Interactions between biotic and climatic disturbances are likely to amplify the aggregate effects of disturbance within forests. Predicting the activity and impacts of introduced or irrupting forest insects and pathogens (FIPs) is challenging. Furthermore, the large diversity of different types of FIPs has limited our ability to incorporate their effects into mechanistic ecosystem models. This research used a generalized functional framework for simulating the effects of FIPs on plant physiology and ecosystems within a forecasting framework that combined continuous observations with ecological models. This forecasting framework can help to understand the near-term impacts of FIPs on ecosystems and the potential combined effects of FIPs and abiotic stress, such as climatic extremes. We used a diverse suite of FIPs that occur in northeastern U.S. forests and capture different pathways of plant physiology impacts and different timescales of stress – gypsy moth (Lymantria dispar), hemlock woolly adelgid (Adelges tsugae), emerald ash borer (Agrilus planipennis), and beech bark disease (Cryptococcus fagisuga) – to test the ability of this framework to simulate and forecast impacts to ecosystem carbon, water, and energy cycling. We conducted modeling experiments to test for potential interactions between the impacts of these FIPs and climatic extremes of growing season temperature and precipitation.
Results/Conclusions
We found that regardless of the FIPs physiological pathway, the timescale of FIPs activity determined aggregate ecosystem impacts, with the largest impacts occurring for slow-acting and persistent FIPs. Although gypsy moth and emerald ash borer caused severe short-term (annual) impacts to ecosystem processes, hemlock woolly adelgid and beech bark disease created much larger overall impacts to ecosystem processes over decades through their persistent presence and stress within forests. A prolonged timescale of FIPs activity also increased the probability of encountering extreme climatic events, which created a synergistic effect on overall tree stress and mortality and resulting ecosystem carbon, water, and energy flux. This framework can provide a quantitative framework for simulating biologically realistic impacts of FIPs on tree stress, which resulted in stronger data-model agreement for larger scale ecosystem processes.