Claim: New analysis links tree height to climate

From the University of Wisconsin-Madison , where they apparently have not heard of Liebig’s Law of the Minimum since they say resources and hydraulic limitation “might” play a role.

MADISON, Wis. — What limits the height of trees? Is it the fraction of their photosynthetic energy they devote to productive new leaves? Or is it their ability to hoist water hundreds of feet into the air, supplying the green, solar-powered sugar factories in those leaves?

Both factors — resource allocation and hydraulic limitation — might play a role, and a scientific debate has arisen as to which factor (or what combination) actually sets maximum tree height, and how their relative importance varies in different parts of the world.

In research to be published in the journal Ecology — and currently posted online as a preprint — Thomas Givnish, a professor of botany at the University of Wisconsin-Madison, attempts to resolve this debate by studying how tree height, resource allocation and physiology vary with climate in Victoria state, located in southeastern Australia. There, Eucalyptus species exhibit almost the entire global range in height among flowering trees, from 4 feet to more than 300 feet.

“Since Galileo’s time,” Givnish says, “people have wondered what determines maximum tree height: ‘Where are the tallest trees, and why are they so tall?’ Our study talks about the kind of constraints that could limit maximum tree height, and how those constraints and maximum height vary with climate.”

One of the species under study, Eucalyptus regnans — called mountain ash in Australia, but distinct from the smaller and unrelated mountain ash found in the U.S. — is the tallest flowering tree in the world. In Tasmania, an especially rainy part of southern Australia, the tallest living E. regnans is 330 feet tall. (The tallest tree in the world is a coastal redwood in northern California that soars 380 feet above the ground.)

Southern Victoria, Tasmania and northern California all share high rainfall, high humidity and low evaporation rates, underlining the importance of moisture supply to ultra-tall trees. But the new study by Givnish, Graham Farquhar of the Australian National University and others shows that rainfall alone cannot explain maximum tree height.

A second factor, evaporative demand, helps determine how far a given amount of rainfall will go toward meeting a tree’s demands. Warm, dry and sunny conditions cause faster evaporation from leaves, and Givnish and his colleagues found a tight relationship between maximum tree height in old stands in Australia and the ratio of annual rainfall to evaporation. As that ratio increased, so did maximum tree height.

Other factors — like soil fertility, the frequency of wildfires and length of the growing season — also affect tree height. Tall, fast-growing trees access more sunlight and can capture more energy through photosynthesis. They are more obvious to pollinators, and have potential to outcompete other species.

“Infrastructure” — things like wood and roots that are essential to growth but do not contribute to the production of energy through photosynthesis — affect resource allocation, and can explain the importance of the ratio of moisture supply to evaporative demand.

“In moist areas, trees can allocate less to building roots,” Givnish says. “Other things being equal, having lower overhead should allow them to achieve greater height.

“And plants in moist areas can achieve higher rates of photosynthesis, because they can open the stomata on their leaves that exchange gases with the atmosphere. When these trees intake more carbon dioxide, they can achieve greater height before their overhead exceeds their photosynthetic income.”

The constraints on tree height imposed by resource allocation and hydraulics should both increase in drier areas. But Givnish and his team wanted to know the importance of each constraint.

The scientists examined the issue by measuring the isotopic composition of carbon in the wood along the intense rainfall gradient in their study zone. If hydraulic limitation alone were to set maximum tree height, the carbon isotope composition should not vary because all trees should grow up to the point at which hydraulics retards photosynthesis. The isotopic composition should also remain stable if resource allocation alone sets maximum height, because resource allocation does not directly affect the stomata.

But if both factors limit tree height, the heavier carbon isotopes should accumulate in moister areas where faster photosynthesis (enhanced by wide-open stomata) can balance the costs of building more wood in taller trees. Givnish, Farquhar and their colleagues found exactly that, implying that hydraulic limitation more strongly constrains maximum tree height under drier conditions, while resource allocation more strongly constrains height under moist conditions.

Most studies of tree height have focused on finding the tallest trees and explaining why they live where they do, Givnish says. “This study was the first to ask, ‘How does the maximum tree height vary with the environment, and why?'”

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38 thoughts on “Claim: New analysis links tree height to climate

  1. Good point. From what I understand, the reason Stratavarius violins were so good was he picked trees that were high in the mountains and it was cold. Therefore, the tree rings were a lot tighter and the instrument had a much better tone quality.

  2. I would venture it is their ability to withstand increasing wind speeds aloft; like those winds that are blowing that tethered barrage balloon.

  3. One thing we can know for certain. Increased CO2 pollution will either stunt trees’ growth or cause them to grow soggy and fall over. Mankind bad; trees good.

  4. “Since Galileo’s time,” Givnish says, “people have wondered what determines maximum tree height: ‘Where are the tallest trees, and why are they so tall?’
    Givnish says. “This study was the first to ask, ‘How does the maximum tree height vary with the environment, and why?’”

    I know this is being picky but it does look contradictory as far as the timeline goes although I am sure that there is a scientific difference between “wondering” and “asking”. The two statements look quite similar to me but centuries apart in time, I bet the ancient Greeks were pondering the same thing.
    Interesting that they appear to be looking at the physical properties and that there is no mention of genetics within a species or is that only important for crop plants.

  5. If suction moves water upward through the vessels and tracheids their height would be limited to about 30 metres. I am inclined to think that it is osmotic pressure in the roots that pushes water up the trunk. If I was conducting research on this I would be looking hard at how the proportions of dissolved chemicals in the roots vary between tall species and not so tall species.

  6. “If suction moves water upward through the vessels and tracheids their height would be limited to about 30 metres.”

  7. Well, Mr Givnish certainly has concern for the planet close to his heart – based in Wisconsin and researching in SE Australia.

  8. AH! That explains why those Arctic Birch trees right up at the edges of the northern tree line and at the edges of the Arctic ice pack are only a few metres high
    Whilst those tropical forest and tropical jungle trees near the equator are many tens or even a hundred or so metres tall.

    Being an old farmer I thought it was because of rainfall and temperature and growing season length and the amount of sunlight and the tree species and the genetics of the tree species and variety and the soil types and the amount and type of nutrients available and the soil biology and leaf and trunk and stem conformation and etc and etc all that allowed trees and plants to grow the way they do and to the heights they do.
    Or at least thats what agricultural scientists have been telling us farmers for the last half a century or so.
    But then who am I to out guess and question these highly qualified tree scientists about why trees grow the way they do?

    We learn something new everyday off the internet [ sarc/ ]

  9. “In moist areas, trees can allocate less to building roots,” Givnish says. “Other things being equal, having lower overhead should allow them to achieve greater height.
    ——————————————————————————————–
    Obviously never met a Weeping Willow, Tulip Poplar, or Louisiana Cypress. The Cypress should win the height race hands down, but doesn’t come close. The tallest Poplar I’ve seen is about 60′. The race for light in a crowded forest makes for taller trees; more effort to grow tall, not wide.

  10. The strength of the wood is important for two reasons: to support the mass of the tree and resist the splitting of the vertical grain of the lower trunk by hydraulic pressure. Interesting that trees, particularly tall trees, have a broadening of the base of he trunk and a buttressing ribs going down into roots. Having grown up on the prairies I had observed an interesting thing about one of my favorite berries, the saskatoon. In dry scrubby foothills country in Alberta, the saskatoon grows only a foot or so high. In Manitoba where I grew up, saskatoons are shrubs 6 to 8 feet high. I remember visiting a former Manitoban living west of Calgary Alberta on a large bushy lot. I recognized the saskatoons growing on the very dwarfed plants on his property that he, himself had not recognized. We picked a couple of pots full and had a wonderful saskatoon pie. Some years later I bought a small farm in eastern Ontario. There were hazlenuts and raspberries and blackberries growing in abundance along one of my fence lines and while picking, I noted purple spots of bird poop on the fence and I looked up and here was a tree about 20 feet high, a trunk about 3 inches in diameter with smooth gray bark. On the profusion of small brances above me, I recognized to my delight… saskatoons! It was a bit more hazardous picking for my Ontario saskatoon pie as birds had thinned the crop, but it made a wonderful saskatoon pie.

  11. “In moist areas, trees can allocate less to building roots,” Givnish says. “Other things being equal, having lower overhead should allow them to achieve greater height.
    Less roots should increase the probability the tree will fall over in the wind.

  12. When I lived in Northern California, I visited Muir Woods on a regular basis. What I read at the visitors center was that the reason the redwoods grew so tall was that 1) they grew in protected valleys and 2) they obtained a good sized portion of their water by pulling it out of the persistent coastal fog. They don’t have to pump water to such great heights. Makes more sense to me.

  13. I’d like to know what their definition of high humidity is. I live in the State of Victoria and it’s certainly not known for its high humidity. During the summer months it is exactly the opposite.

  14. geogeek says:
    August 14, 2014 at 9:46 pm

    geogeek,
    I think you have hit the 3 salient points on TALL tree growth.
    1. Genetics that favor tall tree growth.
    2. Protected valleys and hillsides that do not see high winds or heavy icing/snow falls.
    3. Regular foliar watering from fogs that reduce the vertical ‘pumping’ required by the trees internal plumbing.

  15. If a species of tree is dependent on a number of factors for its maximal height (examples which were given by ROM above) then the potential height such trees would attain would be decidedly limited in a particular environment by any of those factors which are deficient. Thus it follows that in an arid situation, the availability of water would be a deciding factor in the tree’s height, whereas in moister locations, the possible scarcity of nutrients might come into play. From the standpoint of an individual tree, competition means that the overall availability of factors is even more limited, since they would necessarily be shared with the neighboring trees.

  16. Thanks, looncraz (August 14, 2014 at 6:41 pm) for posting the video about how water moves up trees. It’s a fascinating video which explains the phenomenon well but I was surprised that the mechanism wasn’t well known by some of the scientists interviewed by the presenter.

    The ‘cohesion – tension’ mechanism was proposed over a century ago (as it happens, by my grandfather Henry Dixon and his colleague, the physicist John Joly) and seems to have stood the test of time. ‘Cohesion Theory of the Ascent of Sap’ (Proc Roy Dublin Soc, vol x, 1903)

    http://en.wikipedia.org/wiki/Henry_Horatio_Dixon http://en.wikipedia.org/wiki/John_Joly

  17. The graph from the ‘Liebig’ article seems very relevant to dendroclimatology and Briffa’s divergence problem:

    Perhaps the warmer temps of the latter half of 20th c. run into or past the peak of the parabolic gowtth curve. Dendrothemometry makes the implicity assumption that the relationship is linear.

    If the recent warm period resulted in narrower tree rings producing the decline in the derived “proxy” temperature, then earlier warm periods would equally be incorrectly determined to be cold periods.

    With that erroneous assumption of a linear growth/temp relationship, you will NEVER get a historical warm period similar to current climate which will then, as a result of the false assumpition of linearity, always be “unprecedented”, irrespective of what past climate actually was like.

    If you then graft incompatible themometer data onto the treering proxy and hide the divergence problem by cropping off the inconvenient data, you will NECESSARILY get a hockeystick.

    The observed parabolic growth response explains both Briffa’s divergence problem and the lack of similar warm periods in the dendrothemometry proxies.

    Similar warm periods probably are present in the record and show up as ‘divergences’ similar to the current period.

    Evolutionary arguments would suggest that each tree species has the peak of it growth curve near the median of the local historical climate variability. Unless some other data is extracted from the tree-ring samples it is impossible to distinguish unusual warmth from unusual cold.

    Dendrothemometry, by its fundamental false assumption, folds back any warmer than average periods into cooler than average periods as happens in Briffa’s data.

    Against that record any warm period measured by reliable temperature readings will be “unprecedented”.

  18. The world’s tallest known tree was the “Ferguson Tree” calculated as over 500 feet (154m) tall. It was measured by Surveyor Ferguson in 1872 in the Watts River Catchment near Healesville, Victoria, northeast of Melbourne. It was found and measured, as a fallen tree, and it was 435 feet long base to tree break (the top was broken off by its fall). It was 3 feet thick at the break, indicating an original height of over 500 feet.

  19. Greg says: “Unless some other data is extracted from the tree-ring samples it is impossible to distinguish unusual warmth from unusual cold. ”

    Perhaps the isotope ratio used in this paper can be used to distinguish narrow tree-rings caused by warm period stress from narrow tree-rings caused by cold period stress.

  20. Anthony, this article lacks any useful reference to the paper in questions. There is not even a link to where this text came from ( presumably a WISC press release) which would provide that.

    Please provide a link to the source of this text and if possible the authors, title and a DOI for the paper.

  21. looncraz says:
    “If suction moves water upward through the vessels and tracheids their height would be limited to about 30 metres.”

    Very good explanation. Thank you !

  22. Good Article. It could explain some of the Why in the Pine Beetle devastation of our western forests. There simply is not enough water to maintain all the forests planted during better wet times in the Black Hills. Now, with drought coming and going, the climate being warmer due to the return of sunspot activity on an average 100 year basis, the tree line may simply be moving further north from the Equator and to higher latitudes. The Pine Beetle along with fire, logging to prevent the beetle from its work is simply turning forests into grasslands.

    Most Sincerely,

    Paul Pierett

  23. “But if both factors limit tree height, the heavier carbon isotopes should accumulate in moister areas where faster photosynthesis (enhanced by wide-open stomata) can balance the costs of building more wood in taller trees. ”

    I don’t follow the logic here, presumably this is explained better in the paper than in the press release.

    … I wonder what the paper title is …

    ” and currently posted online as a preprint”

    Link?

  24. ***
    ntesdorf says:
    August 15, 2014 at 12:57 am

    The world’s tallest known tree was the “Ferguson Tree” calculated as over 500 feet (154m) tall.
    ***

    You didn’t even mention the species! Eucalyptus I presume. Still, w/o documentation it can’t be “official”.

    Eastern white pines or eastern hemlocks around here in the mid-Appalachians that get above the surrounding canopy & much above 100′ tall don’t last long — blown down or broken by spring windstorms. If they form a self-protective grouping/grove (or in a very protected valley), they can get much taller.

  25. ***
    looncraz says:
    August 14, 2014 at 6:41 pm

    “If suction moves water upward through the vessels and tracheids their height would be limited to about 30 metres.”
    ***

    30 feet, not 30 meters. Atmospheric pressure (14.7 psi) is roughly 30 ft of water.

  26. David Schofield says:
    August 14, 2014 at 11:34 pm
    “James the Elder says:
    August 14, 2014 at 7:34 pm”

    James is a tree.
    ——————————————————————–
    At 5’6″, more of a stump, and at 225lbs, a very sturdy one.

  27. People!
    Looncraz did not make this statement:
    “If suction moves water upward through the vessels and tracheids their height would be limited to about 30 metres”

    He merely quoted it and proved the statement wrong with the video.

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