Not so stressful after all: Epiphytic individuals of accidental epiphytes experience more favourable abiotic conditions than terrestrial conspecifics

Abstract

Vascular epiphytes are mainly associated with tropical and subtropical forest ecosystems. However, the frequent occurrence of accidental epiphytes in temperate forests proves that epiphytic growth of vascular plants is possible in tree crowns at these latitudes. Comparing the abiotic conditions of epiphytic and terrestrial microhabitats in conjunction with intraspecific differences in functional traits of the inhabiting plants, we identified limitations to vascular epiphytism in the study area in a Central European low mountain range. We determined light availability, winter temperatures, soil moisture, nutrient concentrations, and pH of arboreal soil in crotches of broad-leaved trees and in the immediate vicinity of each tree on the ground. Similarly, we quantified total plant water content, relative foliar chlorophyll content, specific leaf area (SLA), leaf dry matter content (LDMC), root-mass fraction, and aboveground nutrient concentrations of 110 pairs of epiphytic and terrestrial conspecifics. Water and nutrient availability were generally high in crotches filled with arboreal soil, suggesting better growth conditions than on the ground. A trophic advantage of epiphytic individuals over terrestrial conspecifics can be deduced from higher plant nutrient concentrations, higher SLA, and lower LDMC. Advantageous growth conditions might even result in higher growth rates and higher fitness of epiphytic individuals. Our findings highlight that vascular epiphytism in the study area is not necessarily limited by abiotic conditions but at least partly by the availability of old and structurally diverse trees providing suitable microhabitats. Accordingly, management actions in these secondary forest ecosystems should incorporate the preservation of old and large deciduous trees in order to sustain arboreal microhabitats and the associated biota.