Without plants on earth there would be no way that any organism could survive. At least one large tree can take in over 2 tons of carbon dioxide in its entire life time. That is a lot. Now multiply that by maybe 5000 and that can change the composition of the atmosphere over a period of time. But due to the problem of deforestation, we are cutting off our major oxygen supply. Sure we need plants to turn into things we need but we don’t need to cut down entire forest to do it.