3 and [see Supporting Information—Figure S7 ].
The germination experiment was conducted on trees in secondary forests, teak plantations and pastures isolated trees. Survival in T. The only other significant difference in survival was found between T. In pasture plots, survival of T. Are populations sufficiently connected to rescue failing local populations in a metacommunity framework? Among the possible refuges in human-modified landscapes there is an increasing number of plantations with allochthonous trees which begs the question of their role as potential stepping stones.
With this study, we focussed on the early live stages of epiphytes and their potential to disperse and establish successfully in three different habitats in human-modified landscape. Anemochorous plant species may benefit from open vegetation Jesus et al. Epiphyte seed dispersal benefits from their elevated growing sites in trees Thomson et al. All V term we measured were well below this empirical threshold Table 2.
This should facilitate the connectivity of populations in a fragmented landscape, in which convective updrafts should be more common than in closed forest. Consequently, we expected a negative correlation of V term and the observed successful colonization of new trees between two epiphyte censuses on pasture trees over 8 years. However, there was only a signal for the bromeliad seeds due to the pronounced difference between Catopsis and all others, and orchid seeds showed even the reverse trend.
This result probably reflects two facts: i interspecific differences in V term were very small Table 2 , and ii successful colonization includes much more than the arrival of diaspores on a new host.
There are many additional processes, some of which were investigated in this study, that mask the expected negative correlation between colonization success and V term. Due to the structural dependence of epiphytes on trees, it is essential that seeds adhere to the bark of a potential host.
We did not find a significant correlation between epiphyte abundance, or species gain, and seed adherence. In contrast, Callaway et al. Again, adherence is only one of several factors influencing successful establishment. We expected a positive correlation of bark rugosity and seed adherence and the data support this notion, although rugosity influenced adherence only over a small part of the entire spectrum. Given a certain degree of rugosity, attachment was unaffected by bark structure Fig.
This seems to be due to different qualities of smoothness that we had not been able to measure. For the fine hairs of bromeliad comas this is apparently sufficient structure to cling to. With our test, we could only determine adherence success at first contact, but we see no reason to assume that this is not also a good proxy for the likelihood of a lasting connection. In general, trees with structured bark facilitate the attachment of bromeliad seeds and it can be expected that even small crevices also improve the likelihood of attachment in orchid seeds or fern spores as well.
Only trees with very smooth bark like eucalypts, which are common plantation trees, stand out as rather problematic for seed adherence. Tree plantations are typically depicted as depauperate in epiphyte species richness e. Merwin et al. However, being structurally less diverse than forest, plantations might provide similarly poor microclimatic conditions for germination and establishment as isolated trees due to the lack of a buffering effect of undergrowth.
In a montane landscape in Ecuador, Werner and Gradstein found seedling establishment significantly reduced in isolated trees compared to forest trees. Their research focussed on tree trunks where habitat-related microclimatic differences are probably much more pronounced than in tree crowns. We conducted our germination and seedling establishment experiments in tree crowns and microclimate differed very little between tree crowns from isolated, plantation and secondary forest trees.
Although tree crowns in teak plantations apparently do not offer a more forest-like microclimate the environment they provide is not unsuitable for epiphytes. The results of a study assessing the epiphyte diversity of plantations and secondary forest patches in the same study region support this statement: some teak plantations hosted quite diverse epiphyte assemblages Einzmann and Zotz However, their value as epiphyte refuge is still debateable since timber plantations have short harvest rotation times ca.
The expectation of higher temperatures in pasture trees compared to secondary forest trees bore out. However, the differences were not large and might be biologically irrelevant for germination. For example Marques et al. Surprisingly, relative humidity was hardly lower in isolated trees than in secondary forest trees either e. Neither germination nor survival differed significantly between trees growing alone, in teak plantations or in secondary forests. The only significant signals and occasional trends we found highlighted the adaption to drier tropical climate of T.
In contrast, a study with an epiphytic orchid in montane Costa Rica by Kartzinel et al. Several reports suggest that bromeliads benefit from a more open habitat Hietz-Seifert et al. Clearly there is a difference in the germination and establishment success of epiphytes in modified landscapes between lowland and humid montane landscapes Werner et al.
Werner and Gradstein studied the establishment of vascular epiphytes on isolated trees in a tropical montane landscape. They concluded that abiotic requirements for seedlings, like microclimatic differences, will increasingly constitute a bottleneck for the persistence of epiphyte communities. The species used in the present study were all collected in already altered landscapes, thus, the lack of a significant reduction in germination and establishment success may not really be surprising, although species differences in these ontogenetic phases were not consistent with the observed differences in species distribution along the studied rainfall gradient Einzmann and Zotz Also, the findings regarding germination and establishment success of bromeliads cannot be representative for all bromeliads, let alone all epiphytes.
In particular, more hygrophilous species will show different comportment, as extremely hygrophilous species are probably already lost in the entire study area, while moderately hygrophilous species are only found in the wetter parts Poltz and Zotz ; Einzmann and Zotz The pronounced drought tolerance of T.
The three other species in our study were less often found in the driest parts of the study region Einzmann and Zotz However, if bromeliads fare so much better in open habitat we would have expected a clearer positive response, which was not the case.
What the results do show is that the microclimatic differences in tree crowns are rather small in the different secondary habitats with no differences in germination and seedling establishment. We studied important processes of the early ontogeny of vascular epiphytes to reach a mechanistic understanding of the long-term viability of epiphyte meta communities in human-modified landscapes. We quantify V term as a proxy for the capacity of long-distance dispersal of the seeds of 13 species of orchids and bromeliads and found very low values.
Attachment of seeds to bark was invariant as long as grooves were at least 1 mm deep. Taken together, dispersal and connectivity may thus be a minor problem in these systems. Furthermore, microclimatic conditions in isolated trees, trees growing in groups like teak plantations or secondary forest patches were not very different. Consistent with similar microclimatic conditions between habitat types, germination and early establishment success were also very similar. Taken together, this suggests that epiphytes with anemochorous propagules can easily colonize new sites in fragmented landscapes, increasing the probability that epiphyte metacommunities are viable in the long run as long as trees are present and disturbance is limited.
This is in line with findings of a number of studies that suggested that some drought-tolerant species may even do better than in closed forest. The following additional information is available in the online version of this article—. Figure S1. Epiphyte abundance significantly differs, but epiphyte species richness does not differ among the five orientations when all the host trees collectively studied in tropical cloud forests Fig 3 , with the abundance and species richness of epiphytes encircling the trunk all direction orientation highest while both were lowest for north-oriented epiphytes.
Our plots are located on the eastern slope, and wind often goes from the mountain ridges along the slopes. The lower epiphyte abundance and species richness of north-oriented epiphytes may be associated with the strong wind in the north which can cause epiphytes to experience higher water evaporation, as well as colder temperatures and lower irradiance. The higher epiphyte abundance and species richness of epiphytes encircling tree trunks all direction orientation , however, suggests that microclimates around the host trees in tropical cloud forest generally favor the development of epiphyte communities.
It is also possible that encircling epiphytes benefit from stronger growth on one side of the trunk that supports growth on less favourable sides.
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This may also explain why both epiphyte abundance and species richness do not significantly differ among the east, south, west and the north. We also find that both epiphyte abundance and species richness differ among the five orientations for each of six host trees, with inconsistent patterns for each orientation in each host tree S7 Table. This is probably related to differences in morphological and physiological characteristics upon different orientations of host trees, including tree architecture [ 6 ], bark roughness [ 7 ], canopy soil chemistry [ 8 ], and branch inclination [ 9 ], as well as light penetration [ 13 ].
This result is also consistent with work by Tremblay and Castro [ 12 ], in which orchids were preferentially distributed on the northwestern side of the bole of hosts. The preference of epiphytes for a specific cardinal position on host trees shows that those wishing to promote the establishment of new epiphyte populations should consider this information to maximize epiphyte survivorship. As hypothesized, when all individuals with different diameters were taken together, epiphyte species richness and tree diameter are positively correlated across the six host tree species Fig 4.
Across species, epiphyte species richness increases with increasing host diameter across all stages of host tree development in tropical cloud forests. Increases in epiphyte species richness with DBH may result directly from increased area for epiphyte colonization and growth coupled with increased exposure to epiphyte propagule rain over the course of a longer host tree life. This pattern may also result from resulting diversity in microenvironments available on larger tree trunks [ 13 , 18 ].
The fact that of the host trees examined had fewer than five epiphytes suggests that host trees are not saturated and that potential exists for further epiphyte colonization. Therefore, our results are consistent with patterns observed by Laube and Zotz [ 41 ], that epiphyte diversity increased with increasing tree size. Our results reinforce the importance of large trees for the maintenance of vascular epiphytes; these large, mature trees play a critical role in maintaining the forest biodiversity in forest managements [ 42 ].
Interestingly, we found evidence that the slope of regressions of breakpoints examining the relationship between epiphyte species richness and tree diameter varied with tree diameter Fig 4. The slope is high when the tree ontogeny is at an early stage but the accumulation of epiphyte species decelerates for as trees enter later ontogenetic stages Fig 4. This suggests that there are two patterns for epiphyte colonization and growth on host trees in tropical cloud forests [ 18 , 23 ].
Several explanations are possible. First, it is possible that in the relatively early stages of tree growth, new habitat is exposed to epiphyte seed rain and, on average, colonization occurs more quickly, and decelerates as prime habitat on the host tree is captured. Second, and related to the first, the early stages of tree growth may be related to the generation of a larger number of relevant microsites that epiphytic species are adapted to, which encourages a wide spectrum of ephiphitic species, while later tree growth simply expands the area of these microsites, resulting in a slower accumulation of epiphytic species.
Thirdly, there may be facilitative interactions among epiphyte species at early stages, as predicted within the stress-gradient hypothesis [ 31 — 33 ]; tree species within this habitat have already been shown to follow patterns expected under this theory [ 43 ].
The initial arrival of epiphytes may ameliorate the environments for the coming of new epiphyte species, contributing to an increased rate in epiphyte species richness at early stage of tree ontogeny. Similar to the second explanation, once tree growth provides all microsites in each zone, the accumulation of epiphyte species slows down, resulting in the slow accumulation of epiphytes on relatively old host trees.
Although saturation of epiphytes on host trees is expected at later stages of host tree ontogeny [ 44 ], we seldom find tree crowns that are completely covered by epiphytes during field work. The rate of colonization and growth for epiphytes is lower in the presence of low air temperature stress [ 44 ] Fig 4 ; as such, it may be unreasonable to expect saturation in mature trees in tropical cloud forest. Future work should explore other potential influences on epiphyte colonization and survival, such as stresses related to temperature and wind.
However, this observation was consistent with our species specific explorations of this relationship S8 Table.
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Regardless, our results do not support the suggestion that host trees at the early stage of development lack the architectural and physiological characteristics suitable for epiphyte establishment. Our results are also consistent with forest community succession theory [ 45 ], in that the early arrival of some epiphytes may facilitate the later establishment of new species. We demonstrate that tropical cloud forests are communities that host a diverse array of vascular epiphytes, and that these are dominated by orchids and pteridophytes.
Both species richness and abundance of epiphytes significantly decreased from the lower to upper crown zones on host trees. Additionally, both epiphyte abundance and species richness did not differ among the eastern, southern, western and northern orientations for all collective host trees, but did differ among the these four orientations for individual host trees.
When all six host species were considered together, vascular epiphyte species richness significantly increased with increasing host tree diameter, which is in contrast with studies predicting that epiphyte species richness had a neutral relationship with host tree size at later host stages [ 22 ]. We found that the rate at which epiphyte diversity increased with tree diameter was high at the early stages of host tree growth, but was lower at the later stages, contrasting with previous research that found no relationship between epiphyte richness and tree diameter at early stages [ 23 ].
Conceived and designed the experiments: XW WL. Performed the experiments: XW MX. Analyzed the data: XW YK. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Vascular epiphytes are important components of biological diversity in tropical forests. Introduction Epiphytes are essential components of biological diversity that germinate and grow upon host plants typically woody perennials , obtaining mineral nutrients and water from water vapour e.
Download: PPT. Fig 1. Diagram of the vertical zones of host trees where epiphyte is distributed. Results Diversity of vascular epiphytes There were a total of individual epiphytes, belonging to 35 species, 24 genera and 9 families S1 Table. Diversity of host trees The surveyed host trees were attributed to 48 species, 34 genera and 23 families, with their DBH ranging from 1.
Distribution of vascular epiphytes among host crown zones When host tree height was taken as a fixed effect, and tree identity was taken as a random effect, no obvious effects of host tree height on epiphyte abundance or species richness were found when all six host tree species were examined using a linear mixed-effects model S2 Table.
Distribution of vascular epiphytes among epiphytic orientations When host tree height was taken as a fixed effect, and tree identity was taken as a random effect, no obvious effects of host tree height on epiphyte abundance or species richness were found when all six host tree species were examined using a linear mixed-effects model S5 Table. Relationships between vascular epiphyte species richness and host tree diameter When each of the six host tree species were analyzed independently, epiphyte species richness was not significantly related to host tree DBH, using a generalized linear model S8 Table.
Fig 4. Relationship between the vascular epiphyte species richness and host tree diameter DBH across all six study species Engelhardtia roxburghiana , Ternstroemia gymnanthera , Syzygium buxifolium , Illicium ternstroemioides , Distylium racemosum and Cyclobalanopsis disciformis , using a regression of breakpoints based on generalized linear model. Distribution of vascular epiphytes among host crown zones and orientations In our study, epiphyte species richness and abundance generally decreased from the TZ, ICZ and MCZ to the OCZ of the host trees Fig 2 , indicating that diversity of vascular epiphytes shows a decreasing trend as we move up the trunk of host trees.
Relationships between vascular epiphyte species richness and host tree diameter As hypothesized, when all individuals with different diameters were taken together, epiphyte species richness and tree diameter are positively correlated across the six host tree species Fig 4.
Conclusion We demonstrate that tropical cloud forests are communities that host a diverse array of vascular epiphytes, and that these are dominated by orchids and pteridophytes. Supporting Information. S1 Table. Vascular Epiphyte species composition and their distributions at crown zones and orientations upon host trees in tropical cloud forests in Hainan. S2 Table. S3 Table. Differences in vascular epiphyte abundance and richness for each of the six host tree species along host tree height and among different host crown zone, using two-way ANOVAs. S4 Table. Difference tests in vascular epiphyte abundance and richness for each of the six host tree species among the four host crown zones, using a one-way ANOVA.
S5 Table. S6 Table. Differences in vascular epiphyte abundance and richness for each of the six host tree species along host tree height and among different host orientations, using two-way ANOVAs. S7 Table. Difference tests in vascular epiphyte abundance and richness for each of the six host tree species among different epiphytic orientations, using a one-way ANOVA.
S8 Table. Parameters for relationships between vascular epiphyte species richness and DBH of host trees for each the six host tree species, using a generalized linear model. References 1. Kress W. The systematic distribution of vascular epiphytes: an update. View Article Google Scholar 2. Benzing DH. Vascular epiphytes: general biology and related biota. UK: Cambridge University Press; Epiphytes and their contribution to canopy diversity.
Plant Ecol. View Article Google Scholar 4. Response of epiphytic bryophytes to simulated N deposition in a subtropical montane cloud forest in southwestern China. Epiphytes improve host plant water use by microenvironment modification. Funct Ecol.
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