Woody species composition, diversity and vegetation structure of two protected areas along a climatic gradient in Burkina Faso (West Africa)

Climate variability added to anthropogenic pressures leads to habitat fragmentation, degradation and loss of forest ecosystem resources in Burkina Faso. Studying vegetation structure and woody species composition is important in monitoring vegetation dynamics for efficient forest management. This study was carried out to characterize woody vegetation along a climatic gradient. Stratified sampling according to four vegetation types was conducted in 120 plots in two protected areas. The plot size was 30 m x 30 m in savannas and 50 m x 10 m in gallery forests. In each plot, all woody species with a diameter at breast height (DBH) >= 5 cm were systematically identified and measured. Diversity indices, structural parameters and species importance values were calculated and compared among the sites and vegetation types. Linear discriminant analysis (LDA) was used to characterize each vegetation type in each climatic zone. The species diversity, tree density and basal area of woody species increased significantly along the climatic gradient from north to south. Discriminant analysis identified two vegetation types: open vegetation (shrub savannas and tree savannas) with moderate species richness and structural characteristics and closed vegetation (woodland savannas and gallery forests) with higher species richness and structural characteristics. The size class distribution showed that irrespective of the climatic zone, each vegetation type has a stable structure. Compensation among species in different diameter classes does not allow the effect of the climatic gradient between the two sites on the diameter class size distribution to be observed. This study revealed that climate is the main driver influencing the diversity of woody species rather than the site-specific conditions at the two sites. In addition to climate, site ecological conditions affect the structural parameters. The results provide a rational basis for planning and management decisions to ensure the sustainable use of resources in the two protected areas.