Evaluation of the Hypotheses on the Formation of Earth Mound Fields in the Federal District of Brazil Through Landscape Element Analysis

Abstract

The Brazilian Savanna houses Earth Mound Fields (EmF), which represent the rarest phytophysiognomy among the fourteen present in the Federal District of Brazil (FDB). However, the EmF origin remains a subject of debate, and biotic and abiotic hypotheses propose divergent mechanisms for EmF’s mound formation. To shed light on the subject, this study evaluated the spatial configuration of 197 EmF on the FDB landscape and characterized their structure. The identified EmF across the FDB territory were georeferenced and overlaid onto aerial images from 2009. The area of each EmF was manually vectorized and its configuration was evaluated using landscape metrics. The structures of four EmF were examined using laser profiling (LiDAR), incorporating metrics related to occupation, morphology, and dispersion. In addition, the elevation of mounds’ tops and the adjacent surfaces was analyzed to assess the altimetric continuity between these elements. The identified EmF spread over 6,556 ha, representing 1.2% of the FDB's territory. Regarding the biotic hypothesis, the metrics associated with the dispersion of EmF’s mounds, their volume, and basal area do not align with the characteristics of termite mounds attributed to the species reported as mound builders. Additionally, the altimetric continuity between mounds’ tops and the external surfaces adjacent to EmF supports the abiotic hypothesis for mound formation.

Keywords:
Landscape Metrics; LiDAR; Phytophysiognomy; Morphometry; Altimetry