© 1997 Heron Publishing—Victoria, Canada
Branch growth and biomass allocation in Abies amabilis saplings in contrasting light environments
David A. King
Ecosystem Dynamics, Research School of Biological Sciences, Australian National University, Canberra ACT 0200, Australia / Received May 14, 1996
Summary
Aboveground biomass allocation, and height and branch growth were studied in saplings of the shade-tolerant conifer, Abies amabilis Dougl. ex Forbes growing in large openings and in the understory of an old-growth forest in western Oregon. The presence
of annual overwintering budscale scars was used to infer extension growth histories; annual growth rings in branches and stems
were used in combination with extension histories to compute partitioning of new biomass among leaves, branches and stems.
Saplings growing in large gaps had conical crowns, whereas understory saplings had umbrella shaped crowns as a result of much
greater rates of branch extension than stem extension. Understory saplings grew slowly in height because of low rates of biomass
production and low allocation of biomass to stem extension. About 40% of new biomass was allocated to foliage in both groups,
but understory saplings allocated more of the remaining growth increment to branches and less to stem than did saplings growing
in large gaps.
These results differ from the patterns observed in shade-tolerant saplings of tropical forests, where allocation to foliage
increases with shading and branch allocation is much lower than observed here. This difference in allocation may reflect mechanical
constraints imposed by snow loads on the evergreen A. amabilis crowns, particularly on flat-crowned understory saplings.
Keywords:
allometry, branch growth, conifer, height growth.
