What determines where a tree grows its branches, and what their shape will be? Is it genetically predetermined or are there other factors at play?
In: Biology
As a tree grows new branches, it develops buds at specific sites just under the outer bark. Some of those buds elongate into branches, which then develop new buds just under the branch’s outer bark. In the spring, you can see the buds on deciduous trees swelling just before leaves or flowers develop from them. Some buds don’t receive enough sunlight, so the tree stops growth in the bud and bark can form over the bud and the bud can remain covered for years -or for the remainder of the tree’s life. Sometimes though, there is a shift in the available sunlight to the tree (perhaps a nearby tree falls over). Buds that have been long covered by bark can be reactivated and can sprout new branches. Cells just under the outer bark sense the available sunlight at that location. Some trees are better at this than others.
“Alternate branching” trees grow a certain amount of stem, then a bud to one side, then more stem, then a bud to a different side -repeat pattern. “Opposite branching” trees grow an amount of stem, then two buds on opposite sides of the branch, then more stem, then two opposite buds – repeat pattern. Recognizing this difference is hugely helpful to identify the tree species. (example: Oaks are alternate. Maples are opposite.)
Characteristics such as the length of stem between buds, the specific placement and direction of buds, the prioritization of certain buds/branches over others and the speed at which a tree grows are determined by a mix of many things including: sunlight, wind, ground-slope, available water, soil quality, air quality, pests and pathogens, human pruning and of course the tree’s inherent genetics.
Thick branches on a tree were all once thin twigs emerging from buds. Trees grow in two basic ways : 1) elongation of buds into branches and 2) thickening of existing branches. The thickness of a branch correlates roughly to that branch’s age. The branch has no other choice but to get thicker with each year (or with each rainy season).
I work with trees daily and never tire of them because each tree is unique!
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