To the untrained eye, the carnelian-red leaves blanketing the green grass at Szymanek Park signal the arrival of autumn in Warminster.
But Philadelphia-area arborist Jason Parker senses something amiss. A “zombie tree.”
“Zombie tree is a term that’s been used to describe a tree that’s dead or dying, maybe on the inside, but doesn’t necessarily look like it on the outside,” Parker said. “You may not understand what’s going on until all of a sudden — the tree is completely dead.”
Anecdotally, Parker is seeing more of the undead these days. Climate change is bringing warmer winters, which is shortening the time trees lay dormant and recover. Bugs and diseases are also active for longer, threatening to sentence trees across the Greater Philadelphia region to a life of decay.
Whether it be from damaging weather conditions, diseases, fungi or insect infestations, a dying tree can be dangerous. They don’t consume human flesh, but they can fall if left untreated. And if a car or a home are in its path, a zombie tree can prove to be costly.
However, for many zombie trees, a death sentence isn’t an inevitability. Parker wants people to check on their beloved trees and be aware of the warning signs.
Warning signs of a zombie tree — and the cure
Drooping trunks, fallen branches, brittle bark and dead leaves are some of the telltale signs. When homeowners are unsure about a tree’s health, Parker recommends calling an arborist for a closer look.
He services the trees through his job at Davey Tree in Szymanek Park. Most of them are in great shape. But there was one tree recently that happened to sit on a section of property at the abutting apartment complex.
The unlucky tree fell victim to the emerald ash borer, an invasive beetle species which wreaks havoc inside of ash trees. Parker noted the S-shaped carvings underneath the tree’s brittle bark — and the fact that all of its leaves had fallen prematurely. He recommended the tree’s removal.
Many of the causes of tree sickness, though, can be treatable. There are trunk injections.
“If it’s an insect or a disease, a lot of times there’s treatments that are available that can help deal with those,” Parker said. “The other thing is good soil care practices. Things like fertilization are really important to just keeping a tree healthy. Trees, just like people, as they get older, they need more and more care. We want to make sure that we’re providing that care.”
In a forest, trees protect each other from the elements. Their leaves give one another a “natural mulch,” Parker said. But in an urban or suburban environment, a lone tree can sometimes need a little help to reduce those stresses.
Untreated trees don’t have decades to live; often it takes just a few years before the damage is irreparable.
“If it’s too far gone, get rid of it as quickly as possible because the other thing is you then can’t safely climb them. Now, you’re talking about crane removals — which costs a lot of money,” Parker said.
Zombie tree meets ghost forest
The phrase “zombie tree” is still somewhat of a misnomer. Most tree tissue is dead xylem and phloem tissue that serve the purpose of supporting the weight of the tree and the formation of bark.
Dr. Kristen Wickert, a forest pathologist with the United States Forest Service, said when a tree is injured, infected or infested, the dead tissue decays. She never heard of the term “zombie tree” during her visits throughout the East Coast studying trees. Nevertheless, she is a fan of the spooky phrase.
“It catches your ear. It makes you think about it and it’s a lot easier to understand than when I use really specific jargon,” Wickert said. “Calling it something as a zombie tree really gets people who are not experts in biology, specifically tree biology, involved or engaged in this and maybe look at the thing that they walk by on their way to work every day in a different way.”
Wickert said each tree species is reacting differently to climate change. Closer to the coastline, rising sea levels are inundating trees whose roots were once dry with brackish water.
The mixture of fresh water with salt water is seeping underground, creating “ghost forests” — where trees lose their pigmentation en masse.
“They can’t breathe. Trees use their roots to breathe and then they’re also kind of getting poisoned by salt,” Wickert said. “So, this brackish water is causing really widespread areas of decline that we call ghost forests and the forest is changing into a saltwater marsh.”
Miles of New Jersey’s Atlantic white cedar forests are at risk.
Zombie tree 101: Replacing a member of the horde
Parker wants homeowners to replace zombie trees. He lives by a saying in the industry: “the right tree in the right place.”
“When you’re selecting a tree, you want to make sure that it’s not going to be something that’s going to be problematic for you in the future,” he said.
The Pennsylvania Horticultural Society (PHS) Tree Tenders program plants saplings for free.
“We do very large fall and spring plantings where residents can request a tree, put in an application and we will kind of take it from there and make every effort to associate the tree with their location,” PHS Director of Trees Dan Preziosi said. “Once the resident is approved, we take great consideration to ensure that we select the right tree for the right place.”
Preziosi recommends everyone to check on their trees given this lengthy period of hot and dry weather. He said they are an important part of healthy neighborhoods across the region.
Trees reduce the heat island effect and oftentimes, these living creatures become a part of people’s lives.
“I might be a little biased but trees, I think, just provide an excellent aesthetic and make people feel more welcome in the environment,” Preziosi said.
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