An exotic insect and pathogen disease complex reduces aboveground tree biomass in temperate forests of eastern North America

Forests store a large portion of global carbon in tree and soil biomass. However, our understanding of the factors that may reduce rates of forest carbon accumulation is incomplete. This study examines the impact of an exotic insect and fungal pathogen disease on aboveground tree biomass in forests of eastern North America. We determine how beech bark disease (BBD) - a pervasive but nonextirpating disease - influences the growth and survival of its host tree, Fagus grandifolia Ehrh., and the effects of changes in the demography of this late-successional dominant tree species on total stand-level aboveground tree biomass. Our analyses use US Forest Service Forest Inventory and Analysis data from eastern states located along a gradient in the time since introduction of BBD. In Maine, where BBD has been present for >50 years, we observed reduced growth and survival of the host tree and reduced overall stand-level aboveground tree biomass compared with states where BBD arrived more recently. Additionally, there is a negative relationship between host tree abundance and overall stand-level aboveground tree biomass. Where beech is most abundant, BBD results in substantial declines in aboveground tree biomass (e.g., 11% in Maine); where beech is less abundant, we expect more modest declines (1%-4%).