Transcript Geomorphic Response to Forest Practice in the Willamette Basin ES 473 ENVIRONMENTAL GEOLOGY Prepared by: Robert Mock INTRODUCTION Willamette Basin forests are suffering from a.

Geomorphic Response to Forest Practice in the Willamette Basin
ES 473 ENVIRONMENTAL GEOLOGY
Prepared by:
Robert Mock
INTRODUCTION
Willamette Basin forests are suffering from a diminishing energy supply and a
loss of ecosystem services. Forest practices are associated with increased soil
erosion and landslides. With disturbed soils, watershed productivity has
historically experienced declining trends. In order to maintain optimum levels of
forest production, balanced by minimized geomorphic effects, alterations in
forest practice is a necessity. This paper examines the relationship between
timber harvesting methods and erosion processes in upland basins of the
Western Cascades. The effects of road construction and clear-cutting are
examined.
Composition of Pacific Northwest Forests
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Primarily composed of evergreen coniferous trees
Effects of Meager Logging Techniques and
Construction of Roads on the Environment
• Use of heavy equipment and high traffic creates soil compaction
• Leads to a diminishing rate of re-growth
• Kills off root systems
• Secretion of ground water and nutrients creating a lower porosity of
soils
Relationships of Environmental Impacts
In analysis of an area of the H.J. Andrews Experimental Forest on Land
below 1000 meters with predominantly altered volcanclastic geology two areas
were evaluated for environmental impacts of forest management practices.
One area was forested land untouched by man, and the other was 25.6% clear
cut with 5% of the land road rights-of-way. The result of the study show that the
clear cut land had 30 times the amount of slide erosion than the forested area.
• Contributes to mass wasting
• Clearcutting destroys the environments ability to regulate geomorphic
processes
• Leaching of valuable recourses like Nitrogen, Phosphorous, and
Magnesium
• Diminishes water absorption
• Removes protection from stream banks
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Adapted to winter-wet and summer-dry environment
• Reduces hill side cohesion of soils
Small streams in forest watersheds comprise 86% of all river channels in the
U.S.
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Forests supply energy, minerals, shade and stability of soils, thus regulating
the rate of stream production
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Erosion from unstable soils affects the stability of substrates and the leaching
of nutrients

Erickson Air-Crane removing logs from an Oregon hillside
Siskiyou, Oregon Clear-cut project
Alternative Logging Practices
• Limit logging to dry grounds
• Limit the amount of roads created
• Use selective cutting/thinning techniques
Conclusions
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The most desirable logging techniques include:
Thinning with minimal road construction
Limit logging to periods when soils are predominantly dry
Use low impact equipment
Create culverts to maintain drainage from streams
Leave buffers around streams
Replant trees and shrubs
Rotation of regions that do get logged
• Leave stream buffers to preserve integrity
History of Oregon’s Logging Industry
• Economic boom from WWII increased timber demand and continued through
the 1940’s and 1950’s
• Clearcutting was dominate practice
• Trees were either yarded out or skidded with a Cat
• Streams were redirected to increase flow and over powered by log transfers
• Logging roads prevailed throughout the terrain
• Minimal restrictions on logging
• Use low impact equipment
• Lighter weight/wider wheel base
• Alternative equipment
• Air-cranes
• Replant trees and shrubs
• Fertilize
• Slash burn when applicable
• Rotate between different regions to prevent overexertion
These techniques are growing in popularity as concerns for geomorphic
processes are growing. Logging practices have changed dramatically
throughout Oregon's history and continue to seek improvement.
References Cited
K. Cromack, Jr., F.J. Swanson and C.C. Grier. A Comparison of Harvesting Methods and their
Impact on Soils and Environment in the Pacific Northwest. 1979, U.S. Department of Agriculture
F.J. Swanson, C.T. Dyrness. Impact of Clear-Cutting and Road Construction on Soil Erosion by
Landslides in the Western Cascade Range, Oregon. 1975, The Geology Society of America.