The commune of Thionck-Essyl (12˚47'08" North and 16˚31'18" West) belonging to the arrondissement of Tendouck (Figure 1) is located in Lower Casamance. It belongs to the coastal South Sudanese climate domain [9] .

The mean annual rainfall over the 1991-2021 series is 1300 mm (Figure 2).

The means of the minimum and maximum monthly temperatures recorded at the Ziguinchor meteorological station are 21.5˚C and 35˚C, respectively, during the 1990 to 2016 series [7] .

The terrain is relatively flat and has several types of soils distributed over two main areas: the continental shelf, and the flooded lands of the rice-growing valleys and mangrove forests.

The land of the continental shelf, has two types of soils: leached tropical ferruginous soils and low to medium desaturated ferralitic soils [11] cited by [2] .

For the study of woody vegetation in agroforestry systems associated with market gardening plots in the commune of Thionck-Essyl, a sample of seven (07) market gardening blocks corresponding to seven (07) of the fourteen (14) sub-districts of the commune was selected, i.e., a sampling rate of 50%. In Niaganane, two of the four blocks were selected, in Daga two of the four blocks were selected, in Kamanar all three blocks of the sub-district were selected and in Batine none of the three blocks were selected because they were not functional.

In each market garden block selected, square plots of 2500 m² each were installed, based on a sampling rate of 25% in relation to the area of each market garden block. Thus, 15 plots were installed in the seven (07) market gardening blocks selected in the sample (Table 1).

For each individual inventoried, the dendrometric parameters were measured. Thus:

F The diameter of the trunk is measured at 1.30 m height using a forestry compass to evaluate the basal area, and establish the horizontal structure of the stand;

F Mean crown diameter is measured with a metric tape in two directions (North-South and East-West) to determine woody cover;

F Tree height is measured with a SUUNTO dendrometer to establish vertical structure.

Trees with a diameter of less than 5 cm at 1.30 m are considered regenerated [12] .

The floristic list was established on the basis of the flora of Senegal [13] . Synonyms were updated on the basis of the Enumeration of Flowering Plants of Tropical Africa [14] .

The data collected was entered into the Excel 2007 spreadsheet program, which

NB: Each sub-neighborhood corresponds to a vegetable block.

was used to create the graphs and tables. The XLSTAT software, version 2014 was used to perform the Principal Component Analysis (PCA). A number of formulas were used to calculate the vegetation parameters:

Specific richness: the total specific richness (S) is the total number of species that the considered stand has in a given ecosystem [15] cited by Ngom [16] . Average specificrichness is the average number of species per survey for a given sample.

The frequency of presence is a method that consists of assessing the distribution of species across surveys. The frequency of presence provides information on the distribution of a species in a stand. It is expressed in %, and is estimated by the following formula:

F = N r i N r × 100

where F = frequency of occurrence expressed as a percentage (%);

Nr_i = number of plots where the species i was found and Nr = total number of plots.

The observed density: it is the number of individuals per unit area (ha). It is the ratio of the total number of individuals in the sample (N) by the sampled area (S).

D = N S

Basal area is the basal area of the tree measured at the base of the tree trunk. It is expressed in square meters per hectare (m²·ha⁻¹). It is therefore obtained from the following formula:

S t = ∑ π ( d 1.3 2 ) 2 S E

With S_t = basal area; d_1.3 = diameter in m of the trunk at 1.3 m; S_E = area of the sample considered in ha.

The cover is the area covered by the vertical projection of the tree crown on the ground. It is calculated in square meters per ha.

C = ∑ π ( d m h 2 ) 2 S E

With C = woody cover; dmh = mean crown diameter in m; S = area of the sample considered in ha.

The Shannon Weaver index (H') considers both abundance, and species richness and is used to assess the distribution of individuals according to species. It is between 0 and 4.5. The index is minimum when all individuals belong to the same species. It is maximum when each individual represents a distinct species [17] . It can be expressed in bits and its formula is:

H ′ = − ∑ p i log 2 p i

p_i is the frequency of species i H' is minimal (equal to 0) if all individuals in the stand belong to the same species.

The Pielou equitability index (E) measures the distribution of individuals within species, independently of specific richness. Its value varies from 0 (particular dominance of one of the species) to 1 (equidistribution of individuals within species) [16] . It is given by the following formula:

E = H ′ / H ′ max

H ′ max = log 2 S (S = total number of species).

The stand regeneration rate (SRR) is given by the percentage ratio of the total number of seedlings to the total stand size.

SRR = Totalnumberofseedlings Totalstandsize × 100

The plant community of the agroforestry systems associated with the vegetable plots is rich in 31 woody species divided into 25 genera from 14 botanical families (Table 2).

The most represented families are Fabaceae, Rutaceae, Moraceae, and Meliaceae with respectively 25%, 12%, 12%, and 9% of the inventoried species.

According to the vegetable blocks, the greatest floristic diversity is observed in the vegetable block of Boutame (Bt) with 19 species distributed in 18 genera and 10 botanical families. The vegetable blocks with the least floristic diversity are those of Gaffanta (Ga) and Gandong (Gd) (Table 3).

The analysis of the table below shows that in the agroforestry systems associated with vegetable plots, the most frequent woody species are: Elaeis guineensis (85%), Mangifera indica, Citrus limon, and Citrus sinensis with 71% each.

o Basal area

The basal area is 45 m²·ha⁻¹ in the agroforestry systems associated with market garden plots in the Commune of Thionck-Essyl. It is higher in the agroforestry systems associated with the market garden plots of Boutame (28 m²/ha), Gaffanta (17 m²/ha) and Baronkol (7 m²/ha). Mangifera indica is the dominant species in these different vegetable plots with 3.65, 4 and 4.12 m²·ha⁻¹/ha respectively (Table 4).

o Woody cover

The woody cover rate is 47% in the agroforestry systems associated with market

Legend: Bt: Boutame, Ga: Gaffanta, Gd: Gandong, Bg: Bougotir, Sa: Saaba, Br: Baronkol, Bl: Bouloube. Present = + and Absent = −.

gardening in the commune. It is highest in Boutame (91%), Gaffanta (63%) and Baronkol (55%). In the agroforestry systems associated with market gardening plots in Boutame and Gaffanta, the species that contributes the most to the cover is Mangifera indica with 52.38% and 45.8% respectively (Table 4).

o Observed density

The observed density of woody species is 67 individuals ha⁻¹ in the agroforestry systems associated with market garden plots in the Commune of Thionck-essyl, and is higher in the market garden plots of Gaffanta (120 plants/ha), Baronkol (112 plants/ha) and Boutame (99 plants/ha) (Table 4). The woody species with the highest densities in these vegetable plots were Mangifera indica (36 individuals/ha) and Elaeisguineensis (53 individuals/ha), respectively.

o Specific diversity

Shannon’s diversity index takes into account not only the specificrichness but also the abundance of each species and is independent of the sample size. Thus, the Pielou Index is more appropriate for comparing stands with different specificrichness.

It appears that the species diversity is quite high in all the market garden blocks with a Pielou Index that exceeds 0.5 everywhere. This diversity is higher in Baronkol (H' = 2.39 bits; E = 0.92) and lower in Boutame (H' = 2.15; E = 0.58 (Table 4).

o Regeneration rate of woody vegetation in agroforestry systems

The regeneration rate of woody vegetation in the vegetable plots of the municipality is 38%. It is highest in the vegetables plots of Gandong (92%), Boutame (46%) and Bouloube (36%) (Table 4).

The Principal Component Analysis (PCA) gives a total inertia of 71.64% (41.60% for the F1 axis and 30.03% for the F2 axis) which is sufficient for a good representation of the information contained in the matrix (Table 5).

Figure 3 represents the typology of agroforestry systems associated with market gardening plots in the Commune of Thionck-Essyl, based on the characteristics of woody vegetation, it allowed us to identify three groups according to the F1 × F2 factorial plan.

Thus we distinguish:

o Group A or agroforestry systems represented by the market garden plots of Bouloube, Saaba, Bougotir and Baronkol. These agroforestry systems are characterized by high specific diversity.

o Group B or agroforestry systems represented by the market garden plots of Gaffanta and Boutame, characterized by a high density, basal area, cover rate, and species richness.

o And finally group C or the agroforestry systems represented by the market garden plot of Gandong, characterized by a high regeneration rate.

There was a strong correlation between density and basal area (r = 0.78), between density and cover rate (0.75) and between cover rate and basal area (0.61). This means that in the commune of ThionckEssyl, agroforestry systems associated with market gardening beara high density of woody vegetation. Their trees have a high basal area and cover. And the parks with trees of a high basal area have a high coverage rate. There was also an inverse correlation between species diversity and regeneration rate, meaning that when the regeneration rate of agroforestry systems is high, the diversity is low.

o Vertical structure

The vertical structure of agroforestry systems associated with market gardening plots is characterized by a predominance of individuals between 2 and 4 m in height (23%), followed by individuals between 12 and 14 m in height (18%). Individuals over 16 m in height are poorly represented with 8% of the stand (Figure 4).

o Horizontal structure

The results showed that the dominant diameter class in the agroforestry systems is [5 - 15 cm] with 31% of the individuals in the stand (Figure 5). This is followed by the classes [25 - 35] and [35 - 45 cm], each with 19% of individuals. Individuals with a diameter greater than 55 cm are poorly represented (4%).