Seed bank dynamics in a Mediterranean grassland.
Changes in the seed bank, seedling emergence and plant density of the most common grass species, and all legume species, were monitored from Oct. 1986 to May 1989 in an unsown Mediterranean grassland in N. Syria. The grassland was grazed by sheep at high (1.7-2.3) or low (0.8-1.1 sheep/ha) stocking rates. The seed bank was greatest in May-June, following pasture maturity, then declined to its minimum in Mar.-Apr. Losses of seeds during summer were mainly due to sheep grazing, while losses in winter and spring were mainly due to germination, although some seeds were eaten by soil fauna and some seeds died. The seed bank, particularly of the small-seeded species (Trifolium tomentosum and T. campestre) was greater under the high than under the low stocking rate. There was little seed carry-over of grasses from season to season (Avena spp. 5%, Heteranthelium piliferum 1%, Bromus spp. 0%), but seed carry-over was greater in legumes (T. stellatum 27%, T. campestre 35% and T. tomentosum 38%). Most seedlings emerged in the autumn, but emergence continued throughout the growing season. Plant density within each year reached a peak in Jan. and declined as spring approached. The ecological and agricultural importance of seed banks in native Mediterranean grasslands is discussed.