| Popis: |
This chapter reviews the available paleoecological information on Pantepui since the Last Glacial Maximum (LGM), in order to reconstruct the ecological dynamics that have led to the present configuration of plant communities and to unravel the potential environmental drivers involved, with emphasis on regional climate changes and fire. To date, no LGM sediments have been retrieved atop the tepuis, so the vegetation of these summits during the last glaciation remains unknown. Some lowland records suggest that cold LGM climates favored downward migration of temperature-sensitive tepuian species, which drove changes in the taxonomic composition of lowland forests. The available paleoecological record of Pantepui ranges from the early Holocene to the present. These records show two contrasting situations. Some tepui summits exhibit a long vegetation constancy extending back to the mid Holocene, whereas others document significant changes in sensitive species that have been associated with regional climatic events such as the Holocene Thermal Maximum (HTM), the latitudinal migration of the Intertropical Convergence Zone (ITCZ), the El Niño-Southern Oscillation (ENSO) variability, or recent climatic shifts such as the Medieval Climatic Anomaly (MCA) or the Little Ice Age (LIA). This has been interpreted in terms of site’s sensitivity and it has been recommended to obtain past records preferably on elevational ecotones, where vertical migrations of species are more easily detected. During the last millennium, fire, most probably of anthropogenic origin and likely originated on the surrounding uplands, has been a major driver of vegetation change on some tepuis. These studies are useful both to understand the biodiversity and composition of present Pantepui plant communities and to test classical biogeographical and evolutionary hypotheses on the origin of biodiversity and endemism patterns. |
