inhibition of lateral buds. decreasing from the top down. by apical buds over many seasons. resulting in trees with an excurrent growth form.
apical control (Wikipedia)
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Many conifers show particularly strong apical dominance, strongest of all being in the family Araucariaceae, showing a single erect central trunk with strongly differentiated horizontal branching. Cuttings of Araucariaceae species taken from a side branch will not develop erect growth. Araucaria heterophylla, New Zealand.
In botany, apical dominance is the phenomenon whereby the main, central stem of the plant is dominant over (i.e., grows more strongly than) other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets.
Plant physiology describes apical dominance as the control exerted by the terminal bud (and shoot apex) over the outgrowth of lateral buds.