Root Extension of Trees in Surface Soils of the North Carolina Piedmont

This investigation was conducted in a clay soil of piedmont North Carolina to obtain data on surface-root extension of hardwood species. Radioiodine in a carrier solution was applied to a 0.5-ft2 area of soil surface. After application of I-131, trees were monitored with a portable scintillation probe and scaler for 3-5 weeks to detect presence of I-131 in stems of trees. A total of 703 stems in 18 species was studied. A high percentage of white oaks showed uptake in the zone nearest the application spot, implying an intensive network of roots close to their trunks. Other species had more extensive patterns of development. Maximum measured distance of root extension ranged from 31.8 ft for dogwood to 54.6 ft for hickory.