In Henry Cuyler Bunner’s poem The Heart of the Tree the poet says:
What does he plant who plants a tree?
He plants cool shade and tender rain,
What role do the trees actually play in bringing rain to the earth?
This is more a science question than a literary one. Anyway, as the poet has mentioned it, trees can bring ‘tender rain’.
The trees help in bringing rain in an indirect way through the process called transpiration. Through transpiration, trees leave the extra water through the stomata on the leaf surfaces. The water evaporates into the air and adds to the moisture of the air. So the air gets saturated faster and brings rain.