The study was conducted in Péni Classified Forest (PCF) located in southwestern Burkina Faso on the National Road 7 at 32 km of Bobo Dioulasso (Figure 1). The GPS coordinates are latitudes 10˚55'02.5" and 10˚56'33" North and longitudes 4˚27'26.5" and 4˚29'37.5" West.

The PCF belongs to the South Sudanese phytogeographical sector (Guinko, 1984). The climate is of the Sudano-Guinean type, over thirty years (1992-2021) in Péni commune is 1064.78 mm. The rainy season extends from May to September, with some rain throughout the year. The rainiest month is August with 281.51 mm. From 1992 to 2021 the average temperature is equal to 27.55˚C with minima of 13.17˚C in December and maxima of 41.54˚C in April. The vegetation is composed of a mosaic of savannahs (woods, grasses, shrubs, and trees)

and gallery forests (Fontès & Guinko, 1995). The main soil types at the study site are ferrallitic soils, poorly evolved soils, and soils with sesquioxide and rapidly mineralizable organic matter (BNDT, 2012).

The sampling method was stratified according to the vegetation units of the PCF. 213 phytosociological plots of 900 m² (30 m × 30 m) and 500 m² (50 m × 10 m) were used respectively in the savannahs and in the gallery forests for the woody stratum, then in each woody stratum, a subplot of 100 m² (10 m × 10 m) was used to inventory the herbaceous stratum (Thiombiano et al., 2016). Ribbons, strings, and stakes allowed the demarcation of the plots. In each plot, the following data were recorded: Site identification characteristics, station conditions, overall recovery rate, list of all species present with an abundance-dominance coefficient according to the Braun-Blanquet (1932) scale. The geographic coordinates of the center of each survey plot were noted using a Garmin 62S GPS. In addition, Observations on the human disturbances were made within each phytosociological survey. These include bush fires, grazing, wood cutting and carbonization (charcoal production site). Their presence in the survey is noted 1 and their absence is noted 0 (Ouoba, 2006).

Floristic richness, species frequency, were calculated and biological and phytogeographical types were determined. The species were determined based on the flora of Lebrun and Stork (1991, 1992, 1995, 1997), Aubréville (1950), Hutchinson and Dalziel (1954, 1958, 1963, 1968, 1972) and the Arbonnier (2019) botanical guide. The nomenclature of species has been adapted to that of the Catalogue of Vascular Plants of Burkina Faso (Thiombiano et al., 2012).

Equation (1) was used to determine species frequencies:

F r = N i N (1)

where Ni is the number of surveys in which a species i is encountered and N is the total number of records. Species were then grouped according to their frequency frequency classes. Sambaré’s (2013) frequency classes were used to distinguish between rare species (Fr ≤ 5%), occasional species (Fr between 5 and 25%), infrequent species (Fr between 25% and 50%), and frequent species (Fr ≥ 50).

For the determination of biological spectra, those defined by Raunkiaer (1934) and adapted for the study of tropical plant formations by various authors (Godron et al., 1968; Aké Assi, 2001, 2002; Ouoba, 2006) were used. As for the phytogeographical spectra, we used those of White (1986). The Excel spreadsheet and the RAWGraphs 2.0 beta (Mauri et al., 2017) software were used to realize the graphs.

These analyses focused on the calculation of diversity indices.

• The Shannon-Weaver Index (H') was used to assess species diversity (Legendre & Legendre, 1998). This index varies according to the number of species present. It is expressed in bits and varies from the lowest diversity (0 bit) to the highest (5 bits). It was evaluated by equation (2) of Kent and Cooker (2003) where:

H = − ∑ i = 1 p i ln ( p i ) (2)

with pi the ratio of the average overlap of species i in the vegetation unit to the sum of all overlaps of all species of the vegetation unit.

• The mode of distribution of species within plant formations (or equitability) is assessed using Piélou’s equitability index (J) (Kent & Cooker, 2003) according to the following equation:

J = H ln ( N ) (3)

where H is the Shannon diversity index, and N is the total number of species in one vegetation unit. This index makes it possible to assess the nature of the distribution of species in plant formations and varies between 0 and 1 (Boubacar et al., 2022). It tends to 0 when there is a phenomenon of dominance and tends to 1 when the distribution of species is regular.

• The probability that two randomly selected individuals belong to the same species was measured using the Simpson index (Magurran, 2004): Equation (4) was used:

D = ∑ i = 1 s n i ( n i − 1 ) N ( N − 1 ) (4)

given species i and N, the total abundance of individuals. This index has a value of 0 to indicate the maximum diversity, and a value of 1 to indicate the minimum diversity. To obtain “more intuitive” values, the reciprocal of the Simpson index represented by 1 − D was calculated, the maximum diversity being represented by value 1, and the minimum diversity by value 0 (Traoré, 2013). This diversity index gives more weight to abundant species than to rare species.

• The similarity between two types of vegetation was verified by the Jaccard index (Cj) (Jaccard, 1908), calculated based on the presence/absence of species, by the following equation:

C j = J a + b + j (5)

where j is the number of species common to two units s of vegetation A and B; a, the number of species on site A and b, the number of species on site B. It tends to 0 when there is no floristic similarity and to 1 otherwise.

The processing of data on the presence or absence of cutting, grazing, bushfires and carbonization outbreaks consisted in relating the number of surveys in which these factors were observed to the total number of surveys. These results, for each factor, were reported as a percentage. The disturbance index was calculated to identify the vegetation units most sensitive to anthropogenic disturbance. Indeed, an ecosystem influenced by human action, the more therophytes and chamephytes become more important (Floret & Pontanier, 1982). This index is formulated and used in several studies (Loisel & Gomila, 1993; Gnahoré et al., 2020).

IP = NumberofChamephytes + NumberofTherophytes Totalspeciesnumber × 100 (6)

The floristic inventory identified 475 species in 321 genera and 87 families (Table 1). This richness is composed of 201 woody and 274 herbaceous. The most represented families are Poaceae (12 %), Fabaceae-Faboideae (11.37%), Rubiaceae (5.89%), Asteraceae (4.21%), Malvaceae (4%), Fabaceae-Caesalpinioideae (3.79%), Lamiaceae (3.58%), Apocynaceae (3.37%), Cyperaceae (3.16%), Combretaceae (2.95%), Vitaceae (2.74%), Acanthaceae (2.53%) and Fabaceae-Mimosoideae (2.32%) with more than 10 species each. 64.93% of this flora is found in shrub savannahs, 61.26% in wooded savannahs, 44% in gallery forests and 23.58% in plantations (Figure 2).

The distribution of this rich floristic within the vegetation units of the PCF is shown in Figure 3. Shrub savannahs are the richest in species with 306 species

grouped into 208 genera and 67 families. They are followed by wooded savannahs with 291 species grouped into 213 genera and 61 families, then gallery forests with 209 species grouped into 168 genera and 63 families. The plantations are the least rich in species and total 112 species grouped into 94 genera and 43 families.

Figure 4 shows that most of the species recorded are very rare in Péni Classified Forest but also in each vegetation unit. Globally, 59.58% of the species int 283 species are very rare with an occurrence of less than 5%. These include Milicia excelsa (Welw.) C.C.Berg, Pentadesma butyracea Sabine, Paullinia pinnata L., Ximenia americana L., Protea madiensis Oliv., Anogeissus leiocarpa (DC.) Guill. & Perr., Canarium schweinfurthii Engl. for woody stratum. Chlorophytum pusillum Schweinf. ex Baker, Elionurus elegans Kunth, Clematis hirsuta Guill. & Perr., Macledium sessiliflorum (Harv.) S.Ortiz, Hyperthelia dissoluta (Nees ex Steud.) Clayton for herbaceous stratum. Among the vegetation units, shrub and wooded savannahs comprise respectively 56.21% and 44.67% of very rare species.

Figure 5 shows the ten most represented families in each vegetation unit. In the shrub savannahs, Poaceae (14.47%), Fabaceae-Faboideae (12.22%), Rubiaceae (5.79%), Asteraceae (4.50%), Combretaceae (4.50%), Malvaceae (4.50%), Fabaceae-Caesalpinioideae (4.18%), Cyperaceae (3.22%), Lamiaceae (3.22%) and Apocynaceae (2.89%) dominate. For wooded savannahs, these are Fabaceae-Faboideae (12.20%), Poaceae (10.80%), Rubiaceae (6.27%), Asteraceae (5.23%), Fabaceae-Caesalpinioideae (5.23%), Malvaceae (4.53%), Combretaceae (4.18%), Apocynaceae (3.83%), Lamiaceae (3.83%) and Cyperaceae (3.48%). In gallery forests, Rubiaceae (7.55%), Fabaceae-Faboideae (6.60%), Moraceae (5.19%), Poaceae (5.19%), Apocynaceae (4.72%), Fabaceae-Caesalpinioideae (4.72%), Malvaceae (4.72%), Acanthaceae (3.77%), Asteraceae (3.77%) and Lamiaceae (3.30%) dominate. In Gmelina plantations, Fabaceae-Faboideae (15.18%), Combretaceae (7.14%), Fabaceae-Caesalpinioideae (7.14%), Fabaceae-Mimosoideae (6.25%), Rubiaceae (6.25%), Dioscoreaceae (4.46%), Apocynaceae (3.57%), Lamiaceae (3.57%), Poaceae (3.57%) and Malvaceae (2.26%) dominate.

The overall Shannon index of the PCF is 4.96 bits, the Pielou equitability index 0.80 and the Simpson reciprocal index 0.99 (Table 2). The wooded savannahs are the most diverse with a Shannon index of 4.57 bits. The lowest diversity is observed in Gmelina plantations (2.94 bits). The pielou equitability index is roughly equal between gallery forests and wooded savannahs with 0.79 and 0.80 respectively, reflecting an equitable distribution of species in these vegetation units. Simpson’s reciprocal index is roughly equal between gallery forests, wooded savannahs and shrubby savannahs with values close to 1 reflecting a maximum diversity within these vegetation units.

The calculation of the Jaccard index shows that there is no similarity between the vegetation units of the PCF except for shrub savannahs and wooded savannahs which share more than 50% of the species (Table 3).

Analysis of the overall biological spectrum of the PCF shows variability in the representativeness of the biological types of the PCF (Figure 6). Phanerophytes and therophytes are dominant in the flora with crude spectra of 42.32% and 30.32% respectively, and weighted spectra of 65.69% and 22.63% reflecting the forest character of the PCF. A significant proportion of geophytes (8%) are also observed.

Within Phanerophytes, microphanerophytes (35%) and mesophanerophytes (23.76%) are the dominant subtypes followed by nanophanerophytes. The phanerophyte vines all combined occupy a proportion of nearly 15% (Figure 7).

The overall phytogeographical spectrum (Figure 8) shows a dominance of Sudanian species followed by Afro-tropical and Sudano-Zambezian species.

Wood cutting is the most observed anthropogenic disturbance factor with a frequency of 100%, followed by pastoral pressure (98.59%), bushfires (80.28%) and finally carbonization (coal making) with a frequency of 37.56% (Figure 9). Figure 10 shows the frequency of disturbances in each vegetation unit. In wooded

and shrub savannahs, the most observed disturbance factors are pastoral pressure, bush fires and wood cutting with frequencies of 100% each. Lakes and gallery forests are less affected by carbonization.

The calculation of disturbance indices shows that shrub savannahs and wooded savannahs are the most disturbed vegetation units in the PCF with indices of 49.01% and 40.20% respectively (Table 4). At the forest level, this index is 41.12%. Some disturbances are illustrated by Figure 11.