South American Lowlands

For South America, records are discussed from the lowlands and the Andes (Fig. 14).

19.4.1. Llanos Orientales (Colombia)

Six lake records from the Llanos Orientales (Wijmstra and van der Hammen, 1966; Behling and Hooghiemstra, 1998, 1999, 2000) indicate that the early Holocene land scape was extensive grass savanna with few woody taxa and small areas of gallery forest along and between the rivers. Annual precipitation must have been lower and the annual dry season longer than they are today. In the middle Holocene, conditions became wetter and the forested area increased: at 6000 B.P. at Laguna Angel, at 7300 B.P. at Laguna Sardinas (Fig. 15), and at 6300 B.P. at Laguna Carimagua. After ca. 4200 B.P., stands of palms (Mauritia or Mauritiella) increased markedly in area in the Llanos. This change in vegetation may have resulted from increased human impact on the savanna under the wettest climatic conditions of the Holocene. The new high-resolution record from Laguna Loma Linda (Table 3), located in the transition area between the savanna and the Amazon rain forest, shows that the grassdominated savanna in the early Holocene changed at ca. 6900 B.P. into savanna vegetation with a greater presence of woody taxa and with a marked expansion of Amazon and gallery forest. At ca. 3900 B.P., forests began to dominate the landscape, indicating a change to wetter conditions with a shorter annual dry season.

19.4.2. Gran Sabana (Venezuela)

Three pollen records from the Gran Sabana in the southeastern Venezuelan savanna include the middle Holocene (Table 3). The pollen record from Santa Cruz de Mapauri shows a predominance of grass savanna with changes in floristic composition indicating oscillations between drier and wetter periods (Rinaldi et al., 1990). The pollen record from Laguna Divina Pastora indicates the presence of a swamp surrounded by treeless savanna between ca. 6100 and 2800 B.P., but forest must have been close by (Rull, 1991). From ca. 28001500 B.P., the swamp changed into a lake, which was larger than it is today and was surrounded by abundant stands of Mauritia. Laguna Santa Teresa also was larger than it is today from ca. 5900 to 4400 B.P. and was surrounded by forest. After 4400 B.P., the lake became smaller and forest retreated, but Mauritia stands expanded markedly (Rull, 1991). In contrast to the lakes in the Llanos Orientales, those in the Gran Sabana are not much older than 5900 B.P., suggesting drier conditions before this age.

19.4.3. Rupununi Savanna (Surinam)

Wijmstra and van der Hammen (1966) studied three sites in the Rupununi savanna in Surinam. Dating control is minimal, but the 650-cm-long core from Lake Moriru located in the northernmost part of this savan

FIGURE 14 South America with sites discussed in the text. AG, Laguna de Agua Sucia; AN, Laguna Angel; AU, Mallín Aguado; AY, Lago Ayauchi; BR, Arroyo Las Brusquitas; BV, Serra de Boa Vista; CA, Laguna Carimagua; CH, Arroyo Sauce Chico; CJ, Carajas; CN, Caunahue; CR, Crominia; CU, Lagoa da Curuga B; EM, Agua Emendadas; EP, Laguna El Pinal; FU, Laguna Fúquene; GE, Serra Campos Gerais; HA, Harberton; HU, Laguna Huatacocha; IG, Morro da Igreja; IT, Morro de Itapeva; KU, Lago Kumpaka; LC, Cerro La China; LO, Laguna Loma Linda; MA, Santa Cruz de Mapaurí; MN, Pantano de Monica; MO, Lake Moriru; MR, Mariname; NC, Fortín Necochea; NE, Lagoa Serra Negra; OL, Lago dos Olhos; PA, Lake Pata; PE, Lago do Pires; PI, Laguna Piusbi (Chocó); PO, Pogo Grande; PR, La Primavera; PS, Laguna Divina Pastora; QU, Empalme Querandíes; RR, Serra do Rio Rastro; SA, Laguna Sardinas; SL, Salitre; ST, Lagoa Santa; SU, Lago Surara; TE, Laguna Santa Teressa.

FIGURE 14 South America with sites discussed in the text. AG, Laguna de Agua Sucia; AN, Laguna Angel; AU, Mallín Aguado; AY, Lago Ayauchi; BR, Arroyo Las Brusquitas; BV, Serra de Boa Vista; CA, Laguna Carimagua; CH, Arroyo Sauce Chico; CJ, Carajas; CN, Caunahue; CR, Crominia; CU, Lagoa da Curuga B; EM, Agua Emendadas; EP, Laguna El Pinal; FU, Laguna Fúquene; GE, Serra Campos Gerais; HA, Harberton; HU, Laguna Huatacocha; IG, Morro da Igreja; IT, Morro de Itapeva; KU, Lago Kumpaka; LC, Cerro La China; LO, Laguna Loma Linda; MA, Santa Cruz de Mapaurí; MN, Pantano de Monica; MO, Lake Moriru; MR, Mariname; NC, Fortín Necochea; NE, Lagoa Serra Negra; OL, Lago dos Olhos; PA, Lake Pata; PE, Lago do Pires; PI, Laguna Piusbi (Chocó); PO, Pogo Grande; PR, La Primavera; PS, Laguna Divina Pastora; QU, Empalme Querandíes; RR, Serra do Rio Rastro; SA, Laguna Sardinas; SL, Salitre; ST, Lagoa Santa; SU, Lago Surara; TE, Laguna Santa Teressa.

na region has two dates: 7585 ± 75 14C yr B.P. for 165195 cm and 6065 ± 95 14C yr B.P. for 105-115 cm. Between ca. 11,500-10,000 and 5600 B.P., the proportions of woodland and grassland savanna changed repeat edly. After 5600 B.P., and especially during the last 3000 years, grassland savanna became dominant, suggesting drier conditions or stronger human influences on the savanna.

Sprra Hamnns Coráis
FIGURE 15 Representative pollen diagrams from the South American lowlands: Laguna Sardinas (Behling and Hooghiemstra, 1998), Lago do Pires (Behling, 1995a), and Serra Campos Gerais (Behling, 1997b, 1998).

19.4.4. Choco Rain Forest in the Pacific Lowland (Colombia)

The pollen record from Laguna Piusbi in the south Colombian Pacific lowlands is the first studied site providing a Holocene history of the Colombian Choco rain forest area (Behling et al., 1998). An earthquake or other catastrophic neotectonic event may have formed the closed lake basin probably ca. 4900 B.P. Pollen and spore data illustrate a very diverse floral composition of the tropical rain forest. The Chocó rain forest ecosystem has been very stable, and no marked changes have occurred since the beginning of the record in the middle Holocene. A very humid climate (annual precipita tion is >7000 mm) has maintained the high biodiversity and stability of the Chocó rain forest.

19.4.5. Amazon Rain Forest

19.4.5.1. Colombia

The Pantano de Monica 1 site is a swamp on the lower terrace of the Rio Caquetá in the central Colombian Amazon rain forest. During the early Holocene, the swamp was smaller and shallower than it is today with abundant Mauritia palm trees. The lower terrace of the Caquetá River must have been better drained than it is today, which may have resulted from changes in the drainage system or from drier conditions than exist today. The records from Pantano de Monica 2 and 3 indicate a drier climate after ca. 3200 B.P. The records from the lower terrace of Rio Caquetá show different forest compositions in the past and indicate that the rain forest environments were not constant during Holocene times (Behling et al., 1999).

Two cores from Mariñame Island, located in the Ca-quetá River bed (5-6 km south of Pantano de Monica), represent the last 11,500 years (Urrego, 1994 /1997). Between 11,500 and 10,200 B.P., open-water conditions prevailed, and the Caquetá River valley was permanently inundated with rapid sedimentation of clay, suggesting relatively wet climatic conditions. At ca. 10,200 B.P., lower water levels with a decreased sedimentation rate probably resulted from a drier climate. Cecropia forest developed on the open floodplains. Seasonally inundated várzea forest, indicating relatively dry conditions, followed this period until 7400 B.P. at one site and until 5100 B.P. at a second site on Mariñame Island. After 5100 B.P., the sites on the island became less subject to direct river flooding, and a Mauritia swamp developed. Urrego (1994/1997) concluded that climate change at least partly influenced the river dynamics in the study area. In general, lower water levels in the Caquetá River during the early Holocene agree quite well with the paleoenvironmental conclusions from Pantano de Monica 1.

19.4.5.2. Ecuador

Most of the pollen records from western Amazonia are from Ecuadorian lakes along the foothills of the eastern Andes and represent only the late Holocene. The pollen record from Lake Ayauchi at ~500 m elevation provides a Holocene history of the Amazon rain forest since ca. 7800 B.P. (Bush and Colinvaux, 1988). A dry interval occurred between ca. 4800 and 3400 B.P. The record from Lago Kumpaka (700 m elevation) represents the environmental history of a perturbed rain forest for the last 6000 years. According to Liu and Colinvaux (1988), the periods of 4800-4200 and 1400-700 B.P. were drier with more seasonal precipitation.

The Lake Pata pollen record from Hill of Six Lakes in northwestern Amazonia shows dense Amazon rain forest with several marked vegetation changes during the middle Holocene (Colinvaux et al., 1996; De Oliveira, 1996). Further study is required to determine whether these changes (e.g., the increase of the palm Mauritia or Copaifera) are due to climate, human disturbance, or other environmental factors. Similarly, the vegetational changes during the middle Holocene (e.g., an increase in Alchornea) at Lago Surara in the Amazon basin are still not understood (Absy, 1979).

Lagoa da Curu^a B (35 m elevation) lies about 15 km from the Atlantic Ocean in northeastern Para State. Pollen data show successions of different palm trees in the diverse Amazon rain forest during the middle Holocene (Behling, 1996). Whether these changes are related to climate change or to human disturbance is unclear. A greater representation of Poaceae pollen and carbonized particles suggest clearance and use of fire by humans.

The >50,00014C year record from a lake on the small table mountain in Carajas (700-800 m elevation) in southeastern Para State shows an expansion of savanna and a drier climate between ca. 8300 and 3200 B.P. After this period, the Amazon rain forest expanded, indicating wetter climatic conditions during the late Holocene (Absy et al., 1991).

19.4.6. Cerrado (Central Brazil)

The sites Agua Emendadas (Barberi, 1994; Salgado-Labouriau et al., 1998) and Crominia (Ferraz-Vicentini and Salgado-Labouriau, 1996; Salgado-Labouriau et al., 1997) are in the central Brazilian cerrado region. The record from the Agua Emendadas palm swamp is barren of pollen before 8000 B.P., suggesting a dry climate with a long dry season in the early Holocene. During a long transitional phase following this period until ca. 5700 B.P., a Mauritia palm swamp developed, suggesting an increase in moisture. During the late Holocene, vegetation and climate were similar to those of today with widespread grass savanna and the presence of a marsh surrounded by cerrado and gallery forest. Pollen data from the swamp near Crominia also show dry conditions in the early Holocene until ca. 7400 B.P., with essentially modern vegetation after ca. 5700 B.P.

19.4.7. Cerrado, Semideciduous Forest, and Mountain Vegetation in Southeastern Brazil

The high-resolution pollen record from Lago do Pires (Fig. 15), located 250 km from the Atlantic Ocean, shows evidence of extended cerrado in this lowland region during the early Holocene until ca. 6300 B.P., indicating a dry season of 5-6 months (Behling, 1995a). From 6300 to 2900 B.P., extensive semideciduous forest predominated in the valleys with cerrado on the hills, indicating higher precipitation and a dry season of about 5 months. From 2900-970 B.P., the pollen record shows more closed cerrado vegetation on the hills and slopes, suggesting a dry season of some 4-5 months. During the latest Holocene, the presence of closed semideciduous forest is indicative of modern climatic conditions.

Lagoa dos Olhos and Lagoa Santa are ~1 km apart and ~400 km from the Atlantic Ocean. The pollen record from Lagoa dos Olhos (De Oliveira, 1992) shows that a mosaic of cerrado and semideciduous forest occupied the region for most of the Holocene, indicating strong seasonality in precipitation. The pollen record from Lagoa Santa (Parizzi et al., 1998) begins at ca. 6200 B.P. during a period of increasing moisture. From ca. 6200-5300 B.P., the record shows the presence of swamp vegetation, indicating drier climatic conditions than those now. After ca. 5300 B.P., the pollen records show a mosaic pattern of cerrado, semideciduous forest, and gallery forest, indicating climatic conditions similar to those of today with a dry season of 3-4 months. Salitre and Serra Negra, which are only a few kilometers from each other but are at different elevations, are further inland, ~750 km from the Atlantic Ocean. Modern vegetation of this mountain region is complex, including mountain vegetation, semidecidu-ous forest, and cerrado. The record from Salitre shows mesophytic semideciduous forest after ca. 9500 B.P., suggesting warmer and drier conditions than previously. At 5700 B.P., a short interval with high percentages of Poaceae indicates an arid interval. After 4400 B.P., the climate became moister, similar to today (Ledru, 1993; Ledru et al., 1994, 1996). The record from Serra Negra indicates that a mosaic of cerrado and semideciduous forest dominated the regional vegetation for most of the Holocene, indicative of a seasonal climate (De Oliveira, 1992).

Morro de Itapeva is located at 1850 m elevation in the Serra da Mantiqueira, which runs parallel to the Atlantic coast west of the Serra do Mar (Behling, 1997a). High-elevation grassland (campos de altitude), Araucaria forest, and cloud forest cover the higher moun tains. During the early Holocene, cloud forest developed close to the study site, indicating a warm-moist climate on the east-facing slopes. However, rare occurrences of Araucaria and Podocarpus suggest a drier climate on the highland itself. Araucaria and Podocarpus increased during the last 3000 years, indicating an increase in moisture.

19.4.8. Araucaria Forest and Campos

Region on the Southern Brazilian Highland and Tropical Atlantic Rain Forest in the Southern Lowland

According to the pollen records from Serra do Rio Rastro, Morro da Igreja, and Serra Campos Gerais (Fig. 15), huge areas of campos vegetation covered the southern Brazilian highland during the early and middle Holocene, suggesting a warm-dry climate with an annual dry season of ca. 3 months (Behling, 1995a,b, 1997a,b, 1998). The initial expansion of Araucaria forest, probably from small areas of gallery forest along the rivers, began at ca. 3200 B.P., suggesting a cooler and somewhat wetter climate than before. A pronounced expansion of Araucaria forest on the highlands, replacing the campos vegetation, occurred in Santa Catarina State (Serra do Rio Rastro and Morro da Igreja) during the last 1000 years and in Paraná State (Serra Campos Gerais) during the last 1400 years. Thus, a very humid climate with no significant dry period characterizes the late Holocene.

Tropical rain forest covers the Atlantic lowland in southern Brazil, and pollen records from this region show no marked changes in climate. The Atlantic lowland and the slopes facing the Atlantic Ocean were apparently wetter than the highlands during the middle Holocene. The record from the Pogo Grande lowland indicates a drier period from 5600-5300 B.P., a slightly moister period from 5300-4800 B.P., and a period moister than today from 4800-3800 B.P.

19.4.9. Pampas (Argentina)

Prieto (1996) summarized the late Quaternary history of vegetation and climate from five sites in the Pampas (see Table 3). During the early Holocene, grassland communities existed until 7800 BP in the central Pampas and until ca. 5700 BP in the southwestern portion. For the late Holocene, the pollen data indicate vegetation of psammophytic and halophytic communities similar to those of today's southern Pampas, associated with communities of moister edaphic conditions. A shift to subhumid-dry climate occurred after 5700 BP at Arroyo Sauce Chico and Cerro La China, at ca. 4400 B.P.

at Fortín Necochea, and before 3200 B.P. at Empalme Querandíes.

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