Investigation of vegetation succession using a lysimeter on experimental embankment slopes

다국어 초록 (Multilingual Abstract)

The introduction of vegetation on slopes is one of the major goals of slope protection activities. To successfully achieve the goal of slope protection activities with regard to slope vegetation, vegetation succession after slope protection activities should be predicted on the basis of the surrounding landscape and ecosystem. To this end, long-term monitoring of the vegetation dynamics is required. Thus, we investigated the vegetation dynamics of experimental embankment slopes from 1980 to 2014, using a lysimeter, to evaluate invasion and growth condition at 7, 10, 32, 34, and 35 years since the start of the experiment. Additionally, uprooting was conducted in 2014 (35 years after the start of experiment). At this time, 16 species comprising 577 individuals of woody vegetation inhabited the experimental sites, the majority of which was Cryptomeria japonica (400 individuals), followed by Chamaecyparis obtusa (96 individuals). Regarding herbaceous vegetation, only a few plants were observed, including one individual of Fallopia japonica and one individual of Eulalia grass, indicating a drastic decrease in the number of species and individuals compared to those in 2013. These results indicate that the dominance of C. japonica and C. obtusa likely resulted from natural selection owing to interspecific competition, and thereby the dense shade canopy (less than 5% relative illuminance in this study) created by these two species can make it virtually impossible for seedlings and/or herbaceous vegetation to grow underneath them. In addition, we found that invasion by these plants on the experimental slopes was greatly affected by the dispersal of seeds from surrounding hillslopes. Consequently, the vegetation status and dynamics of surrounding environments should be preferentially considered when undertaking vegetation slope protection activities.