These red oak are both the same age. They are about 28 years old, they are nearly the same height, and have basically the same soil moisture and nutrient availability. The larger oak is 13 inches in diameter at breast height (DBH), and the smaller oak is 7 inches DBH. Amazing!
Why is are they so different in diameter? It’s because the larger tree is free to grow on three sides, that is, it doesn’t have other trees competing with it for light, so it has a large crown. The smaller tree has competition from all sides, so it has a very small crown.
Why is crown size so important? The larger the crown a tree has, the more leaves the tree has and the more carbohydrates it can produce through photosynthesis. The tree uses carbohydrates for respiration, growing taller and producing more roots, for example, before it puts energy into diameter growth. A tree with a large crown can make a lot of extra carbohydrates that can be put into diameter growth.
This is exactly the reason we do crop tree release. Crop tree release removes competition for from selected crop trees so they can expand their crowns and increase DBH faster. The link below will take you to an excellent crop tree release handbook.
With the good, rich soils in the Driftless, we can grow sawtimber trees in 30 years. That’s pretty darned amazing. Just think how nice that 13″ oak will look in another 50 years!