Lesson 5: Windfirming Treatments

Learning Objectives

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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 studies.

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.



Background Page

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 October.

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:

  • Edge feathering is thinning within the first tree length of the stand edge.
  • 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:

  • Crown modification includes: topping, top-pruning, sailing, spiral pruning.
  • 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 $46–54/tree.
  • 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 the crown.
  • In spiral pruning, branches are removed throughout the crown.
  • Productivity for sailing and spiral pruning treatments is lower than topping.


Modification Study

Page 3 - Results of Chuck Rowan’s Edge Modification Study in Coastal BC
  • 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
Treatment Effectiveness
  • An evaluation of stand conditions enabled the classification of stand hazard are shown here.
  • Use this technique in high risk locations where windthrow impacts are negative.
  • 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 winds.



Page 5

Purpose of this exercise:

  • To encourage learners to observe edge modification treatments and consider operational situations for using them.

Learning Objectives

  • To observe the results of windfirming treatments in the field.
  • To gain experience in recommending windfirming treatments to reduce windthrow risk.

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 treatments.

Key points, before visiting the site…

  • Obtain a description of the treatment history, productivity and costs.
  • 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.