Geo-environmental Changes on a Post-fire Alpine Slope of Mt. Shirouma-dake, Northern Japanese Alps

Long-term geo-environmental changes on a post-fire alpine slope of Mt. Shirouma-dake in the northern Japanese Alps are examined. The fire event occurred on May 9, 2009 on an alpine slope of Mt. Shirouma-dake and spread to Pinus pumila communities and grasslands. The fire resulted in significant damage to P. pumila communities, while that to grassland was minimal. The burning of needles of P. pumila communities exposed the forest floor to atmospheric conditions such as rain, wind, and snow. A map of micro-landforms based on geomorphological field observations was prepared. These micro-landforms were observed for a period of seven years after the fire event. The results do not indicate significant changes to the micro-landforms; however, litter from the forest-floor of burned P. pumila communities was flushed out to surrounding areas. The average thickness of the litter layer of the forest-floor of burned P. pumila communities was 3.5 cm in September 2011, which had decreased to less than 0.5 cm by September 2015. The P. pumila communities on the slope were established on angular and sub-angular gravel having an openwork texture covered with a thin soil layer. It is necessary to pay attention to soil erosion following the outflow of litter because the soil layer can be easily eroded. In addition, ground temperatures of burned and unburned P. pumila communities were measured from 2009 to determine the influence of fire. Ground temperature sensors were installed in the soil at depths of 1 cm, 10 cm, and 40 cm. Diurnal freeze-thaw cycles occurred at a soil depth of 1 cm on the post-fire slope in October and November from 2011 to 2016. However, these cycles did not occur in 2009 and 2010. In addition, the periods of seasonal frost at depths of 10 cm and 40 cm on the post-fire slope were extended by a period of two weeks in comparison to the unburned P. pumilla community. These thermal changes were triggered by a decrease in the thickness of the litter layer in the burned P. pumila community.