Shoot population dynamics of Carex kobomugi, a rhizomatous perennial sedge with a guerilla-type growth form, dominating on Japanese coastal dunes, was examined to detect factors generating the zonal distribution pattern of the plant species. Relative growth rate of shoot (RGRS) and number of branching shoots formed by a mother shoot in a year (NBr) were measured in three populations occurring at three different distances from the shoreline. In 1992 Carex kobomugi shoots at the most inland site (90 m from the shoreline), where Imperata cylindrica var. koenigii dominated and soil-water salinity is always low, showed the lowest RGRS (0.0172 g/g/day from April to June and 0.00079 in July) and the smallest NBr (1.3 shoots/shoot/year averaged for three years). Shoots of the species at the most seaward site (40 m from the shoreline), where the soil-water salinity is always higher than that of more inland sites, showed the highest RGRS (0.0228 from April to June and 0.0093 in July) and the largest NBr (2.5). However, Carex kobomugi population at the 40 m site had high fraction of injured shoots (46% of total shoots sampled), which were recorded as shoots without any greenish above-ground part, and high mortality (0.34) due to temporal flooding of seawater caused by storms. In the intermediate site (70 m from the shoreline), Carex kobomugi had intermediate RGRS and NBr with low injury rate. The NBr value, however, showed a decreasing trend in the three-year observation, suggesting deteriorating effects of intraspecific competition on population dynamics. In the spring of the fourth year, shoots of Carex kobomugi at 70 and 90 m from the shoreline produced 1.2 to 2.0 times higher number of buds per shoot than the three-year-averaged NBrs. This suggests some fractions of the buds were terminated or become dormant through intra- and/or interspecific competition. The scarce distribution of Carex kobomugi at the 90 m site may be dictated by its competitive inferiority to I. cylindrica which has a denser root system and an aggressive growth form of a phalanx type.