Évaluation de l'impact du changement climatique sur l'agriculture

Cet article présente une revue des études d'impact des changements climatiques sur l'agriculture au Maroc, réalisées à l’INRA. Il montre que la pluviométrie a diminué d'environ 25% depuis 1980 et que les températures ont augmenté. Des analyses fréquentielles ont été réalisées pour évaluer les changements climatiques passés et les probabilités d’occurrence de la sécheresse. Des projections climatiques basées sur les scénarios du GIEC montrent que les températures augmenteront et les précipitations diminueront au 21ème siècle, réduisant la longueur de la période de croissance des céréales et les rendements. L'étude de l'impact sur l'aptitude des terres à la céréaliculture prévoit aussi une réduction des zones aptes, notamment dans les plaines atlantiques. L'article décrit ensuite les mesures d'adaptation, telles que les Mesures d’Atténuation Appropriée au niveau National, l'agriculture climato-intelligente et des projets prioritaires identifiés dans ce cadre comme le soutien à l'agriculture de conservation. L'agriculture de conservation et la réintroduction des légumineuses alimentaires dans les rotations sont des pratiques clés pour renforcer la résilience. La gestion des risques climatiques est également cruciale, d'où le développement par l'INRA du système CGMS-Maroc de prévision des récoltes. Ces résultats soulignent la vulnérabilité de l'agriculture marocaine et la nécessité de renforcer l'adaptation

Improvement of vegetation condition and soils fertility in the arid rangelands of Morocco by restoration and rehabilitation techniques

L’amélioration de l’état de la végétation et de la fertilité des sols est une préoccupation majeure pour une réhabilitation réussie dans les parcours dégradés. Cette étude examine l’impact de la mise en repos, de la technique de conservation de l’eau et du sol (CES) et de la plantation fourragère sur le recouvrement de la végétation, la phytomasse, la valeur énergétique de la phytomasse (UF.ha-1), le pH, la matière organique (MO), le phosphore assimilable (P), le calcaire total (CaT), le potassium échangeable (K), le sodium échangeable (Na) et la conductivité électrique (CE) dans cinq sites différents. Les résultats montrent que ces techniques permettent de restaurer les parcours steppiques en induisant une dynamique positive de la végétation et du sol. Ainsi, la mise en repos, la technique de CES et la plantation d’Atriplex nummularia ont entraîné une accumulation de la matière organique dans les sols et ont amélioré le recouvrement, la phytomasse et la valeur énergétique de la végétation avec des valeurs allant jusqu’à 85 %, 2,84 t.ha-1 et 931 UF.ha-1 respectivement. Par contre, le site en pâturage libre est marqué par une phytomasse inférieure à 0,31 t.ha-1, correspondant à une valeur énergétique inférieure à 46 UF.ha-1, et par un recouvrement végétal inférieur à 6 %. Ce site est marqué aussi par des taux du sodium échangeable (Na) et de conductivité électrique (CE) élevés avec des valeurs moyennes de 463,65 mg.kg-1 et 4,66 mS.cm-1 respectivement.Improving vegetation condition and soil fertility is a major concern for successful rehabilitation in degraded rangelands. This study examines the impact of fencing, water and soil conservation technique (CES) and fodder shrub plantations (Atriplex nummularia) on vegetation cover, phytomass, energy value of phytomass (UF.ha-1), pH, organic matter (MO), available phosphorus (P), total limestone (CaT), exchangeable potassium (K), exchangeable sodium (Na) and electrical conductivity (EC) in five different sites. Results show that these techniques can restore the rangeland steppe by inducing a positive dynamics of vegetation and soil. Hence, fencing, CES and Atriplex nummularia trained an accumulation of organic matter in soils and they improved cover, phytomass and energy value of vegetation until 85 %, 2.84 t.ha-1 and 931 UF.ha-1 respectively. On the other hand, the free grazing site is marked by a phytomass less than 0.31 t.ha-1 corresponding to an energy value less than 46 UF.ha-1 and a global cover less than 6 %. This site is also marked by high levels of exchangeable sodium (Na) and electrical conductivity (CE) with average values of 463.65 mg.kg-1 and 4,66 mS.cm-1 respectively

Application de la geomatique pour l'evaluation des ressources pastorales au Maroc

Rangeland or natural arid pastures of Morocco are defined as ecosystems where there is a natural or semi-natural vegetation composed of steppes, shrubs and grassland used mainly for livestock production as climate and soil are unsuitable to agriculture. The arid rangelands of Morocco occupy an area of over 33 million hectares between the isohyets of 100 and 400 mm. These areas represent livelihoods for thousands of people and protect the country from desertification. The main objective of this study is to provide scientific community and decision-makers methodological tools for assessing arid rangelands, based on geomatics and biophysics data. This study is divided in four parts: 1. The first part presents an overview of the threat of the desertification, emphasizes on the causes and consequences of rangeland degradation in Morocco, from literature sources, statistics, climate data and maps. Morocco rangelands are located in ten different pastoral zones that differ from each other by their floristic composition, soil and climatic conditions. According to Globcover map these rangelands are mainly composed by bare soil, herbaceous vegetation, shrubs and deciduous savanna mosaic / shrub or forest. The largest pastoral zones are: the Saharan zone, Pre-Saharan, the Oriental plateaus and the Valley of Moulouya. These zones are the most degraded with respectively 97, 89 and 69% of their total area. Available information on several pilot areas shows that the Moroccan rangelands are degraded due to many factors, which include overgrazing, cultivation, population increase and climate variation. 2. The second part of the study demonstrates the usefulness of remote sensing for assessing drought in arid rangelands of Morocco. Bi-weekly TERRA Moderate Resolution Imaging Spectroradiometer (MODIS 250 meters) data were used for this purpose. A Preliminary mapping by using Landsat TM5 of major land cover types was carried out to extract the pasture area. A comparison of annual and seasonal Normalised Difference Vegetation Indices (NDVI), Vegetation Condition Index (VCI) and rainfall during the time period of 2000–2008 were carried out. Results show significant correlations of either NDVI (r= 0.72**) or VCI (r=0.42*) with past season (3 months) rainfall. NDVI variation is a good indicator of vegetation changes and consequently can give a reliable indication on drought conditions in the study area. NDVI values lower than 0.2 are indicative of drought occurrence. NDVI values between 0.20 and 0.28 indicate average weather conditions and values higher than 0.28 correspond to humid conditions. 3. The third part presents an original knowledge-based approach for mapping the degradation of rangelands in North Africa. The study area is located in the high plateaus of eastern Morocco which include 3.5 million hectares of arid rangeland steppes. The approach consists in using datasets derived from Landsat TM satellite imagery, lithology, phytogeographic data and field indicators. The field indicators are: the steppes composition, perennial vegetation cover, annual perennial production, grazing level and the prevalence of rangeland cultivation. Results show that the knowledge-based approach is a valid method for evaluating rangeland degradation. The proposed knowledge-based approach discriminated between rangeland categories that would not have been discernible using only remote sensing. Overall classification accuracy of rangeland degradation obtained using this approach was 93%. This approach revealed that 11, 36 and 30% of the study area have shown very severe, severe and moderate degradation level, respectively. 4. The fourth part concerns the assessment of Alfa grass (Stipa tenacissima) tussocks at various degradation levels of Alfa grass steppes in the high plateaus of eastern Morocco, based on field hyperspectral data (350 – 2500 nm) and digital images during fall and spring seasons. Digital images of Alfa grass tussocks were taken using a digital camera to classify of the tussocks according to their proportion in green leaves (green, mixed and dry tussock). Assess software (Image Analysis Software for Plant Disease Quantification, APS 2002) was used to obtain the proportion of greenness in each tussock. Hyperspectral data of three states of tussocks (Green, Mixed and Dry tussock leaves) were collected within three degradation levels of Alfa grass steppes (Slight, Moderate and Severe degradation) with the ASD FieldSpec® 3 spectroradiometer. Paired t-test, Normalized difference spectral reflectance (NDSR) and Stepwise Discriminate Analysis were used to discriminate between various tussock status and different Alfa grass steppes. The results indicate that Alfa grass had shown an intraspecific variability in reflectance spectra. The proportion of green leaves in Alfa grass tussock strongly influences the spectral response. The discrimination of different Alfa grass tussock status was better during fall than spring. The spectral behavior of Alfa grass tussock is problematic for the mapping and the assessment of Alfa grass steppes by conventional remote sensing techniques

Monitoring of the dynamics of the natural resources by the geomatic in Morocco

Drylands cover about 40 % of Earth’s land surface and are inhabited by more than 2 billion people who depend mainly on the exploitation of these dryland ecosystem natural resources. However, it is largely recognized that these areas are threatened by the desertification. Desertification is associated with biodiversity loss and contrib-utes to global climate change. In spite of the importance of this phenomenon, it is surprising that there is no consensus on an appropriate method to assess this degradation process. One part of the literature announces catastrophic statistics on the rate of desert extension and surface affected. Others, doubt about the methodology used by these first studies and do not find any obviousness of such an extent of desertification. The overall goal of our study is to develop remote sensing based indicators and models for the assessment of desertification in drylands. For this purpose, the monitoring of vegetation and soil is based on information resulting from the remote sensing and the biophysics data. Hyperspectral (field and remote sensing) and biophysics parameters will be established for the study area through large field campaigns combined with HR-remote sensing data. The Land Cover will be mapped using the Landsat TM images in conjunction with measurements of vegetation parameters such as biomass and vegetation cover. Hyperspectral reflectances of the vegetation and soil inside the study zone will be measured by a Spectroradiometer. Each site will be located by Global Positioning System (GPS). Several RS vegetations indices appropriate for rangeland will be studied and others will be developed. Regression analyses, between the different vegetation indices retained by remote sensing and the biophysics data will be carried out so as to establish a spatio-temporal model linking these indices to the vegetation parameters. This research has started in November 200

Utilisation d'un système expert pour la cartographie de la dégradation des parcours arides

Desurvey projec

Belgique

This study aimed at investigating the potential of vegetation indices and precipitation-related variables derived from remote sensing to assess rangeland production in the arid environment of the Moroccan Oriental region and identifying the challenges linked to that particular biome. Vegetation indices (VIs) and the Standardized Precipitation Index (SPI) computed at various aggregation periods were first integrated into a Random Forest model. In a second step, we studied in more detail the linear relationship between rangeland biomass and one of the spectral indices (ARVI) for the various vegetation formations present in the area. We concluded that, mostly due to the presence of alfa steppes (Stipa tenacissima), and especially to a large proportion of non-photosynthetic vegetation, it is not possible to accurately estimate rangeland production with a global model in this region. We recommend separating Stipa tenacissima from the other species in models and focusing on methods aimed at studying dry and non-photosynthetic vegetation to improve the quality of the prediction for alfa steppes

Phytomass estimation using eMODIS NDVI and ground data in arid rangelands of Morocco

The assessment of rangeland productivity in semi-extensively grazed arid rangelands is a prerequisite for livestock management in relation to sustainable use of pastoral resources. The objective of this study was to assess rangeland productivity based on normalised difference vegetation index (NDVI) images. Data on phytomass were measured on 61 field samples in arid rangelands of Morocco, covering various rangeland categories during autumn (November) and spring (April), i.e. when phytomass is at low and high levels, respectively, for two consecutive years (2008 and 2009). Dekadal EROS Moderate Resolution Imaging Spectroradiometer (eMODIS) NDVI data were linearly regressed to field measurements for these four periods. Results show that phytomass values were correlated with NDVI during spring, with R 2 and RMSE values of 0.82 and 0.3 t ha−1, respectively. This study indicates there is a high potential for operational use of remotely sensed data to estimate rangeland phytomass of semi-extensively grazed rangelands

Désertification des parcours arides au Maroc

Rangeland or natural arid pastures of Morocco are ecosystems where there is a natural or seminatural vegetation composed of steppes, shrubs and grassland. They cover about 82% of the Moroccan arid lands. These areas represent livelihoods for thousands of people and protect the country from desertification. Despite the importance of the rangelands and the threat of desertification, it is surprising that up to date there is no comprehensive assessment of their condition and their evolution, hindering any plan for desertification alleviation. However, the available information on selected pilot areas shows that these rangelands are threatened by desertification. It’s associated with biodiversity loss and contributes to climate change. The leading causes of land degradation are the human actions combined with climate. The establishment of a comprehensive surveillance system based on remote sensing, biophysics and socio-economic data must be envisaged to provide policymakers with an operational tool adapted to the spatio-temporal monitoring of desertification

A KNOWLEDGE-BASED APPROACH FOR MAPPING LAND DEGRADATION IN THE ARID RANGELANDS OF NORTH AFRICA

peer reviewedaudience: researcher, professionalRangelands cover about 82% of the arid area of Morocco. It is generally acknowledged that these areas are threatened by desertification. Monitoring desertification requires accurate knowledge about the current status of rangeland degradation. Remote sensing is widely used to assess changes in land cover, but its use in arid rangelands has limitations because of spectral confusion among various types of land cover. The objective of this study was to assess the severity and spatial extent of rangeland degradation in the high plateaus of eastern Morocco, using a knowledge-based approach combining remote sensing and ancillary data. This approach relies on analyzing datasets derived from Landsat TM satellite imagery, lithology, bioclimatic data and field measurements. The level of rangeland degradation was assessed using indicators such as vegetation parameters, grazing levels and cultivation intensity, which provided a high level of accuracy for mapping and monitoring the degradation of the arid rangelands. The results showed that the total area of degraded rangeland in the high plateaus of eastern Morocco is about 17,417 km², accounting for 48% in the studied area

Amélioration de l’état de la végétation et de la fertilité des sols des parcours arides du Maroc par les techniques de restauration et de réhabilitation

Improvement of vegetation condition and soils fertility in the arid rangelands of Morocco by restoration and rehabilitation techniques. Improving vegetation condition and soil fertility is a major concern for successful rehabilitation in degraded rangelands. This study examines the impact of fencing, water and soil conservation technique (CES) and fodder shrub plantations (Atriplex nummularia) on vegetation cover, phytomass, energy value of phytomass (UF. ha-1), pH, organic matter (MO), available phosphorus (P), total limestone (CaT), exchangeable potassium (K), exchangeable sodium (Na) and electrical conductivity (EC) in five different sites. Results show that these techniques can restore the rangeland steppe by inducing a positive dynamics of vegetation and soil. Hence, fencing, CES and Atriplex nummularia trained an accumulation of organic matter in soils and they improved cover, phytomass and energy value of vegetation until 85 %, 2.84 t. ha-1 and 931 UF. ha-1 respectively. On the other hand, the free grazing site is marked by a phytomass less than 0.31 t. ha-1 corresponding to an energy value less than 46 UF. ha-1 and a global cover less than 6 %. This site is also marked by high levels of exchangeable sodium (Na) and electrical conductivity (CE) with average values of 463.65 mg. kg-1 and 4,66 mS.cm-1 respectively.L’amélioration de l’état de la végétation et de la fertilité des sols est une préoccupation majeure pour une réhabilitation réussie dans les parcours dégradés. Cette étude examine l’impact de la mise en repos, de la technique de conservation de l’eau et du sol (CES) et de la plantation fourragère sur le recouvrement de la végétation, la phytomasse, la valeur énergétique de la phytomasse (UF. ha-1), le pH, la matière organique (MO), le phosphore assimilable (P), le calcaire total (CaT), le potassium échangeable (K), le sodium échangeable (Na) et la conductivité électrique (CE) dans cinq sites différents. Les résultats montrent que ces techniques permettent de restaurer les parcours steppiques en induisant une dynamique positive de la végétation et du sol. Ainsi, la mise en repos, la technique de CES et la plantation d’Atriplex nummularia ont entraîné une accumulation de la matière organique dans les sols et ont amélioré le recouvrement, la phytomasse et la valeur énergétique de la végétation avec des valeurs allant jusqu’à 85 %, 2,84 t. ha-1 et 931 UF. ha-1 respectivement. Par contre, le site en pâturage libre est marqué par une phytomasse inférieure à 0,31 t. ha-1, correspondant à une valeur énergétique inférieure à 46 UF. ha-1, et par un recouvrement végétal inférieur à 6 %. Ce site est marqué aussi par des taux du sodium échangeable (Na) et de conductivité électrique (CE) élevés avec des valeurs moyennes de 463,65 mg. kg-1 et 4,66 mS.cm-1 respectivement.Hachmi Azeddine, Andich Karim, Ezzahra El Alaoui-Faris Fatima, Mahyou Hamid. Amélioration de l’état de la végétation et de la fertilité des sols des parcours arides du Maroc par les techniques de restauration et de réhabilitation. In: Revue d'Écologie (La Terre et La Vie), tome 73, n°4, 2018. pp. 401-413