New Research Highlights the Carbon Losses to U.S. Forests Caused by Pests and Pathogens and How We Can Reduce These Threats

Diverse forests are more beautiful, and more resilient. Photo Credit: Leigh Greenwood

Forested landscapes across the U.S. have always included insects, diseases, fungus, and other native pests as part of their ecologies. These native pests are just one of many types of natural disturbances that are part of the dynamic balance that makes up each unique type of healthy forest. Historically, these disturbances created opportunities for each type of forest to reach its peak biodiversity and resilience.  Thanks to regional and ecological variation, each forest type supports biodiversity in a variety of different ways. In some forests, the age, species, and variety of the trees are crucial drivers of biodiversity, while in others, patches of other ecosystems, like grasslands, come and go over time. Healthy forests are often made of slowly shifting mosaics of habitats, all supporting their own communities of plants and wildlife.

Invasive pests don’t function as a healthy disturbance in the same way as native pests that co-evolved with the forest. Moreover, in some places, the natural ups and downs that have allowed forests and native pests to thrive in a balance over time and space has been disrupted.

Forest pests that come from overseas or from far away ecosystems way across the continent are termed invasive species if they cause serious damage to the trees they infest or infect. Because they did not evolve in tandem with the trees in their invaded range, they can be extraordinarily damaging or even deadly to the trees they attack. In the 1900’s, invasive forest pests like the chestnut blight and Dutch elm disease practically eradicated American chestnuts and American elms from our landscapes, and the more contemporary threat of the emerald ash borer has wiped out more than 100 million ash trees in just about 20 years.

Invasive shot hole borers are killing California trees Photo Credit B. Nobua-Behrmann/UCCE San Diego

Other large disruptive forces affecting our forests that have grown over the last 200 years – including changes in land use, fire suppression policies, unsustainable logging practices, and ecological shifts driven by climate change – have led to less resilient systems for native forest pests as well. For example, insects that prefer trees of a specific age may attack vast stands of similarly-aged trees that grew in the aftermath of a catastrophic wildfire. As a result, these trees are vulnerable to far higher densities of attacking insects than those in more varied landscapes experiencing a multi-year pattern of smaller, less severe, fires. These disruptions have had significant impacts on U.S. forests – including to their ability to sequester carbon.

To better understand the magnitude of the impact pests have had on carbon sequestration in our forests, a multi-disciplinary group of scientists collaborated to produce a new study, “Insect and Disease Disturbances Correlate With Reduced Carbon Sequestration in Forests of the Contiguous United States.” Our research found that forests damaged by insects sequestered 69% less carbon, and those damaged by disease sequestered 28% less carbon, when compared to forests not impacted by one of these severe disturbances. Put another way- the study found that the damage currently being caused by insects and diseases across the lower 48 states is reducing the carbon sequestration potential of America’s forests by roughly 50 million tons of carbon dioxide each year – a lost opportunity to annually sequester the equivalent amount of carbon dioxide emitted each year by more than 10 million cars.

It’s important to know that our study indicates the majority of US forests continue to sequester more carbon than they release. On a landscape scale, forest insects and diseases have not, on average, converted forests from carbon sinks that remove and store carbon to carbon sources that increase the amount of carbon into the atmosphere. But it is very clear that forests impacted by recent and severe insect and disease disturbance have a greatly reduced capacity to sequester carbon. Fortunately, this is a problem we can do something about.

In my role as The Nature Conservancy’s Forest Health Program Director, it’s my job to figure out how we can work with our partners to reduce the impacts on non-native forest insects and diseases across North America. This includes prevention, early detection of new threats, and management of pests already present, as well as long-term programs like pest-resistant tree breeding and biological control organisms. With the information provided by this study, The Nature Conservancy and its many partners can better advocate for the research, science-driven policies, and impactful action needed to contain this threat.

International shipping is a major pathway for forest pest arrival. Photo Credit: Leigh Greenwood

To address the long-term shifts in forests that have enabled native forest pests to reach unnaturally high levels of damage, locally specific management strategies can be deployed to bring forests back into better function and balance. For instance, practices such as ecological thinning and prescribed fire can increase the resilience of historically fire-dependent forests by promoting biodiversity and variations in tree age and spacing. By supporting the overall resilience of these forests to the natural disturbances they face, their carbon sequestration potential can be maintained over time. The stability of that carbon storage is vital to global efforts to address climate change. While some fluctuations in carbon storage are normal and necessary, we must work together to avoid catastrophic disturbances that can significantly damage our forests.

For those pests that have not yet arrived in North America, preventative strategies are crucial to ensure we don’t face faster and more severe tree loss in the future. The global community needs to strengthen shared policies that prevent new non-native forest pests from accidentally traveling along the international supply chain. Improving and enforcing the existing treatment standards for solid wood packaging materials such as pallets and crates can play a key role in preventing new pests from sneaking into U.S. forests.

Within the U.S., federal policies governing the importation of nursery and cut plant stock (such as cut flowers, and tree saplings) could be refined and better enforced, thereby more effectively preventing invasive species that travel on live plant materials. Together, a stronger preventative approach will allow us to maintain our healthy forests without additional pests- and the yet-unknown threats that they may pose.

North American ash trees often turn brilliant colors in the fall. Photo Credit Leigh Greenwood

When invasive forest pests have become more established in the U.S., it becomes very important to create programs that mitigate those losses, whether through “slow the spread” programs (such as the Don’t Move Firewood campaign), seed banking, tree breeding, biological control research, or a wide variety of other interdisciplinary approaches. Controlling the movement and damage of invasive forest pests can reduce losses for years – or even decades – protecting precious biodiversity and carbon storage in forests across the country. With rapidly advancing science in the field of conservation genetics, the potential for new solutions to be brought to scale to help contain these established pests is very exciting. But without diverse populations of the trees we want to protect, the long-term research and implementation of conservation programs based on new technologies might falter. 

Maintaining forest carbon sequestration rates in the face of insect- and disease-based disturbances also provides powerful co-benefits including cleaner air and water, improved wildlife habitat, reduced risks to people living in fire-adapted forest landscapes, and stronger local and rural economies. This research shows that a very wide variety of actions we can take to protect forests from insect and disease disturbances- whether internationally, regionally, or locally- can result in healthier trees that will ultimately support a healthier climate.

Leigh Greenwood is the Forest Health Program Director at The Nature Conservancy.

3 Ways Federal Investment in Trees and Forests Can Support Economic Growth

This article includes excerpts from a longer article published by World Resources Institute. Read the original article here

Photo Credit: Kent Mason/The Nature Conservancy

To reach the United States’ target of reducing net emissions by 50-52% from 2005 levels by 2030, the federal government and non-federal actors will need to increase the ability of natural and working lands to sequester and store carbon. A recent economy-wide analysis finds that reaching these climate goals will require the United States to enable its lands and forests, or its land carbon sink, to remove at least 913 Mt CO2e annually by 2030, which represents a 13% increase in yearly sequestration over 2019 levels. This increase in sequestration would be equal to the emissions from over 20 million cars every year.

To achieve this, the nation must restore trees to the landscape, increase the adoption of climate-smart agricultural practices and protect landscapes that already store carbon. Federal investment and action from all levels of society can allow the United States to achieve the full potential of these pathways, creating jobs and other economic benefits in the process.

Seizing the United States’ Most Promising Natural Climate Solutions

While action is needed across all land sectors, research shows that three tree-based pathways hold the greatest opportunity for enhancing natural carbon removal in the near-term while supporting jobs and economic vitality. WRI analysis shows that these pathways could offer an attractive return on investment: they require a total federal investment of $126.6 billion over 20 years and would support approximately 3.9 million job-years (or 199,000 jobs each year for 20 years). Put another way, 31.4 jobs would be supported for every million dollars of federal investment. Over 20 years, this investment would also generate $226.8 billion in value added to local economies, including $164.4 billion in employee compensation and $12.2 billion in state, federal and local taxes.

Table 1: Economic Impact of Natural Climate Mitigation Pathways

1. Reforesting and Restocking Trees

Trees are a carbon-removing technology that is ready for deployment today. Although building the infrastructure to plant healthy forests at the necessary scale will require considerable investment and work, there are already professionals working to plant and manage trees and forests every day. Federal investment in reforestation and forest restocking could help to expand employment in these sectors, particularly in rural areas, where 67% of job creation potential exists.

Across federal, state, local and private lands, there is an opportunity to reforest historically forested land that has been cleared, disrupted or burned and has lost the ability to sequester carbon. There is also an opportunity to restock, or increase the density of, existing forests in the eastern and midwestern United States where trees have been lost due to disease or disruption, and where increased forested density would not increase fire risk.

Non-federal lands, which include state, local and private lands, hold the greatest potential for carbon removal and job creation. In these lands, 185.4 million acres are eligible for reforestation and restocking. This could remove 156 MtCO2e per year by 2030, and up to 312 MtCO2e per year in 2040 and beyond. Reforestation and restocking on non-federal land could also support 68,100 jobs across multiple sectors annually.

Federal lands offer an additional 18 million acres suitable for reforestation and restocking. Collectively, these lands could sequester an additional 17 MtCO2e per year by 2030 and up to 35 MtCO2e per year in 2040 and beyond. Investment in reforestation and restocking on federal land could support 11,700 jobs annually.

Across both federal and non-federal lands, an annual federal investment of $3 billion per year for 20 years could support 79,800 jobs annually, or 26.8 jobs per one million dollars of investment. Missouri, Ohio, Michigan, Pennsylvania and Wisconsin would see the highest total levels of job creation from reforestation and restocking across all land ownership types.

2. Agroforestry

Agroforestry, or the practice of incorporating trees into agricultural systems, could help expand trees and their climate benefits. This would also benefit farmers and ranchers, as agroforestry can improve soil, crop and animal health, and provide added revenue from forest products and timber. Agroforestry practices with notable climate benefits include silvopasture, or integrating trees into animal agriculture; alley cropping, or interspersing row crops with rows of trees; and planting windbreaks, or strategically placed groups of shrubs and trees that prevent soil erosion and protect crops and livestock. There are approximately 110.9 million acres of U.S. cropland and pastureland that may be eligible for agroforestry and could sequester 156 MMT CO2e per year.

Establishing and maintaining agroforestry systems can be labor-intensive and require specialized expertise, which can further support jobs. However, agroforestry systems can be expensive to establish, which can pose a barrier for farmers. Federal investment can help landowners establish agroforestry systems and support jobs in the process. An annual federal investment of $1.8 billion in agroforestry could support 49,500 jobs annually, or 27.4 jobs per million dollars invested, and provide other economic benefits. Missouri, Ohio, Pennsylvania, South Dakota and Texas would see the highest total levels of job creation from expansion of agroforestry.

3. Wildfire Risk Mitigation

Many forests in the United States, particularly in Western states, are at high risk for severe fire due to widespread tree death from drought, disease and historical fire suppression. Severe fires threaten forest-adjacent communities and permanently damage trees and ecosystems, which can turn forests into a source of emissions. Wildfires also produce pollutants that can increase the risk of respiratory and cardiovascular health problems in people who inhale smoke.

Techniques to reduce severe wildfire risk include removing biomass, strategically thinning out overly dense forests and conducting controlled, low-intensity burns to remove fuels that could feed severe blazes. These kinds of treatments — known as fuel load treatments — do not prevent wildfire from occurring, but they lower the risk of massive fires. Prescribed burning alone could reduce wildfire carbon emissions in the western United States by 18–25% and could increase long-term forest carbon storage by 18 MtCO2 per year through avoided tree mortality.

The increasing frequency of catastrophic wildfires across the United States highlights the importance of ambitious and immediate investment to increase ecosystem health and reduce the risk of severe wildfire. There are over 86.7 million acres of forest in the nation that could be eligible for fuel load treatments. Federal investment could help mitigate the risk of wildfire in these forests and would directly employ prescribed burn professionals and forestry professionals. Fuel load treatment also generates biomass and timber that can have downstream uses that generate employment.

Accounting for both fuel load treatment jobs and jobs supporting wood and biomass processing, a yearly federal investment of $1.5 billion in fuel load reduction could support 69,600 jobs, or 45.2 jobs per million dollars invested. The states with most potential to support jobs related to wildfire risk mitigation are California, New Mexico, Wyoming, Oregon and Idaho.

An Opportunity for Society-Wide Action

While federal action is essential to enhance and protect the land carbon sink, reaching the nation’s climate goals will require states, local governments, the private sector and civil society to push forward their own initiatives to reforest and restock forests and to mitigate wildfire risk. For example:

  • States can create or expand programs that incentivize climate-friendly land management and restock and reforest state-owned lands, like states participating in the US Climate Alliance’s Natural and Working Lands Challenge are doing. States can also work with the federal government to further improve greenhouse gas inventories. States with fire danger can also increase budgets for thinning and prescribed burning.
  • Cities and local governments can expand urban forestry efforts to plant trees in parks and open space. For example, Washington, D.C. aims to have 40% of the city covered by a healthy tree canopy by 2032.They can also help community members living in wilderness-urban interface areas to reduce flammable material near structures and build fire-adapted communities.
  • Businesses can ensure that the agricultural and timber products in their supply chain are sourced from farms and forests that use climate-friendly mitigation practices and increase investments in land-based climate mitigation strategies.
  • Tribal communities, schools and faith-based groups can plant trees and enhance land management practices to sequester more carbon and mitigate wildfire risk.

Note: Where not otherwise specified, economic impact, acreage potential and carbon removal potential were derived as part of analysis for WRI’s working paper The Economic Benefits of The New Climate Economy in Rural America. Please refer to this paper’s appendices for information on methodology.

Haley Leslie-Bole, is a Research Analyst with WRI’s U.S. Climate Initiative, where she works on landscape-scale solutions for climate mitigation and adaptation in the U.S.