ATBC Online Web Program

O36-2
What can fallen branches and vascular epiphytes reveal about the dynamics of epiphyte communities? 

Thursday, 27 June 2013: 08:15
La Paz - B West (Herradura San Jose)
Juliano Sarmento Cabral , Biodiversity, Macroecology & Conservation Biogeography Group, University of Göttingen, Germany
Gunnar Petter , Biodiversity, Macroecology & Conservation Biogeography Group, University of Göttingen, Germany
Gerhard Zotz , Smithsonian Tropical Research Institute, Panama
Holger Kreft , Biodiversity, Macroecology & Conservation Biogeography Group, University of Göttingen, Germany
Vascular epiphytes contribute with approximately 9% to the global vascular flora, but are receive considerable less scientific attention due to limitations to access the forest canopy. Abundance and richness of vascular epiphytes are usually assumed to be strongly influenced by climatic factors, but forest dynamics (especially patterns of branch and tree fall) may also have a profound impact on the community structure. However, little is known about the influence of branch fall on epiphyte dynamics. Therefore, we conducted field work in two old-growth tropical forest sites (Atlantic Submontane Forest in Northeastern Brazil and Caribbean Lowland Forest in Panama) to quantify the fall of branches and epiphytes. We surveyed fallen branches and epiphytes in plots of 2 and 50 m2, respectively. We tested the hypothesis that the dynamics of branch growth and fall influences the distribution of the epiphytic community in the canopy. We tested the hypothesis separately for each study site due to significant differences in fallen branches (higher branch fall in Brazil). One third of all epiphyte individuals (mostly adults) fell off from branches rather than with branches, mostly due to bark shedding out of the trunk. The proportion of fallen branches significantly decreased with increasing branch diameter, with ca. 90% of fallen branches with less than 2 cm diameter at both study sites. The number of juveniles did not significantly vary with branch diameter. However, the total number of individuals, species and the proportion of adults significantly increased with branch diameter at both study sites. Hence, the occurrence of epiphytes in the outer canopy was not limited by recruitment, but by mortality due to branch fall, considering that thinner branches had lower proportion of adults. These results support our hypothesis that the spatial distribution of epiphytes within the canopy might be partially shaped by branch shedding patterns.