Continental estimates of forest cover and forest cover changes in the dry ecosystems of Africa between 1990 and 2000

Abstract

AimThis study provides regional estimates of forest cover in dry African ecoregions and the changes in forest cover that occurred there between 1990 and 2000, using a systematic sample of medium-resolution satellite imagery which was processed consistently across the continent.LocationThe study area corresponds to the dry forests and woodlands of Africa between the humid forests and the semi-arid regions. This area covers the Sudanian and Zambezian ecoregions.MethodsA systematic sample of 1600 Landsat satellite imagery subsets, each 20 km × 20 km in size, were analysed for two reference years: 1990 and 2000. At each sample site and for both years, dense tree cover, open tree cover, other wooded land and other vegetation cover were identified from the analysis of satellite imagery, which comprised multidate segmentation and automatic classification steps followed by visual control by national forestry experts.ResultsLand cover and land-cover changes were estimated at continental and ecoregion scales and compared with existing pan-continental, regional and local studies. The overall accuracy of our land-cover maps was estimated at 87%. Between 1990 and 2000, 3.3 million hectares (Mha) of dense tree cover, 5.8 Mha of open tree cover and 8.9 Mha of other wooded land were lost, with a further 3.9 Mha degraded from dense to open tree cover. These results are substantially lower than the 34 Mha of forest loss reported in the FAO's 2010 Global Forest Resources Assessment for the same period and area.Main conclusionsOur method generates the first consistent and robust estimates of forest cover and change in dry Africa with known statistical precision at continental and ecoregion scales. These results reduce the uncertainty regarding vegetation cover and its dynamics in these previously poorly studied ecosystems and provide crucial information for both science and environmental policies.

Land Cover Change Monitoring Using Landsat MSS/TM Satellite Image Data over West Africa between 1975 and 1990

“…Whereas the first dataset has been produced in this study, the two following datasets were provided by a previous work [31].…”

“…The objective of this validation step using the dedicated TREES validation tool is to eliminate misclassification and to provide better consistency over the whole area. The 1990 dataset has followed an evaluation of regional experts and an independent validation procedure, in addition to an internal rigorous quality control [31]. Accuracy assessment was carried out for the land cover maps of the period 1990-2000 [31] where 338 random 20 km × 20 km sample sites were selected over sub-Saharan Africa.…”

Evolution of Cerrado Vegetal Cover on a River Island Based on Orbital Imaging Data

“…Awareness of these changes is growing and, therefore, a series of studies have been designed to detect and quantify their extent (ten CATEN et al, 2015;GRECCHI et al, 2014;ROCHA et al, 2011). Currently, geo-technological systems and products are indispensable tools for spatial and temporal detection, evaluation and monitoring of problems related to the environment (GÓMEZ et al, 2016;ANDREW et al, 2014;BODART et al, 2013;BODART et al, 2011). This is due to distinct data integration and overlapping at varied scales by geographic information systems (GISs), facilitating decision-making and shifts, if necessary, on land use and occupation policies (BEUCHLE et al, 2015;ten CATEN et al, 2015;MÜLLER et al, 2015;COELHO et al, 2014;GIRI et al, 2013;POTAPOV et al, 2011;DURIGAN & RATTER, 2006).…”

“…For this purpose, Normalized Difference Vegetation Indexes were generated for Landsat 1 (1973( ) and Landsat 5 (1984( , 1990( , 2000 images. Five landscape units were identified in the field: bare soil, Rough savanna, Typical savanna, Forested savanna and Evergreen dry woods.…”

Smallholders’ Tree Planting Activity in the Ziro Province, Southern Burkina Faso: Impacts on Livelihood and Policy Implications

“…In dry Africa, annual net changes of tree cover and other wooded land have been estimated at −0.91 M ha (0.34% annual rate of loss) and −0.89 M ha (0.20%), respectively, between 1990 and 2000 [2], while the annual net change from dense to open tree cover was −0.39 M ha [3,4]. In Burkina Faso, the annual deforestation rate ranged from 0.91 to 1.03% between 1990 and 2010 [5], while total forest area accounted for 56,490 km 2 (21% of the national territory).…”