Forest Cover and Vegetation Degradation Detection in the Kavango Zambezi Transfrontier Conservation Area Using BFAST Monitor

Michael Schultz,Martin Herold,Aurélie Shapiro,Jan Clevers,Craig Beech

doi:10.3390/rs10111850

Abstract

Forest cover and vegetation degradation was monitored across the Kavango-Zambezi Transfrontier Conservation Area (KAZA) in southern Africa and the performance of three different methods in detecting degradation was assessed using reference data. Breaks for Additive Season and Trend (BFAST) Monitor was used to identify potential forest cover and vegetation degradation using Landsat Normalized Difference Moisture Index (NDMI) time series data. Parametric probability-based magnitude thresholds, non-parametric random forest in conjunction with Soil-Adjusted Vegetation Index (SAVI) time series, and the combination of both methods were evaluated for their suitability to detect degradation for six land cover classes ranging from closed canopy forest to open grassland. The performance of degradation detection was largely dependent on tree cover and vegetation density. Satisfactory accuracies were obtained for closed woodland (user’s accuracy 87%, producer’s accuracy 71%) and closed forest (user’s accuracy 92%, producer’s accuracy 90%), with lower accuracies for open canopies. The performance of the three methods was more similar for closed canopies and differed for land cover classes with open canopies. Highest user’s accuracy was achieved when methods were combined, and the best performance for producer’s accuracy was obtained when random forest was used.

Highlights

The Kavango-Zambezi Transfrontier Conservation Area (KAZA) is the largest transboundary conservation area in Africa, straddling the borders of Angola, Botswana, Namibia, Zambia and Zimbabwe (Figure 1)
We studied the performance of degradation detection using BFAST Monitor (BFM) for different canopy cover types, using modifications of existing methods [24,26], accounting for good practices and introducing a new method to refine results
Because this study focused on the measurement of degradation, any pixel characterized by a positive magnitude was discarded from further analysis

Summary

Introduction

The Kavango-Zambezi Transfrontier Conservation Area (KAZA) is the largest transboundary conservation area in Africa, straddling the borders of Angola, Botswana, Namibia, Zambia and Zimbabwe (Figure 1). Between 2007 and 2014, large animal herds changed their movement patterns for several reasons, increasing chances of HWC within KAZA [1], and related economic losses have been incurred, further fueling the spiral of HWC [2]. When animal movement patterns and human-induced land change are known, wildlife corridors can be planned and managed as a suitable solution to manage conflicts [3]. Such efforts are important for nations in slowing down forest decline and conserving or increasing carbon sink capacities of forests, promoted by Reducing Emissions from Deforestation and forest Degradation (REDD+) projects [4]. Monitoring, Reporting and Verification (MRV) of activity data [5] has been proven to create additional revenues

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Discussion

Conclusion