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.