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Big old trees grow faster, making them vital carbon absorbers

Large, older trees have been found to grow faster and absorb carbon dioxide more rapidly than younger, smaller trees, despite…

Large trees don’t slow down with age. Michelle Venter

Large, older trees have been found to grow faster and absorb carbon dioxide more rapidly than younger, smaller trees, despite the previous view that trees’ growth slowed as they developed.

Research published in the journal Nature this week shows that in 97% of tropical and temperate tree species, growth rate increases with size. This suggests that older trees play a vital role in absorbing carbon dioxide from the atmosphere.

William Morris, a PhD candidate from the University of Melbourne involved in the study, says that prior to the study, the common assumption was that as trees aged, their growth rate and carbon absorption decreased. Morris explained that the belief came from two different lines of evidence:

“First, it has been shown that at the whole forest level, young forest acquires mass faster than old-growth forest. Second, studies have shown that the leaves of older trees are less efficient at photosynthesising than the leaves of younger trees.”

But the new study, which involved 403 tree species and was led by authors from the US Geological Survey, examined carbon storage at the level of individual trees rather than forests.

The findings highlight the value of large, older trees, which have been declining in number, as important carbon sinks.

“Previously we thought of big old trees as simply carbon stores. But now we know that not only are they storing lots of carbon, they are also sequestering more carbon and faster than smaller trees,” said Morris.

David Lindenmayer, a professor of environment at the Australian National University, described findings of the study as “immense”, with implications of global significance.

“It highlights another reason why it is really important that we grow as many areas of forest through to being old growth forests as possible,” he said.

“The more carbon we can store in forests, the more chance we have of reducing the mega-effects that are going to arise from massive climate change. Storing large amounts of carbon in forests is absolutely critical to that and the way you do that is you have big, old trees.”

Bill Laurance, a professor at James Cook University’s Centre for Tropical Environmental and Sustainability Studies, agreed that the study reinforces the importance of large, older trees for absorbing carbon.

“That underscores the importance of saving old-growth forests, which harbour most big old trees, if we want to have the maximum benefit for slowing climate change,” he said.

The findings of the study highlight the importance of older trees for forest management programs. Flickr/Ta Ann

The study is also expected to have implications for forest management plans. Morris explained that the new findings can change how individual trees are managed.

“As we now know that the biggest trees are the most valuable as both carbon stores and carbon sinks. If a manager’s goal is to maximise carbon uptake, then maintaining larger trees may be an efficient way to do so,” he said.

Lindenmayer said that the study highlights flaws in forest policy in Victoria and Tasmania, where old-growth forest is often cleared for pulp and timber purposes.

“Native forests, in terms of their value as carbon storage, significantly outweigh their value as pulp and timber. When you add that to the value of biodiversity and water, it’s pretty clear what forest policy should be,” he said.

Join the conversation

52 Comments sorted by

  1. Neville Mattick
    Neville Mattick is a Friend of The Conversation.

    Grazier: ALP Member at A 4th Generation Grazing Station

    Very interesting to read this - thank you.

    The landscape here is about 15Km² variants of Yellow Box, White Box and Blakelys Red Gum in the majority.

    There are few that are over 40 metres tall, with the some around 30 metres and a most at 15 ~ 20.

    Investigating sequestration; I was told that the ecosystem would be "neutral" at best and that NO Carbon offset or value would occur, but for the few square Kilometres of regrowth (in those and about ten other) Tree types found here. I felt that was rubbish at the time, but could not proceed further, maybe I am onto something sustainable for a change?

    I can't tell from the research, were Box, Gum and say Stringybark part of the sequestration assessment?

    Or was it all just Northern Hemisphere species and if so how would that relate to Forest in Australia?

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  2. John Newlands

    tree changer

    I live on the edge of country that can support Dicksonia ferns as shown. My feeling is that edge is retreating back to higher areas that may eventually become disconnected. I also doubt we (the human race) will ever again see 100 metre tall flowering trees. Eucalyptus regnans aka mountain ash or swamp gum even if protected from logging may be finding it too hot, That's either from the sun or people playing with matches.

    On policy issues the likely new government in Tasmania in March says it will allow logging in high conservation areas. To their credit the current federal govt disdains overseas carbon sink offsets. I thought it was cultural cringe before as in our forests weren't good enough.

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  3. James Hill

    Industrial Designer

    Big old trees have a certifiable address and can most probably be seen from space and recognised in photographs.
    so how about a stock marke specialising in the ownership and protection of individual trees.
    And let the stock market decide what they are "worth".
    They are rare, they are old, and they seem irreplaceable.
    If very dodgy art works can achieve such very large prices why not trees.
    After all they can be identified visually, and have "addresses".
    An established provenance as it were.
    Their capacity to store carbon might be just a small part of their ultimate value to cashed up million and billionaires, wondering where to park their cash.
    Oh, and these are "growing" assets, amazing, that the greed merchants haven't worked this one out yet.

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    1. Malcolm Whitmore

      Project Manager

      In reply to James Hill

      You are right to say these trees are irreplaceable but the idea of using the stock market to protect them is fundamentally flawed because every stock market is doomed to fail at some time soon due to the inherent instability of the way money is created by creating debt.
      The example of the Dutch bulb market collapse shows the total disregard for plants that finance has when the debt collector knocks on the door. Market valuation is based on herd instinct .
      We need to stand up and identify these forests and the wonderful trees in them as part of our global commons and it is essential to establish laws that work for the benefit of all creation so as to protect them

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    2. James Hill

      Industrial Designer

      In reply to Malcolm Whitmore

      Thanks Malcolm, it is question of which value system we use.
      But these trees are presently under threat because of the monetary value system.
      Those people who might be employed to "manage" these trees for the "speculators" might correspond to the slaves who continued to feed themselves after the Roman empire collapsed.
      We have to reject this "wilderness" approach which argues that no humans ever be involved with looking after these trees.
      The trees have to be "valued" in order to be protected…

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    3. Michael Shand

      Software Tester

      In reply to James Hill

      Don't be fooled into thinking that financial speculators know what they are doing

      The Pope actually has a very good speech about the problem with current economics

      Remember these are the same guys that still value fossil fuel reserves at a high price and still invest more money into fossil fuel than renewables

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    4. John Harland

      bicycle technician

      In reply to James Hill

      It is certainly a call to reassess the prices people pay to harvest the timber. If a forest has such value standing, it should cost a great deal to be allowed to fell it.

      The present price signals are utterly out-of-proportion to the value of standing old-growth forest and this research emphasises that further.

      If we look at the challenge in terms of value, even using the deeply-flawed linear models of mainstream economics, we can see more clearly the value of alternatives such as retraining and redeploying forest workers, rather than simply unemploying them.

      Old-growth forestry is a highly destructive form of job creation. We can capitalise alternative, productive and creative, jobs much more cheaply.

      We do need to remind ourselves constantly that money values are a poor reflection of real-world value, but they can be a means of shaping more-productive policy than simply bans that become a political badminton at the next election.

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    5. James Hill

      Industrial Designer

      In reply to John Harland

      Thanks John, imagine the value, for example the giant fig tree sighted by Cook in what is now known as the Big Scrub in Northern New South Wales.
      It has since collapsed and died but covered several acres apparently.
      Now some billionaire might be happy to compete with others for bragging rights re adopting such a tree or set up a trust to maintain it for some time to come.
      New trees might be planted in anticipation of some future "large" value.
      And capturing the public's imagination wouldn't be such a bad thing either for their sake as well as the sake of the trees.
      If a tree falls in a forest (by whatever means) does it have an address? which can be seen, if not heard?
      Well these days, yes it does, with satellite mapping, and such oversight would put a break on pillaging.

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    6. James Hill

      Industrial Designer

      In reply to Michael Shand

      Yes Michael, it is wise not to completely trust those who are at the source of the problem.
      But if you are to invoke the new Pope, named it seems after Francis of Assisi, could we also invoke the Parable of the Talents?
      Given equal opportunities to wisely use the "talents" left in their care, the servant who did the most with the opportunity received the highest reward, and the servant who tried and failed was encouraged more that the servant who hid the talents under a rock in fear of losing them…

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    7. Michael Shand

      Software Tester

      In reply to James Hill

      "So perhaps we should hold our noses and tempt the rich to value trees" - you don't understand how the world works

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    8. James Hill

      Industrial Designer

      In reply to Michael Shand

      Please, then, explain???
      How The World Works, by Michael Shand.
      A short tome, perhaps?

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    9. Michael Shand

      Software Tester

      In reply to James Hill

      The very fact that you think that you can convince rich people to care about things they do not care about is silly

      If they do not care about Climate Change - a threat to our species and a direct threat to their children and grand children

      What on earth makes you think you can convince them to care about tree's?

      The short version of how the world works is - "Follow the money trail"

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    10. James Hill

      Industrial Designer

      In reply to Michael Shand

      PS, Michael, I think I anticipated your viewpoint concerning "the money trail" in my original post.
      Feel free to include it in your new book.
      Wherein you compare the values of a work by Van Gogh, and a six hundred year old rainforest tree to people with more money than sense.
      How does rare and irreplaceable work for you?

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    11. Michael Shand

      Software Tester

      In reply to James Hill

      I think we totally agree that rich people should evolve a different value set, as most people should because many of those who are not rich share the same values and aspirations of the rich.

      I think we totally agree the current situation sucks and we should try encourage change

      I think the disagreement is how to affect that change but look, if you are able to influence people's value systems then more power to you, maybe religion could be part of the solution.

      But getting rich people to…

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    12. James Hill

      Industrial Designer

      In reply to Michael Shand

      It may be like women and make up, women wear it for other women.
      And the rich only care what the other rich are up to.
      I understand that there are remnant rainforests on the southern shore of Arabia, and there are lots of rich people in Arabia.
      Who owns these forests and whether they are under threat aside, is there a test case here for individual stewardship of individual trees, for the value of individual bragging rights.
      Yes certainly, wealthy people are only ever likely to invest in a growing…

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    13. Michael Shand

      Software Tester

      In reply to James Hill

      "It may be like women and make up, women wear it for other women. " - It's a good idea, however gates and buffet haven't started a philanthropic trend - the Koch bro's seem just as uninterested as before and trends as we know are only superficial, if they can get the glam and praise without actually making a substantial change they will.

      I dunno, it's a hard one but I guess we have to throw everything we got at the problem

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    14. James Hill

      Industrial Designer

      In reply to Michael Shand

      And they all have their price, for example, to get politicians to do what you want, organise it for them to win votes.
      They all want what they don't have.
      Just publicise a billionaire "philanthropist's" actions to adopt and protect rare and threatened "trees", and see how they lap up the public acclaim otherwise denied them.
      How shall it profit a billionaire if they adopt and protect thousands of old growth trees and save their own souls while they are at it.
      Priceless.

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    15. Mark Poynter

      Forester

      In reply to John Harland

      John

      Just for your information - there has been no old growth logging in NSW, WA and Qld since around 2000, and very little in Victoria since 2006 when all East Gippsland's remaining significant unreserved OG stands were placed into new National Parks.

      There are occassional individual old trees and small patches of old trees harvested in Vic as part of harvesting in mostly younger forests; while well over 90% of old growth forest in Tasmania is also now reserved.

      So ..... old growth logging is no longer a significant issue and hasn't been for a long time. The vast majority of Australia's forests (around 95%) are not being managed for timber supply and are already free to grow into old trees subject to a lack of severe fire.

      It is therefore perplexing that this article is being featured ..... it may be because we have an election in Tasmania in March, and forestry remains a political football down there.

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  4. Chris Owens

    Professional

    Aside from old growth, a major issue is high rotation logging in large areas of state forest preventing these areas from maturing into old growth and the increasing complexity that involves (eg: sites for epiphytic ferns, hollows for wildlife, etc). In some mature, wet sclerophyll eucalypt forests, without disturbance there is succession to rainforest. These older, more humid forests are more resistant to fires and the soil humus feeds creeks long after regrowth are dry as a chip.

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  5. Marino Mangone

    Manager

    The hemp plant is the one of the best, if not the best CO2 absorber on the planet.

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    1. Michael Shand

      Software Tester

      In reply to Marino Mangone

      well, except for algae and sea weed and sea grass

      we should still grow lots of hemp though, to you know, save the environment and stuff

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  6. Yoron Hamber

    Thinking

    Quite interesting, and confusing too :)
    Doesn't the studies oppose each other?

    "“First, it has been shown that at the whole forest level, young forest acquires mass faster than old-growth forest. Second, studies have shown that the leaves of older trees are less efficient at photosynthesising than the leaves of younger trees.” "

    against "they (older trees) storing lots of carbon, they are also sequestering more carbon and faster than smaller trees,”

    one study says old trees less efficient at photosynthesising, and slower aquiring mass. The other that they sequester carbon faster, and more too?

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    1. doug pittard

      ex-sesselpoopser

      In reply to Yoron Hamber

      For balance, in response to the comment in the article on "flaws in forest policy in Victoria and Tasmania, where old-growth forest is often cleared for pulp and timber purposes." you should have indicated how much old growth forest is reserved from logging and how much is available.

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    2. Tim Benham

      Student of Statistics

      In reply to Yoron Hamber

      "“First, it has been shown that at the whole forest level, young forest acquires mass faster than old-growth forest. Second, studies have shown that the leaves of older trees are less efficient at photosynthesising than the leaves of younger trees.” "

      against "they (older trees) storing lots of carbon, they are also sequestering more carbon and faster than smaller trees,”

      I see no opposition. New forests sequester faster than old growth.

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    3. Craig Read

      logged in via Twitter

      In reply to Yoron Hamber

      Yoron, I don't see a contradiction at all.

      New forests acquire mass faster than old-growth forests, while older trees sequester more carbon (and do it faster) than smaller trees.

      I'm guessing this means the mass new forests acquire may have a lower percentage of carbon than the mass that old forests acquire.

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    4. Cris Brack

      Assoc Professor Forest measurement & management at Australian National University

      In reply to Yoron Hamber

      No contradiction. Forest science has known about the relationship between individual tree size and numbers of trees for a century or more - have a google of "the self thinning rule". You can have, say 1000 little trees, each potentially growing slowly individually together, but eventually as they get bigger and occupying more of the site they will start competing and some deaths will occur, ending up with, say 500 much bigger trees ...which will continue to grow until you have only a few very big (very old?) trees. All those little trees had been growing and because there were so many of them the overall forest growth was fast. By the end, there are very few trees, so even if they grow fast the overall growth of the forest is low.

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    5. Yoron Hamber

      Thinking

      In reply to Cris Brack

      Tricky one. What you write is very sensible, but what I'm reacting on is that even though older trees are worse on photosynthesising, they still sequester more carbon? Is it greater magnitude of leafage in old trees that's compensating for that? And if they also acquires less mass in a same time as young trees? Where does this increased sequestering of carbon come from?

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    6. Yoron Hamber

      Thinking

      In reply to John Harland

      Thanks John. Then we have two truths co-existing. It is true that old trees sequester more carbon, then due to to more leafage, but they also grow slower, and have a slower 'metabolism' (photosynthesis)

      To that I would add that I suspect old trees to have a different ecosystem than young tree, especially in areas where foresting is planted anew as the soil will be laid bare every time we cut a 'old' forest down. I find the whole thing devilishly complicated to 'count on' actually.

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  7. Paul Prociv

    ex medical academic; botanical engineer at University of Queensland

    I’m surprised that this is presented as a new discovery. Surely, the mass of a tree is reflected in the number of annual growth rings. Assuming the rings are uniform in thickness (or vary around an average), and the tree has stopped growing heightwise, then mass increase should linearly follow annual growth (ring thickness X circumference). Old trees are irreplaceable in their ecological significance, but young trees are also important in replacing our lost forests. There’s room (and need) for both!

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  8. Dick Adams

    logged in via email @hotmail.com

    Hi, I am interested in the research methodology for this study.

    To calculate a trees MAI and CAI, (mean annual and current annual increment – recognised measurements for a trees volume growth over time) at the very least, you need to measure its DBH (Diameter at breast height) and overall height at fairly regular intervals over a long period of time (decades) to apply a volume determining formula, given volume is biomass and therefore carbon.

    How did this study ascertain growth data for specific samples (trees) over extensive periods of time?

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    1. Cris Brack

      Assoc Professor Forest measurement & management at Australian National University

      In reply to Dick Adams

      I just found the Nature Letter describing the original work. They collected Diameter at Breast Height (DBH) from a range of sources then estimated mass using existing allometric equations. The allometrics largely use just DBH - what used to be called "local" or "one-way" equations because there is only one variable (no height, tree shape, taper, etc). Users of one-way equations were warned not to apply them outside the original forests where the data was collected, but that does not appear to have…

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    2. Dick Adams

      logged in via email @hotmail.com

      In reply to Cris Brack

      Thanks Cris.
      I found the link as well.
      I am not in the research field, but even the layman can identify that the methodology of this study is quite subjective (I don’t mean to cause offence). The findings are contrary to all my practical experience, for what that is worth.

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    3. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to Cris Brack

      Hi Cris,
      I don't have access to the paper, but read the abstract. In that the authors stated that they removed any trees that had 'negative' growth. I wonder how many and if that is valid? I worked with a biometrician for a while who was analysing long term (permanent growth plot) data and he came to the conclusion that some trees do get smaller. Maybe due to a wet year when measured first and a dry year on a subsequent measurement - perhaps that could led to lower DBH measures on subsequent visits.

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  9. Murray Webster

    Forestry-Ecology Consultant/Contractor

    Here is a link to a paper that was published not long ago.
    http://www.mdpi.com/1999-4907/3/3/653
    They came to the conclusion that:
    "forests managed for production provide the greatest ongoing greenhouse gas benefits"
    Interestingly, they included in their calculations things like ongoing storage of carbon in wood products, and the CO2 impact of using alternative higher emissions products like plastic, concrete, steel, in place of wood.
    If measurements are done on a forest then the forest is logged and the measurements done again, that area of forest will of course have less CO2. I think it is a more realistic representation of emissions if the ongoing storage and product substitution are included in analyses along with CO2 sequestration in the regrowing forest.

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    1. John Newlands

      tree changer

      In reply to Murray Webster

      I've had a quick look at that report which is important to resolve contradictory claims by the timber industry in TV ads and groups like the Wilderness Society. Alas I find problems early on. For example on p656 it excludes CO2 from debris burns which is substantial. It omits CO2 burned in diesel powered vehicles and machinery, also substantial. It suggests thinnings will decay to GHGs in 20 years at the most. How then do coal deposits form and remain intact for millions of years?

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    2. Murray Webster

      Forestry-Ecology Consultant/Contractor

      In reply to John Newlands

      Hi John, Yes there is a lot of contradictory scientific studies out there and it appears none of them take absolutely everything into account. Which is why I am sceptical of recommendations such as those made in the article, based on one study.
      This article does not mention the impact of bushfires which are significant eg:
      In the fires that ravaged Victoria 2002-03 and 2009, Victoria lost the 5 remaining trees measured at over 90m tall and a further 35 + trees that were over 85m tall. Many…

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    3. John Newlands

      tree changer

      In reply to Murray Webster

      I hope woodchip derived fuel becomes a reality. That way tree mulchers could do fire hazard reduction with only a lot of noise. It would avoid burnoffs that go wrong and destroy houses, cause asthma attacks with smoke and incinerate critters in hollow logs.

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  10. Neil Burgess

    Planning and Distribution Manager

    Without having read the article in Nature, I would suggest that the argument is part of the truth. A large old growth tree covers a large piece of ground. What the author of the conversation piece does not say is that in the same space, 2, 3 or maybe 4 medium sized trees will be growing rapidly storing more carbon than a single old growth tree.

    In regrowth forest or a commercial operation, trees would be harvested and regrown/replanted allowing the harvested carbon to be potentially stored and new growth to commence storing of carbon. This would exceed the carbon stored by the single old growth tree.

    This does not mean we should cut all old growth. Some of it should be preserved. We just need to recognise the increasing importance of regrowth and plantations.

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    1. Cris Brack

      Assoc Professor Forest measurement & management at Australian National University

      In reply to Neil Burgess

      Humans like BIG things, and certainly big trees are majestic. We value and are awe-struck by an 80 m tall tree much more than a 40 m tall tree. But do two 40 m trees equal an 80 m tall one for value ...what about ten 40 m tall trees? Any what if ten small trees fit into the same area as the 80 m giant - what then is the value per hectare? And what if you are a koala and the trees are eucalyptus? Well the 80 m tall tree has no value to you because there is no way you are going to climb that high…

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    2. Mark Poynter

      Forester

      In reply to Cris Brack

      Chris

      Call me cynical, and taking account of who one of those 'Interviewed' academic is, I wonder whether this article has anything to do with an upcoming election in Tassie about 6 weeks from now, where saving old forests remains a significant political issue.

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  11. Dick Adams

    logged in via email @hotmail.com

    Referring to the photo at the beginning of this article.

    If you plan to visit a forest, please don't be stupid enough to put your child at the base of an old hardwood. They are called widow makers for a range of reasons, not the least of which is they silently drop large limbs from a great height.

    Stupid !

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  12. Jack Bradshaw

    Forest Consultant

    The fact that stands of older trees grow more slowly that stands of younger trees and that older individual trees may grow more rapidly than younger individuals is not new. Confusing the two as is done in this article does not help the argument. The original paper makes this very clear.

    “We highlight the fact that increasing individual tree growth rate does not automatically result in increasing stand productivity because tree mortality can drive orders-of-magnitude reductions in population density…

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  13. Will Hunt

    Farmer

    We have many big old red gum (E. Camaldulensis) on our property, with some of them being well over 400 years old. It is patently bloody obvious that many of these trees are losing carbon at a great rate of knots as they slip into their dotage. Heart wood is succumbing to termites and cockatoos, limbs are dropping off and canopys are thinning out. Young trees (40-100 yrs old) are amassing carbon, but the old ones are dying. The governments attitude is that these old trees are sacred cows which must be preserved at any cost. Which is a bit like keeping the old folks in the nursing homes alive whilst letting the kindergarten kids go play in the trafffic. As I tell my kids, "If yoiu want your grandchildren to be able to have a picnic under a 100 year old tree in 100 years time, you got to get a seedling going tomorrow'
    Where we have managed to get regeneration happening, the old trees look much happier and healthier, but a forest must be in a perpetual state of regeneration. IMHO

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  14. Adrian Goodwin

    Forester

    The important take-home message from the Letter in Nature is that the relative growth rate (ann. increment per unit of mass) of undamaged and non-senescent trees appears to be fairly constant. However, the article is short on plot sampling detail and does not address the possibility that large trees on the best sites have been combined with smaller trees on lesser sites, thereby exaggerating the relative productivity of big trees.

    The unqualified declaration that big trees grow faster is both…

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  15. Kay Harkness

    Secretary

    Very interesting! Makes me wonder if anyone has investigated whether there is a link between and old growth forest and it's underground fungus network. Would it be more developed because left undisturbed and therefore help the tree system?

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  16. Ted O'Brien.

    Farmer.

    From a sequestration quantity point of view, the measure must be made on a land area basis, not individual trees.

    Given an established system, the two factors affecting the rate of sequestration are available moisture, available sunlight and the efficiency of use of these two resources.

    Naturally a big tree will harvest more carbon from the atmosphere than a small tree. But that big tree is displacing a lot of small trees to do this. In an established system, I would not expect big or little to make a lot of difference.

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