PS 41-23 - Estimating the Risk of Forest Carbon due to Invasive Forest Insects

Background/Question/Methods

Northeastern forests are important carbon sinks that are threatened by invasive insects. The state of Massachusetts aims to reach net-zero carbon emissions by 2050, in part by relying on forest carbon sequestration. It is unknown how insects may affect this goal. Three insect species impacting forest carbon in the region are the Asian long-horned beetle, hemlock woolly adelgid, and emerald ash borer. This study uses the LANDIS-II forest landscape model to estimate these insects’ impact on aboveground forest carbon in Massachusetts for 2015 (initial infestation), 2050 and 2105. I focused on nine 3,600-hectare sample landscapes with three initial host tree species abundances (low, medium, high), applying three simulation scenarios: no insects (control), infestation, and salvage logging after infestation. I estimate impacts on forest carbon based on the difference between control and treatment scenarios.

Results/Conclusions

For all insect species on all landscapes, carbon stocks decreased during the initial infestation. Specifically, carbon stores decreased 0.9-1.2 Mg/ha, 5.7-15.9 Mg/ha, and 0.2-1.04 Mg/ha for ALB, HWA, and EAB, respectively. A reduction in 2050 carbon stores was observed for ALB and HWA. However, for the EAB landscapes, carbon stores increased by 2050 when host tree abundance was the lowest. For ALB and EAB, carbon stores increased by 2105 for all landscapes, compared to the control (4.18-5.7 Mg/ha, and 1.6-4.9 Mg/ha, respectively). In contrast, HWA decreased carbon stores (2.9-11.3 Mg/ha) by 2105. Compared to carbon stores in infestation-only scenarios, salvage logging helped mitigate invasive insect species impacts by 2105 by allowing more space for forest regeneration and growth. However, for near-term policy goals (e.g., 2050) insects and logging may hinder the ability of Massachusetts to achieve its carbon goal.