Colonization of old fields by trees vs. shrubs: seed dispersal and seedling establishment1

A. rubrum, 0.7 for F. americana, vs. 0 to 0.02 for the shrubs). For the trees, but not the shrubs, both seed input and seedling emergence in the fields showed a strong relationship to seed source abundance along the field edges, using index values based on the distances from potential source plants. Results of seed augmentation experiments showed that seedling emergence was strongly limited by seed input, but secondarily by environment; more C. racemosa emerged in moister plots and more F. americana and V. dentatum under short vegetation. Once established, seedlings of the shrubs often survived better and grew faster than did the tree seedlings. As a result of net overall differences in seedling emergence and survival, the number of seeds required to get one surviving fifth-year seedling was lowest for the shrubs (20 to 35 seeds), somewhat higher for F. americana (55), and highest for A. rubrum (326).