It may not pick up the trees. I am basing that on an old story that in Vietnam, F111's had ground following radar that would guide the F111 a few hundred feet off the ground in IFR. In some places the jungle growth was 200 feet high or even higher. Needless to say, a few crews did not return.
I have also heard of some recent helicopter stories where the RA was not giving back accurate data while flying over water.