Why Do Trees Rot from the Inside? - Tree 101

September 8, 2023

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Are you a property owner wondering, why do trees rot from the inside? If you have beloved trees on your property that you want to keep, it’s vital to understand this subject! Preventing rot is the best chance you have of saving those trees. It’s also good to know how to treat rot and when a tree needs removal.

Why do trees rot from the inside:

  • Fungal infections
  • Wounds and injuries
  • Not a good decay-resistant species
  • Aging and everyday stress
  • Moisture
  • Cavities and hollow areas

To find out more about tree rot and how to avoid it, keep reading! Also, never hesitate to call a tree services contractor near you when needed. They can usually examine a tree and find reasons for rot, disease, and other such issues. A professional can also recommend the best way of saving that tree, if possible!

why do trees rot from the inside

Why Do Trees Rot from the Inside?

Tree rot is commonly referred to as "heart rot" or "decay." Heart rot is a condition in which the inner, central part of a tree (the heartwood) deteriorates and decays. This often leaves the outer layers (the sapwood and bark) structurally sound. Here are some reasons why trees may experience heart rot:

Fungal Infections

Fungi are a primary cause of heart rot in trees. Fungal spores can enter a tree through wounds, cracks, or other openings in the bark. Once inside, they colonize the heartwood, breaking down the structural components of wood. As the fungi spread and consume the wood, the affected area becomes weak and rots.

Wounds and Injuries

Trees can sustain wounds from various sources, including storms, falling branches, improper pruning, or damage caused by animals. These wounds provide entry points for fungi and other pathogens, which can lead to heart rot.

Decay-Resistant Species

While all trees can potentially develop heart rot, some tree species are more resistant to decay than others. Trees with higher concentrations of natural preservatives, such as cedar or redwood, are less susceptible to heart rot compared to species like oak or pine.

Aging and Stress

Older trees are more prone to heart rot because they have been exposed to environmental stressors, injuries, and pathogens over a longer period. Stress factors like drought, nutrient deficiencies, or pollution can weaken a tree's defenses against decay.


Moisture is essential for fungal growth and wood decay. Trees that are consistently exposed to moisture, whether from groundwater, flooding, or chronic high humidity, are at greater risk of developing heart rot.

Cavities and Hollows

Over time, as heart rot progresses, it can create cavities or hollows inside the tree. These hollows can serve as habitats for wildlife, including birds, bats, and insects, which may further contribute to the tree's decay.

cabling a tree before pruning

How Do You Treat a Tree That Is Rotting Inside?

Prompt treatment is the best choice for saving a tree that’s rotting inside. However, in some cases, the tree might be beyond saving. Check out some steps to consider when dealing with a tree that’s rotting from the inside:

  • Start by consulting a certified arborist or tree care professional. They can assess the extent of the decay, evaluate the tree's overall health, and provide expert guidance on whether the tree can be saved.
  • If the decay is localized and the tree is not in immediate danger of falling, pruning can be done to remove affected branches. Pruning should be precise and follow industry standards to minimize stress on the tree.
  • Minimize additional stress factors that can weaken the tree, such as drought, soil compaction, nutrient deficiencies, or other environmental stressors. Proper care, including watering and fertilizing as needed, can help improve the tree's health and ability to defend against decay.
  • If the decay resulted from a previous injury or wound, ensure proper wound care. Clean the wound, trim any damaged tissue, and apply a wound dressing or sealant to promote healing and prevent further infection.
  • Regularly monitor the tree's condition and take preventive measures. This includes routine inspections to detect any changes in the tree's stability or health. Promptly address any new wounds or signs of disease.
  • For trees with significant decay but structural integrity in the outer wood, support systems such as cabling or bracing may be considered to reduce the risk of limb failure or tree collapse.
  • In some cases, fungicides may be applied to the tree, particularly if the decay is caused by specific fungi. However, fungicide treatments have limited effectiveness and are generally used as a preventive measure rather than a cure for existing decay.

Should a Rotting Tree Be Removed?

The decision to remove a rotting tree should be made after a careful assessment by a tree care professional. They can evaluate the extent of the decay, the tree's structural stability, and its overall health. Here are some key factors to consider when deciding whether to remove a rotting tree:

  • If the decay has progressed significantly and has compromised the structural integrity of the tree, removal is often the safest option. A severely decayed tree is more likely to fall, especially during storms or high winds.
  • Consider the location of the tree in relation to buildings, structures, roadways, pedestrian paths, and areas where people congregate. A rotting tree that poses a risk to people, property, or vehicles should be removed promptly.
  • If the tree is leaning, has multiple dead branches, or shows other visible signs of instability, it may be a hazard. A professional assessment can help determine the level of risk.
  • If the rotting is the result of a disease or pest infestation that cannot be effectively treated, removal may be necessary.
  • Property owners may be liable for damage or injury caused by a fallen tree, especially if it is known to be diseased or structurally unsound. Removing a potentially hazardous tree can help mitigate liability risks.

mushrooms growing along a tree

How Do You Tell If a Tree Is Rotting Inside?

Detecting internal rot in a tree can be challenging. Decay often occurs hidden within the tree's trunk or branches. However, there are several signs and symptoms that may indicate internal rot or decay in a tree:

  • Mushrooms on the trunk or at the base of the tree are a clear sign of decay. These fungi often emerge as a tree begins to break down internally.
  • Visually inspect the trunk and branches for cavities, hollows, or depressions. These can be openings into the internal decay. In some cases, you may notice dead branches or stubs protruding from the hollowed-out areas.
  • Cankers are areas of dead or dying tissue on the tree's bark. They may be sunken, discolored, or have an irregular shape. Cankers can be a sign of internal decay or disease.
  • Hollow or spongy-sounding areas can indicate decayed wood. A tool like a sounding mallet can be used by professionals to assess the tree's internal condition more accurately.
  • Check for cracks, splits, or seams in the bark and wood. These openings can allow moisture and decay organisms to enter the tree, leading to internal rot.
  • The presence of dead or dying branches, particularly if they are large or numerous, can suggest that decay is affecting the tree's vascular system.

A Quick Word From Our Team

Ann Arbor Tree Trimming & Removal Service is happy to explain, why do trees rot from the inside? If you’re near the city, call our Ann Arbor tree services contractors for expert services. We offer pruning, trimming, and removal, for a safe and stunning property you’re sure to love.


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