Abstract
To evaluate the effect of the alien plants on indigenous grassland ecosystem on the riverbank of the Tone canal, we did vegetation survey using random sampling method and used TWINSPAN and statistical modeling. The TWINSPAN divided the vegetation into two alien communities and two indigenous communities. The result of the statistical modeling showed that an alien indicator species Solidago altissima affected on the indigenous species only in population level scale (5 m × 10 m) but not in individual level scale (50 cm × 50 cm), meanwhile another alien indicator species Sorghum halepense f. muticum showed strong and multiscale effect on the indigenous species. That means S. altissima affect indigenous species in large scale, but inside the population of the S. altissima, there can be some indigenous species inside. Thereby, regulation of the density of the S. altissima (ex: shifting the mowing season) may lead to the expansion of the indigenous species. To manage alien plants in this riverbank, we must reference to the community types divided by TWINSPAN and make an effort to bring down the density of the S. altissima and control expansion of the S. halepense f. muticum. Additionally, we recommend our survey method to apply monitoring not only for checking alien species reduction but also for confirming the indigenous ecosystem recovery.
