Dioecy in Five Pinus edulis Populations in the Southwestern United States

Reproduction of five populations of Pinus edulis was investigated from 1979 through 1981, focusing on male strobili and female cone production by trees of varying ages. The majority of the youngest reproductive trees produced only male strobili, whereas slightly older trees produced only female cones. Fully mature trees which were, on the average, older than these two groups produced both male and female reproductive organs. Female trees produced seeds with a higher percentage of full seeds, greater total germination and longer radicle than those of monoecious trees. This reproductive pattern may be an adaptation to stress in young trees or those in arid environments and is discussed in relation to pollen and seed dispersal.