Forest soil needs decades or centuries to recover from fires and logging



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David Blair, Author provided

Elle Bowd, Australian National University and David Lindenmayer, Australian National University

The 2009 Black Saturday fires burned 437,000 hectares of Victoria, including tens of thousands of hectares of Mountain Ash forest.

As we approach the tenth anniversary of these fires, we are reminded of their legacy by the thousands of tall Mountain ash “skeletons” still standing across the landscape. Most of them are scattered amid a mosaic of regenerating forest, including areas regrowing after logging.




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But while we can track the obvious visible destruction of fire and logging, we know very little about what’s happening beneath the ground.

In a new study published in Nature Geoscience, we investigated how forest soils were impacted by fire and logging. To our surprise, we found it can take up to 80 years for soils to recover.

Logging among the charred remains of Mountain ash after the 2009 fires.
David Blair, Author provided

Decades of damage

Soils have crucial roles in forests. They are the basis for almost all terrestrial life and influence plant growth and survival, communities of beneficial fungi and bacteria, and cycles of key nutrients (including storing massive amounts of carbon).

To test the influence of severe and intensive disturbances like fire and logging, we compared key soil measures (such as the nutrients that plants need for growth) in forests with different histories. This included old forests that have been undisturbed since the 1850s, forests burned by major fires in 1939, 1983 and 2009, forests that were clearfell-logged in the 1980s or 2009-10, or salvage-logged in 2009-10 after being burned in the Black Saturday fires.

We found major impacts on forest soils, with pronounced reductions of key soil nutrients like available phosphorus and nitrate.

A shock finding was how long these impacts lasted: at least 80 years after fire, and at least 30 years after clearfell logging (which removes all vegetation in an area using heavy machinery).

However, the effects of disturbance on soils may persist for much longer than 80 years. During a fire, soil temperatures can exceed 500℃, which can result in soil nutrient loss and long-lasting structural changes to the soil.

We found the frequency of fires was also a key factor. For instance, forests that have burned twice since 1850 had significantly lower measures of organic carbon, available phosphorus, sulfur and nitrate, relative to forests that had been burned once.

Sites subject to clearfell logging also had significantly lower levels of organic carbon, nitrate and available phosphorus, relative to unlogged areas. Clearfell logging involves removing all commercially valuable trees from a site – most of which are used to make paper. The debris remaining after logging (tree heads, lateral branches, understorey trees) is then burned and the cut site is aerially sewn with Mountain Ash seed to start the process of regeneration.

Fire is important to natural growth cycles in our forests, but it changes the soil composition.
David Lindenmayer, Author provided

Logging compounds the damage

The impacts of logging on forest soils differs from that of fire because of the high-intensity combination of clearing the forest with machinery and post-logging “slash” burning of debris left on the ground. This can expose the forest floor, compact the soil, deplete soil nutrients, and release large amounts of carbon dioxide into the atmosphere.

Predicted future increases in the number, frequency, intensity and extent of fires in Mountain Ash forests, coupled with ongoing logging, will likely result in further declines in soil nutrients in the long term. These kinds of effects on soils matter in Mountain Ash forests because 98.8% of the forest have already been burned or logged and are 80 years old or younger.

To maintain the vital roles that soils play in ecosystems, such as carbon storage and supporting plant growth, land managers must consider the repercussions of current and future disturbances on forest soils when planning how to use or protect land. Indeed, a critical part of long-term sustainable forest management must be to create more undisturbed areas, to conserve soil conditions.




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Specifically, clearfell logging should be limited wherever possible, especially in areas that have been subject to previous fire and logging.

Ecologically vital, large old trees in Mountain Ash forests may take over a century to recover from fire or logging. Our new findings indicate that forest soils may take a similar amount of time to recover.The Conversation

Elle Bowd, PhD scholar, Australian National University and David Lindenmayer, Professor, The Fenner School of Environment and Society, Australian National University

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

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Comic explainer: forest giants house thousands of animals (so why do we keep cutting them down?)



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Wes Mountain/The Conversation, CC BY-ND

Madeleine De Gabriele, The Conversation and Wes Mountain, The Conversation

Giant eucalypts play an irreplaceable part in many of Australia’s ecosystems. These towering elders develop hollows, which make them nature’s high-rises, housing everything from endangered squirrel-gliders to lace monitors. Over 300 species of vertebrates in Australia depend on hollows in large old trees.

These “skyscraper trees” can take more than 190 years to grow big enough to play this nesting and denning role, yet developers are cutting them down at an astounding speed. In other places, such as Victoria’s Central Highlands Mountain Ash forests, the history of logging and fire mean that less than 1.2% of the original old-growth forest remains (that supports the highest density of large old hollow trees). And it’s not much better in other parts of our country.

David Lindenmayer explains how these trees form, the role they play – and how very hard they are to replace.




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Wes Mountain/The Conversation, CC BY-ND



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

Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation and Wes Mountain, Multimedia Editor, The Conversation

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

Australia’s native rhododendrons hide in the high mountain forests



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Rhododendron lochiae, photographed on Bell Peak.
Image by Dan McLeod

Stuart Worboys, James Cook University

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


The 1800s was a time of colonial expansion across the globe. During this time the great and the good of Britain filled their grand gardens with exotic novelties from all corners of the world.

Amongst these were many species of Asian rhododendron, a diverse and colourful genus of shrubs and small trees, whose high altitude origins made them well suited to the cool temperate climate of England and Scotland.




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Throughout the 19th century, commercial collectors and field naturalists discovered rhododendron species in southern China, the Himalayas, on the high peaks of Borneo, Java and especially New Guinea.

These finds lead Victoria’s government botanist of the time, Ferdinand von Mueller, to speculate about finding rhododendrons on the high tropical mountains on the northeast coast of Queensland. He wrote:

When in 1855 [I] saw… the bold outlines of Mount Bellenden-Ker, the highest mount of tropical Australia, towering to 5,000 feet, [I] was led to think, that the upper region might prove to be the home of species of Rhododendron… forms of plants characteristic of cool Malayan sylvan regions.

But the lofty heights of Mt Bellenden Ker were unknown to European Australians. It would be another 32 years before an expedition led by naturalist W.A. Sayer reached its central peak.



The Conversation, CC BY-ND

Sayer’s expedition, accompanied by two indigenous assistants, reached the mountain’s high ridge after several mishap-filled attempts. It was here they confirmed Mueller’s suspicions. Sayer’s account of its discovery is interesting:

The top of the range is razor-backed, and on travelling along the range beyond the spur by which we ascended, I could not see the sides, they being, if anything, hanging over. We tumbled rocks over, but could not hear them fall.

It was here that I observed the Rhodendron Lochae growing, and asked the Kanaka to get it; but he remarked, ‘S’pose I fall, I no see daylight any more; I go bung altogether;’ so I had to get it myself.

Mueller received the hard-won specimens and named the species Rhododendron lochae (later corrected to R. lochiae) after Lady Loch, the wife of the Victorian Governor.

Since then, rhododendron plants have been found on nine peaks and tablelands in the Wet Tropics region of north Queensland. Populations on peaks south of Cairns are called Rhododendron lochiae, whilst plants growing on mountains to the north of Cairns are considered by some to be a distinct species: Rhododendron viriosum.

Australian rhododendron at Smith College Botanical Garden.
Ren Glover/Flickr, CC BY-NC

Both northern and southern plants are straggly shrubs that grow in thin soils or rock cracks, sometimes in open cloud-swept boulder fields, sometimes in deep shade along creeks, or rarely as epiphytes on moss-covered trees. They produce bunches of gloriously red, bell-shaped flowers, followed by dry brown capsules filled with small winged seeds that are apparently spread by wind.

They grow slowly but with relative ease from cuttings, and are often cultivated in gardens and nurseries in temperate Australia. However, over time knowledge of the precise origin of these cultivated plants has been lost, which means they are unsuitable for detailed scientific investigations.

All of Australia’s rhododendron populations are located at altitudes above 950m in National Parks within the Wet Tropics World Heritage Area. Most are difficult to access, requiring arduous climbs on rough foot tracks through leech-infested rainforest. And yet, although isolated in protected areas, they are threatened by human activities: loss of habitat due to climate change.

Recent climate modelling research published by scientists from James Cook University and the CSIRO predicts significant reductions in suitable habitat for a suite of mountaintop flora species in Australia’s tropics (our rhododendrons were not included in the analysis, but occupy the habitats assessed).

The habitat of many of these species is predicted to disappear altogether well before the end of the century.

Conservationists are racing to preserve samples of native rhododendrons.
Author provided

Using rhododendron as a model, the Australian Tropical Herbarium at James Cook University is working to save these threatened species through “ex situ” conservation – cultivation in temperate zone public gardens, well outside their natural range. Because the threatening process – climate change – is not readily mitigated, establishing precautionary ex situ collections is the only viable conservation intervention for these plants.

With funding from the Australian Rhododendron Society Victoria Branch and the Ian Potter Foundation, and the support of traditional owners, Queensland National Parks and the Wet Tropics Management Authority, we have mounted expeditions to collect samples from most of the known populations.

These expeditions have put expert naturalists into rarely visited and challenging environments. Beyond gathering rhododendron samples, new moss species have been discovered and are being named, a fern previously thought extinct was rediscovered, and beautiful little epiphytic orchids have been found on a mountain where they’d not previously been recorded. Golden bower-bird bowers have been mapped in remote mountain rainforests, and a likely new species of snail has been discovered.




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Australia now has a well-documented and genetically diverse collection of native rhododendron plants thriving in the Dandenong Ranges Botanic Garden.

We plan to expand this work, ensuring the preservation and public display of rhododendron and many other mountain species threatened by climate change.

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

Stuart Worboys, Laboratory and Technical Support Officer, Australian Tropical Herbarium, James Cook University

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

Contrary to common belief, some forests get more fire-resistant with age


Philip Zylstra, University of Wollongong

An out-of-season bushfire raged through Sydney’s southwest at the weekend, burning more than 2,400 hectares and threatening homes.

As the fire season extends and heatwaves become more frequent, it’s vital to preserve our natural protections. My research, recently released in the journal Austral Ecology, contradict one of the central assumptions in Australian fire management – that forest accumulate fuel over time and become increasingly flammable.




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I looked at every fire in every forest in the Australian Alps National Parks and found that mature forests are dramatically less likely to burn. Perhaps surprisingly, once a forest is several decades old it becomes one of our best defences against large bushfires.

The English approach

Within decades of the first graziers taking land in the Australian Alps, observers noticed that English-style management had unintended consequences for an Australian landscape.

In the British Isles, grazing rangelands had been created in the moors by regular burning over thousands of years, and this approach was imported wholesale to Australia’s mountains.

By 1893, however, the botanist Richard Helms had observed that as little as a year after fires were introduced to clear the land, “the scrub and underwood spring up more densely than ever”.

It’s true that, as in the rest of the country, many shrubs in the Alps are germinated by fire. However, the Alps also lie in a climatic zone where many trees are easily killed by fire. As a result, fire produces dense regrowth, and in the worst cases, removes the forest canopy that is essential to maintaining a still, moist micro-climate. Fires burning in this regrowth have abundant dry fuel, and they are exposed to the full strength of the wind.




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Theoretically, that should make regrowth more flammable than old growth, but it is at odds with the widespread assumption that fuels accumulate over time to make old forests the most flammable. Which is the case then? Are old forests more or less flammable than regrowth?

36 million case studies

Looking back over 58 years of mapped fires in the 12 national parks and reserves that make up the Australian Alps National Parks, I asked a simple question: when a wildfire burnt the mountains, did it favour one age of forest over another? If there were equal amounts of forest burnt say, five years, 10 years or 50 years ago, did fires on average burn more in one of those ages than another?

It’s not an entirely new question; people have often studied what happened when a fire crossed into recently burnt areas.

However, instead of just looking at part of a fire, I looked at every hectare it had burnt as separate case study. Instead of only looking at recent fires, I looked at every recorded fire in every forest across the Australian Alps National Parks. Instead of a handful of case studies, I now had 36 million of them.

Consistent with all of the other studies, I found that forests became more flammable in the years after they were burnt; but this is where the similarity ended. Rather than stop there as the other studies have done, I pushed past this line and found something striking. Regardless of which forest I examined, it became dramatically less likely to burn when it matured after 14 to 28 years.

Alpine Ash forests become increasingly flammable until the trees are tall enough to avoid ignition, and the shrubs thin out.
Phil Zylstra, Author provided

The most marked response of these was in the tall, wet Ash forests. These have been unlikely to burn for about three years after a fire, but then the regrowth comes in. Until these trees are about 21 years old, Ash forests are one of the most flammable parts of the mountains, but after this, their flammability drops markedly. When our old Ash forest is burnt, it is condemned to two decades in which it is more than eight times as flammable.

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The forests across the Alps have survived by constructing communities that keep fires small; but their defences are being broken down in the hotter, drier climate we are creating. Roughly the same area of the Victorian Alps was burnt by wildfire in the 10 years from 2003-2014 as had been burnt in the previous 50 years.




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More fire means more flammable forests, which in turn mean more fire; it’s a positive feedback that can accelerate until fire-sensitive ecosystems such as the Ash collapse into permanently more flammable shrublands. Knowing this, however, gives us tools.

The ConversationOld forests are assets to be protected, and priority can be given to nursing older regrowth into its mature stages. It may be the eleventh hour, but we’re better placed now to stand with the forests and add what we can to their fight to survive climate change.

Philip Zylstra, Research Fellow, flammability and fire behaviour, University of Wollongong

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

The world protests as Amazon forests are opened to mining



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The Amazon is the largest rainforest in the world.
Author provided

Beatriz Garcia, Western Sydney University

The Amazon, often described as the “lungs of the Earth”, is the largest rainforest in the world. Its extraordinary biodiversity and sheer scale has made it a globally significant resource in the fight against climate change.

But last week the Brazilian president Michel Temer removed the protected status of the National Reserve of Copper and Associates, a national reserve larger than Denmark.

The reserve, known as “Renca”, covers 46,000 square kilometres and is thought to contain huge amounts of copper, as well as gold, iron ore and other minerals. Roughly 30% of Renca will now be open to mining exploration. Renca also includes indigenous reserves inhabited by various ethnic communities living in relative isolation.

The decision, which has been denounced by conservation groups and governments around the world, comes as the unpopular Temer struggles with a crushing political and economic crisis that has seen unemployment rise above 12%.


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Political and economic turbulence

Brazil is currently in the middle of the largest corruption scandals in its history. Since 2014, an ongoing federal investigation called Operation Car Wash has implicated elite businesspeople and high-ranking politicians, uncovering bribes worth millions of dollars exchanged for deals with the state oil company Petrobas. According to the BBC, almost a third of President Temer’s cabinet is under investigation for alleged corruption.

There is no doubt that Brazil needs to find ways out of recession and unemployment. As the minister of mining and energy has said, “the objective of the measure [to allow mining] is to attract new investments, generating wealth for the country and employment and income for society.”

However it’s not clear that this move will benefit ordinary Brazilians. This is not the first gold rush into this area, and the Amazon still has high indices of poverty and many other challenges.

During the 1980s and 90s tens of thousands of miners flocked to gold deposits in the Amazon, driven by high international prices. One of the most famous examples, “Serra Pelada,” saw 60,000 men dig a massive crater in the Amazon Basin.

These mining operations typically provided little economic benefits to the local populations. Instead, they attracted thousands of people, which led to deforestation, violent land conflicts and mercury pollution in the rivers.

In reality the Amazon and its people deserve a sustainable model of development, which takes advantage of the outstanding biodiversity and beauty of its standing forests. The historical record shows mining is likely to lead to a demographic explosion, and further deforestation, pollution and land conflicts.

The principle of non-regression

One important aspect of international environmental law is called the “principle of non-regression”. The principle states that some legal rules should be non-revokable in the name of the common interest of humankind. Essentially, once a level of protection has been granted there is no coming back.

This principle is reflected in article 225 of the Brazilian constitution, which lays out the right to a healthy environment:

All have the right to an ecologically balanced environment […] and both the Government and the community shall have the duty to defend and preserve it for present and future generations.

The Brazilian constitution also describes the Amazon forest as a “national heritage”. It must then be treated accordingly.


Read more: Deep in the Amazon jungle, Brazil’s ‘hidden cities’ are in crisis


While the Amazon is a fundamental part of Brazil’s history, it’s also an essential part of the global battle against climate change. The Amazon contains half the worlds’ tropical rainforests, and its trees absorb and store vast amounts of carbon dioxide.

According to the Intergovernmental Panel on Climate Change, land use, including deforestation and forest degradation, is the second-largest source of global emissions after the energy sector.

Developed countries around the world have committed resources to help Brazil offset the costs of safeguarding their forests. One example is the Amazon Fund, created in 2008. It has received billions of dollars from foreign governments such as Norway and Germany, to combat deforestation and to promote sustainable practices in the Brazilian Amazon.

But with 14 million Brazilians unemployed, further assistance is required to ensure that they can protect their forests.

As well as governments, companies have also committed billions of dollars to fight climate change and support projects that reduce carbon emissions and promote energy efficiency. Most businesses have also created self-regulatory standards to ensure compliance with international laws and ethical standards.

The decision of the Brazilian government leaves us with two questions. How will the international community honour their commitments to keep global warming below 2℃, if countries begin rolling back their environmental protections? And how will companies involved in mining projects in the Amazon honour their social responsibility commitments and moral obligation towards present and future generations?

The degradation of the Amazon will affect the entire world. The clearing of the Amazon for mining will lead to the emissions of thousands of tons of greenhouse gases, furthering global warming and causing the irreversible loss of biodiversity, and water resources, as well as damage to local and indigenous communities.

The ConversationLet us not take a step back towards more destruction. Rather, let us strengthen the protection of our remaining forests.

Beatriz Garcia, Lecturer, Western Sydney University

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