Abstract
This study was carried out to investigate the possibility of regeneration of pasture by natural reseeding of orchardgrass. In order to know the realities of natural reseeding and to explain it's necessity, vegetational changes which involved density, coverage, stand frequency and buried seeds of various species, stand diameters and distances between stands of orchardgrass were determined in the pastures established at 1976, 1977, 1978, 1979, 1981 and 1982 in Yachiyo public pasture, Obihiro. The frequency of pasture plants, weeds, and self-sown orchardgrass seedlings in lightly grazed pasture were compared with those in conventionally grazed pasture. Changes of density of self-sown orchardgrass seedlings were surveyed at lightly grazed pasture before and after winter (1983-1984). The results obtained were summarized as follows: 1) It was remarkable that SDR_3 of orchardgrass tended to decrease and that of weeds tended to increase with increasing of pasture age. 2) Accompanied with increasing of the distance between orchardgrass individuals, the diameter of orchardgrass plants increased sharply from 7th year. It was shown that the vegetation change of pasture could be caused by the formation of bunchy plant of orchardgrass. 3) The results 1) and 2) suggested that a suitable density of pasture plant was very important to maintain vegetation continuity, but the formation of bunchy plant and decrease of density of orchardgrass is usually followed with conventional utility. In the sense of this fact, the necessity of natural reseeding was brought forward. 4) The density of self-sown orchardgrass seedlings in lightly grazed pasture amounted to 220 plants/m^2. This result proved the reason why the frequency of orchardgrass in lightly grazed area was higher than that in conventionally grazed area. 5) According to the results above-stated, it was assumed that natural reseeding should be applied at 6-9th year after pasture establishment.
