Fig. 6. Correlation biplot from the redundancy analysis (RDA) of the relative frequency of 17 forage and 5 firewood species constrained by forest type, fallow history, and rockiness. In this biplot, correlations between species and the quantitative explanatory variables fallow length, number of cycles, and rockiness are represented by the angle between their vectors, such that the smaller the angle, the stronger the association. The relationship of forest type, YK or KL, with species or with other quantitative variables can be inferred by projecting its centroid on the vector at a right angle; projections at more extreme ends of the vector indicate a stronger relationship between the variables. Finally, the length of a speciesí vector indicates the amount of its variation explained by the first two axes of the ordination. Species' codes as in Tables 1 and 2. The five species used for firewood are indicated by an asterisk.