POST-DISPERSAL CHANGES IN THE SPATIAL DISTRIBUTION OF FAGUS CRENATA SEEDS

Abstract

The spatial distribution of tree seeds is influenced by the behavior of seed dispersers and seed-killing agents. In this study we evaluated the relative importance of multiple seed-killing agents on changes in the spatial pattern of Fagus crenata seeds. The dispersal of seeds and causes of seed death following dispersal were investigated on a 0.6- ha study plot in northern Japan. Seeds were collected using seed traps (n = 110) in the autumn of 1995, as well as directly from the AO layer of the soil, including leaf litter, intermediate, and humus layers (n = 110), in the spring of 1996. A total of 44075 seeds were disseminated into the seed traps, including 17 964 mature seeds; 15% of these were viable the following spring, indicating a large decrease in the abundance of viable seeds during the post-dispersal seed stage. Spatial association of undamaged seeds changed from a positive to independent association between the different dispersal stages, indicating rearrangement of the spatial pattern of seeds through time. During this period, numbers of living seeds generally decreased beneath nonspecific adults compared to those located away from the adults. This change resulted from the spatially different behavior of several biotic and abiotic killing agents. Rodents and fungi attacked the seeds, depending on seed densities and presence of nonspecific adult crowns, respectively, but desiccation was independent of both seed density and nonspecific crowns. The multiple killing agents with different spatial behavior jointly influenced the distributions of recruits entering tree populations.