Paleosols in Hokkaido

Abstract

Hokkaido is divided to three soil regions, that is, the northern, cetnral and southern regions as shown in Fig. 1. But the brown forest soils with leached top horizon are widely distributed in the southern soil region where the occurrence of the podzolic soils could not be expected under the recent bio-climatic conditions. The sequence of the ultimate pH through the profiles of these soils is not only different from that of the podzol but also from the typical brown forest soils. But seeing that the values tend to rise towards the bottom horizons, it may be quite reasonable tosuppose that these soils passed through the podzolization. They might have been regenerated from the former podzolic soils which were formed in the Würm glacial stage, to the equivalent of the brown forest soils, under the warmer climate during post-glacial stage.
On the other hand, there are red coloured soils on the coastal terraces and gentle slopes at mountain foot especially in northern Hokkaido. The profile characteristics of these soils are quite similar to those of the subtropical red soils. But they could hardly be expected to be formed under the present sub-boreal bio-climatic conditions in this region. According to the modes of occurrence of these soils with special references to the topography of the coastal terraces, they should be regarded as the relict red soils which were formed during a warmer stage in the Pleistocene, probably in the Riss-Würm interglacial stage. It is quite interesting from pedogenetical point of view that such discordant paleosols as them are well preserved in situ even in the present sub-boreal bio-climatic conditions.