Appendix F (FIG. F1). Ordination diagram of principal coordinates analysis (PCO), showing the effects of age (early-, mid- and late-successional stages) on the soil C and N of Madrid and Málaga. Each data point represent one 1 × 1 m plot. PCO 1 and PCO 2 indicate both ordination axes. Pearson correlations between the original variables (C and N) and the PCO 1 axis are shown. PCO 1 axis was introduced in the structural equation models of Fig. 5 to represent the synthetic variable named Soil fertility.