GERMINATION, RECRUITMENT AND SURVIVAL IN THE WEEDY ANNUAL MEDICAGO-POLYMORPHA IN SUCCESSIVE WET AND DRY YEARS

Germination, establishment and survival in Medicago polymorpha, a weed y winter annual, were studied during 2 successive seasons in Californi a. Seeds were dormant when produced in spring and remained largely dor mant following exposure to summer conditions. Approximately 40% of via ble seeds in the seed bank were carried over from year to year. Conseq uently, autumn recruitment of seedlings is due in large part to germin ation of seeds produced in previous years. Seedling emergence was most ly simultaneous following the first substantial autumn rains. Survival to reproduction differed between years; few individuals produced seed s prior to senescence in the dry year, whereas in the wet year most ov erwintering individuals successfully produced fruits.