Throughfall alterations by degree of Tillandsia usneoides cover in a southeastern US Quercus virginiana forest

Abstract

Alterations to forest canopy structure directly affect the hydrology and biogeochemistry of wooded ecosystems. Epiphytes alter canopy structure, thereby intercepting rain water, reducing penetration of rain to the surface (as throughfall), modifying throughfall chemistry, and changing throughfall responses to storm conditions. These processes are well established for epiphyte presence-versus-absence; yet, it's unknown how epiphyte-throughfall interactions change across an epiphyte cover continuum (important information for prediction of ecological changes with epiphyte establishment/decline from disturbance). To fill this gap, we monitored throughfall water and dissolved ions (Na + , NH 4 + , K + , Mg 2+ , Ca 2+ , Cl -, NO 3 -, PO 4 3-, SO 4 2-) beneath a common epiphyte (Tillandsia usneoides) across cover percentages (0-20%, 21-40%, 41-60%, 61-80%, 81-100%) for 47 storms. Throughfall amount inversely responded to epiphyte cover, while increasing salt washoff and intracellular leaching. Greater epiphyte cover released NH 4 + and reduced NO 3 -from throughfall. Storm conditions (high vapor pressure deficit, moderate wind speeds, and low intensity) strengthened throughfall responses as T. usneoides cover increased. Factorial MANOVA results revealed significant trends for throughfall ion enrichment/depletion via washoff, leaching and uptake. These data suggest that inclusion of epiphyte alterations to rain water and solute inputs in ecosystem nutrient budgeting studies should consider the full continuum of epiphyte cover represented at that site.

Interstorm Variability in the Biolability of Tree-Derived Dissolved Organic Matter (Tree-DOM) in Throughfall and Stemflow

“…Cedar tree-BDOM was consumed rapidly (within 1-4 days) and yielded 3-63 mg-C m −2 mm −1 of rainfall. A simple estimate of tree-BDOM annual yield using the mean biolability proportion for each hydrologic flux and total tree-DOM annual yields previously computed at this site [14] equates to 21.3-30.2 g-C m −2 year −1 of tree-BDOM, which is 33-47% of the 65 g-C m −2 year −1 of net ecosystem exchange estimated for Georgia (USA) forests [31]. Tree-BDOM proportions and biodegradation rates were not significantly different between throughfall and stemflow, or under epiphyte versus bare canopy conditions.…”

“…Epiphyte presence enriched both stemflow and throughfall with tree-DOM compared to samples collected from bare canopies. The tangled, pendulous morphology of T. usneoides may account for increased tree-DOM concentrations, because it (1) can capture greater aerosols [31] and (2) trap and decompose materials (litter, insect frass, etc.) [32].…”

Spatio-temporal variation of throughfall in a hyrcanian plain forest stand in Northern Iran

“…rainfall characteristics, canopy architecture, branch angle, canopy cover, tree age, leaves shapes, types and dimensions, phonological stages, and even silvicutural practices affect hydrologic behavior of forest stand against input rainfall (Brandt, 1987;Bruijnzeel, 2005;Davudirad et al, 2015;Davudirad et al, 2016;Gay et al, 2015;Guswa and Spence, 2012;Huber and Iroumé, 2001;Molina and Campo, 2012;Nanko et al, 2006;Onozawa et al, 2009;Pérez-Suárez et al, 2008;Pypker et al, 2005;Staelens et al, 2007;Van Stan et al, 2012;Xu et al, 2014). Due to dynamic varia-bility of affecting factors in space and time, the throughfall as an important component of hydrologic cycle in forest ecosystems varies temporally and spatially (Forti and Neal, 1992;Staelens et al, 2006).…”

Wrack and ruin: Legacy hydrologic effects of hurricane-deposited wrack on hardwood-hammock coastal islands

“…For example, soil moisture changes during a case study storm event were synchronous with large changes in salinity that peaked in the mesohaline solution range, 8-12 PSU ( figure 2(d)). These salinity values are several times larger than what has been measured in throughfall (<2 PSU) for a wide range of storms and lab-derived vegetation leachates from forests on Skidaway Island and the nearby St. Catherine's Island (Gay et al 2015. Although infrequent tidal inundation occurred at the site during high spring tides (described in the methods), tidal inundation during this storm was unlikely as high tide elevations were >0.5 m below the approximate elevation of the sensors (figure S1(b), top panel, supplemental materials).…”

“…Installation trenches were carefully filled with the local site-excavated soils. For a case study storm, EC was converted to Practical Salinity Units (PSU) (Fofonoff and Millard Jr 1983); changes during the example storm are hypothesized to be principally derived from sea salts sourced from marine aerosols, throughfall (which has been shown to have low PSU values in previous work at Skidaway Island (Gay et al 2015, the wrack itself, and salts left from occasional tidal inundation (and, of course, from the hurricane storm surge that delivered the wrack). We did not monitor soil moisture and EC vertically through the soils and, therefore, have no direct observations of groundwater and capillary fringe fluctuations during storms.…”