Phytogeography and conservation of neotropical dry forest with emphasis on Columbia

Dry forest is one of the most threatened tropical forests in the world. Human impact has caused its massive transformation but conservation of dry forest has often been neglected across Latin America. In Colombia, less than 10% of the original extension of dry forest remains. This thesis studies the phytogeography of neotropical dry forest and its relevance for conservation using data from 1602 tree species inventories made in dry forests across Latin America and the Caribbean synthesised by The Latin American Seasonally Dry Tropical Forest Floristic Network (DRYFLOR). Clustering and ordination analyses were used to explore the floristic relationships of dry forest across the entire Neotropics, revealing distinctive regional clusters defined by their tree species composition. Colombian dry forests are shown to be part of two wider clusters, one including neighbouring forests in Venezuela and southern Central America, and the second including the inter-Andean dry forests. The high turnover of floristic diversity and endemism within and amongst the main floristic groups demonstrates that to conserve the full species diversity in dry forests across Latin America and the Caribbean will require protecting it simultaneously across multiple regions. A regionally focused study of floristic relationships in the Central American and northern South American dry tropical forest group, using quantitative approaches to conservation prioritization, including a new Conservation Priority Index (CPI), suggests that conservation priority should be placed on the South American Caribbean Coast in the cross-border area of Colombia and Venezuela. This emphasises the need for a biogeographical approach to conservation that cannot be restricted by political borders. Within Colombia, new quantitative floristic data were used to investigate controls of floristic composition in dry forests. Multivariate analyses showed that space related variables explain a larger fraction of the variance of the floristic composition than climatic or edaphic variables. The importance of spatial variables implies that biogeography is a key element in understanding the structure of communities, and that the Andean cordilleras might be acting as geographical barriers isolating these seasonally dry formations. The value of floristic inventory data for assessing the conservation status of tree species using IUCN criteria was assessed in a case of study of the Andean Piedmont dry forest. By combining inventory data from the DRYFLOR database and herbarium records, the number of species for which we have sufficient information to make conservation assessments increases by 16% and the accuracy of predictive species distribution improves for 84% of the species. Together, these results reveal the importance of ecological inventory data as a complementary data source in conservation assessment for dry forest trees in the Neotropics. Finally, the conclusions chapter places these results in the context of conservation planning for Colombian dry forests, including some suggestions for research, policies and actions. These actions include restoration programmes focusing on sustainable harvesting of native dry forest tree species, for example for firewood and other forest resources such as fruits, fibres and medicines. A land use mosaic, including forest fallows and strict conservation areas, may help to guarantee the long-term maintenance dry forest species in Colombia