Ok ive been playing for about a month now and I terraformed all the trees in my city. After all was terraformed, 3 weeks later (which is now), there suddenly spontaneously spawned trees in my city. I suppose after an amount of time they grow again? Dont get me wrong, this is a very good thing, at least for me since im always out of wood. But what I wanna know is how often does this happen? I wont make so many trades if I know how often this happens.

Thanks,
Hemo