Quantification and Variation of Microclimatic Variables Within Tree Canopies - Considerations for Epiphyte Research

Abstract

Forest canopies are incredibly complex self-maintaining biological structures. Conditions above and within the canopy can differ vastly, often resulting in a vertical gradient of microclimate conditions. Canopy epiphytic plants have to deal with climatic variability on much more variable scales compared to many other plant groups. The difficulty of sensor installation and their high cost can explain why it has been ignored in many studies on canopy epiphytes. Direct measurements of microenvironmental conditions are the only accurate way to assess specific intra-canopy environmental conditions, as there is also still a lack of methodologically and financially viable alternatives to allow the collection of this type of data. This study aims to make recommendations for the direct use of microclimate measurements in epiphyte research and to summarize key discussion points concerning the number and placement of sensors required for different types of epiphyte studies. In addition, we presented high-resolution field data from the United Kingdom, where we employed over 56 microclimate sensors, to demonstrate the spatial and temporal variability of radiation, temperature, and relative humidity (RH) in a tree canopy. Our data demonstrated that sensor height in the tree and leaf-set were the most important factors determining microclimate variability in the canopy. For the first time, we have made recommendations regarding the placement and number of sensors required in studies that specifically require the use of microclimate sensors in epiphyte studies in forest canopies.

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

“…The microclimatic data reported here and their three-dimension modelling help to fill a gap in our knowledge of the spatial variation of forest microclimates and to address the question of how microclimatic variation within and below tree canopies impacts community species richness and composition (De Frenne et al, 2019;Ellis & Eaton, 2021;Murakami et al, 2022). In line with previous assessments of microclimatic variation within canopies (see Murakami et al, 2022 and references therein), variations in temperature and RH were progressively buffered from the canopy to the tree base, with a substantially higher day/night difference in temperature and RH in the canopy.…”

“…Despite these expectations, where and when competition and facilitation dominate, if at all, remains relatively unexplored in epiphyte ecology (Francisco et al, 2018; Spicer & Woods, 2022). Furthermore, while the vertical structures of epiphyte communities (Gehrig‐Downie et al, 2013; Mota de Oliveira et al, 2009; Mota de Oliveira & ter Steege, 2015; Zotz, 2016) and, to a lesser extent, associated variations in microclimatic conditions (Murakami et al, 2022; Stuntz et al, 2002; Toivonen et al, 2017), have long been documented, no analysis has, to our knowledge, examined the relationship between microclimatic variation and species composition in a spatially explicit framework. In fact, although forest canopy science has been an active discipline since the 19th century, its progress has been slow, partly due to the limited accessibility of canopies (Nakamura et al, 2017) and the limited availability of fine‐scale microclimatic data (De Frenne et al, 2021), a critical issue for canopy epiphytes (Murakami et al, 2022).…”

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

“…Also, tallest trees could have a vertical stratification of environmental conditions on the tree canopy ( e.g. , light, moisture) ( Murakami et al, 2022 ), providing a highest diversity of microhabitats for a wider range of epiphytes species ( Krömer, Kessler & Gradstein, 2007 ; Fayle et al, 2009 ; Dislich & Mantovani, 2016 ). However, in disturbed habitats ( e.g.…”