© 1991 Heron Publishing—Victoria, Canada
Interrelation between shoot characteristics and solar irradiance in the crown of Pinus contorta ssp. latifolia
Anna W. Schoettle (1) and William K. Smith (2)
1. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, CO 80526, USA / 2. Department of Botany, University of Wyoming, Laramie, WY 82071, USA /
Summary
In Pinus contorta Doug. ssp. latifolia (Engelm.), annual shoot length increment, annual foliage production per shoot, and the daily integral of photosynthetically
active radiation (DPAR) at shoot tips increased with height in the crown, whereas leaf longevity decreased. There was a decrease
in DPAR along the shoot from the tip to beyond the oldest leaves, and the value reached at the point just proximal to the
oldest leaf cohort was the same for all shoots from all crown locations, regardless of the age of the oldest leaves. The results
suggest that shoot elongation, leaf production and leaf retention are controlled by the light environment within the crown.
Because high irradiance promotes leaf production and low irradiance promotes leaf shedding, foliage is not randomly distributed
in the crown.
