1,600 years ago, climate change hit the Australian Alps. We studied ancient lake mud to learn what happened

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Zoë Thomas, UNSW; Haidee Cadd, University of Wollongong, and Larissa Schneider, Australian National UniversityIf you’ve ever visited Australia’s highest peak — Mount Kosciuszko — you might remember the long uphill trek to the summit past some of Australia’s most picturesque and rugged landscapes. Vibrant snow gums, boardwalks with meadows of exquisite alpine plants, and blinding patches of snow.

As you approach the summit, a quartet of stunning blue lakes appear, created by glaciers during the last ice age that carved new valleys out of the mountain.

Lakes like these are windows to the past, offering an opportunity to understand how our climate and environment has changed over hundreds to thousands of years. One such lake, Club Lake — so-named for its resemblance to a suit in a deck of cards — was the focus of our new study.

After studying the lake’s sediment, we learned the Australian Alps experienced a sudden climate change about 1,600 years ago that brought a long spell of warmer conditions. What makes this sudden warming event particularly interesting is that it bears striking similarity to today.

Climate change in the Australian Alps

The Australian alpine region is the traditional home of a number of Aboriginal groups, including the Ngarigo, Walgalu and Djilamatang people. It is also home to highly diverse flora and fauna that occur nowhere else, from billy buttons (Craspedia costiniana) known for their vibrant yellow rosette of tiny flowers, to the broad-toothed rat and its chubby cheeks.

But this unique wildlife is under immense threat from climate change.

By 2100, Australia may warm by at least 4℃, with bushfires becoming more frequent and devastating. The fragile alpine ecosystem will be hit particularly hard by these changes.

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Many of Australia’s alpine species are already near their climatic limits, and are constrained by altitude. They’re at risk of becoming regionally extinct if their climatic thresholds are exceeded. As the temperature warms, treelines move upslope to cooler temperatures, pushing alpine flora and fauna to higher elevations. At some point they can go no higher — they’re squeezed out of their niche.

The critically endangered mountain pygmy-possum, for example, relies on the seasonal snowpack for winter hibernation, but increased temperatures are limiting this habitat.

A dip into the past

Our study showed Club Lake holds vital clues to the link between rising temperatures, loss of native plant species and more frequent fires in the Snowy Mountains.

Lake sediments are used all over the world as indicators of climate and environmental change because of the unique way they trap material. A body of water can act as a seal that ensures sediments are largely undisturbed over time.

We extracted sediments from the bottom of Club Lake to a depth of 35 centimetres. This equates to about 3,500 years of history, approximately 100 years for each centimetre.

Club Lake in Mt Kosciuszko.
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To work out how temperatures have changed over this time, we looked for the presence of molecular fossils, called “lipid biomarkers”. Analysing these biomarkers in the laboratory can tell us what the temperature in the environment was like, hundreds or thousands of years ago.

In the 3,500 years we examined, we detected a gradual warming trend. Superimposed on this, we found a sudden warming event that started 1,600 years ago, and lasted about six centuries. We suspect it was due to an atmospheric phenomenon linking higher tropical sea surface temperatures to southeastern Australia.

We’re not yet sure how much of Australia was affected by this warming, but other research from 2018 measured similar temperature changes in stalagmites from the Yarrangobilly caves 50 kilometres away.

Alpine snow gums (Eucalyptus pauciflora)
Zoë Thomas

What happened during this climate change?

During this unusual warmth, alpine herbs and shrubs declined, while the abundance of trees, particularly eucalyptus, increased. We know this by looking at grains of pollen preserved at different depths within the lake sediment samples, which indicates what types of plants were growing nearby.

We also found small particles of charcoal, produced by bushfires, embedded within the sediment layers. This showed the changes in vegetation also coincided with greater fire activity.

What surprised us most, however, was discovering a large increase in mercury at this time.

Mercury, which occurs naturally in the environment, is the only metal that’s liquid at room temperature, and is particularly sensitive to temperature changes. Higher temperatures enhance mercury deposition from the atmosphere, and our study shows a five-fold increase in mercury flux 1,600 years ago.

Alpine herbfields.
Nicola Pain

Industrial activities over the last 150 years, such as burning coal, have increased the abundance of mercury significantly. Our findings suggest future climate change is likely to increase the risk of mercury exposure not just in cities, but also in the seemingly remote Australian alpine environment.

Mercury contamination is a significant public health and environmental problem. At certain levels it’s poisonous to the nervous system, and it does not easily degrade.

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What can we do?

Insights from the past can help governments, environmental agencies, and scientists come up with effective strategies to protect the vulnerable flora and fauna of the Australian Alps. But it’s not just changes in climate they’ll have to contend with in future.

There are other perils, such as soil erosion and habitat fragmentation from the legacy of sheep and cattle grazing, and tourism. Invasive pests and pathogens are likely to further reduce the resilience of these alpine ecosystems.

Feral horses are a significant threat to native wildlife in Australia’s alpine region.
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Restoration programs over the last 50 years have aimed to revitalise the natural vegetation in the Kosciuszko National Park following 135 years of grazing — finally banned in 1969 — and the environmental damage caused by the Snowy River Hydro-Electric scheme.

More recently, the federal government has committed A$3.5 million towards recovery from the devastating 2019-2020 bushfires. Incorporating Aboriginal knowledge into mainstream fire management is essential for tackling future crises.

This is the critical time for climate action to protect this unique and iconic Australian landscape.

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Zoë Thomas, ARC DECRA Fellow, UNSW; Haidee Cadd, Research associate, University of Wollongong, and Larissa Schneider, DECRA fellow, Australian National University

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

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Where the old things are: Australia’s most ancient trees

Wollemia pine pollen cone. Wollemia pines (found in the wild only in Australia) are one of the most ancient tree species in the world, dating back 200 million years.
Velela/Wikipedia

Cris Brack, Australian National University and Matthew Brookhouse, Australian National University

They say that trees live for thousands of years. Like many things that “they” say, there is a germ of truth in the saying (even though it is mostly false).

The vast majority of trees that burst forth from seeds dropped on the Australian continent die before reaching maturity, and in fact most die within a few years of germination.

But depending on how you define a tree, a very select few trees can live for an astoundingly long time.

What are the oldest trees?

If we define a “tree” as a single stemmed woody plant at least 2 metres tall, which is what most people would identify as a tree, then the oldest in Australia could be a Huon Pine (Lagarostrobos franklinii) in Tasmania, the oldest stem of which is up to 2,000 years old.

However, the Huon Pine is also a clonal life form – the above-ground stems share a common root stock. If that common root stock is considered to be the base of multi-trunked tree, then that tree could be as old as 11,000 years.

But if you accept a clonal life form as a tree, even that ancient Huon age pales into insignificance against the 43,000-year-old king’s holly (Lomatia tasmanica), also found in Tasmania.

King’s Holly, or Lomatia tasmanica, can form clones nearly 50,000 years old.
Natalie Tapson/Flickr, CC BY-NC-SA

Once you accept that a common, genetically identical stock can define a tree, then the absolute “winner” for oldest tree (or the oldest clonal material belonging to a tree) must go to the Wollemi Pine (Wollemia nobilis). It may be more than 60 million years old.

The Wollemi pine clones itself, forming exact genetic copies. It was thought to be extinct until a tiny remnant population was discovered in Wollemi National Park in 1994. The trunk of the oldest above-ground component, known as the Bill Tree, is about 400-450 years old. But the pine sprouts multiple trunks, so the Bill Tree’s roots may be more than 1,000 years old.

There is also substantial evidence that the tree has been cloning itself and its unique genes ever since it disappeared from the fossil record more than 60 million years ago.

How do you date a tree?

If no humans were around to record the planting or germination of a tree, how can its age be determined? The trees themselves can help tell us their age, but not just by looking at their size. Big trees are not necessarily old trees – they might just be very healthy or fast-growing individuals.

A much more reliable way to determine age of a tree is through their wood and the science of dendrochronology (tree-ring dating).

Dendrochronology involves counting tree rings to date a tree. The wider the ring, the more water the tree absorbed in a given year.
sheila miguez/flickr, CC BY-SA

Many trees lay down different types of cell wall material in response to seasonal patterns of light, temperature or moisture. Where the cell walls laid down at the beginning of the growth season look different to those laid down at the end of the season, rings of annual growth can be seen in cross-sections of the tree.

This map of growth patterns can also be cross-dated or correlated with major events like multi-year droughts or volcanic eruptions that spewed material into the atmosphere to be incorporated into the wood of the tree. But the cell walls are more than just calendars.

Why so old?

Individual tree stems can live for so long because of the structure of the wood and the tree’s defence mechanisms. The woody cell walls are very strong and resist breakage.

In fact, scientists have recently discovered that these walls contain a structure – nanocrystaline cellulose – that is currently the strongest known substance for its weight.

Wood can, however, be broken down by insects and fungi. Even though there is little nutrition or energy in wood, there is some – and there are plenty of organisms that will try and use it.

But trees are not defenceless, and can fight back with physical barriers or even chemical warfare. When one tree is attacked by these destructive forces, individuals may even signal to other trees to be aware and prepare their own defences to fight off death and decay.

The death of trees

So why don’t all trees live for centuries or millennia, and why do so many die before even reaching maturity?

Adult Wollemi pines in the wild.
J.Plaza/Van Berkel Distributors

Seedlings and young trees may die because they have germinated in an area where there’s not enough water, nutrients or light to keep them alive as adults. Young trees also haven’t had much time to develop barriers or defences against other organisms and may be browsed or eaten to death.

Some trees simply fall prey to accidents: wind storms, fires or droughts. This is just as well, because there is a vast number of plants and animals – including humans – which rely on the wood and other components of these dead trees for their food and shelter.

But increasingly we may see trees dying because the environment is changing around them and they may not be able to cope. This is not just due to climate change; urban development and agricultural expansion, pollution and even too much fertiliser acting as a poison – even our most remote environments are subject to these changes.

But that doesn’t necessarily mean we will have no more very old trees. The Wollemi Pine’s genes have already survived over millions of years, multiple ice ages and warming periods and even the fall of the dinosaurs and rise of humans. And now,
people have deliberately spread Wollemi Pine trees all around the world so they are living in a wide range of countries and climates, meaning that the risk of them all dying out is substantially reduced.

Maybe we can do the same for other trees, ensuring that trees will outlive us all.

Cris Brack, Assoc Professor Forest measurement & management, Australian National University and Matthew Brookhouse, Research fellow, Australian National University

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

Article: Canada – Tragic Loss of an Ancient Cedar Tree

The following link is to an article that looks at how tree poachers have stolen an 800 year old Cedar from a Canadian forest.

For more visit:
http://grist.org/list/tree-poachers-steal-800-year-old-red-cedar/

China: Ancient Forest Discovered Under Coal Mine

The link below is to an article reporting on how American and Chinese scientists have discovered a massive forest buried under a coal mine near Wuda, in Inner Mongolia, China.

For more visit:
http://gizmodo.com/5886774/extraordinary-298+million+year+old-forest-discovered-under-chinese-coal-mine/

Russia: Silene stenophylla Grows Again

The link below is to an article reporting on how Russian scientists have grown ancient plants from seeds frozen thousands of years ago.

For more visit:
http://geeks.thedailywh.at/2012/02/20/30000-year-old-plants-of-the-day/