Land and Ecosystem Management
The Uneven-Aged Management Project (UAMP)
Hundreds of thousands of acres of young even-aged forest stands were regenerated following clearcutting in the western Cascade forests. The Uneven-Aged Management Project (UAMP) was developed to respond to increased interest in using an uneven-aged silvicultural system to provide increased habitat diversity in young managed plantations, and to accelerate development of late-successional characteristics while yielding wood products.
The UAMP represents one of the first replicated experiments in uneven-aged management to be located in the Pacific Northwest. It is located entirely within the H.J. Andrews Experimental Forest, a sixth field watershed of about 16,000 acres on the McKenzie River Ranger District. This is also within the Central Cascades Adaptive Management Area.
The objective is to determine the ecological and economic tradeoffs involved in converting young (40 to 50-year-old) Douglas-fir plantations at mid-elevation in the central Oregon Cascades to a mixed-species and uneven-aged condition.
The conversion and subsequent management uses an array of partial cutting patterns designed to perpetually favor the establishment and growth of understory trees and other vegetation. This approach differs from alternative silvicultural systems being applied to young even-aged stands in the region as harvest reentry intervals are determined by thresholds in site occupancy (relative density) that are expected to vary among the treatments being tested. Also, in contrast to alternative approaches in other regional studies, there is no maximum stand age for entry; the targeted uneven-aged structure does not rely on stand-level overstory removal for regeneration, and therefore there is no rotation period.
UAMP is a long-term study of three alternative prescriptions for converting stands based partial harvests, commercial thinning, to maintaining stands within a range of relative densities. A “light thin” (individual-tree selection) will range from a Ranger District (RD) of 30 to 50, a “heavy thin” (multistoried stand) from a RD of 20 to 40, and a “gap” (group selection) treatment with 10% of the area in small gaps (gap diameter equal to average tree height, approximately 80 feet currently) and the matrix managed like a light thin. The treatments were applied to stands 10 hectares or larger. The three thinning treatments, plus a control, are replicated four times. The project was implemented through an environmental assessment and timber sale. Pretreatment data was collected on the 16 stands involved in the study between 1997 and 1998. Harvest took place in 1999-2000. Post treatment monitoring was conducted in 2001, 2003, and 2005. Subsequent measurement will occur at approximate 5-year intervals. These data will be used to determine the timing of subsequent harvest entries. The study is designed to span a minimum of 50 years.
Early results suggest that the relatively low-intensity thinning treatments applied as a first entry in the conversion process had little impact on the abundance, size, or diversity of understory vegetation. Disturbance resulted in short-term decreases in understory vegetation cover, particularly tall shrubs. However, within 5 years of treatment, understory vegetation abundance returned to approximate pretreatment condition. Regardless of treatment, shrubs and ferns dominated the understory with coverage that was two to three times that of forbs and grasses. Species richness averaged near 12 species per 0.1-hectares sample plot before treatment and five years posttreatment. Community composition was dominated by a few very abundant species regardless of treatment. Postthinning increases in conifer regeneration were consistent with the density of underplanting. Substantial increases in tree regeneration occurred in the light thinning treatment due to an increased seedling density of the shade-tolerant bigleaf maple. The persistence of planted and natural seedlings of less shade-tolerant species remains to be determined.
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