The Earth consists of many gasses and elements of which oxygen is most abundant.  Most living organisms require oxygen to live. In the process of respiration, oxygen is taken in out carbon dioxide is given out. Trees on the other hand take in oxygen and give out oxygen, which does not lead to lack of oxygen. That is the main reason why we shouldn't cut trees. Trees help in maintaining ecological balance in the atmosphere.
Hi. hopefully you found this helpfull.
In our atmosphere , many elements and gases are present like oxygen, carbon dioxide, nitrogen, etc.
in which oxygen is very much important for animals and humans. Animal inhale oxygen in the process of respiration and release carbon dioxide which is very much useful for trees . Trees take carbon dioxide from environment.
like these trees help in maintaining the ECOLOGICAL BALANCE

hope this may help you. ..