Vascular epiphytes frequently represent the most species-rich life form in tropical forests and can compose >50% of the vascular plant diversity, yet little is known about how these communities change through time. We censused epiphyte communities on emergent trees in secondary forest and old-growth stands to address how epiphyte community diversity and composition changes through time and to determine whether those changes are related to environmental changes that occur in trees during succession. We predicted an increase in epiphyte diversity with tree age as trees in older stands often have more canopy soil, a higher load of non-vascular epiphytes, as well as heterogeneous availability of light and moisture within their crowns. We measured the percent cover of vascular and non-vascular epiphyte species, canopy soil, and bare branch on the largest trees in stands approximately 35, 55, 95, 115, and >500 years in age in the Barro Colorado Nature Monument, Panama. We used stand age as a proxy for the age of the tree, and therefore the epiphyte community. Multivariate statistics were used to determine which factors were associated with epiphyte species composition.
Results/Conclusions
Canopy soil as well as vascular and non-vascular epiphyte cover increased with increasing tree age. In addition, epiphyte species composition differed among forest ages with orchids and bromeliads dominating the oldest trees in early and mid-successional stands, and other groups of vascular plants such as pteridophytes becoming more abundant on trees in older stands. This increase in diversity in older trees could be due to an increase in heterogeneity in light and moisture availability, as well as differences in the amount of canopy soil and non-vascular epiphyte cover, which may increase moisture and nutrient availability for vascular epiphytes. Further studies will address the role of canopy soil and non-vascular epiphytes in driving epiphyte community succession.
