Long-term effects of single-tree selection cutting on structure and composition in upland mixed-hardwood forests of the southern Appalachian Mountains

In 1946, this study was initiated to examine the efficacy of single-tree selection cutting in submesic to mesic mixed-hardwood forests of the southern Appalachian Mountains. Seven stands comprising 40 ha of mixed-hardwood forests plus three unmanaged stands were utilized. Species composition of the overstorey prior to treatment was dominated by species intolerant and mid-tolerant of shade, including oak (Quercus L.) species and yellow-poplar (Liriodendron tulipifera L.). After 10 years of improvement cuttings, the BDq method of regulating stocking was employed. Selective cuttings occurred in 1956–1957, 1962, 1970, 1984 and 2006. Early observations suggested that control of shade-tolerant midstory species might be required to regenerate the mid-tolerant overstory species. In 1972, shade-tolerant species between the 5 and 20 cm d.b.h. classes present in small openings created during the 1970 entry were injected with herbicide in all seven managed stands. In 1986, another treatment which included the complete removal of the shade-tolerant midstory occurred in two of those seven stands. After 60 years, the majority of managed stands have diameter distributions other than the traditional reverse-J shape, including concave and rotated sigmoid shapes. Even after the treatment of shade-tolerant competitors, results suggest that single-tree selection has thus far been ineffective at recruiting the desirable tree species that are intolerant or mid-tolerant of shade. In fact, the density of mid-tolerant oak-hickory and shade-intolerant species in the sapling and pole size classes in the managed stands did not differ from that in unmanaged stands. As applied in this study, the BDq approach to single-tree selection cutting has led to the sapling and pole size classes being increasingly dominated by shade-tolerant species and is not likely to be sustainable, in terms of both desirable species composition and structure, in the long-term.