Ancient mound agriculture

From the press release
French Guianan coastal savannas : a landscape shaped by humans and by nature:
"Raised fields that were built and exploited between 650 and 1250 AD
This study confirms first of all that pre-Columbian farmers built the vast complexes of raised fields found in Guianan savannas. This coastal fringe, considered inhospitable, is subjected to seasonal flooding (an alternation of periods of rain and drought). The Amerindians constructed mounds to make well-drained soil, permitting intensive sedentary agriculture. They thus efficiently applied agricultural engineering to exploit lands that are today considered unsuitable for farming. The researchers succeeded in precisely dating some of these fields: one of the sites dates back to the 12th century, while the second is yet another century older. The analysis of two types of plant microfossils —phytoliths found in the mounds and starch grains, found on fragments of ceramic cooking utensils discovered in ancient Amerindian villages— showed that these farmers cultivated at least three plants: maize —which, astonishingly, is absent from the panel of plants cultivated in the region today—, manioc (cassava) and squash. By constructing these well-drained islands, the Amerindians produced heterogeneity between the well-drained and elevated parts of these landscapes: the biogeochemical composition of the top 50 cm of soils of the two zones is still different today.

Landscapes co-constructed by Man and Nature
Once abandoned, these fields were taken over by Nature. Ants, termites, earthworms, plants and other organisms preferentially colonized these well-drained structures. These “ecosystem engineers” generated self-organized processes. These organisms transport organic matter and mineral soil to mounds and modify the structure and composition of mound soils. Owing to their effect on soil porosity, the infiltration capacity of rain water is nine times greater on the mounds than on the seasonally flooded plain, reducing the susceptibility of mounds to erosion. These biogeochemical mechanisms have thus permitted the maintenance of these elevated structures, where the concentration of resources initially created by humans is conserved."

Some photos in http://www.wired.com/wiredscience/2010/04/lost-amazon-farms/.
It appears that the Taino of Haiti used similar methods Pre-Columbian Hispaniola - Arawak/Taino Indians:
"The Arawak/Taino had a developed system of agriculture which was virtually maintenance free. They raised their crops in a conuco, a large mound which was devised especially for farming. They packed the conuco with leaves to protect from soil erosion and fixed a large variety of crops to assure that something would grow, no matter what weather conditions prevailed."