Modeling the impacts of hemlock woolly adelgid infestation and presalvage harvesting on carbon stocks in northern hemlock forests

Abstract

To better understand the potential impact of the invasive hemlock woolly adelgid (HWA, Adelges tsugae Annand) and presalvage activities on carbon (C) dynamics in northern stands of eastern hemlock (Tsuga canadensis (L.) Carr.), we used the Forest Vegetation Simulator and Forest Inventory and Analysis data to model C storage and successional pathways under four scenarios: presalvage harvesting; HWA-induced mortality; presalvage harvesting plus HWA-induced mortality; and no disturbance (control). Our simulation showed that all treatments differed in total C storage in the short term, with HWA-induced mortality providing the highest total C storage due to regeneration and ingrowth of replacement species combined with retention of standing and downed deadwood. At the end of the 150-year simulation, all disturbance scenarios had significantly lower total C than the control. The cumulative net C gain was lower for the two presalvage scenarios than for the HWA scenario, indicating that allowing HWA to progress naturally through a stand may result in the least impact to long-term C sequestration and net C storage. While differences were not significant on low hemlock density stands, impacts to the estimated 267 000 ha of northeastern forests where hemlock is dominant could result in conversion to red maple (Acer rubrum L.) and a net loss of over 4 million metric tons of potentially sequestered C over the next 150 years.