Wood is created by the photosynthesis of a tree. The tree takes in carbon dioxide, water, and radiant energy from the sun, transforms these through photosynthesis into the carbohydrates mentioned before. The radiant energy that is taken from the sun is transferred to the bond energies of atoms in the glucose molecules as well as into bond energies of carbon. This is the first energy transfer, the energy of the sun transferring to stored energy in the wood.
Image from: http://workwild.ca/2012/11/29/trees-what-age-is-a-good-age/