Shouldn't you be able to see that on sattelit pictures?
TBH, I would like to know how much water it take to grow trees around the highway through middle of desert, but that is for another topic.
There just isn't enough rainfall. Annual average precipitation in the Taklimakan Desert is less than 100 millimeters. With drip irrigation, they can probably keep at it at reasonable expense, but that place is horrid. Just look at it: https://www.youtube.com/watch?v=KuylRKAK1Tc