Forest Investment Account

Abstract of FIA Project 6067005

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Pilot Overview Assessment of Windthrow Along Edges and the Efficacy of Operational Edge Pruning and Topping Treatments at West Island Timberlands

Author(s): Rollerson, T.P.; Whitfield, Tom; Beese, W.J.; Peters, C.M.
Subject: British Columbia, Forestry, Silviculture/Forest Management Systems
Series: Forest Investment Account (FIA) - Land Base Investment Program - Innovative


The edge treatment evaluation pilot study was carried out in Weyerhaeuser's West Island Timberlands unit (WI) on the southwestern coast of Vancouver Island. The WI edge treatment blocks were located within rolling coastal plain areas and hillsides on the western flank of the Vancouver Island Mountains south of Alberni Inlet.
The overall project objectives that are partially addressed by the pilot study are to:
- Document the levels of wind damage (amount and penetration of windthrow) associated with various 'leading edge' crown modification treatments.
- Evaluate the utility of using helicopter surveys to document windthrow along setting edges.
- Document the character and variability of crown modification treatments in the study area.
- Communicate results to field staff to help reduce the potential for wind damage by improving harvesting layout and edge treatments.
A total of 63,425 meters (63 km) of falling boundary was sampled. The sample plots include external setting edges and the edges of strips of retained timber within settings.
There is some indication that operational 'leading edge' crown modification treatments, except for manual topping treatments, are not reducing wind damage along external boundaries; however, as the data set for these treatments is small, this conclusion should be considered tentative.
The distance that windthrow penetrates into a stand edge tends to be affected by some of the same factors that control percent windthrow. Penetration increases as percent windthrow increases. Wind damage tends to vary with changes in boundary exposure.
Both penetration distances and percent windthrow are less on lee boundaries than on windward boundaries.
Wind damage tends to increase with increases in average stand height and wind exposure irrespective of treatment. In many cases changes in other factors such as the width of retained strips and the boundary-slope geometry appear to affect the degree of wind damage more than pruning or topping treatments.

For further information, please contact Derek Ferguson

Updated September 08, 2005 

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