Long-term effects of group selection, single-tree selection, and clearcutting on individual-tree and stand volume growth in northern hardwoods of the Great Lakes region

Abstract Group selection and small patch cutting are widely viewed as more aesthetically acceptable alternatives to clearcutting for regenerating tree species of low shade tolerance, and they may enhance resilience in the face of climate change. However, little evidence is available on how production rates compare with those of other silvicultural systems. We used CANOPY, a spatially explicit, individual-tree model, to investigate the link between individual-tree growth and net volume growth at the stand level under alternative silvicultural systems in northern hardwood forests. The model predicted peak growing space efficiency (volume increment per unit of crown projection area) in the pole or mature stage under all silvicultural systems and a decline for larger and older trees. Trees in uneven-aged stands were generally less efficient, slower growing at a given size, and harvested at more advanced ages compared to even-aged stands. Nevertheless, there was little predicted difference in net growth between single-tree selection, group selection, and thinned even-aged stands. However, stands managed by small patch cutting (800–2000-m2 openings) without thinning, as well as unthinned even-aged stands, had substantially lower net growth and higher mortality rates. The paradox that lower efficiency of trees in uneven-aged stands did not result in lower net growth at the stand level was not explainable by improved efficiency of mature trees due to adjacent canopy gaps or by low harvest volumes of smaller, less efficient trees. Rather, production in even-aged stands was lower than expected due to the slow recovery of merchantable growing stock following clearcutting, which negated the higher productivity of even-aged stands during the mature phase. A secondary factor was the asymptotic trend of production rates beyond an opening size of 200 m2, so that larger openings under group selection or clearcutting did not stimulate higher production levels.