The impact on the senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

During high run-off events the river Sakasagawa carries extremely large quantities of alluvial materials which are deposited in the north east corner of the Senjogahara moor. This study was initiated to examine the effects, both recent and historic, that this periodic and catastrophic inundation has had on the ecology of this area. It also questions the potential importance of alluvial deposition on the conservation of the moor as a whole. From the data presented it is clear that the present day vegetation of the north east corner of the moor represents a mosaic of vegetation reflecting differential levels of damage to the plants, deposition of alluvial material and the establishment of erosion channels in a space-time continum. The results indicate thatMalus Toringo andSalix integra can survive in the areas outside the heaviest flood damage, whereasUlmus Davidiana var.japonica, Betula platyphylla var.japonica andLarix Kaempferi are quite sensitive to flooding. SimilarlySasa nipponica var.nana is intolerant of even light alluvial deposition in contrast toLonicera caerulea var.emphyllocalyx andSpiraea salicifolia which are also still dominant beyond the zone of major alluvial deposition.