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 rainwater, 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 is unknown how epiphyte–throughfall interactions change across an epiphyte cover continuum (important information for prediction of ecological changes with epiphyte establishment or decline from disturbance). To fill this gap, we monitored throughfall water and dissolved ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl–, NO3–, PO43–, SO42–) beneath a common epiphyte (Tillandsia usneoides L.) 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 wash-off and intracellular leaching. Greater epiphyte cover released NH4+ and decreased NO3– 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 or depletion via wash-off, leaching, and uptake. These data suggest that inclusion of epiphyte alterations to rainwater and solute inputs in ecosystem nutrient budgeting studies should consider the full continuum of epiphyte cover represented at that site.