Mapping vegetation on ferruginous substrates using ASTER and gamma-spectrometry images in the Iron Quadrangle, Minas Gerais

Bruno Araujo Furtado De Mendonça,Eliana Elizabet Dos Santos,Aianã Francisco Santos Pereira,Luciano Mozer De Assis,Maola Monique Faria,Carlos Ernesto Gonçalves Reynaud Schaefer,Elpído Inácio Fernandes Filho,Pedro Christo Brandão

doi:10.1590/1806-90882019000400006

Abstract

ABSTRACT The Iron Quadrangle (IQ) region in Minas Gerais is remarkably geobiodiverse, despite a long history of anthropogenic pressures such as mining and urbanization, but still lacks detailed studies on the distribution of its remaining native vegetation in different substrates. In this study, we utilized Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images, besides Gamma-spectrometry (Gamma) survey data associated with existing geological mapping (GM) and extensive fieldwork, to discriminate and quantify remnants of vegetation on ferruginous substrates in the IQ. The Maximum Likelihood (ML) algorithm was used to classify the vegetation types, thus named: open Rupestrian Field, shrubby Rupestrian Field, Capão Forest, Cerrado stricto sensu, Cerrado Field, Seasonal Forests, Pastures and Reforestation (the latter three regardless of substrate type) associated with the predominant substrates (ferruginous ironstone, phyllites, and quartzite). The use of ASTER images alone did not allow a reliable separation of ferruginous and non-ferruginous substrates, but the integration of all different data (ASTER-ML + Gamma + GM) allowed the provisional mapping of the vegetation associated with ferruginous substrates, potentially ferruginous and non-ferruginous substrates. The resulting map shows that the vegetation on ferruginous and potentially ferruginous substrates cover 8.7% and 6.9% of the IQ, respectively. The detailed analysis of the distribution and fragmentation of phytophysiognomies on ferruginous substrates is of great importance for developing strategies to conserve the geobiodiversity of the IQ, and need to be further refined by checking and field mapping by novel approaches.

Highlights

The Iron Quadrangle (IQ) region has a remarkable geobiodiversity (Fernandes, 2016) but lacks detailed mapping of its vegetation formations
The detailed analysis of the distribution and fragmentation of phytophysiognomies on ferruginous substrates is of great importance for developing strategies to conserve the geobiodiversity of the IQ, and need to be further refined by checking and field mapping by novel approaches
Scene 070826 (02), which covers most of the IQ (Figure 1) and has no cloud cover, was used as a reference for the supervised classification

Summary

Introduction

The Iron Quadrangle (IQ) region has a remarkable geobiodiversity (Fernandes, 2016) but lacks detailed mapping of its vegetation formations. Lateritic Rupestrian Fields, termed Ferruginous Rupestrian Fields (or Grasslands), or “canga vegetation,” develop on ferruginous substrates (Vincent, 2004; Viana and Lombardi, 2007). These unique ecosystems, colonized by specialist plants adapted to oligotrophic environments, are capable of tolerating a number of severe environmental filters, such as shallow soils, severe water deficits, low fertility, high oxidized iron concentrations, and low water retention, as well as large daily thermal amplitudes, frequent fires, high sun exposure, and constant winds (Vincent, 2004; Jacobi et al, 2007; Schaefer et al, 2016). The vegetation shows several anatomical, morphological, physiological, and reproductive adaptations that allow it to survive in these environments (Alves and Kolbek, 1994)

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