Germination and Seedling Establishment in California Annual Grassland

Abstract

(1) Data for plant density, germinable seed in the soil, and seed production in annual grassland were obtained at Hopland Field Station, California, U.S.A., in 1973 and 1974. The study combined indirect estimates of numbers of seed in the soil, germination in soil samples containing natural seed, and estimation of plant density. (2) Autumn patterns of establishment differed significantly between the two study years. Plant density increased through the autumn, reaching peaks of 261 8 and 345*3 plants per dM2 in the seventh week after germination began, in 1973 and 1974 respectively. (3) The numbers of germinable seed in the top 6.4 cm of the soil prior to the start of the growing season were 6705 per dM2 in 1973 and 6102 per dM2 in 1974, and thus showed little difference between years. (4) Comparison of depletion of the seed-bank in the soil and increase of plant density showed that seeds germinating in the first week of the growing season produced fewer established seedlings than seeds germinating in the second or third weeks. The few seeds remaining in the fifth and sixth weeks had a high probability for successful establishment. (5) Six species-groups exhibiting contrasting strategies for germination and establishment are discussed in detail.