Compression wood: Happy Thought for 10 December 2021

 Have a Happy Thought: 

 TIL (Today I Learned) that when trees lean, and as tree branches grow, gymnosperms (evergreens) add wood to the compression side of the trunk. Angiosperms* (broadleafs) add wood to the tension side.

* some “primitive” angiosperms add wood to the compression side as well

 

This is called Reaction Wood.

(mind out of the gutter, you!)

 

This is what it looks like when you cut a tree down and look at the rings:



From <https://woodlot.novascotia.ca/book/export/html/462>

 

Anyone who has worked with wood probably already knows this, since tension wood is less dense, and weaker, so more prone to breaking/cracking.

Meanwhile, compression wood shrinks a LOT more than other types of wood as it dries, so it too can cause odd-shaped lumber.

 

Here’s some photos of Reaction Wood in live trees:

 



Image: David Humphries https://arbtalk.co.uk/forums/topic/62463-compressive-amp-tension-reaction-wood/

 

Compression Wood:



Image: David Humphries https://arbtalk.co.uk/forums/topic/62463-compressive-amp-tension-reaction-wood/

 

 

This can also lead to some impressive, and beautiful, spiralling in branches:



Beilschmiedia taraire Lauraceae tarairi.

This twist of asymmetric spiralling growth on the inclined branch is the result of mechanical stress forcing the cambium to be more active on one side than another.

 

 

Shout out to another, and way-more-experienced-than-me NZ blogger Tony Foster for the last two images  <http://bushmansfriend.blogspot.com/2010/12/reaction-wood-compression-wood-and.html>

And thanks to the team at the Completely Arboritrary podcast, especially their episode on the Black Spruce, for letting us know about this!

PS for all of you Portland, Oregon folk, that podcast talks extensively about tress around your hometown, with (recently ex-) Portland City arborist Casey Clapp.

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