Study site and sampling of fungi
Fieldwork was done in the province of Tshopo, located 2° N 2° S and 22° E 28° E [20]. The vegetation from Tshopo is mainly characterized by a tropical evergreen rainforest and some groves of semi-deciduous forests found on hills and plateaus [20,21,22]. These rainforests are mainly dominated by species such as Gilbertiodendron dewevrei (De Wild.) J. Léonard, Brachystegia laurentii (De Wild.) Louis, Scorodophloeus zenkeri Harms, Prioria balsamifera (Vermoesen) Breteler, and Julbernardia seretii (De Wild.) Troupin [20,21,22,23,24].
The fungi were collected between 2013 and 2016, mostly within plots situated in the rainforests of the Biosphere reserve of Yangambi (0° 51′ 01.62″ N; 24° 31′ 43.53″ E) and Yoko reserve (0° 17′ 34.9″ N; 25° 18′ 27.4″ E) (Fig. 1). Monitoring of plots follows Lodge et al. [25], and fungal sampling was performed within forests dominated by Gilbertiodendron dewevrei, Brachystegia laurentii, Julbernardia seretii, Uapaca heudelotii, and Uapaca guineensis and in mixed forests. Three plots of 100 × 100 m were demarcated in each type of forest; each of them divided in a 20 × 20 m grid. Due to the elongated shape of Uapaca heudelotii-dominated forests, more stretched plots were installed in this forest type. In each plot, the aboveground fruiting bodies of all EcM fungi were collected by walking parallel bands covering the entire plot [26]. Unidentifiable fruit bodies were photographed in situ and dried after notes were taken from their macromorphological features (following [18]). Voucher specimens were dried using a field drier [27] and deposited at the herbarium of Meise Botanic Garden (Belgium).
Fungal identification
The identification of voucher specimens was done using macroscopic and microscopic characteristics, as outlined in Eyi-Ndong et al. [18]. The available taxonomic literature only covers a fraction of the Central African rainforest fungi. The following contributions were used for identification: Heinemann [28], Heim [29], Pegler [30], Heinemann and Rammeloo [31,32,33], Buyck [8, 34, 35], De Kesel et al .[4, 9, 16], Verbeken and Walleyn [36], Eyi-Ndong et al. [18], as well as identification keys provided by the Fungus Flora of Tropical Africa (https://www.ffta-online.org/) and Edible Fungi of Tropical Africa (https://www.efta-online.org/). Species names and author’s abbreviations largely follow Index Fungorum (http://www.indexfungorum.org/Names/Names.asp). Unidentified taxa were left out of the analysis.
Ethnomycological data acquisition and treatment
Ethnomycological data on locally consumed fungi were collected from local people living around the Man-and-Biosphere reserve of Yangambi and the Yoko reserve. Data were collected using open, semi-structured interviews (paper fill-in questionnaires). The interviews involved mainly the head of the family, sometimes assisted by other family members. The questions focused basically on the informant’s knowledge concerning the different locally consumed edible fungi. Interviews were obtained from 160 informants, all randomly selected, but belonging to one of 6 ethnic communities (Bakumu, Turumbu, Topoke, Lokele, Ngelema, and Ngando). The entire pool of informants counted 88 men (55%) and 72 women (45%), ranging from 16 to 72 years old. The interviewed communities live in four villages in the vicinity of the Man-and-Biosphere reserve of Yangambi (Yakako, Yalungu, Lyoli, and Lobiloto), 4 suburbs of Yangambi city (IFA, Lusambila, Ekuchu, and Manzikala), and 4 villages surrounding the Yoko forest reserve (Babogombe, Biaro, PK 48, and PK 25).
With an average of 600 households living in the studied area, the average number of studied households revolves around 25 per village (4.2% of the entire pool). Within the 4 suburbs of Yangambi, the distribution of households was 150 (25%), 120 (20%), 80 (13.3%), and 50 (8.3%) respectively reported from Ekuchu, Lusambila, Manzikala, and IFA. According to Gumucio et al. [37], the sample size (n) of the interviewed households should be calculated as follows: n = \( \frac{N}{1+N\times {e}^2} \), where N is the total number of available households and e is the level of precision. With a precision level of ± 7%, the sample size was calculated by the following formula: n = \( \frac{600}{1+\left(N\times {0.07}^2\right)} \) ≈ 152, households that were fitted to 160 informants. Referring to the mean distribution of households per sampling site (villages and suburbs of Yangambi), 7 households were interviewed from each of the 4 villages while 38 from Ekuchu, 30 from Lusambila, 20 from Manzikala, and 12 households from IFA. In each sampling site, all households were numbered. The first numbers referring to the considered sample size were selected randomly using the function “rand.between” of the Excel software.
The analyzed data only refer to locally eaten fungi and allow to present (per species) information on the edible mushrooms’ cultural significance (EMCS). According to Pieroni [38], the edible mushrooms’ cultural significance index refers to the importance or the role that a given fungal taxon or group of fungi plays in the social life of a group of people or a community. Using pictures or fresh sporocarps of edible fungi, the edible mushrooms’ cultural significance for a fungal species corresponds with the sum of the scores for “edibility status” given by all informants, divided by the total number of informants. Edibility status scores or frequencies of mention (FM) were assigned through informants’ answers to the following question: Do you eat this mushroom? (yes = 1, no = 0). A Kruskal-Wallis analysis was used to test the role of ethnicity on the edibility status score, and how this changes according to the different trophic groups.