Summary of qualitative variables from quadrat surveys
Several variables are documented as part of the present study. Table 1 below shows the opinions of the various households, expressed as a percentage in relation to some of the variables of interest documented during the focus group sessions. Household allocations to Genetic Resources appear to differ between the two locations. Collectively, the percentages of households exploiting the 10 types of Genetic Resources do not differ between the Batéké Plateau and Mayombe (Wilcoxon signed-rank test: p = 0.646).
Based on data from six focus groups in the two ecozones, 72 species are identified as GRs 49 of which are common to both Mayombe and the Batéké Plateau (See Supplementary Materials 1). Of these species, 60.89% are identified as plant genetic resources (PGRs). Fish resources (FRs) and zoogenetic resources (ZGRs) account for 12.38% and 26.73%, respectively. Annual (37.98%) and perennial (18.60%) PGRs, together with domesticated animal (16.28%) species, characterize the Mayombe ecological region. On the Batéké Plateau, the most common GRs are domestic animals (28.77%) and annual plant species (27.40%).
The different GRs are exploited over different areas within the two ecological zones. On the Batéké Plateau, nearly 84% of households claim to exploit GRs on small areas, compared with around 67% in the Mayombe. In the latter ecozone, one-third of all households (33.33%) claim to farm GRs on relatively large areas.
In the two study areas, 83.66%of GRs are being exploited by few households over large areas; in contrast, many households would exploit around 16.34% of GRs on small areas. Twice as many PGRs are cultivated on large areas in Mayombe than on the Batéké Plateau.
For the majority of those who were interviewed, the resources that have been cited have no ecological value. Indeed, on the Batéké Plateau, 72.60% of respondents perceive the resources that they are farming as having no ecological value. This proportion is higher in Mayombe, where more than eight out of ten people consider that the resources they exploit have no ecological value. When it comes to the socio-cultural value of harvested resources, the trend remains the same. In both ecozones, more than eight out of ten people believe that the resources they exploit have no socio-cultural value, i.e., 82.19% on the Batéké Plateau and 82.17% in Mayombe.
GRs for household self-consumption
Generally, for a given household living in one of the two ecozones, the proportion of resources that are allocated to self-consumption ranges from a minimum of 0% to a maximum of 100%. Some resources are devoted entirely to self-consumption. On average, a household allocates almost 27% of the species that it farms to self-consumption. With a median of 10%, half of all households dedicate less than 10% of their harvested species to self-consumption. Households are, therefore, largely sellers. However, it should be noted that self-consumption behavior varies greatly from one household to the next (standard deviation; SD = ± 32.93%). The average portion that is dedicated to self-consumption appears to be higher in Mayombe than on the Batéké Plateau (29.14% vs. 22.25%). Moreover, this superiority is confirmed by the values of the 3rd quartile and the median. Indeed, half of all households in Mayombe devote at least 20% of their harvested species to self-consumption, compared with less than 10% on the Batéké Plateau.
The marketing of GRs, an essential survival issue
In general, for a given household in one of the two ecozones, the proportion of resources that are allocated to marketing ranges from a minimum of 0% to a maximum of 100%. This means that some resources are allocated entirely to the marketplace. On average, a household allocates almost 65% of the resources that it produces to sale in local markets. With a median of 80%, half of all households allocate more than 80% of their exploited resources to sales. Households are, therefore, largely sellers, as highlighted in the previous section. From a specific point of view, the average portion that is dedicated to sales seems to be lower in Mayombe than on the Batéké Plateau (58.45% vs. 76.38%). This is more logical given that self-consumption and sales play complementary roles. Moreover, the median confirms this superiority. In Mayombe, half of all households sell at least 76% of their harvested species, while on Batéké Plateau, half of all households sell more than 90% of their harvested species.
Plant families and growth forms inventoried in Mayombe
Observations that were made in the agroforestry fields of Mayombe (Table 2) show 72 species, more than half of which are trees. These species belong to 37 families, with the family Fabaceae being the largest in terms of number (eight species). Moraceae were second (seven species). The two other best-represented families are the Anacardiaceae and Euphorbiaceae, with four species each. The Bombacaceae, Dioscoreaceae, Malvaceae, Musaceae, and Solanaceae are each represented by three species. The remaining families are less well represented, i.e., Amaranthaceae, Apocynaceae, Asteraceae, Verbenaceae, and Zingiberaceae, among others.
GR utilization scores
The overall use of food and non-food species is captured in calculations of indices such as CI, SP and CIA scores. Table 3 shows that before adjusting CI scores, the top 10-ranked culturally important species at the household level in Mayombe and the Batéké Plateau are food species. Manihot esculenta is the highest ranked on the list, followed by Arachis hypogaea, Zea mays, Dioscorea alata, and Musa acuminata (Table 3: Rank 1). Using the adjusted scores, however, Manihot esculenta, which is the top on the list of culturally important food species, fell to 14th place (Table 3: Rank 2). Arachis hypogaea loses its position as the second most culturally important food species, falling to 38th place on the list of 72 species.
Table 4 presents an overview of the species groups obtained using the k-Prototype algorithm for mixed data types (categorical and numerical). The table is divided into two parts. The first part shows the scores calculated for each of the six species groups. The second part describes the characteristics and frequencies of the species in each group.
In the first group, the species that were under consideration have a mean adjusted score of < 0.0055, and all of them are used for wood energy, e.g., Albizia ferruginea, Anthocleista vogelii Planch., Pentaclethra macrophylla Benth., Hymenocardia acida Tul., and Millettia versicolor Welw. ex Bak. The second group includes species with a mean adjusted score < 0.0514. These species have a low food use. About 36% of these species are used for pharmaceutical purposes and most are used for timber, e.g., Ceiba pentandra, Celtis mildbraedii Engl., Entandrophragma angolense, Milicia excelsa, Nauclea diderrichii (De Wild.) Merr., and Terminalia superba. Species that are used for handicrafts account for about 18% of this group. These include, for example, Lannea welwitschii, Musanga cecropioides R. Br., Ricinodendron heudelotii, and Alstonia boonei. In group 3, the average score is below 0.0698. Food use remains low. All species in this group are used for pharmaceutical purposes, e.g., Cola bruneelii De Wild., Carica papaya, Alchornea cordifolia, Pycnanthus angolensis, Celtis mildbraedii, and Millettia versicolor. The last three groups have the highest use scores. In group 4, the species that are listed have been cited for food use in approximately one in three cases. Finally, the last group contains species with an adjusted score of over 0.41 and a CI score in the range of 0.6 to 0.9. This group is strongly dominated by species for food use, with nearly 77% of declarations.
Yams as a component poorly represented in peasant agroforestry fields
A hypothesis that the proportion of yam-growing households in both regions was less than 3% was subjected to the Student’s t-test. In view of the results of the Student’s t-test, at the critical threshold of 5%, there is sufficient evidence to affirm that yam cultivation is carried out in a very low proportion (< 3%) in both ecozones. A logistic regression was performed to investigate the factors that explain why yam is under cultivation or what factors increase the likelihood of a household growing the crop. This model shows that ecozone, the number of households cultivating yams, and household perception of its ecological value are the factors with the greatest impact on the probability of a household cultivating yams. The fact that a household belongs to the Mayombe ecozone and perceives yams as having no socio-cultural value has a positive impact on its probability of growing yams. However, the fact that the species is cultivated by a few households negatively affects the probability of the species being yam.
The results in Table 5 show that if a household is in the Mayombe ecozone it increases its chances of growing yams by up to 5.72 times. Yam is perceived as being grown by many households rather than a small group. Finally, species that are considered to have no socio-cultural value are 3.34 times more likely to be yams than species that are considered to have socio-cultural value.
Specific diversity in peasant agroforestry fields around the Luki biosphere reserve in Mayombe
A total of 86 peasant agroforestry fields have been inventoried. Their surface areas range in size from a minimum of less than one ha to a maximum of one hectare (ha). However, the average size of a unit is around 0.19 ha, with a SD of around 0.2 ha. Furthermore, one unit in two is less than 0.12 hectares in size.
In terms of population density, the villages under consideration have densities ranging from a minimum of 10 inhabitants per km2 to a maximum of 416.67 inhabitants per km2. The average density is around 55.24 inhabitants per km2. However, this distribution is highly disparate, with a standard deviation of 138.44 inhabitants per km2. Three villages out of four have a density of less than 5.00 inhabitants per km2, and one village out of two has a density of less than 1.89 inhabitants per km2.
To capture the species diversity of the different peasant agroforestry fields, the Shannon index was calculated. One field in four has an index below 0.28, and one field in two has an index below 0.44. This indicates a low level of diversity within the units considered. In addition, some peasant agroforestry fields are highly diversified, with an index of 1.0. Finally, 25% of peasant agroforestry fields have a diversity index of over 0.53. As for the number of species per peasant agroforestry field, it ranges from a minimum of two species to a maximum of 17 species. The average number of species per peasant agroforestry field remains close to seven, with a small margin of three species. In 50% of units, there are more than six species.
Links between diversity and population density
We chose a non-parametric approach to detect links between the specific diversity of a peasant agroforestry field and the population density around the Luki Biosphere Reserve.. The data were analyzed using a correlation test based on Kendall’s ranks. The results are presented in Table 6.
The confidence interval at the 5% level (i.e. 95% confidence level) does not include zero (0), indicating a link between the two variables.
To reach a clear conclusion on the association between the two variables, it is important to analyze this link while considering the effect of these sub-groups. The Kruskall–Wallis test is used for this purpose.
Figure 1 clearly shows a variation in average diversity based on density. The study found that villages with low population density have lower diversity compared to those with higher density. This result is consistent with the findings of the Kendall test and is supported by the highly significant Kruskal–Wallis test.
Difference between groups, Kruskall Wallis test.
Based on these bivariate analyses, the hypothesis of a link between the specific diversity of a field and the population density of the villages surrounding the Luki Biosphere Reserve is strongly supported. Furthermore, this association is positive.
Modelling the relationship between species diversity and population density in villages surrounding the Luki biosphere reserve
To simultaneously relate the specific diversity of a field to the population density of the villages surrounding the Luki Biosphere Reserve, a linear regression model has been fitted to the data. The model was globally significant (P-value < 2 × 10–16; R2 = 72.62%). The results show that when density increases by 1%, diversity increases by 0.00135. In other words, when density doubles, diversity increases by 0.135.
Seasonality
The agricultural calendar, agricultural activities in support of livelihoods, and periodic problems that are linked to agrobiodiversity management have made it possible to document seasonality.
To better understand the agricultural calendar according to the opinions gathered in the focus groups in the different villages, we focused on the five important crops with high CI scores, namely, Manihot esculenta, Arachis hypogaea, Zea mays, Dioscorea alata, and Musa acuminata. It is worth noting that ongoing global changes, in particular rainfall-related disturbances, are modifying men’s and women’s perceptions of the ideal cropping season, depending upon the ecozone and village, with a potential effect on cropping times and the availability of foodstuffs on the market.
Overall, households are engaged in land preparation activities three to five months prior to planting in the villages of Mbakana, Kimufu, and Mangala. We also noted that harvesting activities extend throughout the year according to focus group participants in Mbakana. Sale activities in Mayombe are spread out between January and October. Harvesting takes place at the end of each growing season (April to July and November to January). In Mayombe (Kimufu and Mangala), harvesting activities occur from January to March. It should be noted that harvests of crops such as okra and eggplant, once mature, take place every two weeks. The overall observation is also that agricultural activities cover almost all twelve months of the year and have different implications in terms of the efforts of men and women.
Relying only upon agricultural production, in the strictest sense of the term, was inadequate to sustain the livelihoods of households. This is why families resort to hunting in Mayombe throughout the year, according to the men’s focus group of Mangala village. The men’s focus group also revealed that fishing is practiced between June and September, and fruit picking takes place in Mayombe between December and February. Harvesting of firewood and carbonization (charcoal-making) are carried out throughout the year in Mayombe. It should be noted that for both men and women focus groups in Mbakana, fishing, hunting, NTFP (Non-Timber Forest Product) collection, and charcoal burning are performed throughout the year. Edible fruits are harvested between March and January. We found that the question about household livelihood support activities presented some sensitivities for men in Kimufu, a village in the Tsumba-Kituti enclave of the Luki Biosphere Reserve. According to the women of Mbakana, fishing, hunting and artisanal timber cutting are secondary activities that are practiced year-round by some families. As a survival activity, most families or households have only agriculture to resort to in the strictest sense of the word. Households are interested in crops such as eggplant, okra, maize, and cassava.
Litter fall, pest attacks, floods, drought, and proliferation of plant and animal diseases are cited as possible problems that are related to agrobiodiversity management. The women and men who took part in the various focus groups have been able to suggest the periods during which these problems were identified. For the villages in the Mayombe ecozone, both women and men felt that plant diseases and pest attacks (e.g., Gambian pocket rats, cane rats) occur throughout the year. According to the men’s opinions in Mbakana. this is not at all the case for this village on the Batéké Plateau. The major and permanent problem that is frequently cited is the poor quality of the soil. The women of Mbakana do not all agree regarding the sources of these problems. The plant diseases that were cited by women and men in Mangala and Kimufu are the presence of various fungi that are responsible for cassava rot (i.e., Lasiodiplodia theobromae, Cylindrocarpon candidum, Aspergillus niger, A. flavus; Fusarium solani47,48, and a range of diseases referred to as witches’ broom (Candidatus phytoplasma aurantifolia, Candidatus phytoplasma palmicola, or basidiomycete fungi), which affect their productivity. They also reported yam mosaic virus (Potyvirus) and anthracnose (Colletotrichum gloeosporioides). Gambian pocket rat (Cricetomys gambianus) and the large cane rat (Thryonomys swinderianus) were cited as periodic crop pests in the Mayombe ecozone. However, the women of Mangala acknowledged that the Gambia pocket rat and the African civet (Civettictis civetta) are involved in seed dissemination. For the men of Mangala, drought is considered as irregular and due to climate change, which is affecting food crop production.
