Trunks and big branches are, as it were, the beams and rafters of the roof. Smaller plants and leaves form shingles. Leaves use light energy to make sugars out of carbon dioxide from the air. The sugars travel back to the roots below through the bark. Simply said, carbon products come from the tree crown and travel downwards inside the bark, towards the roots.
Much rain causes excess sap to travel upwards from the roots.
Some of this sap is sweated out from the leaves, so proteins and vitamins arrive on the outside, not inside the leaves. These feed bacteria. After the first bacterial colonists, more organisms appear in this new milieu with every rain shower. Fungi, algae and finally mosses, grow on the old Colombian rain forest leaf in Fig. 2. The leaf finally dies and falls off, carrying the hitchhikers on its back to the forest soil.