Dioecy-induced spatial patterns of two codominant tree species, Podocarpus nagi and Neolitsea aciculata

Abstract

1 Spatial patterns of two codominant dioecious tree species, Podocarpus nagi and Neolitsea aciculata, were analysed at Mt. Mikasa, Nara City, Japan. Podocarpus nagi has a higher shade tolerance but a narrower seed dispersal range than N. aciculata. We examined the effects of dioecy on regeneration and coexistence of the two species. 2 Seeds of P. nagi are dispersed by gravity around female trees. Young plants of P. nagi were clumped and showed significant attraction to large female trees and significant repulsion from large male trees. Dioecy therefore affected the spatial heterogeneity of plant density in the P. nagi population. 3 Seeds of N. aciculata are widely dispersed by birds, and young plants of N. aciculata therefore showed no significant attraction to female trees. This wide dispersal of seeds moderated the effects of dioecy on the spatial pattern in N. aciculata. 4 Large N. aciculata trees were clumped and showed significant attraction to large male P. nagi trees, suggesting that growth of N. aciculata is facilitated where young P. nagi plants are uncommon and competition is therefore less intense. 5 One effect of dioecy may be to produce a population structure for P. nagi that promotes its coexistence with N. aciculata.