Rainforest giants with rare autumn displays: there’s a lot more to Australia’s red cedar than timber


Peter Woodard/Wikimedia

Gregory Moore, The University of MelbourneNative deciduous trees are rare in Australia, which means many of the red, yellow and brown leaves we associate with autumn come from introduced species, such as maples, oaks and elms.

One native tree, however, stands out for its leaves with soft autumnal hues that drop in March and April: Australia’s red cedar. Don’t be fooled by its common name — red cedar is not a cedar at all, but naturally grows in rainforests throughout Southeast Asia and Australia.

You may be more familiar with its timber, which I’ve been acquainted with all of my life. My grandmothers had cedar chests of drawers they had inherited from their mothers or grandmothers, and I had assumed they were made from one of the Northern hemisphere cedar species. The wood still smelled of cedar after all this time in family homes – a scent I associate with grandparents and country homes.

By the time I was given one of these chests to restore, I knew much more about the tree and valued the chest of drawers all the more. So, with autumn putting a spotlight on Australian red cedars, let’s look at this species in more detail.

Majestic giants of the rainforest

I first encountered red cedar trees in the sub-tropical rainforests of Queensland and New South Wales in the 1980s. Then, its scientific name was called Cedrela toona and later Toona australis. Now, it’s recognised as Toona ciliata.

The various names reflect a taxonomic history in which the Australian species was once regarded as being separate from its Asian relatives, but all are now considered one.

Two red cedars in a rainforest
Native red cedar trees can grow up to 60m tall.
Shutterstock

The trees are awe-inspiring. Under the right conditions, it can grow to 60 metres tall (occasionally more) with a trunk diameter of up to 7m.

After losing its foliage in autumn, the new foliage in spring often has an attractive reddish tinge. In late spring it has small (5 milimetres) white or pale pink flowers, but they usually go unnoticed in the rainforest because of their height or the density of other tree canopies growing beneath.

Older red cedars have wonderful buttresses at the base of their trunk, a characteristic shared by many tall tropical trees. These buttresses have long been considered an advantage for species that can emerge above the canopy of a rainforest where winds are much stronger, with the buttresses and expanded root systems providing greater strength and resistance to the wind.

These buttresses also greatly increase the surface area of the base of the trees exposed to air, which facilitates the uptake of extra oxygen as the activity of micro-organisms in the soil can leave it oxygen-depleted.

White flowers against the leaves of red cedar
Tiny white flowers are hard to see from the ground in a rainforest.
Forest and Kim Starr/Wikimedia, CC BY-SA

Logged to near extinction

With a wide distribution throughout Asia and Australia, its uses in ancient times were many and varied. In traditional medicine, bark was used or digestive remedies as well as wound dressing and its resin was used for treating skin conditions.

Dyes, oils and tannins used for preparing leather could also be extracted by boiling various plant parts. Today the wood is used for culturing shiitake mushrooms, which are much in demand in restaurants.

But the recent history of red cedar is a typically sad colonial tale. The species belongs to the same family as mahogany (Meliaceae) and, not surprisingly, was exploited for its timber from the early days of colonisation.

Red cedar bannister
You can find red cedar timber in many public buildings across Australia.
denisbin/Flickr, CC BY-ND

The timber is durable, lightweight and suitable for naval use and so was very heavily logged, right along the east coast of Australia from the early 1800s until the early 20th century.

The rich deep red colour of its timber and the fact it was soft and easily worked meant it was used for furniture, ornate carvings in public buildings, town halls and parliaments, such as the State Library in Melbourne. It was also used for implements and handles, and for sailing and racing boats.




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You’ve probably had a close encounter with the lovely red banisters on some of these old buildings that were made of red cedar, often darkened under the patina of so many hands.

The once common and widespread species was logged almost to extinction along the east coast by the mid-1900s, and to the point of practical commercial extinction with little timber available to industry by the 1960s.

So valued was the timber that in the late 1970s, a plan was hatched to remove red cedar from Queensland National Park rainforests using helicopters. Luckily, the idea did not fly and so some great trees persist. The species has a conservation status of concern, but is not considered to be endangered at present.

Leaves of the Toona ciliata
The leaves of red cedar begin to fall in late March.
Peter Woodard/Wikimedia

A terrible pest

The fact they are deciduous makes them potentially very interesting and useful for horticultural use, but that potential remains largely unrealised. And given the value and quality of its timber, you may be wondering why it’s not being grown in plantations across the continent.

The reason is a native moth called the cedar tip moth (Hypsipyla robusta), which lays its eggs on the main growing shoot of the tree. When the eggs hatch the larvae bore down the shoot, which not only results in shoot dieback but also causes the trees to develop multiple stems and branches which reduce its timber value.




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Despite this, they are still planted as a quick-growing ornamental tree for their shade in other parts of the world, such Hawaii and Zimbabwe.

The moths are attracted to the scent of the tree, so they’re very difficult to control. The moth does not attack the tree in South America, for instance, because the moth has not established there, so there are large plantations of red cedar in Brazil.

It’s an interesting reminder: often it’s the little things in ecology that can affect success, or failure. When we humans meddle without knowledge, things don’t necessarily go to plan, usually to our cost.




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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.

An unexpected consequence of climate change: heatwaves kill plant pests and save our favourite giant trees



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Gregory Moore, University of Melbourne

Australia is sweltering through another heatwave, and there will be more in the near future as climate change brings hotter, drier weather. In some parts of Australia, the number of days above 40℃ will double by 2090, and with it the tragedy of more heat-related deaths.

In the complex world of plant ecology, however, heatwaves aren’t always a bad thing. Rolling days of scorching temperatures can kill off plant pests, such as elm beetles and mistletoe, and even keep their numbers down for years.

This is what we saw after the 2009 heatwave that reached a record 46.4℃ in Melbourne and culminated in the catastrophic Black Saturday bushfires. Years later, the trees under threat from the pest species were thriving. Here are a few of our observations.

Saving red gums from mistletoe

In the days following Black Saturday, botanists, horticulturists and arborists noticed a curious heatwave side-effect: the foliage of native Australian mistletoes (Amyema miquelii and A. pendula species) growing on river red gums lost their green colour and turned grey.

The two species of mistletoe are important in the ecology of plant communities and to native bird and insect species. But infestation on older trees can lead to their deaths, particularly in drought years.

Australian mistletoe is not related to the northern hemisphere mistletoes of Christmas kissing fame. They are water and nutrient parasites on their host tree and can kill host tissues through excessive water loss.

A eucalyptus tree trunk covered in leaves on a dried brown grass
The native mistletoe, Amyema miquelii, strangles this eucalyptus coolabah in the Burke River floodplain.
John Robert McPherson/Wikimedia, CC BY-SA

Often mistletoes go largely unnoticed, only becoming obvious when they flower. This is because many have evolved foliage with a superficial resemblance to the host species, a phenomenon known as host mimicry or “crypsis”.

During the Black Saturday heatwave, many mistletoes growing on river red gums died. The gums not only survived, but when record rains came in 2010, they thrived. A decade on, the mistletoe numbers are gradually increasing, but they’re still not high enough to threaten the survival of older, significant red gums.




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We want both mistletoes and red gums to persist. But often the old red gums are last survivors of larger populations that have been cleared — a seed source for future regeneration.

Under-appreciated elms

In many parts of Australia, the exotic English and Dutch elms are important parts of the landscapes of cities and regional towns. Elms provide great shade, are resilient and often low-maintenance. They also provide important environmental services, such as nesting sites for native mammals and birds.

Indeed, as Dutch elm disease decimates elm populations across North America and Europe, Australia can claim to have many of the largest elms and the grandest elm avenues and boulevards in the world, which we often under-appreciate.

A street lined by tall elms
Australia is home to some of the most beautiful elm avenues in the world.
denisbin/Flickr, CC BY-ND

But sadly, over the past 30 years the grazing of the elm leaf beetle, Xanthogaleruca luteola, has threatened the grandeur of our elms. These beetles can strip leaves to mere skeletons, and while the damage doesn’t usually kill the tree, it can make them look unsightly.

On Black Saturday, tens of thousands of elm leaf beetles fell from trees after prolonged exposure to high temperature. So many died, they formed what looked like a shadow under the tree canopies. Beetle numbers remained low for at least five years after that.




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Control programs, which often involve spraying chemical pesticides, were not required in that five year period. This was good for the environment as the chemicals can affect non-target sites and species. And we calculated that this saved well over A$2 million for Melbourne alone, money that could be better spent on parks and gardens (and of course, the elms looked splendid!).

Our iconic Moreton Bay figs

Then there are our magnificent, iconic Moreton Bay figs (Ficus macrophylla). Their large, glossy leaves, huge trunks, veils of aerial roots and massive canopies spread for more than 40 metres, and make them an Australian favourite.

Moreton Bay figs are prone to insect infestations of the psyllid, Mycopsylla fici, which can seriously defoliate trees under certain conditions. The fallen leaves can also stick to the shoes of pedestrians, causing a slipping hazard.

In Melbourne, psyllid numbers that were high before Black Saturday fell to undetectable levels in the following month.

Once again, a heatwave and hot windy weather had done an unexpected service. The incidence of psyllids has remained low for a decade or more now and, as with elm leaf beetles, control measures proved unnecessary and money was saved.

An enromous Moreton Bay fig trunk in a park
Moreton Bay figs are prone to insect infestations.
Shutterstock

Winners and losers

Many urban trees are renowned for their resilience to stress, both natural and human-caused. Climate change is proving a significant stress to be overcome, but we’ve observed how the stress can affect pests and disease species more than their hosts.

This gives the species growing in very tough urban conditions, where they lack space and are often deprived of water and good soils, a slight advantage, which may be the difference between living and dying under climate change.




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Climate change is bringing far more losses than gains. But, occasionally, there will be wins, and those managing pests in our urban forests must take advantage when they present.

If insect pest numbers fall we can direct resources to establishing more trees and ensuring our trees are healthier. The best way to avoid pests and diseases attacking trees is by providing the best possible growing conditions. That way we avoid problems before they arise rather than treating symptoms.

So as you swelter during this heatwave, remember it may not be all bad news for our urban and natural environments. Sometimes, positive outcomes arise when and where we least expect them.




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The Conversation


Gregory Moore, Doctor of Botany, University of Melbourne

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

‘Like finding life on Mars’: why the underground orchid is Australia’s strangest, most mysterious flower



Rhizanthella speciosa from Barrington Tops.
Author provided

Mark Clements, CSIRO

If you ask someone to imagine an orchid, chances are pots of moth orchids lined up for sale in a hardware store will spring to mind, with their thick shiny leaves and vibrant petals.

Moth orchids with purple flowers in a pot
Orchids like this may be what comes to mind when you think of them, but there are actually more 30,000 different orchid species.
Shutterstock

But Australia’s orchids are greater in number and stranger in form than many people realise. Rock orchids, fairy orchids, butterfly orchids, leek orchids and even onion orchids all look more or less the same. But would you recognise a clump of grass-like roots clinging to a tree trunk as an orchid?

What about a small, pale tuber that spends its whole life underground, blooms underground and smells like vanilla? This is the underground orchid, Rhizanthella, and it’s perhaps the strangest Australian orchid of them all.

Even to me, having spent a lifetime researching orchids, the idea of a subterranean orchid is like finding life on Mars. I never expected to even see one, let alone have the privilege of working on them.

Known for almost a century, but rarely seen

The family Orchidaceae is the largest group of flowering plants on Earth, comprising more than 30,000 species. Australia is home to around 1,550 species and 95% are endemic, meaning they don’t occur naturally anywhere else in the world.

Rhizanthella has been known to science since 1928, when a farmer in Western Australia who was ploughing mallee for wheat fields noticed a number of tuber-like plants among the roots of broom bushes. Recognising them as unusual, he sent some specimens to the Western Australian Herbarium.

The species Rhizanthella gardneri occurs in Western Australia.
Fred Hort/Flickr, CC BY-SA

In 1931, another underground orchid was discovered in eastern Australia at Bulahdelah in NSW by an orchid hunter who was digging up a hyacinth orchid and found an unusual plant tangled in its roots. Three quarters of a century later, I was involved in conserving the population of Rhizanthella in this location when the Bulahdelah bypass was built.

And most recently, in September, I confirmed an entirely new species of underground orchid, named Rhizanthella speciosa, after science illustrator Maree Elliott first stumbled upon it four years ago in Barrington Tops National Park, NSW.

Elliott’s discovery brings the total number of Rhizanthella species known to science to five, with the other two from eastern Australia and two from Western Australia.

The pink flower head of the _Rhizanthella speciosa_
The newly discovered species, Rhizanthella speciosa, found in Barrington Tops.
Mark Clements, Author provided

All species are vulnerable

For much of its life, an underground orchid exists in the soil as a small white rhizome (thickened underground stem). When it flowers, it remains hidden under leaf litter and soil close to the surface, its petals think and pink, its flower head a little larger than a 50 cent coin.




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Its pollinator is probably a tiny fly that burrows down to lay eggs in the orchid, mistaking the flower for a fungus.

Today, all Rhizanthella species are vulnerable: the species R. gardneri and R. johnstonii are listed as critically endangered under national environment laws, while R. slateri and and R. omissa are listed as endangered. The most recently discovered species hasn’t yet been listed, but its scarcity means it’s probably highly vulnerable.

Rhizanthella speciosa. The seeds of underground orchids are like ball bearings, and the fruits smell like vanilla.
Mark Clements, Author provided

The conservation of the underground orchid is complicated. Knowing where it exists, and where it doesn’t, is one problem. Another is knowing how to grow it.

All orchid species need a buddy, a particular soil fungus, for their seeds to germinate, and Rhizanthella must have its habitat to survive. Unfortunately, it’s extremely difficult to just grow it in a pot.

Seeds like ball bearings

We also know very little about the biology of Rhizanthella. But here’s what we do know.

We’ve discovered the fungus that buddies up with underground orchids in Western Australia is indeed the same as that in eastern Australia. We know underground orchids tend to grow in wetter forests and that burning will kill them. And we know that after pollination, the seed head of an underground orchid takes 11 months to mature.

The floral structures of four described species of _Rhizanthella_
The floral structures of four described species of Rhizanthella: (a) R. slateri (b) R. omissa (c) R. johnstonii (d) R. gardneri
Chris J. Thorogood, Jeremy J. Bougoure et Simon J. Hiscock/Wikimedia, CC BY-SA

Most orchids have wind-dispersed seeds. Some are so light that drifting between Queensland and Papua New Guinea might be possible, and might explain its vast distribution.

The seeds of underground orchids, however, are like ball bearings and the fruits smell like the famous vanilla orchid of Mexico, whose seeds and pods add scent and flavour to everything from candles to ice cream.

In nature, bats disperse the seeds of the vanilla orchid. So we set up infra-red cameras in Bulahdelah as part of the bypass project to find out what animals might disperse the seeds of the underground orchid. We observed swamp wallabies and long-nosed bandicoots visiting the site where R. slateri grows.

We suspect they disperse the seeds of underground orchids via their excrement, finding the orchid among truffles and other goodies in the leaf litter and soil of the forest floor.

A swamp wallaby in the bush
Swamp wallabies and long-nosed bandicoots may disperse the underground orchid seeds, but they’re locally extinct in WA.
Shutterstock

In Western Australia, these animals are locally extinct. Without bandicoots and wallabies to transport seeds away from the parent plant, the natural cycle of renewal and establishment of new plants has been broken. This cannot be good for the long-term survival of the two Western Australian Rhizanthella species.

An alien in the floral world

Conservation of the underground orchid might require intricate strategies, such as reintroducing bandicoots to a protected area, preventing bushfires and using alternatives to burning to manage the land.

An important first step is to find more populations of underground orchids to help us learn more about them.

Leek orchid
A leek orchid.
Shutterstock

Our work with DNA has shown, in the orchid family tree, Rhizanthella is most closely related to leek orchids (Prasophyllum) and onion orchids (Microtis).

But as you can see from the photo of a leek orchid above, it bears no resemblance to a subterranean flower, like an alien in the floral world.




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The Conversation


Mark Clements, Botanist, CSIRO

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

Snow in summer: when this tree begins to bloom, count down the days to Christmas



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Gregory Moore, University of Melbourne

Often in the lead up to Christmas, the tree with the curious common name “snow in summer” is in full bloom.

Snow in summer (Melaleuca linariifolia) is an Australian paperbark, and is endemic to parts of Queensland and New South Wales. It has spikes of creamy white flowers that grow in dense clusters at the ends of branches and twigs. When in profusion, they look very much like snow-capped foliage.

It intrigued me as a youngster and, not surprisingly, I associated it with Christmas and the images of the snowy festivals of the northern hemisphere, which were such a contrast to our own experiences.




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Depending where you live, Melaleuca linariifolia tends to flower from late October until February, but in many parts of Australia they are in full flower in December. Once they start, however, you must be quick to catch sight of them — the impressive flower show doesn’t last more than a couple of weeks.

Hear the hum of insects

Naturally, snow in summer often grows near water and rivers, and can reach heights of ten to 12 metres (but is often lucky to make it to eight metres).

Close-up of snow in summer flowers
The flowers attract native birds and bees.
Greg Moore, Author provided

Its dense canopy provides excellent habitat for native birds and mammals such as honey-eaters and possums, as it offers protection and great nesting sites. The nectar in its flowers attracts native birds, bees and other insects, and if you wander past when it’s in full bloom, you can hear the hum of insect visitors.




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The fruits develop as hard woody capsules, which only release their seed after a fire or when they dry out. They are like little woody cups about five millimetres across, glued to the woody branches.

Like all paperbarks, the bark of snow in summer is wonderfully spongy and can be quite thick. You can peel it off in sheets, draw and write on it. It also had uses for Indigenous peoples, who would wrap the strips of bark around fish or meat and then bury the food under sand or soil for slow cooking.

Paperbark trunk
The thick, spongy bark of Melaleuca linariifolia can be easily torn off in large strips.
John Robert McPherson/Wikimedia, CC BY-SA

From farms and nature strips to pharmacies

As far back as the 1970s, snow in summer was planted in urban nature strips and as an effective landscape screening plant. While many of those 1970s nature strip trees are gone, those that remain still put on quite a show.

They were also planted widely as a wind break on farms because of its low growing habit and dense canopy. But farmers may have been left disappointed as the trees burnt well in fires and tended to collapse as they reached the end of their useful lives, which could be as short as 20 years.

It has been widely used horticulturally and there are compact forms, such as those named “snowstorm” and “sea foam”, that grow only to about two metres and make hardy garden shrubs.

Snow in summer trees along nature strips
Snow in summer is native to eastern Australia, but has been planted widely elsewhere, such as in California, US.
John Rusk/Flickr, CC BY

For the gardeners, Melaleuca linariifolia is easy to propagate from both cuttings and seed. It has quite an extensive root system that can cause problems if you have leaky pipes. They love water — in fact, they’re what botanists call “luxury water users”, and have little or no control of how much water they take from the soil.

They grow well in almost any soil and it doesn’t matter if they’re occasionally waterlogged, as they tolerate periods of inundation. If you want a plant that will drain a swamp, Melaleucas in general are up for it.

Like many members of the Myrtaceae family — which includes eucalypts and tea tree — Melaleuca linariifoliais are rich in essential oils. One of these, Terpinen-4-ol is found in high concentrations in snow in summer and is an antioxidant and powerful antiseptic.

It can be used as disinfectant and to treat skin problems as it is non-irritant. There is great scientific interest at the moment in its use in anti-bacterial and anti-viral medicines.

Fluffy flowers of snow in summer
Snow is summer typically blooms for only around two weeks every year.
Shutterstock

By any other name

Just to avoid confusion, some of you may know of other plants as snow in summer. The most common is Cerastium tomentosum, which is a low growing ground cover with small white trumpet-like flowers. It is a southern European plant, but has been widely planted in gardens around the world. Likewise, Melaleuca alternifolia is also called snow in summer and was once considered to be a variety of Melaleuca linariifolia.




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Melaleuca linariifolia was one of the first plants I planted in my own first (and only) backyard in the late 1970s.

I always anticipated its flowering and would make sure our children saw the flowers, explained why it was called snow in summer and usually noted the number of days to Christmas. It is one of the trees they remember still.The Conversation

Gregory Moore, Doctor of Botany, University of Melbourne

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

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


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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.




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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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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.

Australia-first research reveals staggering loss of threatened plants over 20 years


Ayesha Tulloch, University of Sydney; Elisa Bayraktarov, The University of Queensland; Hugh Possingham, The University of Queensland; Jaana Dielenberg, Charles Darwin University; Jennifer Silcock, The University of Queensland; Micha Victoria Jackson, The University of Queensland, and Nathalie Butt, The University of Queensland

When it comes to threatened species, charismatic animals usually get the most attention. But many of Australia’s plants are also in grave danger of extinction, and in many cases, the problem is getting worse.

New Australia-first research shows the population sizes of our threatened plants fell by almost three-quarters, on average, between 1995 and 2017. The findings were drawn from Australia’s 2020 Threatened Species Index, which combines data from almost 600 sites.

Plants are part of what makes us and our landscapes unique. They are important in their own right, but also act as habitat for other species and play critical roles in the broader ecosystem.

This massive data-crunching exercise shows that a lot more effort is needed if we want to prevent plant extinctions.

Plants, such as WA’s Endangered Foote’s grevillea, make our landscape unique.
Andrew Crawford / WA Department of Biodiversity Conservation and Attractions

Spotlight on plants

Australia’s plant species are special – 84% are found nowhere else in the world. The index shows that over about 20 years up to 2017, Australia’s threatened plant populations declined by 72%. This is faster than mammals (which declined by about a third), and birds (which declined by about half). Populations of trees, shrubs, herbs and orchids all suffered roughly similar average declines (65-75%) over the two decades.

Of the 112 species in the index, 68% are critically endangered or endangered and at risk of extinction if left unmanaged. Some 37 plant species have gone extinct since records began, though many others are likely to have been lost before scientists even knew they existed. Land clearing, changed fire regimes, grazing by livestock and feral animals, plant diseases, weeds and climate change are common causes of decline.




Read more:
Undocumented plant extinctions are a big problem in Australia – here’s why they go unnoticed


Vulnerable plant populations reduced to small areas can also face unique threats. For example, by the early 2000s Foote’s grevillea (Grevillea calliantha) had dwindled to just 27 wild plants on road reserves. Road maintenance activities such as mowing and weed spraying became a major threat to its survival. For other species, like the button wrinklewort, small populations can lead to inbreeding and a lack of genetic diversity.

Fire, interrupted

Threatened plant conservation in fire-prone landscapes is challenging if a species’ relationship with fire is not known. Many Australian plant species require particular intensities or frequencies of burns for seed to be released or germinate. But since European settlement, fire patterns have been interrupted, causing many plant populations to decline.

Three threatened native pomaderris shrubs on the NSW South Coast are a case in point. Each of them – Pomaderris adnata, P. bodalla and P. walshii – have failed to reproduce for several years and are now found only in a few locations, each with a small number of plants.

Experimental trials recently revealed that to germinate, the seeds of these pomaderris species need exposure to hot-burning fires (or a hot oven). However they are now largely located in areas that seldom burn. This is important knowledge for conservation managers aiming to help wild populations persist.

Endangered sublime point pomaderris (Pomaderris adnata) requires high fire temperatures to germinate.
Jedda Lemmon /NSW DPIE, Saving our Species

Success is possible

A quarter of the species in the threatened plant index are orchids. Orchids make up 17% of plant species listed nationally as threatened, despite comprising just 6% of Australia’s total plant species.

The endangered coloured spider-orchid (Caladenia colorata) is pollinated only by a single thynnine wasp, and relies on a single species of mycorrhizal fungi to germinate in the wild.

Yet even for such a seemingly difficult species, conservation success is possible. In one project, scientists from the Royal Botanic Gardens Victoria, aided by volunteers, identified sites where the wasp was still naturally present. More than 800 spider orchid plants were then propagated in a lab using the correct symbiotic fungus, then planted at four sites. These populations are now considered to be self-sustaining.

In the case of Foote’s grevillea, a plant translocation program has established 500 plants at three new sites, dramatically improving the species’ long-term prospects.

Orchid flower
The coloured spider orchid, found in South Australia and Victoria, is endangered.
Noushka Reiter/Royal Botanic Gardens Victoria

But we aren’t doing enough

Both federal environment laws and the national threatened species strategy are under review. Submissions by research institutions and others have noted a lack of data, recovery actions and conservation funding for plants.

Our research found threatened plant populations at managed sites suffered declines of 60% on average, compared to 80% declines at unmanaged sites. This shows that while management is beneficial, it is not preventing overall declines.

New data on threatened species trends are added to the plant index each year, but many species are missing from the index because they aren’t being monitored.




Read more:
Australia’s threatened birds declined by 59% over the past 30 years


Monitoring of threatened species is undertaken by government and non-government groups, community groups, Indigenous organisations, citizen scientists, researchers and individuals. Without it, we have no idea if species are recovering or heading unnoticed towards extinction.

Woman measuring the height of a plant
Monitoring is essential to know if conservation actions are working.
Rebecca Dillon / WA Department of Biodiversity Conservation and Attractions

Australia has about 1,800 threatened species. Of these, 77% – or 1,342 species – are plants. However the index received monitoring data for only 10% of these plants, compared to 35% of threatened birds, which make up only 4% of threatened species.

If you’re keen to get involved in plant monitoring, it involves just a few simple steps:

  • find a local patch with a threatened plant species

  • revisit it once or twice a year to count the number of individuals in a consistent, well-defined area

  • use the same method and the same amount of effort each visit

  • take great care to not disturb the plant or its habitat when looking for it

  • contribute your data to the index.

Saving Australia’s flora

Australia must urgently change the way we prioritise conservation actions and enact environment laws, if we hope to prevent more plant extinctions.

Critical actions include stopping further habitat loss and more funding for recovery actions as well as extinction risk assessments. It is important that these assessments adhere to consistent criteria. This is something the common assessment method, agreed to by all states and territories, seeks to achieve.

Finally, more funding for research into the impacts of key threats (and how to manage them) will help ensure our unique flora are not lost forever.

Prof Hugh Possingham and Dr Ayesha Tulloch discuss the 2020 findings of the Threatened Plant Index.

CORRECTION: A previous version of this article incorrectly stated that reviews of federal environment laws and the threatened species strategy found a lack of data, recovery actions and conservation funding for plants. While those problems were identified in public submissions to the reviews, the reviews themselves are not yet finalised.The Conversation

Ayesha Tulloch, DECRA Research Fellow, University of Sydney; Elisa Bayraktarov, Postdoctoral Research Fellow in Conservation Biology, The University of Queensland; Hugh Possingham, Professor, The University of Queensland; Jaana Dielenberg, University Fellow, Charles Darwin University; Jennifer Silcock, Post-doctoral research fellow, The University of Queensland; Micha Victoria Jackson, Postdoctoral research fellow, The University of Queensland, and Nathalie Butt, Postdoctoral Fellow, The University of Queensland

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

Tiny treetop flowers foster incredible beetle biodiversity



Hundreds of beetle species seem to be specialists that feed only from small white flowers on trees.
Susan Kirmse, CC BY-ND

Caroline S. Chaboo, University of Nebraska-Lincoln

The Research Brief is a short take on interesting academic work.

The big idea

Biologists have long known that rainforest treetops support a huge number of beetle species, but why these canopies are so rich in beetle diversity has remained a mystery. New research by my colleague Susan Kirmse and me shows that flowering trees play a critical role in maintaining this diversity, and that beetles may be among the most diverse pollinators in the animal kingdom.

We carried out a one-year study in a remote part of the Amazon rainforest in Venezuela. We used a specially built crane to collect a total of 6,698 adult beetles representing 859 species. These were gathered from 45 individual trees of 23 different tree species.

We were surprised to discover that the majority of these beetles – 647, or 75.3% of species found – were living on flowering trees. In fact, 527 beetle species in 41 families were associated exclusively with flowers. Interestingly, the majority of these species – almost 60% – were exclusively found on trees that produce lots of small white flowers.

Overall, this discovery shows that flowering trees are likely among the most important drivers for maintaining the high diversity of beetles in rainforests. But this relationship goes both ways. Our study also suggests that beetles may be among the most underappreciated pollinators in tropical forests.

A tall metal structure emerging from the forest canopy in Venezuela.
Using a specialized crane, the team was able to collect beetles from the very top of the forest canopy.
Susan Kirmse, CC BY-ND

Why it matters

Tropical rainforests are the very heart of Earth’s biodiversity. They harbor about 65% to 75% of all terrestrial species, including the most tree species and the most insects.

After finding such a tight relationship between beetles and flowering trees, we wondered: How many beetle species could be involved in pollination in the Amazon? Our study found an average of 26.35 unique beetle species for every species of tree. With an estimated 16,000 Amazonian tree species, this suggests that there might be more species of flower-visiting beetles than any other insects on Earth, potentially surpassing by far the 20,000 species of bees and the 19,000 species of butterflies.

Our study shows that flowering tree species play an important role as diversity hotspots in tropical rainforest canopies. For policymakers and biologists hoping to preserve or restore rainforests, promoting the cultivation of trees and other plants – especially those with lots of small white flowers that beetles love – could help to maintain species-rich communities. Flowers are a very important resource, providing food and shelter for thousands of insects in addition to beetles. Thus, preserving plant diversity or selecting many different indigenous tree species for reforestation can enhance the diversity of insects.

An image of a iridescent green-blue beetle.
Beetles like the Griburius auricapillus are just some of the hundreds of species that can be found in treetops.
Susan Kirmse, CC BY-ND

What still isn’t known

Our research was the first to describe this tight relationship between beetles and rainforest trees, especially with trees that produce thousands of small, simple flowers. But how this association came to be is still unclear.

Many of the beetle species were found only on trees with this particular type of flower. The trees get an obvious benefit: pollination. But what specifically these trees offer to the beetles requires further study. The simpler flowers are easier for beetles to access, but is the appeal food, like petals, pollen or nectar? Or maybe a home to find mates or lay eggs for the young to grow?

[You’re smart and curious about the world. So are The Conversation’s authors and editors. You can get our highlights each weekend.]

What’s next

To fight the worldwide rapid declines in insect diversity, researchers and conservationists must understand the ecological connections between insects and their food plants. Long-term studies, particularly in research plots like the one we used in Venezuela, allow researchers to collect layers of information that help unravel the complexity of diversity.

Yet such sites rely on political interest and stability. Political instability in Venezuela is preventing our fieldwork from continuing at the Venezuela plot.

While we can’t return to our study site in Venezuela, it is clear that researchers must work together to understand the mysteries of life on Earth. But biologists are racing the clock as large rainforests are destroyed forever.The Conversation

Caroline S. Chaboo, Adjunct Professor in Insect Systematics, University of Nebraska-Lincoln

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

Silky oaks are older than dinosaurs and literally drip nectar – but watch out for the cyanide



Shutterstock

Gregory Moore, University of Melbourne

As we come to the end of spring, look up from the footpath or at the park, and you may spot the fiery flowers of the silky oak, Grevillea robusta.

You may already be familiar with grevilleas – perhaps you have low- growing ground cover and shrub species in your garden.

Some people love the brilliant red, yellow, orange or white flowers of grevilleas. They’re also nesting and roosting havens for small native birds, and so people may plant them to attract wildlife.

Of all the grevillias, the silky oak is the one that catches my eye. It’s the largest and tallest of the species, reaching up to 30 metres. They’re now blooming along the east coast and in some inland places – like huge orange light bulbs dominating the skyline.

A bird feeding on silky oak flower
Silky oaks flowers are a magnet for birds and insects.
Shutterstock

Strong like oak

Grevilleas have an ancestry older than dinosaurs. They originated on the super-continent Gondwana, and are closely related to banksias, waratahs and proteas.

Today, the 360 species of grevilleas occur in Indonesia and Australia and are a diverse group. Their colourful, distinctive flowers lack petals and instead consist of a long tube known as a “calyx”, which splits into four “lobes”.




Read more:
Spring is here and wattles are out in bloom: a love letter to our iconic flowers


Like most other grevillea, silky oak possesses proteoid or cluster roots, which are dense and fine. These roots greatly increase the absorbing surface area and allow plants to thrive in nutrient-deprived soils.

The word “robusta” refers to the fact that the timber is strong like real oak. The freshly split wood has a silky texture, and a pattern and light colour resembling English oak – hence the common name “silky oak”.

Silky oak timber
Grevillia robusta has a silky texture when split for timber.
Shutterstock

Watch out for the cyanide

Grevilleas literally drip nectar, much to the delight of native birds and bees. Aboriginal people enjoyed the sweet nectar straight from the plant or mixed with water — the original lolly water.

But you have to know which species to taste as some, including the silky oak, contain hydrogen cyanide that could make you ill.

Like other grevilleas the silky oak also contains tridecyl resorcinol, which causes an allergic reaction leading to contact dermatitis. The chemical is similar to the toxicodendron in poison ivy.

So when working with silky oaks, you’d be wise to wear gloves, a face mask, protective eye wear (or face shield) and long sleeved clothing. Washing hands and showering at the end of the day is also recommended.

gardening gloves
Wear gardening gloves when handling silky oak, just to be one the safe side.
Shutterstock

A prized timber

Silky oak timber was widely used in colonial times. Then it was marketed as “lacewood”, and that name persists today among some who use it.

Silky oak veneer was used widely in colonial table tops and other furniture. Over the years, silky oak has also been used to make window frames because it is resistant to wood rot.

Overseas, silky oak timber is still widely grown, in timber plantations and as windbreaks.




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


But it’s not widely available in Australia, due to low market demand – the allergens and cyanide it contains means people are generally reluctant to work with it. However silky oak is still highly prized by those who make guitars, and wood turners who make bowls and cabinets.

Painted silky oak window frames
Silky oak timber is rot-resistant and was often used in window frames.
Shutterstock

In the garden

Although an evergreen tree, some specimens are almost semi-deciduous, losing most of their foliage just prior to flowering.

Some specimens of silky oak can be a bit scraggly in their canopy form. They can benefit enormously from a bit of formative pruning when they are young, and perhaps some structural pruning from a good arborist as they get older. A little attention at the right time will be amply rewarded with a safe and great looking tree that can live for 150 years or more.

Silky oak is drought-tolerant. In dry times they often flower a bit later than their usual October blooming, providing a big splash of colour in otherwise drab and difficult years.

The trees can be vulnerable to frost when young, but grow well once taller. This makes the silky oak a potential winner as climate change brings warmer, drier weather.

Silky oaks have been declared an environmental weed in parts of New South Wales and Victoria where it grows outside its native distribution range. They’re also considered an invasive or invader plant in Hawaii and South Africa. However Grevillea robusta is declining in its natural rainforest/wet forest habitat.

In some cities in China, silky oaks have been planted along roadsides with great success. The tree has also gained the Royal Horticultural Society’s Award of Garden Merit for its performance in growing under United Kingdom conditions. That just shows you how one person’s weed is another’s treasure.




Read more:
The river red gum is an icon of the driest continent


The Conversation


Gregory Moore, Doctor of Botany, University of Melbourne

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

Discovering New Flowering Plants Species While Bushwalking in Australia


The link below is to an article that looks at discovering new flowering plant species while bushwalking in Australia.

For more visit:
https://www.lifehacker.com.au/2020/09/find-new-species-of-daisies-on-your-aussie-bushwalks/