Pacific Northwest Research Station

PNW > Research > Large Scale Siviculture Experiments > Suislaw Thinning and Underplanning For Diversity Study

Large-Scale Silvicultural Experiments In Western Oregon and Washington

Siuslaw Thinning and Underplanting For Diversity Study

Initial Installation Years: 1992-1993

Primary Objectives: Characterize the effects of thinning to increase structural heterogeneity and underplanting on stand composition, structure, vegetative diversity, and productivity in young, even-age Douglas-fir stands of high site index in the Oregon Coast Range.

Pre-treatment Conditions: 30- to 33-year-old, even-aged, Douglas-fir plantations.

Locations: Cataract (44.0700°N, 123.9500°W), Wildcat (45.2000°N, 123.7800°W), and Yachats (44.2800°N, 123.9400°W).

Initial Treatments: 3 thinning treatments and 1 unthinned control each replicated 1 time at 3 locations. All thinned treatments and unthinned control were underplanted with a 1:1 mix of Douglas-fir and western hemlock at 10 ft x 10 ft spacing with root rot pockets planted to red alder. Imbedded within each overstory treatment were three underplanting trials. First, two 1-ac areas within each treatment unit were either underplanted with Douglas-fir and western hemlock at 15 ft x 15 ft (species alternating within rows), or left unplanted. In a second conifer species trial, a single subplot per unit was planted with Douglas-fir, grand fir, western redcedar, western hemlock, Sitka spruce, and Pacific yew. Each conifer species was planted at 4.9 ft x 4.9 ft spacing in 13 four-seedling clusters arranged as a 6 x 13 grid of randomly selected clusters, for a total of 52 seedlings of each species. A third planting trial consisted of red alder and bigleaf maple planted in alternate species rows of 16 seedlings at 7.9 ft x 7.9 ft spacing. A total of 48 hardwood seedlings / species / treatment were planted on each site. Conifer planting occurred the winter after the block was thinned; hardwood planting occurred in the winter of 1994 at all three sites.

No Overstory Removal (Control)

No Thin (1a). Passive management. Provide internal reference. Not thinned. Underplanted (see above). No woody debris or other initial treatments.

Light Overstory Removal

Narrow Thin (2a). Grow large overstory trees, create understory-midstory cohorts, recruit coarse wood. Three-step overstory reduction to minimum density, repeated release of underplanted trees and natural regeneration. Thinned 100% of stand to ~100 tpa. Underplanted (see above). Slash cut to facilitate 15 x 15 planting. No woody debris or other initial treatments.

Moderate Overstory Removal

Wide Thin (3a). Grow large overstory trees, create understory-midstory cohorts, recruit coarse wood. Two-step overstory reduction to minimum density, single release of underplanted trees and natural regeneration. Thinned 100% of stand to ~60 tpa. Underplanted (see above). Slash cut to facilitate 15 x 15 planting. No woody debris or other initial treatments.

Heavy Overstory Removal

Very Wide Thin (4a). Grow large overstory trees, create understory-midstory cohorts, recruit coarse wood. One-step overstory reduction to minimum density, single release of underplanted trees and natural regeneration. Thinned 100% of stand to ~30 tpa. Underplanted (see above). Slash cut to facilitate 15 x 15 planting. No woody debris or other initial treatments.

Complete Overstory Removal (Clearcut)

None.

Response Variables: Over-, mid-, and understory vegetation; mosses; snags; woody debris; microclimate; wood production; economics; operational factors; forest floor.

Study Plan: Tucker, G.F.; Emmingham, W.H.; Johnston, S.; Chan, S.S.; Minore, D.; Owston, P.; McCreight, R.W.; Hayes, J.P. 1993. Commercial thinning and underplanting to enhance structural diversity of young Douglas-fir stands in the Oregon Coast Range. Adaptive COPE study plan. On file with: P. Anderson, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Corvallis Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331.

Website: None.

(last accessed 2006-12-06)

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USDA Forest Service - Pacific Northwest Research Station
Last Modified:  Tuesday, 29 January 2008 at 17:11:12 EST