They could be encouraged by saying the importance of trees to them, and how the plants and trees, give out Oxygen by just taking the Carbon-dioxide from the air, Sunlight and water. Also,
they must be made to know about,
2.Excessive CO₂ emission in the air,
3.Mixing of more and more chemicals in the air; and,
4. about Acid Rain.
By making them to know about these, if we say planting more and more trees is the only remedy to control the rate of losing the naturality of the air.
Planting trees will surely give a better result in the mixture of air, by increasing the percentage of Oxygen, around the particular area.
planting trees more and more will make the earth's average temperature to go normal, and the alarming rate of global warming would be gone.
Due to excessive Deforestation, we had lost many trees; and,
most of our forest covers.
is the only remedy for all these.
Thus, we can make them to know about the importance of planting trees, and they can be encouraged to participate. :)
Hope this will help you.