Interactive effects of elevation and forest-use intensity on tropical tree diversity in Veracruz, Mexico.

Land-use change and intensification have a substantial impact on tropical mountain ecosystems worldwide. However, our understanding of how anthropogenic changes affect different facets of tree diversity and community composition as well as ecosystem functioning along elevational gradients remains limited. Therefore, the main objective of my doctoral dissertation was to examine how interactive effects of elevation and forest-use intensity impact tree species diversity, community composition, functional diversity, functional redundancy and forest structure patterns along an elevational gradient. To do that, I used a sampling design in which elevation was crossed with three different levels of forest-use intensity: old-growth, degraded and secondary forest. I developed my research in an elevational gradient located within a global biodiversity hotspot in central Veracruz, Mexico, covering from sea level to tree line. In chapter 1, I assessed how the interactive effect of elevation and forest-use intensity affects tree diversity patterns and community composition. In general, my results showed that interactive effects of elevation and forest-use intensity strongly alter tree diversity patterns and community structure along the elevational gradient. My findings revealed that degraded forests were similar to old-growth forests, in terms of species diversity and composition, suggesting that degraded forest represent important reservoirs of species and may act as a safeguard of tree diversity in human-dominated tropical landscapes. In chapter 2, I investigated how the interactive effects of land-use intensity and elevation impact functional diversity and redundancy of tropical forests, and their implications in term of forest biomass and structure. To the best of my knowledge, the response of functional redundancy along a tropical elevational gradient has not been investigated before. Overall, my results revealed that functional diversity and functional redundancy varied greatly with elevation, but within elevations these two different facets of biodiversity were largely similar across levels of forest-use intensity. Lowland and pre-montane forests had highly redundant and functionally diverse tree communities, suggesting that these forest ecosystems are likely to be resilient to future disturbances. Montane forests, however, were functionally less redundant, suggesting that they could be highly affected by land-use and climate change. In chapter 3, I compiled a novel tree database named BIOVERA-Tree: tree diversity, community composition, forest structure and functional traits along gradients of forest-use intensity and elevation in Veracruz, México. BIOVERA-Tree contains information of 215 tree species distributed in 80 families and 154 genera, BIOVERA-Tree includes on tree diversity abundance, community composition, forest structure, and functional eight traits. My database is a fundamental resource providing detailed ecological information on tropical mountain forest ecosystems. In conclusion, the findings of my doctoral dissertation represent a paramount contribution providing new insights into how the interactive effects between elevation and forest-use intensity affect different facets of tree diversity, tree community composition and forest structure in tropical mountains. Understanding these interactive effects have implications in term of ecosystem resilience of tree communities as well as conservation strategies of tropical mountain forests