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Bio-bullets

Seeing the light for the trees

The mainstream logic, that trees outgrow each other to compete for light, cannot stand acute scrutiny.

professor caricatureProf. Mumblebard claims: “Competition for light is a textbook example of a proven ecological principle. It demonstrably drives the growth of trees and ultimately explains the height of all forests.”

logoRobin and the Honey Badger respond: "Most flowering trees grow in relatively open stands as woodlands or savannas as opposed to dense forests. With such wide spacing, neighbours cannot have crowns broad enough to shade each other and therefore light cannot be in short supply for the dominant plants. The real reason why tropical and subtropical trees{njaccess 2, 3, 4, 5, 6, 7, 8} grow tall is to compete for certain nutrients rather than light. This is because every additional metre of height can theoretically boost the retrieval of nutrients from aerosols and from groundwater. The taller the tree, the greater its area of foliage and the more rapid the total collection of dust on its electrostatic surfaces. Such aerosols tend to be rich in certain nutrients which can enter the leaves directly by foliar absorption. Remaining nutrients in the deposited dust can be absorbed via the roots after being washed down to the ground. Furthermore, wind increases exponentially as height increases, so the taller the tree the more dust it will intercept. The same airflow also promotes transpiration and so boosts the power of the tree to lift dissolved nutrients which have leached from the topsoil to depths beyond retrieval by shorter plants."{!njaccess}… Reveal the hidden half of this response by Robin and the Honey Badger by subscribing here{/njaccess}

 

Please join us here at the Bio-edge with your own comments. In the discussion below we encourage links to any evidence supporting either Prof. Mumblebard or Robin and the Honey Badger. Illustrations are welcome but please cite all sources or we may be forced under copyright to delete your comment.

 

Seeing the light for the trees

Last modified on 16 July 2015

Comments   

0 #1 Greenbrain 2014-02-13 12:05
This bio-bullet is worth thinking about, because in dense forests, saplings can compete for light by racing each other upwards, but the higher they grow the faster they just waste energy on making their stems. So it all seems a bit pointless, like all running hard on a treadmill. Energetically they’re all just staying on the same spot? You’d think the clever one would be the one that just grows sideways and shades its neighbour before its neighbour shades it. What’s the point of growing tall if all the energy you got is just sunk into wood. A plant can’t get that energy back, it’s only released when the tree dies and the wood rots or burns. So, according to light competition, where’s the energy gain in piling on more wood?
0 #2 Johns 2014-02-13 12:41
Multi-functiona lity – a concept forgotten too often by ecologists. In another one of their biobullets Robin and the Honeybadger point out that the clitoris is probably multi-functiona l (see The fossa’s exceptional clitoris proves the rule). I think what many ecologists miss is that so are leaves. Watch this youtube clip and think about multi-functiona lity. www.youtube.com/.../ Those leaves are of course capturing light, but aren’t they also quite a good ‘filter-feeding ’ device for collecting dust? And of course for setting up a transpiration stream from the roots.
0 #3 Phytoforce 2014-02-13 15:33
Well no matter what you say about light competition you’d definitely need it to explain adaptations within the understorey if the forest is dense. Perhaps RHB have a point that light isn’t limiting for the dominant species in the system. But their logic wouldn’t apply to the shorter sub-dominants…
0 #4 Redfern 2014-02-13 17:53
It truly is a puzzle why trees like this one would want to be so tall given that there is obviously no competition for light from any neighbouring trees:


attributed Ethel Aardvark (Creative Commons)
0 #5 Phytoforce 2014-02-14 14:15
@greenbrain The amount of energy sunk irretrievably into wood by tall trees seems to prove that light is a bit superfluous relative to other resources such as water and nutrients.
0 #6 Woodlover 2014-02-14 14:23
And another point suggesting light is not a big deal for tall trees: some of the fastest-growing of trees, e.g. eucalypts and casuarinas, have light-shunning foliage that cast minimum shade.
0 #7 Phytoforce 2014-02-14 14:23
Greenbrain’s point has some interesting implications. Surely it would be more effective to compete for light by growing broad than by growing tall, because at least a wide canopy can directly shade its neighbours?
0 #8 Gronbek 2014-09-23 12:45
This comment stream seems over the top, complicating something that’s already pretty much been solved. Every forester knows that saplings compete with each other for light and that’s what thinning of the stand, whether it’s by deliberate management or self-thinning, is all about. Bringing in all these other tangents for their own sake just damages genuine science in my opinion.

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