The dynamics of epiphyte vegetation is an important but, unfortunately, little addressed topic in epiphyte community ecology.
Peter Hietz and his collaborators did some interesting monitoring studies on orchids and bromeliads in Mexico. You may check out his contributions in ResearchGate
Whereas seedlings may have high mortality, anecdotal evidence suggest that adult clonal epiphytes may in fact be long-lived. For example, I often still found volcanic ashes within living epiphytic bromaliads, 17 years after the last volcanic eruption in the area (see bottom pg. 389 in: Wolf, Jan H.D. (2005). The response of epiphytes to anthropogenic disturbance of pine-oak forests in the highlands of Chiapas, Mexico. Forest Ecology and Management 212:376-393).