Shrinkage of shrub forest and recovery of mire ecosystem by river restoration in northern Japan

Because anthropogenic stressors have caused mire degradations in the subarctic northern Japan such as the drying and the invasion of alder-dominant shrub forest, the Japanese governments recently started a new project to restore a meandering former river channel in the catchment in order to diminish shrub forest and to recover mire ecosystem. In this study, the author developed the integrated catchment-based eco-hydrology model to include the mass transport and vegetation succession processes in the mire (NICE-VEG). NICE-VEG simulated the water/heat budget, the mass transport, and vegetation succession processes iteratively including the competition between two vegetation types (alder-dominant shrub forest and reed–sedge vegetation) in order to evaluate the relationship between drying and alder invasion in the mire and to clarify a method for mire recovery. NICE-VEG reproduced well the alder invasion in the mire so far by various anthropogenic stressors, which indicate that it is important to add newly the growth reduction factor for water table depth in the model. Simulation results indicated that restoring meanders to the river channel could be effective for decreasing discharge and sediment loading of the river, and increasing groundwater level at the downstream of restoration area around the mire. Simulation also forecasted the mire recovery more or less by restoring meanders to the river channel in the future. These results suggest that the policy of river restoration could be effective as one of mire conservation plans for the recovery of mire vegetation. It is powerful to apply the process-based model to assess the linkage of hydrological change and vegetation succession.