Microclimatic variations in tropical canopies: a glimpse into the processes of community assembly in epiphytic bryophyte communities

Abstract

Epiphytic communities live in a unique, three-dimensional micro-habitat space that offers an original framework to disentangle the contribution of environmental filters, biotic interactions and dispersal limitation to community structure at small spatial scales. We took advantage of a tropical canopy crane facility to record and model spatio-temporal microclimatic variation and assess its impact on the composition and phylogenetic structure of epiphytic bryophyte communities. Generalized Dissimilarity Modelling evidenced the crucial role of microclimates in determining the composition of moss and liverwort communities. The shift between negative or non-significant phylogenetic turnover to consistently significant clustering from the base to the canopy suggests that phylogenetic constraints further contribute to shape the assembly of epiphytic bryophyte communities. The slight, but significant correlation between increasing phylogenetic clustering with variation in microclimatic conditions adds to emerging evidence for the role of environmental filtering upon community assembly, including at the small spatial scales of epiphytic communities.

What makes a good phorophyte? Predicting occupancy, species richness and abundance of vascular epiphytes in a lowland seasonal tropical forest

“…81.3% of tropical dominant fern, Asplenium nidus, which can offer a cool and moist microhabitat for arboreal fauna, prefers growing on small trees. Species richness of liverworts was also maximum on small trees (Shen et al, 2022). Altogether, these observations support the idea that epiphytic diversity assessments in tropical forests must also include small understorey trees (Sporn et al, 2010), which should be further considered for conservation.…”

“…Light intensity ('L' , W/m 2 ), air temperature ('T' , • C), relative humidity ('RH' , %) and photosynthetic active radiation ('PAR' , µmol•m −2 •s −1 ) were recorded at 1-hr intervals from 12 trees at five height zones (tree base, middle trunk, inner canopy, middle canopy and outer canopy) from July 2017 to December 2019. To predict the spatial variation of light and microclimatic conditions from the data collected by 54 dataloggers, we modeled hourly variation in T, L, RH and PAR in an X-Y-Z space (thus including tree height and elevation) using Random Forest (Shen et al, 2022) as implemented by the randomForest package (Liaw and Wiener, 2002) in R v4.0.4 (R Core Team, 2021). The microclimatic conditions that prevail on each tree substantially vary from the base to the canopy.…”

“…The microclimatic conditions that prevail on each tree substantially vary from the base to the canopy. Between 2 and 62 m above ground, day (8 a.m.-7 p.m.) relative humidity ranged between 53.6 and 99.9% and day temperature between 12.0 and 31.7 • C (Shen et al, 2022), challenging the description of the global microclimatic conditions that prevail at each host tree. Each epiphytic fern and spermatophyte community was, however, restricted to a specific height zone on a tree (Figure 1B).…”

“…Here, we took advantage of a tropical canopy crane facility to conduct a comprehensive census of vascular epiphytes and record detailed information on both the intrinsic factors of each individual tree and extrinsic factors describing their environment. In particular, the prime importance of microclimates actually experienced by organisms has been increasingly acknowledged (De Frenne et al, 2021), but it is only recently that microclimatic conditions have been monitored, modeled and used to explain the spatial variation of epiphyte distributions (Murakami et al, 2022;Shen et al, 2022). In this framework, we address the following questions: (1) if epiphytes are not randomly distributed among trees, to what extent can we, using a comprehensive description of the characteristics of individual trees and their local environment, predict which trees are likely to host epiphytes and which trees are not, and how epiphytic species richness and abundance vary among individual trees?…”

Vertical variation in leaf functional traits of Parashorea chinensis with different canopy layers

“…Adult individuals of P. chinensis in the canopy may reach heights above 60 m (Deng et al, 2020), which is also the tallest tree of tropical seasonal rainforest in China and means a high proportion of aboveground carbon storage (Tang et al, 2008). Meanwhile, P. chinensis also plays an essential role in maintaining biodiversity and the stability of ecological networks in community (Hu et al, 2022;Shen et al, 2022). Data reveal that large trees are more susceptible to the impact of drought due to changes in precipitation time and amplitude, as well as increasing temperatures (Bennett et al, 2015;Liu et al, 2021).…”