Cone and Seed Weight Relationships in Douglas‐Fir From Western and Central Oregon

Abstract

Cone sizes and weights and seed weights were determined for 89 trees in 9 stands in the Oregon Coast Ranges, Cascade Ranges, and central Oregon. From west to east this represented a transition from mesic to xeric sites and from longer to shorter growing seasons. Differences among regions for all cone traits, and regression coefficients for change in cone and seed weights with distance from the ocean, were significant. Cone size and weight decreased, seed weight increased, and the regression coefficient of seed weight on cone weight, based on trees within regions, increased with distance from the ocean. Geographic variation in cone and seed weights was compared with variation in the phenology of cone and seed development as reported in the literature. This comparison indicated that where relatively large seeds were important to regeneration success and the growing season was short, Douglas—fir showed at least 3 changes in the timing of development as compared with milder sites. (1) The cone growth period was reduced more than the seed growth period. (2) The overlap in time of the developmental cycles of cone and seed was increased. (3) Cones and seeds grew during an increased portion of the growing season.