Cracked Wide Open

Debunking the Myth of Exploding Trees

Winter is going out with a bang. Across North America, trees are cracking under the pressure of recent cold snaps, with extreme temperatures pushing trunks past their breaking point. This “exploding trees” phenomenon has become an internet sensation, leaving perplexed homeowners and social media influencers wondering how trees can come apart at the seams seemingly overnight.

But is this true? Are trees really exploding because of the cold?

“Trees are not exploding all over the place,” Dane Buell, Vice President of Growth Strategy and Compliance at TreeServe confirmed. “This came up as a topic the week that we had some ice storms. Sensationalist articles about it were meant to get people excited, so it’s not really grounded in facts. It’s probably confusing a few conditions that can occur with trees in the winter, combining them, and unfortunately scaring people about trees possibly exploding in their backyard.”

While this may be disappointing to some who wanted to see explosive action, the process behind this phenomenon is just as captivating. Let’s take a closer look at what’s really brewing beneath the surface.

Myth Busted

Frost cracking (or freeze-thaw injury) is an abiotic disorder in trees caused by cyclic differences in winter temperatures. As sunlight warms the outer bark of a tree, the tissue expands. And when temperatures drop at night, the tissue contracts. If this process occurs at a faster rate than the inner layers, the applied mechanical stress can surpass the strength of wood fibers and cause them to separate.

This release of pressure can emit a loud sound that resembles a gunshot. For the everyday homeowner, it may seem like the tree “exploded”. While many may think frost cracking happens suddenly or drastically, but it actually takes a long time for these wood fibers to break apart.

Not all trees are created equally against this disorder. Ash (Fraxinus spp.), poplar (Populus spp.), elm (Ulmus spp.), zelkova (Zelkova spp.), maple (Acer spp.), apple (Malus spp.), and cherry (Prunus spp.) are just some of the many species susceptible to frost cracking.

“The primary ones that I see [affected] are typically young, smooth-barked trees,” Buell noted.

These trees are often re-injured from frost cracking in the same place every year, causing annual layers of woundwood to form on either side of the crack. One can estimate how many years the tree has experienced frost cracking by counting each striation on one side of the crack.

Slipping Through the Cracks

Frost cracking isn’t usually a cause for concern. Many healthy, vigorous trees can temporarily or permanently seal over frost cracks thanks to a process called the Compartmentalization of Decay in Trees (CODIT), also known as the Compartmentalization of Damage in Trees.

“It’s typically not a fatal situation,” Buell assured.

However, there are notable exceptions. Cracks in a weakened tree are the perfect opportunity for pests and pathogens to invade. This can lead to compounding disorders like disease, decline, or even death.

“Anytime we open up the tree’s system, we’re allowing for stuff to get in there – it’s creating an entryway,” Buell warned. “From a stress perspective, you are going to disrupt some of the tree’s vascular system, and that is going to affect the movement of water, nutrients, and carbohydrates.”

While it is very rare for a frost crack to cause catastrophic failure in a tree, winter can increase the likelihood of failure in other ways, like sudden limb drop.

“Ice loads in winter can damage tension wood on the tops of limbs,” Buell said.

He explained that once the tree foliates in the summer, it creates significant structural load, sometimes causing limbs to fail suddenly. In fact, according to research conducted by Arboriculture & Urban Forestry (AUF), residual tree damage can last several years after an ice storm.

“It’s never a single thing that kills trees,” Buell continued. “It’s typically some compilation of things that occur that cause damage – a frost crack, a drought season, an invasive insect. You keep adding that list up and that can be a challenge for the tree.”

Patching Things Up

While frost cracking cannot be prevented, there are measures that might help minimize its impact:

• Practice “right tree, right place”. Match the species to the environment, climate, hardiness zone, and soil.
  
• Properly care for trees using ISA Best Management Practices, including regular watering.
  
• Install white, perforated tree guards temporarily around the trunk in late fall to potentially help regulate surface temperatures.
  
• Monitor and record any significant defects or changes in the tree.
  
• When in doubt, contact an ISA TRAQ Arborist.

Buell offered his insights on how to maintain trees not just in winter, but year-round.

“Reduce drought stress the following year by making sure trees are well-irrigated. Remove soil overburden and make sure you’re properly mulching, not over-mulching. Ensure that the tree is protected against invasive pests and disease by managing these problems and correcting them at the right thresholds,” he advised.

Preventing frost crack isn’t a winter fix.

“It’s all the things we need to do to keep trees healthy.”

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TJ Yurko is an ISA Certified Arborist® (PR-5403A), ISA TRAQ Arborist, and Certified Landscape Horticulturist Technician at his company, Tree J Consulting, where he advises clients on urban forestry and arboriculture best management practices and strategies for tree care operations.