Mediation of stemflow water and nutrient availabilities by epiphytes growing above other epiphytes in a subtropical forest

Stemflow is the most importance source of water and nutrients to epiphytes growing on tree stems that lack access to canopy soils. Many host trees are inhabited by a large number of epiphyte species, often growing in close proximity. The nutrient and water relationships among such co-occurring epiphytes are largely unknown. We examined stemflow quality and quantity before and after passing through a substrate-forming epiphyte, Asplenium nidus, and two nonsubstrate-forming epiphytes, Haplopteris flexuosa and Liparis nakaharai, in a subtropical rainforest in Taiwan. The results indicate that stemflow quantity decreased after passing through these epiphytes. The magnitude of decreases was large for H. flexuosa (63%) and L. nakaharai (74%) but minor for A. nidus (5.6%), possibly because the vertical leaves of the latter collected throughfall, compensating for the water they retained. There was an overall decrease in stemflow ion concentrations after passing through A. nidus, likely due to greater retention than leaching of ions, but an overall increase after passing through L. nakaharai and H. flexuosa, possibly the result of greater leaching than retention. Our results indicate that epiphytes growing under A. nidus received more stemflow with few nutrients and those growing under the two nonsubstrate-forming epiphytes received less stemflow but with more nutrients. Currently, the growth of epiphytes is limited by water at the study site, so that Asplenium provides favourable microhabitat for epiphytes growing below. If climate change lead to drier conditions, substrate-forming epiphytes could become oases in the forest canopy desert and attract more epiphytes to grow underneath.