The natural processes that make a Christmas tree grow into its iconic shape are as complex as building a skyscraper. Each structural element of a tree has its own function.
Conifer trees have both terminal and lateral buds. Terminal buds are located at the tips of branches, and grow upward. Lateral buds give rise to side branches.
And, just as a construction job needs a building contractor to oversee the project, trees rely on the terminal bud to coordinate its growth.
The actions of terminal buds suppress the growth of lateral branches, a phenomenon called “apical dominance.” They produce a plant hormone called "auxin," which flows down the stem through the plant's circulatory system. This inhibits the lengthening of lateral buds, and ensures that the tree grows tall instead of broad, so the tree can “race to the top” for sunlight.
You can test apical dominance by sawing top off the tree. When you snap off the terminal leader, inhibition is released and the lateral buds below respond by growing out, creating bushier, shorter tree.
The phenomenon of apical dominance helps trees maintain a strong central trunk, which provides resilience against wind and heavy snow.
It’s easy to take that Christmas tree shape for granted — they blend into the background of our holiday décor. But I think it’s good to be aware of the complex processes that made your tree the right height and shape to celebrate your holidays.
