Keeping the city cool isn’t just about tree cover – it calls for a commons-based climate response



Where’s the shade? Trees are not an immediate or whole answer to keeping cool.
Cameron Tonkinwise, Author provided

Abby Mellick Lopes, Western Sydney University and Cameron Tonkinwise, University of Technology Sydney

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.


A recent report by the Greater Sydney Commission singles out urban heat as one of four priority areas given our coming climate. It identifies tree canopy as the top response for reducing city temperatures and delivering amenity. However, the public conversation about urban heat often misses the complex relationship between trees, people and the built environment, which challenges this response.

In soon-to-be-published research supported by the Landcom University Roundtable we found that responding to a more extreme climate requires new social practices and new relationships with the commons. Commons are the spaces, resources and knowledge shared by a community, who are, ideally, involved in the regeneration and care of those commons. Trees are an important social commons, but they also present multiple challenges.




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Closing our doors to the great outdoors

For one, trees are an outdoor amenity, but we are spending more and more time indoors. For those who can afford it, air conditioning delivers cooling in the privacy of your own home or car – no need for trees.

However, staying in cool bedrooms and car rides mean less time outdoors and with others, which isn’t ideal for human health and well-being.




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Air conditioning also uses more fossil-fuel-based energy, which generates more greenhouse gas emissions. The result is more climate change.

Mixed feelings about trees

As the Greater Sydney Commission report makes clear, tree canopy in Greater Sydney is roughly proportional to household wealth. The “leafy suburbs” are the wealthier ones. This means tree planting is an important investment in less wealthy parts of the city, which experience more extreme heat days.

Number of days over 35°C recorded in various parts of Greater Sydney (July 2018-June 2019).
© State of NSW through the Greater Sydney Commission



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However, research also shows people have mixed feelings about trees. In comparison to the neat shrubbery and easily maintained sunny plazas we’ve become used to in our cities, trees can be “messy” and “unpredictable”. Leaf litter can be slippery and natives like eucalypts, with their pendulous leaves, provide limited shade. People worry about large trees falling over or dropping branches.

Trees are often at the centre of disputes between neighbours. They can also be perceived as a security problem – if trees reduce visibility they might provide cover for wrongdoers.

In addition, insurance companies can charge a premium if a property is deemed at risk of damage by large trees. As we experience more extreme weather, laws on vegetation clearing are becoming more risk-averse.




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What trees where and when?

Urban development tends to give priority to roads and delivering the maximum number of dwellings on sites. This leaves little space for trees, which need to fit into crowded footpaths with ever-changing infrastructures. For example, will larger trees interfere with 5G?

When juggling priorities in the streetscape, trees often lose out.




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It’s an obvious point, but trees take time to grow. It can take many years for a planted sapling to become a shade tree. In that time there will be no shelter from the heat.

Also in that growing period, which can sometimes be unpredictable, trees need to be nurtured, especially in times of drought. And, once the tree is mature, fingers crossed that extreme weather events do not undo all those years of waiting.

So, while increasing tree canopy sounds like an obvious solution, trees are in fact a complex social challenge. In our research, we point to ways some of these tree-related tensions can be managed.

Shade in the meantime

A structure to support fast-growing vines has been built on one of Darwin’s hottest streets, but even these will take some time to grow.
Darwin We Love It/Facebook

Shade is an important civic resource. Large, mature trees with spreading canopy provide the best shade, so strategic construction bans and tree preservation orders are an obvious first step.

However, if shady canopy is decades off, we need to think about other, creative ways to provide shade in the meantime to ensure, for example, that people of diverse abilities can walk their city in reasonable comfort. This might include temporary shade structures such as awnings, bus shelters and fast-growing vine-trellised walkways (if there is space to create troughs for soil and the structure doesn’t cause access problems).

And, as the Cancer Council consistently reminds us, we all need to adopt more climate-defensive clothing.




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An important alternative is to follow our regional neighbours and start to populate parks and other public spaces at night. This suggests a need for removable shade, so we can take part in activities like stargazing.

Cultivating an intergenerational commons

Mature trees can die back or die altogether, so other trees should be maturing to take their place. Usually, experts design and maintain landscapes for others to enjoy.

However, users of the cooling services of parks could be invited into the process of planning and realising landscape designs. This would give them a say on the trees of which they have “shared custody”. Planting for succession can create an intergenerational sense of ownership over a shared place.

Current planning practices tend to ignore wind and solar patterns. The result is urban forms that make heat worse by prioritising comfortable private interior spaces over the commons of public space. Designing cool cities means using trees, water and buildings to create cool corridors that work with cooling breezes – or even summon these in still, heat-trapping basins like Western Sydney.




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These few examples point to new ways of living with trees as social commons, but they also point to new forms of commoning – collaborative forms of care and governance that invite people to adopt new social practices better suited to living well in the coming climate.

It is a positive step that state development agencies like Landcom aim to demonstrate global standards of liveability, resilience, inclusion, affordability and environmental quality. In so doing, they initiate transitions to these more commons-based ways of living.


In addition to the authors of this article, the Cooling the Commons research team includes: Professor Katherine Gibson, Dr Louise Crabtree, Dr Stephen Healy and Dr Emma Power from the Institute for Culture and Society (ICS) at Western Sydney University (WSU), and Emeritus Professor Helen Armstrong from Queensland University of Technology (QUT).The Conversation

Abby Mellick Lopes, Senior Lecturer in Design, Western Sydney University and Cameron Tonkinwise, Professor, School of Design, University of Technology Sydney

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

When tree planting actually damages ecosystems



Giraffes prefer the open space and scattered trees of the African savanna.
Volodymyr Burdiak/Shutterstock

Kate Parr, University of Liverpool and Caroline Lehmann, University of Edinburgh

Tree planting has been widely promoted as a solution to climate change, because plants absorb the climate-warming gases from Earth’s atmosphere as they grow. World leaders have already committed to restoring 350m hectares of forest by 2030 and a recent report suggested that reforesting a billion hectares of land could store a massive 205 gigatonnes of carbon – two thirds of all the carbon released into the atmosphere since the Industrial Revolution.

Many of those trees could be planted in tropical grassy biomes according to the report. These are the savannas and grasslands that cover large swathes of the globe and have a grassy ground layer and variable tree cover. Like forests, these ecosystems play a major role in the global carbon balance. Studies have estimated that grasslands store up to 30% of the world’s carbon that’s tied up in soil. Covering 20% of Earth’s land surface, they contain huge reserves of biodiversity, comparable in areas to tropical forest. These are the landscapes with lions, elephants and vast herds of wildebeest.

Gorongosa, Mozambique. The habitat here is open, well-lit and with few trees.
Caroline Lehmann, Author provided

Savannas and grasslands are home to nearly one billion people, many of whom raise livestock and grow crops. Tropical grassy biomes were the cradle of humankind – where modern humans first evolved – and they are where important food crops such as millet and sorghum originated, which millions eat today. And, yet among the usual threats of climate change and wildlife habitat loss, these ecosystems face a new threat – tree planting.

It might sound like a good idea, but planting trees here would be damaging. Unlike forests, ecosystems in the tropics that are dominated by grass can be degraded not only by losing trees, but by gaining them too.




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Where more trees isn’t the answer

Increasing the tree cover in savanna and grassland can mean plant and animal species which prefer open, well-lit environments are pushed out. Studies from South Africa, Australia and Brazil indicate that unique biodiversity is lost as tree cover increases.

This is because adding trees can alter how these grassy ecosystems function. More trees means fires are less likely, but regular fire removes vegetation that shades ground layer plants. Not only do herbivores like zebra and antelope that feed on grass have less to eat, but more trees may also increase their risk of being eaten as predators have more cover.

A mosaic of grassland and forest in Gabon.
Kate Parr, Author provided

More trees can also reduce the amount of water in streams and rivers. As a result of humans suppressing wildfires in the Brazilian savannas, tree cover increased and the amount of rain reaching the ground shrank. One study found that in grasslands, shrublands and cropland worldwide where forests were created, streams shrank by 52% and 13% of all streams dried up completely for at least a year.

Grassy ecosystems in the tropics provide surface water for people to drink and grazing land for their livestock, not to mention fuel, food, building materials and medicinal plants. Tree planting here could harm the livelihoods of millions.

Losing ancient grassy ecosystems to forests won’t necessarily be a net benefit to the climate either. Landscapes covered by forest tend to be darker in colour than savanna and grassland, which might mean they also absorb more heat. As drought and wildfires become more frequent, grasslands may be a more reliable carbon sink than forests.




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Redefine forests

How have we reached the point where the unique tropical savannas and grasslands of the world are viewed as suitable for wholesale “restoration” as forests?

At the root of the problem is that these grassy ecosystems are fundamentally misunderstood. The Food and Agricultural Organisation of the UN defines any area that’s half a hectare in size with more than 10% tree cover as forest. This assumes that landscapes like an African savanna are degraded because they have fewer trees and so need to be reforested. The grassy ground layer houses a unique range of species, but the assumption that forests are more important threatens grassy ecosystems across the tropics and beyond, including in Madagascar, India and Brazil.

A flowering aloe in Madagascan grassland.
Caroline Lehmann, Author provided

“Forest” should be redefined to ensure savannas and grasslands are recognised as important systems in their own right, with their own irreplaceable benefits to people and other species. It’s essential people know what degradation looks like in open, sunlit ecosystems with fewer trees, so as to restore ecosystems that are actually degraded with more sensitivity.

Calls for global tree planting programmes to cool the climate need to think carefully about the real implications for all of Earth’s ecosystems. The right trees need to be planted in the right places. Otherwise, we risk a situation where we miss the savanna for the trees, and these ancient grassy ecosystems are lost forever.The Conversation

Kate Parr, Professor of Tropical Ecology, University of Liverpool and Caroline Lehmann, Senior Lecturer in Biogeography, University of Edinburgh

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

Exaggerating how much CO₂ can be absorbed by tree planting risks deterring crucial climate action



A long way to go…
Amenic181/Shutterstock

Duncan McLaren, Lancaster University

Planting almost a billion hectares of trees worldwide is the “biggest and cheapest tool” for tackling climate change, according to a new study. The researchers claimed that reforestation could remove 205 gigatonnes of carbon from the atmosphere – equivalent to about 20 years’ worth of the world’s current emissions. This has criticised as an exaggeration. It could actually be dangerous.

While the paper itself included no costings, the researchers suggested a best-case estimate of just US$300 billion to plant trees on 0.9 billion hectares. That’s just 40 US cents per tonne of carbon dioxide (CO₂) removed. More detailed studies on the costs of carbon removal through reforestation put the figure closer to US$20-50 per tonne – and even this may be optimistic at such large scales.




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Our research suggests that the promises implied in such studies could actually set back meaningful action on climate change. This is because of what we call “mitigation deterrence” – promises of cheap and easy CO₂ removal in future make it less likely that time and money will be invested in reducing emissions now.

Why would anyone expect governments or the finance sector to invest in renewable energy, or mass transit like high-speed rail, at costs of tens or hundreds of dollars a tonne if they – and shareholders and voters – are told that huge amounts of CO₂ can be absorbed from the atmosphere for a few dollars a tonne by planting trees?

Why should anyone expect energy companies and airlines to reduce their emissions if they anticipate being able to pay to plant trees to offset everything they emit, for the paltry price of less than 50 cents a tonne. If studies like this suggest removing carbon is cheap and easy, the price of emitting carbon for businesses – in emissions trading schemes – will remain very low, rather than rising to the levels needed to trigger more challenging, yet urgently needed, forms of emission reduction.

Tree planting is cheaper but less effective at reducing emissions than building zero-carbon infrastructure like electric high-speed rail.
Pedrosala/Shutterstock

A false carbon economy

The promises of cheap and powerful tech fixes help to sideline thorny issues of politics, economics and culture. But when promises that look great in models and spreadsheets meet the real world, failure is often more likely. This has been seen before in the expectations around carbon capture and storage.

Despite promises of its future potential in the early 2000s, commercial development of the technology has scarcely progressed in the last decade. That’s despite many modelled pathways for limiting global warming still assuming – increasingly optimistically – that it will be deployed at a large scale in coming decades.




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This model of tackling climate change goes hand in hand with another tool – pricing carbon emissions. This potentially allows companies to go on emitting by paying someone else to cut emissions or remove CO₂ elsewhere – an approach called climate offsetting. But offsetting makes exaggerated promises of carbon removal even more risky.

Tree planting financed through offset markets would guarantee the polluter could continue emitting carbon, but the market couldn’t guarantee removals to match those emissions. Trees might be planted and subsequently lost to wildfire or logging, or never planted at all.

Trusting in trees to remove carbon in future is particularly dangerous because trees are slow to grow and how much carbon they absorb is hard to measure. They’re also less likely to be able to do this as the climate warms. In many regions of the world but particularly in the tropics, growth rates are predicted to fall as the climate warms and devastating wildfires become more frequent.

Relying on trees to absorb CO₂ from the atmosphere in the future also appears misleadingly cheap because of the effects of economic discounting. Economists discount the current value of costs or benefits more deeply, the further in the future they occur. Models which determine the cheapest mix of policies available all use some form of discounting.

When researchers add carbon removal options like tree planting to these models, they tend to generate pathways for slowing temperature rise which reduce the role of short term action and replace it with imaginary removals late in the century.

This is because discounting over 30 to 60 years makes the removal options look incredibly cheap in today’s prices. Priming models to focus on minimising cost causes them to maximise the use of discounted future removals and reduce the use of more expensive near term emissions reduction.

I am not arguing against reforestation, nor for a purely technological response to climate change. Trees can help for many reasons – reducing flooding, shading and cooling communities, and providing habitat for biodiversity. Incentives for reforestation are important, and so are incentives for removing carbon. But we shouldn’t make trees or technology carry the whole burden of tackling climate change. That demands moving beyond technical questions, to deliver immediate political action to cut emissions, and to begin to transform economies and societies.

This article was amended on July 13 2019 to clarify the proposed costs of carbon removal by reforestation.The Conversation

Duncan McLaren, Professor in Practice, Lancaster University

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

White cedar is a rare bird: a winter deciduous Australian tree



Scamperdale/Flickr, CC BY-SA

Gregory Moore, University of Melbourne

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


White cedar (Melia azedarach) grows naturally across Queensland and northern New South Wales, but is widely planted as an ornamental tree all over Australia. It also grows across much of Asia, and belongs to the mahogany family.

This wide dispersal sees the species given a very wide and diverse range of common names, including: umbrella cedar, pride of India, Indian lilac, Persian lilac, and Chinaberry. It Australia it is known as white cedar due to its soft general-purpose timber.

The name Melia was the Greek name given to the ash tree, which has similar foliage, and azedarach means “poisonous tree” – parts of it are toxic.




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White cedar is something of a rarity among Australian native trees, as it loses its leaves in winter or early autumn. Winter deciduous trees are highly valued in landscape design as they provide all the benefits of summer shade, but allow winter light.



The Conversation

While Australia has an abundance of evergreen tree species and a variety of summer deciduous trees that lose their leaves in summer when water is scarce, we have few winter deciduous native trees. White cedar fits the bill beautifully, and despite a few shortcomings has some very attractive traits.

White cedar is usually a small spreading tree with a rounded canopy up to about 6m in height, but under the right conditions trees can be more than 20m tall, with a canopy spread of 10m or more. They have quite dense foliage composed of dark compound leaves up to 500mm long, which transition from dark green to a pale yellow in autumn.

As a winter deciduous tree they are a very popular native tree that has been widely planted as street trees and in domestic gardens, where specimens of 10-12m are common. The trees are often considered to be short-lived (around 20 years), but in gardens and where irrigation is available some may live for 40 years or longer.

Good specimens of white cedar have many small flowers (20mm) that are white with purple/blue stripes and a wonderful, almost citrus-like scent. The fruits are about 15mm in diameter and bright orange in colour. They are usually retained over winter and so the trees provide a seasonal smorgasbord – shade in summer, autumn foliage colour, orange fruits in winter, and attractive scented flowers in spring.

Many specimens are prolific in their production of fruits and seeds, which readily germinate, underscoring the weed potential of the species under the right circumstances. They can be an invasive species in some parts of Asia and Africa.

Unfortunately as the fruits mature and dry they become as hard as ball bearings. If you mow over them they can fire from under a mower like bullets, and if they land on a hard paved surface they can be a tripping hazard for people who unexpectedly find themselves skating. The fruits and foliage can also be quite toxic if eaten. So this would appear to put a bit a dampener on the use of the tree. However, in recent years non-fruiting varieties of white cedar have become available and these have proven popular as street and garden trees.

A toxic treat

Many parts of the tree are toxic – interestingly, though, not the fleshy part of the fruit. It has evolved to be attractive to the birds that disperse seed. However the seeds are very poisonous, and as few as 6 or 8 seeds can be fatal for children. Fortunately, the seeds are very hard and do not taste very pleasant, so the risk of humans eating them is quite low.

Despite this, white cedar has been widely used as a medicinal plant by indigenous cultures, especially for intestinal parasites. The seeds have been widely used to make beads by indigenous peoples in Asia and Australia, and in some places the tree is called the bead tree.

An easy grower

One of the good things about white cedar is they are easily grown, and cope quite well with the low rainfall in many parts of Australia. They also tolerate a variety of soil types, which is why they have been so widely and successfully spread.

The trees are quite resistant to termite damage and their poison does protect them from grazing mammals and some insects. They can be prone to root problems and it is not uncommon for their trunks to break off at ground level, especially if they have been poorly propagated or planted, which can be a big problem when they are planted as a street tree.




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Although they are related to mahogany, their wood can be quite brittle and easily broken, which means care should be taken when pruning or working on them. When the wood dries it shatters easily and can send shards in all directions when you try to snap it. In Australia the wood can range from light cream to dark brown in colour, and while it is quite a useful wood for carving and furniture, it is not widely used.

As a winter deciduous native tree of smallish stature, with many attractive characteristics, the white cedar really is an Australian rarity, despite how widely it occurs or is planted.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.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.

Built like buildings, boab trees are life-savers with a chequered past



A boab tree in the Kimberley. Boab trees can live for thousands of years and their trunks hollow out as they get older.
Shutterstock

Gregory Moore, University of Melbourne

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


When you are in the northern part of Western Australia, one of nature’s joys is seeing a large boab tree close up, perhaps for the first time.

The boab (Adansonia gregorii) is a native to this part of Australia, but is related to the broader group of species called boababs that live in Madagascar and Africa – but more on that connection later.

Boabs are also called bottle trees, the tree of life, boababs and Australian boababs. Some of the indigenous Australian names include gadawon and larrgadi.

From their iconic swollen trunks, to living up to 2,000 years and the many uses for their “superfood” fruits, here’s what makes boab trees so fascinating.



The Conversation

The ‘upside-down tree’: trunks that save lives and lock up prisoners

While the boab in Australia is not quite as well-documented as the African species, specimens have been recorded at over 1,000 years of age. Some living trees have been estimated to be nearer to 2,000 years old.

And while it’s difficult to age the trees, several specimens of the African species have been dated at 2,000 or more years old.

Australian boabs can grow up to 15 metres tall at maturity and have swollen, attention-grabbing trunks called a caudex, which may be up to five metres in diameter.

The African boab species, A. digitata, can be much taller, at 25 metres high and with a diameter of up to 15 metres.




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In such dry continents, the caudex is a life-saver, often containing water, which was tapped by Indigenous folk. It has been estimated that some of these huge old trees can hold more than 100,000 litres of water in their trunks.

In Africa, these massive trunks have been used as shelters, homes, farm sheds and, more recently, even shops and bars.

Sadly in Australia, legend has it the huge trunks were used to make lock-ups for Indigenous people and other prisoners.

The infamous Boab Prison Tree, just south of Derby in Western Australia, was said to have once held Indigenous prisoners.
Shutterstock

It’s not just the trunk that can stop you in your tracks. The boab has a unique branching structure, one that looks more like a root system than a canopy.

Some locals in Africa will tell you the tree was dropped from heaven to earth and landed upside down. So the African species of boab is sometimes called the upside-down tree.

Boab fruits are ‘superfoods’ and its shell has many uses

A. gregorii, the Australian boab species, has large, attractive white flowers up to 75 millimetres in length. Its round fruits are edible and sought after by birds, mammals and humans. The fruit gives rise to some of the common names for the tree, such as monkey bread tree and dead rat tree. The latter comes from the appearance of older fruits in the canopy looking a bit like … well, dead rats?




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In fact, there’s great interest in fruits from the African species, A. digitata, which are considered a “superfood” because of their high levels of antioxidants, calcium, potassium, magnesium, fibre and vitamin C. It’s assumed many of these traits will be shared by the Australian boab, but there is little research as yet to prove it.

Fruit of the African boab tree fruit are initially covered in velvety fur.
Ton Rulkens/Wikimedia, CC BY-SA

The soft part of the fruit is surrounded by a hard, coconut-like shell that’s initially covered in a velvety fur. The hard shell has been used for cups and bowls, but has also been intricately carved and decorated by Aboriginal artists in Africa and Australia. If the seeds are left inside the fruit as it dries, they can be used for toys like rattles.

On both continents, Aboriginal people have eaten the white powder that surrounds the seeds. The leaves are rich in iron and the pulp from the fruits tastes like cream of tartar.

The Indigenous people of both continents were also well aware of the medicinal uses of the fruits. The bark and leaves of the trees also treat various ailments, but particularly those associated with digestive disorders.




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But at present there is very little modern research on the medicinal and dietary aspects of either the baobab or boab.

How the boab tree got to Australia

One of the mysteries surrounding the boab is how it got to Australia – the Australian species has clear affinities with related species in continental Africa and Madagascar.

A baobab tree, Adansonia digitata, in Tarangire National Park, Tanzania. Its journey from Africa to Australia remains a mystery.
Yoki/Wikimedia, CC BY-SA

There are three intriguing theories.

The first is that all of the boababs originate from the super-continent Gondwana – consisting of Africa, South America, Antarctica, Australia, India and Madagascar – before it fragmented almost 80 million years ago. But A. Gregorii and A. digitata are so similar genetically that, given the millions of years that have elapsed, this theory is now in question.

The second theory comes from recent DNA analysis of the species. It suggests they separated more recently, perhaps only 70,000 years ago, which raises the question, were humans involved in their journey? But did they come to Australia from Africa, or from Australia to Africa? The latter is a less likely scenario given the direction of ocean currents.

And the third theory is that fruits arrived on the Australian shore after an epic ocean voyage from Africa.




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Boabs are usually found in the remote outback of Australia, but in 2008, a large 750-year-old boab was transported from Warmun in the Kimberley to Perth and transplanted in Kings Park.

Transplanting such a large tree is both daunting and fraught, with a high chance of failure, but the deciduousness and growth habit of the boab gave some cause for optimism about a successful outcome. For the reward of having a large old boab growing in Perth, it would be worth it.

After a period of stress, the tree appears to be coming good, reflecting the toughness of the species.

A large, mature boab is a splendid tree of arid Australia that inspires awe in all who experience them close up. They really are a beauty and a bottler of a tree!


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.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.

This centuries-old river red gum is a local legend – here’s why it’s worth fighting for


Euan Ritchie, Deakin University

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


In Dr Seuss’s The Lorax, his titular character famously said:

I am the Lorax. I speak for the trees. I speak for the trees, for the trees have no tongues.

In the midst of a global extinction crisis, the Lorax’s call to preserve what is precious couldn’t be more apt. The greatest threat to the survival of species globally continues to be habitat destruction and modification.




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A potential and local victim of this ongoing environmental catastrophe is a single tree, and a tree I have a deep personal connection with. The tree I refer to is Bulleen’s iconic 300-year-old river red gum (Eucalyptus camaldulensis).

To me this tree has been a constant in my life. While everything else has changed around me, it has stood there, solid, just as solid as its red gum fibres are known to be.

As a child I fondly remember looking up at this tree in awe, as we’d often stop at the nearby service station on a hot summer’s day to buy a cold drink or ice-cream on the way to Saturday sport, the nearby Birrarung (Yarra River), or my grandmother’s house.



The Conversation

Bulleen’s majestic river red gum

It’s estimated to be approximately 20 metres in height with a canopy spread of 17 metres. And its trunk measures a whopping two metres across.

The tree is thought to be the oldest remnant of a once substantial red gum forest, and was saved by a local resident when the rest of the area was cleared for the construction of a service station.

It now faces destruction, as it is within the preferred path of construction for Victoria’s North East link.




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While the measurements of this tree are impressive, the splendour and value for me is that it has survived for so long and, in more recent times, against tremendous odds.

Surviving against all odds

The Bulleen red gum stands beside one of Melbourne’s busiest roads and the immediate area is covered with concrete and bitumen. The tree’s roots and health have therefore been challenged for a long time, and yet this massive red gum stands, as if in defiance of the modern world and the development that has encircled it.

Since this tree has survived for so long, it undoubtedly holds a special connection with so many: the Wurundjeri-willam people of the Kulin Nation, members of Australia’s famed Heidelberg school of artists who lived and worked in the near vicinty, everyday commuters that have driven or walked by or stopped to admire it, or the war verteran Nevin Phillips who once apparently defended it with his rifle against it being chainsawed.

Very old trees such as Bulleen’s river red gum deserve our respect and protection, for these trees have substantial environmental, economic and cultural value.
National Trust

Further proof of the value of this tree to so many is that it was awarded The National Trust of Australia’s (Victoria) 2019 Victorian Tree of the Year.

Why we must speak for and save old trees

I grew up near this tree and, like the Lorax, I would like to speak for it.
Trees as old as the Bulleen river red gum are now increasingly rare in our world, and beyond their strong personal and cultural values, including in some places as Aboriginal birthing sites, they are tremendously important for other reasons as well.




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These trees provide shade and help keep our cities cooler, improve our mental health and wellbeing, and store considerable amounts of carbon aiding our fight against climate change.

Perhaps most importantly, under their bark and in their cracks and hollows, they provide homes for many of Australia’s precious but increasingly imperilled native wildlife, including bats, birds, possums and gliders, snakes and lizards, insects and spiders.

These homes are prime wildlife real estate, especially in our big cities, where such large old trees are vanishingly rare but where considerable wildlife, common and threatened, still persists. And yet more could survive with a helping hand from us.

A powerful owl chick in a tree hollow, in outer Melbourne.
John White (Deakin University)

As cities like Melbourne continue to grow around the world, there will be more and more cases where arguments of progress are used to justify the further destruction of what nature remains. But progress shouldn’t come at any cost, and in the case of preserving iconic and valuable trees such as Bulleen’s river red gum, it would seem there’s more than enough reasons to ensure this tree’s life and its many values continue.

Perhaps again the wise sage, the Lorax, says it best.

Unless someone like you cares a whole awful lot, Nothing is going to get better. It’s not.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University

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

The sexy gum: a love story



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Dr Michael Whitehead is campaigning to rename the Gimlet Gum to the Sexy Gum.
Author provided (No reuse)

Michael Whitehead, University of Melbourne

It is perhaps poetic that a region most famous for its lack of trees lies so close to one of Australia’s greatest tree-based spectacles. The Nullarbor Plain, our famous, flat, featureless expanse is literally named for its absence of trees (“arbor” being Latin for tree).

And if you ever get to drive west along the longest stretch of dead-straight road across this iconic landscape, you will come to know the highlights that characterise the experience: the cliff-top views of the Great Australian Bight and the idiosyncratic roadhouses.




Read more:
A detailed eucalypt family tree helps us see how they came to dominate Australia


Then finally, a landscape of low shrubs gives way to mallee trees and woodland vegetation. Somewhere between Caiguna and Fraser Range you’ll see your first Eucalyptus salubris, also known as a gimlet gum, or joorderee by the Ngadju people.

It was on a recent botanical research trip chasing scraggly emu bushes that I stumbled upon, and fell in love with, Eucalytpus salubris. The trunks were what instantly caught my eye, slender with graceful twists, all the more observable for the brilliantly shining coppery bark.



The Conversation

The sexy gum

The tree first appears in European record during early explorations crossing east of the Darling Range. Then, it was called “cable gum” after the gently twisting grooves in the trunks.

Later the tree was given the common name of “gimlet” after a form of hand drill. Unfortunately this name stuck and today the species remains “gimlet” – a wholly unattractive moniker for such a splendid tree.

But our imaginations need not be held hostage by the stubborn colonialists who named our flora after such dreary things.




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Stringybark is tough as boots (and gave us the word ‘Eucalyptus’)


That’s why I’m campaigning to update the common name to something more universal, more marketable, something truer to its sensual twists and smooth, glowing bronze surface.

Eucalytpus salubris is the Sexy Gum.

Love goes where my eucalypt grows

E. salubris is a dominant species forming woodlands on deep soils east of the Darling Range. And while much of its former range in the Wheatbelt of Western Australia has been cleared, extensive populations of E. salubris remain in the astonishing stronghold of the Great Western Woodlands.

Those who have walked in a mature woodland understand the pleasure of wandering unimpeded in the shade of widely spaced trees.

Widely spaced trees of the Great Western Woodlands.
Keren Gila/Wikimedia, CC BY

The Great Western Woodlands offers this experience on a grand scale. At around 16 million hectares they are the largest tracts of intact temperate woodlands on Earth, occupying an area larger than England and Wales combined.

And it is not just size that is impressive about these woodlands.

The Great Western Woodlands are a renowned hotspot for eucalypt diversity, home to around 30% of Australia’s eucalypt species in just 2% of its land area.

As one of the more common species throughout the area, E. salubris plays a critical ecological role, providing habitat for several threatened bird species including the rotund and charismatic Mallee fowl.




Read more:
We need to think about fire in Tasmania’s forests


Due to its remoteness and unreliable rainfall, the Great Western Woodlands has avoided the widescale grazing and clearing that has degraded neighbouring areas to the south and west.

But despite the value of this untouched landscape, most of the area is “orphan country” with no formal management policies in place. Some 60% of the Great Western Woodlands is unallocated crown land, unmanaged and open access.

This is a plus for visitors wanting to experience it now, but raises important concerns about the long-term security of the area.

While remote, threats to the Great Western Woodlands do exist. Chief among them is the increasing frequency and intensity of bush fires.

Most eucalypts are resprouters with the ability to regenerate burned canopies from buds under the bark. There are, however a number of species, such as Mountain Ash, that will die following canopy fires and can only regenerate from the soil seedbank (called “reseeders”).




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Mountain ash has a regal presence: the tallest flowering plant in the world


E. salubris, the sexy gum, is one such reseeder. While the traditional occupants of the land used fire as a land management tool, they also knew E. salubris woodland took hundreds of years to regenerate and were careful to never burn the canopy of old growth forests.

The eye-pleasing spectacle of mature open Eucalytpus salubris woodland above red soil and blue-bush therefore exists today thanks to careful management from this era, and deserves careful handling to ensure its ongoing future.

An ambassador for the Great Western Woodlands

Late in the day, when the Sun’s glancing rays light up the bark of E. salubris, punctuating a pastel blue-green woodland with glowing streaks like molten metal, it’s hard to not stop for at least a moment and be impressed.

And while E. salubris’ role as keystone species might be important ecologically, I think the Sexy Gum can be similarly important as ambassador and draw-card for the Great Western Woodlands.

Its golden tones and metallic lustre conjures just the appropriate impression for the WA Goldfields. It is totally Instagram-able, and I don’t think it’s a hard sell to convince people E. salubris is a spectacle worth getting off the beaten track for.The Conversation

Michael Whitehead, Research Fellow in Evolutionary Ecology, University of Melbourne

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

A detailed eucalypt family tree helps us see how they came to dominate Australia



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In Australia you can have any tree you want, as long as it’s a eucalypt.
Shutterstock

Andrew Thornhill, James Cook University

Eucalypts dominate Australia’s landscape like no other plant group in the world.

Europe’s pine forests consist of many different types of trees. North America’s forests change over the width of the continent, from redwood, to pine and oak, to deserts and grassland. Africa is a mixture of savannah, rainforest and desert. South America has rainforests that contain the most diversity of trees in one place. Antarctica has tree fossils.

But in Australia we have the eucalypts, an informal name for three plant genera: Angophora, Corymbia and Eucalyptus. They are the dominant tree in great diversity just about everywhere, except for a small region of mulga, rainforest and some deserts.

My research, published today, has sequenced the DNA of more than 700 eucalypt species to map how they came to dominate the continent. We found eucalypts have been in Australia for at least 60 million years, but a comparatively recent explosion in diversity 2 million years ago is the secret to their spread across southern Australia.

Hundreds of species

The oldest known Eucalyptus macrofossil, from Patagonia in South America, is 52 million years old. The fossil pollen record also provides evidence of eucalypts in Australia for 45 million years, with the oldest specimen coming from Bass Strait.

Despite the antiquity of the eucalypts, researchers assumed they did not begin to spread around Australia until the continent began drying up around 20 million years ago, when Australia was covered in rainforests. But once drier environmental conditions kicked in, the eucalypts seized their chance and took over, especially in southeastern Australia.

Eucalypts are classified by their various characteristics, including the number of buds.
Mary and Andrew/flickr, CC BY-NC-SA

There are over 800 described species of eucalypts. Most of them are native only to Australia, although some have managed to naturally escape further north to New Guinea, Timor and Indonesia. Many eucalypts have been introduced to other parts of the world, including California, where Aussie eucalypts make cameos in Hollywood movies.

Eucalypts can grow as tall trees, as various multi-trunk or single-trunk trees, or in rare cases as shrubs. The combination of main characteristics – such as leaf shape, fruit shape, bud number and bark type – provided botanists with enough evidence to describe 800 species and estimate how they were all related to each other, a field of science known as “taxonomy”.

Since the 1990s and early 2000s, taxonomy has been slightly superseded by a new field called “phylogenetics”. This is the study of how organisms are related to each other using DNA, which produces something akin to a family tree.

Phylogenetics still relies on the species to be named though, so there is something to sample. New scientific fields rely on the old. There have been a number of eucalypt phylogenetic studies over the years, but none have ever sampled all of the eucalypt species in one phylogeny.




Read more:
Stringybark is tough as boots (and gave us the word ‘Eucalyptus’)


Our new paper in Australian Systematic Botany aimed to change that. We attempted to genetically sample every described eucalypt species and place them in one phylogeny to determine how they are related to each other. We sampled 711 species (86% of all eucalypts) as well as rainforest species considered most closely related to the eucalypts.

We also dated the phylogeny by time-stamping certain parts using the ages of the fossils mentioned above. This allowed us to estimate how old eucalypt groups are and when they separated from each other in the past.

Not so ancient

We found that the eucalypts are an old group that date back at least 60 million years. This aligns with previous studies and the fossil record. However, a lot of the diversification in the Eucalyptus genus has happened only in the last 2 million years.

Gum trees are iconic Australian eucalypts.
Shutterstock

Hundreds of species have appeared very recently in evolutionary history. Studies on other organisms have shown rapid diversification, but none of them compare to the eucalypts. Many species of the eucalypt forests of southeastern Australia are new in evolutionary terms (10 million years or less).

This includes many of the tall eucalypts that grow in the wet forests of southern Australia. They are not, as was previously assumed, ancient remnants from Gondwana, a supercontinent that gradually broke up between 180 million and 45 million years ago and resulted in the continents of Australia, Africa, South America and Antarctica, as well as India, New Zealand, New Guinea and New Caledonia.

The eucalypts that grow natively overseas have only made it out from Australia in the last 2 million years or less. Other groups in the eucalypts such as Angophora and Corymbia didn’t exhibit the same rapid diversification as the Eucalyptus species.




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Renewable jet fuel could be growing on Australia’s iconic gum trees


What we confirmed with the fossil record using our phylogeny is that until very recently, and I mean in terms of the Earth being 4 billion years old, the vegetation of southeastern Australia was vastly different.

At some point in the last 2-10 million years the Eucalyptus arrived in new environmental conditions. They thrived, they most likely helped spread fire to wipe out their competition, and they then rapidly changed their physical form to give us the many species that we see today.

Very few other groups in the world have made this amount of change so quickly, and arguably dramatically. The east coast of Australia would look very different if it wasn’t dominated by gum trees.

The next time you’re in a eucalypt forest, take a look around and notice all of the different types of bark and gumnuts and leaves on the trees, and know that all of that diversity has happened quite recently, but with a deep and long link to trees that once grew in Gondwana.

They have been highly advantageous, highly adaptable and, with the exception of a small number of species, are uniquely Australian. They are, as the press would put it, “a great Australian success story”.The Conversation

Andrew Thornhill, Research botanist, James Cook University

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

Greenwashing: corporate tree planting generates goodwill but may sometimes harm the planet



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Missing the wood for the trees.
iDraw/Shutterstock

Benjamin Neimark, Lancaster University

Trees do a lot more for us than you probably think. Their roots prevent soil from eroding, their canopies provide shade and their leaves decompose into nutrients for crops, which feed livestock. Trees provide homes for a diverse range of wildlife and tree crops, such as coffee, rubber, and hardwoods, support countless livelihoods and entire economies. Trees also mark boundaries and hold immense spiritual, cultural and social value for smallholder communities around the world.

In the 1980s, charities proposed planting more trees to halt “desertification” in the Sahara Desert. This involved “afforestation” – planting trees where they had not grown for a while and “reforestation” – replacing recently lost tree cover.

Today the idea is growing strong, and an array of private companies from adult website Pornhub (yes, Pornhub) to clothing brand Ten Tree are using trees as a marketing tool.




Read more:
Pornhub has planted a few more trees, but don’t pretend it’s being responsible


Saving face or saving forests?

Businesses can offset their environmental impact by planting trees or supporting other forms of habitat restoration, so as to “pay off” the damage they cause locally. As climate change escalates, trees are in vogue for their potential to soak up the carbon dioxide we keep putting in the atmosphere.

The United Nations (UN) has even adopted a scheme for offering local communities and governments some sort of financial payout for saving trees from deforestation. This “economy of repair” has been adopted by some of the largest companies in their commitments to corporate social responsibility. One such programme is the Green Belt Movement – a Kenyan conservation NGO started by the late professor and Nobel Prize recipient Wangari Maathai.

Tree planting around the Sahara Desert has overwhelmingly relied on local efforts rather than businesses.
Niels Polderman/Shutterstock

Maathai’s original mission was to empower local people, particularly women, to overcome inequality through leading forest restoration and resisting the expanding Sahara Desert. Despite the involvement of charities and businesses, research has suggested that in programmes like these, it is farmers and local people, not companies, which make the biggest contributions to planting new trees. Since local people also inherit responsibility for them, it’s important that projects devised by outside parties are planned and executed wisely, and in the community’s interest.




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Africa’s got plans for a Great Green Wall: why the idea needs a rethink


While some may argue that tree planting is a win-win for the environment whoever does it, offsetting is just another way of corporate greenwashing. Environmental damage in one place cannot somehow be fixed by repairing habitats elsewhere, sometimes on the other side of the world.

Here are some of the ways in which indiscriminate tree planting can cause more harm than good.

Plantations are not forests

Diverse forests are often cleared for agricultural production or industrial use, and replaced by uniform stands of the same species selected because of their ability to grow fast.

Tropical forests in some cases take up to 65 years to regrow and their diversity cannot be replicated by a monoculture of reforested plots.

Ecologically illiterate

Reforestation and afforestation schemes must decide which species are appropriate to plant – native or exotic, multi-purpose or fast growing, naturally regenerating forests or managed plantations. Sometimes the wrong species are selected and Eucalyptus (Eucalyptus globulus) is one such poor choice.

Eucalyptus is usually chosen because it is fast growing and economically valuable. Yet, it is exotic to many places it is now planted and requires lots of water, which drains the water table and competes with native crops.

In Europe, replacing broad-leafed native oak trees with faster growing conifers has meant that forest cover on the continent is 10% greater than it was before the industrial revolution. However, the new trees are not as good at trapping carbon but do trap heat more efficiently, contributing to global warming. Clearly, tree planting without due caution can do more harm than good.

Trees need care – lots of it

Tree species take a long time to grow and need continual care. However, tree planting schemes usually “plant and go” –- meaning they do not put resources into managing the trees after they are placed into the ground. Young trees are particularly vulnerable to disease and competition for light and nutrients and if not cared for, will eventually die.

Newly planted tree saplings may need three to five years of frequent watering to survive.
A3pfamily/Shutterstock

Trees are political

Trees planted by states or private donors may choose sites without consulting local communities, ignoring any of their customary land rights and management regimes. This locally-owned land may be in fallow or have different economic, cultural or spiritual uses.

Blundering into planting in these places may exacerbate tensions over land tenure, spreading disinterest in tree care and stewardship. Dispossessed locals may move to existing forests and clear land for food production. Tenure rights over trees are also not always owned by whole households either, but divided between gender. Planting trees and asking questions later may sow tensions over land ownership for long after the project departs.

It’s no surprise that trees are on the green economy agenda, but this does not necessarily mean that planting them is “green” or helpful for social harmony. Allowing trees to regrow naturally is not always effective either, as trees are unlikely to survive on their own. Community involvement is therefore crucial.

This means real consultation over site and species selection, property rights over the trees, their products, and the land they grow in and who takes on the labour to keep the trees alive after they are planted. If companies are serious about planting trees then they need to care about the communities that live with them and not just their own reputations.The Conversation

Benjamin Neimark, Senior Lecturer, Lancaster Environment Centre, Lancaster University

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

Lord of the forest: New Zealand’s most sacred tree is under threat from disease, but response is slow



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Tāne Mahuta is New Zealand’s most sacred tree, but its days will be numbered if it is infected with kauri dieback disease.
from http://www.shutterstock.com, CC BY-SA

Matthew Hall, Victoria University of Wellington

Tāne Mahuta is Aotearoa New Zealand’s largest living being – but the 45m tall, 2,500-year-old kauri tree is under severe threat from a devastating disease.

Nearly a decade after the discovery of kauri dieback disease, it is continuing to spread largely unchecked through the northern part of the North Island. Thousands of kauri trees have likely been infected and are now dead or dying. The Waipoua forest, home of Tāne Mahuta and many other majestic kauri, is reported to be one of the worst affected areas.

For Māori, who trace their whakapapa (lineage) to the origins of the earth, Tāne Mahuta is kin. The threat of losing this tree should electrify the fight against kauri dieback.




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People are ‘blind’ to plants, and that’s bad news for conservation


Call to close the forest

Named after Tāne, the son of Ranginui the sky father and Papatūanuku the earth mother, Tāne Mahuta is a highly revered taonga, or treasure. In Māori mythology, it was Tāne who brought trees and birds to earth.

The loss of this ancestor, with a presence that has been known to move some to tears, is incalculable.

Kauri dieback has been recorded metres from this ancient tree, despite the best efforts of a prevention programme that has been in place since 2009. Much of the focus of the programme has been on encouraging behaviour change by forest users (following paths, washing boots) and upgrading tracks (from mud to boardwalks). A new national pest management plan proposes more of the same.

As part of a prevention programme to limit the spread of kauri dieback, visitors to kauri forests are encouraged to spray their shoes with a disinfectant.
Eli Duke/WIkimedia Commons, CC BY-SA
Signs remind visitors in the Waitākere Ranges about precautions against the spread of kauri dieback disease.
from Wikimedia Commons, CC BY-SA

In my view, the most notable, and frustrating, aspect of this programme is the significant resistance to close kauri forest tracks to people, who, along with wild pigs, are one of the major vectors of the disease.

Te Kawerau ā Maki, a Māori tribal group with mana whenua (customary authority) over the land of the Waitākere forest in the Auckland region, have maintained a consistent stance that the only way to protect kauri forests is to close them to humans. In November 2017, they placed a rāhui (temporary closure) over the entire forest area, severely frustrated by the lack of effective action to control kauri dieback by Auckland Council.

A rāhui is not legally enforceable, and it was largely ignored by forest users who continued to enter and spread the disease. Eventually, six months later, Auckland Council voted to close the majority of tracks, but Te Kawerau ā Maki have viewed this as too little, and possibly too late.

Keeping the forest open

In a similar laggardly vein, the Department of Conservation has only just put forward a proposal to close or partially close 24 kauri forest tracks. This proposal is currently going through a consultation process, which seems inappropriate when dealing with an immediate biosecurity crisis.

The proposal does not include the Waipoua forest and the track that leads to Tāne Mahuta, or to other significant kauri such as Te Matua Ngahere. The department says:

the decision to propose track closures is not taken lightly, but has been considered in situations where there is high kauri dieback risk, low visitor use, high upgrade and ongoing maintenance costs, and a similar experience provided in the vicinity.

Tāne mahuta draws hundreds of thousands of tourists to the Waipoua forest area. This, combined with the fact that forest tracks are generally in good condition has led to the decision to keep the forest open. For now, the tangata whenua (local Māori with authority over land) support it.

Tāne Mahuta draws hundreds of thousands of visitors to the kauri forests in the north of New Zealand.
from http://www.shutterstock.com, CC BY-SA

Relinquishing our claims

Although we know that our human presence in kauri forests will lead to the certain death of the trees, many people still wish to venture into the forests, to walk or to hunt, regardless of the consequences.

Whether conscious or not, the value assessment here must be that the right of kauri trees to live and flourish is of lesser value than some fleeting recreation on a weekend afternoon. As people kept blindly tramping into the Waitākere forest, infection rates increased from 8% to 19% in just five years.

What I find most disturbing here is that government agencies tasked with preserving the “intrinsic values” of native species are prepared to let this happen for pragmatic and economic reasons. This is one of those situations where competing values can’t be balanced.

The life and flourishing of kauri must be prioritised above all else, whatever the economic or recreational hit. This means letting go of our claim to kauri trees as “natural and recreational resources” and acknowledging them for what they are – our living, spiritual, intelligent kin.

Kauri or kiwifruit

Pragmatically, our assistance to kauri also necessitates that we re-assess the value we place on the survival of kauri from an economic perspective.

Funding of less than NZ$2 million per year for the kauri dieback programme pales in comparison to the magnitude of the response to recent agricultural biosecurity threats.

In 2010, a huge response to the incursion of a microbial pathogen (Pseudomonas syringae pv. actinidiae, or Psa) in kiwifruit vines saw a NZ$50 million fund created to fight the disease.

In 2015, after a single Queensland fruit fly was caught in a trap in February, a large coordinated response, with local, restrictive biosecurity control orders in place, resulted in eradication in October, at a cost of NZ$13.6 million.

With such funds, it would be much easier to enforce the closure of kauri forests, until more long-term measures, such as improving genetic resistance, become possible.

At the end of last year, Minister for Forestry Shane Jones was quoted expressing a similar opinion, following the government’s announcement that it would attempt to eradicate the cow disease Mycoplasma bovis.

If it’s possible for us to move swiftly and cull diseased cows and stop the transport of potentially diseased cows off private farms, we need a similar level of vigour in safeguarding areas where our kauri are still strong.

The ConversationFor the survival of Tāne Mahuta, we should close off kauri forests immediately and boost funding for the implementation of the dieback management programme.

Matthew Hall, Associate Director, Research Services, Victoria University of Wellington

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