Why are the world's older trees disappearing?

Dead old tree Older, bigger trees are dying all over the world

Gloriously grand, gnarly and twisted, big old trees are the kings of the forest, providing food and shelter for humans and animals since the dawn of time.

And they make pretty nifty places to build treehouses too!

But now scientists say these ancient giants are under threat. According to a report published recently in the journal Science, death rates have increased alarmingly among trees between 100 and 300 years old.

Start Quote

They're being cooked by higher temperatures or being burnt in fires”

End Quote Prof David Lindenmayer Australian National University

Swedish forestry records dating back to the 1860s were the first hint that researchers found of the scale of the problem. A 30-year study of Mountain Ash in Australia showed that big trees were dying at 10 times the normal rate in years when there wasn't a big fire.

The problem, they say, is global. The causes varied.

"We're seeing mass mortality in many systems," said Prof David Lindenmayer from the Australian National University.

Bigger means weaker

From California's Yosemite National Park, to the African savannahs, to the Brazilian rainforest, the older bigger trees are being lost regardless of climate and environment.

"They're being cooked by higher temperatures or being burnt in fires. We don't always see the differential, that the older, bigger trees are more prone," said Prof Lindenmayer.

Bark beetles Spruce trees felled by bark beetles in Alaska

Across an agricultural landscape like Australia, there are many bigger older trees visible. But, according to Prof Lindenmayer, the positive appearance is deceiving.

"Not one of these trees has been able to reproduce successfully, because of grazing," he said referring to the damage done to saplings by hungry cattle and sheep.

"We have 5-10 years left where they are still producing seeds, we need to control the grazing process - we need to work with land owners."

As well as logging and farming, humans are also introducing new species that are proving deadly to big trees.

"We are changing the world in so many ways at once," says another of the authors, Professor Bill Laurance of James Cook University.

"We are moving organisms and disease and pathogens - all over the planet weeds and other exotic species are proliferating like crazy!"

Anyone who has been keeping track of the ash dieback story in recent months would probably agree.

Good man bad man

In many cases it is the combination of factors that is proving toxic for trees. In the western part of the US, pine bark beetles have thrived, partly because of changing temperatures.

"The populations are building up because they would normally be killed off by winter," said Prof Laurance, "but the winters are becoming so much milder they are proliferating and in some cases are wiping out entire forests."

But while the presence of humans has been a major factor in increasing deforestation and the clearing of land for farming, the absence of humans can also be a threat to trees.

A report about the Peruvian Amazon says that farmers are leaving rural areas for jobs in the cities. The authors argue that this actually increases the threat of fires damaging trees.

"When you have more fallow land," said lead author Maria Uriarte, "and fewer people around to work at control, that combination generates those big fires."

When it comes to trees, we just can't seem to do right for doing wrong.

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Matt McGrath Article written by Matt McGrath Matt McGrath Environment correspondent

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  • rate this

    Comment number 36.

    10.Giles Cowley - ".......The solution? Depopulation + common sense......"

    Yeah, right......there is no such thing as common sense.......it is a figment of your & main other slack thinkers' imaginations:


  • rate this

    Comment number 35.

    We all have the opportunity to help .Everyone should plant 5 trees this spring.You,ll see the fruits of what you have done in a couple of years time and know that you planted it .You will be the one who helped a little bit .

  • rate this

    Comment number 34.

    EVERY tree in the UK over, say, 25 years should automatically have a Tree Preservation Order (TPO) on it so no-one can cut it down unless a planning application is made and granted by the local council. For forests in overseas countries, I fear there is little hope until corruption is iradicated first - My teacher always told me, "forests are the lungs of the world" tell that to politicians..

  • rate this

    Comment number 33.

    and we're part of a vast interplanetary system stretching 700 billion miles long

    with nine planets and sun we think the earths the only one that has life on it although we could be wrong

  • Comment number 32.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • Comment number 31.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • Comment number 30.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 29.

    26 Skeerbs - Considering most of the UK used to be entirely covered in trees, I often wonder why we don't start replanting them on unused & worthless land. They'd probably be better for the environment than windmills, and look nicer too. In a couple of decades we'd also have a great new source of sustainable fuel & building material.
    Perhaps even genetically modify them to grow faster.

  • Comment number 28.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 27.

    Anyone who thinks the world can last forever with the punishing it has taken post industrialisation is deluding themselves. If the ecosystems all collapsed overnight and everyone died earth would only be just another dead rock in space anyway and that would be that blotto extinction. The earth has also seen it's best days already and if the patient (or victim) is sadly deteriorating - 'shrugs'.

  • rate this

    Comment number 26.

    Well, we aren't managing most of these "specimen" trees any more are we. Most of these trees were never meant to be specimens, or subject to TPOs. They were a harvested commodity, either grown for single main trunks or coppiced and pollarded. These are mature trees coming down in their prime, just like they would in ages past when used as a crop. Start managing the tree crop and things will be ok.

  • rate this

    Comment number 25.

    #23 Oops I just noticed that I mangled my sentence in that last post. - It was meant to be the ‘speed’ of the photosynthesis - and the ‘energy’ in the light. . . Another bad day. : (

  • rate this

    Comment number 24.

    Tree preservation orders on large mature trees mean they can often be left isolated and exposed in developed land, deprived of the wind protection of surrounding smaller, younger trees. They also lose the biodiversity that gives protection from various pests.

    Roots may be cut for foundations, soil mechanics affected by drainage, and many other factors.

    No surprise nor mystery here.

  • rate this

    Comment number 23.

    #20 LUFC_FR, #21 Ed

    I don't think that it is CO2 levels that are the primary limit the speed of plant and tree growth. There is the speed of the light energy available, the photosynthesis reaction itself, nutrient supply and internal transport, overall temperature, water availability, and so on. Hotter climate might make plants grow faster in some places but it also encourages dessert growth.

  • rate this

    Comment number 22.

    Old trees dying - just an ongoing part of the death of nature. In physics terms from one point of view living things are essentially anti-entropy pumps & reservoirs. I might suggest that something is going wrong with this ability to fight entropy. If the ability is treated as a quantum field it explains a lot - & suggests that we humans have done something that is disrupting the ability generally.

  • rate this

    Comment number 21.

    "If CO2 has been rising, (it hasn't for the last 15 years) then trees would be thriving, not dying."

    Please provide a reference to a scientific study for this extraordinary assertion.

    Anyone can make wild claims, but without being backed by scientific evidence they are worth nothing.

  • rate this

    Comment number 20.

    CO2 is food for vegetation, especially trees.
    If CO2 has been rising, (it hasn't for the last 15 years) then trees would be thriving, not dying.

  • rate this

    Comment number 19.

    I cannot read the article. It is paywalled.

  • rate this

    Comment number 18.


    Although the root system of a living tree is comparable with its branches, they often cannot be torn out of the earth and bedrock fissures, so snap off when it falls.

    Look at some pics of those felled by recent storms.

  • rate this

    Comment number 17.

    Eddy from Waring if you look carefully you'll see the tree has little or no roots when it should normally have a root system roughly equal to the branch system [hence the difficulty in pulling out tree stumps] which means the roots died long before the tree fell over.


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