Feedback and regime shift of mire ecosystem in northern Japan

Because anthropogenic stressors have caused degradation of the Kushiro Mire, in subarctic northern Japan, seen as drying and invasion of alder-dominant shrub forest, the Japanese government recently started a project to restore a meandering former river channel and so diminish the shrub forest and recover the mire ecosystem. This paper describes the further development of the National Integrated Catchment-based Eco-hydrology (NICE) model with surface-unsaturated–saturated water processes and land-surface processes assimilated with satellite data to include mutual interaction and feedback of hydrogeologic and vegetation dynamics in the mire. NICE iteratively simulated hydrologic cycle, elevation change, and vegetation succession, including the competition between two vegetation types (alder-dominant shrub forest and reed–sedge vegetation), to evaluate nonlinear relationship between drying and alder invasion in the mire and to examine a method for mire recovery. NICE reproduced well the heterogeneous alder invasion in the mire, implying that the study made some progress in explaining the positive feedback between geomorphology and eco-hydrology on irregular slopes and in heterogeneous vegetation, whereas most previous studies have considered regular slopes and their relation to string or maze patterns. Simulation results predicted that restoring meanders to the river channel would decrease the discharge and sediment loading of the river, increase the groundwater level downstream, and achieve a degree of mire recovery in the future. The heterogeneous vegetation succession is discussed in relation to regime shift in transient simulation. These results suggest the effectiveness of river restoration in conservation plans for mire recovery, and the importance of the process-based model in assessing the linkage of hydrological change and vegetation succession.