Effects of Organic Matter Retention and Management on Long-term Productivity of Pacific Northwest Coastal Douglas-fir Plantations

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Study overview (word document)

STUDY OBJECTIVES:

The objectives of this study are to: 1) add to the strategic database that can be used to develop soil management guidelines for intensively managed Douglas-fir sites in the Pacific Northwest; and 2) understand the implications of a range of site resource allocation treatments on soil processes, the microenvironment, and seedling/tree growth. A representative soil/landform suitable for intensive forest management was chosen for the test site. The specific tasks to be completed as part of this investigation include:

  1. Develop nutrient budgets for various levels of harvest utilization and organic matter removals from a typical Site II+ Douglas-fir stand.
  2. Evaluate the effects of increased harvest utilization and organic matter reductions on soil processes and Douglas-fir growth over a 40-year rotation.
  3. Determine whether increased soil compaction/disturbance due to mechanized harvesting results in reduced stand productivity, and if tillage is an effective ameliorative treatment.
  4. Evaluate the effectiveness of fertilization to mitigate organic matter removal impacts and determine its effects on nutrient supply and seedling and stand growth.
  5. Assess the effects of intensive vegetation control and fertilization on vegetation changes, nutrient allocation to the crop, and stand development and growth.

Background:

This study was initiated to determine the implications of various soil management and site-resource allocation treatments on long-term site productivity for a representative site in western Washington that will be intensively managed for Douglas-fir (Pseudotsuga menziesii Franco) production. Heretofore, no well-replicated study existed in western Washington that determined the implications of various harvesting/organic matter retention strategies on soil processes and Douglas-fir growth. There were also no large-plot studies capable of assessing the long-term impacts of harvesting-related soil disturbance or intensive weed control treatments. In addition, it was desired to determine the role that various mitigation treatments could play in ameliorating any negative impacts that resulted from such treatments; e.g., fertilization as a replacement for nutrient capital removal, or soil tillage as a mitigation for soil compaction effects from mechanical harvesting.

This study was initiated in the spring of 1998 after several years of discussions about study objectives and design among scientists within the following organizations: Weyerhaeuser Company, the University of Washington Forest Soils Department, the U.S. Forest Service, PNW Research Station, Olympia Forestry Sciences Laboratory, Olympia, WA, and the U.S. Forest Service Pacific Southwest Research Station, Redding, CA.