Size Differences, Sex Ratio, and Spatial Distribution of Male and Female Water Tupelo, Nyssa aquatica (Nyssaceae)

Abstract

Many dioecious plant species show spatial segregation of the sexes along a gradient of habitat quality. This study explores the spatial distribution and size of male and female Nyssa aquatica (water tupelo) trees along a water depth gradient. Individuals were mapped to determine the spatial distribution of male and female trees and the relationship between distribution of males and females and water depth. Nearest neighbor analysis indicated that males and females were randomly distributed in space. Comparisons among plots, however, indicated that there were more male trees in the shallowest plot. Height and diameter at breast height were measured for each tree. Males were significantly larger in height and basal area than females. Coring of male and female trees indicated that size differences between the sexes cannot be attributed to age differences, suggesting that male water tupelo trees allocate more resources to growth than do female trees.