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Abstract: The previously recorded vegetation constancy during most of the Holocene, atop some summits of the Guayana tabular mountains (or tepuis), led to the hypotheses of either environmental stability or site insensitivity. As high-mountain biomes are considered to be especially well suited for recording past environmental changes, a palynological study on the uppermost summit of the Chimantá massif was designed to test its suitability for these purposes. A peat sequence was obtained spanning the last ~13.0cal kyr BP, but an acceptable resolution for paleoecological reconstruction is available only for the last ~4000years. Around 4.3cal kyr BP, the modern vegetation was established and has remained virtually unchanged until today; minor paleoenvironmental changes recorded in other sequences around 2.5cal kyr BP were not detected here. The main paleoclimatic trends are in good agreement with other neotropical records, especially from Lake Valencia and the Cariaco Basin. It is concluded that high-altitude tepuian sites are useful to record paleoenvironmental changes of moderate to high intensity but once a dense vegetation cover is established, gentle shifts remain hidden due to the capacity of plant communities to absorb the changes. The best sites for paleoecological research atop the tepuis are those lying on or near altitudinal ecotones, especially between the meadows and the paramoid shrublands (~2200m elevation). Sites within the meadow domain, as most well-studied so far, are relatively insensitive to Holocene paleoenvironmental changes. [Copyright &y& Elsevier]

The article discusses the biodiversity loss, migration, and conservation of neotropical vascular plants in the Guayana Highlands threatened by global warming. It cites the findings of the study conducted by Nogué and colleagues which showed that 75-80% of species of the vascular flora are in danger of extinction. It talks on the possible migration rates of species in Guayana Highlands as a response to ongoing global warming and stresses the importance of complementing in situ conservation approaches with other methods. It states that ex situ actions must be adopted such as preserving germplasm units and construction of greenhouses as these will help maintain, revive, and improve the facilitation of natural migration.

A letter to the editor is presented which discusses the bureaucratic challenges of conducting biodiversity research in the Guayana Highlands of Venezuela.