Research

Project web site contains more detailed information  

PNW Funded Projects
2001
2000
1999
1998
1997
1996
1995

PNW Project Overview 1998

Effects of Organic Matter Retention and Management on Long-Term Productivity of Pacific Northwest Douglas Fir Plantations

Principal Investigator:  
Dr. Robert B. Harrison, University of Washington, College of Forest Resources

Awarded: $10,000

Project Description:
From a holistic point of view, the use of intensively-managed forests primarily for wood production can offer an important role in the maintenance not only of industries and communities that rely on wood production, but also provide the ability to protect other areas of forest land that would not then be required to produce wood products at high rates. A key element of utilizing intensively-managed forest plantations in this "big picture" is to ensure that high levels of productivity from intensively-managed plantations are sustainable in the long-term, and that intensive management does not degrade the soil resource upon which productivity is built.

There currently is only one unreplicated study in the Pacific Northwest that evaluates the implication of different organic matter removal levels on Douglas-fir productivity and how nutrient amendments mitigate nutrient losses, and it is located on relatively low productivity sites (Bigger and Cole, 1983; Compton and Cole, 1991) at the College of Forest Resource's Pack Forest.

The specific objectives of the work outlined in the study are:
1)  To develop nutrient budgets for various levels of organic matter removal from typical
     highly productive Site II Douglas-fir stands.
2)  To evaluate the effects of increased harvest utilization (biomass removal) and soil
     compaction on organic matter, nutrients, and soil physical properties in the first 40
     years after planting.
3)  To determine whether increased harvest utilization and soil compaction in the high
     utilization treatment result in reduced productivity of the subsequent stand.
4)  To evaluate the effectiveness of ameliorative fertilzation and tillage on organic
     matter, nutrients, soil physical properties and subsequent stand growth, and 
5)  To assess the effect of weed control on nutrient redistribution, soil properties, and
     stand development and growth.

This study will be conducted on a Douglas-fir Site II soil, which is commonly intensively managed for Douglas-fir and is more productive than Site III or IV soils (where most previous nutrient budget data has been gathered). Four blocks will tentatively be established in the McDonald Tree Farm in Southwest Washington on the Boistfort or Melbourne soil series. Researchers may determine the impacts of compaction and tillage in the total-tree organic matter removal treatment because ground-based harvesting is most likely to create the highest level of soil compaction at this utilization level. Researchers will also test whether tillage or weed control (or a combination of the two) has an effect on restoring productivity compared to the non-compacted, weeded, and fertilized treatment.

The ONRC contribution, along with contributions from the National Council for Air and Stream Improvement and support from Weyerhaeuser Corporation, support the development of biomass regression equations and nutrient pools in the study plots. This work will make it possible to predict nutrient removal levels for a wide range of harvest scenarios as well as the overall ecosystem nutrient pools. This work is critical in terms of understanding the potential for intensive management effects on nutrient levels.

Project Status:
Project continued.
Interim report received in December 1999.

Project Progress:
A randomized complete block design experiment has been initiated to address the effects of soil management practices (i.e. harvesting intensity and organic matter removal, nitrogen fertilization, weed control, soil disturbance, and tillage) on the continued productivity of coastal Douglas-fir plantations.  A total of twelve treatments (see table 1 below) representing combinations of the variables noted above will be replicated four times in 0.63-acre plots (48 total), that consist of an internal measurement plot of 0.26 acres surrounded by a buffer.  Treatment and measurement plot boundaries have been installed and tree diameter and height measurements have been recorded.  Initial stand volume (alive and dead and standing by species, Douglas-fir and western hemlock) has been summarized.  Pre-treatment sampling of site characterization has included understory vegetation, forest floor organic material, soil samples, coarse woody debris, and aboveground tree biomass.

This study also contributes to a database determining full growth potential of Douglas-fir due to weed control and fertilizer, and a unit-area database for ground-based logging soil disturbance impacts and amelioration guidelines.  Subsets of this design can be replicated elsewhere to expand the database to develop more region-wide guidelines on organic matter management, vegetation control and logging disturbance impacts on Douglas-fir growth.

Presentations to date:

•       Tom Terry, Rob Harrison, and Barry Fleming.  Pacific Northwest Soils Council Meeting. Jan 29, 1999: Study design and status report.

•       Tom Terry and Rob Harrison. Soil Science Society of America. October 18-22, 1998.  Presented poster “Effects of organic matter retention and management on long-term productivity of Pacific Northwest coastal Douglas-fir plantations.”

•       Rob Harrison.  UW Stand Management.  Cooperative Meeting. September 24-25, 1998: Study design and status report.

•       Tom Terry and Rob Harrison. North American Forest Soils Conference. August 9-14, 1998. Presented poster “Effects of organic matter retention and management on long-term productivity of Pacific Northwest coastal Douglas-fir plantations.”

origin & mission     research    education    the center    home