SLF on a silky oak

Garry Brockley

I was called out to a job in Stafford this week, when i saw the limb on the ground i had to take some photos.
The limb itself measured 8.5 meters, according to the customer when it released there was only a small sound.
Note how cleanly this seperated from the main trunk and the role of cambium buildup at the top and the discolouration on the top section.
now its hard to see on the photo but when you look at the limbs shape its almost an hour glass shape, it narrows from the top and underneath then fattens out to a normal shape, i have seen this before on several beech trees in the uk but didnt see any significance in the shape, i have also seen this on a couple of eucalypts over here but these are still attached so i will be keeping an eye on them to see if there is any change.








Has any one else found this hourglass shape on sudden limb failures?
G

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Sean Freeman

Nice pics, with good detail...the final shot shows some interesting indications of past injury extending down to the tension side of the recent failure..certainly might help explain the loss in structural integrity of the tissues on the tension side of the recent failure.




You can also see evidence in the first pic too....

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Eric Frei

I think that's a pretty unique failure we're looking at.

What is the dia of that limb at attachment point where it failed?

Certainly for it to come off clean is unusual, no tearing down. You can see no evidence of it being cracked prior, like a storm damaged limb that was partly broken then failed a year later etc as no discolouration.

On the trunk you can see wound wood on the upper part of the wound, the tree's been prepping for this failure. Maybe it was cracked? Interesting, sort of want to investigate more.

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Sean Freeman

The second painted pic inserted again since it seemed to have vanished from my previous post.

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Eric Frei

Pity the shadow is on that pictuire, makes it harder to detect if there was exposure to the inner wood prior to failure.

Have a look at this though, we have wound wood on both ends, and if you look closely it's almost like they were growing in opposition to each other like an included co-dominant.

Likely that there was a wound, perhaps even a crack not very deep. Likely that there was sufficient transportation of sugars (from the underneath) to grow additional wood. Likely that both sides of the wound/defect grew wound wood and assisted in the failure whilst attempting to seal off the wound.

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Garry Brockley

Thats what i was thinking that there was maybe damage on the upper side and both rolls of cambium seem to have forced this banch away from the main trunk, but i couldnt work out why it came away so cleanly no tearing ect are there any diseases specific to silky oaks that attack the cellulose and lignin? if so this could be the reason, however i have seen no signs of decay or weekness on the tree.
I have left the stump in the unit it will still be there hopefully so i can get more photos and maybe disect it.

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Sean Freeman

Many fungi capable of digesting lignin selectively but none that I am aware of particular to Grevillea sp alone.

From your pics certainly seems like a reduction in cellular integrity extending from the tension (upper) side of the union, just how far that extend through the union and how it compromised the branch collars hard to say with any certainty....more than likely combination of numerous fungi and just as important the ingress of oxygen from the wound site.

I agree with Eric there would most likely be some pressure between the two sets of woundwood but enough alone to force a healthy union apart....doubt it.

What did the limb look like, if it had not failed still attached? growing at right angle to the stem, or with an elbow sending up foliage parallel to the stem creating almost a competing codominant?

Eric Frei

Not force it apart but assist. It's not a healthy union either. We see co-dominants tear out easily with the bottom section staying attached or ripping out.

Without tension wood on the upper side, and a place for fungi to enter with the gap between trunk and branch being open, and as you have mentioned the attachment point could well be a collarless union it's likely that all these factors led to the failure.

Look at the branch here, often trees will repeat a flaw throughout their canopy on an individual basis. Like I have encountered ironbarks where almost all unions were included co-doms with decent sized "elephant ears". The anomaly consistently repeated in the one tree but not necessarily for the broader species.

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