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  • Thanks to Brilliant for supporting this episode of SciShow.

  • Go to Brilliant.org/SciShow to learn more.

  • {♫Intro♫}

  • There are a few forests out there where the trees are especiallypolite.

  • The tops, or crowns, of these trees don't touch each other, leaving a few inches of

  • space all around -- creating a bizarre, beautiful spiderweb of gaps in the canopy.

  • Scientists refer to this phenomenon as crown shyness.

  • It's observed only in specific circumstances -- only in certain species, and often in stands

  • of trees that are all the same species and age.

  • And while scientists don't fully understand why it happens, they do have a few different

  • hypotheses.

  • The first thought is that crown shyness might be caused by contact between trees.

  • When wind makes the trees sway back and forth, some that are too close may bump into each

  • other, causing branches to break and leaves to fall, which is costly for the tree.

  • Trees can combat this by growing taller than their neighbors and out-competing them for

  • sunlight and other resources.

  • But trees can only grow so tall.

  • And lodgepole pines, which are the tree of choice for studying crown shyness, cap out

  • their crown size well before that -- when they are about eight to ten meters high.

  • When the tree reaches ten meters high, it's more likely to hit other trees when it's

  • windy, which causes the branches of the crown to break once more.

  • This damage to the tree's branches limits the growth of future branches until eventually,

  • they stop growing back, creating a small gap between the trees' crowns.

  • But when the trees are artificially immobilized so that they don't hit each other, they begin

  • expanding their crowns again.

  • This may help explain why crown shyness is usually seen in mature stands of certain species.

  • The crowns have reached their maximum width, so the space between them is maintained.

  • Another potential cause of crown shyness could be the result of a physiological response

  • to the shade of other trees.

  • Leaves contain pigments to absorb light.

  • Chlorophyll, the primary pigment used in photosynthesis, and it absorbs red light.

  • So if boughs of nearby trees are causing shade, the light that comes through is going to have

  • less red light because of shading from the leaves.

  • Instead, that light will include a relatively large amount of far-red wavelengths, the extreme

  • end of visible red light that isn't absorbed by leaves.

  • Specific pigments called phytochromes pick up on the ratio of red to far-red wavelengths.

  • If they detect a lot of far-red light, the trees promote upward growth instead of outward

  • growth and try and escape the shade.

  • But that just means we run into the height cap again.

  • The trees can't grow taller anymore, and the branches won't grow outward towards

  • other trees because of the shade, which leaves that space between them.

  • One other possible explanation for crown shyness involves an idea known as allelopathy.

  • According to some scientists, this is a phenomenon where plants produce specific chemical compounds

  • that influence the growth and behavior of neighboring plants.

  • Some researchers have hypothesized that similar chemical compounds could be released by the

  • leaves of theseshytrees, and they limit the growth of their neighbors.

  • But such a compound has never been identified, and many ecologists are far from sold on the

  • idea.

  • There probably isn't one specific cause for tree politeness.

  • Instead, it's likely that crown shyness occurs as a result of multiple mechanisms.

  • But whatever the cause, these shy trees are a sight to see.

  • These trees make incredible patterns.

  • If you want to know more about the math behind this spectacle, you might enjoy Brilliant.org's

  • Beautiful Geometry course, which uses fascinating patterns to teach you to love math.

  • All of Brilliant's courses can help you cultivate your math and scientific thinking

  • skills.

  • From math to computer science, they can help you learn more about the rules that shape

  • our world.

  • Each course is designed to pull you in with interactive quizzes and hands-on guided problems.

  • No dry walls of text here.

  • Best of all, you can get 20% off an annual Premium subscription if you're one of the

  • first 200 people to sign up at Brilliant.org/SciShow.

  • {♫Outro♫}

Thanks to Brilliant for supporting this episode of SciShow.

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B1 中級

なぜこれらの木は触れることを拒否するのか? (Why Do These Trees Refuse to Touch?)

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    林宜悉 に公開 2021 年 01 月 14 日
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