Abstract
Arboreal epiphytes (plants residing in forest canopies) are present across all major climate zones and play important roles in forest biogeochemistry. The substantial water storage capacity per unit area of the epiphyte “bucket” is a key attribute underlying their capability to influence forest hydrological processes and their related mass and energy flows. It is commonly assumed that the epiphyte bucket remains saturated, or near-saturated, most of the time; thus, epiphytes (particularly vascular epiphytes) can store little precipitation, limiting their impact on the forest canopy water budget. We present evidence that contradicts this common assumption from (i) an examination of past research; (ii) new datasets on vascular epiphyte and epi-soil water relations at a tropical montane cloud forest (Monteverde, Costa Rica); and (iii) a global evaluation of non-vascular epiphyte saturation state using a process-based vegetation model, LiBry. All analyses found that the external and internal water storage capacity of epiphyte communities is highly dynamic and frequently available to intercept precipitation. Globally, non-vascular epiphytes spend <20% of their time near saturation and regionally, including the humid tropics, model results found that non-vascular epiphytes spend ~1/3 of their time in the dry state (0–10% of water storage capacity). Even data from Costa Rican cloud forest sites found the epiphyte community was saturated only 1/3 of the time and that internal leaf water storage was temporally dynamic enough to aid in precipitation interception. Analysis of the epi-soils associated with epiphytes further revealed the extent to which the epiphyte bucket emptied—as even the canopy soils were often <50% saturated (29–53% of all days observed). Results clearly show that the epiphyte bucket is more dynamic than currently assumed, meriting further research on epiphyte roles in precipitation interception, redistribution to the surface and chemical composition of “net” precipitation waters reaching the surface.
Highlights
How Big Is the Epiphyte Bucket?Hydrologists have long represented landscape elements along the rainfall-to-runoff pathway as “buckets” [1], or water storage elements, with various “holes” where water may escape by evaporation [2] or drainage to another landscape element, be it the litter [3], soils [4], or beyond.During storms, the first bucket that rainfall encounters in vegetated ecosystems is the plant canopy via interception [5]
This section focuses on models that examine water storage, filling and emptying dynamics for lichens and bryophytes (LiBry [15]), the phytotelmata of pitcher plants [59], and data showing saturation dynamics of canopy soils at various elevations of the Monteverde Cloud Forest (Costa Rica); which demonstrate that these “open” buckets may often be available for rainfall interception
For the vascular epiphyte bucket, it is important to note that current hydrologic theory limits interception water storage solely to the plants’ externally held water [72]
Summary
Hydrologists have long represented landscape elements along the rainfall-to-runoff pathway as “buckets” [1], or water storage elements, with various “holes” where water may escape by evaporation [2] or drainage to another landscape element, be it the litter [3], soils [4], or beyond. Different leaf surface structures may differ in their precipitation interception mm of rainwater in Costa Rica [26]; phytotelmata can result from multiple leaf efficiency or water storage capacity, for this example: does thestorage outer capacity leaf surface tank-leaves configurations in epiphytes [35] and tank leaf water does of notbromeliad include droplets interact differently with passing rain droplets than the foliage. Anomalus leaves which have a thin hydrenchymal layer (Figure 2a)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
