PS 11-151 - Simulating the interactions of invasive insects on forest and wood product carbon in northeastern US

Abstract: Climate change is predicted to have fewer direct impacts on northeastern forests compared to other forested regions of the US. However, the growing regional threat of indirect impacts such as invasive insects may influence the landscape and landowner response behaviors. In response to tree damage or mortality from invasive insects, landowners have been shown to salvage harvest insect-damaged trees, which affects regional wood products markets, and therefore the carbon stored both on the landscape and in harvested wood products. To better understand the long-term impacts of invasive insects in northeastern forests, we used Landis-II and PnET-Succession to simulate fifty years of forest change in two landscapes in New England, one landscape focused on high ash abundance areas, since it is the host of emerald ash borer, and the second landscape focused on high hemlock abundance areas, host of hemlock woolly adelgid. Both insect pests are currently pervasive in southern New England forests. Within each landscape, we simulated the presence of hemlock woolly adelgid and emerald ash borer, along with ecosystem impacts from these insects alone and two versions of salvage harvest following invasive species presence. For each scenario, we explored potential aboveground live and downed carbon impacts of the two host species and subsequent harvesting, as well as the fate of carbon in wood products from salvage harvesting using a Massachusetts variant of the HWP-C vR model. We looked at the sensitivity of carbon pools to a potential new long-term wood product market, such as hemlock cross-laminated timber (CLT). We compared both ecosystem and carbon impacts across each scenario. We found that although insects can have devastating effects on individual trees and stands, and host density does play a role in the initial severity, New England’s mixed species forests are less affected at a landscape scale by these insects. Relative abundance and diversity were not significantly altered 50 years after insect introduction. However, carbon pools had a slightly more complicated relationship with invasive insect and wood product scenarios. In scenarios with insect-induced tree mortality, there is an initial pulse of carbon stored as downed wood, with some of this carbon slowly being emitted through decay. Generally, hemlock landscapes were larger net-emitters than ash landscapes, since hemlock is higher abundance and ash often goes into longer-term products. However, the introduction of long-term wood products for hemlock has the potential to limit net-emissions from these landscapes over the 50-year scenario.