Paper is made from many materials, the most important being trees.
It is from my TOEFL preparation book and I know what it means throughout seeing the translation in my language. But I don't understand that why it put 'being' after adjective which is important. I think that the meaning of sentence should be:
Paper is made from many materials and the important thing is trees.
Being trees is important material for making paper.
Do you understand my question? Please help.