Kids: Why don't tree branches grow straight up?
This is one of Buck82's photos. It was taken in in Kenroku-en in Kanazawa City, Japan.
Tree branches grow outward and upward and downward and every which way. Why don’t tree branches just grow straight up towards the sun?
A tree branch’s job is to provide a way for tree leaves to act as a net for sunlight.
Trees need light for photosynthesis, which is how green plants generate their energy. The branch will grow to give the most leaves the most light – even if that means growing sideways.
There are other factors that affect the way branches grow as well. Gravity pulls the branches downward. And branch growth is affected by the wind.
Part of the trade-off any tree has to make is between gathering light, staying stable in the wind, and succeeding against nearby competitors. So when branches grow crookedly, that’s part of a tree’s overall survival strategy.
Trees have sensors that detect light and gravity. From the moment a tree begins its life, it knows which end is up. Trees will generally attempt to grow toward the light and away from gravitational pull.
But, as a tree gets older, its branches tend to grow more outwards than upwards. That’s so the tree can cast a wider net to catch the light of the sun.
Our thanks to:
Dr. Robert B. Jackson
Assistant Professor
Department of Botany
Nicholas School of the Environment
Duke University
Durham, NC
Plants don’t want to grow close to the sun they just want to make sure that they can get sunlight. Growing up, especially early in the plants life, ensures that they will not be in the shadow of other plants. Once they are high enough to not be in the shadow of other plants they will grow so as to increase their catchment area: sideways and usually crooked.