Trees are big and take up a lot of room, but there's way way way more dirt than trees. Good soil is actually upwards of 5% organic matter which is non-trivial.

Trees are big and take up a lot of room, but there's way way way more dirt than trees. Good soil is actually upwards of 5% organic matter which is non-trivial. 5% of all the good dirt left in the world is a very big number and probably dominates the weight of trees on the planet.