Mapping Forest Degradation due to Selective Logging by Means of Time Series Analysis: Case Studies in Central Africa

Abstract

Detecting and monitoring forest degradation in the tropics has implications for various fields of interest (biodiversity, emission calculations, self-sustenance of indigenous communities, timber exploitation). However, remote-sensing-based detection of forest degradation is difficult, as these subtle degradation signals are not easy to detect in the first place and quickly lost over time due to fast re-vegetation. To overcome these shortcomings, a time series analysis has been developed to map and monitor forest degradation over a longer period of time, with frequent updates based on Landsat data. This time series approach helps to reduce both the commission and the omission errors compared to, e.g., bi-or tri-temporal assessments. The approach involves a series of pre-processing steps, such as geometric and radiometric adjustments, followed by spectral mixture analysis and classification of spectral curves. The resulting pixel-based classification is then aggregated to degradation areas. The method was developed on a study site in Cameroon and applied to a second site in Central African Republic. For both areas, the results were finally evaluated against visual interpretation of very high-resolution optical imagery. Results show overall accuracies in both study sites above 85% for mapping degradation areas with the presented methods.

A Bayesian Approach to Combine Landsat and ALOS PALSAR Time Series for Near Real-Time Deforestation Detection

“…The main limiting factor for optical-based approaches in tropical regions is missing data due to frequent cloud cover [19,[23][24][25]. Often, annual composites are generated to decrease data gaps in mediumresolution optical imagery [9,18,26].…”

Logging Roads in Tropical Forests: Synthesis of Literature Written in French and English Highlights Environmental Impact Reduction Through Improved Engineering

“…Articles in BFT were among the first to make use of this finding and suggested the use of logging roads as indicators of the extent of logging disturbance in tropical forests Mayaux et al, 2003;Bourbier et al, 2013). Despite some technical drawbacks (De Wasseige and Defourny, 2004), it is now the de facto standard across all tropical regions to use roads as indicators for human dominance of tropical forests (Asner et al, 2004a(Asner et al, , 2004b(Asner et al, , 2009Souza et al, 2005;Laporte et al, 2007;Hirschmugl et al, 2014;Gaveau et al, 2014). The spatial distribution, i.e.…”

Multi-temporal analysis of radiometric changes in satellite images of forest edges to infer selective-logging areas in the Amazon forest

“…480108/2007-2, Proc. 573810/2008-7 (2009-2014, 610042/2009-2) and Project PROCAD/CAPES (Coordination for the Improvement of Higher Education Personnel). Philip Fearnside and two anonymous reviewers provided comments on the manuscript.…”

“…Timber extraction is one the primary human activities that has contributed to forest degradation in the tropics (Hirschmugl et al 2014). Logging affects tropical forests at the continental scale and is difficult to detect, making monitoring a challenge to be overcome.…”