; BP 223 Niamey ; Tel (00227) 98 88 99 98 RESUME Les forêts classées de Dan kada Dodo et Dan Gado, constituant le complexe forestier d'une superficie 11630 ha, sont situées dans la région de Maradi au centre-sud du Niger. La présente étude vise à caractériser la végétation ligneuse de ce complexe forestier sur le plan de sa composition floristique et de sa structure. Les données ont été collectées au moyen des relevés floristiques, de mesure du diamètre à 1,30 m pour les arbres et par le comptage des individus à diamètre < 5 cm dans 288 placettes de 20 x 20 m. Les indices de diversité ont été calculés sur la base des fréquences spécifiques. L'analyse a mis en évidence une faible richesse floristique avec 31 espèces ligneuses appartenant à 15 familles dont les plus dominantes sont les Mimosaceae (24,24%) et Combretaceae (15,15%). Les microphanérophytes sont plus abondants (94,24%), marquant le caractère arbustif de la végétation du complexe forestier. La chorologie de la flore est caractérisée par des espèces à distribution Soudano-Zambézienne (59,5%) suivies des Soudaniennes (31,8%). La faible densité des ligneux (425,19± 08 individus/ha) serait due entre autres aux conditions climatiques précaires et à la pression des populations riveraines. La structure diamétrique s'ajuste à la distribution de Weibull et montre une prédominance des individus jeunes.

Pterocarpus erinaceus is a native tree species of the Guineo-Sudanian and Sudano-Sahelian zones where natural stands are under constant pressure and heavily exploited for timber, animal feeding and others uses. A part from the overexploitation, climate change could also become a serious threat to the species natural distribution. For that purposes, this study aims to assess the vulnerability of P. erinaceus potential niche to climate change within its natural distribution area in West Africa. Niche predictions are based on 6,981 natural occurrence of the species and 19 global bioclimatic variables available through WorldClim. The future niche of the species is predicted according to three concentration pathways (RCPs 2.6, 4.5 and 8.5) of BC model for 2050 and 2070, thanks to Maxent software. P. erinaceus is currently reported from Senegal to Cameroon. Its potential niche covers the Sudano-Sahelian zone and the Dahomey gap on approximately 17.42% of the total area of these countries. In general, the niche of the species is not sensitive to climate change, regardless of the climate scenario and the year. Compared to its initial niche, the niche of the species will increase from 22.33% to 43.61% in 2050 and from 27.12% to 53.61% in 2070. However, this ecological expansion observed mainly in the Gulf of Guinea, will be associated with a considerable decrease in the Sahel and central Nigeria. This study shows the importance of promoting the development of innovative silvicultural strategies for the extension and restoration of natural stands of P. erinaceus in order to meet sustainably the timber needs of the West African region. It helps also to strengthening the roles of natural forests in providing ecosystem services and mitigating climate change effects.

Structure des peuplements naturels de Pterocarpus erinaceus Poir.dans le domaine soudanien, au Niger et au Burkina Faso erinaceus augmente de manière significative (P < 0,003) de la zone sahélo-soudanienne à la zone soudano-guinéenne : 1,2 ± 0,7 pied/ha dans la zone sahélo-soudanienne ; 2,6 ± 2,2 pieds/ha dans la zone nord-soudanienne ; 6,1 ± 4,6 pieds/ha dans la zone sud-soudanienne ; 15,0 ± 1,1 pieds/ha dans la zone soudano-guinéenne. L'analyse des structures en diamètre et en hauteur révèle une augmentation de la fréquence des individus jeunes suivant le gradient pluviomé-trique. Par contre, l'intensité de l'exploitation est plus élevée dans les zones les moins arrosées, où l'espèce s'avère menacée.B o i s e t f o r ê t s d e s t r o p i q u e s , 2 0 1 5 , n° 3 2 5 ( 3 ) PTEROCARPUS ERINACEUS 71 B o i s e t f o r ê t s d e s t r o p i q u e s , 2 0 1 5 , n° 3 2 5 ( 3 )

Pterocarpus erinaceus Poir (Fabaceae) is an endemic, highly exploited and threatened plant species in arid and semi-arid zones of West Africa. This study was conducted at the sub-regional level across three countries, namely Burkina Faso, Niger and Togo. These countries represent a spatial ecological gradient of P. erinaceus distribution to collect information on population structure and silviculture operating standards that could guide the industry, ensure species regeneration and establish appropriate management strategies for the species. Data were collected in P. erinaceus populations by means of forest inventories. Results showed that the average tree density was 1.17 ± 0.75 trees/ha in the Sahelian zone, 49.20 ± 63.2 trees/ha in the Sudanian zone and 110.9 ± 1.15 trees/ha in the Guinean zone. The average stem diameter values were 26.63 ± 7.89 cm (Guinean zone), 29.02 ± 15.44 cm (Sudanian zone) and 49.63 ± 19.44 cm (Sahelian) with noticeable variability (CV = 53.6%). Significant differences for these parameters were noted between the zones (P b 0.001). The average total height in the populations of the Sudanian zone (9.51 ± 2.75 m) were significantly less (P b 0.001) than in the other two zones (10.18 ± 2.27 m for the Sahelian zone and 14.16 ± 2.88 m for the Guinean zone). The merchantable heights were between 4.08 ± 1.35 m (Sahelian zone) and 3.63 ± 2.63 m (Guinean zone) and varied significantly from one zone to another (P b 0.001). The distribution of trees in diameter classes varied depending on the climate zone: modal distribution with most classes ranging from 30-65 cm in the Sahelian zone and 15-45 cm in the Sudanian zone and an "L" model distribution in the Guinean zone (most classes ranging between 10 and 25 cm), while the distribution of height classes showed a modal form for all climate zones. Two minimum diameters of exploitation (MDEs) could be determined: 35 cm for the Guinean and Sudanian zones (P = 316.6% and P = 53.4%, respectively) and 65 cm for the Sahelian zone (P = 111.9%) for a rotation period estimated at 20 years for all the climate zones.

The present work was launched to assess the floristic composition and structure of the native forest food species in order to tackle malnutrition. It was carried out in four natural forest from villages in two agro-ecological zones (two villages per agro-ecological zone) in southern Mali. In each natural forest, data were collected in 10 plots of 50 x 50 m using sampling systematic to one degree. In each plot, all tree were measured. Dendrometric data were collected on each tree (diameter at breast height or d.b.h and total stem height). In each plot, the total number of seedlings (diameter at breast height < 3 cm) was carried out within five 25 m² plots using sampling systematic to two degrees. The inventories were recorded 89 native forest species belonging to 73 genera and 30 botanical families. Native edible species were represented 34.83% of the overall inventoried species. Significant differences were observed between natural forest for average density per hectare, average height and average basal area. The high density was observed in Badogo (71 trees.ha -1 ), while the less in Sorobasso (24 trees.ha -1 ) which present the high regeneration rate (2.88%). The analysis of population diameter structures for Saba senegalensis, Vitellaria paradoxa, Lannea acida, Lannea microcarpa, Lophira lanceolata, Parkia biglobosa and Borassus aethiopum showed variable trends. Domestication and vegetative propagation strategies of the species are needed to ensure the availability of the resource to combat malnutrition.

Pterocarpus erinaceus is an endemic and threatened plant species in arid and semiarid zones of West Africa and is highly exploited for timber, animal feeding, and various medicinal uses. The species is currently native to the Guinean forest-savannah mosaic ecoregion and reported from Senegal to Cameroon. The values of the main characteristics of the P. erinaceus forest stands (density, average diameter, average height and average stem height) vary significantly (P < 10−3) from the Guinean zone to the Sahelian zone. It has high technological performance and can be classified as heavy and very hard wood with a density of the order of 0.80 ± 0.07 g/cm3 and an average hardness of 12 ± 3.7 g/cm3. The species is the subject of large-scale international traffic between West Africa and Asia, which is by far the greatest threat to the species. The various uses induce repeated mutilation and increase pressures on the species resulting in a significant reduction in its natural populations. In response to this situation, measures are proposed, including large-scale plant production strategies, the definition of minimum felling diameters, policy measures, etc., to meet the restoration needs of natural stands of P. erinaceus and the fight against climate change.

Pterocarpus erinaceus (Poir) is currently the most exploited and threatened spontaneous tree species in the Guinean-Sudanian and Sudano-Sahelian zones in West Africa. This work analyzed the density and color parameters of P. erinaceus wood in the phytogeographic zones (Sudanian, Guinean and Sahelian) in three countries in West Africa (Togo, Burkina Faso and Niger). The results obtained by studying 451 specimens taken from 95 trees showed significant differences in basic density and color parameter values (P < 0.001) based on phytogeographic zones. Individual tree samples from the Sahelian zone were denser (780 ± 63 kg · m − 3), darker (L* = 48.3 ± 0.6) and redder (a* = 8.2 ± 2) than those in the Guinean zone (basic density = 684 ± 53 kg · m−3; L* = 59.7 ± 0.5; a* = 6 ± 0.2) and the Sudanian zone (basic density = 725 ± 70 kg · m−3; L* = 53.7 ± 0.40; a* = 7.30 ± 0.2). At intra-tree scale, the results did not show a significant variation of basic density according to the number of rings counted from the pith (P > 0.05). This indicated that the age of the trees has little influence on the basic density of P. erinaceus wood.

The commune of Dantchandou is one of the main sources of wood supply in western Niger, causing a disorganization of the structure and composition of the landscape. The objective of this study is to evaluate the impact of cultivation, pasture, fallow land and the influence of the villages on the dynamics of the plant communities of the commune of Dantchandou. The data were collected in the different land use and land cover units (flat, slope, depression and foot of the plateaus). Plots of 50 m x 20 m were set in each sampling site taking into account the homogeneity of the vegetation in order to avoidedge effect. Thus, for the characterization of the vegetation, three transects were retained. A total of 76 surveys were conducted. Our results show an inventory of 151 plant species including 125 herbaceous species and 26 woody species distributed among 101 genera and 28 families. In fields and fallows 106 species were recorded which belong to 81 genera and 23 families. In the fallows the floristic composition is of 58 species from 47 genera and 17 families. On the plateaus 111 species belong to 24 families were recorded. The Shannon diversity index is higher in fallows with 5.16 bits followed by fields with 5.08 bits and finally on plateaus with 5.05 bits. This landscape diversity is linked to the different types of land use, shorter fallow periods, expansion of agrosystems, overgrazing resulting in the substitution of indigenous species by invasive species.