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Remote Sens. 2014, 6(3), 2408-2434; doi:10.3390/rs6032408
Article

Local Vegetation Trends in the Sahel of Mali and Senegal Using Long Time Series FAPAR Satellite Products and Field Measurement (1982–2010)

1,* , 2,4
, 3
, 4
 and 1,5
1 Institute of Geography, University of Bayreuth, D-95440 Bayreuth , Germany 2 CREAF, Cerdanyola del Vallès, E-08193 Catalonia, Spain 3 Centre de Suivi Ecologique, Dakar-Fann BP 13532, Senegal 4 INRA-EMMAH, UMR 1114, Site Agroparc, F-84914 Avignon, France 5 BayCEER, University of Bayreuth, D-95440 Bayreuth, Germany
* Author to whom correspondence should be addressed.
Received: 17 January 2014 / Revised: 27 February 2014 / Accepted: 3 March 2014 / Published: 19 March 2014
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Abstract

Local vegetation trends in the Sahel of Mali and Senegal from Geoland Version 1 (GEOV1) (5 km) and the third generation Global Inventory Modeling and Mapping Studies (GIMMS3g) (8 km) Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) time series are studied over 29 years. For validation and interpretation of observed greenness trends, two methods are applied: (1) a qualitative approach using in-depth knowledge of the study areas and (2) a quantitative approach by time series of biomass observations and rainfall data. Significant greening trends from 1982 to 2010 are consistently observed in both GEOV1 and GIMMS3g FAPAR datasets. Annual rainfall increased significantly during the observed time period, explaining large parts of FAPAR variations at a regional scale. Locally, GEOV1 data reveals a heterogeneous pattern of vegetation change, which is confirmed by long-term ground data and site visits. The spatial variability in the observed vegetation trends in the Sahel area are mainly caused by varying tree- and land-cover, which are controlled by human impact, soil and drought resilience. A large proportion of the positive trends are caused by the increment in leaf biomass of woody species that has almost doubled since the 1980s due to a tree cover regeneration after a dry-period. This confirms the re-greening of the Sahel, however, degradation is also present and sometimes obscured by greening. GEOV1 as compared to GIMMS3g made it possible to better characterize the spatial pattern of trends and identify the degraded areas in the study region.
Keywords: land degradation; greening; drought; Sahel; FAPAR time series; GIMMS3g; Geoland; biomass observations; Senegal; Mali land degradation; greening; drought; Sahel; FAPAR time series; GIMMS3g; Geoland; biomass observations; Senegal; Mali
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Brandt, M.; Verger, A.; Diouf, A.A.; Baret, F.; Samimi, C. Local Vegetation Trends in the Sahel of Mali and Senegal Using Long Time Series FAPAR Satellite Products and Field Measurement (1982–2010). Remote Sens. 2014, 6, 2408-2434.

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