Good eye! There is indeed a maple tree right behind the oak tree.
I've heard allelopathy from a couple of friends and a couple of places online, which I can't link to because of new-member restrictions on posting outside links. (But for anyone who's interested, if you google red oak allelopathy you'll find a few things.)
Perhaps red oaks are more allelopathic than other oaks? Not, like, black walnut allelopathic but maybe an effect.
