Seasonal physiology and growth of planted oaks with implications for bottomland hardwood restoration

Abstract

Afforestation and reforestation of once dominant bottomland hardwood forests in the southeastern United States can provide ecosystem services and wildlife habitat. However, challenges of prior site conditions, seasonal flooding, soil texture and lack of nearby seed sources can necessitate planting of seedlings to achieve desirable results, particularly for large-seeded species like oaks. Therefore, the objectives of this study were to compare growth and survival of two species of oaks common to southeastern and bottomland hardwood forests, cherrybark oak (Quercus pagoda Raf.) and willow oak (Quercus phellos L.) from 1-0 bareroot, conventional container (0.24 L) and large container (3.8 L) planting stocks across two growing seasons. Additionally, we sought to compare physiology across seedling types to determine the underlying differences in functioning that led to the growth responses. Despite above average rainfall, growth was modest particularly at the site that was previously pasture land and for willow oak which also exhibited net dieback. Two-year survival was adequate (> 75%) for bareroot and large container seedlings but was suboptimal (~ 50%) for conventional container seedlings. Large container seedlings had about 40% higher photosynthetic rates and 70% higher water use efficiencies compared to bareroot and conventional container seedlings. Cherrybark oak exhibited greater stomatal regulation across the growing season than willow oak, however all seedling types displayed increased stomatal conductance and decreased water use efficiency throughout the growing season. Overall, these findings highlight the importance of matching species to site conditions and providing competition control particularly on grassland sites and during above average rainfall conditions.