Floristic composition of a woodland pasture grazed by Hokkaido native horse in Shizunai, Hokkaido, northern Japan

Abstract

We examined the floristic composition of the woodland pastures of deciduous broad-leaved forests in Shizunai, Hokkaido, northern Japan. The woodland pasture was composed of six community types of Quercus crispula forest and two community types of Fraxinus mandshurica var. japonica forest. The floristic composition of plant communities in the woodland pasture were compared to that of Carpino-Quercetum grosseserratae and Syringo-Fraxinetum mandshuricae in the southern Hokkaido. In almost all the cases, forest floor of Q. crispula forest was predominated by Sasa. However, grazing by the pastured horses, there were some communities in which Sasa cover had declined or the forest floor had changed to non-Sasa communities. In the woodland pasture, the following plants were found out with higher constancy in both Q. crispula forest and the F. mandshurica var. japonica forest; Antenoron filiforme, Adenocaulon himalaicum, Cryptotaenia japonica and Geum japonicum. Further, Agrimonia pilosa var. japonica, Acanthopanax divaricatus, Persicaria yokusaiana and Plantago asiatica are typically found in the Q. crispula forests and the F. mandshurica var. japonica forests under intensive grazing. Ranunculus silerifolius, Stenactis annuus, Oxalis fontana and Patrinia villosa are typically found in dryer habitats in the Q. crispula forests under the most intensive grazing. There was a negative correlation between the coverage of Sasa and the number of species. Non-Sasa communities have more numerous species than the average number of species of Q. crispula forests in the southern Hokkaido. There was a correlation between coverage of Sasa and grazing season. The degree of degeneration of Sasa cover was more remarkable in the summer paddock than the winter paddock. The pioneer plants, the alien plants, feeding crops and weeds were brought into forest by horses, and this caused the floristic composition of pastured forest to become more complicated. The forest grazing changed the forest vegetation into a floristic composition characteristic of pasture.