Characteristics of humic substances in humid subalpine forest soils in Central Taiwan

The study site, 2700 m a.s.l., is located in the central Taiwan. A globally rare combination of the mean temperature (ca. 9.5 °C) and total annual precipitation (ca. 4100 mm) makes studies on pedogenic and edaphic processes of the moist soils in this area worthwhile. The study was undertaken to investigate distribution and characteristics of humic substances in this subalpine forest ecosystem. Fulvic acids comprised a higher total organic carbon fraction (1.8 to 25%) than humic acids (1.1 to 13.4%). Fulvic acids were more mobile and migrated downwards to deeper horizons. Comparatively, humic acids were distributed more in the surface horizons. The hu- mification index, based on E4/E6, showed that humification varied in different horizons even in the same profile. The AlogK and RF values indicate that the types of humic acids extracted from Tsuga forest soil are grouped as P or A types, whereas Rp or B types are in Picea forest soil, suggesting a high degree of humification of humic acids in such soils. Features of the absorption spectra were consistent with the classification of humic acids with A logK and RF values. Humification indices and humic acid types in these subalpine soils indicate that they are similar to acidic soils elsewhere with abundant rainfall and cold climate.