If
one sold his land and retained the trees on it for himself, he has a
certain amount of land around the trees, so that if his trees die, he
is entitled to plant others.
In fact, even Rabbi Akiva would agree to the ruling about trees. The
tree weakens the surrounding soil, and the seller worries that if the
tree dies, the buyer may tell him, “Uproot your tree and be gone!” and
thus the seller reserves land around the trees for himself.