Successional dynamics of an Appalachian pin oak (Quercus palustris Münchh.) swamp forest

Abstract

Bottomland forests provide ecosystem services, such as nutrient exchange and pollution entrapment, and generally improve aquatic and riparian habitats. In West Virginia, little is known about the development and resiliency of isolated bottomland sites dominated by Quercus L. species, which have declined in area primarily from human impacts (e.g., draining and development). In this study, we used vegetation surveys and tree-ring analysis to investigate successional dynamics and the timing and drivers of recent overstory mortality in a remnant stand located on the floodplain of the Meadow River. Our results indicate a rapid change in vegetation cover at the site between 2011 and 2017, with a significant decrease in tree canopy cover and an increase in light-demanding, flood-tolerant, herbaceous species cover. Historical trends in tree establishment indicate an absence of Quercus palustris Münchh. recruitment after the 1960s and an increase in the recruitment of Acer rubrum L. and other shade-tolerant species. Furthermore, temporal trends in hydroclimate-tree growth relationships suggest that an increasingly temperate climate and higher water table benefited A. rubrum at the expense of Q. palustris beginning in the 1990s. Taken together, these findings suggest a gradual, multidecade process of plant community reorganization beginning in the mid-20th century. This process might have continued unabated, but flooding and persistent high water in 2003 amplified the wetting trend and initiated the progression of widespread overstory mortality. Our results suggest that Q. palustris forests in the Meadow River wetlands are maintained by infrequent stand-replacing disturbances (i.e., prolonged inundation), but the current long-term wetting trend could create site conditions unfavorable to tree growth. Furthermore, these findings highlight the need for additional analysis of bottomland vegetation dynamics in the Appalachian Mountains, where increased hydroclimate variability, including extreme flooding, is predicted.