The effects of crop tree release and fertilization of young yellow-poplar on low and medium quality Southern Appalachian sites were compared. In June of 1989 96 individual 10 year-old yellow-poplar crop stems were treated in factorial combinations. The crop trees were either released, using a 4% triclopyr ester in kerosene basal spray. fertilized with 224, 291 and 243 kg/ha of N, P, and K; released and fertilized, or left untreated. These treatments were repeated in June of 1992. In 1992, treatments were slightly different. Crop trees were released mechanically, and only nitrogen was applied at 224 kg/ha. After five years, only release resulted in significant growth responses. Released trees responded positively to increased sunlight and horizontal space by increasing their uptake of nitrogen and iron - elements essential for photosynthesis. This led to an increase in foliage production, and presumably, an increase in total photosynthesis. Released trees reacted to the increased growing space by filling in the space created by release. Released trees increased both diameter and crown volume growth; unfortunately, they did so at the expense of height growth, which was decreased by crop tree release. Current stem wood volume, was therefore not increased. / Master of Science