PhD Dissertation: 

Dehouegnon Thierry HOUEHANOU (2012). Ecological gap analysis: Assessing the ecological effectiveness of Pendjari Biosphere Reserve in biodiversity conservation in Benin (West Africa). UNIVERSITE OF ABOMEY-CALAVI, Benin. 179 pages.

PhD Promotor: Prof.  Dr. Ir. Brice A. SINSIN.

SUMMARY: Since protected areas are often assumed to be the best way to conserve biodiversity, the current study assessed the ecological effectiveness of Pendjari Biophere Reserve in conservation of some biodiversity targets. In chapter 1 (general introduction) the study’s background, objectives, some theoretical concepts and the thesis structure are presented while Chapter 2 presents the study area Chapter 3 estimates the local preferred uses of three trees target species. Traditional ecological knowledge linked to these species was documented. These species are Afzelia africana Sm., Pterocarpus erinaceus Poir. and Khaya senegalensis (Desv.) A. Juss, multipurpose trees widely used in Africa, yet endangered in their natural environments. The preferred used has been analyzed by means of a cultural importance index. Local ecological knowledge on their conservation was investigated among local people living around Pendjari Biosphere Reserve in Bénin. In total, 160 repondents belonging to four ethnic groups (Gourmantche, Waama, Berba and Peulh) were interviewed in twelve villages. Male and female respondents, aged between 20 and 90 years, were randomly selected in each ethnic group. For each species, a cultural importance index was calculated combining frequency and importance of use. This index allowed us to identify differences in use intensity within and among ethnic groups. Traditional ecological knowledge was tested as a dependent variable of ethnicity. The results showed that A. africana was widely used as medicine, fodder and crafting by most communities, whereas P. erinaceus was the preferred source of fodder for all local people. K. senegalensis was mostly used as medicine and fuel wood by most communities, except by the Peulh who prefer using it as fodder. The use of these trees as source of fuel wood was mostly reported by women while their religious uses were reported by old men from the Gourmantche ethnicity. Medicinal and fodder use of A. africana, fodder use of P. erinaceus and medicinal use of K. senegalensis had the highest overall cultural importance index value. Knowledge relating to local extinction of the target species and their sustainable use varied among socio-cultural groups. These findings have been used so as to propose conservation strategies towards an effective conservation of these tree species. Chapter 4 assesses the effectiveness of the Pendjari Biosphere Reserve to conserve habitat species composition and population structure of A. Africana Sm., P. erinaceus Poir. and K. senegalensis (Desv.) A. Juss. The following two research questions were addressed: (i) do protected habitats of these tree species differ from those unprotected in species composition? (ii) Have population structures (expressed by density and size class distribution) of these tree species been positively affected by this protected area? One hundred and twenty (120) plots were randomly sampled in the protected and surrounding unprotected habitats by inventorying plant species. For the three target species, we measured adult and juvenile, densities and recorded size classes. According to floristic composition four habitat groups were identified in relation to human disturbance, vegetation type, official protection status and moisture. There were protected savannas, unprotected savannas, old fallows and gallery forests. The estimated adult densities of A. africana were similar between protected (13.64 tree/ha) and unprotected savanna (17.44 tree/ha) while for P. erinaceus the adult density was significantly higher in protected (11.74 tree/ha) than in unprotected savanna (4.76 tree/ha). Estimated adult density of K. senegalensis was also significantly higher in protected gallery forest (40.00 tree/ha) than in unprotected one (28.89 tree/ha). Juvenile densities of A. africana, K. senegalensis and P. erinaceus were higher in protected habitats than in unprotected ones but the difference was not significant. In all cases, protected area was effective for maintaining large individuals. Skewness coefficient indicated that populations of investigated trees were declining in their protected habitats. However, the case of A. africana and K. senegalensispopulations seemed to be knocker in the protected area. Our results would suggest PBR to be effective in protecting savanna habitats against fragmentation and it should be required to define and applymanagement strategies for conserving effectively A. africana and K. senegalensis in the protected area in future. In Chapter 5 we assessed the effectiveness of Pendjari Biosphere Reserve to conserve woody species composition, diversity and structure of savannas, the most widespread vegetation type of the study area. The results showed that the two savanna types yielded a total of 58 species representing 44 genera and 23 families with Combretaceae, Mimosoideae, Caesalpinioideae and Rubiaceae as the most abundant families in descending order. However, some species had high Importance Value Index (IVI) in unprotected savanna while others showed the same scheme in protected savanna. Higher values of species richness, Shannon–Wiener’s diversity and Margalef’s index were found in the protected savannas comparatively to the unprotected ones at tree layer level. The number of individuals and the densities were significantly higher in protected savannas compared to the unprotected ones at shrub layer level. As far as the basal area is concerned significant higher values were found in the protected savanna compared to the unprotected one at the two layer levels. From these findings it can be concluded that the effectiveness of PBR to conserve savannas structure and woody diversity depends on the woody layer. However, woody species composition change in relation to savanna conservation status may be also evident according to interrelation specific-use-species. Chapter 6 studied stand structure and spatial distribution of A. africana as helpful to understand its primary seed dispersal mode. Spatial distribution pattern of adult trees and juveniles of the species, spatial relationship between those two life-stages and stand structure were investigated in A. africana dominated savannas. Results showed that A. africana displayed in the Reserve random distribution at large distance scales considering all individuals. However, aggregated distribution was observed at small scale (up to 9 m) in some areas. The adults displayed in all areas a random distribution either at large and small distance scales. The spatial distribution pattern of juveniles followed the same trend of distribution of all pooled individuals and revealed a clumping distribution up to 9 m and random distribution at large scales. The spatial relationship between adults and juveniles did not reveal a positive association between them either at small or large scale. Stand structure also showed a variation for some structural parameters: tree-density and basal area in the Reserve. We suggest that seed dispersal mode by gravity should be the primary seed dispersal mode of A. africana. Chapter 7 assessed the potential effectiveness of PBR on preventing mistletoes proliferation on Shea tree individuals. Shea tree infestation by mistletoes was assessed in two contrasted habitats: land use areas (fields and fallows) and protected area (PBR). Results showed that about 80% of Shea trees are infested in land use area while only 27.3% of trees in PBR were infested. Overall, heavily infested Shea trees had significantly larger trunks and heights, mainly in land use areas. The land use area was shown to be correlated with high and very high Shea tree infestation degrees while the other infestation degrees (very weak, weak and moderate) were correlate with both areas. Therefore Shea trees growing in protected areas are better protected against mistletoe plant parasites than those on cultivated land. Chapter 8 deals with Variation of mistletoes impact on Shea tree fruit yield in contrasting habitats and implication for its conservation. Forty-one (41) weakly and 41 heavily infected Shea tree individuals with similar size were selected in protected area and in its adjacent parklands. Shea tree traits such as diameter at breast height, canopy diameter, tree height, canopy height, number of fruit yielded, number of parasite stumps and a built impact index ratio were assessed on each Shea tree individual. Two-way ANOVA showed that mistletoe did not impact fruit yield significantly either in parklands or in protected area. Hierarchical cluster analysis tended to group all pooled Shea trees based on habitats. One-way ANOVA and canonical discriminant analysis performed on quantitative traits revealed that Shea tree groups were significantly discriminated and many infested Shea tree individuals in parklands were characterized with highest value of number of infestation stumps (n) and impact index ratio. Considering correlation between traits, a variation was found between the two contrasted habitats. Findings have been used to implement some Shea tree conservation plans. Chapter 9 deals with the general discussion on effectiveness of the PBR to conserve biodiversity. The PBR was found to be relatively effective in targets biodiversity conservation. However, management actions need to be addressed to improve biodiversity conservation in this Biosphere Reserve.

  • Vue globale des 5 bâtiments du Laboratoire d’Ecologie Appliquée (LEA). (Photo credit: Dr Akomian Fortuné Azihou / LEA, Octobre 2018)