A spatial desertification indicator for Mediterranean arid rangelands: a case study in Algeria

Abstract

Sheep and goat production is the main and sometimes only agricultural activity available to populations living on rangelands in the arid regions around the Mediterranean. Desertification threatens large areas of Mediterranean arid rangelands but remains difficult to describe, quantify and accurately locate for management purposes. A methodology is described which estimates a Spatial Rain-Use Efficiency Index (SRUEI) and its potential use to evaluate rangeland condition at a large scale. It is based on an Aboveground Net Primary Production (AGNPP) map generated from field herbage mass measurements and a rainfall spatial distribution map derived from local elevation–rainfall gradients with the whole resulting from satellite imagery processing and GIS technology. The area of the case study was in the Nâama–Mecheria region located on the High Plateau south of Oran (Algeria). It covers ~215 000 ha, receiving ~200 mm year–1 of winter and spring precipitation. The Nâama–Mecheria SRUEI-derived map clearly shows the degradation gradient declining away from the settlements. The Mecheria AGNPP 2007 map and associated grazing rings indicate that the Mecheria cooperative flocks may ingest 48–57% (Range Use Factor) of the rangeland’s seasonal plant production, which is barely compatible with sustainable rangeland use. When adding the effect of fuel wood collection by local residents and rain-fed arable cropping, the Nâama–Mecheria region is undoubtedly heading towards a slow but certain desertification of its fragile arid rangelands unless correcting measures are implemented. The SRUEI and associated results are powerful tools that allow rangeland conditions to be mapped, and which can be employed in planning and pursuing sustainable management of rangelands in such arid areas.

How to avoid unsustainable side effects of managing climate risk in drylands — The supplementary feeding controversy

“…This region in the high plateaus of southern and eastern Morocco is connected to similar landscapes in Algeria (Saïdi and Gintzburger, 2013) and Tunisia (Abdelkader et al, 2008). In North Africa, sagebrush steppes cover an area of approx.…”

Approcher la densité des ligneux par l’indice perpendiculaire de végétation : cas d’une savane arborée au nord de la Tanzanie

“…S'agissant de la surface de 49 pixels de 30 m de résolution (4 ha) qui localisent chacun de nos points de mesure, ce choix constitue non seulement un élément important dans la segmentation (plus cette surface est grande et homogène, meilleure est la segmentation des classes de densité), mais aussi un repère indispensable pour compenser l'incertitude de localisation géographique des relevés de terrain. Saïdi et Gintzburger (2013) ont montré l'importance de cette surface dans la fiabilité géographique des cartes produites.…”

“…Le calcul de cet indice a pour but de diminuer fortement la signature spectrale des sols nus et de ne conserver que celle de la végétation. Autrement dit, cela revient à calculer la distance euclidienne entre un point correspondant à la réflectance de la végétation et une droite, laquelle correspond à la réflectance du sol nu dans ces longueurs d'onde (Gintzburger et al, 2009 ;Saïdi et Gintzburger, 2013). L'IPV se calcule par l'équation suivante :…”

“…Avec le logiciel Erdas Imagine utilisé pour le traitement d'image, la mise en relation des valeurs moyennes de l'IPV avec les densités mesurées a été réalisée sur des zones de 7 x 7 pixels, soit une surface de 4 ha. Cette surface constitue non seulement un point important dans la classification, mais permet également de compenser l'incertitude de localisation géographique des relevés de terrain (Saïdi et Gintzburger, 2013). Plus cette surface est grande et homogène, meilleure est la segmentation des classes de densité.…”

Analysis of Vegetation Change and Mapping Tree Species in Mountainous Area Using Multi-Source Satellite Data: A Case Study of Djebel El Ouahch, Algeria

“…Other works studied the vegetation cover change using Multispectral, Hyperspectral imagery, or orthophotography at local scales [15,16]. However, no previous work has been performed in the massive of Djebel El Ouahch, which have not received adequate attention to monitor patterns of vegetation change over the last 30 years and to assess the tree species diversity using multi-source satellite data approach.…”