Morphological acclimation to understory environments in Abies amabilis, a shade- and snow-tolerant conifer species of the Cascade Mountains, Washington, USA
Akira S. Mori (1, 2), Eri Mizumachi (3) and Douglas G. Sprugel (4)
1. Forest Ecology Laboratory, School of Resource and Environmental Management, Faculty of Applied Science, Simon Fraser University,
Burnaby, BC V5A 1S6, Canada / 2. Corresponding author () / 3. Laboratory of Forest Ecology, Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University,
Oiwake-Cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan / 4. College of Forest Resources, P.O. Box 352100, University of Washington, Seattle, WA 98195, USA / Received June 25, 2007; accepted September 4, 2007; published online March 3, 2008
Summary
Light-related plasticity in a variety of crown morphology and within-tree characteristics was examined in sun and shade saplings
of Abies amabilis Dougl. ex J. Forbes growing in two late-successional forests with different snow regimes in the Cascade Mountains of Washington,
USA. Compared with sun saplings, shade saplings typically had broad flat crowns as a result of acclimation at several scales
(needle, shoot, branch, crown and whole sapling). Shoots of shade saplings had a smaller needle mass per unit of stem length
than shoots of sun saplings, a feature that enhances light-interception efficiency by reducing among-needle shading. The low
annual rate of needle production by shade saplings was associated with a longer needle lifespan and slower needle turnover.
Reduced needle production within a shoot was reflected at the branch level, with lateral branches of shade saplings having
a smaller needle mass than branches of the same length of sun saplings. Reduced allocation to needles permits greater investment
in branches and stems, which is necessary to support the horizontally expanding branch system characteristic of shade saplings.
Mean branch age of shade saplings was significantly higher than that of sun saplings. Shade saplings had lower needle mass
per unit of trunk biomass or total biomass, reflecting greater investment in the trunk as a support organ. Increased investment
in support organs in shade was more evident in the snowier habitat. The observed morphological acclimation makes A. amabilis highly shade and snow-tolerant and thus able to dominate in many late-successional forests in snowy coastal mountain regions.
