Then there would be no life on earth.Trees for the major source of oxygen,coal,food and many essential things.It is impossible to live without it.Although we may have substitutions for it but they are limited stocks which are not sustainable.
If there will be no tree then there will be no oxygen. and the gas which life is oxygen it means that their will be no life. if their is no tree then their will be no petroleum, furniture, food any many important things . actually the fact is that tree are the only source of our life directly or indirectly we extract every thing from trees.if there is no tree life is totally impossible. 
       i hope that this will help u.