Threats to Connecticut Tree and Forest Health

InsectsDiseasesInvasive Plants - Forest FragmentationHow to Help

CT DEEP monitors and assesses the factors that influence the health of Connecticut's forests. We work in cooperation with state, federal, and municipal, and non-governmental agencies to detect, manage, and treat all factors that negatively impact our state forests.


Native and non-native invasive insects can cause significant damage to forests. Some that impact forest health across Connecticut's landscape include:  

The Two Lined Chestnut Borer, is a native insect that can severely impact oak trees in Connecticut, particularly following drought and Spongy Moth (previously referred to as gypsy moth) outbreaks

Invasive insects are often transported through international trade and make their way across the country in cargo, shipping materials, and even personal travel. For this reason, the Department of Energy and Environmental Protection has firewood regulations in place to stop the spread of invasive insects.

Currently, there are several invasive insects that impact or are expected to impact Connecticut forests:

For a comprehensive guide to invasive insects and corresponding control methods, retrieve content from the Connecticut Agricultural Experiment Station.

Hemlock Wooly AdelgidGypsy Moth LarvaeEmerald Ash Borer AdultSouthern Pine Beetle AdultAsian Longhorned Beetle


Diseases can be caused by a variety of organisms, including bacteria, viruses and, most commonly, fungi. Some of the most serious causes of tree mortality within the state have been diseases, including chestnut blight and Dutch elm disease

Both of those diseases are invasive diseases, but there is a large number of equally deadly diseases that can affect trees that are not necessarily recent invaders. These include the many anthracnose diseases that affect trees such as oaks and dogwoods to verticillium wilt, which also has a vast host range. Oak wilt is another common disease, targeting oak species, but affecting the red oak group more than the white oak group.  

Become familiar with one of the newest pests to affect Connecticut forests. Beech Leaf Disease (BLD) is a novel disease affecting American beech (Fagus americana) in North America. Symptoms of BLD have been observed in European beech (Fagus sylvatica), Oriental (Fagus orientalis), and Chinese (Fagus engleriana) beech species, which are occasionally planted as ornamentals. Early symptoms of BLD include dark stripes or bands between lateral veins of leaves that are visible immediately upon bud break in the spring. Affected leaves may be unevenly distributed in the lower canopy. Banding is most apparent when viewed from below. Leaves with severe symptoms are heavily banded, shrunken, and crinkled with a thickened leathery texture that often leads to chlorotic banding later in the season. 

The Connecticut Agricultural Experiment Station has a webpage dedicated to recognizing tree defects and diseases.

Invasive Plants

Invasive plants have the ability to thrive and spread widely outside their native range. Where active forest management lacks, it is common for non-native plants to outcompete native vegetation. This significantly limits tree regeneration and the establishment of beneficial native herbaceous and woody plants to which our wildlife is adapted.  As a result of the damage invasive plants create, there are now travel laws that ban the movement of plants across certain state and country borders. The USDA provides more information on the specific travel laws.

Invasive plants:

  • Impact water quality,
  • Compromise wildlife health and the associated food chain (see Bringing Nature Home on planting for biodiversity),
  • Prevent the establishment and growth of native vegetation,
  • Reduce forest health, resiliency, and adaptability,
  • Impact recreational opportunities, making outdoor areas impassible and unsightly,
  • Can impact human health, increasing the likelihood of contracting Lyme disease (specific to Japanese barberry),
  • Decrease larger biomass and carbon storage potential,
  • Decrease biodiversity, and
  • Impact timber production and forest products industry.

Furthermore, invasive plants disproportionately benefit from climate change due to their broach environmental tolerances, extended leaf phenology, more effective exploitation of changed environments, and more aggressive colonization of new areas. 

The Connecticut Connecticut Invasive Plant Working Group (CIPWG) maintains an Invasive Plant List of invasive plants in Connecticut, including trees. Since new, southerly invasive species are expected to enter Connecticut, it's important to stay up-to-date with your identification and knowledge. 

CIPWG's Invasive Plant Photo Journal is a picture guide to these plants that also describes the places where these plants are likely to be found.

There are many native alternative species to invasive plants. 

There is a lot of information on-line about invasive plants, both to help identify and also learn about them and to find assistance to for controlling invasive plants.

As a starting point to learn more or find out how you might get assistance as a landowner to fight invasives, it is suggested you visit the website of the USDA Natural Resources Conservation Service (NRCS).

Birch tree with broken limbPoor tree healthFire in Forest

Forest Fragmentation

Fragmentation is an issue related to the health of forests as opposed to individual trees.  Forests are complex ecosystems. When forests are fragmented - broken into smaller parcels - and then managed in an uncoordinated manner, this fragmentation can have impacts on both the vegetation and the wildlife. Breaks in the canopy, for example, let light into the interior of the forest, causing a shift in the plants that are capable of growing there.  

Common causes of fragmentation include:

  • Construction of roads,
  • Use of land for agriculture,
  • Development of utility corridors, and
  • Building of subdivisions.

Changes resulting in fragmentation have a more permanent effect on the forest.  This is what distinguishes them from, for example, harvesting of trees. After a harvest, the canopy will restore itself and the forest can regain its former characteristics.

The Center for Land Use Education and Research (CLEAR) is dedicated to examining Connecticut's forest fragmentation. On the CLEAR website you can view changes by individual town or by the overall loss of Connecticut forests since 1985.

How to Help
  • Contact the right professional for identified tree issues.
  • Prevent the spread of invasive plants and insects: do not dispose of living ornamental plants, fish, animals, or insects in ecosystems such as water bodies or forests.
  • Clean recreational gear, including bicycle tires, boats, and boots, after any outing to prevent the spread of invasive species to other areas.
  • Do not carry firewood long distances. Burn it where you buy or cut it.
  • Monitor your property for invasive plants, insects, and tree diseases and damage. Contact your Service Forester or Urban Forester for guidance.
  • Learn how to control invasive plants and manage invasive insects around your property.
  • When you need a tree care professional, hire one that you trust.
  • Avoid planting invasive ornamental plants on your property. Plant native species instead.
  • Reduce your carbon footprint. One important way of doing this is to substitute concrete, plastics, steel with wood products. Support local and shop CT Grown.

Forestry Main Page

For more information, please contact the Division of Forestry or 860-424-3630


Content last updated in April 2022.