Urbanization is a landscape transformation process that is manifested by spatial expansion relative to human development. The present study aimed at the characterization of the spatio-temporal dynamics of Niamey city over the past 38 years (1975-2013) through a diachronic analysis of Lands at satellite images and application of landscape ecology principles. It sought to: (i) analyze the spatiotemporal pattern of land use land cover change of Niamey city and (ii) identify the driving forces for the land use land cover change in Niamey and their implications. Thirteen LULC classes were identified and grouped into three broad categories namely “Built-up area”, “Agricultural zone” and “Vegetation area”. The “Agricultural zone”, more specifically the class "Rain-fed farmland" represent the landscape matrix (over 37% of the landscape) throughout the period considered for the study. “Built-up area” dominated by “suburb quarter” experienced its lowest expansion rate during the interim period T2 (1989-1999).Analysis of the landscape spatial structure and configuration revealed that the landscape is fragmentation and highly heterogeneous. In general, urbanization in Niamey could be characterized by progressive densification and sprawl along communication lines. Key words: Urban dynamics, landscape indices, remote sensing, Niamey, land use land cover.

The increasing severity of Striga gesnerioides attacks on cowpea across West Africa has been related to its prolificity, seed mobility and longevity, and adaptation to aridity, in a context of agricultural intensification. To understand this fast extension, we analyzed (1) the distributions of the crop and the witchweed with ecological niche modeling and multivariate climate analysis, and (2) the chronological information available from collections and the literature. The ecoclimatic envelope of S. gesnerioides attacks on cowpea is the same as on wild hosts. Consistently, the modeled distribution of cowpea infestations is closely similar to the simple superposition of the parasite model (involving all hosts) and the crop model. Striga gesnerioides infestations are restricted to the driest component of the cultivated cowpea ecoclimatic niche, corresponding to the Sahelian and Sudano-Sahelian belts and the Dahomey gap. Thus, the parasite distribution, determined by its own requirements, does not constrain cowpea cultivation under Guinean climates. The spatial and temporal distributions of S. gesnerioides field infestations are consistent with an earlier impact on cowpea production in eastern West Africa, related itself to a similar trend in cowpea cultivation intensification from Niger, Nigeria and Benin to Burkina Faso and Ghana. Mali and Senegal were affected later, and literature reports of Senegalese strains of S. gesnerioides from the wild developing virulence on cowpea offer a model for the diffusion of witchweed parasitism by multilocal evolution, through host-driven selection, instead of epidemic diffusion. A contrario, in Côte d’Ivoire, cowpea is much less widespread, so the parasite has remained confined to the wild compartment. Thus, both historical and ecogeographic analyses refute the vision of S. gesnerioides as an invader. Instead, they point to the increasing importance and intensification of the crop, and the consequent loss of biodiversity, as the main drivers of the extension and diversification of its crop-specific strains.

Tendances évolutives des paysages semi-arides anthropisés au Niger: cas des communes rurales d’Aguié, Tchadoua et Gangara (Région de Maradi)

Land degradation is a major issue in the Sahel region. Numerous investments have been made in implementing sustainable land management (SLM) actions to reverse land degradation. Our work aims to (i) describe the variety of degraded land reclamation actions (DLRAs) and (ii) map the stakeholders acting in Niger. A time series (2008–2021) of georeferenced public data was collected and organized using a harmonized nomenclature. The results show that about 279,074 ha could be analysed in our study. Dug structures are the most widespread technique, while treated land is mostly devoted to single agricultural or pastoral uses. DLRAs are unevenly distributed in the Niger. More than 100 stakeholders were part of the effort to restore degraded land in the country—some playing a specific role, while others, such as the Government of the Niger, were responsible for mobilizing funds for implementing sustainable land management programs, while also carrying out certain programmes of their own. Our study points out the added value of creating a geolocalized dataset and, in future, a spatialized database management system to (i) deploy targeted sustainable land management actions complementing past and ongoing actions and (ii) create synergy between all the stakeholders.

The study aimed to analyze the process of Landuse/Landcover change of two rural communes (SaéSaboua and Chadakori) of Maradi region (Republic of Niger) over the past 28 years (1986 – 2014),through landscape structure analysis by diachronic cartographic approach and landscape indices. Mixedclassification of temporal series of Landsat images led to identifying six Landuse/Landcover (LULC)classes, namely ”cultivated land under shrubs and trees”, ”cultivated land under trees”, “continuouscropland”, ”fallow/pasture land”, ”forest reserve”, and ”settlement”. The composition and structure ofthe studied landscapes have greatly changed from 1986 to 2014. The class ”cultivated land under trees”was the landscape matrix in 1986 with 38.65% of landscape total area but in 2001 and 2014 the class”continuous cropland” became the landscape matrix. The changes also affected the ”forest reserve”which was transformed to smallholder agricultural land from 1986 to 2014. The area occupied byclasses ”cultivated land under trees” changed from 38.65% in 1986 to 8.78% in 2014; and from 1986to 2014, the area occupied by ”fallow/pasture land” has decreased of about 16%. The decrease in theseclasses was in favor of ¨continuous crop land¨, ¨settlement¨ and “cultivated land under shrubs and trees”which respectively gained 38%, 0.3% and 8.15% of their areas in 1986. The results of this study reflectthe problem of access to land and even land saturation in semi-arid region, a consequence of strongpopulation growth. They also contribute to a better rethinking of agricultural practices in order to initiateadaptation and resilience strategies for the population facing food insecurity and poverty.