Late Pleistocene and Holocene environmental history of the Iguala Valley, Central Balsas Watershed of Mexico

Abstract

The origin of agriculture was a signal development in human affairs and as such has occupied the attention of scholars from the natural and social sciences for well over a century. Historical studies of climate and vegetation are closely associated with crop plant evolution because they can reveal the ecological contexts of plant domestication together with the antiquity and effects of agricultural practices on the environment. In this article, we present paleoecological evidence from three lakes and a swamp located in the Central Balsas watershed of tropical southwestern Mexico that date from 14,000 B.P. to the modern era. [Dates expressed in B.P. years are radiocarbon ages. Calibrated (calendar) ages, expressed as cal B.P., are provided for dates in the text.] Previous molecular studies suggest that maize (Zea mays L.) and other important crops such as squashes (Cucurbita spp.) were domesticated in the region. Our combined pollen, phytolith, charcoal, and sedimentary studies indicate that during the late glacial period (14,000 -10,000 B.P.), lake beds were dry, the climate was cooler and drier, and open vegetational communities were more widespread than after the Pleistocene ended. Zea was a continuous part of the vegetation since at least the terminal Pleistocene. During the Holocene, lakes became important foci of human activity, and cultural interference with a species-diverse tropical forest is indicated. Maize and squash were grown at lake edges starting between 10,000 and 5,000 B.P., most likely sometime during the first half of that period. Significant episodes of climatic drying evidenced between 1,800 B.P. and 900 B.P. appear to be coeval with those documented in the Classic Maya region and elsewhere, showing widespread instability in the late Holocene climate.agricultural origins ͉ ecological contexts ͉ microfossils ͉ paleoecology

The cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexico

“…The potential vegetation of the region is tropical deciduous forest, seen today in remnants scattered throughout the region. Vegetational reconstructions indicate that a species-diverse seasonal tropical forest flourished there after the Pleistocene ended and until systematic human disturbance began (27). The native vegetation contains legumes and many other plants that would have been important subsistence resources, such as Pithecolobium dulce, Prosopis spp, Leucaena spp., Spondias spp., palms, Dioscorea spp., and others (27).…”

“…Vegetational reconstructions indicate that a species-diverse seasonal tropical forest flourished there after the Pleistocene ended and until systematic human disturbance began (27). The native vegetation contains legumes and many other plants that would have been important subsistence resources, such as Pithecolobium dulce, Prosopis spp, Leucaena spp., Spondias spp., palms, Dioscorea spp., and others (27). Bedrock in the study area is predominantly limestone, although extrusive igneous formations are found in the eastern portion of the area.…”

Profile of Dolores R. Piperno

“…Combining studies of climate, vegetation, and land-use history with archaeological work, Piperno and her colleagues have developed a picture of human occupation together with the agricultural and environmental history of the region. Their analyses of phytoliths and pollen from the lake cores found the same kinds of environmental shifts as in other regions of the lowland tropics, with a rapid and marked transition to the present warmer, wetter climate taking place at the end of the Ice Age approximately 10,000 years ago (5).…”

“…Piperno sampled sediments from the lake edges specifically because she thought that people would have used these fertile areas. Indeed, they found phytoliths from maize and a domesticated species of squash in these areas that are probably at least 8,000 years old (5). Her Inaugural Article (5) focuses on the microfossil evidence from the lakes.…”

“…To remedy that, Piperno and her colleagues have been studying lakes and archaeological sites in the region (5). Core samples they have taken from three lakes and a large swamp showed that the oldest of these sites is approximately 14,000 years old.…”