Structure Condition Services Stressors
An invasive pest is an insect or disease that is not native to our region’s forests and causes extensive damage where it is introduced, such as emerald ash borer and Dutch elm disease. Most of our most problematic invasive pests originate from Europe and Asia because those locations have many tree species that are closely related to those found in Vermont. When invasive pests are introduced to an area, native trees can succumb to serious damage because they have not evolved to develop chemical and physical defenses against them. To quantify the damage caused by invasive insects and diseases, we use the USDA Forest Service Insect and Disease Surveys (IDS), which are annual aerial surveys of forest disturbance, including damage caused by insects and diseases1. Here, we summed the total area mapped by pests that we could determine as invasive to Vermont. A high score means that there is a low amount of damage to trees from invasive insects and diseases.
Invasive pests pose a unique problem to native forests by attacking species that have few defenses against them. Historically, these have caused the decline of some species in the region (e.g., American chestnut, American elm). We see this occurring at present with emerald ash borer (EAB) in many states throughout the country. The data presented here are from aerial detection surveys (ADS) conducted by the Vermont Division of Forestry and the USDA Forest Service, and it is expected that as EAB continues to be detected in the state, the acres of forest affected by the insect will increase in the coming years. Here, we summed the total area mapped by pests that we could determine as invasive to Vermont. The current year is scored as the difference between the minimum and maximum (+10%) values in the record. Annual scores were computed as the deviation from the data target, scaled from 1-5.
Josh Halman, Forest Health Specialist; Vermont Department of Forests, Parks and Recreation (2020)
The score is calculated using a target value and the historical range of the the entire long-term dataset. The higher the score, the closer this year's value is to the target.
Once the score is computed for each year, the trend in scores over time is calculated. If the trend is significantly positive or negative, the long-term trend is marked as increasing or decreasing respectively.
Distance between target and maximum (scaled 1-5)
|Directionality of scores||
Lower values in the data are better.
|Minimum value used in scoring||
Data minimum - 10% of range
|Maximum value used in scoring||
Data maximum + 10% of range
To quantify the damage caused by invasive insects and diseases, we use Insect and Disease Surveys (IDS), which are annual aerial surveys of forests conducted by the State of Vermont and the USDA Forest Service to map forest disturbance1. Here, we summed the total area mapped by pests that we could determine as invasive to Vermont. The target was set as the lowest possible acreage (either the minimum value in the data minus 10% of range or 0, whichever was greater), and the current year is scored for where it falls between the target and the upper scoring bounds (maximum value in the dataset plus 10% of the range), scaled to be between 1 and 5.
Acid rain harms forests and other ecosystems by damaging leaves and leaching nutrients.
The length of the growing season varies from year to year, but large or persistent changes can be problematic to forests.
Ozone can cause many negative impacts to forests by reducing regeneration, productivity, and species diversity.
Mercury is a toxin that persists in the environment for long periods by cycling back and forth between the air, water, soil and organisms - resulting in long-term, negative effects to forest ecosystems.
Warmer winter minimum temperatures can allow for non-native species to proliferate, while at the same time stressing native forest trees.
Higher maximum summer temperatures can stress forests, reducing productivity and health.
Changes to precipitation can alter the water balance in Vermont’s forests, causing either drought or deluge.
Snow insulates the soil and tree roots from cold temperatures and provides water when it melts.
Climate change will continue to result in more extreme weather events, which can stress forests beyond what they are accustomed.
Lack of sufficient precipitation can cause both immediate and long-term stress to trees.
As native trees are not adapted to defending themselves from non-native, invasive insects and diseases, widespread damage and mortality can result.