Spatial pattern, floral sex ratios, and fecundity in dioecious Aralia nudicaulis (Araliaceae)

Abstract

Aralia nudicaulis L. (Araliaceae) is a perennial understory herb of the boreal forest which forms large clones by means of an extensive subterranean rhizome system. Populations are dioecious and pollinated primarily by bumble bees. To examine the relationships between the spatial pattern of sexual morphs and female fecundity, all flowering ramets were mapped in a 1-ha block of spruce–fir forest in central New Brunswick and the fecundity of females determined. Within the block, A. nudicaulis exhibited a 2.5:1 sex ratio of male/female flowering ramets. Ramets of the sexual morphs were negatively associated owing to cloning and a reduced likelihood of flowering in female ramets under dense canopy compared with males. Pattern analysis of the sex ratio of flowering ramets revealed a monotonic decline in variance with block size indicating that samples of sex ratio using small quadrats are likely to give misleading estimates for this species. The fecundity of females exhibited no systematic positional variation within the forest block. In most cases fecundity was not correlated with male and female flowering density, ramet sex ratio, and several subjectively estimated habitat variables. It is proposed that the long flight distances of pollinators, pollen carry-over, and the predominance of male flowers at the site interact to dampen out spatial effects on fecundity.