Timber harvest and drought interact to impact oak seedling growth and survival in the Central Hardwood Forest

Abstract

AbstractOak (Quercus) is a dominant component of the overstory in the Central Hardwood Forest region, but is currently failing to regenerate throughout much of its range. Loss of oak as a canopy dominant species would be devastating to the numerous species of wildlife that rely on acorns as a food resource. Intolerance to shade, competitive interactions, and herbivory (especially by deer) all contribute to oak regeneration failure by suppressing oak seedling growth and reducing survival. Timber harvest is one way to create light conditions favorable for shade‐intolerant oak seedlings, but other biotic factors, especially competition and herbivory, continue to play a role in oak seedling growth and survival following harvest. We experimentally planted oak seedlings in several timber harvesting treatments and under varying conditions of herbivory and interspecific competition to assess the relative importance of these drivers of early oak life history and their interaction with timber harvest. Overall, seedling survival over the 4‐yr study was negatively related to competition but not herbivory, and growth was negatively related to herbivory but not competition. Herbivore pressure was generally mild across the study area. Abiotic factors also played an important role: Severe drought during the first two growing seasons (2011–2012) had a negative effect on both growth and survival, especially for seedlings in harvest openings and on southwestern‐facing slopes (sites that should normally favor shade‐intolerant oak). Meanwhile, a partial harvesting technique (shelterwood harvest) increased available light for oak regeneration while appearing to buffer against the effects of the drought. More extreme weather conditions, brought on by climate change, will likely present challenges for forest managers seeking to regenerate oak via timber harvest. Phased harvesting systems like shelterwoods, in addition to their other advantages, may mitigate the impacts of drought while still encouraging oak seedling growth.