Monitoring of the evolution of rangeland phytomass in a semi-arid environment with remote sensing: case of the Moroccan Oriental region.

Date: 2012 - 2019

Researcher involved: Marie LANG, PhD student

Rangelands account for 65% of the world’s dryland areas (Millennium Ecosystem Assessment 2005) and constitute natural or semi-natural ecosystems, used mainly for livestock production in regions made unsuitable for agriculture due to climate and soil conditions (Stoddart et al. 1975; Society for Range Management 1989). In North Africa, natural rangelands represent two-thirds of the non-desert zone in Algeria, Egypt, Libya, Morocco and Tunisia. These natural pastures are the main source of feed for livestock, which, when converted to sheep equivalents, represent an interannual average of approximately 91 million sheep (Dutilly-Diane 2006). Rangelands are crucial for pastoralists as their income primarily depends on livestock. In this kind of extensive land-use system, characterised by low human and livestock population densities and using relatively low levels of inputs, animal growth depends mostly on the pastures’ grazing capacity (Niamir-Fuller et al. 2012; Alkemade et al. 2013).

In pastoral areas of Morocco, rainfall is the main limiting factor of natural vegetation production. Besides, rangeland biomass production highly fluctuates in space and time due to high latitudinal and interannual variability of rainfall (Gommes et al. 2009). In addition, rangelands of Morocco are suffering from human-induced degradation, mainly due to overgrazing and cultivation. Recent studies on the dynamics of the natural vegetation show a reduction of the steppe areas, a change in their floristic composition and a drop in rangeland productivity (Mahyou et al. 2016). The overgrazing impacts the floristic composition, causes a decrease in the perennial vegetation cover and the development of invasive plant species (Dutilly-Diane 2006; Mahyou et al. 2016).

This already precarious situation worsens during periods of severe drought where significant forage deficit is observed. Faced with this situation of continuous degradation, it is essential to develop methods for accurate estimation of the phytomass in the Moroccan rangelands, in order to quantify the fodder availability for livestock and ensure the sustainability of the resource. The use of remote sensing data has become the most effective approach to phytomass estimation (Bella et al. 2004; Baeza et al. 2010; Jia et al. 2016). Indeed, traditional methods have been shown to be incompatible with monitoring of phytomass change in rangelands as they are often time-consuming, complicated to archive and diffuse, and updating them is always a difficult and costly operation.

Vegetation indices reflect, among others, the photosynthetic activity of the vegetation and are therefore increasingly used to remotely monitor rangeland phytomass (Jin et al. 2014). Despite the importance of rangeland in North Africa, research on rangeland phytomass estimation by remote sensing data is lacking.  

The general objective of this study is to assess the productivity of arid rangeland of Morocco through the use of remote sensing. In a first part, we compare the predictive power of various vegetation indices and biophysical indicators derived from low (eMODIS, 250 m x 250 m per pixel) to high (LANDSAT and Sentinel 2, 30 m x 30 m per pixel) to assess rangeland phytomass. In a second phase, we apply that model to study the evolution of the rangeland vegetation cover through time and identify areas characterised with critical vegetation cover degradation.

References

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