SPATIAL AND TEMPORAL PATTERNS OF EASTERN WHITE PINE REGENERATION IN A NORTHWESTERN OHIO OAK STAND

摘要

Eastern white pine (Pinus strobus L.) was often associated with oaks (Quercus spp.) on upland sites in presettlement forests of the upper Great Lakes region, but widespread logging and subsequent fires in the late 1800s converted these upland sites to fire-tolerant oak forests. Although white pine regeneration is occurring in these second-growth oak forests, white pine regeneration patterns in oak forests of the Great Lakes region are not well documented. We examined white pine regeneration in the southern Great Lakes region in an oak stand within the Oak Openings region of northwestern Ohio, where white pine plantations established in the 1940s have served as seed sources for white pine invasion of surrounding oak-dominated forests. White pine regeneration was aggregated in high-density clumps in the oak stand, with a mean white pine to white pine nearest-neighbor distance of 1.8 m. Eighty-one percent of invading white pine established during a 6-yr interval that corresponded with an extended period of below-average annual available water deficits (i.e., conditions were more moist than normal). No white pine recruitment has occurred in the oak stand in the last 15 yr since the 6-yr establishment interval, and we hypothesize that favorable white pine colonization sites in the oak stand were occupied during the initial invasion event. White pine regeneration in these oak forests may proceed in "leaps and bounds," with white pine expanding 100-300 m by clumped regeneration into new areas during unique regeneration events. White pine's present ability to reproduce successfully in northwestern Ohio appears related to reductions of historic fire frequencies.