CONTROL OF SEEDLING EMERGENCE BY GROUND COVER AND SEED PREDATION IN RELATION TO SEED SIZE FOR SOME OLD-FIELD SPECIES

1. A field experiment was conducted to test whether control of seedling emergence by ground cover and seed predation depended on seed size. Sown seeds of 12 old-field species with seed masses ranging from 0-06 to 12-2 mg were used for the test. Species response to experimental removal of ground cover and (or) to the addition of a cage to reduce seed predation was recorded. Results were used to determine the relationship between seed mass and effects of ground cover and (or) seed predation on seedling emergence. 2. Adding a cage to reduce seed predation did not increase seedling emergence significantly for each of the four species with the smallest seeds (<0.14 mg). In contrast, seedling emergence increased significantly for each of the eight species with larger seeds. 3. Experimental removal of ground cover increased seedling emergence significantly for the four species with the smallest seeds. Seedling emergence also increased significantly for two species with larger seeds and hard seed coats. The remaining six species only responded to removal of ground cover when seed predators were present. 4. Experimental results indicate that control of seedling emergence by seed predation is directly related to seed size while control by ground cover is inversely related to seed size. Under natural conditions, the combined effect of ground cover and seed predation may reduce seedling emergence equally for species with small seeds and with large seeds.