A tree seems to pull itself out of the ground. Its roots disappear into soil, so soil looks like the obvious source of the trunk.
But remove the water and examine what remains. Most of that dry mass is organic matter built through photosynthesis, not mineral matter lifted from the earth.
Carbon dioxide enters the leaves through microscopic pores. The tree fixes its carbon into sugars, then rearranges those compounds into cellulose, lignin, bark, roots and fruit. Carbon that was moving invisibly through the atmosphere becomes a structure strong enough to stop wind.
Soil still matters. It supplies mineral nutrients, and roots supply water. Water contributes matter too. Sunlight supplies energy, not substance. But minerals form only a small fraction of a tree’s dry mass. The dominant source of its carbon enters through the leaves.
This is easy to miss because roots are obvious and gas is not. We imagine growth as extraction from below.
A tree is not mainly soil standing up.
It is atmospheric carbon made load-bearing.