Aspects of the Population Ecology of Charlock

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Abstract
An initial survey was made of the numbers of charlock plants in 3 permanent quadrats over a 3 yr in areas of increasing charlock density in an arable field. Plant size was positively correlated with plant density suggesting that, at densities of < 20 plants m-2, intraspecific competition did not operate. Experimental plots were established with plant populations of charlock comparable to those in the field. The treatments were autumn or spring cultivation, presence or absence of cereal and zero, low or high charlock density. Plants and seedlings were counted continuously over 3 yr and seed fall was estimated. Maximum numbers of plants were established in autumn and in spring. The autumn populations arose from newly shed nondormant seeds but were destroyed either by climate or cultivation. The spring population arose from dormant seeds after rain when soil temperature at 10 cm was above 4.4.degree. C. Climate was the major factor influencing plant population and reproductive capacity. Drought associated with high levels of radiation markedly reduced plant numbers and seed production in the 2nd year. Charlock was suppressed by the presence of cereal but competitive effects were subsidiary to those of climate and cultivation. Annual seedling emergence was .apprx. 2.5% of the seed population. Estimates from published data showed that the annual death rate of charlock seed in soil is .apprx. 17.9%. Using an exponential model it is possible to show that when potential parent plants are elimnated by herbicides, the viable buried seed population witll be diminished by about 1 order of magnitude each decade, but will be restored by 1 reproductive season every 11 yr.