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Connecticut's Forest Health

InsectsDiseasesInvasivesStorms and Climate ChangeForest FragmentationHow to Help

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


Certain insects can cause significant damage to forests despite being native to the area. For example, the Two Lined Chestnut Borer is severely impacting oak trees in Connecticut.


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.

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


Animals are considered invasive when they occupy areas outside of their native range and, by doing so, cause harm to either the environment, economy, or human health.

For a comprehensive guide to invasives and how to control them, please visit the Connecticut Agricultural Experiment Station.

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

Invasive plants have the ability to thrive and spread widely outside their native range. In areas where management is minimal, it can be expected that the non-native plant will outcompete native vegetation. As a result of the damage these 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: 

    • surrounding waters,

    • animals and the associated food chain (see Bringing Nature Home on planting for biodiversity),

    • native vegetation, and

    • recreational opportunities, making outdoor areas impassible and unsightly.

The Connecticut Invasive Plant Working Group (CIPWG) maintains an Invasive Plant List of invasive plants in Connecticut, including trees.

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.

Birch tree with broken limbPoor tree healthFire in Forest

Storms and Climate Change

Severe weather accounts for regular tree damage across the state. Stormwise is a collaborative forest vegetation management program involving DEEP, UConn, local municipalities and utility companies, with the goal of reducing the risk of tree-related storm damage to power lines.

The Arbor Day Foundation offers information about how trees combat climate change and the importance of maintaining a healthy 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
  • Do not dispose of living ornamental plants, fish, animals, or insects in ecosystems such as water bodies or forests. They may adapt to the conditions where you release them.
  • Clean gear after any outing to prevent the spread of invasive species to other areas. This includes boats, clothes, boots, etc.
  • Do not carry firewood long distances. It is best to burn it where you buy or cut it.
  • Monitor your property for invasive plants, insects and tree diseases and damage.
  • 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.
  • Assess trees year round for defects such as hanging limbs and large cracks. 
  • Avoid planting invasive ornamental plants on your property. Plant native species instead.

Trees and Urban Forests: Learn More  | Forestry Main Page

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


Content last reviewed February 2020