[CANUFNET] spiral pruning

[Julian Dunster]

In the Lower Mainland of BC a few of us initiated spiral pruning as a 
technique to reduce the likelihood of windthrow, in the early 90's. 
Initially it was mainly Douglas-firs, hemlocks, and redcedars along new 
edges as development occurred. Later it was tried on isolated trees.

As an edge treatment for newly exposed trees in a forest it works well. 
It opens up the edge to be more 'porous' and the wind dissipates back 
into the forest stand without triggering windthrow. As a treatment for 
individual trees trees it is less successful, and on Douglas-fir, very 
harmful. When we started it over two decades back, we had heard a little 
about branch clashing, wind sail etc and it seemed a logical approach. 
It turns out that, at least in Douglas-fir, the branches need to clash. 
When they were removed  as part of spiral pruning they moved a lot more 
in strong winds and increased branch failure resulted, which in turn 
allowed other branches to move more and encouraged additional branch 
failure. I recall seeing isolated Douglas-firs that had been spiral 
pruned, looking very motheaten years later, with massive amounts of 
limbs broken off. The trees not touched seemed just fine and few had 
fallen down.

These days I would not prescribe spiral pruning for an individual tree 
that is isolated. I would still recommend it as part of edge treatment 
for newly exposed trees (any species) in forest conditions. It should 
not be prohibited in all circumstances. Like many treatments there is a 
time and place where it can be very effective as means of meeting 
defined management goals.

On Behalf of Dunster and Associates Environmental Consultants Ltd.


Dr. Julian A Dunster R.P.F., R.P.P.., M.C.I.P., ISA Certified Arborist,
ASCA Registered Consulting Arborist # 378,
ISA Tree Risk Assessment Qualified
BC Wildlife Danger Tree Assessor
Honourary Life Member ISA + PNWISA

www.dunster.ca

Distributor for Air Spade. www.air-spade.com

North American Distributor for Rinntech equipment. www.rinntech.com

On 11/05/2015 8:47 AM, Hamilton, Emily wrote:
>
> Good morning,
>
> We are looking into justification for or against spiral pruning here 
> at the City of Surrey and I was wondering if anyone had any experience 
> or documentation that they'd like to share related to this. Any thoughts?
>
>
> Thank you,
> Emily
>
> Regards,
>
> Emily
>
> Emily Hamilton | Environmental Technician - Arboriculture
>
> COS_Tag_pp_cmyk-200
>
> **
>
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>
> Trees and Landscape Section, Building Division – Planning and Development
>
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