Locating Amazonian Dark Earths (ADE) using vegetation vigour as a surrogate for soil type

Abstract

Amazonian Dark Earths (ADE) are patches of archaeological soils scattered throughout the Amazon Basin. These soils are a mixture of charcoal, nutrient vegetable matter and the underlying Oxisol soil. ADE are extremely fertile in comparison to the surrounding soils and they are sought after by local residents for agricultural food production. Research is being conducted to learn how ADE were created and to explore the possibility of replicating them to sequester carbon and to reclaim depleted soils in the Amazon Basin. A factor limiting the success of this research is our current inability to locate ADE sites hidden beneath the tropical forest canopy. We use annual time-series Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) satellite imagery from 2001 to 2005 and harmonic analysis (HA) to examine the spectral differences between forest vegetation growing on ADE and forest vegetation growing on non-ADE. There is a significant difference between the reflectances of vegetation growing on the two soil types, due primarily to lower EVI values over ADE during the dry season (multiple analysis of variance (MANOVA) p-value = 0.040). A logistic model is used to create a predictive map of ADE location.