Beyond the mangrove forests, vast savannahs which are flooded with the turning of the seasons, lies the Guiana coastline, stretching nearly 1600km from the mouth of the Amazon to the Orinoco delta. This low-lying and apparently uniform strip of coast reveals some of its particularities only from a few metres up in the air. It was indeed from a ULM that archaeologists noticed regular patterns of mounds of earth of varying size and shape. These vast open environments, currently of limited interest to local populations, are under study by European archaeologists and ecologists. Are these structures human constructs or termite nests?

The origin of these mounds has long been a subject of debate, and remains so in other regions of South America where similar formations are found (in Bolivia, Venezuela, Colombia, Ecuador, etc) due to the large number of termites in these countries and the known ability of these social animals to build the highly regular mounds their nests are comprised of (in Brazil and Africa in particular). The research project has been running for three years and brings together researchers in archaeology and ecology to study the mounds in the coastal savannahs of French Guiana. It has shown that they are the remains of old agricultural systems (raised fields) built by the Amerindians before the European conquest. ULM flights over the coast of French Guiana and the examination of aerial photos taken by the French National Geographical Institute (IGN), have made it possible to draw up a complete map of the raised field complexes that can be found on both the island of Cayenne and in the Mana rice fields. These old workings of the landscape have enabled farmers to grow their crops on little islands safe from flooding.

Archaeological excavations carried out in close proximity to the raised fields, on the zones lying above the flooded plains, have revealed pottery and the remains of houses and old fires which had been hidden beneath the earth and vegetation. Analysis of the sculpted forms on the pottery along with carbon-14 dating, has revealed that Amerindians lived here and cultivated the savannahs between 800 and 1000 years ago. In the same way as fragments of pottery have made it possible to determine the history of human occupation on the site, the composition of plant life there can be revealed by studying the pollen (samples of which were gathered on the pottery) and microfossils (called phytoliths) which remain intact in the earth after the plant has decomposed. By analysing the pollen and phytoliths it has been discovered that corn, manioc, and marrows were grown on the raised fields, providing the basis of the diet of these Amerindian peoples.

While they were originally used to protect crops from flooding, a whole host of organisms has since found refuge on these mounds that were abandoned by men nearly 800 years ago.

Amongst these organisms, ants, termites, worms, and plants are known for their “ecosystem engineering” of their environments. They act on the physical and chemical properties of the soil, thus modifying the quality of their own environment and that of other organisms. Ants transport large quantities of insects and bits of foliage as they go around looking for food, and like termites they transport particles of earth from layers deep underground up to the surface when building and cleaning their subterranean nests. Worms also play an important role by making galleries in the soil, which are then ideal for plant roots to infiltrate, and by turning over the earth via the ejection of their casts to the surface. The root network of plants helps stabilise and drain the soil whilst their foliage, by providing shade, helps reduce water evaporation and thus maintains a certain level of soil humidity. All of these activities are combined and concentrated on these mounds, meaning the soil is less prone to the erosion caused by the three metres of annual rainfall and facilitated by the seasonal fires. In the absence of human activity, the successive action of ants, termites, worms, and plants on the mounds helps keep these structures above water level. The coast of French Guiana is therefore made up of landscapes which are formed neither purely by human behaviour nor purely by the workings of nature. They are a new sort of environment formed by the interaction between pre-Columbian agricultural landscaping and the natural engineers that now ensure their maintenance and survival.

Unfortunately these landscapes are now under direct threat by development projects (for quarries and cattle rearing) which could result in their total destruction. We need to protect the raised fields of French Guiana for their outstanding biocultural heritage in which the interaction of ants and men still has many secrets to yield.