Traditional plant use in Burkina Faso (West Africa): a national-scale analysis with focus on traditional medicine

Burkina Faso (BFA) is a landlocked country in central West Africa, covering an area of 274,000 km². Large parts of the population of BFA live in rural communities [1] and strongly depend on traditional plant products for their daily life [2‐5]. Some of the plant species traditionally used in BFA are of regional and global economic importance (e.g. Adansonia digitata, Parkia biglobosa, Sclerocarya birrea, Tamarindus indica, Vitellaria paradoxa).

While the connection between useful plants and the daily-life products derived from them is mostly dissolving in modern societies, this link remains much clearer in many rural communities, where traditional plant use often is essential for multiple parts of the daily life. This includes the use of crop plants as food for humans and livestock, the use of woody plant parts for fuel, construction or tool manufacture as well as the application of plants in traditional medicine and for religious purposes. In many cases the traditional use of plants is closely linked to considerable floristic knowledge and appreciation of the used species, not seldom in a spiritual-mystical way [2].

The traditional plant use around the globe represents an invaluable reservoir of knowledge and a large potential of yet “undiscovered” use of natural resources. There are numerous examples for traditional knowledge of plant use as a starting point for the development of products used in modern societies, such as drugs, industrial resources or cosmetic products [6]. A large amount of yet undiscovered resources is to be expected in global plant diversity [7]. However, due to changes in human population structure and the decreasing interest of younger generations in traditional lifestyle, a considerable amount of the knowledge on traditional plant use is in danger of being lost [3, 4]. This effect is even increased by the influence of climate change and land use change leading to an increasing habitat loss for many used plant species. A clear, comprehensive scientific documentation of traditional plant use is thus an indispensable tool to preserve this valuable knowledge and the basis for a further sustainable use of biodiversity. Especially, an understanding of plant use in a larger spatial and plant-systematic context might help to focus future research effort and improve conservation strategies.

Our analyses included all plant species known from BFA (including introduced species) [52]. The plant use information was based on 47 different references published between 1971 and 2014 [2‐5, 7, 8, 10, 23, 24, 26, 27, 30, 31, 33‐63]. These sources included ethnobotanical studies from Burkina Faso as well as information from floras of Burkina Faso and neighbouring countries. We included data from neighbouring countries, as the different ethnic groups of the Burkinabé population are also present in neighbouring countries, and the plant use is expected to be relatively homogenous within these groups. See Additional file 1 for a detailed information on the source material. A literature database compiled by the authors was completed with a literature search in the databases of PubMed and Web of Science using combinations of the keywords “Burkina Faso” and “plant use”, “useful plant”, “medicinal plant”, “ethnobotany”, “traditional medicine”, “medicinal plant”, “traditional plant use”, “ethnobotanique”, “plante utile”, “utilisation plante”, “plante médicinale” respectively. From the result we included studies that were based on ethnobotanical interviews in Burkina Faso and that reported unambiguous scientific plant names as base for our analyses (but see Additional file 2 for a list with vernacular names for the most common species). We explicitly excluded studies that were solely concerned with pharmacological screenings or agricultural practices as well as articles dealing only with one single species. The latter was done to avoid overweighting and refers to only a few economically important species that are well covered with the dataset. The African plant database [64] was used as reference for scientific plant names, and synonyms were included under their accepted name. We used keywords to categorize the detailed information from literature into ten plant use categories: construction, cultivation, firewood, fodder (animal nutrition), traditional medicine (TM), human nutrition, ornament, religion and art, tools and craft, veterinary. The categories were chosen to reflect the most common uses and are orientated on the level 1 and 2 states of the Economic Botany Data Collection Standard [65]. See Additional file 3 for a classification of each species to the 10 use categories.

To further investigate the use of plants in TM we classified the detailed medicinal information from the references into 22 health disorder categories. We followed the Economic Botany Data Collection Standard [65] for the classification. The classification-scheme was slightly modified to meet the local characteristics. Three categories were added: Child specific (i.e. all medication directed specifically to children or growth disorders), internal organs (including liver, spleen and kidney disorders) and oral/teeth (oral hygiene, oral and tooth disorders). Disorders related to the circulatory system and blood were combined to one category. We classified the plants using over 500 keywords and a subsequent visual check of each species description.

We used the number of references citing the use of a species and the number of use categories (see above) per species to calculate the relative importance index and to rank species according to their usefulness. The RI was calculated following [28]:

With: RFC = relative frequency of citation (Frequency of citation/Number of References), RNU = Relative number of use-categories (Number of uses/Maximum number of uses of a species).

Out of the 2067 known plant species of Burkina Faso 1033 (50%) had a traditional use recorded. Figure 1 shows the use of plant species in 10 different use categories. Most species were used for traditional medicine (36% of all species) followed by human nutrition (21%) and animal fodder (19%).

The purpose of traditional use was highly related to plant family. Fabaceae, Poaceae and Malvaceae were the plant families with the most species relevant for traditional plant use. The twelve most species rich families in BFA differed with regard to the amount of species used and the purpose of use (Figure 2). While most of the families were employed in multiple categories, some families were only used for specific purposes. The two most species-rich families in the country, Fabaceae and Poaceae, were of special importance for human nutrition and animal fodder. Together they comprised 29% of all species used for human nutrition and approximately 62% of all plant species known to be used as fodder. The Fabaceae were also of special importance in TM, comprising 18% of all plants used in traditional medicine. Intriguingly, species of some families were rarely used in any way. Especially Cyperaceae and Convolvulaceae included only a low number of useful species (Figure 2).

Table 1 shows the 20 “top used” plant species in the country according to the relative importance index. Khaya senegalensis, Adansonia digitata and Diospyros mespiliformis were the top ranked species. The list includes five Fabaceae, two Malvaceae and two Combretaceae species. All species listed in Table 1 are woody plants. See Additional file 4 for a usefulness evaluation of every species with at least one known use in the country.

We found a clear phylogenetic clustering of plant use. The fact that species of some families are preferentially used for specific purposes is an often recorded fact and has been attributed to specific traits more common in these families [3, 17]. For example the preferential use of Poaceae and Fabaceae species for human and animal nutrition can be related to the often nutritious fruits or seeds in these families.

In the case of TM the phylogenetic clustering might well be related to the presence of phytochemical compounds [5, 8, 15]. Inversely, the relative sparse use of Cyperaceae species has been related to the relative low content in phytochemicals in this family [3]. Interestingly, many plant species are applied as remedy only in few health disorder categories (Additional file 6). While the general link between plant use and pharmacological activity is debated controversially, the clear phylogenetic pattern and the specific use of most species shown here might help to guide drug screenings.

The fact that more than one third of all plant species of BFA have a known medicinal use stresses the importance of TM for the population, especially in the rural communities, of the country. The high number of medicinal plants used to address infections/infestations, digestive system disorders and genitourinary disorders is a clear indication of the importance of these disorders in the country. Especially digestive system disorders are documented to be specifically common in West Africa [12]. The identification of malaria, icterus and gastro-intestinal disorders as main targets for traditional medicine is consistent with other studies and is most likely related to the high number of infections and the importance of these diseases in the people’s lifes [6, 12, 26]. Malaria and malaria related symptoms were by far the most targeted diseases in this study, which accounts for the large number of malaria cases in BFA. Malaria is a major threat to the people in the country, with 3.5 million recorded cases in 2008 (thereof 50% among children under 5 years [66]) and has been reported as a main target for traditional medicine in BFA [11]. At the same time malaria is an example for the successful use of natural products and traditional medicine to guide drug screening and development [5, 6, 8, 67]. This is of special importance, as resistance against commonly used drugs is becoming a severe challenge for malaria treatment in the region [68].

The “top usefulness” rankings of plant species (Table 1 and Table 2) are the first comprehensive assessment of this type on a national scale. Generally our rankings were successful in identifying plants of known high importance, and agree well with local scale assessments. Ten of the species shown in Table 1 (Adansonia digitata, Diospyros mespiliformis, Vitellaria paradoxa, Balanites aegyptiaca, Tamarindus indica, Parkia biglobosa, Annona senegalensis, Sclerocarya birrea, Detarium microcarpum and Ximenia americana) were identified as important plants in the traditional agroforestry systems of the Sudanian zone in Benin [69]. In another study nine species from Table 1 (Khaya senegalensis, A. digitata, D. mespiliformis, V. paradoxa, T. indica, P. biglobosa, Pterocarpus erinaceus, Anogeissus leiocarpa and D. microcarpum) were ranked within the thirty most important woody plant species across multiple ethnic groups and multiple use categories in Northern Benin [70]. The same study includes seven of our twenty top useful medicinal plants (Table 2) in a list of the most important medicinal plants in this area (T. indica, V. paradoxa, A. digitata, K. senegalensis, P. erinaceus, Sarcocephalus latifolius and Entada africana). A third study identified A. digitata, V. paradoxa, T. indica, D. microcarpum and P. biglobosa as key species for plant use of the Gourounsi people in central BFA [36]. A study in the Pendjari Biosphere Reserve in Benin evaluating non-timber forest products agreed in ranking eight of the top 20 species presented here in a list of the 15 most important used species (K. senegalensis, A. digitata, D. mespiliformis, V. paradoxa, T. indica, P. biglobosa, L. microcarpa and Ficus sycomorus)[71]. Of course, these results must be interpreted carefully. Some species identified as commercially important in other studies were not ranked as top use species in our list (especially Vitex doniana). This might be explained by a rather focused use (and thus a lower relative importance index). See Additional file 4 for a usefulness ranking list including more species. Additionally, the ranking is depending on the reference studies used to build the database and the characteristics of the relative importance index. While a high number of studies mentioning use of a species and a large number of different use categories can be interpreted as indicator of species importance, a low number of uses or references does not necessarily mean that a species is not of high value for specific purposes or on a local scale [3]. Generally, the ranking should be understood as a tool to identify a set of key species with a relative high use value across the country. Identifying such species is an important prerequisite for conservation planning [36].

Plant use highly depends on social factors and differs considerably between different ethnic groups and locations. Interview-based studies are a key to understanding and preserving traditional ethnobotanical knowledge. However, in times of climate change, when large scale conservation strategies are urgently needed, large-scale analyses of plant use are equally necessary. Including key economic species for local communities into conservation planning can highly increase the success of these efforts and make sure that they benefit as many people as possible.

We revealed a clear systematic pattern of traditional plant use throughout BFA, and identified the importance of specific plant families for specific uses. This systematic pattern is especially interesting in the context of plant use in traditional medicine, as it might correlate with pharmacological activity. The evaluation of usefulness of each plant species using the relative importance index has provided a robust hit list of the “top useful” species in the country and will be an important tool in focussing future conservation effort and possibly pharmacological screening. Our results are of interest for applied research, as a detailed knowledge of traditional plant use can a) help to communicate conservation needs and b) facilitate future research on drug screening.