Population Dynamics of the Wild Daffodil (Narcissus Pseudonarcissus): I. Clonal Growth, Seed Reproduction, Mortality and the Effects of Density

Abstract

The rates of reproduction and mortality, the relative importance of clonal growth and seed reproduction, and the effects of density on wild daffodil performance in clumps at Brigsteer Wood, Cumbria [Scotland, UK], are reported. The fates of individually-located plants in an open and a shaded site were followed over 4-6 yr. Counts were made of the numbers of capsules, seeds and seedlings and of the proportions of plants of different age-states. Clumps of different sizes were measured to investigate the effects of density on performance and reproduction. The half-lives of adults varied from 18-12 yr in open and shaded sites, respectively. The probability that an adult will be recruited as a result of clonal growth in an open site was 4.5 .times. 10-2, and in a shaded site 1.5 .times. 10-2/adult per yr. the corresponding probabilities for seed reproduction were 0.49 .times. 10-2 and 0.087 .times. 10-2/adult per yr. The relative proportion of adults and subadults in the population changed according to canopy conditions. Under a fully shading canopy the percentage of adults varied from 56-74%; in open sites the percentage of adults rose to 86% 3 yr after canopy clearance, but declined to only 27% after 10 yr. There was a close relationship between mean dry weight per bulb at the end of the growing season and clump density, expressed as the growing-space available to bulbs. The percentage of shoots producing flowers was also positively related to growing-space. The relationship between growing-space and clonal growth in clumps was complicated by the tendency of bulb units to split up at high density. Control of the size of the adult population may be primarily through the plastic response of clonal growth to density.