Date: Wed, 18 Apr 2012 15:59:02 +0100
From: arborico@xxxxxxxxxxx.com
Subject: Re: [Bulk] Re: Pruning Induced Stress
To: uktc@xxxxxx.tree-care.info
________________________________
From: Scott Cullen <dscottcul@xxxx.net>
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Sent: Wednesday, 18 April 2012, 13:50
Subject: Re: [Bulk] Re: Pruning Induced Stress
----- Original Message -----
From: DOMINIC GANE
To: UK Tree Care
Sent: Wednesday, April 18, 2012 7:55 AM
Subject: [Bulk] Re: Pruning Induced Stress
SC Dom, thoughtful reply. Not to minimize any of it, but to make this a
bit more focused I've deleted a lot...
DG Thanks, I am prone to waffle around a bit, apologies.
SC That alone is a potentially important point. Do root/soil flora
become parasitic or negative agents under some conditions rather than just
fluctuating on their own? Pruning as a potential trigger is interesting
but less key than the basic toggle. Do they parasitize root tissue that is
now also "excess" to the remaining live crown? Or, insatiable, consume
more?
DG IMO and with respect to symbionts we are looking at a continuum of
benefit to parasitism. Parasitism being a benfit to one partner only. I
have seen this in establishing Eucalyptus colonised with Glomus (endo's)
in broad terms the innoculated trees exibited lower growth parameters and
biomass production than unioculated controls. However it depends on your
measure the Glomus innoculted trees also exhibited a degree of resistance
to herbivory. The reduced growth was transient however the lower biomass
was presetn at the end of the investigation. The reduction in growth may
have been due to the fungal partner "taking" rather more carbohydrate than
was compensated for by the additional nutrients supplied to the Euc's. In a
pruning scenario we reduce the trees ability to produce carbs. All other
factors being equal I can't really conceive of a situation, where one
partner in a symbiotic relationship would move towards parasitism. I have
done anothr
piece of work looking at in vitro interactions between Suillus (ecto) and
Armillaria, it appeared that limiting carbs available to the Suillus
inhinited its ability to produce anti fungal compounds allowing greater
Armillaria growth. I caution against reading too much into this as it was a
fairlly small investigation and conducted under highly artificial
conditions.
SC Indeed. In ecology there is something called the precautionary
principle. Don't fool with things when you don't know the outcome,
especially if a negative one is irreversible. On the other hand - and it
applies broadly but thinking in terms of tree management - we have nothing
but paralysis if we don't do anything because we aren't entirely sure of
the outcome. Tony gives the examples of coppice and pollard, we know fruit
trees are pruned a certain way for production, we've seen magnificent
hedges and I know of whole landscapes that are "size maintained"
successfully (though it's not my tradtional approach I have been
impressed). I'm unconvinced that a fully hands off followed by fell and
replace approach is either most cost effective or what tree owners want.
So we would do better with a better understanding of the continuum of
gentle caress, useful push and fateful shove.
DG I agree, I think we could do more to improve the supporting communities
as well, we just dont know what. I would like to see some more directed
research into urban mycs. There appears to be a strong inverse correlation
reported in the literature between myc abundance and diversity and
saprophyte abundance. High myc in rural environments and low in urban.
Linked to anthropogenic nitrogen deposition,
SC Somewhere above I think you spoke of resilience. I can't help
thinking that maintaining resilience - as the variables allow it - may be
dependent on minimizing deep shocks and wide swings that may make the
system "brittle," to use the metaphor of working matreials.
DG I agree, with the caveat that we may be gradually deforming the system
plastically until we reach the point that it no longer functions or,
borrowing from structural engineering, corroding the steel reinforcement in
the concrete. However, I guess we are talking an improvement in sustainable
yields at lower inputs rather than absolute terms.
DG IMO, for what it is worth, I think we are missing a trick with
beneficial soil communities particularly mycorrhizal symbionts. Reported
benefits cover the list of urban tree stressors, except pruning perhaps.
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