Effects of suppression history on growth response and stem quality of extant northern hardwoods following partial harvests

In uneven-aged stands, tolerant hardwood trees often sustain various degrees of suppression before they recruit to the merchantable tree layer. Whether this suppression influences stem quality development and growth potential of the trees in the future is still largely unknown. Using a retrospective approach, we assessed the influence of suppression history on tree growth response and the probability of stem damage following different intensities of partial harvest. Sugar maple and yellow birch samples were obtained from uneven-aged stands in northwestern New Brunswick, Canada. Results indicated that the likelihood of a tree possessing stem damage increased with length of suppression but decreased with increasing residual stand basal area (SBA) and site quality. Basal area increment (BAI) of both sugar maple and yellow birch was negatively influenced by period of suppression. BAI of yellow birch was higher than for sugar maple. Also, BAI increased with year since treatment but decreased with SBA for trees with diameter at breast height (DBH) larger than the subject tree's DBH for both species. BAI increased in small-to medium-sized trees (10-35 cm DBH), reached a maximum at 35 cm DBH, and then declined for larger trees (DBH > 35 cm) in both species. Generally, trees on better quality sites had higher growth. However, we observed a significant effect of site quality on BAI for sugar maple only. Hence, we conclude that the partial harvesting system that is designed to provide growing space for intermediate or sub-canopy trees that have shorter suppression history would increase growth rate of residual trees while maintaining stem quality at the northern limit of tolerant hardwoods.