Holocene vegetation dynamics on the Apakará summit of the neotropical Guayana Highlands and potential environmental drivers

The Guayana Highlands (GH) are natural laboratories to study the influence of environmental drivers on neotropical ecosystems. The GH summits have been characterized by constant vegetation patterns during the Holocene, except for a few sites close to altitudinal ecotones. Here, we report a new pollen record showing two significant vegetation shifts, from Myrica forests to tepuian meadows (5340 cal yr BP) and then to Chimantaea shrublands (2720 cal yr BP). These changes are analyzed in terms of potential forcing factors such as regional climate changes, fire and autogenic succession. The first shift occurred shortly after the Holocene Thermal Maximum and the onset of a cooling/drying trend. A charcoal peak was coeval with this change suggesting some potential influence of fire. Autogenic processes related to lake infilling might have also been involved. The second vegetation shift took place during a phase of increased precipitation variability due to an ENSO intensification. The establishment of Chimantaea shrublands started at the end of this phase coinciding with another charcoal peak (2300 cal yr BP). These results support the idea of relevant ecological changes in the GH during the Holocene, the apparent vegetation constancy recorded in other GH summits could be due to site insensitivity.