Summer limb/branch drop

[difflock]

But I understood SLD was associated with dry (but could however be high humidity) STILL hot days.

I would also have associated it more with the south of England, in summer/late summer (but dont know why)

I would buy into the "over extension" of large horizontal branches.

But many Oak and Beech appear to carry large apparently ridicuously overextended branches without incident.

I did note in the failure that I photoed that a crack had formed and had had time to weather in the tension side.

I also note this in at least one other incident photo posted above.

But I would have understood this to not really be SLD type failure.

I.e it could just be "the final straw" of an ongoing slo-mo incremental process that, that when it for whatever reason, fails in perfect conditions we "notice" and puzzle over.

But if it had failed in windy or stormy conditions we would take for granted?

Edited July 12, 2013 by difflock

[treeseer]

"I would buy into the "over extension" of large horizontal branches.

But many Oak and Beech appear to carry large apparently ridicuously overextended branches without incident."

 

Hence the difficulty in prioritising which limbs to reduce. Exposure to weather, and targets, seem to matter most.

 

"I did note in the failure that I photoed that a crack had formed and age weathered in the tension side. I also note this in at least one other photo"

 

Good point; aerial inspections should take a close look at these areas, known as 'hot spots', on long limbs. right around where Massaria colonises?

[Gary Prentice]

I find it somewhat odd that we can put a man on the moon (supposedly!), but at present, are unable to explain this phenonomon. We seem to know so little, take for granted, what's so close to us.

[treeseer]

explain this phenonomon.

 

Wood weakened by moisture stress, ends too heavy. What else to say?

 

[Gary Prentice]

explain this phenonomon.

 

Wood weakened by moisture stress, ends too heavy. What else to say?

 

 

See the opening post!

 

As I understand it, this is still largely unexplained and at the theoretical stage and unproved.

 

 

Edit.

And pardon me for musing:001_tt2:

[daltontrees]

I am gripped! What is moisture stress, and how does it weaken wood? And why in some species more than others?

[treeseer]

Well there I did it; I hate the term 'stress', but lazily used it.

 

I'll go back to focusing on overextension, and let the academics muse and ponder on water movement and tissue qualities and other less visible aspects.

 

zipindelip

[daltontrees]

Well, 'stress' does have a genuine recognised meaning in the tree sense, being where a tree is pushed almost to its functional limits but will recover when the factor pushing it is removed. The extreme is 'strain' which is irrecoverable stress.

 

On the other hand, in mechanics (which I suppose includes biomechanics) stress is a measure of force per area, say XkN/m2. It has the same dimensions as pressure. Strain is extension divided by original length say Xm/Ym and so is dimensionless.

 

I though you were literally referring to the stress (mechanical) in wood changing with its moisture state, which was dumb of me since it can't - neither the load nor the cross sectional area can change and so the stress can't. However, if the tensile strength of wood can change with moisture content, that would be interesting and could in itself be enough to explain summer branch drop.

 

Finding figures for tensile strength of green wood is pretty much impossible but to put it in perspective it could be of the order of 25 MegaNewtons per square m. Which is enormous. That would be 2,500 tonnes per m2. Which is like saying if you could make a rope of just over 1.12m diameter using a column of uniform Beech wood it would be able to lift the Blackpool Tower.

 

So, general question, if tree components as we are told have a safety factor of 3 or 4 built in, and even this can be exceeded presumably by over-extension, how can these limbs survive occasional gales and then succumb to rainfall or just fall off on a still evening?

[Jesse]

Thanks for dredging up the article. Some good guesses on causation re transpiration etc., but every case I've seen, the branch was outside the crown outline and overextended.

 

So it can be chalked up in large part to gravity. (Brilliant huh?) Makes one believe in periodic reduction of sprawling limbs over public spaces; a 5-year cycle perhaps. Especially with previous occurrences. It's easier to prioritize based on probability when one focuses on the single factor of sprawl, but not easy nonetheless. The 1983 management options seem a bit draconian.

 

I like that approach .

[Mark Bolam]

No one knows why it happens, yet.

There are some good theories on here.

 

My extensive studies have revealed that SLD hardly ever happens, and there's f-all we can do about it.