Ethnohistorical and archaeological data from various countries in South America show that flooded savannas or swamps were generally cultivated under demographic pressure, when slash-and-burn agriculture on higher ground became insufficient. For example, the numerous Creoles’ gardens that can be seen on the sandy ridges on the aerial photographs show how a small number of people can occupy and use up the high areas of the coastal plain. At the end of the eighteenth century, soil exhaustion and leafcutter ant (Atta spp.) infestation in the hills of Cayenne Island forced people to seek new land for cultivation. For that reason, Europeans began to make polders in the marshes east of Cayenne Island.
Construction, maintenance, and cultivation of raised fields require well-organized communal work. Furthermore, specialized groups probably carried out such labor under the leadership of a central authority because the management of hydrological works requires precise planning. It is difficult to evaluate the demography of the raised field builders because the fields may have been used for longer or shorter periods of time. However, the extension and the number of raised fields suggest significant population growth on the coast. People living in the villages on the sandy ridges did the work necessary to build raised fields and causeways. Sedentarism was possible thanks to an abundant coastal fauna and to a permanent agricultural production system. Looking at population density in other cultivated tropical lowlands and supposing that the western coastal plain of French Guiana was uniformly inhabited and that raised fields were cultivated permanently, population density could have been 50-100 persons/km2 (Jean Hurault in Rostain 1991). That implies that approximately 200,000 people might have lived on the western French Guiana coast at this time. Such numbers are not surprising. In the lower San Jorge River in Colombia 500,000 ha of drained fields have been identified. On the basis of surface area of residential platforms a population density of 160 persons/km2 is estimated between AD 200 and 900 (Plazas and Falchetti in Denevan et al. 1987).
One site is particularly interesting for estimating the number of persons relying on raised fields production. The Piliwa group is located at the extreme west of the French Guiana coast, on the left bank of the Mana mouth (Figure 13.1). Ridged fields are distributed in parallel and perpendicular groups in a flooded depression 1200 x 50-150m between two sand ridges parallel to the river bank (Figure 13.7). The modern Kali’na village of Awala is located on the southern sand ridge, extending to the west along the river beach. The archaeological site is probably located at the same spot. Ridged fields are nowadays under water during the rainy season, but they emerge during the dry season (Figure 13.8). This site is isolated from other raised fields complexes (Figure 13.1), so it can be assumed that only one village cultivated these raised fields. The surface of all the ridged fields is 90,371 m2, or 90 ha, which represents about three-quarters of the whole surface of the depression (Figure 13.9).
There is a large variation in the average of the cultivated surface for one consumer among the Amazonian groups (Descola 1986 synthesizing various references): 405 m2 among the Yanoama (Niyayoba-Teri); 607 m2 among the Yanoama (Jorocoba-Teri); 810 m2 among the Cubeo; 900 m2 among the Central Yanomami; 1,371 m2 among the Achuar; 1,970m2 among the Siona-Secoya; 2,632 m2 among the Kuikuru.
In French Guiana, the average surface cultivated by the slash-and-burn technique in the forest by one family shows few variations among the different modern groups (Gely 1984): 0.33 ha for the Kali’na of the lower Mana; 0.42 ha for the Wayana of the upper Maroni; 0.51 ha for the Wayapi of the upper Oyapock; 0.75 ha for the Palikur of the lower Oyapock; 0.81 ha for the Boni (Maroons) of the lower Maroni.
In conclusion, the garden size for one family must reach between 0.5 and 0.8 ha in order to achieve self-sufficiency for one year. A larger size allows farmers to produce surplus food for trade (Gely 1984).
It must be noted that the productivity of raised fields was probably much greater than with shifting cultivation. For instance, in the state of Barinas in the Venezuelan Llanos, a modern farmer using pre-Columbian drainage to cultivate maize, beans, manioc and other crops got two successful harvests of maize each year, which indicates the potential of the drained fields technique for regular double cropping (Spencer et al. 1994). On the middle Orinoco, modern Karinya use a highly productive agriculture on drained fields requiring only about 0.39 ha per household (Denevan and Schwerin 1978).
On the basis of these various data, it can be suggested that between 500 and 1000 persons could have lived from the production of the 90 ha of the Piliwa ridged fields.
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