Influence of slope orientation on sex ratio and size distribution in a dioecious plant Bursera fagaroides var. purpusii (Brandeg.) McVaugh and Rzed. (Burseraceae)

It has been hypothesized that environmental variability can influence the sex ratio of a plant population, and it has been observed that in stressful environments, male plants are more abundant than females. However, it is unknown whether this is due to differential mortality rates between males and females. In this study, we analyzed sex ratio, mortality, and size distribution in a population of the neotropical tree/bush Bursera fagaroides in two different environments (east- and west-oriented slopes) over a 10-year period. We determined that the sex ratio favored males in the more stressful environment (east-facing slope) and that females were significantly larger in the less stressful environment (west-facing slope). Despite a significant difference in size between sexes by slope aspect, the difference in sex ratio cannot be explained by slope or by mortality during the 10 years of observation.