The Dynamics of Seed Bank Size and Seed State of Medicago Lupulina

Abstract

SUMMARY (1) The annual dynamics of seed bank size and seed state were recorded for Medicago lupulina (black medick) in an abandoned pasture in southern Ontario, Canada. (2) The seed bank density of Medicago lupulina was relatively small (600-2000 seeds m-2) compared with those reported for other pasture species (3700-55 000 m-2), but roughly the same as the density reported for another legume, Trifolium dubium (2500 m-2). (3) The seed bank was smallest following spring and summer germination and largest in late winter when most seeds had been detached from parent plants. (4) The lowest seed density (600-1100 m-2) was recorded in grass-filled hollows. It was 2-3 times greater on ridges. (5) In both ridge and hollow habitats the seeds, which have a hard seed coat, remained dormant throughout most of the year. The largest transition between dormancy states occurred during winter months when seed coats were scarified and innately dormant seeds entered a state of enforced dormancy. (6) Between 78 and 85% of some experimentally introduced seeds germinated within twelve months, mostly in the spring (April-May). It was estimated that normally only 30-40% of the natural seed bank would germinate in a single year. Medicago lupulina apparently has a persistent seed bank in the study area. (7) The regenerative strategy of Medicago lupulina was compared with that of Hieracium floribundum which dominated ridge habitats in the study area. While both species had flourishing populations on ridges in the pasture, most seeds of H.floribundum survive for no more than 1 year, and recruitment to the population is mainly vegetative. The strategy of Medicago lupulina appeared to be better suited to colonizing small patches of bare ground created by the activities of animals or by erosion.