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


AP

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.
Shutterstock

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.
Shutterstock

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.

Peatlands worldwide are drying out, threatening to release 860 million tonnes of carbon dioxide every year


Shutterstock

Yuanyuan Huang, CSIRO and Yingping Wang, CSIROPeatlands, such as fens, bogs, marshes and swamps, cover just 3% of the Earth’s total land surface, yet store over one-third of the planet’s soil carbon. That’s more than the carbon stored in all other vegetation combined, including the world’s forests.

But peatlands worldwide are running short of water, and the amount of greenhouse gases this could set loose would be devastating for our efforts to curb climate change.

Specifically, our new research in Nature Climate Change found drying peatlands could release an additional 860 million tonnes of carbon dioxide into the atmosphere every year, by around 2100. To put this into perspective, Australia emitted 539 million tonnes in 2019.

To stop this from happening, we need to urgently preserve and restore healthy, water-logged conditions in peatlands. These thirsty peatlands need water.

Peatlands are like natural archives

Peatlands are found across the world: the arctic tundra, coastal marshes, tropical swamp forests, mountainous fens and blanket bogs on subantarctic islands.

They’re characterised by having water-logged soil filled with very slowly decaying plant material (the “peat”) that accumulated over tens of thousands of years, preserved by the low-oxygen environment. This partially decomposed plant debris is locked up in the soils as organic carbon.




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Peatlands can act like natural archives, letting scientists and archaeologists reconstruct past climate, vegetation, and even human lives. In fact, an estimated 20,500 archaeological sites are preserved under or within peat in the UK.

As unique habitats, peatlands are home for many native and endangered species of plants and animals that occur nowhere else, such as the white-bellied cinclodes (Cinclodes palliatus) in Peru and Australia’s giant dragonfly (Petalura gigantea), the world’s largest. They can also act as migration corridors for birds and other animals, and can purify water, regulate floods, retain sediments and so on.

Giant dragonfly on a branch
The giant dragonfly (Petalura gigantea) is listed as endangered under NSW environment law.
Christopher Brandis/iNaturalist, CC BY-NC

But over the past several decades, humans have been draining global peatlands for a range of uses. This includes planting trees and crops, harvesting peat to burn for heat, and for other land developments.

For example, some peatlands rely on groundwater, such as portions of the Greater Everglades, the largest freshwater marsh in the United States. Over-pumping groundwater for drinking or irrigation has cut off the peatlands’ source of water.

Together with the regional drier climate due to global warming, our peatlands are drying out worldwide.

What happens when peatlands dry out?

When peat isn’t covered by water, it could be exposed to enough oxygen to fuel aerobic microbes living within. The oxygen allows the microbes to grow extremely fast, enjoy the feast of carbon-rich food, and release carbon dioxide into the atmosphere.

A marsh in Les Sables d Olonne, France. Some peatlands are also a natural sources of methane, which is a more potent greenhouse gas than carbon dioxide.
Arthur Gallois, Author provided

Some peatlands are also a natural source of methane, a potent greenhouse gas with the warming potential up to 100 times stronger than carbon dioxide.

But generating methane actually requires the opposite conditions to generating carbon dioxide. Methane is more frequently released in water-saturated conditions, while carbon dioxide emissions are mostly in unsaturated conditions.




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Emissions of methane – a greenhouse gas far more potent than carbon dioxide – are rising dangerously


This means if our peatlands are getting drier, we would have an increase in emissions of carbon dioxide, but a reduction in methane emissions.

So what’s the net impact on our climate?

We were part of an international team of scientists across Australia, France, Germany, Netherlands, Switzerland, the US and China. Together, we collected and analysed a large dataset from carefully designed and controlled experiments across 130 peatlands all over the world.

In these experiments, we reduced water under different climate, soil and environmental conditions and, using machine learning algorithms, disentangled the different responses of greenhouse gases.

Our results were striking. Across the peatlands we studied, we found reduced water greatly enhanced the loss of peat as carbon dioxide, with only a mild reduction of methane emissions.

A swamp forest in Peru.
Rupesh Bhomia, Author provided

The net effect — carbon dioxide vs methane — would make our climate warmer. This will seriously hamper global efforts to keep temperature rise under 1.5℃.

This suggests if sustainable developments to restore these ecosystems aren’t implemented in future, drying peatlands would add the equivalent of 860 million tonnes of carbon dioxide to the atmosphere every year by 2100. This projection is for a “high emissions scenario”, which assumes global greenhouse gas emissions aren’t cut any further.

Protecting our peatlands

It’s not too late to stop this from happening. In fact, many countries are already establishing peatland restoration projects.

For example, the Central Kalimantan Peatlands Project in Indonesia aims to rehabilitate these ecosystems by, for instance, damming drainage canals, revegetating areas with native trees, and improving local socio-economic conditions and introducing more sustainable agricultural techniques.

Likewise, the Life Peat Restore project aims to restore 5,300 hectares of peatlands back to their natural function as carbon sinks across Poland, Germany and the Baltic states, over five years.

But protecting peatlands is a global issue. To effectively take care of our peatlands and our climate, we must work together urgently and efficiently.




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People, palm oil, pulp and planet: four perspectives on Indonesia’s fire-stricken peatlands


The Conversation


Yuanyuan Huang, Research Scientist , CSIRO and Yingping Wang, Chief research scientist, CSIRO

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

Spiders are cloaking Gippsland with stunning webs after the floods. An expert explains why


Darren Carney

Lizzy Lowe, Macquarie UniversityStunning photographs of vast, ghostly spider webs blanketing the flood-affected region of Gippsland in Victoria have gone viral online, prompting many to muse on the wonder of nature.

But what’s going on here? Why do spiders do this after floods and does it happen everywhere?

The answer is: these webs have nothing to do with spiders trying to catch food. Spiders often use silk to move around and in this case are using long strands of web to escape from waterlogged soil.

This may seem unusual, but these are just native animals doing their thing. It’s crucial you don’t get out the insecticide and spray them. These spiders do important work managing pests, so by killing them off you would be increasing the risk that pests such as cockroaches and mosquitoes will get out of control.




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Using silk to move around

What you’re seeing online, or in person if you live locally, is an amazing natural phenomena but it’s not really very complicated.

We are constantly surrounded by spiders, but we don’t usually see them. They are hiding in the leaf litter and in the soil.

Spider webs blanket the ground in Gippsland
When floods happen, spiders use silk to evacuate quickly.
Darren Carney

When these flood events happen, they need evacuate quickly up out of holes they live in underground. They come out en masse and use their silk to help them do that.

You’ll often see juvenile spiders let out a long strand of silk which is caught by the wind and lifted up. The web catches onto another object such as a tree and allows the spider to climb up.

That’s how baby spiders (spiderlings!) disperse when they emerge from their egg sacs — it’s called ballooning. They have to disperse as quickly as possible because they are highly cannibalistic so they need to move away from each other swiftly and find their own sites to hunt or build their webs.

Small spiders have been seen on a post in Gippsland after floods.
AAP Image/JEFF HOBBS

That said, I doubt these webs are from baby spiders. It is more likely to be a huge number of adult spiders, of all different types, sizes and species. They’re all just trying to escape the flood waters. These are definitely spiders you don’t usually see above ground so they are out of their comfort zone, too.

This mass evacuation of spiders, and associated blankets of silk, is not a localised thing. It is seen in other parts of Australia and around the world after flooding.

It just goes to show how versatile spider silk can be. It’s not just used for catching food, it’s also used for locomotion and is even used by some spiders to lay a trail so they don’t get lost.

Don’t spray them!

The most important thing I need readers to know is that this is not anything to be worried about. The worst thing you could do is get out the insecticide and spray them.

These spiders are making a huge contribution to pest control and you would have major pest problems if you get rid of all the spiders. The spiders will disperse on their own very quickly. In general, spiders don’t like being in close proximity to each other (or humans!) and they want to get back to their homes underground.

If you live in Gippsland, you probably don’t even need to clear the webs away with a broom. There’s no danger in doing so if you wish, but I am almost certain these webs will disperse on their own within days.

Until then, enjoy this natural spectacle. I wish I could come down to see them with my own eyes!




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The Conversation


Lizzy Lowe, Researcher, Macquarie University

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

Bones and all: see how the diets of Tasmanian devils can wear down their sharp teeth to blunt nubbins


Zoos Victoria, Author provided

Tahlia Pollock, Monash University; Alistair Evans, Monash University; David Hocking, Monash University, and Marissa Parrott, The University of MelbourneTasmanian devils are expert scavengers, with strong jaws and robust teeth that give them the notorious ability to eat almost all of a carcass — bones and all.
Scientists have even found echidna spikes in their poo.

But regularly crunching through bone comes at a cost: extreme tooth wear. In our new study, we analysed the skulls of nearly 300 devils, and show how regularly crunching through bones wears a devil’s teeth down from sharp-edged weapons to blunt nubbins.

Tasmanian devils are endangered and their wild population is continuing to decline. A key part of conserving this marsupial is by maintaining healthy and happy devils in captivity.

Understanding how their food affects their teeth can help us see if captive devils have the same types of tooth wear as their wild counterparts, and look for signs of any unusual or harmful wear.

Is there anything a devil won’t eat?

Tasmanian devils are the largest marsupial carnivore alive today. As scavengers, they occupy a unique niche in the Australian ecosystem by disposing of dead animal carcasses.

Devil standing over a dead carcass
Captive Tasmanian devils are given a variety of foods to replicate what they’d find in the wild. This photo was taken during a carcass feed at Healesville Sanctuary.
Zoos Victoria, Author provided

Devils are highly opportunistic and can eat many different types of prey. While their favourites are the carcasses of native mammals such as wombats and wallabies, they’ll also eat reptiles, amphibians, birds, fish, and even insects.

We know this because we find hair, feathers, scales, small bones, claws and more in their poo.

Almost nothing is off limits to devils — they’ll even have a go at a stranded whale given the chance. Although devils prefer to scavenge, they’re also accomplished hunters.




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But due to a transmissible cancer, devil facial tumour disease, wild numbers of these remarkable marsupials have plummeted by around 80%.

Right now, 45 Australian zoos and wildlife sanctuaries, plus an island and a fenced peninsula, are collaborating to maintain a healthy population of disease-free devils. It’s important for these institutions to provide captive animals with the right kinds of food for their health and to help make their future release back to disease-free wild locations successful.

Devils naturally wear their teeth down from sharp points and edges to blunt, almost flat surfaces by regularly eating bones.
Tahlia Pollock, Author provided

This is especially crucial for carnivores, who rely on tough foods to help them develop strong jaws.

Like hyaenas, but stronger

The types of food an animal eats will wear their teeth down differently. For example, big cats such as lions prefer to eat the softer parts of a carcass, like flesh or organs, and leave the bones behind.

Spotted hyaenas, however, will happily eat the bones. As a result, hyaenas have incredibly high tooth wear compared with lions.

This might not hinder the hyaena or devil as much as you might think. Both have very strong jaws that can compensate for the loss of sharp teeth. In fact, devils have the strongest bite force per body weight of any living mammal.

In the interactive below, you can check out 3D models of devil skulls to get a better idea of how much their teeth wear down.

Comparing wild and captive diets

By comparing the tooth wear of wild and captive devils, we can see if captive animals are encountering enough hard foods in their diets.

In the Save the Tasmanian Devil Program — an initiative of the federal and Tasmanian governments — captive devils are given a variety of small and large foods at different times, replicating what they’d find in the wild.

We found no signs of different or harmful tooth wear in captive devils, and they showed much the same patterns and types of wear as wild devils.




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However, we noticed captive devils wore their teeth more slowly than those in the wild. This may be due to eating higher quality food, such as carcasses that were fresh, whole, and yet to be scavenged.

This means captive institutions are doing a good job of providing devils with the right types of food for their teeth and encouraging wild behaviours.

Part of the health check for wild devils involves looking at their teeth. This particular devil has nice sharp tips and edges on their canines and molars.
Marissa Parrott/Zoos Victoria, Author provided

Collecting data about Tassie devils after they’ve been released confirms this. In 2012 and 2013, devils were released onto Maria Island in Tasmania after being born and raised for around a year in captivity.

Encouragingly, these devils kept the behaviours required to scavenge and hunt prey, and had diets similar to wild devils.

How you can help save Tasmanian devils

Our research is one small, but promising, piece in the overall puzzle. While captive research and breeding programs help conserve the Tasmanian devil, there are ways you can help, too.

Because they like to scavenge the carcasses of dead animals, road kill is especially tempting for devils. But being so close to the road is dangerous and road mortality is the second-biggest killer of wild devils.

So take care on the roads to help wildlife, especially if driving at night. And if you’re in Tasmania and see a devil that’s been hit on the road, log it in the Roadkill TAS app.

This will help identify road kill hotspots and protect this impressive, but endangered, species.




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The Conversation


Tahlia Pollock, PhD candidate, Monash University; Alistair Evans, Associate Professor, Monash University; David Hocking, Curator of Vertebrate Zoology and Palaeontology at the Tasmanian Museum and Art Gallery (TMAG) | Adjunct Research Associate at Monash University, Monash University, and Marissa Parrott, Reproductive Biologist, Wildlife Conservation & Science, Zoos Victoria, and Honorary Research Associate, BioSciences, The University of Melbourne

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

DIY habitat: my photos show chainsaw-carved tree hollows make perfect new homes for this mysterious marsupial


William Terry, Author provided

William Terry, Southern Cross UniversityEnvironmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique photos from the field.


As a result of logging and severe bushfires, Australian wildlife is facing a severe shortage of tree hollows — holes in the trunks and branches of large old trees. More than 300 species of birds and mammals, including possums, bats, cockatoos, owls and kookaburras, rely on tree hollows for shelter or breeding.

A sacred kingfisher using a natural tree hollow for nesting.
William Terry

In Australia, hollows are usually formed through the decay of a tree scar, and it can take hundreds of years for tree hollows big enough for medium-sized animals to form naturally.

This includes phascogales — the rat-sized, carnivorous marsupials that live in open woodlands across Australia and are the focus of my research and photography. But like many of Australia’s forest-dwelling mammals, phascogales are vulnerable to extinction.

So with hollows becoming harder to find, I venture into forests and study how well artificial hollows, made with chainsaws, can replace them. And, incredibly, it’s working: my research shows phascogales and other native animals are enthusiastically moving into the new real estate.

Meet the mysterious brush-tailed phascogale

Phascogales are an important species to Australia but, unfortunately, their cryptic behaviour and nocturnal habits mean people rarely see them.

Brush-tailed phascogales live in trees, but will come to the ground to forage for food among leaf litter and fallen timber.
William Terry
Phascogales belong to the same family as the Tasmanian devil, quoll (pictured) and the tiny antechinus.
William Terry, Author provided

Phascogales feed on insects after stripping bark from eucalypts. But through my close interactions and radio tracking, I’ve documented phascogales eating other more unusual foods, including bird eggs and sometimes even small birds, such as grey-shrike thrush.

I’ve also recorded them taking dead birds, such as the rosella pictured below. They even have a reputation among farmers as being a fierce chicken killer, but this may be exaggerated.

A phascogale inspects a dead crimson rosella it found at the base of a tree. Moments later, this phascogale dragged the bird away. It was unclear what happened next.
William Terry

Phascogales have an unusual life. Shortly after mating between April and May, all males die at about 11 months of age from stomach ulcers. This frees up resources for the next generation of young joeys that will emerge from the nest in early summer.

But will they survive in the future?

Tragically, at least one species, the brush-tailed phascogale, is threatened with extinction, primarily due to habitat loss, climate change, and feral predators such as foxes and cats.

The brush-tailed phascogale (Phascogale tapoatafa tapoatafa) occurs across the eastern side of Australia, from southern Queensland to Victoria. It’s now extinct in South Australia.

Likewise, the much smaller red-tailed phascogale (Phascogale calura) once survived across a vast swathe of land from Western Australia to Victoria. Today, it survives only in small pockets in the Western Australia wheatbelt.

Brush-tailed phascogales were once known as ‘bottle-brush squirrels’, due to the stunning resemblance of its tail to the iconic native flowers.
William Terry
The red-tailed phascogale has been lost from much of its former range and now only exists in the Western Australian wheatbelt.
William Terry, Author provided

Household cats are a particularly major issue for phascogales, and many cat owners in central Victoria have a story about their cat bringing home a phascogale (so please keep your pet cat inside at all times).




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Last year, research confirmed climate change would reduce the available areas phascogales could survive. This research found areas with a phascogale-friendly climate would decline by up to 79% in Queensland, 67% in Victoria and 17% in NSW, by 2070.

Climate change also threatens to bring longer, more frequent and severe heatwaves. For phascogales and many other mammals, this could be a death sentence.

Tree hollows with thick walls can protect the animals sheltering inside from the high temperatures outside.

But these are getting increasingly rarer, and this is where my research on chainsaw hollows comes in. Thick-walled hollows may be very important for the long-term survival of phascogales and other species in a warming climate.

A relative to the phascogale, the tiny agile antechinus commonly uses tree hollows on the ground.
William Terry, Author provided

Carving them a home

A chainsaw hollow is a cavity constructed inside a tree. A faceplate is then attached over the top, with a hole drilled into it for the animal to enter. They offer refuge for Australia’s endangered mammals and birds.

For our project, we carved 45 chainsaw hollows in dry forests and woodland where phascogales are known to occur. We also installed similar-sized nest boxes — which are more commonly used to offset the loss of hollows — on nearby trees. We monitored these for two and a half years.

A chainsaw hollow constructed for phascogales.
William Terry, Author provided
Chainsaw hollow creation is a specialised skill. Here, tree climber Lachlan installs a chainsaw hollow on a red ironbark tree.
William Terry, Author provided

Research from 2018 shows nest boxes offer little protection from outside temperatures. I’ve collected data, which is not yet published, that confirms this.

My research shows chainsaw hollows provide 27% more protection from extreme temperatures during heatwaves compared to nest boxes, which provided almost no protection.




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Two phascogales peeking out of a nest box.
William Terry, Author provided

So it’s no wonder we observed and recorded phascogales and the more common sugar glider (Petaurus notatus) more frequently sheltering in chainsaw hollows than in nearby nest boxes.

Other animals used the chainsaw hollows, too. This includes the feather-tailed glider, yellow-footed antechinus, and the white-throated treecreeper.

Brush-tailed phascogale inspects a chainsaw hollow.
Sugar gliders also frequently used chainsaw hollows.
William Terry

But like nest boxes, the chainsaw hollows showed signs they would be only an interim measure, requiring maintenance with bark growing over entrance holes and issues with a buildup of moisture.

In any case, further research into this species is needed, as it will aid land managers to conserve this enigmatic species as more challenges are thrown their way into the future.




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Photos from the field: the stunning crystals revealing deep secrets about Australian volcanoes


The Conversation


William Terry, PhD Researcher, Supervision by Associate Prof. Ross Goldingay, Southern Cross University

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