Progress Report for Regional Agenda 2020 Projects
Date: June 1, 2007
Project title: "Effects of organic matter retention and management on long-term
productivity of Pacific Northwest Douglas-fir plantations: nutrient process and leaching
responses."
AF&PA Agenda2020 pathway and your Station Priority (if possible)

Agenda 2020 Research Pathway: Soil productivity (Effects of intensive management
on soil productivity).

PNW Priority 3.4: Produce wood within sustainable frameworks.
Project location (county and state)

Molalla, OR (Clackamas County) and Matlock, WA (Mason County)
Investigators (names, titles, departmental affiliations, email address)

Robert B. Harrison, Stand Management Cooperative, University of Washington,
Seattle, WA, 98195-2100. Email: robh@u.washington.edu.

Stephen H. Schoenholtz, Virginia Water Resources Research Center, Virginia Tech
University, Blacksburg, VA. Email: Stephen.Schoenholtz@vt.edu

Timothy B. Harrington, USDA Forest Service, PNW Research Station, Olympia,
WA. Email: tharrington@fs.fed.us
Sources of funding (all sources over life of project by year and source, also include
in-kind contributions and other, indirect support)
2005
Agenda 2020 to Univ. Washington $30,000; Univ. Washington (ICR) $15,480; Univ.
Washington from SMC (support for Dr. AB Adams) $8,113; from Gessel Fund
(scholarship for Cindy Flint) $21,360; from CFR (Rob Harrison 0.5 month) $4,767; Total
funding $65,480.
Agenda 2020 to Oregon State University $20,000; Oregon State University Cost-Share
$13,802; Total funding $33,802.
2006
Agenda 2020 to Univ. Washington $25,000; Univ. Washington ICR $12,900; Univ.
Washington SMC (Dr. Adams) $8,350; CFR teaching scholarship for Cindy Flint)
$14,240; from CFR (Rob Harrison 0.5 month) $4,767; Total Funding $65,352.
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Agenda 2020 to Oregon State University $25,000; Oregon State University Cost-Share
$15,208; Total funding $40,208.
2007
Agenda 2020 to Univ. Washington $20,000; Univ. Washington ICR $10,320; Univ.
Washington SMC (Dr. Adams) $8,684; CFR teaching scholarship for Cindy Flint)
$14,810; from CFR (Rob Harrison 0.5 month) $5,057; Total Funding $58,871.
Agenda 2020 to Oregon State University $30,000; Oregon State University Cost-Share
$16,367; Total funding $46,367.
Research objectives (describe succinctly and list hypotheses to be tested, when
appropriate)
The research objectives are to:
1) Develop an additional level of the nutrient budget [leaching of carbon (C) and
nitrogen (N)] for various levels of organic matter removal from Douglas-fir stands.
2) Evaluate effects of increased harvest utilization, and woody material retention,
vegetation control, and fertilization on soil-water quality and nutrient and C fluxes, as
possible limits on the productivity of the subsequent stand.
Null Hypothesis regarding effects of management on mobilization of nutrients:
H-1: Nutrient mobilization is not related to increasing intensity of organic matter
removal.
Hypothesis H-1 would be rejected if soil "A" horizon nutrient concentrations are
significantly different among organic matter retention treatments.
H-2: Nutrient mobilization is not related to weed control.
Hypothesis H-2 would be rejected if soil "A" horizon nutrient concentrations are
significantly different between the two levels of weed control.
Null Hypotheses regarding effects of management on nutrient loss from site by leaching:
H-3: Nutrient loss is not related to increasing intensity of organic matter removal or weed
control.
Hypothesis H-3 would be rejected if nutrients leaching below the rooting zone are
different among treatments.
H-4: Nutrient loss is not related to weed control.
Hypothesis H-4 would be rejected if nutrients leaching below the rooting zone are
significantly different between the two levels of weed control.
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Null Hypotheses regarding effects of management on carbon leaching into deep soil
horizons (a potential sink for long-term soil carbon):
H-5: Carbon movement into deep soil horizons is not related to increasing intensity of
organic matter removal or weed control.
Hypothesis H-6 would be rejected if dissolved organic C (DOC) leaching below the
rooting zone is different among treatments.
H-6: Carbon movement into deep soil horizons is not related to weed control.
Hypothesis H-6 would be rejected if DOC leaching below the rooting zone is
significantly different between the two levels of weed control.
Results to date (bullet statements summarizing significant findings (<1 page); in
early stages of project, list goals met (e.g., site installation, etc.)

A total of 40 lysimeters (20 at 100-cm depth and 20 at 20-cm depth) were installed at
each of the Matlock and Molalla sites.
 Sampling began at Matlock in April 2005 for nitrate (NO3-), ammonium
(NH4+), dissolved organic N (DON) and DOC.
 Sampling began at Molalla in November 2005 for NO3-, NH4+, DON and
DOC.

Dissolved inorganic N (DIN = NO3- + NH4+) dominates soil-solution total N
concentrations at 100 cm depth at the Matlock site, and is primarily driven by NO3(Fig. 1). Similarly, DIN at 100 cm depth is dominated by NO3- (Fig. 2), with
NH4+concentrations at or near analytical detection limits (data not shown) at the
Molalla site.

At both the Matlock and Molalla sites, no differences among treatments in soil water
DOC or DON have been observed. At Molalla, Both DOC and DON were higher than
reference plots in most months of the 2005-06 water year, but no observable
differences were observed in 2006-07 (Figs. 3 and 4).

For most sample periods at Molalla, NO3- was higher following weed control (WC),
with relatively more being leached from the whole-tree harvest (WT) than the boleonly harvest (BO) (Fig. 2). However, at the Matlock site, weed control dramatically
increased the total N leaching in the BO treatment, although it did not affect N
leaching in the WT treatment (Fig. 1).

At Matlock, control of competing vegetation has resulted in smaller biomass and N
pools in the understory, and greater seedling biomass and N pools as of 2006 (Year 3;
Fig. 5), although no treatment-related changes in the soil N pool are evident at this
time.
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Project status and recent activity (describe progress made relative to proposal and
recent, significant activity)
This part of the overall Matlock/Molalla project is on schedule. Lysimeters were actually
installed significantly ahead of funding at the Matlock site in early 2005, and the soil
conditions were ideal for this system to work. At this time, two full years of monthly
collections have been made since April, 2005. The studies have also made great strides
forward in terms of the quantification of the C and N pools in addition to the lysimetery
characterizing C and N fluxes. In the summer of 2006, soil bulk density was determined
to a depth of 100 cm at the Matlock site to allow for soil pool calculations. Both
understory and seedling biomass and nutrient contents were determined at that time. The
culmination of these efforts is represented in a complete picture of the N-cycle at the
treatment-level (Fig. 5). The ability to monitor changes in this type of schematic over the
course of stand development, as well as make comparisons across a range of sites, strikes
at one of the core objectives of AF&PA Agenda 2020 Program to “produce wood within
sustainable frameworks,” as well as our independent regional study objectives.
Soil water content has been measured at Molalla on a monthly basis since November,
2005 during time periods when sufficient soil water is available (approx. Nov-June).
Replacement of all 20 cm lysimeters and ten of the 100 cm lysimeters due to initial
lysimeter failure in 2005 did not improve the success rate of sample collection at Molalla
during 2006 or 2007. It is likely that heterogeneity of soil pore distribution and the
presence of textural discontinuities contribute to lysimeter failure rather than flaws in
design or construction. There are no plans at this time to install more lysimeters at
Molalla. However, data from lysimeters installed in a companion study will be used to
substantiate any analysis in this study.
In addition, a number of studies relating the soil properties of the Matlock and Molalla
sites to forest productivity and C sequestration were carried out by Brian Strahm as part
of his Ph.D. research. The results of Brian’s work across all three regional LTSP studies
(Matlock, Molalla, and Fall River) indicate that the variable-charge soil mineralogy
common to the region, in conjunction with the soil pH regimes associated with coniferous
vegetation, provide the soils with a unique anion exchange capacity that may be strongly
related to forest productivity through nutrient retention in a plant-available form.
Additionally, this work has illustrated a unique mechanism for soil C sequestration.
Planned activities and goals (describe the next steps and short term goals for the
project, and the value added from continued funding)
Now that all of our field installations are in, we will continue to collect and analyze
samples. Soil water will continue to be collected on a monthly basis from the 100 cm
lysimeters to continue to monitor C and N leaching losses from the site. Laboratory
chemical analysis for DIN (NH4 and NO3), TN, and DOC will continue to be performed
immediately after collection on a monthly basis.
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We are making a concerted effort to keep Scotch broom (Cytisus scoparius) from
becoming more prevalent in the weed-controlled plots by hand-pulling it as collections
are taken. The situation will be monitored, and we may make some special efforts in the
future for its control.
We are currently working with the collaborators of the Fall River LTSP Study to produce
a strategic framework within which all three studies share common objectives for the
sake of making comparisons across a range of site productivity indices. In this way, the
core objectives of all regional LTSP studies will be strengthened. The Fall River LTSP
Study is currently in its eighth year. In order to improve the validity of such
comparisons, it is extremely important for the Matlock and Molalla sites (in their fourth
year) to continue to receive the funding necessary to maintain the current level of
monitoring.
Publications (list all publications from the project, including those in press or under
review; please also send copies of relevant manuscripts, reports, or publications)
Adams, A.B., R.B. Harrison, T.B. Harrington, R. Greggs, J. Madsen, S.H. Schoenholtz,
B.D. Strahm and C. Dimock (Flint). 2005. N and C leaching responses to Douglas-fir
harvesting intensity and competing vegetation control on a glacial outwash soil in
western Washington. Proceedings of the 69th annual meeting of the Soil Science Society
of America, Salt Lake, UT.
Strahm, B.D., R.B. Harrison, B.L. Flaming, T.A. Terry, C.W. Licata, and K.S. Petersen.
2005. Factors affecting nitrogen mobility: Organic matter retention and variable-charge
soils. p. 165. In C.A. Harrington and S.H. Schoenholtz (eds.) Proc. of Productivity of
Western Forests: A Forest Products Focus. Gen. Tech. Rep. PNW-GTR-642. Portland,
Oregon: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research
Station.
Manuscripts in review:
Strahm, B.D., and R.B. Harrison. Electrochemical controls on the biogeochemistry of
low molecular weight organic acids in variable-charge soils. (in second review with Soil
Biology and Biochemistry)
Strahm, B.D., and R.B. Harrison. Mineral and organic matter controls on the sorption of
macronutrient anions in variable-charge soils. (in second review with Soil Science
Society of America Journal)
Completed dissertation:
Strahm, B.D. 2006. Abiotic Retention Mechanisms of Organic and Macronutrient
Anions in Variable-Charge Soils. Ph.D. diss. Univ. of Washington, Seattle.
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Presentations (list all presentations from the project made by investigators; include
name of presenter, title, meeting title and location, and date).
Strahm, B.D. 2004. Factors Affecting Nitrogen Mobility: Organic Matter Retention and
Variable Charge Soils. presented at PNW Stand Management Cooperative (Apr 20-21)
Troutdale, OR
Strahm, B.D. and R.B. Harrison. 2004. Nitrate Sorption in a Variable Charge Soil of the
Pacific Northwest. Soil Science Society of America (Nov 1-4) Seattle, WA
Strahm, B.D. 2005. Post-harvest N Dynamics: Impacts of Harvest Intensity and Soil
Mineralogy. presented at PNW Stand Management Cooperative (April 20-21) Troutdale,
OR
Harrison, R.B., T. Terry, C. Harrington, T.B. Harrington and S. Schoenholtz. 2005. PNW
long-term productivity studies: Progress report. presented at PNW Stand Management
Cooperative (April 20-21) Troutdale, OR
Strahm, B.D. and R.B. Harrison. 2005. Anion Sorption in Variable-Charge Forest Soils.
Soil Science Society of America (Nov 6-10) Salt Lake City, UT
Harrison, R.B., A.B. Adams, Dave Briggs, Eric Turnblom. 2005. Impact of Management
on Ecosystem C in the Pacific Northwest. Soil Science Society of America (Nov 6-10)
Salt Lake City, UT
Strahm, B.D. and R.B. Harrison. 2005. Nitrate Sorption in a Variable Charge Soil of the
Pacific Northwest. UW-CFR Graduate School Symposium (Feb 25) Seattle, WA
Strahm, B.D. and R.B. Harrison. 2005. Nitrate Sorption in a Variable Charge Soil of the
Pacific Northwest. Northwest Forest Soils Council (Jan 28) Vancouver, WA
Strahm, B.D. and R.B. Harrison. 2006. Anion Sorption in Variable-Charge Forest Soils.
Northwest Forest Soils Council (Feb 3). Vancouver, WA.
Harrison, R.B., Dave Briggs, Bob Gonyea, Randy Collier and AB Adams. 2006. Nitrogen
fertilization impacts on C sequestration in Pacific Northwest Forests. Invited presentation
at the American Geophysical Union. May 23-26. Baltimore, MD.
Harrison, R.B., T. Terry, A. Ares, C. Harrington, T.B. Harrington and S. Schoenholtz.
2006. PNW long-term productivity studies: Progress report. presented at PNW Stand
Management Cooperative Spring meeting (April 26-27) Hood River, OR
Harrison, R.B., D. Briggs, A.B. Adams, E. Turnblom, T. Terry, T.B. Harrington and S.
Schoenholtz. 2006. LTSP PNW affiliate sites: 4 years of results at Fall River, WA, and
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early results from Matlock, WA and Molalla, OR. USFS LTSP Technical committee
meeting. March 20-23. Charleston, South Carolina.
Slesak, R.A., T.B. Harrington, and S.H. Schoenholtz. 2007. Control of competing
vegetation following harvesting: effects on nitrogen leaching, mineralization, and
Douglas-fir foliar status. Poster presentation at the International Mountain Logging and
13th Pacific Northwest Skyline Symposium. Corvallis, OR. April 1-6.
Slesak, R.A., S.H. Schoenholtz, and T.B. Harrington. 2006. Soil C cycling following
timber harvest in response to logging debris and herbicide application. Presented at the
annual meeting of the Soil Science Society of America, Indianapolis, IN. November 1216.
Slesak, R.A., S.H. Schoenholtz, and T.B. Harrington. 2006. In situ measurement of bulk
soil and microbial respiration in clearcuts of the Pacific Northwest. Poster presentation at
the annual meeting of the Soil Science Society of America, Indianapolis, IN. November
12-16.
Slesak, R.A., S.H. Schoenholtz, and T.B. Harrington. 2006. Carbon cycling following
timber harvest in response to logging debris retention and control of competing
vegetation. Poster presentation at the national annual meeting of the Agenda 2020
program, Washington D.C. November 3.
Slesak, R.A., S.H. Schoenholtz, and T.B. Harrington. 2006. A research approach for the
assessment of soil C cycling in response to woody debris and herbicide treatments
following timber harvest. Poster presentation at the Northwest Forest Soils Council
annual winter meeting, Vancouver, WA. February 3, 2006.
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Figures:
Matlock Total N Concentration (100cm)
4.5
BO-NWC
BO-WC
-1
Total Nitrogen Concentration (mg L )
4.0
WT-NWC
WT-WC
3.5
Reference
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Apr-05
Jul-05
Oct-05
Jan-06
Apr-06
Jul-06
Oct-06
Jan-07
Apr-07
Figure 1. Total N soil-solution concentrations at 100 cm depth at the Matlock site.
Figure 2. Nitrate-N soil-solution concentrations at 100 cm depth at the Molalla site.
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Figure 3. Dissolved organic C soil-solution concentrations at 100 cm depth at the
Molalla site.
Figure 4. Dissolved organic N soil-solution concentrations at 100 cm depth at the
Molalla site.
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BO-WC
BO-NWC
WT-WC
WT-NWC
74
35
29
9.5
31
5.1
9.0
4.7
Matlock N Pools and Fluxes (kg ha-1)
Understory (2006)
3,600
Douglas-fir (2006)
Soil (2004)
Leaching (2005-2007)
4.4
17
17
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Figure 5. Nitrogen pools and fluxes during the first few years of stand establishment at
the Matlock study site.