Wood is often classified by hardness. The wood from most pine? trees is rather soft, where the wood from oak? is much harder. Additionally wood from different types of trees have different colors and grain densities. Because of these differences, and the fact that some woods take longer to grow than others, wood from different types of trees is valued differently.
While mahogany? is a dark, dense, hardwood which is excellent for fine crafting, Balsa? is light, soft, and almost sponge like, which makes it useful in other ways, like model building.