Figure 2. Physical and chemical soil similarity of sample sites across Amazonia.

The figure shows the study sites—coloured by habitat type—on the first two axes of a Principle Component Analysis for (A) physical properties (silt, clay and fine, coarse, and total sand fraction) and (B) chemical proprieties (phosphorus (P), exchangeable bases (Na, K, Ca, and Mg), the sum of all exchangeable bases (SB), exchangeable aluminium (Al and H+Al), saturation index by aluminium (m), base saturation index (V), effective cation exchange capacity (t), and cation exchange capacity (T)). The blue rows show the values of each variable loadings in the two firs PCs. For physical PCA we can observe that flooded forest (igapós and várzeas) are associated with negative values in the first PC axis and a more spread distribution of terra-firme and campinas. For chemical PCA there is no separation of flooded forest, but campinas group in most positive values in the first PCA axis followed by terra-firmes.