EFFECTS OF THE LENGTH OF THE SNOW-FREE PERIOD ON LEAF LONGEVITY IN ALPINE SHRUBS - A COST-BENEFIT MODEL

Leaf longevities of three woody dwarf-shrub species were investigated in relation to the length of the snow-free period in a mountain area i n Hokkaido, northern Japan. Leaf longevity of a deciduous species, Sie versia pentapetala, slightly increased with increasing length of the s now free period. In contrast, the leaf life-span of two evergreen spec ies, Phyllodoce aleutica and Rhododendron aureum, decreased with incre asing snow-free period. These trends are consistent with a cost-benefi t model for leaf longevity as a function of the changing length of the yearly period favorable for photosynthesis. Hence the plastic changes in leaf longevity with varying snow-free periods were concluded to be adaptive traits for maximizing photosynthetic gain for the plants.