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Pacific Northwest Research Station
Large-Scale Silvicultural Experiments In Western Oregon and Washington
Forest Ecosystem Study
Initial Installation Years: 1991-1993
Primary Objectives: Determine if woody plant species diversity, spatial heterogeneity in vegetation, and vertical diversity in vegetation can be manipulated through variable-density thinning and underplanting that do not require replacing the existing stand. Determine if enhancing the growth and diversity of woody plants will be accompanied by increased abundance and diversity of ectomycorrhizal fungi. Determine if increasing den availability through direct intervention (creating cavities in live trees and adding nest boxes) will increase flying squirrel populations.
Pre-treatment Conditions: 55- to 65-year-old, even-aged Douglas-fir stands.
Locations: Fort Lewis (46.9900°N, 122.6900°W).
Initial Treatments: 2 thinning x den augmentation treatments and 2 unthinned control x den augmentation treatments each replicated 4 times at 1 location.
No Overstory Removal (Control)
Control, no den augmentation (1a). Not thinned. Not planted. No den augmentation. No woody debris or other initial treatments.
Control, den augmentation (1b). Identical to FES treatment 1a but with den augmentation (i.e., nest boxes installed and/or cavities created).
Light Overstory Removal
Moderate Overstory Removal
Variable Density Thinning, no den augmentation (3a). Root-rot thinning applied to ~15% of stand: low vigor trees removed and apparently healthy trees retained, producing residual densities of ~16 tpa > 7.9 in dbh (RD 1.5, metric). Light thinning applied to 50–60% of stand: thinning of subordinate and codominant trees > 7.9 in dbh to reduce the density of overstory to RD 6 (metric) with a thinning ratio d/D of 0.8–1.0, or ~125 tpa with an average spacing of ~19 ft between trees. Heavy thinning applied to 25–30% of stand: thinning of subordinate and codominant trees > 7.9 in dbh to reduce the density of overstory to RD 4 (metric), or ~75 tpa with an average spacing of ~24 ft between trees. Marking guidelines specified retention of all large standing dead trees and all deciduous trees. Not planted. No den augmentation. No woody debris or other initial treatments.
Variable Density Thinning, den augmentation (3b). Identical to FES treatment 3a but with den augmentation (i.e., nest boxes installed and/or cavities created).
Heavy Overstory Removal
Complete Overstory Removal (Clearcut)
Response Variables: Over-, mid-, and understory vegetation; arboreal mammals; small mammals; birds; arthropods; amphibians; snags; woody debris; fungi; soils; microclimate; forest pathology; roads.
Study Plan: Carey, A.B.; Thysell, D.R.; Brodie, A.W. 1999. The Forest Ecosystem Study: background, rationale, baseline conditions, and silvicultural assessment. Gen. Tech. Rep. PNW-GTR-457. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 129 p.
(last accessed 2006-12-06)
US Forest Service - Pacific Northwest Research Station