Characterisation of the woody flora in sites developed on the plateau and slope of the Satara land reclamation site for sylvo-pastoral purposes (Simiri/Niger commune)

Introduction

Niger is a Sahelian country that has been experiencing a decline in its plant and wildlife resources for decades, as a result of land degradation (Larwanou, 2005) [1] . This degradation has been spectacular since the 1970s, following the disappearance of the plant cover that protected the soil (Zoubeirou and Karim, 1997) [3] . Cultivated land, grazing land and forests are among the resources most affected (Moussa et al., 2024) [3] . The Tillabéri region (western Niger) is one of the areas that has suffered most from land degradation. In the past, this region had enormous forest resources, including tiger bush. The biodiversity of the latter has been significantly reduced by the droughts of the 1970s and 1980s and by human activities (Moussa et al., 2022; Vieri et al., 2014) [4,5] . The consequences include the degradation of vegetation cover, the appearance of glacis, the silting up of watercourses and a fall in agricultural yields, in a context of demographic growth (Vieri et al., 2014; FAD, 2008) [5,6] . It should be emphasised that these consequences further weaken people's resilience to shocks, including food insecurity. In view of the growing vulnerability of populations, a number of techniques have been developed for reclaiming agro-sylvo-pastoral land. Commonly known as Water and Soil Conservation/Soil Defence and Restoration (CES/DRS) techniques, these promote, among other things, the regeneration of plant cover, water infiltration and improved soil fertility (Laminou et al., 2020; Moussa et al. 2025) [7,8] . The results of these CES/DRS techniques are highly variable in space (Douma et al., 2011; Amani et al., 2021) [9,10] . It is in this context that the present work was carried out with a view to studying woody vegetation in two different components of a landscape unit. The aim was to assess the woody flora at the top and on the slope of the Satara plateau in western Niger.

Materials and Methods

Study area and sites

The rural commune of Simiri is the study area (Fig 1). The main town of the commune is located 78 km from Niamey (the capital of Niger). The area is characterised by the landscape units (plateaux, sandy skirts, glacis and lowlands) that characterise western Niger (Ambouta et al., 1996) [11] . On the plateaux, regosol and lithosol soils formed on clayey sandstone from the Continental Terminal are found (Ambouta, 1997) [12] . The soils of the sandy skirt and glacis are of the tropical ferruginous type with little leaching. Alluvial soils are found in the lowlands (Moussa et al., 2013) [13] . The climate is Sahelian, with annual rainfall ranging from 200 to 400 mm (Laminou et al., 2020) [7] .

Study of ligneous vegetation

The inventory was systematic and covered planted and spontaneous woody species in land reclamation techniques crossed by transects. The dendrometric parameters measured were height, trunk diameter at 20 cm and 1.30 m and crown diameter (Fig 4). All woody species with a diameter of less than 1.3 m were considered to be young regenerations. One (1) control site was identified in each geomorphological unit, in which a 50 m x 40 m plot was set up for the various observations. Four (4) to three (3) 100 m x 100 m plots were set up in each layout to assess the survival rate of planted woody plants.

Estimation of carbon stock

The determination of the amount of carbon present in the different tree components was done based on the allometric equations of FAO (1997) [14] and adapted according to the carbon stock models for the different tree components by Boulamane et al. (2013) [15]. The carbon stock models for the different tree components are:  Trunk SCTr = 191 x (D2H);  Branc SCBr = 46 x (D2H);  Leaf SCF = 5,4 x (D2H); D: diameter at 1.30 m; H: tree height; D and H in metres; SCTr: carbon stock in the trunk; SCBr: carbon stock in the branches and SCF: carbon stock in the leaves.

Results

Floristic composition of ligneous plants

The inventory of woody vegetation revealed 9 species in six ( 6) families (Table 1). On the developed sites, the dominant families in terms of number of species and specific contribution were Mimosaceae, Caesalpiniaceae and Combretaceae. The species Acacia senegal and Guiera senegalensis are present in all the managed sites. The species present in all the control sites (reference site) is Guiera senegalensis.

Frequency and specific contribution of woody plants

Planted species are the most common. They represent an average specific contribution of 71.08%. This specific contribution is 48.25% for Acacia senegal and 20.02% for Eucalyptus camaldulensis (Table 2).

Wood density

The density of woody plants varies from one site to another and from one species to another (Table 3). With a density of 1,301 plants per ha, the site on the slope has the densest vegetation. This high density is the result of the strong presence of the species Guiera senegalensis, which has a density of 872 plants/ha. www.extensionjournal.com

Survival rate and woody cover

The survival rate of the woody species planted, the average cover and the auger area vary from one site to another. The survival rate of species planted on the plateau is lower than that of species planted on the slope (Table 4). On the other hand, the average cover and basal cover are greater in the site planted on the plateau.

Height and diameter of woody plants

The average height, average trunk diameter and average crown diameter of woody plants on the plateau site are the highest (Table 5). The average height and trunk diameters at 20 cm of the woody plants on the slope were the lowest. However, one of the sub-sites on the slope has ligneous plants whose height makes it possible to measure the various trunk diameters.

Distribution of woody individuals in height classes

The height class of less than 1 m dominates on all the sites (

Carbon stock in woody plants

It was found that a tree stored an average of 7.65 kg of carbon in its aerial part in the site developed on the plateau (Table 6). This is the site that stored the most carbon because of the volume of woody individuals and its large surface area.

Discussion

The inventory of woody species revealed a rich flora of nine (9) species divided between six (6) families, dominated by the Mimosaceae family. Planted and volunteer species numbered five (5) and four (4) respectively. The species Acacia senegal was planted in all the sites recovered. It is complemented by Eucalyptus camaldulensis on the plateau and Bauhinia rufescens, Prosopis juliflora and Ziziphus mauritiana on the slope. Acacia senegal and Guiera senegalensis are present in all the restored sites. The specific contribution of Guiera senegalensis was 100% in the control site on the slope. The presence of this species in this untreated area proves that Guiera senegalensis is a resilient species. These results are similar to those of Gagara (2009) [16] , who found 14 species belonging to eight (8) families dominated by Mimosaceae on the sylvo-pastoral half-moons (in Niger). This dominance of Mimosaceae has been confirmed by other studies carried out in the Sahelian zone, in particular by Ganaba (2005) [17] , on the impact of water and soil conservation schemes on the regeneration of woody resources in the Sahelian region of Burkina Faso, Salifou (2018) [18] in the Chadakori zone (Maradi/Niger) and Mohamed (2008) [19] in the Sudano-Sahelian zone of Senegal. The indigenous species Guiera senegalensis has a specific contribution of 80% (on the embankment), clearly higher than that of Acacia senegal, Prosopis juliflora and Ziziphus mauritiana, which are planted species. The spontaneous species Guiera senegalensis, which regenerates on the slope, would be favoured by the development work (trench) and the texture of the soil. Piliostigma reticulatum and Boscia senegalensis are found on the plateau and Combretum micranthum on the slope. The success rate (survival rate) of the woody species planted in the trenches (site developed on the slope) corresponds to 69.75%. These results differ from those found by GIZ (2012) [20] , which obtained a survival rate of 60% in the trenches. The success rate obtained on the plateau is 59.12%. This result is comparable to that found by Salifou (2018) [18] . The 59.12% survival rate on the plateau (Eucalyptus camaldulensis species in benches) is similar to that obtained by Noma (2018) [21] on the same plateau, but lower than that found by Laminou et al. (2020) [7] , which is 64.44% in the Simiri zone. In terms of density, the site developed on the plateau recorded a low value, which can be explained by the frequency with which wood is periodically cut on this site. Acacia senegal and Eucalyptus camaldulensis are the most densely planted species, with densities of 223 and 36.5 trees/ha respectively. With the exception of the Guiera senegalensis species on the slope, all the planted species have a higher density than the spontaneous species. The average density (170.5 plants/ha on the plateau) is lower than those obtained by Blamah (2004) [22] and Ganaba and Kiema (2000) [23] , who obtained 209 plants/ha and 230 plants/ha respectively in the Sahelian region of Burkina Faso. As regards dendrometric parameters, in general, the heights of the species present in the managed sites are greater than those in the control sites. For the height class below 1 m, Acacia senegal and Boscia senegalensis dominate, and are respectively spontaneous and planted species. In the same height class, Guiera senegalensis is more important at all sites. The carbon stock stored by woody vegetation on the plateau site was estimated at 11,439.23 kg. This quantity is greater than that of the slope, which is 5,888.5 kg. The quantity of carbon sequestered is practically negligible in the control sites.

Conclusion

At the end of this study, it emerged that the development had had positive effects on the return of woody flora. This was reflected in an improvement in the richness of the flora, plant cover, spontaneous regeneration, particularly on the slope, and ecosystem services such as wood production and carbon storage. Dominated by the species Guiera senegalensis, spontaneous regeneration is much more important on the slope than on the plateau. In terms of carbon stock, the site developed on the plateau recorded the highest stock due to the greater volume of woody individuals and surface area than the site on the slope. The better survival rate obtained on the slope is due to the texture of the soil and the type of structure. The development of the plateau (summit and slope) makes it possible to regenerate ecosystem services, which will be progressive if the site is well maintained and used.

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