Seedfall Pattern of Several Species of Bird‐Dispersed Plants in an Illinois Woodland

Abstract

I investigated spatial patterns of seedfall for several species of bird—dispersed plants in an east—central Illinois maple—hackberry woodland. Seed density around naturally growing fruiting plants and artificial fruit displays in treefall gaps was monitored with seed traps and compared with seedfall in undisturbed forest. Around individual fruiting plants, seedfall decline with distance from the seed source. Seedfall was highest near the source, but if the tail of the seed shadow crossed the edge of a treefall gap, there was usually another, smaller seedfall peak, producing a bimodal pattern. Among fruiting species, small seeds were dispersed farther and were much more likely to be dispersed into adjacent treefall gaps than large seeds. Seeds dispersed out of a treefall gap had a higher probability of falling into an adjacent treefall gap than would be expected if seeds fell uniformly around a source. Natural seedfall around a treefall gap was highest at the edge of the gap, lower in the center of the gap, and lowest in the undisturbed forest. About 50% of the seeds of bird—dispersed plants in the study area were estimated to have fallen into treefall gaps (16.8% of area). If seedling survival is higher in treefall gaps than in undisturbed forest for the bird—dispersed plants in the study area, patterns of seedfall indicate that furgivorous birds benefit the plants by (1) dispersing most seeds into treefall gaps, (2) by increasing the diameter of the seed shadow over that produced by gravity, (3) increasing the probability that a plant's seeds will be located at the site of a future treefall gap.