Including dynamics in the equation: Tree growth rates and host specificity of vascular epiphytes

Abstract

Abstract The forest canopy is home to a rich biota. One salient feature are the dynamics of the habitat‐building trees, which are growing and eventually vanishing. Tree species strongly differ in growth rates, final size and longevity. Nevertheless, these inherent dynamics have been a blind spot in studies on host specificity of vascular epiphytes (vascular plants dwelling on trees without parasitizing them)—not least because tree growth rates and longevity are usually unknown in highly diverse tropical forests. The present study aims at tackling this blind spot. We compared epiphyte abundances (>23,000 individuals) found on 285 individuals of four focal tree species in a lowland moist forest in Panama. Data on repeated dbh censuses from a permanent tree plot provided the unique opportunity to estimate the age of our sampled trees. We compared the relative importance of tree longevity for host biases with that of other host tree characteristics, namely microclimatic conditions and bark acidity, rugosity and stability. The studied tree species differ in host quality and epiphyte species partly differ in host preferences. The conclusions concerning relative host tree quality depend hugely on whether or not different tree growth rates are considered. Comparing these conclusions allows important insights into the role of tree longevity in shaping epiphyte communities. Relating tree trait differences to the observed distributions of epiphytes among the focal tree species shows how the simultaneous action of various tree characteristics causes host biases. Synthesis. This study highlights the substantial but, up to now, hidden role of different tree growth rates for host tree specificity of vascular epiphytes. Future investigations need to consider this possibly confounding factor adequately to avoid spurious conclusions.