The Allelopathic Influences of Sassafras albidum in Old‐field Succession in Tennessee

Allelopathy seems to be the mechanism that allows Sassafras albidum to maintain itself in relatively pure stands through many stages of old—field succession. Field studies revealed that 10 species consistently occurred exclusively outside of clump canopies and 7 other species predominated beneath the sassafras canopy. We suggest that annual herbs are being effectively excluded from the understory flora. 2—pinene, α—phellandrene, eugenol, safrole, citral, and d—camphor were isolated were within and outside of sassafras stands from leaves, litter, soil, and roots. Germinating seeds watered with aqueous leachates of leaves, litter, and canopy washings showed varying degrees of radicle reduction during germination. Germination on soil discs from beneath sassafras stands was significantly lower in four of the test species; in seeds overwintered in sassafras litter it was significantly lower in all species. There was a positive correlation between α—phellandrene concentration and reduction in radicle growth in Acer negundo and Ulmus americana. Sufficient incoming and buried seeds were available to support a richer and more abundant understory flora than was found in the vegetational survey. The different modes of sassafras for releasing phytotoxins into the environment at different times of the year operate to continually influence its surroundings.