The effects of stand density on frequency of filled seeds and fecundity in lodgepole pine (Pinuscontorta Dougl.)

Abstract

In lodgepole pines self- and cross-pollination initiate the development of seeds with equal frequency, but self-pollination results in filled seeds only 17% as frequently as cross-pollination. A study of the frequency of initiation of seed development and filled seeds in 17 stands of lodgepole pine differing in spacing and growth form of trees indicates that both the quantity of pollen produced by a tree and the density of conspecific individuals influence the frequency of filled seeds. Moreover, the positioning of a cone relative to the top and bottom or windward and leeward sides of a tree influences the frequency of filled seeds. Genetic markers used in controlled crosses indicate that cross pollen fertilizes significantly more than half the filled seeds resulting from crosses with equal mixes of self and cross pollen. The effect of density of conspecifics and growth form of trees on the frequency of filled seeds gives an adaptive basis for the facultative shift in sex ratio in lodgepole pine. It also suggests an adaptive basis for the high frequency of dioecy in wind-pollinated, woody perennials of the Great Basin Region. This relationship also has practical implications for the management of breeding systems for seed production and reforestation.