COST OF REPRODUCTION IN DOUGLAS-FIR

The balance between allocating energy resources to reproduction or growth has considerable theoretical interest. Conflicting ecological requirements and evolutionary pressures often necessitate a trade-off in energy allocation. We obtained measurements on seed-cone production and annual ring width of 365 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees from 29 open-pollinated families for 8 years. Phenotypic, genetic, and environmental correlations were computed for seed-cone production and ring width for each year. Five of the eight environmental correlations were negative (range -0.077 to -0.305), reflecting the reality of the trade-off in physiological terms. Six of the eight genetic correlations were negative (range -0. 199 to -0.776), indicating that a trade-off exists at the genetic level between energy allocation to reproduction and to somatic growth. These findings agree with the current theory of life-history evolution.