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Nonnative Invasive Insects and Diseases Decreasing Carbon Stored in U.S. Forests

Hemlock woolly adelgid-induced hemlock mortality in Great Smokey Mountains National Park. Photo by Songlin Fei, Purdue University

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A Minute with the Scientist

Randy Morin: So, I had done a study specific to Emerald Ash Borer, where we estimated the amount of mortality that Emerald Ash Borer was causing using the FIA [Forest Inventory Analysis] data, and then, I was attending a conference and delivering a presentation about that research and one of the people in the audience came to me after the meeting and said, ‘You know, have you ever thought about trying to do some similar work, but bringing in all the different invasive pests that we have that are causing problems?’

And so, we went back and forth with that and started kind of digging into what data is available. And so, being able to quantify what these pests have done could be important information for, you know, deciding how many resources to dedicate to fighting any one of these invaders. Because sometimes we don't quite know right away how big of a problem they are going to be.

My name is Randy Morin, I’m a research forester with the Northern Research Station FIA program, and this was about a three year project from initiation to publication, where we used about 93,000 field plots that were sampled by the Forest Inventory Analysis program from across the country, and those plots typically are measured over a 5-10 year remeasurement cycle that varies across the country. So, the data came from about a 10-15 year period, overall.

Photosynthesis feeds trees and has a significant benefit for people, too, namely the removal of carbon from the atmosphere and into live tree biomass through a process called “sequestration.” However, USDA Forest Service scientists and a colleague found that increased tree mortality from the impacts of nonnative insects and diseases results in the transfer of carbon stored in live trees into dead material, much of which will eventually return to the atmosphere by decomposition. This threatens the estimated 76 percent of carbon sequestration in North America that comes from forests.

Worldwide, forests are increasingly affected by nonnative insects and diseases, some of which cause substantial tree mortality. U.S. forests have been invaded an estimated 450 tree-feeding pest species. Researchers with the Northern and Southern Research Stations and Purdue University used 92,978 forest plots distributed across the conterminous United States, established and monitored by the Forest Service’s Forest Inventory and Analysis (FIA) program, to estimate biomass loss associated with elevated mortality rates caused by the 15 most damaging nonnative forest pests. Insects such as the emerald ash borer, gypsy moth, and hemlock woolly adelgid and diseases including Dutch elm disease, beech bark disease, and laurel wilt disease are among the 15 most damaging nonnative species. The results indicate that these species caused an additional annual loss of 5.53 Tg C of increased tree mortality, an amount comparable to carbon emissions from 4.4 million cars or one-fifth of all wildfires annually. In addition, 41 percent of the total live forest biomass in the conterminous United States is at risk to future loss from these 15 pests. This study demonstrates the value of FIA data to assess broad-scale changes in forests and indicates that forest pest invasions, driven primarily by globalization, are creating a large risk to forests in the United States and have significant impacts on carbon dynamics.