Girdled Ash Trees

girdled ash tree

tree worker removing dead ash tree

girdled ash tree

You may have noticed ash trees (Fraxinus americana and Fraxinus pennsylvanica) in the garden with markings cut around their lower trunks. These intentional cuts, known as girdling, are part of a management strategy used to control the decline and eventual death of these failing ash trees.

What Does Girdling Do?

Girdling happens when the bark and the layer beneath it, called the vascular cambium, are removed in a ring around the tree’s trunk. This interrupts the flow of nutrients and water between the roots and leaves. Without this vital connection, the tree cannot survive.

Girdling can occur naturally through animal activity or human activity, but it is often caused by invasive pests such as the Emerald Ash Borer.

Why Have These Trees Been Girdeled?

Almost all ash trees in Rhode Island are currently affected—or will soon be affected—by the Emerald Ash Borer (EAB) (Agrilus planipennis), a small, metallic green invasive beetle native to Asia. Since its accidental introduction to North America, EAB has become a serious threat to ash trees, its preferred host. The beetle’s larvae burrow beneath the bark and feed on the cambium, disrupting the tree’s ability to transport water and nutrients. This damage effectively girdles the tree, leading to decline and death within a few years.

The spread of Emerald Ash Borer has resulted in widespread ash mortality across much of the region. In some areas, up to 99% of ash trees have been lost, dramatically altering forest ecosystems and urban landscapes alike.

Because EAB infestation and the eventual death of our ash trees are inevitable, we must take proactive steps to manage their decline. Purposefully girdling select ash trees allows us to slow the process rather than waiting for EAB to do so naturally. This approach gives us more time to safely plan and carry out removals. With more than 100 ash trees throughout our gardens, removal is a complex process that requires significant time, care, and resources.

Emerald ash borer (Agrilus planipennis). Photo: David Cappaert, Bugwood.org

Emerald ash borer adult in its tunnel. Photo: Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org

Why Do Ash Trees Matter?

Ash trees are a quiet but essential part of our landscape. Their broad canopies provide cooling shade, filter the air we breathe, and create food and shelter for countless birds, insects, and mammals.

When ash trees are lost on a large scale, the effects ripple outward—ecosystems are disrupted, familiar landscapes change, and the forest's structure is altered.

As sunlight suddenly reaches the forest floor, plants that once thrived in shade may struggle, while new species move in, reshaping the balance of the understory and the experience of the landscape we walk through.

What Can Be Done to Save the Ash Trees?

While it is unlikely that Emerald Ash Borer can be fully eradicated at this stage, there are still steps that can be taken to help protect individual ash trees.

Systemic Insecticides

The most effective control method involves using insecticides that move through the tree's vascular system. Treatments are most effective when applied in the spring (mid-April to mid-May).

• Trunk Injections (Best for large trees/high value): Performed by professionals using emamectin benzoate, these provide long-term protection for 2–3 years.

• Soil Drenches/Injections (Best for smaller trees): Homeowners can apply products containing imidacloprid to the soil, which are effective for trees under 15 inches in diameter.

• Basal Trunk Sprays: Applying dinotefuran to the lower trunk.

  
  

Preventative Measures

• Do not move firewood: It is a major cause of spread; use only local firewood.

• Keep trees healthy: Proper watering and care can reduce stress, though they cannot stop an EAB attack alone.

• Monitoring: Look for D-shaped emergence holes, bark splitting, and canopy dieback.

When to Treat or Remove

It is important to note that while chemical treatments can be effective, they are costly and must be repeated for the life of the tree. For this reason, our ash trees were not treated. As a small, nonprofit public garden, we did not have the financial and logistical resources necessary to treat and preserve them long-term.