Succession of Vegetation in the Human-Induced Soil Degraded Area in the Kitakami Mountains

Abstract

Soil degradation in the Kitakami mountains, northeast Japan, started from the Edo era as a result of felling of the native beech forest to create grasslands and this is believed to have given rise to the severe climatic conditions prevailing in the area. The objective of this study is to estimate the environmental conditions which prevailed on the Kitakami mountains at the inception of the degradation by examining vegetational succession. Samples from three sites (Kamisodegawa, Aomatsusawa and Hayasaka) showing forest, grassland, and bare lands were examined.
The study area has been dominated by beech forest with Sasa understorey at least since the Holocene, as suggested by the presence of phytoliths of Bambusoideae and broad leaf tree origins. However, the former type of phytolith, is by far, the most abundant. The severity of the climate, by itself, is reflected in the presence of Pooideae origin phytoliths (phytoliths associated with cold climate) in the soils above the buried A horizons of grassland and secondary forest. The present condition of the pasturelands is also revealed by the presence of phytoliths of Zoysia origin phytoliths (associated with overgrazing) in the surface horizons of the grasslands. The low degree of humification of humic acids, is also a reflection of the severe environmental condition. The results show that even though the study area is covered by grassland vegetation, it is still susceptible to erosion.