Classification of Vegetation over a Residual Megafan Landform in the Amazonian Lowland Based on Optical and SAR Imagery

Édipo Cremon,Hiran Zani,Dilce De Fátima Rossetti

doi:10.3390/rs61110931

Abstract

The origin of large areas dominated by pristine open vegetation that is in sharp contrast with surrounding dense forest within the Amazonian lowland has generally been related to past arid climates, but this is still an issue open for debate. In this paper, we characterize a large open vegetation patch over a residual megafan located in the northern Amazonia. The main goal was to investigate the relationship between this paleolandform and vegetation classes mapped based on the integration of optical and SAR data using the decision tree. Our remote sensing dataset includes PALSAR and TM/Landsat images. Five classes were identified: rainforest; flooded forest; wooded open vegetation; grassy-shrubby open vegetation; and water body. The output map resulting from the integration of PALSAR and TM/Landsat images showed an overall accuracy of 94%. Narrow, elongated and sinuous belts of forest within the open vegetation areas progressively bifurcate into others revealing paleochannels arranged into distributary pattern. Such characteristics, integrated with pre-existing geological information, led us to propose that the distribution of vegetation classes highlight a morphology attributed to a Quaternary megafan developed previous to the modern fluvial tributary system. The characterization of such megafan is important for reconstructing landscape changes associated with the evolution of the Amazon drainage basin.

Highlights

The sharp contrast between forest and open vegetation has been one of the most intriguing features of the Amazonian ecosystem, and numerous publications have discussed this issue (e.g., [1,2,3,4,5,6,7]).Changes in the physical environment over geological time have been the most frequently claimed hypothesis to explain such occurrences [3,8,9,10,11,12]
It is intriguing that such occurrences are not randomly distributed, but they are confined to several large-scale, triangular-shaped morphologies related to residual megafan depositional systems [19] due to their resemblance to many megafans described in the literature [20,21,22,23,24]
The first and third quartile of open vegetation classes (Ovw and Ovgs) were promptly distinguished in bands 5 and 7 of TM images, as well as in the HV and HH polarizations of synthetic aperture radar (SAR) data, with the latter being useful for this purpose

Summary

Introduction

The sharp contrast between forest and open vegetation has been one of the most intriguing features of the Amazonian ecosystem, and numerous publications have discussed this issue (e.g., [1,2,3,4,5,6,7]).Changes in the physical environment over geological time have been the most frequently claimed hypothesis to explain such occurrences [3,8,9,10,11,12]. It is intriguing that such occurrences are not randomly distributed, but they are confined to several large-scale, triangular-shaped morphologies related to residual megafan depositional systems [19] due to their resemblance to many megafans described in the literature [20,21,22,23,24]. This is because megafans are characterized by extensive (i.e., >103 km2)

Methods

Results

Discussion

Conclusion