Last week, John Lechner, the very talented author-illustrator of The Clever Stick and the Sticky Burr stories, had this to say on his blog:
“Many people stop looking at trees after the leaves fall off, but this is when I think trees become the most interesting.”
I love this statement. Not only are leafless trees interesting, they are truly beautiful. Look at the wonderful shape of my maple. The branching seems random and yet it is nearly symmetrical. The result is a lovely giant teardrop shape.
As I contemplated this over a cup of steaming tea last week, I couldn’t help but wonder about the physiological purpose behind the tree’s overall shape and branching pattern. I knew there had to be one. There are no coincidences in the natural world.
So I did some research, and here’s what I discovered.
Tree branching has a lot in common with the branching of rivers and streams within a watershed, lightning bolt branching, the distribution of plant roots underground, and the branching of blood vessels inside your body. And it’s no accident that the collection of tiny tubules in your lungs looks a lot like a maple tree tipped on its side.
Branching allows water, nutrients, gases, and other materials to be collected or distributed efficiently over large areas. A tree’s leaves need to be spread out over a large area so that they can collect plenty of sunlight or photosynthesis. Similarly, roots spread over a large area can absorb more water and minerals from the soil. But once the tree takes in these materials, it needs a way to move them from one area to another.
A tree contains two transport systems—the xylem and the phloem. The xylem carries water and minerals from the roots up the trunk and out the branches to the leaves. The water combined with carbon dioxide from the air to make sugary food. Then the phloem carries the food from the leaves back to the rest of the tree.
It turns out the shape and distribution of the tree’s branches and roots maximizes the efficiency of moving materials from top to bottom and bottom to top. Pretty cool.