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The influence of trees on soil characteristics beneath and around the sub-canopy area has been well established in tropical and temperature regions. A hypothesis may be inferred which predicts an amelioration of the soil between the tree canopies as a function of increased canopy cover. This hypothesis has been tested at two sites in open vegetation dominated by Acacia tortilis trees and shrubs. Three different canopy cover classes were used as independent variables whereas all other soil-forming factors (Jenny, 1941) (such as climate, parent material, slope, and time) were relatively uniform within each site. The hypothesis was refuted at one side and verified at the other by means of ANOVA and Canonical Variate Analysis. Total nitrogen and organic carbon increased and the C/N-ratio decreased as the canopy cover increased in the latter site. Here a lower pH (CaCl2) correlated with high organic carbon. At the site where the hypothesis was verified the number of individual tree and shrubs was higher and the size was smaller compared to the other site. This structural difference may influence the effect of wind erosion and is suggested as an explanation of the discrepancy in results.