Abstract

In this paper the analysis of Land sat images and plant ecological assessment were used to determine the land use change, plant diversity and the main plant community patterns in most environmentally disturbed areas of northern Togo. Floristic data in the survey areas were collected using transect and sampling methods which were both based on Braun Blanquet phytosociology concept. Several numerical processes were then retained to analyze the floristic data such as Detrended Correspondence Analysis (DCA), Hierarchical Clustering and Indicator Value (INDIVAL). The first two analyses were to define the plant groupings while the third was to name the plant communities found. The logical technique of RGB-NDVI suggested by Sader and Winne as an essential tool for land use assessment was applied to remote sensed data covering three time periods (1987, 2000 and 2007). The Normalized Difference Vegetation Index (NDVI) was then applied to both images after atmospheric correction before stacking them to obtain a RGB_NDVI composite image. Finally an unsupervised classification followed by post-classification process was applied to the RGB_NDVI image. All the results from these analyses show that seven plant groupings can be found in this area which mostly represents the physiognomy of shrubby savanna. The most frequent, abundant and typical plant species to Sudanian area are Terminalia laxiflora, Crotalaria graminicola, Vitellaria paradoxa. Great mutations in land use change are well perceptible after analysis. In overall the harvest of plant resources was higher between 1987 and 2000 while the regrowth of biomass was limited and unequal. The areas characterized with biomass clean and or regrowth is well represented in term of superficies, which denote the level of anthropogenous disturbance factors prevailing in this zone. However, there are certain zones where changes have not happened yet such as a few dimensions in riparian forests, though according to the field observations these riparian forests and their neighboring wooded vegetation are very disturbed. The rivers, pounds, barren lands and the scattered villages are also considered as no change areas.

Key words: Normalized difference vegetation index (NDVI), land use change, biodiversity, plant community, Togo.