Summer Limb Drop.

klimbinfool

klimbinfool

Location
magalia california
Summer limb drop is very prominent in our area. Ive always known it as the tree taking up much water and then the limb structure would break usually in a defective area, but not always. Ive seen many limbs fall with no defects whats so ever.This led me to asking more questions about what really happens when the limb is loading up and then releases water, because the limbs are usually falling in the evening or early moring .

So with that , give me some explanations and see if they match up with answer that the Urban Forester gave me.

Good luck !

Thanks
Greg
 
Here is my thoughts on Sudden Limb Drop:

A branch will lose water through the leaves. On hot days there is a huge amount of water pumping out of the limb into the leaves and into the air.
I think that at some point in this process the tree cuts off the water supply to a paticular branch in order to conserve the water resource for the remainder of the tree.
The branch continues to pump out the water it does have left, dries itself out and becomes something like 2/3s or more lighter than it was for it's history up to that point.
This weight change is rapid. Reaction wood and commpresson wood that built up for the life of the limb is specificlly designed to carry/hold the limb for it's weight with alot of allowences.
When the weight of the limb is reduced to that extreme extent, and the water is non-existant, the limb lifts and "pops" off at the branch bark coller or close to it.
I would like to know if I am krazy or if this theory has any merit.
thanks for your responses
Frans
 
Greg,
I don't have any scientific proof here, but I tend to think that it may have to due with the limb wood loosing water too fast and drying out. Then, this would result in less flexability and a loss of turgor. Anyone?
 
I guess my last reply didn't go through .

The Urban Forester for the City of Chico gave me this answer.

Durin the process of uptake the cells within the limb are swelling enormously.Transpiration occrures, releasing water as fast as it can. During this process, wood fibers are being fractured from shrinkage, therefor causing failure.

Depending on angle of the limb, foliage, fruit, cones, defects, amount of water already retained in the limb, etc: will determine how, when and where it will break.Unfortunatly , on a healthy limb , we wont have a clue as to where it will break. So , reducing the limb structure as we know, will help prevent this problem.

My thought was that that the tree would actually shut of the release of water at a certain point or could not transpire fast enough , loading the limb and then causing failure. Although, as the summer goes on , limb drop becomes less and less. Do the trees become acclimated to this process ?

thanks
Greg
 
I heard of someone in Australia writing their thesis on the sudden limb drop phenomena.
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I know the Karri trees in Western Aus (euc. diversicolor) are reknowned for summertime drops. But I think that the eucs are mostly dropping limbs as a forest self pruning phenomenon- trying to compete with their siblings for light vertically. Would it be in effect outside of that environment?
 
In my experience when a branch falls off a tree due to what ever reason there is always a weakness there already whether it be included bark,pathogens over leave or fruit production,This theory of the wood drying out seems a bit strange to me.If a tree is loosing more water than it
can take up then I would have thought it would close its stomata down to slow down transpiration.Also if one branch was drying out then others would also.It would not be isolated to one branch.In my opinion it comes down to a constant or increasing force on the branch by gravity(or wind)on a point that is already weakened by some other factor,the branch falls off!!!!Find the cause of weakness and you have your answer...I'm going to stick my neck out here.There is in my opinion no such thing as the summer branch drop as phenomenon,Just alot of individual cases happening around the same time for many different factors.The only common factor being the force!!!!"maybe them Jedi's" HMMM
 
http://home.wi.rr.com/sanbornstrees/summer%20limb%20drop/

here are some pics I took of a SLD I worked on a few years ago. Too bad I corrupted a few of them getting them on my server. I had 5, now 3.

Every tree I've seen SLD happen had at least some micro deffects in the wood. I think there is something to the theory that micro climatic changes can cause the branch to engorge with water, but there still needs to be some place for the failure to begin.

In thes pictures the circumferential growth was not consistant, and a layer of several cells were slightly discolored and dry, or brash as Russ Carlson explained it to me. Possibly old squirril damage?

So the tree was transpireing rapidly, then a calm hit the area and the local air was saturated enough so transpiration quit, while translocation was still occuring. This overloaded the branch just enough for the brash area to shear, and the rest of the branch pealed out and landed on the ladies front walk.

My theory at least.
 
Hi John I think the theory is a sound one.I just have a problem understanding this water engorgement that keeps coming up.Maybe I'm completely off base here so to speak but I would have thought that transpirational pull is equal to transpiration rate.If this is true When transpiration slows down so will the transpirational pull
If this is the case then the amount of water in the branch tissues should not change much??????
My theory is pretty much the same as yours.There is aweakness in the branch already and there is an increasing force on the weak point.There is a large force differetial between winter weight and summer weight The reason it falls in summer is because thats when it is most under load from leaves transpiration elongation of shots translocation,ETC When your working your hardest if you have a weakness thats when its going to show.I believe that summer branch drop should actually be called THE STRAW THAT BROKE THE DONKEYS BACK DROP..
Summer is the secondary cause not the primary as far as I can see Therefore we shouldn't really blame the summer for it???????
 
The way I've heard it is that there is some flow that will keep moving after transpiration has stopped.

Another that came back to me is that the tree has wilted to conserve moisture and then at night the flow starts back up again and the weight change is too sudden for the defect.

In eithert case the wieght does not have to be all that much in it's self, becuase of the leverage it puts on the limb being way out on the tips.

Seems a lot of it happens in late summer, so second or third flush of fresh growth can have an impact.

My feeling is that it is a confluance of variables that percipitate the deffects failure, or the proverbial straw.

People are looking for one root casue, I think there are many, due to the failures happening in calm conditions with other climatic variables; cool or hot, dry or damp, night or day.....

For anyone studying this, I think a good resourse would be utility workers. I've talked to linemen who say they see it all the time.
 
I am trying to find some research on the.topic. but the links are dead :-(
have been Googleing it for the last 30.minutes, without any useful.results.
anyone knows where to.look?
 
Well, believe it or not, there is scientific evidence that SLD is caused by limb girdling insects that are active and chewing during the spring/summer season!

I personally think the little buggers do their chewing/damage during the early spring. This causes the branch beyond the girdling point to dry out, lose elasticity, and the wind does the rest.

I know this occurs on some tree species, whether it happens on all and is the primary driver of SLD is an open question of course.

jomoco
 
Thanks for that, Jomoco.
I'll read the article tonight.
I just don't think that thees insects are feeding in the cold danish climate. But I am looking forward to read obout it.

The only other scientific article, regarding summer limb drop, I have found, is in Journal of Arboriculture from 1983 :-/

Anybody know of a newer article??
 
Just came across the term: "BRASH WOOD". What does that mean? Have never heard that english term before....

In my book "A photographic guide to the evaluation of hazard trees", by Matheny and Clark, it is written: "sudden limb drop may also be associated with structural defects such as internat cracks and BRASH WOOD".
 
[ QUOTE ]
Ive seen many limbs fall with no defects whats so ever.

[/ QUOTE ]

Depends on whether you consider overextension (outside crown outline) or heavy end weight to be "defects". They are typically conditions of concern. I've never seen SLD where the limb was inside the crown outline, or had good interior laterals.

Liontailing is definitely a predisposer here, and light reduction a preventive treatment.
 
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