Effects of Flooding and Light on the Performance of Potential Replacement Species in Black Ash Wetland Forests

Abstract

Within black ash wetlands in the western Great Lakes region, black ash (Fraxinus nigra Marshall) is a foundational species that controls hydrologic regime, nutrient cycling, and wildlife habitat. The role of black ash in these stands makes them particularly vulnerable to the invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae). One strategy that has been suggested to mitigate the impact of this invasive insect is the increase of tree species diversity through artificial regeneration, however, there is limited information available on how potential replacement tree species respond to shade and flooding. We used controlled greenhouse and field experiments that manipulated flooding duration and intensity as well as shade to explore early survival, growth, and physiology of 23 different tree species that vary in shade and flood tolerance. Measurements of seedling physiology, growth, and survival were taken throughout the growing seasons of 2020 and 2021. Results indicate that bald cypress was able to tolerate the most extreme flooding conditions simulated in the study: water table at the soil surface for 15 weeks. American elm, sycamore, and river birch were tolerant of water tables between 0 and 14 cm below the soils surface for up to 15 weeks. Northern white cedar, red maple, tamarack, swamp white oak, and yellow birch had high survival and growth rates with the water table at the soil surface for up to 6 weeks. Finally, black walnut, sugar maple, white spruce, white oak, red pine, and bitternut hickory responded poorly to flooding of any duration. Results indicate that water table depth has a greater influence on seedling growth and gas exchange rates than light reduction, especially at light levels likely to be found in black ash wetlands. Since shade treatments were generally not a significant impediment to early growth, survival, and gas exchange rates, natural resource managers should focus on matching the flood tolerance of potential replacement species to local site hydrology.