Demographic analysis of interspecific interaction in sand dune plants

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Carex Kobomugi is a major component of coastal sand-dune vegetation in Japan. It is hypothesized that the restricted distribution of this species to sand dunes is due to competitive exclusion by other inland species like Imperata cylindrica var.koenigii, beacuse without interspecific competition, Carex kobomugi can survive and grow in an inland condition. In a sand dune system at Ajigaura, central Japan, we monitored shoot population dynamics of this species at places with and without coexistence of Imperata cylindrica. At the end of a growing season, we excavate the plots to determine the connection between the mother and daughter shoots. In Carex kobomugi, a mother shoot produced two types of daughter shoots : one type attached to the mother shoot and the other produced at a distance from the mother with a rhizome. The proportion of the former type of shoots was smaller in a plot where Imperata cylindrica was dominant than in a plot without Imperata cylindrica. This implies that under crowded conditions with Imperata cylindrica, the shoot of Carex kobomugi tend to regenerate in a gap which was created by their mother shoot. From a transition matrix model, we could not find evidence which supports the reduction of growth of the shoot population of Carex kobomugi by the presence of Imperata cylindrica.