Late Quaternary Aridity and Holocene Moisture Fluctuations in the Lake Valencia Basin, Venezuela

Abstract

Lake Valencia is one of few sites to provide paleoecological data for the Neotropical lowlands. A prior pollen analysis of late Glacial and early Holocene sediments from Lake Valencia indicated extreme aridity during the Pleistocene followed by only slightly more mesic conditions as the Holocene began. The present study confirms the aridity of the late Glacial, but suggests that the early Holocene was considerably more mesic. Data presented for the mid and late Holocene indicate that effective moisture has varied, but that climates were never again as mesic as the early Holocene. In general, arid conditions prevailed except from 5200 to 2200 BP. The vegetational record begins (°13 000 BP) with savanna surrounding a saline marsh. The watershed near the lake was not part of refugium for mesophytes, as has been suggested. As the Holocene began, halophytic littoral and shoreline communities formed around a shallow, saline lake. The coverage of savanna decline and contained scattered scrub. These communities were replaced (°9800 BP) by semievergreen and deciduous subtropical forests with Brosimum predominant. Over the past 8300 yr essentially modern vegetational associations existed with the watershed. Mesic forests retreated to higher elevations during the mid—Holocene as forests at lower elevations became more open and deciduous. Extensive weedy vegetation persisted on the unstable flood plains. Forests expanded somewhat 5200 to 2200 yr ago but have since declined in extent.