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.

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[in Japanese]

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Twenty years ago, broadleaved trees at different seral stages were planted using the so-called “natural planting ” technique in order to restore a broadleaved forest on a slope at the Akandana Parking Area. The following six species were planted on the slope: Taxus cuspidata, Betula platyphylla var. japonica, Betula ermanii, Weigela hortensis, Sorbus commixta, and Quercus crispula. Seed sowing was also used on another slope. For this slope, the seeds of the following seven species were sown: Amorpha fruticosa, Torreya nucifera, Lespedeza cuneata., Alnus hirsute Turcz. var. sibirica, Dactylis glomerata, Phleum pretense, Artemisia princeps. The purpose of this study was to understand the differences in the community structure between the two slopes. We established four plots on each slope and investigated from 2012 to 2013. Clear differences were found in the vertical stratification between the two slopes: several layers, i.e. tree layer, subtree layer, and shrub layer, were detected on the “ natural planting method ” slope, but mostly mono layer, i.e. tree layer, was detected on the “ sowing method ” slope. In addition, a difference was found with respect to seedlings: there were 1,606 seedlings on the “ natural planting ” slope, but only 30 seedlings on the other slope. Furthermore, all the sown species, except Alnus japonica, disappeared from the sowing slope. On the basis of these results, we concluded that planting different types of trees will maintain a developed forest, in community structure and seedlings, comparing with seed sowing.

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We in vestigated the effects of mowing on the growth of Rudbeckia laciniata L., an invasive alien species in Japan, and discussed the possibility of eradicating this species by this method. Seedlings of R. laciniata were cultivated in pots, and the time from seed sowing until flowering was examined. Further, the effect of eight mowing treatments with varying frequency and time of mowing on the plant height, number of stems, percentage of flowering individuals, and number of flowers per individual were investigated. Since the growth of plants from the spring season onward is affected by the belowground biomass accumulated during the previous year, we also measured the dry weights of the above- and below-ground parts of plants in all the treatments at the end of November. The period from seed sowing to flowering for R. laciniata was two years. In the non-mowing treatment two years after seed sowing, the plant height was 118 cm and all individuals produced flowers, with an average of 11 flowers per individual. The mowing treatment at the end of June and August (i.e., mowing twice a year) was reliably shown to inhibit flowering and subsequent seed set. However, mowing even three times a year-end of June, August, and October, could not exhaust the belowground biomass of the plants. Our study results indicate that it is difficult to eradicate R. laciniata by mowing alone. Therefore, for effective elimination of this species, firstly, flowering and seed set should be controlled by mowing large areas, followed by the removal of individual plants as much as possible, by hand pulling.

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[in Japanese]

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