Yes. Coupons = Free Trees. The existing courses were made by, essentially, beta testers, some of whom went and bought and paid for speed trees and other assets. If there are any, decent, trees available, I'm personally not aware of them. Yes, you can make your own trees out of Unity, but mine looked like crap. Only one guy that I know of, made his this way and he's since switched to speed tree.
Course Forge without trees = really unhappy new course designers. The speed tree modeller from Speedtree is $20/mo. The good thing is, you can make all the trees you can in one month, stop the service and keep all your trees forever and ever, amen. You can also, pay another $20 and use it another month. But, PP really wants people to have some trees right out of the box and getting people coupons to purchase trees is the best they could come up with.