Guatemalan forest synthesis after Pleistocene aridity

Abstract

Sediments from two lakes in the Peten Department, Guatemala, provide palynological evidence from Central America of late Pleistocene aridity and subsequent synthesis of mesic forests. Late Glacial vegetation consisted of marsh, savanna, and juniper scrub. An early Holocene temperate forest preceded a mesic tropical forest with Brosimum (ramon). Thus "primeval" rain forests of Guatemala are no older than 10,000 to 11,000 years and are considerably younger Holocene (10,[0][1][2][3][4][5][6][7][8]500 B.P.) (3, 4) but are unsubstantiated by palynological data from Central America. Evidence of late Glacial (15,000-10,000 B.P.) aridity in the Neotropics comes from pollen studies in the savannas of northern South America (5), the Galapagos Islands (where the lowest sections are devoid of pollen) (6), an undated diagram from the Amazon Basin (7), and Lake Valencia, Venezuela (8, 9, 36). Supporting data for the Neotropics come from geomorphic studies (10, 11) and deep sea cores (12)(13)(14). Much of equatorial Africa and Indo-Malaysia were also arid during the late Glacial (15-17). In Central America, montane lakes have been either too youthful (18) or uninformative with regard to lowland paleoclimates (19,20). Shallow lakes in the karst lowlands were dry when water tables responded to the lower sea levels of glacial episodes, and they provide incomplete records (21). Sediments from Lakes Quexil and Salpeten, Department of Peten, Guatemala (Fig. 1), provide an opportunity to obtain paleoecological data covering the Pleistocene-Holocene transition for the Central American lowlands. The pollen data complement interpretations based on sedimentology (22).The low-lying Peten (200-400 m) receives between 900 and 2500 mm of annual rainfall, with a pronounced dry season between January and May. Mean monthly temperatures range between 220C and 290C (23). Internal drainage predominates within the Peten Lake District. Edaphic factors make Salpeten (area = 2.6 kM2, maximal depth = 32 m, average depth = 7.8 m, elevation = 104 m) considerably more saline than Quexil (area = 2.1 kM2, maximal depth = 32 m, average depth = 7.2 m, elevation = 110 m) although the lakes are only 20 km apart (23,24). Lake Quexil lies 1 km from Lake Petenxil, which was studied by Cowgill et al. (25) (Fig. 1). The vegetation is not a true rain forest, but rather a semievergreen seasonal forest. According to Lundell (26), mature forests of the northern Peten are composed of three major tree associations characterized by Swietenia (mahogany), Manilkara (chicle), or Brosimum alicastrum (ramon). Brosimum frequently dominates associations covering archaeological ruins, fostering speculation that these trees were nurtured by the Maya for economic purposes (26). Other common arboreal genera (26, 27) include Calophyllum, Pouteria, Cecropia, Bursera, Spondias, Cryosophila, Ficus, and Piper. METHODSPrevious studies of Lake Quexil and other lakes in the Peten have described the Holocene record (28). The Quexil H core was believed to have terminated just short...

Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago

“…Similarly, a strong aridity signal is directly recorded by low lake levels in central México due to reduced northern excursion of the ITCZ, trade wind circulation, and ensuing reduced oceanic-land moisture transfer (Markgraf et al, 2000) that would have been reflected in ecosystem response. For example, forest on the Pacific side of the Central America contained a mosaic of high and low altitude forest species; a similarly novel type of forest has also been shown for Mera, Ecuador (Liu and Colinvaux, 1985) and Peten, Guatemala (Leyden, 1984). Of the two sites that record the warm evergreen forest biome at this period a site in Guatemala was dominated by Chenopodiaceae, Juniperus, Pinus and Quercus.…”

“…This appears to be a regional signal as early Holocene evergreen forests of northern Venezuela were replaced by semi-deciduous elements during the mid-Holocene (Leyden, 1984). Enhanced precipitation 756 R. Marchant et al: Pollen-based biome reconstructions for Latin America over Central America would have been accompanied by a northward shift of the ITCZ, enhanced southerlies and cooler equatorial sea surface temperatures .…”

A cooling event during the Younger Dryas Chron in Costa Rica

“…Seasonal southward displacement during cooling events of the ITCZ results in reduced precipitation in the area. The regional trend of drier Pleistocene climates is further supported by evidence from Guatemala (Leyden, 1984) and Panama (Markgraf, 1989;Bush et al, 1992).…”

An 85-ka record of climate change in lowland Central America

“…Pollen analysis of Lake Quexil Core 80-1 indicated that glacialage vegetation was dominated by temperate xeric thorn scrub, suggesting that Peté n climate was colder and drier during glacial periods of the late Pleistocene (Leyden, 1984;Leyden et al, 1993Leyden et al, , 1994. The finding had important ecological implications because it indicated that Peté n's seasonal tropical forest is no older than $11 ka (Deevey et al, 1983;Leyden, 1984).…”