An overview on epiphytism as a direct mechanism of facilitation in tropical forests.
RUIZ-MIRANDA, C. R.
Direct facilitation is characterized by the positive effect of one individual on the other through changes in abiotic conditions and the creation of novel habitats. We aimed to present a systematic review of the literature about direct facilitation in tropical forests, emphasizing knowledge gaps and suggesting future lines of inquiry. We asked: (1) What is the existing literature about direct facilitation in tropical forests? (2) What kind of methodological approach (experimental or observational) has been more used? (3) What kind of study, pairwise species or community level, are more common? (4) What vegetative habits are more common between facilitators and facilitated species? (5) What hypotheses are more commonly tested? (6) How often epiphytism has been approached as facilitation? Based on literature search, we found thirty-five studies examining direct facilitation in plants mainly in the Neotropics (69%). The number of observational and experimental studies was similar. Most studies were based on pairwise comparisons of species. Trees were the most common nurse plants representing 51% of the studies, followed by shrubs (20%). This was the same for facilitated plants: trees corresponded to 48% and shrubs to 21%. The most common facilitation mechanism in tropical forest was the improvement of aboveground microclimate conditions (43%). Epiphytism is still marginally explored (11%, only 4 out of 35 studies) as a direct mechanism of facilitation. Given that about nine per cent of the world vascular flora are epiphytes that demand facilitators to survive, it is timely to widen the scope of field studies about facilitation towards such direct mechanisms.