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Towering Giants Of Teleological Beauty

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“Keep walking back with your kite.  There you go.  Now stop where you are.  The distance between you and me right now is equivalent to about half the height of California redwoods—the tallest trees on earth.  Can you imagine that?” This was my stab at an illustration of how tall trees can really get.  But my eight year old son was having none of it.  “Wind all that string around the reel Dad, and let’s go home!”  Disappointed as I was with his response to my efforts, it was plainly obvious that he had to see something a lot more well-grounded than an unwound length of string tied onto a diamond-shaped piece of flyable canvas.

Once home he grabbed the Seasonal Forest installment of BBC’s mega-documentary Planet Earth out of the movie cabinet, slotted it into our DVD player and jumped into the couch with a bowl of ice cream in hand.  As the acclaimed naturalist David Attenborough piled superlative upon superlative into his accompanying narration, I could see in my son’s gawping eyes that cogs were turning deep in the grey matter of his brain.  He had finally grasped the enormity of these organisms.  I kept quiet as he listened intently:

“One grove of redwoods in California contains three of the tallest trees on earth.  Over 100 meters high: the size of a 30 story building.  These forests were growing long before humans walked the earth.  They were in their prime 20 million years ago and existed before the Swiss Alps or the Rocky Mountains were even raised.  There is more living matter in a forest of giant conifers than in any tropical rain forest…..A giant Sequoia, a relative of the redwood, is the largest living thing on earth.  Known as General Sherman, it’s the weight of ten blue whales.  Higher up in the nearby mountains we find bristle cone pines- the oldest organisms on the planet.  Some have been here for five thousand years.  They were alive before the pyramids were built and were already three thousand years old when Christ was born” (1)

“Wow Dad, isn’t that just mind-blowing?”  Not wanting to see my son’s fervor dwindle I nabbed a copy of popular science writer Len Fisher’s How To Dunk A Doughnut off the shelf, knowing full well that in its pages lay a weighty passage on the physics of  tree growth.  Following Attenborough’s helpful words, I read the passage out loud verbatim:

“The leafy crown of the largest known specimen, the ‘General Sherman’, towers eighty-three meters above the tourists passing below.  The water supply for the leaves is drawn up from the soil by capillary action.  The menisci of these huge columns of water reside in the leaves, and a quick calculation shows that the capillary channels containing the menisci can be no more that 0.2 micrometers wide- about one-hundred-and-fiftieth of the diameter of a human hair.  The pressure across such a tiny meniscus can support a continuous column of water, of which there are many in the bundles of tubes called the xylem, which runs up the trunk below the bark” (2)

“So what is the height limit of the redwood, Dad?”  Six years ago, an adventurous group of botanists from Arizona and California published their estimate after making it up to the tree tops of the Humboldt Redwoods State Park in California using mechanical ascenders and dropping tape measures to the ground below (3,4).  Scaling up tree trunks is certainly not a job for the acrophobic, me included.  But the effort paid off.  And the group got a Nature paper out of it.  Three factors- (i) transpiration, (ii) water adhesion and (iii) surface tension- work in concert to draw water up the tree.  The high tensile strength of water ensures that the long watery columns running up the trunk do not break (5).

As water evaporates from the leaves at the uppermost reaches of the redwood through transpiration, a negative pressure (low water potential) builds up.  This is most marked at midday when transpiration ‘pull’ generates a pressure of approximately -18 atm.  At such levels, cavitation (cold boiling/embolisms) risks along the water columns are at their greatest.  Trees get around this threat by decreasing the aperture size of the stomatal pores on their leaves thereby reducing transpiration rates.   The unfortunate byproduct of this is that further growth is limited- without additional photosynthetically-derived carbon being absorbed through stomata trees cannot increase in size (3).

A higher leaf mass:area ratio for leaves at greater heights also increases resistance to CO2 diffusion in the leaf once again reducing photosynthesis and carbohydrate availability for further growth.    Low water potentials lead to reduced leaf cell turgidity which is why leaves at the upper reaches of Redwoods are considerably smaller than those in the lower crown (3,4).  One of the physiological consequences of this is a reduced enzymatic discrimination between the Carbon-12 and Carbon-13 forms of CO2 (3).  Indeed there is a close correlation between redwood tree height and the foliar abundance of 13C.

Across the 2,200 year life spans of the tallest redwoods, severe droughts are likely to have created water potentials low enough to produce cavitation (3).  The evidence is overwhelming- most tall redwoods have multiple tree tops that have died and been repeatedly replaced (3).  But these same specimens also enjoy protection from neighboring trees against buffeting winds that would otherwise damage the tall canopy.  Having traipsed through forests aplenty in our home state of Wisconsin, wind protection is certainly one benefit that my son can readily grasp.

The maximum height attainable by these trees is inseparably linked not only to the physical and chemical properties of water but also to the mineral composition of the soils upon which they grow.  In his seminal volume Nature’s Destiny, biologist Michael Denton wrote of the teleological conclusions that naturally follow:

“It is the high surface tension of water which draws water up through the soil within easy reach of the roots of plants that assists its rise from the roots to branches in tall trees.  Large terrestrial plants would probably be a physiological impossibility if the surface tension of water was similar to that of most liquids….water is uniquely and ideally adapted to serve as the fluid medium for life on earth in not just one, or many, but in every single one of its known physical and chemical characteristics…There seems little doubt that were it not for the almost universal occurrence of clay minerals in soil, there would be no large terrestrial plants on earth and consequently no large terrestrial mammals.  It is surely a “coincidence” of great significance that the very rocks which by virtue of their viscosity and density will inevitably form the crustal rocks on a planet like the earth are weathered by the two substances water and carbon dioxide, the key ingredients of any carbon-based biosphere, into a substance that forms the ideal substratum for the growth of plants” (6)

There is of course a question that awaits its time: “Dad can we climb a redwood?”  When the moment comes to define my boundaries, I will have my scripted answer at the ready: “Son, I agree that those trees are towering giants of teleological beauty.  But the angel-holding knurl at the top of our Christmas Douglas fir is about as high as I dare go.  Let’s just leave it at that”.  I rest confident that my retort will be graciously accepted.

Further Reading

  1. Planet Earth: The Complete Series, A BBC/Discovery Channel/NHK Co-Production (2007)
  2. Len Fisher (2002) How To Dunk A Doughnut: The Science Of Everyday Life, 1st Ed, Weidenfeld & Nicolson, London, p.12
  3. G.W.Koch, S.C.Sillett, G.M.Jennings, S.D.Davis (2004) The limits to tree height, Nature Volume 428, pp. 851 – 854
  4. Michael Hopkin (2004) Height limit predicted for tallest trees, See http://www.k8science.org/news/news.cfm?art=919
  5. Don Garlick (2007) How Can Redwoods Grow So Tall? The Journal, Humboldt County, October 11th, 2007, See http://www.northcoastjournal.com/outdoors/2007/10/11/how-can-redwoods-grow-so-tall/
  6. Michael J. Denton (1998) Nature’s Destiny: How The Laws Of Biology Reveal Purpose In The Universe, The Free Press, New York, NY, pp. 30, 45, 87
I'm quoting from the park brochure: "Sequoias grow naturally only on the west slope of California's Sierra Nevada range. Redwoods grow naturally only in a narrow strip along the Pacific Coast." The sequoias in the park are Sequoiadendron giganteum. The redwoods in the quote are Sequoia sempervirens. I believe these are what Acipenser is referring to as sequoias and redwoods. There are no sempervirens in Sequoia National Park. jpg564
utidjian @6, Like this? Sequoia evolution I jest... HouseStreetRoom
Collin, Yes. (How hard can it be to Google "sequoia evolution"?) utidjian
Acipenser, So those members of the genus are pretty similar to modern redwoods? Collin
Collin: That is one of the simplest strong arguments against evolution that I’ve ever seen. All excepting the part where fossil remains of members of the genus, which include coastal redwoods and sequoias, date back more than a hundred million years or so. Acipenser
jpg564, That is one of the simplest strong arguments against evolution that I've ever seen. Collin
I visited Sequoia National Park earlier this year. I was struck by acouple facts presented at the visitor's center. Sequoias live about as long as they have existed: about 2500 years. Also, the wood does not decay due to the high tannin levels; bugs and fungus can't digest it. So unless it burns up, a fallen sequoia remains where it fell indefinitely. We essentially can view the entire history of this species. So the question is, what did they evolve from? There are only distinct other species of trees (Sugar Pines, Douglas Fir, etc) but no transitional forms. Did random mutation cause sequoia to sprout from another species? jpg564
Beautifully written and a pleasure to read,,, Here are a few notes on water that I've picked up,,, When we look at water, the most common substance on earth and in our bodies, we find many odd characteristics which clearly appear to be designed. These oddities are absolutely essential for life on earth. Some simple life can exist without the direct energy of sunlight, some simple life can exist without oxygen; but no life can exist without water. Water is called a universal solvent because it has the unique ability to dissolve a far wider range of substances than any other solvent. This 'universal solvent' ability of water is essential for the cells of living organisms to process the wide range of substances necessary for life. Another oddity is water expands as it becomes ice, by an increase of about 9% in volume. Thus, water floats when it becomes a solid instead of sinking. This is an exceedingly rare ability. Yet if it were not for this fact, lakes and oceans would freeze from the bottom up. The earth would be a frozen wasteland, and human life would not be possible. Water also has the unusual ability to pull itself into very fine tubes and small spaces, defying gravity. This is called capillary action. This action is essential for the breakup of mineral bearing rocks into soil. Water pulls itself into tiny spaces on the surface of a rock and freezes; it expands and breaks the rock into tinier pieces, thus producing soil. Capillary action is also essential for the movement of water through soil to the roots of plants. It is also essential for the movement of water from the roots to the tops of the plants, even to the tops of the mighty redwood trees. Capillary action is also essential for the circulation of the blood in our very own capillary blood vessels. Water's melting and boiling point are not where common sense would indicate they should be when we look at its molecular weight. The three sister compounds of water all behave as would be predicted by their molecular weight. Oddly, water just happens to have melting and boiling points that are of optimal biological utility. The other properties of water we measure, like its specific slipperiness (viscosity) and its ability to absorb and release more heat than any other natural substance, have to be as they are in order for life to be possible on earth. Even the oceans have to be the size they are in order to stabilize the temperature of the earth so human life may be possible. On and on through each characteristic we can possibly measure water with, it turns out to be required to be almost exactly as it is or complex life on this earth could not exist. No other liquid in the universe comes anywhere near matching water in its fitness for life (Denton: Nature's Destiny). bornagain77

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