How the size and shape of dried leaves can turn small flames into colossal bushfires


Shutterstock

Jamie Burton, University of Melbourne; Alexander Filkov, University of Melbourne, and Jane Cawson, University of Melbourne

The 2020-21 fire season is well underway, and we’ve watched in horror as places like K’gari (Fraser Island) burn uncontrollably, threatening people and their homes and devastating the environment.




Read more:
The K’gari-Fraser Island bushfire is causing catastrophic damage. What can we expect when it’s all over?


To lessen the impact of fires, we need to know when they are likely to burn and how intensely. Central to this is the flammability of litter beds — the layer of dead leaves, needles, twigs and bark on the forest floor.

Every large fire begins as a small fire, igniting and initially spreading through the litter bed, but what makes some litter beds more flammable than others?

Aerated litter beds fuel bigger fires

Over the past few years, fire scientists across the world have been busy tackling this burning question. In tropical forests in the Amazon, oak forests in North America and eucalypt woodlands in Australia, they have been collecting leaf litter beds and burning them in the laboratory to understand why litter beds from some plant species burn differently to others.

Each of these studies focused on leaf litter beds made up of a single species, and each identified a range of drivers of flammability. These drivers relate to both the characteristics of the individual litter particle (leaf, needle or branch) and the litter bed itself.




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Our new research sought to consolidate these studies to find the common drivers of flammability between different single-species litter beds from different parts of the world.

From our meta-analysis, we found “litter packing” and “litter bulk density” were key factors in litter bed flammability.

Litter packing is a measure of how many gaps are between the dried leaves, needles and branches, and is important for determining how much air is available for burning. Likewise, litter bulk density is a measure of how much litter there is, and is important for determining how quickly and how long litter burns.

Oak tree litter bed
The litter bed from oak trees. The curly leaves create air gaps throughout the litter bed, which lead to bigger fires.
Jamie Burton, Author provided

We found loosely packed litter beds spread fire faster, burned for shorter periods of time and were more consumed by the flames. Importantly, we found this was universal across different types of litter beds.

We also identified the characteristics of leaves, needles and branches that cause variations in litter packing and litter bulk density.

For example, if the litter particles are “curly” and have a high surface area to volume ratio, then they’ll form litter beds with low packing ratios which burn faster and have higher consumption. Examples include leaves from some oak (Quercus) species.




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Tree ferns are older than dinosaurs. And that’s not even the most interesting thing about them


At the opposite end, small and less curly leaves form densely packed litter beds which are less aerated. Examples include coast tea tree (Leptospermum laevigatum) and conifers with small needles such as Larix and Picea. This results in slower moving fires, which do not consume all the litter.

For eucalypt litter beds, things are a little more complicated. Some species have thick and flat leaves which pack densely, so fire spreads more slowly and less litter is consumed. Other species, such as the southern blue gum (Eucalyptus globulus), have larger leaves which tend to pack less densely, so fires burn more quickly with taller flames.

Eucalyptus litter bed
The litter bed of eucalyptus trees.
Jamie Burton, Author provided

How can this information help us manage fires?

Of course, under extreme fire weather conditions, any litter bed will burn. However, at the beginning of a fire or under mild conditions, differences in litter characteristics may strongly influence how that fire spreads. Research on this can be useful for many aspects of fire management and planning.

For example, if we know which plants produce less flammable litter, we can select them for planting around houses, landscaping in fire-prone areas and also use them as green firebreaks to reduce the risk to people and homes. If a fire was to start, it may spread less quickly and be less intense, making it easier to contain and put out.

_Allocasuarina_ needle litter
Allocasuarina species with long thin needles tend to pack loosely, leading to faster flame spread and shorter burning times.
Jamie Burton, Author provided

But also it may not be that straightforward. When deciding which species to plant, the flammability of living plants needs to be considered, as well. Some plants that have less flammable litter may actually be highly flammable as a living plant. For example, although coast tea tree may form densely packed litter beds, the high oil content in the leaves makes it highly flammable as a living plant.

Our findings could also be used for predicting fire behaviour. For example, our results could be integrated into fire behaviour models, such as the Forest Flammability Model, which uses information on the composition and structure of the plant community to predict fire behaviour.

Next steps

Our study provides information on what leaf and litter characteristics affect flammability in litter beds composed of a single species. But in many forests, litter beds are made up of a variety of plant species, and more research is needed to understand what happens to litter packing and flammability in these multi-species litter beds.

Sydney red gum
The bark of the Sydney red gum tends to take longer to ignite, but burns for longer than its leaves.
Shutterstock

Besides different species, litter beds also contain different components such as twigs and bark. For example, in a mature wet eucalypt forest, bark and twigs can make up to 44% of the litter bed.

And for some eucalypt species, we already know bark burns differently to leaves. For example, the flaky bark of the Sydney red gum (Angophora costata) tends to take longer to ignite, but burns for a longer time compared to its leaves.

With fires becoming more frequent and fire seasons becoming longer, research into litter bed flammability has never been more needed.




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The Conversation


Jamie Burton, PhD Candidate, University of Melbourne; Alexander Filkov, Senior research fellow, University of Melbourne, and Jane Cawson, Research Fellow in Bushfire Behaviour and Management, University of Melbourne

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

The Tasmanian tiger was hunted to extinction as a ‘large predator’ – but it was only half as heavy as we thought



Smithsonian Institution/colourised by D.S. Rovinsky

Douglass Rovinsky, Monash University; Alistair Evans, Monash University, and Justin W. Adams, Monash University

Until it was hunted to extinction, the thylacine – also known as the Tasmanian tiger or Tasmanian wolf – was the world’s largest marsupial predator. However, our new research shows it was in fact only about half as large as previously thought. So perhaps it wasn’t such a big bad wolf after all.

Although the thylacine is widely known as an example of human-caused extinction, there is a lot we still don’t know about this fascinating animal. This even includes one of the most basic details: how much did the thylacine weigh?

An animal’s body mass is one of the most fundamental aspects of its biology. It affects nearly every facet of its biology, from biochemical and metabolic processes, reproduction, growth, and development, through to where the animal can live and how it moves.

For meat-eating predators, body mass also determines what the animal eats – or more specifically, how much it has to eat at each meal.

Catching and eating other animals is hard work, so a predator has to weigh the costs carefully against the benefits. Small predators have low hunting costs – moving around, hunting, and killing small prey doesn’t cost much energy, so they can afford to nibble on small animals here and there. But for bigger predators, the stakes are higher.

Almost all large predators – those weighing at least 21  kilograms – focus their efforts on prey at least half their own body size, getting more bang for the buck. In contrast, small predators below 14.5 kg almost always catch prey much smaller than half their own size. Those in between typically take prey less than half their size, but sometimes switch to a larger meal if some easy prey is there for the taking – or if the predator is getting desperate.

The mismeasure of the thylacine

Scan of article from Launceston Examiner
The March 14, 1868 edition of the Launceston Examiner featured tales of a ‘hyena’ that managed to kill 25 sheep.
trove.nla.gov.au

Few accurately recorded weights exist for thylacines – only four, in fact. This lack of information has made estimating their average size difficult. The most commonly used average body mass is 29.5kg, based on 19th-century newspaper accounts.

This suggests the thylacine would probably have taken relatively large prey such as wallabies, kangaroos and perhaps sheep. However, studies of thylacine skulls suggest they didn’t have strong enough skulls to capture and kill large prey, and that they would have hunted smaller animals instead.

This presented a problem: if the thylacine was as big as we thought, it shouldn’t be able to live solely on small prey. But what if we’ve had the weight wrong the whole time?




Read more:
Why did the Tasmanian tiger go extinct?


Weighing an extinct animal

Man taking a scan of a stuffed thylacine
Ben Myers of Thinglab scans a Museums Victoria thylacine.
CREDIT, Author provided

Our new research, published today in Proceedings of the Royal Society B, addresses this weighty issue. Our team travelled throughout the world to museums in Australia, the United States, the United Kingdom and Europe, and 3D-scanned 93 thylacines, including whole mounted skeletons, taxidermy mounts, and the only whole-body ethanol-preserved thylacine in the world, in Sweden.

Based on these scans, we created new equations to estimate a thylacine’s mass, based on how thick their limbs were – because their legs would have had to support their entire weight.

We also compared the results of these equations with a new method of digitally weighing 3D specimens. Based on a 3D scan of a mounted skeleton, we digitally “filled in the spaces” to estimate how much soft tissue would have been present, and then used our new formula to calculate how much this would weigh. Taxidermy mounts were easier as there was no need to infer the amount of soft tissue. The most artistic member of our team digitally sculpted lifelike thylacines around the scanned skeletons, and we weighed them, too.

Building and weighing a thylacine. Scanned skeletons (lop left) were surrounded by digital ‘convex hulls’ (top right), which then had their volume and mass calculated. The skeletons were then used in digitally sculpting lifelife models (bottom left), each with their own unique stripes (bottom right).
Rovinsky et al.

Our calculations unanimously told a very different story from the 19th-century periodicals, and from the commonly used estimate. The average thylacine weighed only about 16.7 kg – not 29.5 kg.




Read more:
Friday essay: on the trail of the London thylacines


Tall tales on the tiger trail

This means the previous estimate, based on taking 19th-century periodicals at face value, was nearly 80% too large. Looking back at those old newspaper reports, many of them in retrospect have the hallmarks of “tall tales”, told to make a captured thylacine seem bigger, more impressive and more dangerous.

It was based on this suspected danger that the thylacine was hunted and trapped to extinction, with private bounties already placed on them by 1840, and government-sponsored extermination by the 1880s.

Graphic showing the size of thylacines relative to a woman
Thylacines were much smaller in stature than humans or grey wolves.
Rovinsky et al., Author provided

The thylacine was much smaller than previously thought, and this aligns with the smaller prey size suggested by the earlier studies. Predators below 21 kg – in which we should now include the thylacine – all tend to hunt prey smaller than half their size. The “Tasmanian wolf” probably wasn’t such a danger to Tasmanian farmers’ sheep after all.

By rewriting this fundamental aspect of their biology, we are closer to understanding the role of the thylacine in the ecosystem – and to seeing exactly what was lost when we deliberately hunted it to extinction.The Conversation

Douglass Rovinsky, PhD Candidate, Monash University; Alistair Evans, Associate Professor, Monash University, and Justin W. Adams, Senior Lecturer, Department of Anatomy and Developmental Biology, Monash University

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

How big is the Moon? Let me compare …



The size of the Moon can be deceptive when viewed from Earth.
Flickr/Ovi Gherman, CC BY-NC-ND

Jonti Horner, University of Southern Queensland

Even though we can see the Moon shining brightly in the night sky – and sometimes in daylight – it’s hard to put into perspective just how large, and just how distant, our nearest neighbour actually is.

So just how big is the Moon?

The Moon passing in front of Earth, captured by the Earth Polychromatic Imaging Camera (EPIC), more than a million kilometres away from our planet.

That answer isn’t quite as straightforward as you might think. Like Earth, the Moon isn’t a perfect sphere. Instead, it’s slightly squashed (what we call an oblate sphereoid). This means the Moon’s diameter from pole to pole is less than the diameter measured at the equator.




Read more:
Why the Moon is such a cratered place


But the difference is small, just four kilometres. The equatorial diameter of the Moon is about 3,476km, while the polar diameter is 3,472km.

To see how big that is we need to compare it to something of a similar size, such as Australia.

From coast to coast

The distance from Perth to Brisbane, as the crow flies, is 3,606km. If you put Australia and the Moon side by side, they look to be roughly the same size.

The Moon vs Australia.
NASA/Google Earth

But that’s just one way of looking at things. Although the Moon is about as wide as Australia, it is actually much bigger when you think in terms of surface area. It turns out the surface of the Moon is much larger than that of Australia.

The land area of Australia is some 7.69 million square kilometers. By contrast, the surface area of the Moon is 37.94 million square kilometres, close to five times the area of Australia.

The Moon rising above Uluru: You’d need five Australias to cover the land mass of the Moon.
Flickr/jurek d Jerzy Durczak, CC BY-NC

How far is the Moon?

Asking how far away is the Moon is another of those questions whose answer is more complicated than you might expect.

The Moon moves in an elliptical orbit around the Earth, which means its distance from our planet is constantly changing. That distance can vary by up to 50,000km during a single orbit, which is why the size of the Moon in our sky varies slightly from week to week.

Notice the difference in size? The Moon viewed from Earth at perigee (closest approach at 356,700km on October 26 2007) and apogee (farthest approach at 406,300km on April 3 2007).
Wikimedia/Tomruen, CC BY-SA

The Moon’s orbit is also influenced by every other object in the Solar System. Even when all of that is taken into account, the distance answer is still always changing, because the Moon is gradually receding from the Earth as a result of the tidal interaction between the two.

That last point is something we’ve been able to better study as a result of the Apollo missions. The astronauts who visited the Moon placed an array of mirror reflectors on its surface. Those reflectors are the continual target of lasers from the Earth.

By timing how long it takes for that laser light to travel to the Moon and back, scientists are able to measure the distance to the Moon with incredible precision, and to track the Moon’s recession from Earth. The result? The Moon is receding at a speed of 38mm per year – or just under 4 metres per century.

Drive me to the Moon

Having said all that, the average distance between the Moon and Earth is 384,402km. So let’s put that into context.

If I were to drive from Brisbane to Perth, following the fastest route suggested by Google, I would cover 4,310km on my road trip. That journey, driving across the breadth of our country, would take around 46 hours.

The full Moon rising over the Perth Hills, in Western Australia, in 2016.
Paean Ng/Flickr, CC BY-NC-ND

If I wanted to clock up enough kilometres to say that I’d covered the distance between the Earth and the Moon, I’d have to make that trip more than 89 times. It would take five-and-a-half months of driving, non-stop, assuming I didn’t run into any traffic jams on the way.

Fortunately, the Apollo 11 astronauts weren’t restricted to Australian speed limits. The command module Columbia took just three days and four hours to reach lunar orbit following its launch on July 16 1969.

An eclipse coincidence

The equatorial diameter of the Sun is almost 1.4 million kilometres, which is almost exactly 400 times the diameter of the Moon.

That ratio leads to one of astronomy’s most spectacular quirks – because the distance between the Earth and the Sun (149.6 million kilometres) is almost (but not quite) 400 times the distance between the Earth and the Moon.




Read more:
Explainer: what is a solar eclipse?


The result? The Moon and the Sun appear almost exactly the same size in Earth’s sky. As a result, when the Moon and the Sun line up perfectly, as seen from Earth, something wonderful happens – a total eclipse of the Sun.

The total solar eclipse seen from north Queensland in November 2012.

Sadly, such spectacular eclipses will eventually come to an end on Earth. Thanks to the Moon’s recession, it will one day be too distant to perfectly obscure the Sun. But that day will be a long time coming, with most estimates suggesting it will occur in something like 600 million years’ time.

The moonwalkers

While we’ve dispatched out robot envoys to the icy depths of the Solar System, the Moon remains the only other world on which humanity has walked.

Astronaut Buzz Aldrin was the second man to walk on the Moon and one of the few moonwalkers still alive today.
NASA

Fifty years after that first adventure, the number of people to have walked on the Moon who are still alive is in sharp decline. Twelve people have had that experience but, as of today, just four remain.




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Five ethical questions for how we choose to use the Moon


Vast as the Moon is, those 12 moonwalkers barely scratched the surface. Hopefully, in the coming years, we will return, to inspire a whole new generation and to continue humanity’s in-person exploration of our nearest celestial neighbour.The Conversation

The Moon over the Sydney Opera House.
Flickr/Paul Carmon, CC BY-NC-ND

Jonti Horner, Professor (Astrophysics), University of Southern Queensland

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

New research unlocks the mystery of leaf size



File 20170831 9971 75oye6
Leaf sizes vary according to a complex mix of temperature and water.
Peter Wilf/Supplied

Ian Wright, Macquarie University

Why is a banana leaf a million times bigger than a common heather leaf? Why are leaves generally much larger in tropical jungles than in temperate forests and deserts? The textbooks say it’s a balance between water availability and overheating.

But new research, published today in Science, has found it’s not that simple. Actually, in much of the world the key limiting factor for leaf size is night temperature and the risk of frost damage to leaves.

As a plant ecologist, I try to understand variation in plant traits (the physical, chemical and physiological properties of their tissues) and how this variation affects plant function in different ecosystems.


Read more: How we found out there are three trillion trees on Earth


For this study I worked with 16 colleagues from Australia, the UK, Canada, Argentina, the US, Estonia, Spain and China to analyse leaves from more than 7,600 species. We then teamed the data with new theory to create a model that can predict the maximum viable leaf size anywhere in the world, based on the dual risks of daytime overheating and night-time freezing.

These findings will be used to improve global vegetation models, which are used to predict how vegetation will change under climate change, and also to better understand past climates from leaf fossils.

Conifers, which grow in very cold climates, grow thin needles less vulnerable to frost.
Peter Reich

From giants to dwarfs

The world’s plant species vary enormously in the typical size of their leaves; from 1 square millimetre in desert species such as common eutaxia (Eutaxia microphylla), or in common heather (Calluna vulgaris) in Europe, to as much as 1 square metre in tropical species like Musa textilis, the Filipino banana tree.

But what is the physiological or ecological significance of all this variation in leaf size? How does it affect the way that plants “do business”, using leaves as protein-rich factories that trade water (transpiration) for carbon (photosynthesis), powered by energy from the sun?

More than a century ago, early plant ecologists such as Eugenius Warming argued that it was the high rainfall in the tropics that allowed large-leaved species to flourish there.

In the 1960s and ‘70s physicists and physiologists tackled the problem, showing that in mid-summer large leaves are more prone to overheating, requiring higher rates of “transpirational cooling” (a process akin to sweating) to avoid damage. This explained why many desert species have small leaves, and why species growing in cool, shaded understoreys (below the tree canopy) can have large leaves.

Rainforest plants under the tree canopy can grow huge, complex leaves.
Ian Wright

But still there were missing pieces to this puzzle. For example, the tropics are both wet and hot, and these theories predicted disadvantages for large-leafed species in hot regions. And, in any case, overheating must surely be unlikely for leaves in many cooler parts of the world.

Our research aimed to find these missing pieces. By collecting samples from all continents, climate zones and plant types, our team found simple “rules” that appear to apply to all of the world’s plant species – rules that were not apparent from previous, more limited analyses.

We found the key factors are day and night temperatures, rainfall and solar radiation (largely determined by distance from the Equator and the amount of cloud cover). The interaction of these factors means that in hot and sunny regions that are also very dry, most species have small leaves, but in hot or sunny regions that receive high rainfall, many species have large leaves. Finally, in very cold regions (e.g. at high elevation, or at high northern latitudes), most species have small leaves.

Understanding the mechanisms behind leaf size means leaf fossils – like these examples from the Eocene – can tell us more about climates in the past.
Peter Wilf/Supplied

But the most surprising results emerged from teaming the new theory for leaf size, leaf temperature and water use with the global data analyses, to investigate what sets the maximum size of leaves possible at any point on the globe.

This showed that over much of the world it is not summertime overheating that limits leaf sizes, but the risk of frost damage at night during cold months. To understand why, we needed to look at leaf boundary layers.

Every object has a boundary layer of still air (people included). This is why, when you’re cold, the hair on your arms sticks up: your body is trying to increase the insulating boundary of still air.

Larger leaves have thicker boundary layers, which means it is both harder for them to lose heat under hot conditions, and harder to absorb heat from their surroundings. This makes them vulnerable to cold nights, where heat is lost as long-wave radiation to the night-time sky.

So our research confirmed that in very hot and very dry regions the risk of daytime overheating seems to be the dominant control on leaf size. It demonstrated for the first time the broad importance of night-time chilling, a phenomenon previously thought important just in alpine regions.

Still, in the warm wet tropics, it seems there are no temperature-related limits to leaf size, provided enough water is available for transpirational cooling. In those cases other explanations need to be considered, such as the structural costs and benefits of displaying a given leaf area as a few large leaves versus many more, smaller leaves.

The view from a canopy crane at the Daintree in Queensland.
Peter Wilf

These findings have implications in several fields. Leaf temperature and water use play a key role in photosynthesis, the most fundamental plant physiological function. This knowledge has the potential to enrich “next-generation” vegetation models that are being used to predict regional-global shifts in plant nutrient, water and carbon use under climate change scenarios.

These models will aid the reconstruction of past climates from leaf macrofossils, and improve the ability of land managers and policymakers to predict the impact of a changing climate on the range limits to native plants, weeds and crops.

The ConversationBut our work is not done. Vegetation models still struggle to cope with and explain biodiversity. A key missing factor could be soil fertility, which varies both in space and time. Next, our team will work to incorporate interactions between soil properties and climate in their models.

Ian Wright, Associate Professor in the Department of Biological Sciences, Macquarie University

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

Haiti: Plan to Replant Forests


The link below is to an article concerning Haiti’s plan to replant its forests and double the size of them by 2016.

For more visit:
http://www.guardian.co.uk/world/2013/mar/28/haiti-plant-millions-trees-deforestation

Blackbutt Reserve


Kevin's Daily Photo, Video, Quote or Link

Since I was unable to visit Gap Creek Falls the other day, I decided I might pop in to have a look at the new animal enclosures at Blackbutt Reserve near Newcastle. I will say straight off the bat that I do have something of a prejudice against Blackbutt Reserve, as I see the place as nothing like a natural bush setting, it being far too ‘corrupted’ by human activity, weeds and the like. Having said that it is a good place for a family or group outing/event. It certainly has its place, but it is not a true nature reserve (in my opinion).

Visitor Centre

ABOVE: Visitor Centre

I do think that some well designed animal and bird enclosures at Blackbutt could lift the value of the reserve dramatically and make it a really great place for families, especially young families. There are opportunities for educational visits for kids, possible environmental…

View original post 182 more words

Antarctica: Grand Canyon Landscape Fuelling Ice Melt


The link below is to a very interesting article concerning a landscape buried beneath the Antarctic ice that is similar to the Grand Canyon in size. It also plays a significant role in the current Antarctic ice melt.

For more visit:
http://www.bbc.co.uk/news/science-environment-18959399

Africa: Kavango Zambezi Transfrontier Conservation Area


The link below is to an article on the Kavango Zambezi Transfrontier Conservation Area (KAZA), established in 2011 by Angola, Botswana, Namibia, Zambia and Zimbabwe. It is a huge conservation area the size of Italy.

For more visit:
http://news.nationalgeographic.com/news/travelnews/2012/03/pictures/120327-africa-parks-conservation/

Australian Wilderness Adventures: Episode 001 – Cathedral Rock National Park


Today I have uploaded the first episode in what will be a growing series of documentary-like videos for my YouTube channel (Kevin’s Wilderness Journeys). This series of videos will focus on national parks and reserves in Australia (especially New South Wales), with a view to providing useful information for people who may be interested in visiting the national park being considered in any particular episode. I am hoping to provide a preview of the main attractions in each national park and the facilities available for visitors. Hopefully these will whet the appetite for those who view the videos and provoke a desire to actually visit the national parks under consideration.

This first episode focuses on the Cathedral Rock National Park, with a look at the Cathedral Rock Track and the Woolpack Rocks Track. There will be more episodes to come, including episodes on Dorrigo National Park, Bongil Bongil National Park and Myall Lakes National Park – among others. Hopefully in time better equipment will improve the quality of videos available – but none-the-less, I do think the videos are useful to some degree as they are.

The actual size of the video I have in my archives for the first video is 2.85 GB, so there is a fair reduction in file size (and therefore quality) to get the videos online and within the limits of YouTube file sizes and length.