The role of woody debris in riparian zones Jon M. Flinders.
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Transcript of The role of woody debris in riparian zones Jon M. Flinders.
The role of woody debris in riparian zones
Jon M. Flinders
• Wildlife nesting and rearing sites
• Mediation of stream temperatures
• Habitat for rare plants
• Growth of trees
Riparian areas are important for forested landscapes
• Trees growing in riparian areas may enter river channel through natural and human processes
• Production of dead wood is often called “woody debris” or WD
• The significance of WD has been realized in last couple of decades
Importance of trees
Historical Perspective • 1800’s to early 1900’s rivers &
streams used to transport logs
• Rivers cleared to prevent log jams • Splash dams were used in streams
Post-World War II
• Fisheries Mangers thought woody debris obstructed migration of anadromous fish
• Removed logjams with the intention of opening new reaches of streams & rivers
• Thus, many rivers and streams have not recovered to pristine undisturbed conditions
The Role of Woody Debris
1. Creates Pools & Stream Complexity
• Salmonids need pools for feeding locations
• Logs extending across streams deflect the current
The Role of Woody Debris
2. Traps sediments
• Moderates sediment transport rates
• Protects salmonid spawning areas & invertebrate pop. from sediment deposition
The Role of Woody Debris
3. Stores organic material
• Most organic material stored is allocthonous material
• Organic material is an important energy source for invertebrates
The Role of Woody Debris
4. Provides habitat for salmonids
• Fry utilize WD for refuge from predators
• Pools created allow over wintering areas
Input of Debris in Stream Channels
NATURAL PROCESSES:• Bank failure
• Blow down
• Avalanches
• Collapse due to ice or snow
Input of Debris in Stream Channels
HUMAN CAUSED:• Logging major source of woody
debris and major loss
• Usually small debris entering channel- Less stable- More prone to movement
Debris Management
MANAGEMENT IDEAS:• Buffer strip • Predetermined fraction of
timber• Double rotation basis
- 150 yrs instead of 75 yrs• Substitute structures
- Large boulder- Rock-filled gabions
Debris Management
CONCLUSION:• Removal of large, stable debris causes
loss of important habitat and decline in fish populations
• Thus, need to have a management goal of conserving large, stable debris prior to logging