Survival and growth of underplanted replacement tree species in black ash wetlands threatened by emerald ash borer in Minnesota, USA

Abstract

Black ash (Fraxinus nigra) wetlands in the northern US Lake States are threatened by emerald ash borer (EAB), with the impacts expected to be severe because of the foundational role of this species in controlling ecosystem functions. Underplanting before mortality from EAB is one approach being considered to replace black ash and maintain ecosystem functions. We report on third-year survival and growth responses of five underplanted tree species (red maple, silver maple, American elm, balsam poplar, and swamp white oak), to differences in seedling stock size, understory competition, and browse protection. After three years, silver maple and swamp white oak had similarly high survival (> 90%), followed by red maple (70–90%) and American elm (50–80%). Balsam poplar had almost no survival. There was no effect of stock size, browse protection, or understory competition on tree survival. Swamp white oak had the highest diameter growth, followed by red maple, silver maple, and American elm. Stock size had a modest effect on growth, while browse protection and understory competition were weak predictors. Relative height growth was negative across all species, indicating a net loss in height from either winter cold damage or browsing. Relative height growth was similar regardless of stock size, browse protection, and understory competition. Our results show promising survival and growth for silver maple and swamp white oak when underplanted in black ash wetlands. However, patterns in height growth suggest that future canopy openings, either via harvests or EAB-induced mortality, may be necessary to recruit replacement species into the canopy.

Citation

Palik, Brian J.; Slesak, Robert A.; Kastendick, Douglas N.; Kovalenko, Katya; D’Amato, Anthony W.; Toczydlowski, Alan; Grinde, Alexis R. 2025. Survival and growth of underplanted replacement tree species in black ash wetlands threatened by emerald ash borer in Minnesota, USA. New Forests. 56(6): 71. https://doi.org/10.1007/s11056-025-10141-6.