To actually observe a tree growing, you would need extreme patience. At the very beginning, when the first shoot sees the sun, you would notice the changes if you devoted a few weeks to watching it. But it takes decades for a tree to mature and grow to full size and for us to learn how it grows.
I discovered a simpler way: by studying the flames in a log fire, I learned how the tree grew. The characteristics of the flames reveal its growth. A mighty oak takes many years to mature into a strong, majestic tree, its wood burns in much the same way: a long-lasting fire, with strong flames and hot embers. The ideal fire to heat your home.
Much the same is true of beech, which has similar characteristics to that of oak. Both are strong, powerful and slow-growing trees and they burn that way too.
Spruce, on the other hand, is a fast growing and shorter lived tree. Its logs burn quickly and fiercely. Giving you a fire that is short and hot. Ideal for getting your fire started, but not always practical for heating your home, as this requires a big wood store.
Just another fascinating aspect of wood as a source of energy. You can try this for yourself. Watch pine, ash, elm and birch burn to see how they grow.