Germinable seeds and periodicity of germination in annual grasslands
AuthorsJ. A. Young
R. A. Evans
C. A. Raguse
J. R. Larson
Authors AffiliationsJ. A. Young was range scientists, Science and Education Administration/Agricultural Research, United States Department of Agriculture, Reno, Nevada; R. A. Evans was range scientists, Science and Education Administration/Agricultural Research, United States Department of Agriculture, Reno, Nevada; C. A. Raguse was Professor, Department of Agronomy and Range Science, and Agronomist in the Experiment Station, Davis; J. R. Larson was range conservationist, Pacific Southwest Forest and Range Experiment Station, Forest Service, United States Department of Agriculture, Fresno, California.
Hilgardia 49(2):1-37. DOI:10.3733/hilg.v49n02p037. February 1981.
Germinable seed reserves and periodicity of germination of the plant species in annual communities were periodically and intensively sampled from 1974 through 1977 at the Sierra Foothill Range Field Station (SFRFS) and the U.S. Forest Service’s San Joaquin Experimental Range (SJER). One hundred samples of surface soil with accompanying litter were taken every 8 weeks, except when they were taken 1, 3, and 5 weeks after annual initial rains.
Few germinable seeds (mostly exotic annual legumes at SFRFS) were carried over from year to year. Dominant annual grasses had virtually no annual carryover. Litterborne and soilborne seed reserves gradually increased as the current year’s crop was dispersed. Through the fall, each species exhibited its own pattern of increased germ inability, which was highly dependent on its inherent afterripening requirements. In years when the initial fall rains resulted in simultaneous germination, the flush of germination began within a week, and by 5 weeks the reserve of germinable seeds was largely exhausted. The seedlings that established in these years accounted for only 20 to 30% of the germinable seeds present in the litter and surface soil before the initial rain. When the communities were subjected to 2 years of extreme drought (1975-76 and 1976-77), established seedling density and subsequent seed reserves dropped dramatically; species composition, however, remained relatively stable. Near-normal moisture conditions in 1977-78 resulted in near-normal communities except that a higher percentage of the seed reserve became established plants than before the drought.
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