Are young trees or old forests more important for slowing climate change?



Jeremy Kieran/Unsplash, CC BY-SA

Tom Pugh, University of Birmingham

Forests are thought to be crucial in the fight against climate change – and with good reason. We’ve known for a long time that the extra CO₂ humans are putting in the atmosphere makes trees grow faster, taking a large portion of that CO₂ back out of the atmosphere and storing it in wood and soils.

But a recent finding that the world’s forests are on average getting “shorter and younger” could imply that the opposite is happening. Adding further confusion, another study recently found that young forests take up more CO₂ globally than older forests, perhaps suggesting that new trees planted today could offset our carbon sins more effectively than ancient woodland.

How does a world in which forests are getting younger and shorter fit with one where they are also growing faster and taking up more CO₂? Are old or young forests more important for slowing climate change? We can answer these questions by thinking about the lifecycle of forest patches, the proportion of them of different ages and how they all respond to a changing environment.




Read more:
Using forests to manage carbon: a heated debate


The forest carbon budget

Let’s start by imagining the world before humans began clearing forests and burning fossil fuels.

In this world, trees that begin growing on open patches of ground grow relatively rapidly for their first several decades. The less successful trees are crowded out and die, but there’s much more growth than death overall, so there is a net removal of CO₂ from the atmosphere, locked away in new wood.

As trees get large two things generally happen. One, they become more vulnerable to other causes of death, such as storms, drought or lightning. Two, they may start to run out of nutrients or get too tall to transport water efficiently. As a result, their net uptake of CO₂ slows down and can approach zero.

Eventually, our patch of trees is disturbed by some big event, like a landslide or fire, killing the trees and opening space for the whole process to start again. The carbon in the dead trees is gradually returned to the atmosphere as they decompose.

The vast majority of the carbon is held in the patches of big, old trees. But in this pre-industrial world, the ability of these patches to continue taking up more carbon is weak. Most of the ongoing uptake is concentrated in the younger patches and is balanced by CO₂ losses from disturbed patches. The forest is carbon neutral.

A misty forest scene.
New trees absorb lots of carbon, old trees store more overall and dead trees shed their carbon to the atmosphere.
Greg Rosenke/Unsplash, CC BY-SA

Now enter humans. The world today has a greater area of young patches of forest than we would naturally expect because historically, we have harvested forests for wood, or converted them to farmland, before allowing them to revert back to forest. Those clearances and harvests of old forests released a lot of CO₂, but when they are allowed to regrow, the resulting young and relatively short forest will continue to remove CO₂ from the atmosphere until it regains its neutral state. In effect, we forced the forest to lend some CO₂ to the atmosphere and the atmosphere will eventually repay that debt, but not a molecule more.

But adding extra CO₂ into the atmosphere, as humans have done so recklessly since the dawn of the industrial revolution, changes the total amount of capital in the system.

And the forest has been taking its share of that capital. We know from controlled experiments that higher atmospheric CO₂ levels enable trees to grow faster. The extent to which the full effect is realised in real forests varies. But computer models and observations agree that faster tree growth due to elevated CO₂ in the atmosphere is currently causing a large carbon uptake. So, more CO₂ in the atmosphere is causing both young and old patches of forest to take up CO₂, and this uptake is larger than that caused by previously felled forests regrowing.

The effect of climate change

But the implications of climate change are quite different. All else being equal, warming tends to increase the likelihood of death among trees, from drought, wildfire or insect outbreaks. This will lower the average age of trees as we move into the future. But, in this case, that younger age does not have a loan-like effect on CO₂. Those young patches of trees may take up CO₂ more strongly than the older patches they replace, but this is more than countered by the increased rate of death. The capacity of the forest to store carbon has been reduced. Rather than the forest loaning CO₂ to the atmosphere, it’s been forced to make a donation.

So increased tree growth from CO₂ and increased death from warming are in competition. In the tropics at least, increased growth is still outstripping increased mortality, meaning that these forests continue to take up huge amounts of carbon. But the gap is narrowing. If that uptake continues to slow, it would mean more of our CO₂ emissions stay in the atmosphere, accelerating climate change.

Overall, both young and old forests play important roles in slowing climate change. Both are taking up CO₂, primarily because there is more CO₂ about. Young forests take up a bit more, but this is largely an accident of history. The extra carbon uptake we get from having a relatively youthful forest will diminish as that forest ages. We can plant new forests to try to generate further uptake, but space is limited.

But it’s important to separate the question of uptake from that of storage. The world’s big, old forests store an enormous amount of carbon, keeping it out of the atmosphere, and will continue to do so, even if their net CO₂ uptake decreases. So long as they are not cut down or burned to ashes, that is.The Conversation

Tom Pugh, Reader in Biosphere-Atmosphere Exchange, University of Birmingham

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

Smart city planning can preserve old trees and the wildlife that needs them



File 20180629 117377 112lzty.jpg?ixlib=rb 1.1
Mature trees have horizontal branches that are attractive to wildlife and birds.
from shutterstock.com

Philip Gibbons, Australian National University

Australia’s landscapes are dotted with mature eucalypts that were standing well before Captain Cook sailed into Botany Bay. These old trees were once revered as an icon of the unique Australian landscape, but they’re rapidly becoming collateral damage from population growth. Mature eucalypts are routinely removed to make way for new suburbs.

Good planning can ensure many more mature eucalypts are retained in urban developments.
Philip Gibbons

This has a considerable impact on our native fauna. Unless society is prepared to recognise the value of our pre-European eucalypts, urban growth will continue to irrevocably change our unique Australian landscape and the wildlife it supports.




Read more:
Trees are a city’s air conditioners, so why are we pulling them out?


Why are old eucalypts worth saving?

In urban landscapes, many consider large and old eucalypts a dangerous nuisance that drop limbs, crack footpaths and occupy space that could be used for housing. But when we remove these trees they are effectively lost forever. It takes at least 100-200 years before a eucalypt reaches ecological maturity.

Birds use old eucalypts as places to perch or nest.
Philip Gibbons

As trees mature, their branches become large and begin to grow horizontally rather than vertically, which is more attractive to many birds as perches and platforms where they can construct a nest.

Wildlife also use cavities inside ageing eucalypts. These are formed as the heartwood – the dead wood in the centre – decays. When a limb breaks it exposes cavities where the heartwood once occurred.

This is such a ubiquitous process in our forests that around 300 of Australia’s vertebrate species, such as possums, owls, ducks, parrots and bats, have evolved to use these cavities as exclusive places to roost or nest.

Mature trees also support high concentrations of food for animals that feed on nectar, such as honeyeaters, or seed, such as parrots.




Read more:
Concrete jungle? We’ll have to do more than plant trees to bring wildlife back to our cities


One study found that the number of native birds in an urban park or open space declines by half with the loss of every five mature eucalypts.

How can we keep old trees?

Decaying heartwood in older eucalypts leads to some large branches falling. This is when most eucalypts are removed from urban areas. So we remove trees at the exact point in time when they become more attractive to wildlife.

Plantings around the base of a mature eucalypt discourage pedestrian traffic or parked cars.
Philip Gibbons

A well-trained arborist knows that old — or even dead — eucalypts don’t need to be removed to make them safe. A tree is only dangerous if it has what arborists call a target. Unless there is a path, road or structure under a tree, then the probability of something or someone being struck by a falling branch is often below the threshold of acceptable risk.

Progressive arborists first focus on eliminating targets. For example, they might plant shrubs around the base of dead or rapidly ageing trees to minimise pedestrian traffic, rather than eliminating trees.

Where targets can’t be managed, trimming trees can remove branches that have a high risk of falling. Trees can also be structurally supported (braced) to remain stable. Such trees remain suitable as habitat for many native species.

Developers can plan around old trees.
from shutterstock.com

How to design around trees

The removal of mature eucalypts is, in part, due to urban developers not considering these trees early in the planning process.

I have worked with one developer on the outskirts of Canberra to identify important trees. The developer then planned around, rather than in spite of, these trees.

The outcome has been around 80% of mature trees have been retained. This is much greater than the proportion of mature trees retained in other new urban developments in Canberra.




Read more:
Trees versus light rail: we need to rethink skewed urban planning values


The ConversationAustralia’s population is projected to double in 50 years, so our suburbs will continue to infill and expand. This will result in the continued loss of our mature eucalypts unless our approach to planning changes.

Philip Gibbons, Associate professor, Australian National University

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

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



Image 20170412 25888 1jhrjzu
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 Conversation

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.

Bulahdelah


Kevin's Daily Photo, Video, Quote or Link

So I was right about my day when I spoke of it yesterday. Not a lot going on today, so today’s post will be more about yesterday. I hope that makes perfect sense to everyone – it sounded even worse with the original way I was going to write it (I was trying to be clever, so went for simplicity in the end).

Bombah Point Ferry

The Punt at Bombah Point On the Punt

On the Punt

To get to Bulahdelah from Hole in the Wall, you need to go via Bombah Point and the ferry service there. I guess you could also call it a punt. Many people still call it that. Anyhow, as the pictures show, it doesn’t cover a great distance. How much is the charge for this journey – at the moment it’s $5.00 AU. Seems a little excessive for something that’s over in less than 5 minutes. Still, there is a…

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Climate Change: Threat to Old Growth Trees


Climate change is emerging as a major threat to old growth forest and old large trees in particular.

For more visit:
http://news.mongabay.com/2012/0126-big_trees.html

Mount Everest to be Given a Clean Up


The world’s highest mountain, Mount Everest, is to be given a clean up. Everest, which was first climbed by Edmund Hillary in 1953, has become something of a garbage tip. Everything from climbers rubbish to dead bodies has been left on the mountain. Now a Nepalese expedition made up of twenty Sherpa mountaineers and eleven support crew is seeking to remove some of the garbage left behind since that first ascent.

The government of Nepal wants to clean up the popular tourist attraction, bringing down rubbish that includes old tents, climbing equipment and the odd body. Global warming has led to much of the rubbish (and several bodies) no longer being covered by snow and ice.

Over 300 people have been killed attempting the climb to the top of the world, the Mount Everest summit.

For more on this story, see the Reuters article at:

http://af.reuters.com/article/worldNews/idAFTRE63I0XE20100419

NSW Road Trip 2010: Packing & Getting Ready


It is now the day prior to the NSW Road trip 2010. I have begun packing and getting ready for the journey that lies ahead. I don’t expect to be taking a lot of gear, as I won’t be doing a lot of cooking, washing, etc, on this trip.

I have learnt that it is important to not assume that you have everything you need and then find out the day before that you may not – I already knew this of course, but having recently moved, I no longer have everything that I once did. For example, I do not presently have a sleeping bag. I got rid of the last one because it was old and smelly, and I planned to buy another. But a lot has happened since mid 2007 when I packed to move – including a near fatal car accident that put my purchasing plans well and truly on hold, and they then slipped into the area of my mind that ‘forgets.’

So now I have no sleeping bag – but that isn’t too important as I don’t believe I really need one this time round. It is a road trip, with several cabin stops along the way and only caravan parks with powered sites for the rest. I will take a couple of blankets should I need them (which I don’t believe I will – it will be quite hot in the outback this time of year).

Of course it is not just the sleeping bag that is missing. I am also missing a fly cover for the tent, but thankfully I had two tents so I’m OK there. There are a number of other items missing also, but I don’t really need them this time round. Thankfully I have spotted all this now, which means I can plan to purchase what I need for future adventures, back pack camping, etc. I had of course planned to buy these items, but with the passing of time I forgot.

Anyhow, the packing is under way and I just hope I don’t forget something I wish I had packed when I am on the journey. I’m relatively sure I haven’t – which isn’t to say That I have forgotten something.

What I’d like to remember – and tomorrow I’ll know for sure if I have – is how I packed the car, so that everything was easily accessible. I was fairly well organised for this sort of thing when I was doing it fairly regularly several years ago – but it has been a while. Minimal gear wisely packed, without leaving anything necessary behind – that’s the key for this type of journey and vacation.

This will be the first time however, that I have a bag dedicated to my online activities – laptop, digital camera, web cam, flash drives, etc. I hope to keep an accurate and useful journal online at the kevinswilderness.com website, with photos, comments, route map, etc. So this is a ‘new’ bag that I need to organise in the overall scheme of things.

Anyhow, packing is now underway and coming to a conclusion. The journey will soon kick off.