I've flown a few combat contests where there are trees in the combat zone, and flying around behind the trees, up over them, and generally playing chicken with anything out there is fair game. So, no, it won't block the radio, but it's real easy to crash, usually in to the very tallest part of the tree.

fwiw, if you have a handy valley, or hill, you can also fly behind that, and put your airplane out of site. My home field has a long mostly straight ditch, with one nasty turn towards the end, and guys "run the valley", putting the plane out of sight as long as they dare. Many a balsa debris field is the result, but it's good fun for the foolhardy.