Windthrow Flashcards
Traditional management approach for windthrow
• The traditional approach
– location of block boundaries along “windfirm” edges to reduce windthrow
–progressive salvage of damaged areas.
Current windthrow practice
Current Practices
- prediction and management
- role of windthrow as a natural disturbance agent is recognized
- when windthrown areas are salvaged, retention of some structural features is desired
Best practices
- strategies to minimize and recover windthrow
- identification and evaluation of windthrow risk
- integration of windthrow risk into choice of silvicultural system
Salvage should not compromise site objectives.
• Risk to wildlife tree patches is minimized.
Windthrow challenges
recognize that some windthrow in reserves may be non-harmful or even beneficial
• identify what level of windthrow may be acceptable.
What is included in windthrow assessments
- Evaluate the biophysical hazards
- Evaluate the consequence of windthrow
- Determine the risk for windthrow
- Prescribe a management strategy
Catastrophic vs endemic windthrow
Catastrophic windthrow: Caused by peak winds which recur infrequently and cause breakage.
• Endemic windthrow: Caused by peak winds which recur every 1 to 3 years, causing more uprooting than breaking.
Five characteristics in biophysical assessment
- Topography
- Soil
- Individual tree
- Stand characteristics
- Existing Windthrow Pattern and windthrow risk
3 parts to the windthrow triangle
Topographic exposure
Stand
Soils
What does topographic exposure refer to?
Wind accelleration and turbulence as well as dominant wind direction.
What is more important for wind firmness? Height or rooting depth.
Height will create a higher hazard (trumping root depths)
Biophysical hazard vs treatment risk
‘Biophysical Hazard’ is the combination of the topographic, soils and stand hazard components. (Pre treatment condition risk)
• ‘Treatment Risk’ is the way in which a particular treatment (the harvest plan) increases or decreases the potential for windthrow
What does fetch refer to
The extent of the open area that wind can travel across and pick up speed.
5 tree lengths or more (high risk)
Less than 2 tree lengths (low)
Windthrow risk vs consequence
Windthrow Risk’ is the likelihood of damage from endemic winds. It is the combination of Biophysical Hazard and Treatment Risk.
• ‘Windthrow Impact’ (consequence) refers to the potential harm windthrow could cause if it occurs..
What are some location and design practices to reduce windthrow
Location and Design
- Natural features-wind firm edges
- Locate away from topographic breaks (gullies)
- Log up to the feature such as power lines
- Buffer features such as riparian reserve or WTP
- Leave areas oriented parallel to wind
- Reduce fetch length with reserves
What are the treatments
Topping: removal of top and upper branches
Top pruning: branches pruned from upper crown
Spiral pruning: removal of branches throughout crown in a spiral
Sailing: removal of windward branches on lower crown
