Palaeovegetational and palaeoenvironmental trends in the summit of the Guaiquinima massif (Venezuelan Guayana) during the Holocene

Abstract

The summits of the table mountains (tepuis) from the Neotropical Guayana region are remote environments suitable for palaeoecological studies with evolutionary, biogeographical and palaeoclimatic implications. Here, using palynological analyses of two radiocarbon-dated peat bogs from a tepui summit, the Holocene palaeovegetational trends are reconstructed, and related to possible forcing factors. Because of the pristine character of the Guaiquinima summit, the recorded palaeoenvironmental changes are probably due to natural causes, which makes them valuable archives of the natural component of climatic change at a millennial time scale. The sequence begins with pioneer communities or meadows similar to present-day ones, between about 8.4 and 4.5 ky BP. After this date, and until about 2 kyr BP the expansion of gallery forests suggests an increase in precipitation, documented also at regional (Neotropical) level. Between ca. 2 kyr BP and the last century, gallery forests are replaced by forests characteristic of the upper Guaiquinima altitudes, coinciding with a regional phase of reduced moisture. The present-day meadows, established relatively quickly during the last century, substituted the former upland forests. In the locality studied, the main controlling factor of the vegetation during the Holocene seems to have been the moisture balance. In contrast to other tepui summits, there is no clear evidence for changes linked to temperature oscillations. This could be due to the elevation of the site, far from any characteristic ecological boundary, that makes it insensitive to this parameter.

Refugial isolation and secondary contact in the dyeing poison frog Dendrobates tinctorius

“…Furthermore, factors affecting the observed split between W and E groups predate the Holocene and the Last Glacial Maximum and are congruent with the estimated timing of divergence across this divide in the similarly distributed Guianan Atelopus (Noonan & Gaucher 2005). Secondary contact between these refugia appears to have occurred more than once (older westward expansion of E group and recent eastward expansion of W group) and may have been driven by precessional cycles that have occurred at regular intervals for relatively short periods of time (∼11 000 years) and appear to have superceded the effects of Pleistocene temperate glaciation within Amazonia (Bush et al 2002;Bush 2005) and the Guianan region specifically (Rull 2004a(Rull , 2004b(Rull , 2004c(Rull , 2005a(Rull , 2005b. Indeed, increased aridity does appear to have affected biotic distributions but was not associated with glacial cycles but rather with these precessional variations in insolation, nor was it the sole factor as fluctuations in temperature and atmospheric concentration of CO 2 were also associated with these cycles and presumably affected habitat continuity.…”

“…, 2005 and Mayle et al . (2004) and applied specifically to the Guiana Shield by Rull (2004aRull ( , 2004bRull ( , 2004cRull ( , 2005aRull ( , 2005b invokes changes in temperature and atmospheric CO 2 levels associated with precessional cycles as the dominant factor influencing the historical continuity of Amazonian communities. This theory is founded on the observed palynological and palaeoclimactic record which indicates cyclic, altitudinal migration of floral communities throughout the Pleistocene.…”

Geochronological database and classification system for age uncertainties in Neotropical pollen records

“…For the generation of the recalibrated age models, stratigraphic dates were not used. Use of these layers would ignore the possibility that for example the palynologically detectable onset of the Holocene was asynchronous throughout Graf (1989Graf ( , 1992; Weng et al (2004Weng et al ( ) 1134 Cerro Toledo CT Ecuador −4.38 −79.12 0 20 000 Behling (2009, 2010) Rull (1991Rull ( , 1996Rull ( , 2005bRull ( ) 1581 Amuri tepui AMU-1 Venezuela 5.17 −62.12 0 5500 Rull (1991Rull ( , 1996Rull ( , 2005b northern South America. Therefore any further inferences on spatial leads, lags, or synchroneity would become flawed.…”

Unexpected biodiversity loss under global warming in the neotropical Guayana Highlands: a preliminary appraisal

“…A similar situation is found for S. squarrosa , which is not part of the present analysis because it is not strictly a GH species, but is equally endangered of habitat loss. This species occurs between 1200 and 1600 m altitude, as the absolute dominate of the extensive meadows of the Guaiquinima massif (Rull, 2005a), one of the largest Guayanan table mountains, with more than 1000 km 2 of summit area (Steyermark & Dunsterville, 1980). Because the maximum altitude of this massif is of about 1600 m (Berry et al , 1995), an upward shift of 400 m, equivalent to a warming of 2.4°C, would be enough for S. squarrosa to entirely loose its habitat.…”