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Floristic Composition, Structural Analysis and Socio-economic Importance of Legume Flora of the Commune of Mayahi, Niger, West Africa

Floristic assessment plays a crucial role in managing and conserving phytodiversity. Thisstudy tried to determine the floristic composition, woody structure and socio-economic importance of the legume flora in the commune of Mayahi. We used plot method based on systematic sampling approach to inventory legume species within the parklands in September 2012. We recorded 55 legume species belonging to 24 genera in 56 relevés. Fabaceae is the dominant family among the legume botanical families in the parklands of the commune of Mayahi. The average woody legume density is 62 individuals per hectare in the commune of Mayahi. The woody legume species of highest average density are Faidherbia albida and Piliostigma reticulatum. While the total basal area of legumes of the commune is 1.12m2 / ha in the Mayahi commune. The crown cover varies according to the vegetation types but it is higher in the Goulbi N'kaba forest reserve. Legume flora provides a myriad of benefits to the people of Mayahi. The present study recommends furtherresearch that examines the impact of human activities on the legume flora of the parklands in the commune of Mayahi.


INTRODUCTION
Niger has four climatic zones climatic zones that have contributed to the formation of The Sudanian and Sahelo-Saharan environments characterized by a great biodiversity of both animals and plants. Niger covers a surface area of 1,267,000 sq km. It is located between the longitude 0°16' and 16° East and the latitude 11°1' and 23°17' North. Niger human population was estimated at 19.8 million people and a population growth rate at 3.9 % (World Bank, 2016). About 80% of its human population lives in rural areas where it derives various ecosystem services (INS, 2011).Indeed, vegetation changes is one of the greatest ecological problems in Niger. Niger' ecosystems are prone to the high pressure due to the high population expansion that exercises great demand such us the firewood, absence of fallow and expansion of agricultural lands to forest areas. In addition, the climate vagaries has also huge impact of vegetation in Niger. Added to that, ecosystems of Niger are prone to unsustainable management due to such as inappropriate agricultural practices, illegal and unsustainable logging activities and unsustainable pastoral activities (CNEDD, 2006).
Such practices lead to compositional and structural changes of vegetation and biodiversity loss, which would have huge impacts on the environment and socio-economic setup of the Niger communities. Legume species are known to be critically important in an ecosystem in terms of building and conserving soil fertility. Most legume species have nodules on the root systems, which enable them to absorb the atmospheric nitrogen and convert it into the nitrogen the plant needs for its development. Therefore, legume flora plays a crucial role in the ecological systems. For instance, in Niger, legume flora provides a myriad of benefits such as firewood, timber, fodder, melliferous, gun and food species, traditional medicine for human and animal (Hamidou et al., 2015 andSoulé et al., 2017).Legume species belong to the order of leguminosae that comprises three main botanical families such asCaesalpiniaceae, Fabaceae or Papilionaceae and Mimosaceae. Leguminosae is oneof the largest and most useful orders in the world. For instance, Bellefontaine(2005)  Botanical evaluation such as floristic composition, dendrometric analysis studies are important for providing information on species richness of the ecosystems, useful for the ecosystem management goal and help in apprehending ecology and functions of ecosystem (Pappoe et al., 2010). Data on the floristic composition and structure of ecosystem is also useful in managing sustainably the ecosystem (Addo-Fordjour et al., 2009).The aim of this study was therefore, to list the floristic composition and make structural analysis of the legume flora of the commune of Mayahi in Niger.

Study area
The commune of Mayahi is located in Maradi region of Niger republic. The commune of Mayahi has an estimated population of 94,160 inhabitants in 2011 (PDC, 2011).The commune of Mayahi has fifty nine (59) administrative villages and tribes. The capital of the commune is Mayahi. Agriculture is the principal economic activity of the people of the commune of Mayahi. Vigna unguiculata (cowpea) andArachis hypogaea (peanut) constitute the cash legume crops. Animal husbandry is the second economic activity of the people of the commune of Mayahi. One of the major vegetation types of the commune of Mayahi is parklands that consists of croplands and pasturelands with the scattered woody species. The people of the commune of Mayahi exploit many parklands services such as firewood, forage for livestock, food (fruits, leaves). They exploit the parklands for medicinal purposes. The climate of the commune of Mayahi is the Sahelian type, characterized by a short rainy season usually three to four months from June to September. The total amount of rainfall estimated in 2015 was 380.9 mm (DDA, 2015).The study sites were Mayahi urban commune, Digaba, Guidan Sani, Guidan Alou, Koren Habjia, Loda, Dan Amaria, Achalou, Kotaré, they were randomly selected.

Inventory Sampling design
The survey took place in September 2012, whichis the period of the maturity of herbaceous species in Sahel (Saadou, 1990). A systematic sampling technique was used due to the homogeneity of the landscape to collect vegetation data. Plots of size 50m x 50m (2500m 2 ) were used for woody species, one subplots of 100 m 2 (10 mx 10 m) at one corner of the main plot and subplots of 1m x1 m for herbaceous density at the four corners and one at the centre of the large plot. We constructed also five subplots at the angle and one at the centre of the large 5 m x 5 m for recording the seedlings.Plots were laid systematically at every 500m along transect lines, which were 500m apart from each other. Ringing pole, tape meter and GPS were used the fieldwork. All the plot sizes used correspond to the minimum areas for agroforestry systems and steppe (Mahamane & Saadou, 2008). The plots were shown in Figure 1.

Data collection
We did firstlySystematic counting of all the plant species in the subplot of 100m 2 and secondly in the large plot. Thirdly,we used destructive method for the herbaceous biomass; we removed all the herbaceous species within the five subplots in each large plot. Nevertheless, we separated only the herbaceous legume within the five sub plots in each large plot. We counted the fresh herbaceous legume manually.If there were some woody species within the large plot, we took some dendrometric variables such as height; circumference at 1.30 m for the tree and 20 cm for the shrubs and crown cover were measured. We considered tree as any woody plant superior to 7 m of height and less than 7 m was considered as shrub. We used ringing pole and tape meter for the dendrometric variables measurement. We also measured the widest diameter and perpendicular diameter of the woody crown by using tape meter. Furthermore, the seedling were recorded. Theseedling refers to any woody plant, which is diameter is less than 2 cm and the height less than 1.3 m. Additional plant species occurring outside plots but were also recorded only as present and were added to the final legume floristic list. Finally, we used ethnobotanical questionnaire to collect the socio-economic data about the importance of legume flora to the people of the commune of Mayahi. We took some pictures that explain the use of legume flora in the commune of Mayahi. We used two approaches for specie identification. Firstly, we have identified the majority of the species in the field. Further, we used also some books for the identification in field such as the flora of Hutchinson (1972), Adventrop (1995) and Michel Arbonnier (2002). For theunknown species, we produced the herbarium and submit to the Department of biology University Dan Dicko Dan Koulodo of Maradi for the specie identification.

Data analysis
All the collected vegetation data were taped in Excel. After, the legume vegetation data were extracted from the entire data. For the description of legume structure, woody species density, height, diameter at breast height (DBH), basal area, crown cover and regeneration rate were used. We analysed the data with Excel for following information about the legume flora of the vegetation of the Mayahi commune. We calculated: -Density (N) of a specie or group of species is the number of individuals per unit of (nb/ha). Further, the average woody species density was the ratio of the total number of individuals to the total survey area, and then reported to the hectare. ; where R (%) = total crown cover, S = total survey area, Di is the average diameter of the individual crowns, and N is the total number of individuals.The crown cover is expressed in percentage of plot area. However, as we measured the circumference, we used the formula circumference (C) = diameter x Pi = d.π, so you get a diameter = Circumference(C) divide by π. Where the value of π = 3.14. -Rate of regeneration (Rr)is defined as the ration of the total number of sapling/seedlings counted over the total plot area per hectare. Rr =Total number of seedlings/ Area (ha).Descriptive statistic was used for analysing the questionnaire data. Pterocarpuserinaceus was not recorded at all during the inventory. This confirms also the result of Boubacar (2010) who found out that Pterocarpuserinaceus has disappeared from the department of Mayahi. This was also supported during our interview with the villagers of the commune of Mayahi that Pterocarpuserinaceus from their commune.The absenceof Pterocarpuserinaceus in the inventoried flora of the commune of Mayahi confirms the findings of Arbonnier (2004) who reported that the specimen of the Pterocarpuserinaceus decrease and tend towards extinction in Niger. Furthermore, Sokpon et al. (2006) stated that Pterocarpuserinaceus has disappeared from many sites in Niger. Moreover, Rabiou et al. (2015) found out that in the Sahelian zone and even Niger W Park there were lack of seedling of Pterocarpuserinaceus indicating that the specie faces a problem of regeneration. Added to that Parkiabiglobosawas not also inventoried during our fieldwork in the commune of Mayahi. From the interview with the people of the commune of Mayahi, Parkiabiglobosa has also disappeared from their commune. In addition, the specie Prosopis africana is also rare in the commune of Mayahi because during all our prospection, only three individuals have been obtained and the population of the commune among the threatened species classifies this specie.

Structural Analysis
-Legume woody species density The average woody legume density is 62 individuals per hectare in the commune of Mayahi. The woody legume species of highest average density are Faidherbia albida and Piliostigma reticulatum ( Table 2  -Crown Cover The woody crown cover of the commune of Mayahi varies according to the land use and land cover types. It is higher in the Goulbi N'kaba valley (table 3), because Goulbi N'kaba forest is an environment highly protected by the foresters of the commune of Mayahi. Added to that Goulbi N'kaba vegetation belongs wetlands vegetation. The high crown cover observed in the forest of Goulbi N'kaba valley may be due the level of environmental perception of the surrounding population of forest degradation consequences. On the other hand, it is less elevated in farmlands, which explains the protection of woody plant by the principle of tree tenure and ownership. In addition, this may be due to the practice of natural assisted regeneration. The crown cover is lower in the fallow lands, which may be due the pastoral pressure as there is scarcity of pastoral land in the commune and illegal logging.  -2, Issue-3, May-Jun-2017  http://dx.doi.org/10.22161/ijeab/2.3.38  ISSN: 2456-1878 www.ijeab.com Page | 1326 was determined in order to assess their contribution to biomass -Diameter and Height of Some woody legume species distribution in three geomorphological units : Plain, Valley and Plateau Analysis of the figure 2 shows that Faidherbia albidais distributed in all geomorphological units, with greater density at the plain. The diameter and height all have a symmetrical structure at plateau and plain. The high density in these units is due to large Faidherbia albidaparklands we meet at some locations such as Guidan Alou Guidan Sani, etc.

Fig.2: diameter distribution (a) and height distribution (b) of Faidherbia albida
The structure of diameter and height of Piliostigma reticulatum shows a predominance of young individuals at the level of the plain whereas the aged individuals are totally absent (Fig3). This can be explained by the exploitation of individuals with large diameter in agroforestry systems. Moreover, the species is represented on the plateau only by individuals with an average diameter and at the level of the valley, this class is absent.

Fig.3: diameter distribution (a) and height distribution (b) of Piliostigma reticulatum
The analysis of the graph 4 shows that Acacia tortilisis well distributed in the plain and in the valley than in the plateau. Both parameters have a bell structure, which means that the specie recovers well in these units. Indeed, this specie dominates the physiognomy of the vegetation of Goulbi N'kaba, which is a protected area. This also supports the high crown cover we observed in the Goulbi N'kaba forest. In short based on the height distribution of the three legume woody plants, the woody legume flora of the commune of Mayahi has two strata such as tree stratum and shrub stratum.

Socio-economic Importance
The questionnaire data analysis from 52 people reveal that the legume species provides a diversity of services to the population of Mayahi commune. They are source of medicines, f odder, firewood, human food and they protect their croplands against wind and water erosion. Faidherbia albida and Acacia tortilis constitutes the main fodder woody legume plant in the commune. They are also source of firewood and timber. Acacia senegalandAcacia seyal provides natural gum to the commune. For instance, the leaves of Vignaunguiculataare consumed as salad in the commune.Arachishypogaea and Vignaunguiculata are the main cash legume crops in the commune.

IV.
CONCLUSION The parklands of the commune of Mayahi are floristically diverse in legume species. The inventoried flora has 55 legume species belonging to 24 genera and 3 legume botanical families Fabaceae are the best represented among the legume botanical families in the parklands of the commune of Mayahi. Structural analysis revealed that the woody legume flora health is good state but the woody legume flora is under pressure due to human activities. The socio-economic analysis showed that the legume flora provides a myriad of services to the people of Mayahi. The study recommends further study that will examine the impact of anthropogenic activities on the legume flora of the commune of Mayahi.

V.
ACKNOWLEDGEMENTS Authors are grateful to the rural population of the commune of Mayahi mainly the head of the villages who gave us the accommodation during our stay in their different villages. Special thanksgo to captain Traoré Lamine the director of environment of the commune of Mayahi for thesupport during our stay in Mayahi commune. Our sincere acknowledgments go to the UniversityDan Dicko Dankoulodo of Maradi, Niger mainly to the professors Saadou Mahamane and Ali Mahamane who provided the financial and botanical assistances to carry out the study.