Background
Feeding a dramatically growing population while conserving natural resources is one of the greatest contemporary challenges decision makers face. Concerns are even greater in areas where people rely on these natural resources for their daily needs. Interestingly, there is a growing interest in integrating native Plant Genetic Resources (PGR) into formal farming systems, as a critical step towards achieving the Millennium Development Goal 1 “
combating extreme poverty and hunger” [
1]. Similarly, with regard to land use dynamics, this step is perceived as a more realistic approach to conservation [
2‐
4]. Conservation of PGR is vital not only because of their prominent role in food and agriculture [
5] but also for the adaptation of certain cultivars to predicted changes in the climate, diseases and pests in the future [
5‐
7]. The growing interest on agroforestry systems as the future of PGR conservation can be explained by the optimal ecological conditions and the protection provided to plants in these traditional farming systems [
6]. Among these traditional farming systems, Home gardens (HGs) have attracted attention in the last decades.
HGs are a cultivated space, generally adjacent to a household or slightly further away but still easily accessible [
8]. The number of studies focusing on HG has recently increased worldwide with special focus on their roles in improving rural households’ livelihoods while conserving biodiversity. For instance, HGs have been reported to support food system [
9‐
12], mitigate economic hardship and provide additional income for households [
13‐
16]. In addition, they enhance the empowerment and social position of women [
17‐
19]. HGs have been also reported effective in agro-biodiversity conservation [
20‐
22], ecosystem services provision [
23] and culture preservation [
17,
24,
25].
However, information on African HGs (as compared to their tropical Latin American counter parts) is relatively poor. They have been for long time been neglected by academic research and development policies [
26‐
28]. Existing literature on African HG focuses mainly on their contribution to global household food and nutrition [
29‐
36], uses and traditional knowledge associated to them [
37] as well as their plant diversity and potential contribution to biodiversity conservation [
22,
38‐
41]. However, with the current socio-cultural dynamics in Africa i.e. erosion of traditional knowledge of plant and associated uses [
42], westernization of production and consumption systems [
43,
44], increasing use of improved crops [
45,
46] and rapid population growth [
47], traditional HGs are threatened [
11]. Thus, their potential for biodiversity conservation is questionable. In this line, how local factors shape ownership of HG and how these factors coupled with garden features determine plant diversity and structure in HG are important questions to be addressed. Investigating these aspects of HGs is a prerequisite to ensure effective mainstreaming of HGs into future conservation and production policies. Therefore, this study explored the socio-economic factors influencing HG ownership and how these factors combined with intrinsic characteristics of HGs, shape their plant diversity and structure across three bio-geographical zones in the republic of Benin.
Traditionally, women and old men used to cultivate fields close to their village, while the younger men often set their fields a bit further from their village [
48]. With this traditional specialization in land use, we expected home gardens to be mostly owned by women and old persons. In addition, as western school education influence lifestyle including farm production purposes [
38], we expected home gardens to be owned mainly by uneducated people. As home gardening is an agricultural practice, we expected HGs to be owned mainly by people with on-farm activities. We also expect to find significant interactions among these factors. Furthermore, based on previously reported influence of socio-economic conditions of HG owners [
38,
49‐
51] and intrinsic characteristics [
51‐
53] on plants maintained in HGs in Latina America, we predicted that plant diversity in HG would also increase with age and size of the HG, both increasing with the age of the owner.
In this study, plant diversity refers to the diversity of cultivars, landraces, ecotypes, wild relatives and wild plants, deliberately maintained in HGs. It excludes weedy species which are spontaneous vegetation, removed by the owner as often as possible. Furthermore, by shaping plant diversity in HG, ecological conditions [
50], socio-economic factors , preferences of HG owners but also market opportunities [
40,
41] control the structure of the HGs in maintaining an assemblage of herbs, vines, shrubs and trees. Generally, the HGs structure refers to the composition, including spatial arrangement of the woody component, vertical stratification and temporal arrangement of the different components [
54]. Here, we focused on composition (with plant richness and diversity of CWR as estimates) and vertical stratification (with prevailing plant group as estimate) and did not address the temporal arrangement of the HGs. Like many tropical HGs [
54], we predicted HGs in Benin to be diversely composed and multilayered. We further predicted that the structure of the HGs would be dependent upon bio-geographical zones and socio-economic conditions of the HGs owners.
Discussion
This study analyses how socio-economic conditions of people and HGs characteristics determine ownership, plant diversity as well as structure of HG.
The fact that probability of HG ownership increases with age suggests that adult and elderly people are more involved in gardening activities than young people. This finding supports previous observations [
14] in Nicaragua, [
70] Texas (USA) and [
71] central Italia. Such finding, particularly for old persons could suggest that gardening activities do not require intensive physical efforts and thus are adapted to declining capacity of old people to reach distant farms or/and need to have useful plants species at hand for daily use. In the particular context of the study area, women and older men are known to keep cultivation fields close to their village including HGs, while the younger men rather use distant fields [
72].. While there was no discrepancy in HG ownership between adult men and women, at an earlier age (<30), it was more likely to find young women owner of gardens than young men and inversely at a later age (>60). Early involvement of women in home gardening is consistent with the trend previously observed in Latin American HGs [
14,
18,
52]. Such observation could be explained by the local and cultural context of the study area, which predisposes women at earlier age to home gardening. Indeed, there is a discrepancy between young men and women in access to school [
73] with less enrolment for young women. Thus the latter are more involved in household related works than younger men. The early involvement of young women in gardening activities is probably not a deliberate choice but rather a strategy to gain a certain social status, enhance their livelihoods and purchase power [
18], particularly in a patriarchal context of African societies where farmland property right is largely male-dominated [
74]. Our data also support the hypothesis that the education level does not affect HG ownership. This observation is not necessarily associated with the low school enrolment rate of developing countries. For instance in a case study from a developed country (Texas, USA) [
70] HG owners were also irregularly distributed among education levels with no obvious trend. However, we remarked that more HG owners were less educated, probably because people with higher education level have access to other job opportunities and thus may have less time to allocate to home gardening.
In the study area we detected two ways to own a HG: non-inheritance i.e. own initiation and inheritance. Inheritance of HG was consistently more seen in young informants than for adults and old informants.
Because only 18 % of the observed variation in HG ownership was explained by age, gender and education level, in the future additional characteristics (i.e. status in household, farmland asset, distance from farm, number of farms, etc.) as well as local context (i.e. importance of animal rearing, Land tenure, market opportunities, etc.) should be combined to develop reliable predictive models of HG ownership.
Plant diversity in HG is assumed to be determined by complex socio-economic and ecological factors [
49,
50] as well as intrinsic features of HG [
75,
76]. While our data partially support this hypothesis, our analyses suggest that this should be placed into a specific context. For instance in this study neither the age of gardener, gender, education level nor size of HG were found to significantly influence plant diversity (species richness) in HGs. These observations are inconsistent with previous studies in tropical HGs. Indeed age and gender of the garden caretaker were previously reported to be significant variables explaining differences in agro-biodiversity among households in the Peruvian amazon [
77] where an increase of 10 years in age corresponded to a predicted increase of 1.40 species in the garden. Also, garden size significantly influences species richness in different regions worldwide (e.g. Niger [
76]; Northeastern Brazil [
75]; Indonesia [
78]). While these trends were not observed in Benin, our data rather revealed that the age of the HG significantly determined its plant diversity (
p-value < 0.033). The older the HG, the more diversified the species (richness) (Table
3, Fig.
5), which is congruent with observations in Amazonian villages [
49] but contradicts findings in Mexico [
52] and in Indonesia [
53], where plant diversity in young HGs was higher than in older ones. Beyond differences in socio-economic and ecological contexts among these regions, the discrepancies observed in this study would suggest that (i) the age of HG is not a comprehensive and reliable predictor of plant diversity in HGs and (ii) it should be considered in its context, for instance by accounting for the age of the gardener. Indeed, our findings support that plant diversity in HGs is determined by interaction of age of HG with age of gardener. While plant diversity within HGs decreased with the age of HG for young owners, it increased with the age of HG for adult and was stable with age of HG for elderly people. These results could be explained by the following two reasons. First, young people tend to produce plants with attractive market value [
38]. As such, diversity of plant within their HGs would continuously be adapted to local market demand. Second, young people who generally inherited their HGs may have little knowledge about all plants maintained within these HGs. Consequently they could selectively use and manage plants of interest and then cause depletion of unknown plants. In contrary, adult people might be less market-oriented and therefore cultivate plants regardless of their cash value.
Plant diversity in HG was also influenced by the interaction of the size of HGs and age of the gardener. Indeed, plant diversity decreased with increasing size of HG for young and adult persons and increased with increasing size of HG for the elderly. Such observations indicate a trend of simplification of home gardens diversity with increasing HG size across generations and could suggest a critical decline of the plant diversity maintained in HG across generations. Indeed, the age of the owner of the HG is very important because plant acquisition is known to be a lifelong undertaking [
77].
Only 11 % of the total variation of plant diversity among HG was explained by the here-considered variables (age, gender, education level, age and size of HG) suggesting that there is a need to integrate supplementary factors such as land assets, social capital, culture and labor into the model [
77]. Additionally, there is a need to better understand the function of a HG in a specific context. While their contribution to agro-biodiversity conservation is obvious [
20,
22], in many cases, HGs are primarily devoted to food and non-food productions [
11]. With agricultural dynamics including production orientation, changes on HGs structure have been reported [
79,
41]. In the study area some gardens were converted into “small farms” for conventional herb of vegetables production (Gbedomon R.C., field observations). Personal observations, which should be tested in the future, suggest that models explaining HG ownership and their plant diversity could be improved by a prior typology of HGs, which could be used as a dummy variable in the models.
Three categories of HGs were distinguished in the study area: (i) herb based gardens, (ii) herb and shrub gardens and (iii) palm and lianas gardens. Herbs based gardens were the most encountered from Humid to Semi-arid zones, indicating that herbs are an invariable HG component as reported by [
39,
80]. Herb and shrub based HGs were mostly encountered in Humid and Semi-arid zones while palms and lianas were mostly encountered in sub-humid and semi-arid zones. In southern Benin (Humid zone), where land availability is very low due to high population density [
60], herbaceous plants are preferred over shrubs, trees and palms, presumably because of their short reproductive cycle, which allows an efficient management of land, a flexibility in species composition management as well as abundant harvests in the growing season. In middle and north Benin (sub-humid and semi-arid zones), the short reproductive cycle of herbaceous species could be a solution against the declining length of the rainy season [
81]. Because of more land availability in these zones [
48], HGs are larger, which allows maintenance of shrubs, palms and trees (i.e. individuals of
Parkia biglobosa, Vitellaria paradoxa or Palm species).
According to our findings, HG structure is dynamic and it is influenced by the socio-economic conditions of the HG owner as well as ecological conditions, as reported elsewhere [
49,
50]. Women, presumably because of their specific daily needs, generally owned herb-based or herbs and shrub-based HGs. These categories of HGs shelter seasonal, annual or biannual plant species that likely provide relatively stable year-round products for household consumption. Women are known to use HG products for daily consumption of the household rather than for sale or gifts [
82]. In contrast, young people are mainly interested in wild or semi-wild species with attractive market values [
38]. HGs owner characteristics and ecological conditions, as well as local context could also influence the structure of HGs. This has been illustrated in a recent study suggesting that market access and marketing opportunities led to changes in the structure, composition and function of HGs [
40,
41].
Conclusion
This study showed that HG ownership is more dependent upon interactions between socio-economic factors than between the individual effects of these factors. Similarly, interactions between these factors and intrinsic features of HG better explained the differences in plant diversity among HGs. While plant diversity (species richness) was not determined by age or gender of the HG owner, these variables significantly affected plant composition (prevailing plant groups) within HGs. The observed early involvement of women in home gardening evidences their traditional responsibility in being responsible for HG. Furthermore their important interest in herbs and shrubs demonstrate a gender-biased (in favor of female) asset for conservation of agro-biodiversity especially CWRs, landraces and wild leafy vegetables. Therefore, training programs aiming at agrobiodiversity conservation should focus on women.
The study also shows a positive correlation between plant diversity and HG size but a decreasing effect of owners’ age (generational) on plant diversity. In absence of interventions and in the context of current social and agricultural change, the risk of simplification and dissolution of HG, previously projected [
11], seems to be a real challenge. Urgent actions are required to actively integrate HGs into national conservation strategies.
Finally we conclude that HG ownership as well as plant diversity of plant in HG are affected by many correlated factors, i.e., socio-economic, demographic, local context, ecological conditions and intrinsic features of gardens etc. Thus, miss-specification or simplification of complexity could lead to wrong models and misinterpretations. Scientists and decision makers should therefore account for that risk when formulating policies.
Competing interests
The author(s) declare that they have no competing interests.
Authors’ contributions
RCG, ABF and AEA designed the study. RCG, VKS and AFRI supervised the field data collection. RCG, VKS and RGK processed the data, performed the statistical analysis and RCG drafted the manuscript with contributions of ABF and VKS. All authors read and approved the final manuscript.
RCG is a PhD student in agro-ecology at University of Abomey-Calavi. He is working on HGs as a new perspective for phytogenetic resources conservation in Benin.
ABF (PhD) is a Senior Lecturer in natural resources management and conservation biology at University of Agriculture of Kétou, and postdoc fellow at Albert-Ludwigs-Universität Freiburg.
VKS and AFRI are PhD students in conservation biology of wild palm species at University of Abomey-Calavi.
RGK (PhD) is an Associate Professor in Biometry and Forest modeling University of Abomey-Calavi; Young Affiliate of the Third World Academy of Sciences. He is leading the Laboratory of Biomathematics and Forest Estimations.
AEA (PhD) is an Associate Professor in conservation genetic, forest Ecology & ethnobotany at University of Abomey-Calavi; Young affiliate of the World Academy of Sciences and IUCN-SSC-CWRSG Regional Leader for sub Saharan Africa.
All authors are members of a working group on HGs and CWRs at the University of Abomey-Calavi (Benin).