Functional Ecology of Vascular Epiphytes

Abstract

The epiphytic life form characterizes almost 10% of all vascular plants. Defined by their mechanical dependence throughout their life and their non‐parasitic relationship with the host, the term epiphyte describes a very heterogenous and taxonomically diverse group of plants. This article explores the functional ecology of this group, acknowledging from the start that our current knowledge is highly biased, e.g. with a strong focus on particular families like bromeliads or orchids. This bias goes along with a number of problematic and weakly founded generalizations in the literature. Our article covers a set of particularly important aspects of epiphyte ecology, e.g. germination, water and nutrient relationships, and biomechanical aspects of the epiphyte‐host relationship. Throughout our article, we describe ways for future research projects to reach a more comprehensive and representative understanding of the biological responses to the varying challenges of the arboreal habitat, and emphasize that the study of epiphytes should not only be of interest to the narrow expert: a comparison of the functional ecology of epiphytes and ground‐rooted terrestrials offers unique perspectives to understanding both evolutionary and ecological, phenotypic responses to the diverse habitats of vascular plants in general.

Putting vascular epiphytes on the traits map

“…However, data on CAM are biased by the prominence of bromeliads. Excluding bromeliads, the proportion of CAM in our epiphyte dataset (9.9%) is similar to a global estimate of 7% of all vascular plants (Winter & Smith, 1996), which questions the general importance of CAM for epiphytes (Zotz, Hietz, et al, 2021). Also, whereas average δ 13 C values are highest in epiphytes, in the range of C3 plants δ 13 C values do not differ between epiphytes and herbs, so we reject the hypothesis of generally higher water use efficiency, at least as estimated via carbon isotopes.…”

Physiological ecology of Mexican CAM plants: history, progress, and opportunities

“…Vascular epiphytes are elements occurring in almost all ecosystems of the world, but they are particularly diverse in evergreen rain forests and cloud forests of tropical and subtropical regions (Silvera & Lasso 2016). Vascular epiphytes O n l i n e f i r s t constitute a heterogeneous group that represents approximately 10 % of the tracheophytes, with more than 31,000 species distributed in 79 families, although the vast majority (80 %) belong to the Orchidaceae, Bromeliaceae and Polypodiaceae (Zotz et al 2021). In Mexican flora, the proportion of vascular epiphytes is 7.8 %, with approximately 1,813 species distributed in 37 families, mainly in the Orchidaceae (50 %), Bromeliaceae (13 %) and Polypodiaceae (7 %) and are found with greater diversity in the cloud forest or mesophyllous mountain forest (Espejo-Serna et al 2021).…”

“…It has been estimated that most epiphytic species exhibit CAM photosynthesis (Zotz & Hietz 2001, Lüttge 2004, Andrade et al 2007, Silvera & Lasso 2016, Zotz et al 2021. About 50 % of the approximately 30,000 epiphytic species of the Orchidaceae family are CAM (Winter & Smith 1996, Silvera & Lasso 2016.…”

“…About 50 % of the approximately 30,000 epiphytic species of the Orchidaceae family are CAM (Winter & Smith 1996, Silvera & Lasso 2016. In Bromeliaceae, CAM is common in the Bromelioidae subfamily (90 % of species; Zotz et al 2021), and less common in the Tillandsioidae subfamily (28 % of species; Crayn et al 2015). Also, all epiphytic cacti are CAM (Zotz et al 2021).…”

Holding on or falling off: The attachment mechanism of epiphytic Anthurium obtusum changes with substrate roughness

“…For example, bark roughness was assessed visually (Adhikari et al, 2012; Ceballos et al, 2016), in terms of furrow depth and width on the bark (Lewis and Ellis, 2010) or by means of folding a thin cotton thread to conform to every asperity and crevice over a certain length of the bark (Callaway et al, 2002). However, it is questionable whether the scale at which roughness is studied so far is relevant (Zotz et al, 2021a). More specifically, there is still a lack of understanding regarding how the roots interact with their host substrate: What is the attachment mechanism of epiphytic roots to their substrate?…”