An act of God, or just bad management? Why trees fall and how to prevent it


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Gregory Moore, The University of MelbourneThe savage storms that swept Victoria last week sent trees crashing down, destroying homes and blocking roads. Under climate change, stronger winds and extreme storms will be more frequent. This will cause more trees to fall and, sadly, people may die.

These incidents are sometimes described as an act of God or Mother Nature’s fury. Such descriptions obscure the role of good management in minimising the chance a tree will fall. The fact is, much can be done to prevent these events.

Trees must be better managed for several reasons. The first, of course, is to prevent damage to life and property. The second is to avoid unnecessary tree removals. Following storms, councils typically see a spike in requests for tree removals – sometimes for perfectly healthy trees.

A better understanding of the science behind falling trees – followed by informed action – will help keep us safe and ensure trees continue to provide their many benefits.

tree lying on home
We must try to stop trees falling over to prevent damage to life and property.
James Ross/AAP

Why trees fall over

First, it’s important to note that fallen trees are the exception at any time, including storms. Most trees won’t topple over or shed major limbs. I estimate fewer than three trees in 100,000 fall during a storm.

Often, fallen trees near homes, suburbs and towns were mistreated or poorly managed in preceding years. In the rare event a tree does fall over, it’s usually due to one or more of these factors:

1. Soggy soil

In strong winds, tree roots are more likely to break free from wet soil than drier soil. In arboriculture, such events are called windthrow.

A root system may become waterlogged when landscaping alters drainage around trees, or when house foundations disrupt underground water movement. This can be overcome by improving soil drainage with pipes or surface contouring that redirects water away from trees.

You can also encourage a tree’s root growth by mulching around the tree under the “dripline” – the outer edge of the canopy from which water drips to the ground. Applying a mixed-particle-size organic mulch to a depth of 75-100 millimetres will help keep the soil friable, aerated and moist. But bear in mind, mulch can be a fire risk in some conditions.

Root systems can also become waterlogged after heavy rain. So when both heavy rain and strong winds are predicted, be alert to the possibility of falling trees.




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People inspect trees fallen on cars
A combination of heavy rain and strong winds can cause trees to fall.
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2. Direct root damage

Human-caused damage to root systems is a common cause of tree failure. Such damage can include roots being:

  • cut when utility services are installed
  • restricted by a new road, footpath or driveway
  • compacted over time, such as when they extend under driveways.

Trees can take a long time to respond to disturbances. When a tree falls in a storm, it may be the result of damage inflicted 10-15 years ago.

tree uprroted
This elm, growing very close to a footpath, fell in Melbourne during a 2005 storm.
Author provided

3. Wind direction

Trees anchor themselves against prevailing winds by growing roots in a particular pattern. Most of the supporting root structure of large trees grows on the windward side of the trunk.

If winds come from an uncommon direction, and with a greater-than-usual speed, trees may be vulnerable to falling. Even if the winds come from the usual direction, if the roots on the windward side are damaged, the tree may topple over.

The risk of this happening is likely to worsen under climate change, when winds are more likely to come from new directions.

4. Dead limbs

Dead or dying tree limbs with little foliage are most at risk of falling during storms. The risk can be reduced by removing dead wood in the canopy.

Trees can also fall during strong winds when they have so-called “co-dominant” stems. These V-shaped stems are about the same diameter and emerge from the same place on the trunk.

If you think you might have such trees on your property, it’s well worth having them inspected. Arborists are trained to recognise these trees and assess their danger.




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car bumper stopped at fallen tree trunk
Storms can trigger falling trees which block roads.
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Trees are worth the trouble

Even with the best tree management regime, there is no guarantee every tree will stay upright during a storm. Even a healthy, well managed tree can fall over in extremely high winds.

While falling trees are rare, there are steps we can take to minimise the damage they cause. For example, in densely populated areas, we should consider moving power and communications infrastructure underground.

By now, you may be thinking large trees are just too unsafe to grow in urban areas, and should be removed. But we need trees to help us cope with storms and other extreme weather.

Removing all trees around a building can cause wind speeds to double, which puts roofs, buildings and lives at greater risk. Removing trees from steep slopes can cause the land to become unstable and more prone to landslides. And of course, trees keep us cooler during summer heatwaves.

Victoria’s spate of fallen trees is a concern, but removing them is not the answer. Instead, we must learn how to better manage and live with them.




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Here are 5 practical ways trees can help us survive climate change


The Conversation


Gregory Moore, Doctor of Botany, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Asking people to prepare for fire is pointless if they can’t afford to do it. It’s time we subsidised fire prevention



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David Bowman, University of Tasmania

Once again, Australia is on fire. This year it’s the turn of Western Australia and South Australia, where bushfires are threatening homes and lives. In the south of Tasmania, conditions are dry and the region is entering a period of peak fire danger.

In the lead up to every bushfire season, the mantra is the same each year: prepare, prepare, prepare. Remove the fuel load. Clean out the gutters. Mow lawns, tidy gardens, create a burnbreak between bushland and your house. Identify your strengths and weaknesses. Have a plan.

After 40 years studying the interaction between humans and fire, I have seen this mantra rolled out every year — and watched, every year, as it is comprehensively ignored by large numbers of people. Why? Because they are bad or lazy? No.

The fact is asking people to prepare for fire is pointless if they can’t afford to do it. If you don’t have time or money (or both), it doesn’t matter how many times authorities tell you to prepare. It’s not going to happen. What if we had a system, like Medicare, where the cost of these fire prevention measures was subsidised by the public system?




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We know the current system doesn’t work

Institutions such as local fire authorities, councils or governments can say “we have done our bit and we expect the community to do their part and manage their risk, their property, their bushfire plan”.

But it’s just passing the problem along to the next person, without considering whether they’re able to actually take up that advice.

For years, authorities have essentially handed people a very formidable and expensive checklist of things to do, right up to the level of retrofitting your house to be compliant with modern building standards. These are significant time and financial investments.

The cost of failing to prepare is huge. Bushfire often spreads by embers landing in a series of unprepared properties. If your neighbours don’t make their home defendable, chances are it may cause your house to burn down.

There are many reasons people don’t prepare, and a key one is affordability. If you’re not physically able to get up a ladder to clean your gutters or mow around your property and remove fuel load — and you can’t afford to pay someone to do it — what are you supposed to do?

You might think, “Well, if people choose to live in a bushfire prone area then that’s their problem. Why should they get subsidies?” But there are many reasons people might not be able to prepare, including poverty, old age, and health issues.

And if they don’t prepare, it won’t just affect them; it could create a vector for the fire to spread to other properties. Research suggests disasters, including fires, are more likely to occur in low socioeconomic areas.

A man cleans leaf litter out of gutters.
Many people are not physically able to get up a ladder to clean gutters and can’t afford to pay someone to do it.
Shutterstock

It’s time to look at preventative fire measures the same way we look at preventative healthcare.

Our taxes fund Medicare and public health measures because Australian society recognises it’s cheaper in the long run. It’s cheaper than allowing low-level health problems to fester until they become so threatening they have to be dealt with in the mind-bogglingly expensive emergency department.

In the same way, subsidies for household bushfire preparation would help prevent the vast taxpayer expense incurred for emergency fire-fighting when fire strikes.

What might the system look like?

The system could take many forms.

State governments already give vouchers to citizens to incentivise spending in one area. Think of the NSW government’s Active Kids or Creative Kids voucher systems, or its planned dining and entertainment voucher system.

So why not give vouchers you can use to pay someone to clear your gutters, mow your lawn or clear dry grass and other fuel loads?

Insurers could offer lower premiums to people who take action to reduce fire risk around their home by ember-proofing or installing gutter-guard, for example (in the same way there are insurance benefits if you make your house more resistant to being broken into).

A burnt out house.
Insurers could offer lower premiums to people who take action to reduce fire risk around their home.
Shutterstock

Perhaps councils could offer lower rates for low-income people who, in exchange, pay for measures to reduce their fuel load.

Or we could have a bulk-billing system, where you can ask a service provider to assess your home’s risk and do basic fire load reduction, and it’s charged to a Medicare-style system.

To me, these ideas make a lot more sense than more punitive measures being considered in some places, where authorities could clear a fire risk around a house themselves and simply send the bill to the occupant or land owner.

The punitive system just puts more pressure on people who may not be able to afford to reduce their home’s fire risk, much less deal with going to court to dispute a bill they’ve been sent. It also means people are less likely to trust and cooperate with fire authorities.

That sounds expensive

Yes, I know these ideas are expensive. So is Medicare. So is the pension system. So is the public health response that helped Australia drive the COVID-19 epidemic into submission. But they’re worth it, aren’t they?

And do you know what else is expensive? Doing the same thing every year, even though it doesn’t work.

We have just been through an enormously expensive bushfire royal commission. And as fire expert Kevin Tolhurst points out here, we’ve had 57 formal public inquiries, reviews and royal commissions related to bushfires and fire management since 1939. A huge expense to taxpayers.

We know the cost of the Black Summer fires ran into the billions, with costs to the health system, individuals, businesses and emergency services.

Aerial fire suppression aircraft are expensive. Having 100-day firefighting campaign is an extraordinary drain on the public purse — and that’s before you even start counting the cost of economic disruption that comes with it.




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It sounds a bit radical

I know! But radical change is what’s needed — and it’s possible. In early 2020, I wrote it was time to re-arrange the Australian school calendar around fire seasons and people said this was crazy. But then a few months later we completely rearranged schooling around the pandemic — an idea that, in January, would have seemed completely unworkable.

It turns out radical change is possible when push comes to shove. And for climate change-related fire risk, push really has come to shove.

Our current system involves telling people to create “a defendable space” around your house. I’ve been on Google Earth to look to at how that’s played out in many bushland suburbs; you don’t need to be a genius to work out there they are not defendable spaces.

Climate change adaptation does feel radical, but it’s also necessary.

If we are sitting round going into a hotter, drier, more fire-prone world, what are we doing if we are not enabling people to adapt?


This story is part of a series The Conversation is running on the nexus between disaster, disadvantage and resilience. You can read the rest of the stories here.The Conversation

David Bowman, Professor of Pyrogeography and Fire Science, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why do dingoes attack people, and how can we prevent it?



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Dingoes are usually solitary, but can forage in groups near human settlements where food is abundant.
Klaasmer/Wikimedia Commons, CC BY-SA

Bill Bateman, Curtin University and Trish Fleming

The case of Debbie Rundle, who was attacked by dingoes at a mine site in Telfer, in Western Australia’s Pilbara region, evokes our instinctive horror at the idea of being attacked by wild animals.

Rundle suffered severe leg injuries in the incident, and said she feared she may have been killed had her colleagues not come to her aid.




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We know that there are carnivores throughout the world with the potential to kill us. And while most of us will never come face to face with a hungry wolf, lion, tiger or bear, such attacks do unfortunately still occur.

In the scale of things, such attacks are very uncommon – although that is little consolation to the victim. Australia’s dingoes are no exception; despite some infamous examples, dingo attacks on humans are mercifully rare. But people will still understandably want to know why they happen at all, and what can be done to prevent them.

Why do wild animals attack?

Research on wolf attacks shows that, absent the influence of rabies which can increase wolves’ aggression, two common factors associated with attacks are that they often happen in human-modified environments, and by animals that are habituated to human presence.

These two variables are obviously linked: many species of mammalian carnivore are highly adaptable, and soon learn that human settlements are sources of food, water and shelter.

These human resources can have a profound effect on the behaviour of wild animals. Abundant human food often reduces animals’ aggression towards one another, and can result in the presence of much larger numbers of individuals than normal.

This is equally true of dingoes. Although they are usually observed alone, it is not uncommon to see groups of ten or more dingoes foraging at rubbish dumps associated with mine sites in the Tanami Desert of central Australia. There are thought to be around 100 dingoes that forage in and around the Telfer mine where Rundle was attacked.

Waste food may inadvertently entice animals to human settlements, and this may lead to predators becoming habituated to human presence. In Canada, a young man fell victim to a wolf attack at a mine site; the local wolves were reported to be used to humans, and would even follow rubbish trucks to the tip. They may have come to associate human smells with the provision of food.

Animals that are habituated to humans lose some of their natural wariness towards them. This is typical of many animal species that adapt to urban habitats, and while this may be an appealing trait in squirrels or garden birds, it can be quite different if the animal is a predator capable of attacking a human.

Coyotes can be dangerous, especially when they get used to living in human environments.
Marya/Flickr/Wikimedia Commons, CC BY-SA

In the United States, there have been many reports of coyotes attacking humans. The coyote, like the dingo, is reasonably large (typically weighing 10–16kg) and can be found in close association with urban areas. The coyote’s natural range has expanded as wolves (their competitor) have dwindled, and their numbers have increased in and around cities where they find copious and consistent supplies of food and water.

A survey of reported attacks on humans by coyotes showed that many were “investigative”, often involving the animal trying to steal something they perceived as food from the person. Other attacks by coyotes could be identified as “predatory”, in which the victim was pursued and bitten, and often occurred when the coyotes were in a group.




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The Telfer dingo attack similarly appears to have been investigative – a young dingo climbed onto a table and grabbed Rundle’s phone. But the incident turned nasty when Rundle (perhaps understandably) followed the dingo that had her phone; this seemed to trigger a defensive or predatory attack from two other dingoes.

On Queensland’s Fraser Island, more than half of the recorded aggressive incidents by dingoes towards humans happened when the person was walking or running, suggesting that a “chase” response may have been involved.

The Telfer site, like other mine sites, has strict rules about putting waste food in bins, and managers have been proactive in training workers to not feed dingoes, in an attempt to prevent just such attacks. Rundle certainly seems to have followed these rules.

Unfortunately, in her case, other variables contributed to the attack – an investigative approach by one dingo that stole an item (that may have smelled of food) seems to have turned into an aggressive group attack when she followed the animals.




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What can we do to prevent such attacks? Mine site managers already do much to reduce the likelihood of such incidents by reducing dingoes’ access to food. Fencing off eating areas or storing food in cages – as is done at Fraser Island – can help in this regard.

Interestingly, many people believe that it is best not to act aggressively when they encounter a large carnivore, but in reality it depends on the species. For wolves and pumas, the best tactic seems to be to shout and throw objects to put them off.

The ConversationUltimately, the onus is on individual people to be aware of the potential danger of wild predators, and always to treat them with wariness and respect.

Bill Bateman, Senior Lecturer, Curtin University and Trish Fleming, Associate Professor

This article was originally published on The Conversation. Read the original article.