Abstract:
Quercus-Pinus forests of the eastern US span > 13 million ha. It is important for managers to understand the methods used to sustain Pinus spp. in these mixtures or progress toward a more natural mixture of hardwoods. Understanding developmental and successional patterns in this forest type can help assess the need to actively manage natural processes, or to inform silvicultural prescriptions to achieve management goals. Little research has been conducted on localized disturbance processes in Quercus-Pinus forests. I examined 60 canopy gaps in a Quercus-Pinus forest on the Cumberland Plateau in Alabama to analyze their influence on development and succession. Most canopy gaps (53%) were single treefall events caused by snapped stems. The majority of gap maker trees (56%) were Pinus individuals while 44% were hardwoods. Most gaps (58%) closed by height growth of subcanopy trees. The majority of these gap filler taxa were hardwoods: Quercus (39%), Carya (14%), Pinus (14%), Nyssa Sylvatica (12%), and other (15%). Significant positive relationships existed between gap size and sapling diversity (r² = 0.15, P = 0.002), tree diversity (r² = 0.21, P = 0.0002), and total stem diversity (r² = 0.29, P < 0.0001). The number of Pinus gap makers and the number of gaps projected to fill by subcanopy recruitment of hardwoods indicated the forest was in the latter stages of a composition shift from Pinus to a much stronger Quercus component. To maintain a Pinus component, managers would likely need to create canopy gaps larger than those documented here and remove hardwood competition from the regeneration layer.
