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Update 10/27/99
Effects of Organic Matter Retention and Other Soil Management Practices on Long-term Productivity of a Pacific Northwest Coastal Douglas-fir Site
Robert B. Harrison, Associate Professor of Forest Soils
Robert L. Edmonds, Professor of Soil Microbiology
Dale W. Cole, Professor of Forest Soils
Amy Sidell and Barry Flaming, Graduate Students
College of Forest Resources, University of Washington
Thomas A. Terry, William Scott, & Ron Heninger, Senior Scientists
Weyerhaeuser Corporation
Alex Dobkowski, Senior Research Forester Weyerhaeuser Corporation
Richard Miller, Emeritus Soil Scientist USDA Forest Service, PNW Station
Summer Progress Update
Harvesting operations at the site have recently been completed and experimental treatments are currently being installed. All trees in the study area have been hand-felled and forwarded with a shovel-forwarder and/or cable system to minimize soil disturbance. Thirty-two plots were bole-only harvested with slash material redistributed over the plots. Eight plots received a total tree harvest with removal of the entire above ground portions of the trees, including green branches and foliage.
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Harversting Opperations at Site
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In an additional eight plots, “total tree plus” levels of organic matter removal were reached by removing all above ground tree biomass plus all woody material on the forest floor greater than 3-cm diameter, including large old growth logs. Future work will involve field sampling to estimate the quantity and nutrient content of organic matter retained on the plots. The site will be replanted with genetically improved Douglas- fir stock this winter.
The amount of organic matter and nutrients removed from the plots during harvesting operations will be estimated with the use of regression equations of tree biomass that are presently being developed. Thirty-two Douglas-fir trees representing the site diameter distribution were selected for this purpose. The biomass of live and dead branches has been measured by previous field sampling and subsamples were taken for nutrient analysis. Tree boles were divided into eight sections of equal length, and a four-inch cookie was cut from the middle of each to estimate wood density, bolewood and bark weights, and nutrient contents. The same procedures will be used with twelve western hemlock trees to quantify the contribution of this component.
Eight of the bole-only harvest plots have received a “soil disturbance” treatment by making 8 evenly spaced passes across the plot with a shovel-forwarder. Soil audits have demonstrated that this treatment has affected up to fifty percent of the plot area in some way. Graduate student Barry Flaming has been sampling soils to quantify the changes in soil bulk density with depth seen as a result of this treatment. Four of these plots will be tilled in the near future to evaluate the ameliorative potential of this practice. Additional work on this project includes the installation of ceramic lysimeters this fall to gather data for a leaching study funded by the Olympic Natural Resources Council.