Phytogeography of Talamanca Montane Quercus Forests, Costa Rica

Abstract

Phytogeographical patterns of the vascular generic flora of the montane Quercus forests in the Cordillera de Talamanca, Costa Rice, have been studied. With the exception of orchids and bromeliads, 114 families and 253 genera have been recorded, of which eighty are trees, seventy-seven shrubs, forty-four herbs, twenty-one climbers and thirty-one ferns. About 75% of all genera are tropical in distribution. The remaining 25% is made up of temperate (17%) and cosmopolitan (8%) genera. The neotropical element is best represented and contributes to almost half of the genera (46%), whereas the tropical afroamerican element is worst represented (3%). This overall spectrum does not differ much from the spectrum of woody genera alone. Only the percentage of cosmopolitan genera is significantly reduced among the woody genera since most cosmopolitan genera are herbs (14%) and ferns (29%). Tree genera are mainly neotropical, tropical malayo-american and pantropical in distribution, while shrub genera are principally neotropical (over 60%, mostly Andean-centered), pantropical and northern or southern temperate. Herb genera are basically neotropical, pantropical and wide-temperate, climber genera mainly neotropical and pantropical, while fern genera expose fundamentally cosmopolitan, pantropical and neotropical distributions respectively. The Talamanca woody spectrum has been compared to spectra available from Mexican and Colombian montane Quercus forests. Analysis reveals a greater phytogeographical affinity with the Northern Andes than with the Mexican Neovolcanic Belt. This is probably due to the Nicaraguan depression, which separates mountain ranges on the Central American landbridge and thus serves as a mayor barrier to dispersal of montane plant taxa in the Neotropics. Also the drier climatic conditions prevailing in Mexican montane forests may play an important role in floristic (dis)similarity trends.