Predicting distributions of charcoal in Amazonian soils: approaches from earth and space
Abstract
The direct linkage between fire and human activity in Amazonian rainforests is evidenced in both remote sensing datasets and field-based research. Paleoecological and archaeological data suggest the synergy has persisted millennia, and that human populations may have equaled modern numbers before European contact. Pre-Columbian people used fire to clear forests, but also combined charcoal with other materials to form Amazonian Black Earths (ABE), a nutrient rich anthrosol believed to be capable of sustaining large-scale permanent societies in such nutrient-poor tropical settings. The majority of impacted sites are found on bluffs overlooking Amazonian rivers, which are considered 'preferred' settings. Here, we examine predictions about preferred settings and the distributions of charcoal resulting from pre-Columbian human activity in western and central Amazonia using proxies from both earth and space. Soil sampling, stratified based on distance from river and forest seasonality, was used to determine whether preferred locations had higher probabilities of impacts. We analyzed more than 351 soil cores for ABE and macroscopic charcoal (> 500 μm) in the upper 20 cm of soil (representing modern fires), and in soils > 20 cm depth (representing historic fires). ABE was absent from all sites, but logistic regressions indicated that probabilities of finding soil charcoal significantly decreased as distance from river increased in aseasonal forests. However, in more seasonal forests, the probability of finding charcoal was increased, although distance from river was not a significant factor. Alternately, the location of ABE and charcoal mainly along major rivers may be an artifact of sampling. To look at distributions of ABE across broad spatial scales that may not be accessible from the ground, we used Hyperion satellite images to detect canopy chemistry differences resulting from various soil nutrients (i.e. soil enrichment occurring at ABE sites). Our initial findings indicate that bands with a wavelength around 2400 nm are useful in distinguishing ABE sites from non-ABE sites. We are analyzing over 1400 Hyperion images and a database of more than 700 locations of ABE and non-ABE sites. We stress the importance of having non-ABE site information, because archaeological surveys often do not report lack of archaeological evidence. We will also integrate additional geographical database parameters, PALSAR satellite imagery, and more ground-truthed non-ABE site locations in our analyses to strengthen our statistical models. Our interdisciplinary research project proves a unique development in bridging the remote sensing forest ecology group, field-based forest ecologists, and paleoecological and archaeological researchers.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC33E..07M
- Keywords:
-
- 1615 GLOBAL CHANGE / Biogeochemical cycles;
- processes;
- and modeling