This root map shows a poplar tree excavated in USDA hardiness zone 6 in compacted (1.8 g/cc) sandy loam soil. The root system in compacted soil largely develops throughout the top few inches of soil. Lateral roots grew fairly straight and ranged from 1 to 5 inches deep.
This poplar tree found an uncompacted soil pocket (see arrow) and produced roots down to about 9 inches in this pocket. These deep roots branched more and followed cracks and crevices. Note how the one main lateral root turned 180 degrees after it emerged from the trunk.