Looks like it's all about physics. You have stressed trees with internal
tensions of around 15 atmospheres which is suddenly released by humid weather
giving rewetting of the wood. This happens on my fruit trees in France and
they go bang when the pressure is released. I would think this kind of power
would find any weakness in a branch.
From: Andersonarb@xxxx.com
Date: Sat, 22 Aug 2009 11:35:46 -0400
Subject: Re: "Summer" branch drop and compromised root systems
To: uktc@xxxxxx.tree-care.info
In a message dated 21/08/2009 18:37:48 GMT Standard Time,
rupert_baker@xxxxxxxx.co.uk writes:
On a similar subject, came across a big Cedrus atlantica which had shed
limbs, breaking about 1/3 to 1/2 way out along their length. Tree had old
snags showing similar patterns of failure. The current ones appeared to be
associated with old lateral branch losses/prunings, with discoloration
evident in the central wood of the stem, and on one limb, a very
distinctive
failure along one annual growth line - like a ring-shake. Any thoughts on
causation on these?
Without the benefit of ever having been anywhere their native range Rupert
I'd put down the failure of Atlas Cedars (usually blue) entirely down to
their growing away from their native ranges, the weather doesn't suit them
at
all. In particular snow seems to do for them: I recall heavy snow in the
early eighties wreaking havoc amongst Cedars generally and Atlas Cedars
seemed to get damaged almost as often as it snowed. I imagine that like
Monterey Cypress they grow differently depending on the local climate.
Of course we don't seem to see snow so much these days so we've not seen
quite so many damaged ones. Having said that my crew were up one earlier
this
week that was showing a very nice hazard beam crack, which I imagine would
have broken a long time ago if we'd actually seen a decent snowfall.
(Sorry should that be a "snow-event?")
When I get round to splitting the firewood from the Atlas I'll look out for
any discolouration that might relate to broken stubs or something but my
vague recollections of splitting or sawing Atlas logs doesn't throw up any
instant memories of specific defects. Certainly not ring shake, although
come to think of it, I recently moved a few Cedar posts that we've had
stacked
up for a while and several of them cracked without showing any obvious
decay.
To go back to the SBD subject in the header I've seen a couple of trees
that have shed branches in the last coupla weeks, a HC definitely was
related
to past damage and some end-loading and the Beech simply due to a included
bark and end-loading. I wouldn't really have called it SBD other than it
was; er.... "Summer" and "Branches" had "dropped."
Dunno how you'd make out that such a thing was an evolutionary development
but then again Vera et al really mean we need to reconsider what the
natural habitat of tree really is and how their evolution might not have
been in
woodlands but in a savannah-climax-environment.
Does that make any sense?
Bill.
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