Spooky Season has arrived, so this is a great time to cover a scary topic for your trees – DECAY.

 

 

All joking aside, most decay in trees is caused by fungi.  Fungi can break down the structural building blocks of plant cell walls such as lignin and cellulose, thereby potentially weakening the integrity of wood in trees.  This weakening of wood fibers can have important implications for the trees you care for.  Trees can respond to the presence of decay in different ways, including compartmentalization and response growth.  These natural responses can sometimes allow a tree to survive for extended periods after a fungal infection.

 

Knowing which signs to look for on the exterior of trees can help landowners and property caretakers identify indicators of decay. The location of such signs is also an important consideration in assessing a tree for decay.  Is the decay in the sapwood or heartwood? Has a cavity already formed?  A plastic mallet can be used to help find cavities in trees.  Hollows will resonate and create a sound very different than the fibers of healthy wood.

 

Internal decay and large cavities, as displayed above, can be hidden beneath tree bark. While trees may live for many years with significant decay, this can weaken the structure to the point of creating hazards.

 

Conks are the fruiting bodies of some fungal species and come in many shapes and sizes.  Are there conks on the buttress roots?  Is there a conk on the trunk several feet above the ground?  These all have different implications for the tree, which can often be recognized by competent professionals.  Many arborists are familiar with decay fungi and can identify fungal groups that are known to be more aggressive in causing tree decay such as Ganoderma and Armillaria.

 

Two examples of fungal fruiting bodies on tree branches. The presence of these bodies indicates some form of decay within the tree.

 

By recognizing the signs of decay in trees and monitoring response growth and cavities over time, tree stewards can make informed decisions on how long a tree should be retained with decay fungi present.  External factors when evaluating a tree with decay include potential targets and the value of those targets (including people, property, and nearby infrastructure). If the tree is in the middle of a forest and away from paths or infrastructure, there is no need to intervene. The decay fungi are fulfilling an important ecological function by acting as a natural recycler of nutrients in the food web while also potentially creating habitat for other organisms such as bats, birds, and other fauna. Conversely, if the tree exhibiting significant signs of decay is situated in a small front yard with targets such as people, residences, and a busy street, the potential implications are much more severe, and further investigation by an expert may be warranted.

 

 

Spiders are just one example of how important decaying wood is for fungi, insects, arthropods, and animals.

 

The concept of risk tolerance may also factor in decisions regarding trees with fungi. As humans, we all have varying levels of risk thresholds in our daily decisions.  One person may be very risk-averse and choose to remove a tree, while another may be quite tolerant of the same risk, knowing that trees provide so many other functions in our landscapes.

 

If you are unsure about potential decay concerns or overall tree health questions, it is best to connect with a certified arborist. You can find three lists for certified arborists on our website linked below.

 

 

In our urban trees, fungi often find a way to invade a tree after an avoidable mechanical injury caused by human activities such as string trimming and mowing.  Such injury risks can be minimized with a properly maintained mulch ring around the base of the tree.  Sadly, once a tree has a fungal infection, treatment options are quite limited.  Spooky indeed, especially if you’re the tree. 

 

Thank you,

 

 

Our next talk will be on November 10th at 12 pm- 1 pm with Northwest District Forester, Chelsea Hanson. This webinar will cover the “Right Tree, Right Place” philosophy. This philosophy follows the idea that if the right tree is selected for a given site and ecosystem, it will be significantly better than a tree that is not suited for the site.

 

A Zoom link to join the discussion will be sent in October's Between the Branches newsletter!