Succesional trajectories of eastern deciduous forests driven by invading insects and diseases: Regional analysis

Background/Question/Methods - While invasions of individual non-native phytophagous insect species are known to affect growth and mortality of host trees, little is known about how multiple invasions combine to alter forest dynamics over large regions. In this study we integrate geographical data describing historical invasion spread of the hemlock woolly adelgid, Adelges tsugae, gypsy moth, Lymantria dispar, emerald ash borer, Agrilus planipennis, and beech scale, Cryptococcus fagisuga, with regional forest inventory data collected by the US Forest Service’s Forest Inventory and Analysis program to quantify the individual and combined impacts of these pest species.

Results/Conclusions -  Analyses indicate that regional impacts of these insects on their hosts sometimes occur surprisingly slow but act to change regional forest succession pathways. While emerald ash borer appears to be in the process of quickly eliminating the vast majority of its hosts, impacts of the other species are slower and more subtle on a regional scale.   American beech and Eastern hemlock commonly co-occur in late scuccessional forests and in the absence of invading pests, these shade-loving species are increasing in dominance. However, invasions by the adelgid and the scale are reversing successional trajectories and ultimately leading to declines in the dominance, most strongly for Eastern hemlock Such results demonstrate how forest insect invasions can profoundly modify forest dynamic processes, resulting in long-term changes in forest ecosystems.