EFFECTS OF FLOWERING ON THE SHOOT DYNAMICS OF CAREX-BIGELOWII ALONG AN ALTITUDINAL GRADIENT IN SWEDISH LAPLAND

Flowering may have considerable influence on the shoot dynamics of many clonal plants, as the growth of an individual shoot is terminated with the production of an inflorescence by the apical meristem. Aboveground shoot dynamics of a long-lived clonal sedge, Carex bigelowii, were investigated by comparing 3 populations along an altitudinal gradient for 5 yr. No correlations were found between shoot survival, shoot emergence or proportion of shoots flowering and the density or aggregation of shoots. All new shoots were vegetatively produced, emerging mainly in early or mid summer. At the most severe upper site, survival of the younger age classes was highest, but lower for the older age classes, resulting in the fastest turnover rates at the upper site. Responsive death (not including the death of flowering shoots) in winter and summer was about equally important at the upper and intermediate sites, whereas 82% of the shoots at the lower site died during winter. Flowering varied greatly between years, especially at the upper site, where 32% of shoots flowered in 1986, compared to between 1-6% in the other years. Shoots arising early in the season had a much greater probability of flowering early in their life. At all sites, flowering was followed by a corresponding decrease in shoot numbers, due to the programmed death of the flowering shoots. The mean size in one year of shoots which died in the following year was less than that for shoots remaining vegetative; those which flowered in the following year were larger than vegetative shoots. Floral initiation in a shoot is dependent on shoot size and a developmental period of some years. After flowering, the shoots die, population size decreases, then gradually increases until the next flowering event, such as in 1986. Population size thus changes in a cyclical way. The extent of flowering, therefore, directly controls the growth and performance of the plant by restricting the number of meristems available for production of photosynthetic tissue. -from Authors