Document: YVE-3-29-24

Effect of light intensity and sapling size on crown morphological plasticity and biomass partitioning in boreal conifers with contrasting shade tolerance.

CLAVEAU, Y.* ¹, C.MESSIER ¹ and PHILIPG.COMEAU ²

GREF interuniversitaire, Montréal, QC, Canada ¹
British Columbia Ministry of Forest, Research Branch, Victoria, BC, Canada ²

Abstract:
The interacting effects of a gradient in light intensity and sapling height on crown morphological plasticity and biomass partitioning were studied for various conifer species in the boreal forest of Canada. These species were: balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca [Moench.] Voss), jack pine (Pinus banksiana Lamb.), subalpine fir (Abies lasiocarpa [Hook.] Nutt.), interior spruce (a complex of white spruce and Engelmann spruce (P. engelmannii Parry ex Engelm.)) and lodgepole pine (Pinus contorta Dougl. var. latifolia). The sampled saplings covered a large gradient of sizes (between 30 and 320 cm in height) and light levels (four classes: 0-10, 11-25, 26-50 & 51-100% of full sunlight). Pine showed less crown morphological plasticity with respect to light than firs and spruces as has been previously reported. But unlike other studies, we found that size interacted with light availability in determining this plasticity. For example, live crown ratio generally decreased with light in spruces and firs, but it also decreased with increasing size in the lower light classes. We used leaf area ratio (LAR) as a descriptor of biomass partitioning and we found that it decreased strongly with increasing size up to approximately 1 meter, for all species and light conditions. This suggests a mechanism by which, in low light (and hence carbon limiting) conditions, trees rapidly loose their capacity to tolerate shade with increasing size. A better knowledge about how boreal trees respond to shade is essential for the development of silvicultural systems that more closely emulate natural disturbances.

Keywords: shade tolerance, boreal conifers, height and light interactions

This abstract is being presented at: 8:00 AM in session:
Poster Session #1: Light Relations.