Epiphyte influence on stemflow and nutrient cycling in a subtropical mixed ombrophilous forest

Resumen

Epiphytes play a fundamental role in rainfall redistribution and nutrient fluxes, particularly through stemflow modulation. Although stemflow represents a small fraction of total precipitation compared to throughfall, it is ecohydrological as it concentrates water and solutes at the tree base. This study quantifies the influence of the epiphytes Aechmea sp., Hypnum cupressiforme Hedw., and Campyloneurum phyllitidis (L.) C. Presl on stemflow dynamics and nutrient cycling in a Mixed Ombrophilous Forest (Araucaria Forest) in Southern Brazil. Monitoring was conducted between July 2022 and July 2023, measuring gross precipitation, throughfall, and stemflow across thirteen host trees before and after experimental epiphyte removal. Canopy characteristics and nutrient fluxes were also analyzed and statistically evaluated. Results indicated that stemflow volume was higher in the presence of epiphytes and decreased after their removal, demonstrating that the magnitude of this hydrological effect is species-specific. The association between C. phyllitidis and H. cupressiforme, as well as the isolated presence of H. cupressiforme, promoted higher stemflow yields, whereas the removal of Aechmea sp. and H. cupressiforme led to a reduction in volume. Regarding nutrient dynamics, calcium (Ca²⁺) and potassium (K) exhibited the highest mean concentrations. Following epiphyte removal, a substantial increase in the concentration of most nutrients was observed, particularly for K (exceeding 70%), while sodium (Na⁺) was the only element to show a reduction across both study periods. It is concluded that epiphytes regulate nutrient retention in the canopy and influence forest hydrology, potentially increasing or reducing stemflow.

Keywords: araucaria forest, ecohydrology,epiphytism, nutrient flux, rainfall partitioning.