Why do trees only reach a certain height? After all, the top of the trees produces new leaves every year, so the branch on which they grow must always become longer, right?

This question has occupied biologists for years. There is no really clear answer, but in most cases it boils down to this:

To provide a leaf at the top of the tree with water, barrels must be installed. Since these barrels do not remain functional (air bubbles enter them and then they die and become the heartwood of the tree), a tree invests in new barrels every year. A leaf at the top of a crown is then ‘more expensive’ because very long vessels are required. At a certain height (depending on the location), the carbon stock of the tree is already depleted in spring with the mere replacement of the barrels and leaves for the height already reached. The tree does get thicker because barrels are constantly being replaced, but the crown remains the same.

As a result, tree height (of one species) is a clear characteristic of the location quality: on a good location, oaks grow higher than on poor or dry soil.