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Fallen trees could be more dangerous than you think. Here's why

By Yasmin Jeffery, Tuesday March 26, 2019 - 19:45 EDT
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One arborist said as many as one in 10 trees he works on will spring back upright. - ABC licensed

While fallen trees may be a fascinating sight, they could be more dangerous than they look.

A 12-year-old Queensland boy was left with serious injuries after playing around a fallen tree on his grandmother's property the day after storms last year.

by the tree after it suddenly sprang back into place in South Burnett.

The 12-year-old has since made an almost full recovery, but sustained a broken femur, eight broken ribs, two collapsed lungs and a squashed heart in the incident.

Here's what causes trees to spring back upright after falling, and what you should do if you come across a fallen tree.

What causes trees to spring back upright?

Benjamin Inman, an arboriculture consultant at Trees Are Cool, says severe storms can cause trees to fail from their root plates — the part of the root system that supports the tree.

Severe weather conditions alter the soil's structure, and if the soil structure around a tree becomes too weak, that tree's entire root plate can lift and "fail".

"Once that's done, the tree root's still normally connected on one side, and therefore there's still a lot of pressure," he says.

"For a tree to spring back, there would have to be a lot of tension or compression forcing it back into position," which the weight of the tree itself can provide.

So, once a tree's root plate has been lifted and failed, Mr Inman says it can take as little as a gust of wind to cause the entire tree to spring back upright.

"It's known in our industry that once a root plate is seared with a tree like that, that is the danger zone," he added.

How often does it happen?

Kurt Brown, a Queensland arborist for more than 30 years, says it is not unheard of for trees to fall over and then rise again after storms.

The Sunshine Coast Tree Works arborist said: "It's not as normal as trees falling over and staying down — that's obviously the norm — but in certain situations when a tree's fallen over, if you cut the log off, quite often the root ball will spring back into the hole it came from."

Mr Brown adds trees can also flip back after storms if they fall on top of each other, flexing the timber.

"It depends on the situation, but at the stage where people start either cutting [fallen trees] or moving them, it is quite a normal occurrence.

"So, it is sort of rare that it will stand up all by itself, but, say people are walking on it, it can be that disturbance that could release whatever's holding it down.

"Obviously, there are a lot of varying factors from tension — it depends how much tension the tree is under at this stage."

But, Mr Brown says: "Out of around 10 houses that we visit with fallen trees, there'd be at least one that would spring back up."

While experts can tell from the "body language" of a tree how much pressure it's under and therefore how dangerous it is, the public shouldn't try and make the same judgment, he warns.

What are the warning signs?

If a tree falls in your backyard after a storm, Mr Inman says you first need to check whether its base has started to lift.

The other thing to look for is cracks in the soil which can show if the tree has moved in the ground.

But Mr Inman stresses the best practice is to call for help — experts can install tree motion sensors to measure movement and determine whether the tree in question still has good stability.

However, "If you're in a rainforest, say, in a storm environment, being in that environment in the first place is not the best".

"Whenever there's a large storm event, the best place to be is indoors.

"If there's a fallen tree already, the best practice is to stay away. It's not a plaything, and it's not a jungle gym that you can now climb on.

"They do move, and it's possible for them to spring back to how they once were."

What should you do if you see a fallen tree?

Mr Inman describes playing around fallen trees as "one of the most dangerous things to do", and says parents should take care to make sure their kids are aware of the dangers.

"One of the things I've seen in my career — especially after and during storm events — is people taking selfies amongst storm-damaged trees, but these things are dangerous and people need to leave them to be attended to by the experts," he says.

"After storm damage, it's highly recommended that people don't go wandering about among fallen trees. This is how accidents happen.

"When a tree's failed, all it takes is a gust of wind — a simple gust of wind — to tip the balance again and have the whole thing slap back down again."

Mr Brown agrees, saying people should stay away from fallen trees, "no matter how big or small" — and leave it to the professionals to deal with them.

"In a storm event, fallen and spring-loaded trees can be quite common, and if [the public is not] aware of it, they are putting themselves and others in danger.

"Leave it alone and call your local tree service professionals or the SES — that's what they're there for — and just keep your family away."


© ABC 2019

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