Characteristics and genesis of placic horizon in subalpine montane forest soils i northeastern Taiwan

摘要

Placic horizons occurred between the overlying E horizon and the underlying argillic or cambic horizon in the two subalpine forests, Chilanshan (CLS) and Szyuanyakou (SY) area. The thickness of the placic horizon in CLS area (Hapludults) was 20 mm, while that in SY area (Placorthods and Dystrudepts) was 30 to 60 mm. Redoximorphic features are evidence of wetness and of leaching and translocation of Fe. In both pedons, Fe_o/Fe_d ratios were much higher in the placic horizons compared with the other horizons. High clay contents in both pedons inhibited the downward movement of surface water. Reduction and oxidation processes associated with various favorable hydrological conditions are considered to be the main pedogenic processes that formed the placic horizons in soils in CLS area. Subsequent evolution of the landscape of the original soils in SY1 area, with partial truncation of the original soil and emplacement of a younger and deeper depositional material on the eroded surface, created the modern soil, which is classified as an Inceptisols. The environmental conditions, such as relatively flat landscape, clayey soil, and very high precipitation have enhanced this process.