[CANUFNET] spiral pruning

Mon May 11 14:22:07 EDT 2015

Well, just to “put the fox amongst the chickens”, here us how we approach
this issue.  We do not support “spiral pruning” for the reasons given by
Julian.  Whether a stand-alone conifer or a ‘new forest-edge’ condition, if
the tree is judged to be an important tree to retain, but considered at risk
of windthrow, we generally advocate a very modest reduction in the height of
the tree.  This typically translates into nothing larger than a 4 – 5”
pruning cut and the removal of 5 – 10’ of the leader.  We make it clear to
our clients that the tree is now classified as a “managed tree” that will
require periodic aerial inspection and maintenance.  For instance, it is
beneficial to return to the tree 3 – 5 years later to simplify the new
leaders that typically form from the branches arising beneath the pruning
wound to a single leader.

We find that this approach provides the maximum amount of stability with the
least amount of damage to the tree and its SULE.  The procedure is gentle
enough not to subvert the tree’s natural response to high, gusty wind
events, which to fare-back in the stem, branches, twigs and leaves as a unit
to reduce the overall windage of the tree.  The procedure reduces the
opportunity for wind to enter and windmill within the interior of the
canopy, which tends to flex limbs in directions they are not adapted to and
causing unnecessary limb failure, as Julian notes.

This approach is to be distinguished from the practice of “topping” in the
following respects:

}  “Topping” typically removes 25 – 50% of the canopy of a tree, and the
most photosynthetically productive fraction at that;  depending upon the
live-crown ratio we confront, our procedure removes approximately 5 – 10%.

}  “Topping” results in a large topping wound that is generally to large to
compartmentalize effectively; our procedure does not.

}  “Topping” triggers a stress response in the tree, as it attempts to
replace the large amount of canopy lost.  This draws down the photosynthate
reserves in the tree and results in the development of overly-vigorous
leaders with weaker wood strength.

We have been fortunate to have had a case study to field test this procedure
at a landscape scale along the shoreline of one of Vancouver Island’s
windiest lakes.  A Riparian strip of second or third-growth Douglas Fir
forest 15 – 20m wide and several kilometres long was left standing on the
lower slope of the lake.  Recreational lots were created along the length of
the site, with building sites placed within falling distance of the remnant
forest trees (against our advice).  We have been observing the site for six
years since the initial tree management.  In six years, there have been two
failures of the several hundred modified edge-trees, both along the water’s
edge and compounded by an increase in the lake level.  In contrast, 11 trees
in an unmanaged/undeveloped section of the site with fewer than 100 trees
failed during an extreme wind event. 

I appreciate that this kind of approach would be difficult to sell in a
municipal setting, given the orthodoxy within the arboricultural community
against topping, however defined.  Still, it as an evidence-based approach,
we consider it defensible and welcome comment on its merits or deficiencies.
Let the games commence J.

Best regards,

Jeremy Gye

President and Senior Consultant

cid:image001.jpg at 01CFD0BD.F440FD90

O:     (250) 544-1700

F:     (250) 544-2059

C:     (250) 883-4533

E:      <mailto:jgye at gyeandassociates.ca> jgye at gyeandassociates.ca

 <http://www.gyeandassociates.ca/> www.gyeandassociates.ca

From: CANUFNET [mailto:canufnet-bounces at list.web.net] On Behalf Of Ken Byrne
Sent: May-11-15 9:22 AM
To: Canadian Urban Forest Network
Subject: Re: [CANUFNET] spiral pruning

Hello Emily,

Just to add to Julian’s comments if you want some further documentation the
following link has some Best Management Practices for edge treatments
starting about page 7-28.

https://www.for.gov.bc.ca/ftp/hbt/external/!publish/web/ems2/BCTS-Coastal-Wi
ndthrow-Manual.pdf 

Cheers,

Ken

Description : cid:image004.png at 01CBBBDD.C07E2490

Ken Byrne, PhD, RPF

Researcher / Chercheur

Forest Operations Division / Division des opérations forestières

2665 East Mall, Vancouver, BC  V6T 1Z4

( 604-222-5709

+ Ken.Byrne at fpinnovations.ca

www.fpinnovations.ca <http://www.fpinnovations.ca/> 

From: CANUFNET [mailto:canufnet-bounces at list.web.net] On Behalf Of Julian
Dunster
Sent: May-11-15 9:12 AM
To: canufnet at list.web.net
Subject: Re: [CANUFNET] spiral pruning

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

CITY OF SURREY

Trees and Landscape Section, Building Division – Planning and Development

13450 104th Ave, Surrey, BC, Canada V3T 1V8
T 604.591.4560  <http://www.surrey.ca/> www.surrey.ca/treeprotection  

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