The spread and dominance of the invasive native hay-scented fern in the understory is one of the most significant changes that has affected the forest ecosystems in the northeastern United States in the last century. We studied changes in the distribution and dynamics of hay-scented fern at a large scale over a 10-yr period in Pennsylvania. The study included 56 stands covering 1,009 ha in two ecoregions. Hay-scented fern was more widely distributed and occurred at higher densities in the Allegheny Plateau ecoregion vs. the Ridge and Valley. Hay-scented fern abundance was positively associated with overstory red maple abundance in both ecoregions. After overstory removal, the density and distribution of hay-scented fern tended to increase and remain at elevated levels in stands that were not treated with herbicide. Herbicide treatments resulted in temporary reductions in fern densities and created a “window of opportunity” for the establishment of tree regeneration.

Nomenclature: Hay-scented fern, Dennstaedtia punctilobula (Michx.) Moore; red maple, Acer rubrum L.