[A-CG33_28PO1] Environmental changes in the Japanese Alps region

[ACG33-P02] Effects of forest harvesting on winter microcrimate and sedmiment movements in mountainous area

*Fumitoshi IMAIZUMI¹, Ryoko NISHII², Kenichi UENO², Kousei KUROBE³ (1.Graduate Shool of Agriculture, Shizuoka University, 2.Faculty of Life and Environmental Sciences, University of Tsukuba, 3.Graduate School of Life and Environmental Sciences, University of Tsukuba)

Keywords:freeze-thawing, sediment movement, soil creep, frost heave, dry ravel, forst harvesting

Activities of periglacial processes are controlled by the hillslope microclimate (i.e., air and ground temperatures, ground water content) that is highly affected by land cover conditions. Thus, forest harvesting in periglacial areas possibly affects activities of sediment movement (i.e., soil creep, dry ravel) by changing the microclimate of hillslopes. Knowledge on the effect of forest harvesting on sediment movement are needed to protect aquatic ecosystems as well as to develop better mitigation measures for preventing sediment disasters. We also observed difference in the microclimate as well as sediment movement between harvested and non-harvested artificial forests in a periglacial area. The field observation was conducted in Ikawa University Forest, University of Tsukuba, in southern Japanese Alps. In this region, air temperature frequently rises above and falls below 0 degree in winter. Forest harvesting changed both temperature and water condition of hillslopes; diurnal fluctuations in the ground surface temperature in the harvested area (about 15 degree) were much larger than that in the non-harvested area (about 3 degree). In the period without rainfall, water content ratio of soil in the harvested area was lower than that in the non-harvested area. Difference in the freezing and thawing frequency between the harvested and the non-harvested area was also observed by interval cameras. In the period without snow cover, diurnal frost heave was observed almost everyday in the harvested area. In contrast, diurnal frost heave in the non-harvested was observed only several times in one winter. Consequently, forest harvesting changes both microclimate and activities of periglacial processes. Meanwhile, the volume of sediment captured by sediment traps was not clearly different between the harvested and the non-harvested areas. In the harvested area, we found that a large volume of sediment was captured by litters and branches of harvested trees left on the hillslopes. Therefore sediment supply rate from harvested area may be also affected by other factors, such as existence of litters and branches on the ground surface.