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Criterion 4 Indicator 21
  Forest ecosystems receive much of their nitrogen and other nutrients from the decomposition and recycling of organic matter, including decayed leaves or needles, branches, fallen trees, and roots. When the soil is rich in organic matter, this attribute helps to improve water retention, maintain good soil structure, aid infiltration of water into the soil, store more carbon, and promote growth of soil organisms. Organic carbon in soil is a major component of the global carbon cycle. Soil carbon levels are influenced by agricultural and forestry management practices. Because most organic matter is located near the soil surface, its overall status is also greatly affected by natural or human disturbances. Thus, it is essential to understand the dynamics of soil organic matter and nutrient cycling in order to maintain and manage terrestrial and aquatic ecosystems in a sustainable manner.

Can This Indicator Be Quantified
Standard definitions exist for different kinds of soil organic matter and soil carbon, as do procedures for sampling and analyzing field samples. However, information is almost nonexistent on historical levels in natural stands. This lack of historical data makes it difficult to interpret levels found in forest plantations and degraded areas that have been reforested. Since the early 1960s, fertilization and stand manipulation studies have produced localized data on major soil nutrients and organic matter. Some studies tracked loss of soil nitrogen, other nutrients, and organic matter after forest fires and prescribed burns used to reduce logging slash. Little information exists for soil micro-nutrients measured in both natural and planted forests.

Overall, organic carbon levels are higher in western Oregon soils than in eastern Oregon. One study found that in western Oregon, soil organic carbon increased with annual temperature, annual precipitation, actual evapotranspiration, clay content, and available water-holding capacity, and decreased with slope. The range was 0.9 to 24 kilograms of carbon per square meter in the upper layers of the soil (0 to 20 centimeters in depth). The relative order, from highest soil organic carbon levels to lowest, was: Coast Range, Willamette Valley, Cascades, southern Oregon.
Decomposing materials need an optimum carbon-to-nitrogen ratio. When carbon levels are too high compared to nitrogen, decomposing microbes have a low activity level. Most Pacific Northwest forests are nitrogen-limited, so fertilizing with nitrogen or nitrogen and phosphorus generally enhances productivity, organic matter decomposition, and nutrient recycling.
In eastern Oregon, the productivity of understory vegetation may be related to competition for soil nutrients, soil moisture, and the maintenance of below-ground processes. Some harvest practices, such as burning logging slash in piles, create conditions in which organic matter and nitrogen are volatilized and surface soil structure is damaged.
Some activities, such as the construction of forest roads and trails and multiple entries for thinning, create conditions in which organic matter and nutrients are removed from forests, through erosion or faster decomposition in disturbed areas. Since the 1970s, new logging practices have minimized site disturbance and reduced the loss of organic matter and nutrients.
Shorter rotations and whole-tree harvesting leave less debris on the ground, and can potentially reduce the amount of organic matter and nutrients added to the soil. Such practices in Oregon have not yet led to documented productivity declines over a single rotation. In other countries, however, resource managers and the public have raised concerns about long-term nutrient changes over successive rotations of fast-growing conifer and hardwood species.

Data Source and Availability
Several databases contain information on chemical and physical properties of forest soils in Oregon. These sources are described briefly below. Table 21-1 lists web site addresses where soils data can be obtained.
An Oregon State University project developed a literature review summarizing the cumulative effects of forest practices in Oregon on soil, water, and other resources (Beschta, et. al., 1995). The review included a summary of vegetation, soil compaction, fertilization, and soil biota effects on soil physical and chemical properties.
The H. J. Andrews Experimental Forest Master Bibliography lists peer articles, project reports, and graduate theses from Oregon State University and other institutions (Table 21-1). These references include such topics as nutrient cycling and erosional processes in disturbed and undisturbed natural and planted forests found in the central Cascades and other areas in Oregon.
The Natural Resources Conservation Service (NRCS) has produced the National Soil Characterization Database (NSSL). (See Table 21-1.) This database has estimated physical and chemical properties for named soil series and phases of soil series mapped intensively (1:24000) on public and private lands in Oregon. Soil property estimates are based on laboratory data from select soil profiles.
The State Soil Geographic database (STATSGO) has over 200 map units for Oregon on a 1:250,000 base map compiled from intensive soil survey maps (Table 21-1). Over 25 physical and chemical soil properties and interpretation attributes are estimated, for up to 20 soil components in each map unit. The minimum map unit or polygon is 1,544 acres, a feature that limits database use to broad planning activities.
Homann and others (1998) used the attribute properties for 87 STATSGO map units and other soils databases to make a preliminary assessment of soil organic carbon storage in western Oregon. This study also explained how soil properties on the site, as interpreted from 6 kinds of maps, affected model outputs that estimated changes in organic carbon from one area to another, assuming climate changes such as increases in air temperature and monthly rainfall.
The U.S. Forest Service and Bureau of Land Management (BLM) have done extensive soil mapping and characterization work on federal forest lands. In the 1970s, soil sub-groups were mapped (1:63360) for land types on national forests for a soil resources inventory; limited profile descriptions and lab data are available. Since the 1980s, intensive soil surveys (1:24000) have been completed for about one-third of all national forest lands. Direct links will be available between U.S. Forest Service and Natural Resources Conservation Service soil databases for physical and chemical data of mapped units. This will occur as the Terrestrial Module (TERRA) in the U.S. Forest Service’s National Resources Information System becomes fully operational (Table 21-1).
The Stand Management Cooperative, in the College of Forest Resources, University of Washington, has data on soil organic matter, nutrients, and growth data for Douglas-fir and hemlock stands studied at 175 active/inactive sites in Oregon (Table 21-1). About 500 soil profiles are included. At four active sites, micro-nutrient and soil litter are monitored at 4-year intervals. These sites were part of the Regional Forest Nutrition Research Project that started in 1969; it was incorporated into the Stand Management Cooperative in 1991.
Some industrial timber companies collect or have collected soils data to correlate productivity of trees in their plantations with soil properties, and to determine if fertilizers are needed. Results and interpretations are usually proprietary. An exception is information shared through tree genetics or stand management cooperatives. The Oregon Department of Forestry and Oregon State University are members of both cooperatives.
Table 21-1. Databases with information on soil organic matter and soil nutrient status of forests in Oregon
Databases with information on soil organic matter and soil nutrient status of forests in Oregon
Database NameContentsInternet or e-mail access
Master Bibliography Andrews Exp. ForestReferences on nutrient cycling and processeshttp://sequoia.fsl.orst.edu.lter/pubs/bibliofr.htm
NSSL National Soil Characterization DatabaseChemical & physical properties for soil series, phases, and mapped componentshttp://www.statlab.iastate.edu/soils/nsdaf/main.html
STATSGO State Soil Geographic DatabasePhysical & chemical properties for 217 map units in Oregonhttp://www.ftw.nrcs.usda.gov/statsgo.html
SMC Stand Mgmt. CooperativeSoil physical/chemical and tree growth data for 175 sitesCollege of Forest Resources, Univ. Washington, Seattle, rcollier@u.washington.edu
TERRAsoils and other terrestrial ecological polygonshttp://fsweb.r6.fs.fed.us/terra_web/main.html
Western Oregon soil organic carbon6 approaches to estimate soil carbon, using 499 pedonsPeter Homann, Western Washington Univ., Bellingham, homann@cc.wwu.edu

Reliability of Data
Standard quality assurance and quality control protocols are used in mapping and analyzing soils. These protocols are followed in field and laboratory data collected for NSSL, STATSGO, the University of Washington Stand Management Cooperative, U.S. Forest Service, and BLM databases.
Homann and others (1998) showed that estimates of soil carbon in western Oregon, done for 0 to 100 centimeter depths using coarse-scale maps, were 5 to 30 percent lower than values estimated from STATSGO and some regional approaches. It is not known what the implications are for other regions in Oregon. These findings do emphasize that recent and detailed soil profile data provide the best estimates of soil organic carbon for a large geographic region. Similar detailed and recent methodology is also needed to quantify relationships between physical and chemical properties of forest soils with the productivity of overstory and understory forest species.

Forest soil and productivity studies can range from small plots and a single species located in one part of a small watershed, to many hardwood or coniferous species found across one or more large ecoregions. Existing studies have usually focused on small localized areas. As forest managers become more concerned about sustaining productivity on forest lands and more broad-scale information is needed, future studies will likely be landscape-level and will extend across one or more broad geographic and climatic regions.
Coarse-layer maps such as the Soil Map of the World and the Major Land Resource Area map provided a very broad overview of soil conditions across the state. For modeling efforts across one region, STATSGO and pedon-based approaches seemed to work best. When developing regional and state-wide models that relate soil organic matter and nutrient status to forest productivity, the researcher must determine which soil physical and chemical properties are randomly distributed or skewed across the landscape. Estimated or predicted values can be higher or lower than anticipated if it is assumed that such associations are all symmetrical or all randomly distributed.

Recommended Action for Data Collection
Forest lands that have few soil profile descriptions should be identified, as well as their ownership. Ongoing and future soil surveys should use intensive mapping and sampling methods, so that the overall resolution for data is the same for forest lands as it is for crop lands. Forest lands that have already been mapped intensively can be identified; for these lands, the researcher can then correlate soil properties with available tree growth data. A coordinated program is needed to collect and analyze data from stand exams, the U.S. Forest Service’s current vegetation survey, the Pacific Northwest Research Station’s Forest Inventory and Analysis, and forest health monitoring. The coordination would make it easier for researchers to discover the detailed relationships between soils and forest productivity, stand structure, and overall forest health. In such work, spatial procedures and detailed soil map approaches used by Homann and others (1995, 1998) could be explored before trying other methods.


Selected References
Beschta, R. L., and J. R. Boyle, C. C. Chambers, W. P. Gibson, and others. 1995. Cumulative effects of forest practices in Oregon: literature and synthesis. Oregon State University, Department of Forest Resources, Corvallis, OR.
Homann, P. S., and P. Sollins, H. N. Chappell, A. G. Stangenberger. 1995. Soil organic carbon in a mountainous forested region: relation to site characteristics. Soil Sci. Society Am. Journal 59:1468-1475.
Homann, P. S., and P. Sollins, M. Fiorella, T. Thorson, J. S. Kern. 1998. Regional soil organic carbon storage estimates for western Oregon by multiple approaches. Soil Sci. Society Am. Journal 62:789-796.
Pritchett, W. L., and R. F. Fisher. 1987. Properties and management of forest soils (2nd edition). John Wiley and Sons, New York, NY. 494 pp.
Riegel, G. M., and R. F. Miller, W. C. Krueger. 1992. Competition for resources between understory vegetation and overstory Pinus ponderosa in northeastern Oregon. Ecological Applications 2:71-85.

People Interviewed
  Karen Bennett, USDA Forest Service, Siuslaw National Forest, Corvallis, OR.
Bernard Bormann, USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR.
Kermit Cromack, Forest Science Department, Oregon State University, Corvallis, OR.
Peter Homann, Western Washington University, Bellingham, WA.
Mark Johnson, Environmental Protection Agency, Corvallis, OR.
Duane Lammers1, USDA Forest Service, Pacific Northwest Region, Corvallis, OR.
Chad McGrath, Natural Resources Conservation Service, Portland, OR.
Dick Miller, USDA Forest Service (retired), Pacific Northwest Research Station, Olympia, WA.
Phil Sollins, Forest Science Department, Oregon State University, Corvallis, OR
  1. Completed technical review of draft before its submission to ODF.