SHOOT GROWTH DYNAMICS AND SIZE-DEPENDENT SHOOT FATE OF A CLONAL PLANT, FESTUCA-RUBRA, IN A MOUNTAIN GRASSLAND

The relation of the within-season and between-season patterns of shoot growth were compared in a clonal grass with long-lived shoots, Festuc a rubra, in a mown mountain grassland. The growth rate of shoot length from spring to summer in a year was almost constant for each shoot ir respective of spring shoot length each year. The annual shoot growth r ate from spring to spring was negatively correlated with the shoot len gth in the first spring. Shoots of different length and age therefore tended to converge over time to a population of identical shoot size, suggesting an equalizing effect of growth pattern on size structure. S hoot size (shoot length and number of leaves) influenced the fates of shoots. Larger shoots showed an increased incidence of both flowering and formation of intravaginal daughter shoots and a decreased incidenc e of death in the subsequent time period. The fates of shoots were ind ependent of their age. Although the negatively size-dependent spring-t o-spring annual shoot growth rate acted to decrease shoot size variati on, the remaining variation within the shoot population was still suff icient to generate different fates of shoots. These fates were not rel ated to the previous life history of individual shoots. There was a si gnificantly positive effect of the shoot size at initiation on its lif e expectancy. This was mainly attributable to the positively size-depe ndent survival rate of shoots in the early stage (<1 year old) of shoo t life history. Later on (>1 year old), shoot size had little effect o n the survival rate of shoots. Once small young shoots have survived t his early stage (<1 year old) in life history, they can grow vigorousl y, little affected by competition regardless of shoot size, and conver ge to a stable size structure of shoots of similar size. Only shoot si ze in the early stage (<1 year old) of life history is important for t he persistence of a shoot population.