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Field and laboratory experiments at Tumamoc Hill, Tucson, Arizona, U.S.A., demonstrated that Ferocactus wislizeni, a common perennial cactus in the northern Sonoran Desert, has a between-year seed bank. In laboratory studies, F. wislizeni seeds lost dormancy during storage at room temperature and had a light requirement for germination. Field experiments suggested that as much as 2% of the annual seed crop might escape post-dispersal predation even when unprotected; where suitable safe sites exist, a higher percentage might escape. Germination of seed recovered monthly from above- and below-ground components of an artificial seed bank showed that seeds can survive at least 18 months in and on the soil. Seed banks enable F. wislizeni to take advantage of favorable rains and temperatures throughout the growing season, thus increasing the number of opportunities for germination. Moreover, seed banks enable F. wislizeni to respond hugely when the climate seems especially favorable, thus producing the large cohorts necessary to compensate for high seedling mortality. (C) 2000 Academic Press.