WIND DISPERSAL CAPACITY OF PINE SEEDS AND THE EVOLUTION OF DIFFERENT SEED DISPERSAL MODES IN PINES

Pine seed mass is isometrically related to samara shape among smaller seeded pines (< 165 mg), but not when larger seeds are included (putative bird-dispersed pines excluded). Among the largest pine seeds samara length declines with increases in seed mass. Consequently, disc-loading increases and dispersal capacity declines at an accelerating rate with increases in seed mass. The acceleration in disc-loading may arise in part from the energetic costs of constructing long-scaled cones to house the seeds and their wings. Regardless of the mechanism, the consequences for seed dispersal mode are great. For example, pine seeds weighing less than about 100 mg should be dispersed well by wind; all 38 species with seed masses less than 90 mg have adaptations for wind dispersal. Pines whose seeds weigh more than 90 mg are dispersed poorly by wind and usually have adaptations for bird dispersal (15 of 22 species).