Branch mortality influences phorophyte quality for vascular epiphytes

Abstract

Trees generate resources for other guilds (e.g., lianas), including the production of supporting branches for the establishment of epiphytes. In a tropical dry forest of central Mexico, we studied whether branch mortality is associated with phorophyte quality. For a one-year period, we monitored the survival of branches with and without vascular epiphytes in tree species with high epiphyte loads (Bursera copallifera (Sessé & Moc. Ex DC.) Bullock, Bursera glabrifolia (Kunth.) Engl.) and low (Bursera fagaroides (Kunth) Engl., Conzattia multiflora (B.L. Rob.) Standl., Ipomoea pauciflora M.Martens & Galeotti, Sapium macrocarpum Müll.Arg.). The lowest (C. multiflora) and highest (I. pauciflora) branch mortalities occurred in phorophytes with low epiphyte loads, whereas branch mortality in S. macrocarpum was 60% and in all Bursera species was <25%. In B. copallifera and B. glabrifolia, the highest branch mortality was in branches with epiphytes, suggesting a negative influence of these plants, but mortality was also associated with larger/older branches. At the end of monitoring, 95% of the epiphytes of I. pauciflora were growing on dead branches. We conclude that branch mortality is low in phorophytes with high epiphyte loads; but in phorophytes with low epiphyte loads, branches can be ephemeral or long lasting. Low epiphyte abundances in phorophytes with long-lasting branches can be caused by other traits that remain to be examined (e.g., seed capture).