An Analysis of Nigerian Savanna: I. The Survey Area and the Vegetation Developed over Bima Sandstone

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Abstract
The work described in this paper is part of a quantitative vegetation survey which is being carried out in conjunction with a reconnaissance soil survey of part of north-east Nigeria. This paper describes the analysis of the vegetation found on the Bima sandstone which is one of the more important and extensive geological parent materials of the area. Ninety-two half-acre sample plots were measured on this formation, all arboreal growth being recorded by species and diameter class. Of the 90 species, recorded, 56 occurred with sufficient frequency to permit an analysis of their occurrence in all possible pairs to be carried out using a chi-squared test of significance. It was found that 39 species each showed significant association of occurrence with at least two other species. These 39 species were plotted on a constellation diagram. This diagram is capable of breakdown into groups of species which have ecological significance in terms of site preferences. Four such groups are distinguished, each of which represents a distinct site class and has sufficient areal extent to be used as a mapping unit. On the basis of its floristic composition, each plot was allocated to a group and the group means of the relative frequency, density and dominance of each species calculated. In addition, group means with their standard errors were calculated on an acre basis for the stocking of all species (density), height and total basal area and an interpretation of these in terms of environmental factors is given. The vegetation community represented by each group is named and the practicability of these groups as mapping units, with particular reference to their recognition on aerial photographs, is discussed.