THE INTERACTION BETWEEN LEAF LONGEVITY AND SHOOT GROWTH AND FOLIAR BIOMASS PER SHOOT IN PINUS-CONTORTA AT 2 ELEVATIONS

Leaf longevity ranged from an average of 5 to 18 years in individual trees of lodgepole pine (Pinus contorta Dougl. ssp. latifolia D.K. Bailey) from six even-aged stands in central Colorado, USA, of which three were at an elevation of 2800 and three at an elevation of 3200 m. Leaf longevity was 38% greater and annual shoot growth increment was 33% less in trees growing at 3200 m than in trees growing at 2800 m elevation. There was no difference in leaf biomass per shoot between the trees at the two elevations. These results suggest that leaf longevity is greater on shoots with low annual growth potential. Thus, a slow-growing tree at high elevation (low annual shoot growth potential) can have the same amount of foliage per shoot as a fast-growing tree at lower elevation. This plasticity in leaf longevity enables a consistency in foliar biomass per shoot, which may contribute to the wide range of sites and environments that lodgepole pine occupies successfully.