Thursday, November 8, 2018

Change in Amazon Climate 2000 Years Ago – Part II

Continued from the previous post, regarding the development of the continent of South America, and specifically the current Amazonian Basin. Also, looking at what climatologists and environmental scientists have learned about this Basin—which is about the size of the continental United States, and covers all or part of nine nations—and the appearance of the rain forest and current flora and fauna of the area.
    After all, one would think that if this area had been submerged for so long, then rose up inundated with moisture, rivers, swamps and the like, as well as annual floods lasting months, there would be some study of the area and why this area, called Amazonia or the Amazon Jungle today, is so different than most of the rest of South America.  
The Amazon Basin is within a very low-lying basin and is filled tributary rivers, plus numerous swamps, and boggy low-lands covering 1.7 billion acres, of which 1.4 billion acres are covered by the rainforest

While the Amazon represents over half of the planet's remaining rainforests, and it is the largest and most species-rich tract of tropical rainforest in the world, it has always been considered void of human development—a pristine wilderness. Of this paradigm, neotropical scientist, John Francis Carson, has stated that “There is a polarized debate amongst Neotropical archaeologists and ecologists over the extent of Pre-Columbian anthropogenic environmental impacts in Amazonia.” As a result of findings of pre-Columbian occupation of the Amazon, Carson added, “The Bolivian Amazon has yielded some of the most impressive evidence for large and complex pre-Columbian societies in the Amazon basin, yet there remains relatively little data concerning the land use of these societies over time” (Carson, vol.25, Is.8, pp1285-1300).
    In fact, Charles C. Mann, the author of 1491, states: “For years the standard view of North America before Columbus's arrival was as a vast, grassy expanse teeming with game and all but empty of people. Those who did live here were nomads who left few marks on the land. South America, too, or at least the Amazon rain forest, was thought of as almost an untouched Eden, now suffering from modern depredations.”
    Currently, however, a growing number of anthropologists and archaeologists now believe that the image of this old paradigm is basically false. Mann goes on to suggest that “the Western Hemisphere before Columbus' arrival was well-populated and dotted with impressive cities and towns—one scholar estimated that it held ninety to 112 million people, more than lived in Europe at the time—and Indians had transformed vast swaths of landscape to meet their agricultural needs.“
    It is currently postulated that such Indians used fire to create the Midwestern prairie, perfect for herds of buffalo; and that they also cultivated at least part of the rain forest, living on crops of fruits and nuts. The Amazonian wilderness, which was always believed to have been untouched by the hand of man, has now been found to have an increasing number of archaeological sites across the Amazon basin as evidence for large, complex societies, supported by intensive agriculture and management of forest and aquatic resources (Katie Bacon, “The Pristine Myth,” The Atlantic, Boston, March 2002).
More than 1100 tributory rivers, such as this one shown above, flow into the Amazon on its way from the high Andes in Peru to the Atlantic Ocean between the Brazilian and Guiana cratons along its 4,345-mile length

According to John Francis Carson, “The long and continuous occupation, which predates the establishment of rainforest in the region, suggests that pre-Columbian land use may have had a significant influence on ecosystem development at this site” (John F. Carson, Jennifer Watling, and Francis E. Mayle, “Pre-Columbian Land Use in the Ring-Ditch Region of the Bolivian Amazon,” The Holocene, SAGE Journals, Washington DC, May 1, 2015).
    What few mention is that this discovery of pre-Columbian occupation of the Amazon Basin dates only to about 2000 years ago. In fact, other studies have shown that a natural shift to wetter climatic conditions could have converted Amazon grasslands into rainforest around 2,000 years ago (Alaister Doyle, Amazon rainforest grew after climate change 2,000 years ago,” Reuters, Oslo, Sweden, July 7, 2014). To this, Carson added: “Other aspects of pre-Columbian cultures, such as their chronology, land use practices and subsistence strategies, are also poorly understood.” He and his team used palaeoecological methods to improve their understanding of the scale, nature, and legacy of land use associated with pre-Columbian geometric earthwork cultures in north-east Bolivia (J.F. Carson, “Pre-Columbian Land Use and Human Impact in the Bolivian Amazon,” University of Edinburgh Press, Scotland, June 30, 2014, pp1285-1300)
In the southwestern corner of the Amazon Basin, the Llanos de Moxos, a grassland that cover a 48,700-square-mile region in the lowlands of northern Bolivia, with portions in Brazil and eastern Peru, is flooded seasonally each year

The Llanos de Moxos, also known as the Beni Savanna or Moxos Plains, is one of the largest seasonally flooded wetland areas in South America, and is located in a tropical savanna ecoregion of northern Bolivia. This region occupies the southwestern corner of the Amazon Basin, and is crossed by numerous rivers that drain the eastern slope of the Andes Mountains. While surrounded by Amazon tropical moist broadleaf forests to the north, west and south, and the Madeira-Tapajós moist forest to the east, this low relief of the savannas, coupled with wet season rains between 51-inches in the east to 79-inches annually in the west, and snowmelt from the Andes, cause up to half the land to flood seasonally.
    While the Madeira-Tapajós is in the area of the Brazilian Mato Grosso (“thick bushes”), which is an entire state of flat landscape, alternating great chapadas, or plateaus, and grass-covered open pasture plains, or pantanals that are defined by seasonal inundation and desiccation. The region of the Amazon Rain Forest comprises a mosaic of savannas and wetlands, with islands of forest and gallery forests along rivers, and forest islands rising above surrounding swamps, while canals and causeways once connected areas of human settlement, radiating outwards from large mounds. Ring-ditches were found in many areas, circling areas of human settlements. This entire area is believed to have  been the setting for many complex pre-Columbian societies, many of which constructed agricultural earthworks including raised fields for agriculture.
    In fact a 31,000-square-mile swath of savanna has been identified as having raised fields which were used for agriculture—the dating of which is difficult to pinpoint because these archaeological remains have not preserved well in the tropics, but it is believed to be in the last century BC to about 1400 AD.
    However, disagreements about the anthropogenic origin of many of the earthworks in the Llanos de Moxos persist, authorities disagree on the number and social complexity of the people who constructed the earthworks, some postulating a large population, others a small population which built the earthworks over a long period of time. Stonework, characteristic of the highland civilization west of the Llanos, was not a feature because there was no surface stone in the area (Clark L. Erickson, "Lomas de ocupacion en los Llanos de Moxos," Arqueologia de las Tierras Bajas edited by Alicia Duran Coirolo and Roberto Bracco Boksar,, Uruguay: Comision Nacional de Arqueologia, 2000, pp207-226).
    The point is, Carson and his team tested the assumptions about the Amazon Basin using coupled local- and regional-scale paleoecological records to reconstruct land use on an earthwork site in northeast Bolivia within the context of regional, climate-driven biome changes. This approach revealed evidence for an alternative scenario of Amazonian land use, which did not necessitate labor-intensive rainforest clearance for earthwork construction. Instead, it showed that the inhabitants exploited a naturally open savanna landscape that they maintained around their settlement despite the climatically driven rainforest expansion that began 2,000 years ago across the region.
The area of Itenez Province and the Llanos de Moxos in Bolivia and the overall Rainforest of the Amazon Basin

Their study was conducted in Iténez province  in the Beni Department of northeast Bolivia at the geologically defined boundary between the terra firme (nonflooded undulating hills) humid evergreen rainforest on the uplands of the pre-Cambrian Shield and the seasonally flooded savannas of the adjacent Beni sedimentary basin. This is where the earthwork construction and agriculture on terra firme landscapes currently occupied by the seasonal rainforests of southern Amazonia may not have necessitated large-scale deforestation using stone tools. This finding implies far less labor—and potentially lower population density—than previously supposed. Their findings demonstrated that current debates over the magnitude and nature of pre-Columbian Amazonian land use, and its impact on global biogeochemical cycling, are potentially flawed because they do not consider this land use in the context of climate-driven forest–savanna biome shifts through the ages.
    This, then, brings us to the point regarding when the Amazon Basin rose and the forests began.
(See the next post, “Change in Amazon Climate 2000 Years Ago – Part III, regarding what climatologists and environmental scientists have learned about the Amazon Basin and the appearance of the rain forest and current flora and fauna of the area)

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