Lesson 5: Windfirming Treatments
In this lesson, participants will:
- know where and how some specific management practices are being
used in BC to reduce the likelihood of windthrow
- know the cost and effectiveness of these techniques based on recent
This lesson contains 7 pages. Much of the content is presented as screens
with accompanying text descriptions. Read the linked reference
articles for more background information.
Edge modification study results are courtesy of Chuck Rowan RPF, BCMOF,
Vancouver Forest Region.
Where cutblock boundary placement is restricted to achieve management
or engineering objectives, edge treatment may be an option. The requirement
to retain riparian, gully and biological reserves has led to experimentation
with edge treatment methods such as feathering, manual tree topping
and pruning, and helicopter top pruning.
Insights into the design of edge treatments can be gained from examining
the behaviour of old block edges with similar characteristics to the
proposed edge. Feathering is most likely to be effective where old edges
have experienced partial damage. Topping has been used to reduce the
wind load on riparian and gully reserve trees.
Chuck Rowan of the BCMOF Vancouver Forest Region has tested a variety
of manual and helicopter topping/top-pruning techniques on Vancouver
Island and the Queen Charlotte Islands. Results after four years indicate
that topping, pruning and feathering do reduce damage compared to controls.
It is critical to complete treatments before the first winter winds
In coastal BC, topping and pruning treatments are ‘specified operations’
and costs can be incorporated into the stumpage appraisal for a cutblock.
Page 2 - Edge Feathering and Crown Modification
- Edge feathering is thinning within the first tree length of the
- Where possible, retain the most windfirm trees.
- Don’t feather edges in dense stands of slender trees.
- Feathering mimics the pattern of partial damage that develops along
moderate risk boundaries.
- During salvage, leave standing and leaning trees in place if possible.
- Crown modification includes: topping, top-pruning, sailing, spiral
- Removing the top 1/3 of the crown reduces wind loading by 50%.
- Topping and top pruning can reduce tree vigour and cause trees to
produce multiple leaders.
- There are helicopter-based techniques for topping and top pruning.
- Heli-saw productivity ranges from 12–44 trees/hour, costing $19–68/tree.
It is best suited to mature stands.
- Heli-shear productivity ranges from 9–37 trees/hour, costing $23–91/tree.
It is best suited to 2nd growth stands.
- Manual topping productivity ranges from 1.3–1.9 trees/hour, costing
- Sailing and spiral pruning are manual arboricultural techniques
that preserve the top of the tree.
- In sailing, windward branches are removed from the lower 2/3 of
- In spiral pruning, branches are removed throughout the crown.
- Productivity for sailing and spiral pruning treatments is lower
Page 3 - Results of Chuck Rowan’s Edge Modification Study in Coastal
- Compared to damage in controls, pruned, topped, and feathered treatment
units had 30–50% less wind damage during the first winter after treatment.
- Treatment units with combined feathering plus crown modification
had 65% less damage than untreated controls.
- For the blocks with more than one year of post-treatment measurements,
the majority of damage occurred during the first winter. There is
a slight increase in standing tree mortality in the fourth year after
treatment in some of the pruned/topped treatment units.
- Untreated trees in the pruned and topped treatment units are more
vulnerable than treated trees of similar size in these units.
- In the control units – slender trees were more vulnerable, trees
with rotten branches or mistletoe were more vulnerable.
- Stands with a higher amabilis fir component were more vulnerable
than stands with a higher cedar component.
- Only 30% of new leaners blew down over the second winter.
Page 4 - Operational Considerations
- An evaluation of stand conditions enabled the classification of
stand hazard are shown here.
- Use this technique in high risk locations where windthrow impacts
- This treatment removes 30% of crown overstorey trees.
- Limit treatment to 0.5–1 tree length into the stand.
- Important to treat before felling the block, or prior to winter
Purpose of this exercise:
- To encourage learners to observe edge modification treatments and
consider operational situations for using them.
- To observe the results of windfirming treatments in the field.
- To gain experience in recommending windfirming treatments to reduce
Page 5 - Exercise Background
There are three edge modification trials in BC. The Akan Creek trial
was established near by Terry Rollerson of the BCMOF Vancouver Forest
Region in 1991. The Keogh River trial was established by the BCMOF,
Western Forest Products, and the Forest Research Engineering Institute
of Canada (FERIC) in 1994. Starting in 1996 Chuck Rowan of the BCMOF
Vancouver Forest Region began establishing a large trial with sites
on Vancouver Island and the Queen Charlotte Islands. Results from these
studies indicate that topping, pruning and feathering do reduce wind
damage compared to controls. It is critically important to treat the
edge before the first winter winds. Contact Chuck Rowan for current
results from these projects and for copies of the project reports.
Page 6 - Action – Arrange to visit an area with edge modification
Key points, before visiting the site…
- Obtain a description of the treatment history, productivity and
- Find out if the treatment included an evaluation of windthrow risk
and expected level of damage without treatment.
- Enquire whether the treatment plan included an evaluation of the
effectiveness of treatment at reducing damage.
- Consider the operational variables for the treatment (tree height,
branch size, percent of crown removed, tree classes treated).
- Consider alternative edge modification strategies and equipment
that might have been employed.