Abstract
The organic matter from the A horizons of five soils developed under a shrubby cover and under pine groves in a Mediterranean high-mountain area has been studied. The characteristics of humic acids (HA) are compared with those reported by other researchers in a variety of environmental conditions. The organic matter from pine groves has a higher C/N ratio, a greater content in fresh or littletransformed organic matter, and a lower humic extract than that of shrublands. In general, the humic acids show a low humification index, with greater relative proportion of aliphatic chains and less condensed aromatic-type structure as the pH and base saturation diminish. The climatic extremes which typify these ecosystems, very cold winters and very dry summers, together with the acidity and low base saturation of the soils, seem to be the determining causes of the low-humification index. Felbeck's hypothesis of alteration of plant components appears to be the principal process controlling the humic-acid evolution of the organic matter in these soils.
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