Protecting the 823 million acres of forests that cover the United States does more than conserve trees. The U.S. forest products industry employed nearly 1 million people and produced $350 billion worth of products last year.
Additionally, the U.S. Department of Agriculture (USDA) reports that American forests, wood products, and urban trees collectively offset annual carbon dioxide (CO2) emissions by roughly 10%–15%.
Unfortunately, our woodlands are at risk. The Nature Conservancy estimates that an average of 50+ million acres is damaged each year by disease and insects — especially non-native invasive species. To protect this economic powerhouse and climate change fighter, effective forest pest management is more important than ever.
In this blog, we’ll discuss different types of forest pests, strategies for controlling them, and the consequences of outbreaks. We also cover forest integrated pest management (IPM) practices and new methods and technologies that can help us preserve this precious resource.
Understanding Threats to Forest Health
Every part of a tree, from its roots to its branches, is vulnerable to pests. Some damage is unavoidable and may come from a tree’s natural cycle. But we’re focusing on serious threats that require intervention from pest control professionals.
Insects and disease are the two most common threats to trees, according to the North Carolina Forest Service. Here’s a brief overview of these two menaces.
Native Insects
Indigenous insects are an important part of a healthy forest ecosystem. But certain kinds can become a problem. When environmental and biological conditions are right, they reach outbreak status.
Common native insects that can threaten trees include:
- Southern pine beetle — These are aggressive tree-killing beetles that periodically damage extensive areas of pines from New York to Florida to Texas. Since 1973, this beetle has caused almost $4 billion in economic damage.
- Forest tent caterpillar — This is the most common and destructive tent caterpillar in North America. Outbreaks usually occur across enormous areas of the Lake States. Infestations can result in intense defoliation, particularly to aspen. Defoliation causes reduced tree growth, top-kill, and tree mortality.
Source: Jay Sturner from USA, CC BY 2.0, via Wikimedia Commons
- Two-lined chestnut borer — These pests usually attack drought-weakened oaks or trees that are in declining health. They construct galleries that can girdle and kill branches and trees within one to three years.
Non-Native Insects
Native insects become an issue when they reach outbreak status. Non-native invasive species can endanger forest health even in small numbers. Invasive species lack natural predators and native flora lacks natural resistance mechanisms. This allows invasive species to flourish quickly. They cause significant damage to natural and urban woodlands.
There are many invasive insects in the country right now. These are just a few:
- Emerald ash borer — This species is native to Asia. Emerald ash borers were first discovered near Detroit in 2002 and likely arrived on solid wood packaging material. Their larvae feed on the inner bark of ash trees. Doing so disrupts the tree’s ability to transport water and nutrients. They are currently active in 35 states. Infestations have killed millions of ash trees and have racked up hundreds of millions of dollars in damages.
D-shaped exit holes.
- Hemlock woolly adelgid — This insect was first observed in the 1950s. It attacks eastern and Carolina hemlock trees by feeding on sap. This species is native to China and Japan with populations active in 17 eastern states. Colonies are responsible for extensive mortality and decline of hemlock trees in the eastern United States.
- Spongey moth — This moth (formerly known as gypsy moth) was introduced in the 1860s from Europe. During outbreaks, caterpillars feed on many different trees — especially oaks — and can cause millions of acres of trees to defoliate.
Disease
Diseases are caused by parasitic pathogens like fungi, bacteria, and plant rusts. Like insects, most microorganisms are an essential part of a healthy ecosystem. But under specific circumstances, they, too, can cause harm. The U.S. Forest Service defines tree disease as any harmful deviation caused by a persistent agent that impacts the normal functions of a tree.
Diseases caused by pathogens include:
- Armillaria root rot — This fungus grows into honey-colored mushrooms. The disease affects many deciduous and evergreen trees. When the roots become infected, it makes trees more susceptible to breaking or falling over in storms.
- Dutch elm disease — This fungus-based disease affects native elm trees. It is usually introduced by the small European elm bark beetle and the native elm bark beetle. When the insects feed on healthy trees, they introduce pathogen spores that disrupt water movement and infect roots. As an infected elm dies, it eventually becomes a vector for spreading the disease. Beetles also use dead branches to create breeding clusters.
Source: Frankie Fouganthin, CC BY-SA 4.0, via Wikimedia Commons.
- White pine blister rust — All five-needle pines are susceptible to this non-native fungus. It spreads through a complex life cycle involving infected wild currant and gooseberry bushes. Infected pines form cankers (a localized disease area). Cankers start small but can eventually encircle entire stems. Once a canker surrounds an area, all portions beyond the canker are killed.
The Role of Forest Pest Control
Forest pest control relies on early detection and protective measures to maintain or reduce the effects of disease or infestation. But this can be a difficult task. Close examination of towering trees that sprawl hundreds of acres is nearly impossible.
Additionally, most pests can’t be stopped by simply applying pesticides or setting traps and calling it a day. The interconnected nature of these ecosystems calls for a diversified approach. That’s where forest IPM comes in.
Integrated Pest Management
IPM is a science-based practice that controls pests while minimizing risks to people and the environment. IPM strategy involves the following steps:
- Monitoring and identifying pests
- Evaluating the data to determine the acceptable threshold of damage
- Choosing the appropriate management strategy
- Monitoring the results
Monitor
Monitoring (or scouting) provides essential information that helps catch problems before irreversible damage has occurred. Changes and trends act as indicators of forest health on an annual basis.
To build a plan, professionals collect information from many sources. Common sources include ground surveys, aerial detection, and remote sensing. Not all insects, weeds, or pathogens need to be controlled. Monitoring helps identify pests accurately and ensures appropriate actions are taken if necessary.
Identify
Correct identification finds answers to several questions like: What kind of pest is present? How much damage has occurred? How bad is the infestation? How much damage will occur if no action is taken?
Identification also eliminates the chance of killing off beneficial organisms.
Evaluate
Once a pest is identified, forest managers must determine at which point damage requires action. Sometimes, no intervention is needed. In those cases, the managers keep a careful eye on the issue until damage has reached the action threshold.
Economic, environmental, and human population risks are also weighed against the cost and effort of treatment. In other words, is the juice worth the squeeze?
Choosing a Management Strategy
When an outbreak requires action, pest managers use one or more of the following methods to control infestation and disease.
Cultural Management
Cultural management strategies manipulate the environment to favor the plant and reduce the pest’s chances of survival.
Examples of cultural control are selective pruning, planting disease-resistant species, and choosing appropriate planting site locations. All of this can reduce the likelihood that the pest can colonize, grow, or reproduce.
Mechanical Management
Mechanical management uses physical methods to remove or prevent pests. Options include fences, screens, barriers, sticky traps, and nets. Weeds can be managed by tilling or mowing. Sometimes it’s as simple as knocking pests off a plant with a high-powered water spray or squashing them on sight.
Biological Management
Biological management uses methods and technologies that address the spread and ultimate damage caused by pest infestation.
One natural biological control method involves introducing a pest’s natural enemy into an infested area. This is used extensively to control non-native invasive species. But it’s a long process and can take a decade to complete.
Chemical Management
Chemical pesticides are important tools used to protect and maintain forest health. They must be used carefully, however. With IPM, pesticides should only be used when necessary and alongside previously mentioned approaches.
Pesticides should be selected and applied carefully to minimize possible harm to people, nontarget organisms, and the environment. Because improper pesticide use can create potential risks, training is necessary.
Forest Pest Outbreak Consequences
As we mentioned at the beginning of the blog, U.S. forests offer many ecological and economic benefits. The consequences our country faced during previous outbreaks show that we must work to prevent future ones.
Tree Species Losses
While protection and conservation efforts have improved the situation, the following trees have flirted with extinction thanks to past outbreaks.
Dutch elm disease killed at least 43 million American elm (Ulmus americana) trees. So devastating were the effects that very few surviving elm tree strains are able to resist the disease.
Chestnut blight nearly wiped out native chestnut trees (Castanea dentata) in the 1950s. Today, efforts to bring back the American Chestnut involve a hybrid tree that is part native chestnut and part Chinese chestnut.
Source: Claudette Hoffman, CC BY-SA 3.0, via Wikimedia Commons
White pine blister rust devastated the whitebark pine (Pinus albicaulis). In 2022, the U.S. Fish and Wildlife Service listed it as a threatened species under the Endangered Species Act.
An example of an ongoing battle involves the white ash (Fraxinus americana). The emerald ash borer killed an estimated 50 million ash trees. A current effort to stop the spread includes statewide campaigns to halt the transportation of firewood to prevent unintentional spread of the bug.
Economic and Environmental Impacts
Economically, a 2016 study published in Ecological Applications found that tree pests cost $4.5 billion per year in damages.
The effects of climate change draw additional attention to the environmental consequences of damaged forests. A 2021 study led by Cornell University, a team of scientists from The Nature Conservancy, the USDA Forest Service, the Cary Institute of Ecosystem Studies, and Purdue University found that tree pest outbreaks reduce U.S. forests’ ability to capture and store climate-changing CO2.
According to the study, areas damaged by insects captured and stored 69% less carbon than undamaged ones. Diseased areas capture 28% less carbon. In total, current damages caused by pests reduce the CO2 capture potential of America’s forests by roughly 50 million tons each year – the equivalent of emissions from over 10 million cars.
While the consequences of these outbreaks are vast, all hope is not lost.
Future Outlook
Pest control is one piece of a larger strategy experts recommend for protecting U.S. forests. The scientists who worked on the 2021 climate impact study propose these three methods to help reduce further damage:
- Implement improved management practices such as ecological thinning and prescribed fire. This can increase resilience by promoting biodiversity and variations in tree age and spacing.
- Strengthen policies that prevent more invasive species from entering North America. Policies should focus on stronger regulations for imported plants in nurseries and improving treatment standards for solid wood packaging materials (pallets and crates).
- Promote “slow the spread” programs like the Don’t Move Firewood campaign to reduce the movement of established pests into non-infested areas.
New Pest Control Technology
Integrated Pest Management has been around for decades. But some scientists are developing new technologies to help the process keep up with modern demands.
Unmanned aerial vehicles (drones) are one technological advancement that has become more popular for monitoring large wooded areas. The most recent breakthrough, however, is the development of autonomous drones that pilot themselves.
Deep Forestry, a Sweden-based start-up is working alongside the USDA and the European Commission to develop autonomous drones. According to Deep Forestry, the new drones can scan 1,000 trees every 20 minutes. Scans accurately identify the species, height, diameter, trunk volume, and location of each individual tree.
If these claims are true, this automated analysis can provide plenty of new data for scientists and managers. Additionally, drones equipped with near-infrared light cameras can measure vegetation health using the Normalized Difference Vegetation Index. Healthy leaves reflect more infrared light than unhealthy or dead ones.
Artificial intelligence (AI) is also entering the pest management scene. In 2019, researchers at the Stevens Institute of Technology developed a new technology that combines highly sensitive vibration sensors and AI to discover wood-boring insects inside trees.
After recording the vibration patterns produced by the emerald ash borer and the Asian longhorn beetle, the researchers developed software that uses an AI algorithm to pinpoint the pest’s vibrations. The same algorithm also filters out other vibrations caused by external factors like wind and aircraft.
With the software finished, the researchers developed sensors that were strapped to trees and conducted a field test in a New Jersey national forest. The new sensor accurately detected insects in all infested trees and did not detect any in healthy trees.
As the technology continues development, it could someday be used to spot infestation in trees before damage is visible.
Conclusion
Our forests demand attention and protection. Their economic and environmental value is too great to lose. And the threats they face today are too important to ignore. Thankfully, dedicated forest managers, pest control professionals, and environmental scientists are doing their part to protect this amazing natural resource.
To encourage pest control professionals to engage in this preservation effort, Certified Training Institute is proud to offer forest pest management courses in most states. To get started, select a state under the Recertification tab and type forest into the course filter.
While there is still a lot of work to do, we are hopeful that the vast wooded landscapes across the country will continue to grow, thrive, and make the world a better place.
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