|Publication Type:||Journal Article|
|Year of Publication:||1993|
|Authors:||J. H. D. Wolf|
|Journal:||Annals of the Missouri Botanical GardenAnnals of the Missouri Botanical Garden|
The difficult accessibility of the canopy of tropical rainforests is probably one of the main reasons why information about the nonvascular tree crown flora is scarce. In this paper full attention is paid to the epiphytic bryophytes and lichens of 59 bark type selected canopy trees, divided over 15 sites along an altitudinal transect ranging from 1,000 to 4,130 m in the Central Cordillera, Colombia. Species-area curves indicated that sampling at each investigated site (altitude) was adequate within the restrictions imposed by the sampling method. Ordination analysis revealed that altitude as a complex ecological factor explained most of the variation in the data. Alpha and beta diversity patterns along the gradient were different for mosses, liverworts, and macrolichens. As to liverworts, species richness reached its peak of approximately 100 taxa per altitude at a mid-altitudinal range from 2,550 m to 3,190 m. The distribution of individual taxa showed that the belt of greatest liverwort richness coincides with a contact transition zone. Several hypotheses (mass effect, ecological equivalency, and species overlap) predict highest species diversity at such a transition zone. All are based on the assumption that community composition results from between community interactions rather than from within community (niche) relationships. The validity of this presumption is further indicated by the low number of liverwort taxa (20.5%) exclusive to the belt of greatest richness, assuming that habitats are saturated. Species turnover appears greater for bryophytes on this tropical mountain than on temperate mountains in North America. The general increase in biomass of nonvascular canopy subsamples with altitude coincides with a rise in humidity.