How do trees grow?

Trees amaze me and are so thought-provoking. There is science on “how” trees grow but it still amazes me to think about how that process actually plays out.

Have you ever watched a tree grow? Some would say they grow too slowly to watch.  But I have heard people tell me my entire career as an Arborist, that they remember when a tree was just a sapling and now it takes up their entire yard. Or, they don’t even remember when the tree was planted or how it got there, but the trunk diameter is 30 inches. Trees grow slowly, but in some sense, they also grow quickly.  

I must have missed a class or wasn’t paying attention when they taught us how an acorn turns into a 100-foot oak tree. I don’t remember when I asked these questions, and I don’t have all the specific detailed answers in my head, but here is what I think I know:

• An acorn, that may weigh a couple of grams, has stored energy to start to grow a taproot and in turn, its first two leaves.  
• The now small sapling turns into a bigger sapling that then turns into a small tree.
• Trees get all they need from the living soil, water, air, and the sun.
• It is through photosynthesis that trees obtain carbon from the atmosphere which gives the trees their mass (weight).  Carbon Dioxide in and Oxygen out.  The Carbon left in the tree is why trees are known to be good carbon sinks (carbon sequestration).

Now we have an idea of how trees grow. But how do they really grow? Trees grow out at the tip of their branches and roots with cells called apical meristems. This is where the cells reproduce. The trunk also grows in diameter (grows out) when new cells are created in the cambium area of the tree (xylem and phloem). So, tree tips grow and tree root tips grow and trees get fatter, but they do not grow upward from the ground like you sometimes see in cartoons. Imagine that fence, birdhouse, or anything else attached to a tree; as the tree grows the height of those items does not rise.

I recently thought about my career as an Arborist and how 25 years ago the trees in Richmond were 25 years younger. They were 25 years shorter and they were 25 years smaller in diameter. I remember ropes were sold as either 120 feet long or 150 feet long. 150 feet, when you double the rope, could get you to the top of most of the trees in Richmond (about 75 feet). Of course, there were a lot of trees for which these ropes were not long enough but it did get us to the top of most trees. Today, I don’t believe any of our climbers use ropes less than 200 feet. How tall will the trees be in another 25 years?