Population Ecology of Melilotus Alba in a Limestone Quarry

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Abstract
Emergence, survival and reproduction of M. alba individuals colonizing an abandoned limestone quarry near Syracuse, New York, [USA], were assessed by mapping plants and measuring their development in permanent quadrats during 1976, 1977 and 1978. Two sites were examined in which total plant density differed: the sparse and the dense sites. In each year at both sites, seedling emergence occurred predominantly in the spring; summer and autumn emergence was limited. Cohort survivorship and plant development were influenced by temperature, by rainfall during the 1st year of growth, by site conditions and by date of emergence. When 1st-yr conditions were relatively cool and moist, cohort survival was linear and .apprx. 3% of the cohort survived to reproduce. Under hotter drier conditions, survival was concave (proportionally higher mortality soon after germination than later), and < 1% survived to reproduce. In hot dry years, survival and development were better on the dense site. Summer cohorts were less successful than were spring cohorts. Unlike other biennial species, which respond to high density by delaying reproduction, M. alba always flowered and died in the 2nd yr of growth. Seed output of M. alba was not reduced under dense conditions. In this species, restriction of population growth at high density may be due to density-dependent self-thinning, rather than to the delayed reproduction and reduced fecundity which is typical of most biennials.