Drought resistance does not explain epiphytic abundance of accidental epiphytes

Accidental epiphytism is common among vascular plants in forest ecosystems around the globe. A frequent observation in surveys of accidental epiphytes is the occurrence of few species with high epiphytic abundance, while most co-occurring terrestrial species are rarely found as epiphytes.

Based on the general assumption that water is the major limiting factor for epiphytic plants, we hypothesised that differences in drought resistance of accidental epiphytes explain the difference in epiphytic abundances.

We exposed 16 species with different epiphytic abundance in central Europe to experimentally induced drought during germination and growth of juvenile plants.

Drought resistance differed substantially among species but did not correlate with their epiphytic abundance, neither during germination nor during juvenile growth.

In central Europe, accidental epiphytes are usually found on moss cushions or in accumulated arboreal soil on their host tree. In such water-storing substrates, water availability might be less limiting than it is for obligate epiphytes that typically grow on bare bark, which would explain the lack of a correlation between drought resistance and epiphytic abundance of the studied species. Hence, other factors must explain the consistent differences in epiphytic abundance, e.g. dispersal traits and mass effect.