Epiphyll specialization for leaf and forest successional stages in a tropical lowland rainforest

Questions: The importance of tropical rainforest gap dynamics in biodiversity maintenance is not fully understood, in particular for taxa other than trees and lianas. We used epiphylls on rainforest leaves to study the importance of leaf- and forest-scale succession in determining biodiversity patterns by characterizing community change with leaf age in gaps and closed-forest habitats. We asked: 1. Do epiphylls show specialization for leaf and forest successional stages? 2. Can early and late-successional epiphyllous species be recognized at these two scales? 3. How do epiphyll presence, species richness, and cover change with leaf and forest successional stages? Location: Barro Colorado Island, Panama. Methods: Data were collected from 420 leaves, in three age groups and at two heights on shrubs in gaps and closed forest. We calculated turnover and nestedness components of dissimilarity to evaluate the importance of species replacement or accumulation during leaf and forest succession. Using generalized linear mixed models we determined what factors explain epiphyll species occurrence, richness and cover. Results: Closed forest contained more liverwort and lichen specialist species than gaps. Specialist species were identified for older leaves only. Dissimilarity between leaves within age groups was dominated by turnover within and between forest successional stages. Dissimilarity between leaf age groups, at the site level, was dominated by nestedness, i.e. species accumulation. Both in forest and gaps, epiphyll presence and cover increased with leaf age for all taxa except fungi, while species richness increased only for lichens. Conclusions: Early and late forest successional stages both contribute to epiphyll species richness by harboring specialized species. Among leaf successional stages, young leaves contain a mere subset of the species found on older leaves. Epiphyll communities do not follow classic succession, in the sense of changes being driven by species replacement, but are characterized by species accumulation through time

Phylogenetic diversity and the structure of host-epiphyte interactions across the Neotropics

Understanding the mechanisms driving community assembly has been a major focus of ecological research for nearly a century, yet little is known about these mechanisms in commensal communities, particularly with respect to their historical/evolutionary components. Here, we use a large-scale dataset of 4,440 vascular plant species to explore the relationship between the evolutionary distinctiveness (ED) (as measured by the 'species evolutionary history' (SEH)) of host species and the phylogenetic diversity (PD) of their associated epiphyte species. Although there was considerable variation across hosts and their associated epiphyte species, they were largely unrelated to host SEH. Our results mostly support the idea that the determinants of epiphyte colonization success might involve host characteristics that are unrelated to host SEH (e.g., architectural differences between hosts). While determinants of PD of epiphyte assemblages are poorly known, they do not appear to be related to the evolutionary history of host species. Instead, they might be better explained by neutral processes of colonization and extinction. However, the high level of phylogenetic signal in epiphyte PD (independent of SEH) suggests it might still be influenced by yet unrecognized evolutionary determinants. This study highlights how little is still known about the phylogenetic determinants of epiphyte communities

Responses of Tree Seedlings near the Alpine Treeline to Delayed Snowmelt and Reduced Sky Exposure

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

Supplementary code and data from: Towards more reproducibility in vegetation research"

<p>Data include an assessment of availability and accessibility of data and code for all the articles published in <em>Journal of Vegetation Science</em> and <em>Applied Vegetation Science</em> in the period 2013-2013.</p> <p>Data consist of one csv file: <code>editorialdata_2211.csv</code>.  A detailed description is provided in the README file. </p> <p>Code consists of one R script to reproduce the main stats in the article and figure 1: <code>editorial_stats_and_plots.R</code>:</p&gt

Branchfall as a Demographic Filter for Epiphyte Communities: Lessons from Forest Floor-Based Sampling

<div><p>Local variation in the abundance and richness of vascular epiphytes is often attributed to environmental characteristics such as substrate and microclimate. Less is known, however, about the impacts of tree and branch turnover on epiphyte communities. To address this issue, we surveyed branches and epiphytes found on the forest floor in 96 transects in two forests (Atlantic rainforest in Brazil and Caribbean rainforest in Panama). In the Brazilian forest, we additionally distinguished between edge and core study sites. We quantified branch abundance, epiphyte abundance, richness and proportion of adults to investigate the trends of these variables over branch diameter. Branches <2 cm in diameter comprised >90% of all branches on the forest floor. Abundance and richness of fallen epiphytes per transect were highest in the Brazilian core transects and lowest in the Panamanian transects. The majority of epiphytes on the floor (c. 65%) were found attached to branches. At all three study sites, branch abundance and branch diameter were negatively correlated, whereas epiphyte abundance and richness per branch, as well as the proportion of adults were positively correlated with branch diameter. The relationship between branch diameter and absolute epiphyte abundance or richness differed between study sites, which might be explained by differences in forest structure and dynamics. In the Panamanian forest, epiphytes had been previously inventoried, allowing an evaluation of our surveying method by comparing canopy and forest floor samplings. Individuals found on the forest floor corresponded to 13% of all individuals on branches <10 cm in diameter (including crowns), with abundance, richness and composition trends on forest floor reflecting canopy trends. We argue that forest floor surveys provide useful floristic and, most notably, demographic information particularly on epiphytes occurring on the thinnest branches, which are least accessible. Here, branchfall acts as an important demographic filter structuring epiphyte communities.</p></div

Epiphytes in the canopy and their relationship with forest floor trends.

<p>(A) epiphyte abundance and (B) species richness in the canopy directly above the Panamanian transects (n = 29) as a function of branch diameter. Proportion of individuals (C) and species (D) found on the forest floor compared to the transects' total abundance (forest floor and canopy). (E-F) Non-metric multidimensional scaling of transects based on species composition and abundance considering (E) all individuals found on the forest floor and canopy (n = 18 forest floor and canopy pairs) and (F) only individuals on substrate < 10 cm in diameter (n = 17). Forest floor and canopy pairs are indicated by the same numbers in E-F (legend in F). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128019#pone.0128019.s006" target="_blank">S2 File</a> for the number of individuals and species censed within the whole crane plot (c. 0.9 ha). Solid lines give the values predicted by the estimated GAMMs, whereas dashed lines show 95% CI in A-D. Lines connecting numbers indicate convex hulls in D-F. We excluded the thinnest branch diameter class in C and D due to overall low abundances in the canopy (see A-B). Box-plots show the median as central line, 1.5 interquantile range as whiskers, and outliers as circles.</p

Comparisons between study sites. Several measures characterizing forest structure, branch abundance, epiphyte abundance and epiphyte richness.

<p>Comparisons between study sites. Several measures characterizing forest structure, branch abundance, epiphyte abundance and epiphyte richness.</p

Summarizing scheme of the expected trends with increasing branch diameter.

<p>We expect a decrease in water stress, mechanical disturbance and branch abundance with an increasing branch diameter. These drivers plus the increase in branch age should lead to higher epiphyte colonization and survival and an increase in epiphyte abundance, richness and proportion of adults per branch.</p

Branch abundances as a function of branch diameter.

<p>A) Brazilian core transects (n = 30). B) Brazilian edge transects (n = 30). C) Panamanian transects (n = 36). Box-plots show the median as central line, the first and third quantiles as the bottom and top box limits, 1.5 interquantile range as whiskers, and outliers as circles. Solid lines show fits from GAMMs with 95% CI indicated by dashed lines.</p