Impacts of previous maintenance of river embankments on the grassland communities by changing soil properties

Abstract

River embankments can be the potential semi-natural habitats for grassland species, although the recent disturbances for maintenance would alter overall vegetation of river embankments. For evaluating possibility of grassland species conservation in vegetation of river embankments, we aimed to clarify how does the previous maintenances (i.e. disturbance history) influence current species composition and diversity in grassland vegetation by changing soil properties. We conducted vegetation and soil surveys at 64 plots along the slope of embankments of the Tone River, Chiba and Ibaraki Prefectures, Japan, separated into 36 and 28 plots at disturbed and undisturbed embankments, respectively. We tested environmental factors (i.e., maintenance history, location of the river embankment, slope aspect, and interaction effects of the maintenance history and location) affecting species richness and soil properties of river embankments by using generalized linear models (GLMs) and linear models, respectively. We also evaluated species recovery through time by testing the significance of relationships between elapsed time (since last maintenance) and the richness values of all and grassland species. We found that disturbance history influenced current grassland species richness and soil properties (e.g. bio-available soil P and percentage of fine sand) and grassland species have recovered gradually in the disturbed river embankments located on the outer periphery of the reservoir. For achieving synergy between flood mitigation and grassland conservation goals, grassland vegetation maintained on disturbed river embankments located on the outer periphery of the reservoir can be targets for restoration of grassland species.