Trees are 90% air. You can go over them, around them under them or through them. They are the only reason I still carry a 1-iron. But if a number of trees in succession limit your options, I tend to frown on them. Usually, they don't bother me. I can jack a shot over just about any tree (thank god for my 60). But given my drothers, I prefer trees not be play. I tend to block them out in design because as TD stated, they die, then you have a different hole. You can always cut em down but they are had to put back. So I design for them not there, then if they die, the hole stands on it's own merit.