Microclimatic variation in tropical canopies: A glimpse into the processes of community assembly in epiphytic bryophyte communities

Abstract

1. Epiphytic communities offer an original framework to disentangle the contributions of environmental filters, biotic interactions and dispersal limitations to community structure at fine spatial scales. We determine here whether variations in light, microclimatic conditions and host tree size affect the variation in species composition and phylogenetic structure of epiphytic bryophyte communities, and hence, assess the contribution of environmental filtering, phylogenetic constraints and competition to community assembly.2. A canopy crane giving access to 1.1 ha of tropical rainforest in Yunnan (China) was employed to record hourly light and microclimatic conditions from 54 dataloggers and epiphytic bryophyte communities from 408 plots. Generalized Dissimilarity Modelling was implemented to analyse the relationship between taxonomic and phylogenetic turnover among epiphytic communities, host-tree characteristics and microclimatic variation.3. Within-tree vertical turnover of bryophyte communities was significantly about 30% higher than horizontal turnover among-trees. Thus, the sharp vertical variations in microclimatic conditions from tree base to canopy are more important than differences in age, reflecting the likelihood of colonization, area, and

Disentangling the roles of chance, abiotic factors and biotic interactions among epiphytic bryophyte communities in a tropical rainforest (Yunnan, China)

“…These results were unexpected because, in line with a number of studies supporting the application of the stress-gradient theory in plant communities (Casalini & Bisigato 2018;Kjaer et al 2018;Muscarella et al 2018; but see- Maestre et al 2006;Qi et al 2018), positive and negative interactions are thought to prevail in communities exposed to harsh and mild environmental conditions, respectively. Although microclimatic conditions substantially vary in terms of daily variations in light exposure, temperature and relative humidity along a tree (Shen et al 2022a), at first sight generating strong stress gradients from the base to the canopy, the stress-gradient hypothesis is not always supported, even along apparently strong stress gradients (Maestre et al 2006;Qi et al 2018). For instance, Scherrer et al (2019) similarly failed to identify changes in biotic interaction patterns among plant communities along an elevation gradient, and no support for the stressgradient hypothesis was reported among epiphyllous bryophyte communities from gap and closed forest sites (Me zaka et al 2022).…”

“…Although microclimatic conditions substantially vary in terms of daily variations in light exposure, temperature and relative humidity along a tree (Shen et al . 2022a), at first sight generating strong stress gradients from the base to the canopy, the stress‐gradient hypothesis is not always supported, even along apparently strong stress gradients (Maestre et al . 2006; Qi et al .…”

“…Sampling protocols and environmental data collection were described in Shen et al . (2022a,b) and are briefly summarized below. Bryophyte species composition was determined for 408 plots of 1600 cm 2 on 42 Parashorea chinensis host trees using a stratified sampling across three height zones: lower trunk (from tree base to the middle height of the trunk), upper trunk (from the middle height of the trunk to the lowest third of the canopy), and canopy top (from to the middle third of the canopy to the upper third of the canopy).…”

“…Forty‐six environmental variables were recorded or derived (Table 1), including microclimate (relative humidity and temperature; HYS15 air temperature and relative Moisture Sensors, Unism) and light (intensity and photosynthetically active radiation; LI‐190R Quantum Sensor, LI‐COR Biosciences) recorded at 1‐h intervals from 12 trees (one in the lower trunk, two in the upper trunk, and two in the canopy) from July 2017 to December 2019 and predicted in an x‐y‐z space (Shen et al . 2022a) using Random Forest (Liaw & Wiener 2002).…”

“…seasonal rain forest (101°34 0 59.1 00 E, 21°37 0 2.6 00 N) in Xishuangbanna National Natural Reserve (Yunnan, SW China). This site was chosen because of the availability of comprehensive, fine-scale information on environmental conditions and epiphyte species distributions (Shen et al 2018(Shen et al , 2022a, which could be collected thanks to an 81m-tall canopy crane (TCT7015-10E, Zoomlion Heavy Industry, Changsha, China), whose 60-m-long arm provides access to the canopy within a 1.1-ha circle.…”