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Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty?

1
Geology & Geography, Georgia Southern University, Statesboro, GA 30460, USA
2
Biology, Franklin & Marshall College, Lancaster, PA 17603, USA
3
Plant Ecology & Nature Conservation, University of Potsdam, 14476 Potsdam, Germany
4
Ecosystem Science & Management, Texas A&M University, College Station, TX 77843, USA
*
Author to whom correspondence should be addressed.
Geosciences 2019, 9(8), 342; https://doi.org/10.3390/geosciences9080342
Received: 30 April 2019 / Revised: 18 July 2019 / Accepted: 1 August 2019 / Published: 5 August 2019
(This article belongs to the Special Issue Advances in Rainfall and Evaporation Partitioning)
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. View Full-Text
Keywords: precipitation; interception; bromeliad; vascular epiphyte; non-vascular epiphyte; lichens; bryophytes; water storage capacity precipitation; interception; bromeliad; vascular epiphyte; non-vascular epiphyte; lichens; bryophytes; water storage capacity
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Hargis, H.; Gotsch, S.G.; Porada, P.; Moore, G.W.; Ferguson, B.; Van Stan, J.T., II. Arboreal Epiphytes in the Soil-Atmosphere Interface: How Often Are the Biggest “Buckets” in the Canopy Empty? Geosciences 2019, 9, 342.

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