Traditional uses of Detarium microcarpum Guill. & Perr. (Fabaceae) and potential for its valorisation as fuelwood

Detarium microcarpum Guill. & Perr. is a common multipurpose small tree species of Sudanian and Sudano-Guinean savannahs with high potential for use as fuelwood but little valued in forestry programs. The present study aimed at assessing the current local uses of D. microcarpum, factors determining its use as fuelwood and determine the geographical areas with the socio-cultural groups which is most suitable for its integration into fuelwood programs. An ethnobotanical survey was conducted among 1074 people selected randomly. Factors determining D. microcarpum use as fuelwood were identified through a binary logistic regression. Factorial Correspondence Analysis established the relationship between socio-cultural groups and the use of D. microcarpum parts or organs. A total of 62.47% of respondents know and use at least part of D. microcarpum . The trunk and branches are the most used organs (35.12%), primarily as fuelwood. The determinants of D. microcarpum use as fuelwood are the phytogeographic district (a proxy for the resource availability), gender, sociolinguistic group, and educational level. D. microcarpum is more used as fuelwood by women. The use of D. microcarpum as fuelwood is more pronounced in about 63% of the national territory. This study confirms the potential of D microcarpum as fuelwood to be promote. © 2022 International Formulae Group. All rights reserved.


INTRODUCTION
Ethnobotanical studies are useful for understanding the uses of forest resources in a given region and informing forest policy. Indeed, peoples have always had traditionally rich ethnobotanical knowledge through the cultural and ecological diversity of the environment in which they live (Gbesso et al., 2013). This knowledge and local uses may or may not be influenced by socio-cultural characteristics such as ethnicity, age, gender, educational level, religion, or occupation (Sop and Oldeland, 2011), and a plant perceived as highly useful by one ethnic group may be considered of little use, or even useless, by another group (Ilumbe, 2010). Also, knowledge of the use and management of species by local communities can help improve the conservation of species at local and regional levels (Kouaro et Tasso, 2010) by providing basic information for the selection of the species on which the emphasis should be put in management plans to meet not only the needs of populations but also to improve the conservation status of species (Dossou et al., 2012).
D. microcarpum, also called small detar or sweet detar, is a tree up to 10 m tall that occurs naturally in the arid regions of West and Central Africa, from Senegal and The Gambia to Sudan (Kouyaté et van Damme, 2006). It is found in shrub savannas, wooded savannas and open forests, as well as in dry forests and fallows (Arbonnier, 2002). It generally grows on marginal soils such as sandy and lateritic soils (Kouyaté, 2005), thereby involving little or no land use competition with agricultural crops. It is reproduced by rejection, suckers and spontaneously sprouted seeds (Kouyaté, 2005). This capacity suggests the possibility of vegetative propagation of D. microcarpum which is necessary for its domestication. Regarding the species growth, it can reach 50 cm height after a year and 120 cm after 7 years (Bastide and Ouedraogo, 2008). D. microcarpum is also a species that supports stress such as cutting (Batiano et al., 2001;Sawadogo et al., 2002) and could therefore be conducted in thickets. Traditionally, the entire tree is cut during the dry season (February-May) for fuelwood stocks in anticipation of the rainy season (Kouyaté, 2005).
D. microcarpum is also used for food, energy, veterinary, artisanal, industrial, and medicinal purpose. In Benin, the proportion of food uses is 26.23% against 81.18% for the wood category energy (Agbo et al., 2017). According to Kouyaté et al. (2002), women classified D. microcarpum (fruit, firewood), Parkia biglobosa (Jacq.) R. Br ex G. Don (fruit) and Vitellaria paradoxa CF Gaertn (fruit) as the three most important forest species in Mali. In Burkina-Faso, the wood of D. microcarpum is particularly valued by households as firewood because of its high calorific value about 1968 KJ/kg (Kabore, 2001), which leads also to its high exploitation (Agbo et al., 2017). In Benin, the demand of domestic source of energy situation is increasing, and it is important to identify alternative sources of energy to meet local population needs.
Assessing the knowledge diversity and usage patterns of D. microcarpum could help in determining sustainable management and domestication strategies of the species. The present study aimed at capitalizing the knowledge and local uses of D. microcarpum, in order to provide the basis for its rational and sustainable management.

MATERIALS AND METHODS Study area
This study was conducted in ten (10) Divisions (i.e. Alibori, Borgou, Atacora, Donga, Zou, Hill, Couffo, Mono, Plateau and Atlantic) out of the twelve (12) of Benin ( Figure 1). The two departments of the far south of Benin (i.e. Littoral and Ouémé) were excluded because D. microcarpum was not observed during the exploratory phase. In each Division, the districts were chosen based on the presence of the species for investigations. In each district, the nearby villages (distance ≤ 10 km) of D. microcarpum dominated plant vegetation were selected for ethnobotanical studies. Study villages are characterized by a strong sociolinguistic and cultural diversity (Dicko et al., 2017).

Ethnobotanical surveys
Ethnobotanical surveys were conducted based on a semi-structured questionnaire administered to individuals belonging to different sociolinguistic groups. Preliminary sampling for the survey included 30 randomly selected people in each studied department. The percentage of respondents who know at least one use of D. microcarpum was calculated and the number of respondents (Table 1) was determined afterward using Dagnelie (1998) formula: Where N is the sample size, U_ (1-α / 2) ^ 2 is the normal random variable value for a probability value α = 0.05; U_ (1-α / 2) = 1.96; p = the proportion of respondents who know and use parts of the species and the 8% margin of error (Assogbadjo et al., 2011;Dicko et al., 2017). The sample size calculated for each department was then divided among different sociolinguistic groups for that department (Table 1).

Determinants of D. microcarpum use as fuelwood
For identifying the socio-demographic and ecological characteristics that determine D. microcarpum use as fuelwood in the study area, a binary logistic regression was used under R software, version 3.4.2, with the Package MASS (Venables and Ripley, 2002). Specifically, we assessed whether the probability of a respondent using the species for fuelwood is related to certain sociodemographic and ecological characteristics. The response variable is the use of the species as fuelwood and is coded as 1 (uses the species) or 0 (does not use the species). Explanatory variables included phytogeographic district, sociolinguistic group, gender, age, marital status, religion, education level, and household size. Several models were compared using the Akaike Information Criterion (AIC) (Akaike, 1974). For the sake of parsimony, we chose the model that has the smallest value of AIC and the smallest number of terms that influence D. microcarpum use as fuelwood.

Relationship between sociolinguistic groups and the use of D. microcarpum organs or parts
The relationship between sociolinguistic groups and the uses of D. microcarpum parts or organs was described using Factorial Correspondence Analysis (FCA) was carried out under the software R (version 3.4.2) with the FactoMineR package and from a data table with socio-linguistic groups (in rows) and parts / organs of D. microcarpum (in columns).

Frequencies of opinions regarding the use of D. microcarpum organs / parts
Out of a total of 1074 people surveyed, 671 people know and use at least part of D. microcarpum (Figure 2a). The trunk and branches are the most used organs (35.12% of respondents), followed by fruits (28%), leaves (15.64%), roots (10.24%) and bark (10.14%). Sap and flower are the least used parts by the respondents (0.66% and 0.20% respectively).

Uses of D. microcarpum
Different uses are reported by the local populations surveyed according to D. microcarpum parts used. The trunk and branches of the species are more used as fuelwood (47.47% and 24.80% of uses reported by respondents ( Figure 2b). Food uses represent 27.70% of all reported uses. The bark, leaves and roots are mainly used for medicinal purposes (respectively 97.94%, 84.85% and 95.83%, Figures 2c, 2d, 2g). The flowers play a magico-mystical role (66.67%, Figure 3e) while the fruits / almonds are exploited in the diet (96.91%, Figure 2f). As for the sap, it is mainly used to trap birds (54.55%, Figure 2h).
Roots are more used to treat stomach pain (2.79% of respondents). The bark is most exploited to treat malaria (2.79%), stomach pain (2.79%) and hemorrhoids (2.79%). The trunk and branches are more used as fuelwood (60.15% and 4.06% respectively). As for the leaves, they are mainly used by respondents to treat malaria (13.19%), for the vigor of children (4.82%), as a leaf vegetable (4.06%), to treat yellow fever (3.55%), and to treat diarrhea (2.79%). The flowers are used as a lucky charm (0.48% of the respondents). Sap is more exploited as a glue to trap birds (1.27%). Fruits constitute a food and are eaten raw or processed into fruit juice (64.72% of respondents). For the therapeutic uses, the principal mode of use of D. microcarpum organs is the decoction (72.25% of the respondents), followed by the infusion (24.05%), the maceration (2.50%) and milling (1.20%).

Relations between sociolinguistic groups and organs uses
The Factorial Correspondence Analysis between the sociolinguistic groups and the uses of D. microcarpum organs or parts shows that the first factorial axis explains 40.45% of the total variance and the second axis gives information on 23.59% of the variations (Figure 3). Thus, the first two factorial axes account for 64.03% of the total variance. These first two axes were therefore retained to describe the relationship between the uses of D. microcarpum and sociolinguistic groups.
Axis 1 is positively correlated with leaves and roots use of D. microcarpum on the one hand, and with the sociolinguistic groups Adja, Ahoussa, Aizo, Ani, Fon, Idasha, Mahi, Nago, Sola, and Taneka on the other hand. This axis is negatively correlated with the use of sap, branch, and fruit on the one hand, and then on the sociolinguistic groups Agouna, Bariba, Mokole, Peulh and Yendé.
Axis 2 is positively correlated with the use of the trunk and flowers of D. microcarpum on the one hand, and the sociolinguistic groups Biali, Dendi, Ditamari, Gando, Goun, Kounteni, Kotafon, Lokpa, Waaba, Yom, Yoruba. and Zerma. On the other hand, the exploitation of the bark as well as the sociolinguistic groups Boo, Gourmantché, Kotokoli, Koura and Serima are negatively correlated to this axis ( Table 2).

Determinants of D. microcarpum use as fuelwood
Factors determining the use of D. microcarpum as fuelwood in the study area are phytogeographic district, Gender, sociolinguistic group, and educational level (Table 3).
D. microcarpum is more commonly used as fuelwood by women (Figure 4a) belonging to the sociolinguistic groups Gourmantché, Kounteni, Boo, Monkole, Gando and Bariba (Figure 4b). In addition, this use for fuelwood decreases with the educational level ( Figure 4c) and is more pronounced in the phytogeographical districts of Borgou-Nord, Atacora and Borgou-Sud covering together about 63% of the national territory (Figure 4d).

DISCUSSION
The present study focused on the ethnobotany of D. microcarpum to examine possibilities of its promotion as fuelwood. It is a multipurpose species widely used in the study area in the energy, medicinal, food and cultural fields. Ethnobotanical knowledge is indeed considered in the management of forest resources because it offers opportunities for understanding ecological processes in relation to the knowledge of local populations (Dicko et al., 2017). The conservation of a resource in an environment is strongly determined by the interaction between the resource and the activities carried out by the local populations. The most important parts of the plant used by local population are the trunk and branches, fruits, leaves, roots and bark. The majority of respondents mentioned that the wood (trunk and branch) of D. microcarpum is heavily used as firewood. Similar results were obtained by Kouyaté (2005) in Mali, Kristensen and Balslev (2003) in Burkina and Agbo et al. (2017) in southern Benin. D. microcarpum is used for fuelwood due to flame intensity and the small amount of smoke emitted (Tondoh & Degrande, 2015). In the present study, D. microcarpum is more commonly used as fuelwood by women. Women prefer firewood to those of Terminalia spp., Pterocarpus erinaceus and Isoberlinia doka, because it catches fire quickly, even when it is wet (Kouyate, 2005) and is easy to split or to machine (Kaboré, 2001). D. microcarpum is more exploited for the supply of firewood and is an important source of income for the populations (Kouyaté, 2005). Unlike the fruits, the fuelwood trade of D. microcarpum is well known in the south of Mali and the fuelwood stere in rural areas was sold between FCFA 1000 and FCFA 3000 in 2005, depending on the middle and the season of the year (Kouyaté, 2005). The preference of D. microcarpum by women for home energy is confirmed in other studies (Dao et Lamien, 2020).
These results are not correlated with those of Dieng et al. (2016) in Senegal where D. microcarpum was not among the preferred species for firewood species because, according to the groups interviewed, the species is not a hard-wooded tree and other species that are more suitable for this purpose were available. To some communities as M'Bèlimè, the use of D. microcarpum trunk as firewood is defended. This taboo reported in many sociocul-tural areas in Mali could be understood as a conservator measure (Kouyaté, 2005). This conservatory taboo is also recorded for Faidherbia albida and Vitex doniana, in north Cameroun, believed to drive you crazy if burned and their smoke believed cause leprosy, conflicts and inevitably dissolution of the family (Seignobos, 2019), is not noticed for D. microcarpum in Benin by the present study. This preference and consumption of its firewood militate in favor of the domestication of D. microcarpum to produce fuelwood.
Determinants of the use of D. microcarpum as fuelwood in the study area are gender, educational level, sociolinguistic group, and phytogeographic district. The hypothesis following knowledge dynamics of gender and educational level (Gaoue et al., 2017) suggests that various individual sociocultural and demographic characteristics such as gender, ethnicity and literacy levels are correlated with the level of knowledge and use of plants by an individual (McCarter & Gavin, 2015). Thus, women tend to know more about the local medicinal flora, while a high literacy rate and better access to health and formal education is often negatively correlated with knowledge of medicinal plants (Voeks & Leony, 2004). These same observations are made for D. microcarpum in the context of the use of its wood for domestic energy by the local populations.
According to Gaoue and Ticktin (2007), socio-demographic characteristics are not always the only factors influencing endogenous knowledge. The present study revealed that D. microcarpum is more widely used in northern Benin, particularly in the phytogeographical districts of Borgou-Nord, Atacora and Borgou-Sud. For Gaoue et al. (2017), the proximity of the resource can also influence its use. Our observations in the field confirm that D. microcarpum is more common in northern Benin. Further studies on the ecology of this species and its spatial distribution are needed to discuss a possible correlation between the local abundance (availability) of the species and its use for energy purposes by rural communities in the phytogeographical districts of Borgou-Nord, Atacora-Chain and Borgou-Sud. Indeed, the availability hypothesis (Gaoue et al., 2017) suggests that plants are more used when they are more accessible to local populations or are more abundant locally (Albuquerque, 2006).
For other studies, wood physical characteristics are also factors of species use as firewood. A direct relationship was observed between the physical properties of the fuelwoods and their locally perceived qualities (Ramos et al., 2008). These locally perceived qualities are relative in general to ashes production, moisture fractions, flame intensity, burn time, spark or smoke production (Ramos et al., 2008;Froumsia et al., 2016).
The ethnobotanical survey conducted in this study showed endogenous knowledge regarding the importance and use of D. microcarpum parts or organs and allows to classify it in the multiuse species for rural populations in Benin since all its parts are used. Apart from the high exploitation of D. microcarpum wood as fuelwood, its fruit is also highly consumed by local people. A fair compromise should therefore be found between the use of D. microcarpum as fuelwood and its exploitation as a fruit tree. Thus, data on the minimum diameter of fruiting and the diameters used for wood energy are necessary. Commercialization of the products (wood, fruits) of D. microcarpum can be a promising pathway and a substantial source of income for local populations, which further justifies its domestication. Given the energetic qualities of D. microcarpum and its preference by consumers as domestic energy source (Kouyaté, 2005;Agbo et al., 2017), the marketing of its wood could contribute effectively to compensate for a large part of the domestic energy needs of both rural and urban populations in Benin. Therefore, it's necessary to evaluate the local abundance and structure of species, its management mode for sustainable wood fire exploitation.

Conclusion
The present study identified factors influencing uses of D. microcarpum as fuelwood and established the links between uses of the species and the sociolinguistic groups. The sociodemographic and ecological parameters that significantly influence the use of D. microcarpum as fuelwood are the phytogeographic district, the gender, the sociolinguistic group and the educational level of the respondents. The species trunk and branches are the most used parts, primarily for energy purposes (firewood and charcoal). It is therefore opportune to study the possibilities of promoting the species as fuelwood in Benin to alleviate energy problems. For a better management of this important wood-energy species for the local populations, certain elements will still have to be specified such as the disponibility and the structural characteristics of the species populations in Benin, the determination of the calorific value of D. microcarpum wood, its forestry to favor its multiplication and its ecological preferences for its better growth after planting.

COMPETING INTERESTS
The authors declare that they have no competing interests.

AUTHORS' CONTRIBUTIONS
TAS designed the study, analyzed and interpreted the data, and wrote the original draft. AD participated in the study design, provided guidance during data collection, and edited the manuscripts. HSSB participated in the study design and was a major contributor in the writing of the manuscript. EA and AKN contributed in the study design. All authors read and approved the final manuscript.