EFFECT OF THE LIGHT ENVIRONMENT ON SEED-GERMINATION OF RED ALDER (ALNUS-RUBRA)

Red alder (Alnus rubra Bong.) seed showing strong phytochrome activity in the laboratory was tested to determine whether the phytochrome eff ect could influence germination under light conditions experienced in the field. Seeds in sealed Petri dishes were placed beneath three type s of overstory cover (clearcut (no overstory); Douglas-fir (Pseudotsug a menziesii (Mirb.) Franco) (coniferous evergreen overstory); and red alder (broad-leaved deciduous overstory)) and seven types of understor y cover (control (complete darkness); uncovered; 1-cm mineral soil; le af litter; moss; swordfern; and non-evergreen herbs). Germination was highest in clearcuts (68.6%), intermediate in Douglas-fir stands (47.4 %), and lowest in red alder stands (11.7%). Covers of understory veget ation, leaf litter, and mineral soil significantly reduced germination , with the greatest reduction occurring where understory vegetation wa s dense enough to significantly reduce the ratio of red:far-red light. These findings concur with field studies of red alder seedling establ ishment and suggest that the phytochrome sensitivity of red alder seed plays an important role in this species' success on disturbed habitat s.