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Remote Sens. 2016, 8(11), 948; doi:10.3390/rs8110948

Environmental and Anthropogenic Degradation of Vegetation in the Sahel from 1982 to 2006

Department of Geographical Sciences, University of Maryland, College Park, MD 20782, USA
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Received: 14 June 2016 / Accepted: 10 November 2016 / Published: 13 November 2016
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Abstract

There is a great deal of debate on the extent, causes, and even the reality of land degradation in the Sahel. Investigations carried out before approximately 2000 using remote sensing data suggest widespread reductions in biological productivity, while studies extending beyond 2000 consistently reveal a net increase in vegetation production, strongly related to the recovery of rainfall following the extreme droughts of the 1970s and 1980s, and thus challenging the notion of widespread, long-term, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends. It is hypothesized that, in addition to rainfall, other meteorological variables and human land use have contributed to vegetation dynamics. Throughout most of the Sahel, the interannual variability in growing season ΣNDVIgs (measured from satellites, used as a proxy of vegetation productivity) was strongly related to rainfall, humidity, and temperature (mean r2 = 0.67), but with rainfall alone was weaker (mean r2 = 0.41). The mean and upper 95th quantile (UQ) rates of change in ΣNDVIgs in response to climate were used to predict potential ΣNDVIgs—that is, the ΣNDVIgs expected in response to climate variability alone, excluding any anthropogenic effects. The differences between predicted and observed ΣNDVIgs were regressed against time to detect any long-term (positive or negative) trends in vegetation productivity. Over most of the Sahel, the trends did not significantly depart from what is expected from the trends in meteorological variables. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by negative, and, in some areas, positive trends. To explore whether the negative trends were human-induced, they were compared with the available data of population density, land use, and land biophysical properties that are known to affect the susceptibility of land to degradation. The spatial variations in the trends of the residuals were partly related to soils and tree cover, but also to several anthropogenic pressures. View Full-Text
Keywords: productivity; vegetation; land degradation; desertification; Sahel; remote sensing; residual trends; RESTREND; NDVI; rain-use efficiency; RUE productivity; vegetation; land degradation; desertification; Sahel; remote sensing; residual trends; RESTREND; NDVI; rain-use efficiency; RUE
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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. (CC BY 4.0).

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MDPI and ACS Style

Rishmawi, K.; Prince, S.D. Environmental and Anthropogenic Degradation of Vegetation in the Sahel from 1982 to 2006. Remote Sens. 2016, 8, 948.

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