Reaching the canopy on the ground: incidence of infection and host-use by mistletoes (Loranthaceae and Viscaceae) on trees felled for timber in Amazonian rainforests

There is a profound absence of knowledge of infestation prevalence and host-use by mistletoes of mature South American tropical rainforests. In this study, we fill this gap using information gathered from felled trees at a logging concession area in Amazonian Brazil. We sampled individuals of 18 tree species, which occurred in two forest physiognomies; open forest with canopy interrupted by palm trees and closed, denser forest, with emergent trees. We hypothesized that infection incidence would be higher in open than in closed forest, irrespective of the mistletoe species involved. In addition, we expected that mistletoe parasitism would be higher on host species that were more abundant, taller, deciduous, and had less dense wood. We sampled 870 individual trees in both sites combined. All but one host species was infected by at least one species of mistletoe. We found 13 mistletoe species/morphospecies, Loranthaceae (7) and Viscaceae (6), parasitizing very different hosts. Mistletoe infection incidence was higher in the closed forest (10.3%) than in the open forest (5.4%). In the closed forest, host height influenced incidence positively, while deciduousness had a negative influence. Our results show that mistletoes are common in the canopy of pristine tropical forests and, contrary to expectations, that infection incidence was higher in the closed forest. The positive relation between infection incidence and host height in this forest type suggests that emergent trees have higher chances of being infected than individuals of correspondent species in the lower forest layers.