Thanks Geoffrey for the evidence, it seems that E Mannifera is well
able to be brittle without galah assistance. But I do urge you and
anyone with an interest to look at the almost incredible extent and
location of chewing on the trees I mapped in previous post. I'm told
by my tree surgeon friend that this chewing goes to the Cambium
layer. This layer is responsible for all new growth including scar
tissue, while the disappeared layers above (phloem and bark) are
responsible for protection and downward transport. Without new
growth for several years on the upper side, the branch is seriously
weakened in its highest tension location. Additionally, without
protection the exposed old growth becomes dried and subject to rot,
so is weaker again. It takes years or decades for the scar tissues
to re-cover such large areas even if the galahs move on to another
sport, and in this time there is ample opportunity for the forces of
decay to do their work.
I don't think most bird-lovers are aware of the extent of such
behaviour and resulting damage. If it weren't such a serious
risk/problem, arborists wouldn't be spending their time installing
galah-proof barriers to these parts of at-risk trees. The damage is
very obvious even standing underneath and I recommend the Corroboree
Park short stopover if you go past for Christmas.
PS I don't know if it really is galahs alone or various cockatoos
that are responsible.
At 10:10 AM 24/12/2009, Geoffrey Dabb wrote:
Ah yes, the Three Horsemen of The Suburban Apocalypse: Dogs, Noise and
Trees.
Some astute observations there, Julian. I doubt that bark-chewing
contributes much to limb-shedding by E Mannifera, the aptly named Brittle
Gum. I recently had to have one removed from the nature strip,
unfortunately. It was a wonderful spreading tree of great height, the
largest of its class, that had benefited from intermittent watering over a
life of some 46 years. A victim of its own vigorous growth, each year it
would shed a few branches and about every second year a large one that would
have been death to anyone beneath and a write-off for any vehicle. I had to
tell people not to park near it on days like we are having at the moment.
However this year a large branch came through a window, and a few months
later about a quarter of it thumped down in the driveway. Incidentally, if
you are in a similar position it is important for any property damage claim
that you make 'dangerous tree' representations beforehand.
The point is that none of the fallen limbs showed any disease or prior
damage, although some were naturally hollow. The brittleness is caused by
the growth habit which sees heavy, often fresh, foliage at the end of
over-long tortuous branches that twist and work in the wind. The species is
simply unsuitable for street planting, unfortunately.
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