White oak sapling dynamics across the eastern US: Quantifying a bottleneck to sustainability

The long-term sustainability of white oak (Quercus alba L.), an ecologically and economically important species in the eastern United States (US), appears to be threatened by demographic constraints. Earlier research has highlighted widespread bottlenecks in the process of recruiting white oak saplings (2.5 cm - 12.7 cm dbh) into small trees (dbh ≥ 12.7 cm). Thus, the fate of white oak saplings is a key component in understanding whether shortfalls in larger size classes are due to an onset of challenges when white oaks reach the small tree size or are an artifact of unsustainable sapling dynamics. Using Forest Inventory and Analysis (FIA) data, we examined sapling population dynamics, including rates of recruitment into the sapling size class, mortality and removals of sapling sized stems, and outgrowth of saplings into the small tree size class across the eastern US and regionally. Across the eastern US white oak study region, white oak saplings exhibited slightly positive net population growth in 2020, but 13 of the 41 ecological sections that made up our study region had flat or declining sapling populations, and another 7 sections had sapling densities too low to support meaningful trend estimates. Mortality rates for saplings exceeded recruitment for many northern and mid-Atlantic sections, while parts of the Interior and Appalachian Plateaus and Boston Mountains showed stronger sapling accumulation. Compared to saplings of other tree species that were examined, white oak saplings had 1) low mortality rates and 2) a tendency to stall, often for more than 15 years, without growing into the small tree size class. Our results suggest management opportunities may exist for delayed release of white oaks persisting in the sapling stage, particularly in regions where sapling dynamics are slow. Sapling persistence may provide a buffer against regeneration failures, but it does not guarantee eventual canopy recruitment for stalled saplings. Understanding where white oak saplings persist or fail to accumulate offers a more refined lens for diagnosing bottlenecks and promoting sustainable management.