I have two silver birch trees side by side (about 3 ft apart). There is a small block of flats next to our house and last summer a resident from that block took it upon themselves to lop my silver birches. They cut the upwards growing trunks (which were about 3 inches diameter) clean across at a height of about 10 feet from the ground. This left only the smaller branches which were growing out sideways from just below this point. I am looking for ideas as to how to (a) make sure the trees survive, and (b) encourage the lower branches to growupwards to replace the shape and coverage lost from the main trunk. Any advice gratefully received.