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j.smith84

reaction wood ?

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Wherever wood is on a tree, its make up is partly a localised stress, and so may vary in compressive or tensile strength and annual increment by proportions of lignin, cellulose and cell numbers and density. There are probably some simple linear relationships between stress and these components.

In conifers the overall effect seems to be more wood and lignin rich, but in broadleaf denser wood with more cellulose.

I should look this up to verify it but I haven't the time.

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4 hours ago, daltontrees said:

Wherever wood is on a tree, its make up is partly a localised stress, and so may vary in compressive or tensile strength and annual increment by proportions of lignin, cellulose and cell numbers and density. There are probably some simple linear relationships between stress and these components.

In conifers the overall effect seems to be more wood and lignin rich, but in broadleaf denser wood with more cellulose.

I should look this up to verify it but I haven't the time.

The salient point being in hardwoods the extra cellulose give strength in tension (the top of the branch) and in softwoods the extra lignin gives strength in compression (the bottom of the branch).

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Where there is a wound liek a tear-out or a pruning cut, the idealised circular cross section of a stem or branch has been compromised and there is localised stress around the wound, leading to reaction wood which is also ultimately CODIT wall 4 too. There may therefore be flexure alternating between tension and compression, whether it's gymnosperm or angiosperm. It's always worth taking a load of slices through an occluded wound and noting the ring history of woundwood and the colour/density of the early and late wood.

 

I'm still winging it, still haven't time to look up the full answer.

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