USDA Forest Service

Land and Watershed Management

Land and Watershed Management Program
Pacific Northwest Research Station
Olympia Forestry Sciences Laboratory
  3625 93rd Ave. SW
Olympia, WA 98512
(360) 753-7747
Corvallis Forestry Sciences Laboratory
  3200 SW Jefferson Way
Corvallis, OR 97331
(541) 750-7250
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United States Department of Agriculture Forest Service.

Genetic and Silvicultural Foundations for Management

Selected Studies

Alternative Silvicultural Treatments for Young Plantations in the Pacific Northwest

Constance A. Harrington, Dean S. DeBell, and Leslie C. Brodie,
Pacific Northwest Research Station, 3625 - 93rd Ave. SW, Olympia, WA 98512-9193

Picture of a plantation with uniform spacing Many forest plantations have uniform spacing and species composition. Wood production was usually the original management objective.  
Picture of a Butterfly For some plantations, objectives have changed to include wildlife habitat and recreation. These other values may be produced with treatments that increase diversity in stand structure and species composition. Picture of a Hare

What we did and why

We selected treatments that differ in their effects on stand structure and species diversity. These treatments -- other than the control -- require multiple entries to meet their goals.

Silvicultural treatments Future stand condition
  • Control
  • Uniform thinning
  • Thinning, plant other species
  • Thinning plus gaps
  • Thinning plus gaps, plant other species
  • Stand development w/o treatment
  • Uniform size, structure and species composition
  • Uniform size and structure, accelerated species diversity
  • Diverse size and structure
  • Diverse size and structure, accelerated species diversity
Picture of a plantation at Mt. St. Helens National Volcanic Monument The oldest installation is on the Mt. St. Helens National Volcanic Monument. Five plots of each treatment were installed in 1994-5. When the initial thinning was done, the plantations were mostly Douglas-fir and 10 to 13 years old. Trees were 7 m tall and 11 cm in diameter.

Photograph of a plantation with uniform thinning Photos taken the year of the thinning: on the left is an example of uniform thinning; on the right is a thinning with gaps of different sizes. Photo of a plantation with nonuniform thinning

5-year Results

Ttreatment differences exist in tree size and growth rate, stand structure, and cover of understory plants.

Diameter graph
Height to live crown graph
Mean percent herbaceous cover graph
Cover of herbaceous plants (2 and 5 years after thinning) decreased in the control and increased with thinning and gap creation.
The control treatment had a lower percentage of trees in the larger diameter classes.

Percent of trees by size class graph

What's next?

Other installations of this trial have been established in WA and OR. We plan to measure tree growth, stand structure, and understory vegetation. We invite others to evaluate additional responses or to establish additional installations. For further information, contact Connie Harrington; e-mail, or phone 360-753-7670.

USDA Forest Service - GenSilv Team
Last Modified: Saturday, 15 October 2016 at 18:38:02 CDT

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