The trees of the Water People: archeological waterlogged wood identification and near-infrared analysis in Eastern Amazonia

Abstract

Trees have always been important to provide wood as a building material for human settlements. In prehistory, houses on stilts were commonly built in or near to bodies of water. This strategy allowed defense against attacks and subsistence fishing. In Brazil, archeological pile dwelling sites are found only in Maranhao state, Eastern Amazonia. These sites were inhabited by the “Water People” between 1230 and 1050 BP. Considering the many different tree species in the area, the present work aimed to identify the archeological waterlogged wood used most by these inhabitants. The studied archeological site is named “Encantado,” and it covers 13 hectares and has 171 identified waterlogged wood pillars. Although the “environment conditions” (with dry and flooding periods) to which the pillars were submitted were harsh, the wood anatomy was preserved; additionally, despite the homogeneity of wood anatomy, it was possible to identify seven groups that might correspond to different species and/or trees. Of those, the majority (32 samples) was identified as the genera Tabebuia/Handroanthus, both popularly known as “ipe.” In addition, the ipe samples had the spectrum collected with the near-infrared spectroscopy (NIR) as a complementary method for wood characterization. NIR and principal component analysis (PCA) data allowed the differentiation of ipe samples with ca. 80% of variation between data. However, PCA did not separate them according to their types. Further, when NIR spectra of wood pillars were compared with recently sawn ipe wood, the samples were separated; therefore, the latter cannot be used to identify waterlogged wood.