Now-a-days we see so many people insisting upon saving the environment, growing more trees, "Go-GREEN", etc. Trees are also part of Krishna's creation and killing them mercilessly is also an offense. Srimad Bhagavatam being amala-puran and practical theistic science for people of all ages - very nicely explains the importance of preserving trees. When Maharaj Parikshit inquired about the potency of the Supreme Lord, by which he brought out the secondary creation, Sukadeva Goswami explained to him about the activities of king Prachinabarhi and his ten sons Pracetas - who were bestowed with responsibility of increasing the population. The Pracetas underwent long austerities under water and when they emerged from water, they saw the entire surface of the world covered by trees. Somehow they were annoyed by this and using the mystic power gained by their austerities - started burning the trees to ashes using fire coming from their mouth. When Soma - king of the trees and predominating deity of the moon saw their misuse of powers, he advised them very nicely - not to misuse their anger in destruction of trees which are created by Krishna for a very special purpose. In verses 6.4.7 through 15 of Srimad Bhagavatam, King Soma very nicely insists on the importance of trees.
Soma says that duty of government or king is not only to protect the citizens, but also other living entities like animals and trees. No living entity should be killed mercilessly. He also explains how fruits and flowers of trees serve as food for birds, insects - grass and legless entities serve as food for the cows and buffaloes and food-grains serve as food for human-beings. In verse 6.4.12-13 he says
tokaanaam pitarau bandhu / drshah pakshma striyaah patih
patih prajaanaam bhikshunaam / grhy ajnaanaam budhah suhrt
"As the father and mother are the friends and maintainers of their children, as the eyelid is the protector of the eye, as the husband is the maintainer and protector of a woman, as the householder is the maintainer and protector of beggars, and as the learned is the friend of the ignorant, so the king is the protector and giver of life to all his subjects. The trees are also subjects of the king. Therefore they should be given protection."
antar deheshu bhutaanaam / aatmaaste harir ishvarah
sarvam tad-dhishnyam ikshadhvam / evam vas toshito hy asau
"The Supreme Personality of Godhead is situated as the Super-soul within the cores of the hearts of all living entities, whether moving or nonmoving, including men, birds, animals, trees and, indeed, all living entities. Therefore you should consider every body a residence or temple of the Lord. By such vision you will satisfy the Lord. You should not angrily kill these living entities in the forms of trees."
If we are unable to help anyone, at least we must refrain from hurting them. So even if we don't plant and grow trees, let us not indulge in the sinful act of killing them but rather protect the existing trees in whatever way we can for His pleasure.