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Can spectral analysis of digitised images help us distinguish spatially periodic landscapes of natural and human origin? A case study of complexes of mounds in coastal savannas of French Guiana

Delphine Renard (Centre d'Ecologie Fonctionnelle et Evolutive)
Doyle McKey (Centre d'Ecologie Fonctionnelle et Evolutive)

Abstract

Many savannas of coastal French Guiana are characterized by periodic landscapes in which a seasonally flooded matrix is pockmarked by thousands of regularly spaced mounds representing agricultural raised fields created by pre-Columbian Amerindians during the late Holocene. However, there exist many examples of highly regular landscapes of natural origin. When direct archaeological evidence is scanty, can ‘signature’ clues in the spatial structure of landscapes reveal the imprint of ancient human actions? Using spectral analysis applied to digitised aerial photographs, we quantified the periodicity (regularity in distance between mounds), intensity (periodic variation as a proportion of the total variation) and orientations of mounds in savanna landscapes. The patterns we identified have never been detected in landscapes of natural origin. Interestingly, these ‘signature’ features could enable us to distinguish spatially periodic landscapes of manmade and natural origin and could thus help guide archaeological research in similar wetland landscapes of unknown origin.