Modelling socioeconomic determinants for cultivation and in-situ conservation of Vitex doniana Sweet (Black plum), a wild harvested economic plant in Benin

Findings indicated that wild species represented the major part of the edible tree resources diversity in the twelve surveyed communities, meaning that local people still rely to a great extent on nature for their livelihoods. Out of the top 15 most valued woody plants, eleven have a high market value and species such as A. occidentale, V. doniana, and P. biglobosa combined high market and nutritional values. Vitex doniana stood out as the most important wild tree species followed by P. biglobosa, with both falling just behind A. occidentale which is an important cash crop in the surveyed communities. This result is consistent with findings by several authors who investigated the use of plant diversity in rural livelihoods in the West African sub-region [16,36-38]. Parkia biglobosa and V. doniana were already reported among the most valued NWFP resources in southern Benin [12], in Burkina Faso and Cameroon [39]. The two species are almost always used together in local cuisine where the local mustard “afintin” processed from seeds of P. biglobosa is used as seasoning for cooking leaves of V. doniana into a much appreciated popular vegetable dish in the region, known as “fonman”. Therefore, the current results call for a close attention for safeguarding and valuing these species.

Cultivation appears to be the best management option to sustain both species and livelihoods when the value of a non-wood forest product (NWFP) and quantities harvested are high [1]. This opinion was also backed by Kupzow [5] who supported that plant cultivation is most stimulated by economic demand and highlighted that many cultivation experiments resulted in nothing because they failed to take economic aspects into consideration. Studies have revealed that black plum has an important market [13], that keeps expanding and this represents an incentive for its cultivation and conservation [40]. The species was also mentioned as present in at least 20% of traditional agroforests, from a countrywide survey in Benin [21]. In these conditions, cultivation of black plum is likely to be successful. In fact, V. doniana has the highest use value among the wild tree resources of importance to local livelihoods, especially for women and illiterate people, who tend to value it more than any other tree species. We also found that people with higher educational level seemed to value cash tree crops more highly than others, namely E. guineensis, A. occidentale, and T. grandis by decreasing order of importance. This could be an indication of the erosion of local value among the more “westernized” households. The educational elite classify resources almost solely based on market value of species, completely ignoring the social and cultural values associated with them. Another consideration is that they have less contact with wild resources in nature. Migrants also seemed to value V. doniana and P. biglobosa more highly than autochthons to whom the cash tree crop A. occidentale is the top most important. In fact, in the local land tenure systems migrants who are not owners of land have no right to plant perennial species. However, they have free access to wild resources in the nature, a fact which could explain this high value they attributed to the wild species. Overall, these variables are significantly important and should be carefully taken into account when selecting stakeholders in wild resource conservation programmes.

Results clearly indicated that black plum is a multipurpose species, a characteristic of most NWFPs [41]. The inventoried uses confirmed the current state of knowledge on the species as reported by previous studies [12,16,40,42]. The high IAR values confirmed that knowledge of these uses is well distributed among user communities and the species is important in rural livelihoods. Exploitation of the species is profitable for all age groups, but more so for women than men. This is explained by the fact that men are most involved at the primary stage of exploitation, as primary collectors; while women are more involved in the wholesale and retail of processed leaves and fruits. By the law of profit distribution along the market chains of NWFPs, wholesalers and retailers (involving mainly women) obtain the bigger profit [43]. Species of this type are classified under the “women goods” categories of NWFPs [44].

Overall, juvenile trees are more vulnerable to disruption caused by destructive harvesting practices and wild fires. Therefore, much of any regeneration dies out at the end of the dry season. Overharvesting of leaves reduces fruiting ability of the overharvested trees, and this coupled with fruit harvesting obviously reduces the possibility of regeneration from seed. All these represent important threats to survival of wild populations. Nonetheless, the current level of roots and bark harvesting for medicinal purposes is low and does not add significantly to existing threats.

The analysis of access to resources of different landscapes indicated an incipient privatization of V. doniana trees occurring in farmlands and fallows. In fact, trees that are spared during land clearance for agriculture become the property of the farm owner. This tenurial system enhances conservation, as harvesting is better scheduled and competition with other harvesters is limited. On common lands (woodlands and savannas) trees are often cut down to harvest the leaves when they are too difficult to climb. The trunk and branches left out are then used to make charcoal or fuel wood. In farms, when the owner grants a usufruct right to a person to harvest trees on his or her fields, that person is not allowed to cut V. doniana trees. These kinds of measures protect the species.

From our data, local communities did not report any variants of V. doniana that can be subject to artificial selection in the sense of Blancas et al. [3]. However, referring to Blancas et al. [3]’s classification of the different management types, we distinguished the following categories which are considered as in-situ actions:

Other categories such as “seed sowing” and “propagation of vegetative parts” described by Blancas et al. [3] were observed at a very low proportion (3.93% used seeds and 1.68% used stem cuttings). These two categories were classified as ex-situ management by Blancas et al. [3]. However, based on the definitions of in-situ and ex-situ conservation by the CBD [34], we rather identified them as in-situ management, as these activities entirely happened in farms in the case of V. doniana.

Men have better knowledge of tree phenology (especially the fruiting period) than women, although women were the most involved in V. doniana exploitation. This is explained by the fact that men are the most involved in the primary collection of the resources and thus are more in contact with the species in its natural habitat. In addition, the autochthons have better knowledge of the biology of the species than migrants. Explanation to this might be that the autochthons have been in contact with the species for long time and knowledge is transmitted through generations. This indicates the importance of indigenous people’s ecological knowledge on NWFPs. It was also found that local knowledge of people is eroded with schooling. This negative effect was also reported by Chukwuone [10] where schooling had negative effect on involvement of local people in NWFPs cultivation in Nigeria. At the current state, conservation initiatives are very poor in the study area, with very limited on-farm sparing of trees during land clearance for agriculture. This has been reported by N’Danikou et al. [12] and Dadjo et al. [40]. With regard to this and taking into account the pace with which the resource is harvested, wild populations of V. doniana are undoubtedly under threat. Based on the current level of local conservation initiatives, V. doniana falls under steps 1 and 2 of the domestication process [6,35]. Step 1 is characterized by wild plants maintained on farms during land preparation (e.g. clearance, burning and weeding) due to their proven utility and regular need, and their scarcity within household’s compound limits. These spared plants are regularly observed to learn about their reproductive biology. In Step 2, farmers start giving more care to the protected plants (e.g. weeding, protection against animal damage) for their survival and their normal growth; a sort of ownership on the plants starts [35]. It is important to note that up to Step 2, no modification of plants has occurred due to selection; but plants just incidentally co-evolved to adapt to the disturbance imposed by human activities in the environment [6].

Based on the current demand for V. doniana products and the intensity of the harvest, cultivation would be the best option to sustain the species and also the livelihoods of the different user groups. However, V. doniana is still at the earlier stage of the domestication process as indicated above and is still intensively collected from the wild. Thus, it is vital to understand what could motivate resource users to engage in cultivation of the species. From our study and based on the conditional inference tree statistical approach, four main variables have important effects on the decision-making process to cultivate V. doniana in the surveyed communities. This is partly consistent with previous studies in this domain [12,21]. First, an important proportion of users have expressed their willingness to cultivate the species for its importance in household food consumption and income. The second important parameter to be considered is schooling and literacy. Findings indicated that the use value of V. doniana to people declines with schooling. In this respect, awareness needs to be raised to sensitize elite classes. A third variable weighting in the cultivation of the species is the land tenure. Tenants were less likely to accept cultivation. In fact, the land tenure system in southern Benin and in any other parts of the country does not grant the tenants the right to plant trees [25]. Perennial species and most often trees are used to mark ownership of land. Thus, individuals with no property right on land may be willing but not ready to invest into cultivation of the species. At fourth and the most important, tenure size is key to the decision to cultivate and to maintain the species in-situ. People with larger parcels of land were eager to allocate bigger plots for the agroforestry of the species and were more likely to consider cultivation. Where land is available gender is an important factor in the likelihood for V. doniana cultivation. Although women’s use value of the species was higher than men’s, the men were more likely to plant the species. This could in fact be explained by the tenure system in which women have less access to land. There are also other variables such as the importance of wild-harvesting, the location and the cost of seedlings that were considered by people in their decision making. The threshold of XOF 650 (USD 1.44) found is well reflected in the positive relationship between the cultivation opportunity ratio (COR) and the likelihood to cultivate. All those who proposed a seedling acquisition cost below this threshold were not willing to cultivate.

Several wild resource conservation programmes have failed around the world due to the lack of clear understanding of local drivers for success [10]. Gepts et al. [4] indicated that the success of conservation through use and restoration of biodiversity requires continued and increased research, and policies. Our findings pinpoint the main socioeconomic factors that trigger the success of conservation and management of threatened wild harvested plant resources with high economic value. Motivated local communities should be at the heart of conservation management, and we demonstrate that there is considerable willingness to engage in conservation of a locally threatened economically significant wild species. The availability of land was the most important element in our study with gender and lack of awareness of the importance of local foods among the elite class. The determined affordable cost of seedlings for farmers is a good entry point for nursery development. The negative values found for the cultivation opportunity ratio is also a good indication of the willingness of people to grow V. doniana in their farmlands and conserve wild populations. This means that less effort would be needed to get this category of participants involved.

The present study also encompasses the principle of complementarity between biological diversity conservation strategies. In fact, each of the elements treated in this paper (i.e. cultivation and in-situ conservation) have both positive and negative outcomes for biodiversity conservation, which need to be discussed. Plant cultivation can result in important setbacks if not well managed, despite its important advantages [45]. A plant cultivation programme that is not sustainably managed could lead to genetic drift and important biodiversity loss caused by high selection and breeding of superior lines. In the case of wild-harvested species such as V. doniana which have not been evaluated genetically, it is necessary to conserve wild populations in their natural habitats and in ex-situ genebanks (if possible) while they are undergoing domestication; in order to safeguard the gene pools in the species for future breeding purposes. Besides, there are examples of successful domestication of plant species whereby this undertaking has increased diversity. For instance in the case of maize which, despite the long history of selection and genetic improvement it has undergone, developed a huge diversity of cultivars. This was possible thanks to the ecological diversity of agricultural landscapes, which promoted the spread of cultivars and their adaptation to a diversity of agroecological niches [46], but also due to conservation of ancestors in the wild and ex-situ in genebanks. In the other hand, despite its positive effect in safeguarding diversity, in-situ conservation can also have adverse effects. In fact, populations that are conserved in-situ undergo natural selection. Although this favours coevolution and adaption to the changing environment, a fact which is sought in breeding for adaptive traits, a great diversity of genes is lost during the process. The weakest individuals which cannot survive changes that occur in the natural environment, though they may possess other useful traits for future breeding purposes, disappear and new genetic material of surviving individuals is established. Taking all the above into consideration, Article 9 of the Convention on Biological Diversity (CBD) advocates that in-situ conservation, as far as possible and as appropriate, be complemented by ex-situ measures [34].

From our findings, there is an avenue for domestication of V. doniana and conservation managers and horticulturalists should consider means to alleviate agronomic constraints such as keeping the plants at a shape and height to facilitate harvesting. Based on intrinsic characteristics and behavior of plants in the agricultural environment, domestication of V. doniana would just require adaptation to the agricultural environment [5]. Early results of horticultural trials indicated that the species responds very well in agroforestry systems (authors’ unpublished data). In the debate on where and when domestication of wild species takes place it is often argued that the key determinant is the ecological but also the intrinsic characteristics of the wild plant or animal species which rendered them suitable for domestication which downplays the cultural, social and technological prowess of the hunter-gatherers themselves [4]. The authors, however, argue that in addition to biological and ecological traits, there are socio-cultural and economic factors influencing the genetic make-up of farmer bred varieties. In this regard, our findings make an important contribution to practical NWFP conservation. They are particularly relevant for the future of ethnobotanical studies aimed at providing advice to conservation management. The decision making process in the co-management or participatory natural resource management frameworks should use holistic approaches that integrate the social, cultural and economic dimensions of the local people in relation to wild plants use. Selection of participants in conservation and domestication programmes should be based on criteria that help to recruit members that are most likely to take actions to good ends. The approach used in the current research is simple and can be applied to any wild harvested resource similar to black plum. Nonetheless, future investigations of this type should dig further into the characteristics of locations that might make their inhabitants more active in wild resource cultivation. Chukwuone [10] identified the distance to reach harvesting sites and level of resource depletion. The effect of market access should also be further investigated. In our study access to market was not investigated as a variable, as all villages have relatively easy access to a market. Another important area of investigation is the analysis of the value chain of the species and the role of the stakeholders in a scenario of an organized commercial production of the species. Final, it is worthwhile noting the limitation of testing the relationship between presumed single explanatory variables and a response variable which is under the control of several factors. In our study the conditional inference tree model seemed most robust to unveil the rationale behind the decision making process about cultivation and in-situ conservation of species. This calls for caution when drawing general conclusions from inferential statistics on a phenomenon which is under the control of complex social, biological and environmental factors [47].