Abstract
The Notsukezaki sand spit pasture has been considered as a typical pasture vegetation of Subartic climatic zone in Japan. We investigated the seasonal and yearly trend of the vegetation during the years of 1972-1974. The results of investigation are as follows: 1. The flora of the pasture vegetation was consisted of about fifty species. The dominant species of the community were Festuca ruba, Thermopsis lupinoides, Carex verna var. microtricha and Agrostis hiemals, and the other major species were such as Rosa rugoa, Geranium yesoense var. pseudapalustre, Potentilla egedei var. groenlandica, Galium verum var. trachycarpum and Calamagrostis langsdorffii, mast popular constituents of the semi-natural coastal grassland in Hokkaido. In addition, Poa pratensis and Trifolium repens which were widely colonized in the island were also present. 2. The maximum number of species was recorded in July, and the ground was primarily covered by Festuca rubra and Thermpris lupinoides which dominated throughout the whole growing season. In spring, summed dominant ratios (SDR_3) of Polygonatum humile, Fritillaria camtshatcensis and Poa mcrocalyx var. scabiflora were increased. Thermpris lupinoides, Agrostis hiemalis, Ranunculus francheti, Geranium yesoense var. pseudo-palustre and Trientalis europaea var. europaea were prevailing in summer. In fall, Poa pratensis, Stachys japonica var. villosa, Scutellaria strigillosa, Trifolium repens and Elymus mollis were increased in the sward. 3. The dominant species in the grassland were essentially unchanged since 1972. But some species such as Thermopsis lupinoides and Calamagrostis langsdorffii gradually declined with advancing years. On the contrary Carex verna var. microtricha, Trifolium repens and Luzula capitata incleased their density. 4. The vegetation of Notsukezaki sand spit pasture seems to be changed from Thermopsis lupinoides-Calamagrostis langsdorffii community of tall-grass type to Festuca rubra community of short-grass type by trampling of domestic animals and motor cars. 5. Degree of succession of the pasture vegetation in summer was rather stable since 1972 to 1974, but the difference in DS values between grazed plots and protected ones indicates that the degree of succession of Notsukezaki sand spit pasture has been lowered by the grazing of beasts and other artificial pressures.
