LONG-TERM ECOSYSTEM PRODUCTIVITY (LTEP) PROGRAM

GOVERNING RESEARCH PLAN

FOR THE INTEGRATED RESEARCH SITES

Prepared by

Susan Little, Bernard Bormann, Larry Bednar,

Trish Wurtz, John Zasada, Mike McClellan,

Lauri Shainsky, James Boyle, Mike Castellano

Mike Amaranthus, Connie Harrington,

Darlene Zabowski, and Mike Geist

This version of the research plan was updated from the original plan signed in 1992. The update reflects a changed program name (previously long-term site productivity), actual research sites selected, newer figures, and makes minor editorial corrections. Other changes to the study are not included in this update (B. Bormann, April 2, 2000).

RESEARCH PLAN FOR THE LTEP INTEGRATED RESEARCH SITES

Introduction

The USDA Forest Service, USDI Bureau of Land Management, and other stewards of the land have been charged with the challenge of maintaining forest productivity for current and future generations. Forest productivity is the ability of the land to provide a combination of resource values such as fiber, water, air, quality experiences and biological diversity. Long-term ecosystem productivity is the capacity of the site to support forest ecosystems over generations of humans and trees, as measured against some defined reference. Our desire to maintain long-term ecosystem productivity, and the legal mandate to do so, includes a desire to maintain options for future use as well as the sustained production of the current mix of forest products and intangible resources. In this research plan we will refer to potential productivity—approximated by gross primary productivity derived from models, and referenced by indices of soil quality and genetic potential—and to the net and cumulative production of specific products and forest attributes such as net primary productivity, wood volume, nesting sites, forage, and species diversity.

Long-term ecosystem productivity is determined by the cumulative interaction of soil, biota, climate, natural disturbance, and human activity. Two recent proceedings capture current knowledge of productivity and have references for specific topics (Perry and others 1989; Gessel and others 1990). Nearly all forestry research contributes in some manner to our understanding of ecosystems and the management of forests. However, most research to date has focused on short-term responses of individual components of ecosystems to individual events and manipulations. Thus, a fragmented body of knowledge has evolved in which research methods and language are specialized by discipline and individual disciplines are pursued at different locations and scales. Although some individual processes and responses are adequately understood, integration and synthesis are difficult at best.

The focus for the research proposed here was derived from discussions within a broad community of people interested in long-term ecosystem productivity (see Appendix I). The authors developed specific objectives, hypotheses, and design in response to the community's input. Two primary mechanisms by which forest management may influence long-term productivity were identified and form the basis for the two basic questions posed by this research plan:

· Does altering the pattern of succession through species manipulations influence long-term ecosystem productivity? and,

· Does the amount, timing, and distribution of organic matter left on-site influence long-term ecosystem productivity?

The integrated research sites are being established as a network of long-term research sites to address these as well as other questions that are truly long-term and complex, and demand that research disciplines integrate in concept, in application, and in analyses. The research sites will provide a setting for continual observation, discussion, and involvement across disciplines, management, and interested publics. Research on these sites will be conducted in a 200-year context, allowing for several generations of crop trees. In order to provide for the needs of land managers in the near future—prior to completion of long-term studies—research from these sites will contribute to conceptual and numerical modeling of long-term processes and responses on a continuing basis. Our desire is to provide a legacy of integrated information on productivity and to provide a context for basic research that will result in more efficient research and more successful incorporation of results into models.

The integrated research sites are the cornerstone of a broader LTEP Program, led by the USDA Forest Service Pacific Northwest Research Station in cooperation with Pacific Northwest and Alaska Regions and with the USDI Bureau of Land Management, Oregon State Office. Research under the Program includes research on belowground processes, retrospective, and chronosequence research on ecosystem productivity, modeling long-term productivity to evaluate consequences of management decisions, and investigations on the effects of specific management practices on long-term ecosystem productivity.

Background

Net Primary Productivity

Sustainable forest productivity is the ability of the land to produce a wide array of products and values on a perpetual basis within broad environmental limits. Thus, the most appropriate measure of forest production is likely be an index which integrates across this array and quantifies values and resources such as timber, grazing, wildlife, fisheries, water, visually attractive landscapes, recreation, microbes, biodiversity, habitat and other ecosystem properties. Ideally, measures of sustainability would be derived from changes in overall production over long time periods, independent of changes in environmental limits. However, overall production is often not quantifiable because of widely varying units of measure, and changes in climate. Thus, surrogate measures of sustainability are needed that closely relate to the production of as many products and values as possible and at the same time can be directly measured. The LTEP Program will use total ecosystem production-- net primary production (Npp)—and components of Npp as the principal surrogate measure of long-term ecosystem productivity. We do not, however, preclude use or development of other surrogate measures.

Components of Npp form the basis for the conceptual model that drives and will be driven by the research proposed here (fig. 1). Primary producers or autotrophs (plants) capture light energy through photosynthesis. Gross productivity (Gpp) is the cumulative dry matter added to the ecosystem through photosynthesis. Npp is Gpp minus the dry mass lost during maintenance and growth respiration (R_a):

Gpp=Npp + R_a. [1]

Changes in net storage of carbon resulting from additions or losses are defined as net ecosystem production (NEP). Losses of carbon other than R_a result primarily from the respiration of heterotrophs (R_h). Heterotrophs are animals and non-photosynthetic microbes and plants that depend on the energy fixed in organic molecules during photosynthesis by autotrophs.

Npp= NEP + R_h [2]

NEP is defined as change in storage of carbon in all forms during a defined period and include changes in carbon content in plant, animal, and microbial biomass, and changes in detritus—all dead organic matter such as soil humus, litter, and downed logs. Further divisions of changes in biomass are useful, such as stem and forage production. These are often the type of production managers are most concerned with.

Figure 1. Net primary production and its relation to net ecosystem production, respiration, and the production of ecosystem goods (such as wood products) and services (such as changes in soil organic matter).

Measurement of Npp can be problematic, mostly because of difficulties in quantifying belowground and detritus production, as well as other outputs or losses. Our approach follows that of Bormann and Gordon (1989), which focuses on three principal components of Npp: soil respiration; changes in soil organic matter; and changes in aboveground biomass.

Succession, Management, and Implications For Long-Term Productivity

Change is a fundamental characteristic of forest ecosystems. The rate and nature of change is a function of species composition (including plants, animals, soil organisms, fungi and other biota), site conditions, and the frequency and severity of disturbance in a given ecosystem. Succession is the sequence of change in biotic communities that occupy an area. Succession involves numerous processes by which species influence the physical environment and replace one another over time (Connell and Slatyer 1977, Bormann and Likens 1979, Kimmins 1987, Oliver and Larson 1990).

The mechanisms of succession in biotic communities are complex; numerous mechanisms and pathways exist for a given site's progression from one set of species (or "sere") to another. Although seres are often described only in terms of the primary producers, i.e., plants, changes in plant composition can cause changes in other species (e.g., animals, soil organisms, and others). Conversely, animals and other organisms may be a major cause of change in the composition of the primary producers. Forest succession can be either autogenic, whereby organisms make changes in the site which favor the development of other species, or allogenic, whereby geologic or climatic processes cause changes in the physical environment which lead to changes in the biota (Kimmins 1987, Oliver and Larson 1990).

In this research plan, we are concerned with secondary succession, the progression of plant communities that occur following disturbances such as fire, windthrow, and timber harvesting. Secondary succession is distinguished from primary succession in that the former occurs on sites that have some level of soil development and previously supported vegetation. The species composing the forest vegetation that develops following disturbance fall into one of several categories (Kimmins 1987, Halpern 1988, 1989, Oliver and Larson 1990). Residual species occurred in vegetative form before disturbance and some portion of the plant survived the disturbance. These species can rapidly dominate a site and in extreme cases prevent the establishment of species which otherwise may have dominated later succession. Examples of these species developing from roots and rhizomes are Rubus spp., Populus tremuloides, Vaccinium spp., and Galtheria shallon. Others develop from basal sprouting Acer spp., Corylus, Salix spp., and Arbutus menziesii. A final group can develop by layering, one of the best examples of this is Acer circinatum. Invader species become established from seeds entering the area from adjacent stands. Species of all of growth forms (trees, shrubs and herbs) can be part of this group. They can all establish at the same time; dominance is determined by growth rate and longevity. Examples of these species are Epilobium spp., Senecio spp., Alnus spp., Betula, many of the commercial conifers, and Salix spp. Another group of species are represented in the buried seed pool. These species may or may not be present on the site in vegetative form prior to disturbance. The classic examples are species that occur in the early successional flora but are only present in seed form in later successional stages. Following disturbance, seeds germinate and the species are present for several to many years depending on life form and growth characteristics. Some of the best examples are Ceanothus spp, but other examples are various Rubus spp., Geranium sp, Corydalus sp. and Sambucus spp. Knowledge of how different species recolonize disturbed sites will aid us in prescribing means of achieving the different seral treatments.

Three proposed mechanisms that determine the relationship among dominant species (and less obvious but important species such as nonvascular plants, soil flora, and soil fauna) and the pathways of succession include facilitation, tolerance, and inhibition (Connell and Slatyer 1977, Kimmins 1987). Facilitation occurs when individual species modify the environment in such a way that it becomes more suitable for the invasion of other species than for its own regeneration. Tolerance occurs when the environment is satisfactory for the establishment of any of the potential invading species, and species dominance is based mainly on which species happen to arrive first, their growth form, rate of growth, longevity, and the physiological ability to tolerate the current environmental conditions. Inhibition occurs when species modify the environment in such a way that prevents the recruitment of other species or significantly prolongs the recruitment period. These processes are not mutually exclusive and may all occur simultaneously on the same site. The importance of each will be determined by species composition, disturbance regime, and growth and reproductive characteristics of the species involved.

Successional patterns following disturbances such as harvesting or wildfire are known to varying degrees in Alaska, Oregon and Washington (see for example Stewart 1978, Van Cleve and Viereck 1981, Franklin and Hemstrom 1981, Foote 1983, Alaback 1984, Kimmins 1987, Halpern 1988, 1989, Oliver and Larson 1990). Most research to date has focused primarily on changes in species composition and cover of trees and associated vascular plants. Some studies have dealt with nonvascular species and microorganisms. However there is little information on the relationship of changes among different trophic levels as a result of forest management activities.

Forest management practices often result in shortening or eliminating some parts of the successional sequence. For example, use of herbicides or site preparation techniques in combination with planting favored timber species can result in a reduced duration of early seral species. As a result, the influence of some species is eliminated or reduced. The long-term impacts of practices that alter succession are not known in detail. The importance of some individual species whose tenure on a site is often shortened is known to some extent. The potential detrimental effect of the elimination of species such as alder and Ceanothus, which fix nitrogen, can be assessed in a general way. However, there is little information on the role of other non-crop species in determining long-term ecosystem productivity or the effects of eliminating or reducing their time of occupancy.

Forest management in the Pacific Northwest is evolving, particularly with respect to harvesting strategies. Past approaches used narrowly defined methods and blanket prescriptions. Now, case-by-case evaluations are made which seek to achieve landscape objectives as well as efficient production of timber. This evolution is leading to more partial cutting, uneven-aged management, and retention of individual trees or groups in an even-aged setting (e.g., Eubanks 1989). Some of the products and values tangible at the landscape-scale depend more on species composition, distribution, and stand structure than on achieving maximum growth of selected tree species. Thus, there is a need to understand the impact of management practices at the stand-scale in ways that relate to landscape-scale questions. In order to assess the effects of harvesting and other management practices on productivity, we need to be able to relate changes to easily identifiable states or stages of forest development. Forest successional development provides a framework for such assessments. This plan seeks to use this framework to examine the consequences of directed forest successional development and associated links of ecosystem structure and function, as they relate to productivity on various spatial and temporal scales.

Organic Matter and Long-term Ecosystem Productivity

Organic matter (OM) is any and all material on a site, living and dead, containing carbon compounds derived from living organisms, including specific components, such as the forest floor, soil organic matter, and downed woody debris. Total ecosystem OM may be divided into categories defined by structure or function. Structurally, OM may be usefully divided into foliage, branches, stems, roots, standing dead, forest floor (including down logs and branches), soil organic matter (SOM), dissolved OM, volatilized OM, and animal biomass. Many functional definitions are possible also, with OM divided into photosynthetic, respiring, and detrital components or into categories based on relative OM recalcitrance, expressed as half-life or turnover time. A structural approach will be used in the design and implementation of this study.

Organic matter has multiple functions in forest ecosystems that may determine forest productivity, including as a primary reservoir of nutrients, essential to plant and animal growth; as the energy source for heterotrophs; and as a structural material that functions as habitat (e.g., snags, down logs) and that creates soil horizons and aggregate structures that buffer ecosystems against physical forces. Examples of buffering activity include organic horizons that protect soil from erosion, plant canopies that moderate wind speed and radiative heating or cooling, and coarse woody debris on steep slopes and in stream channels that reduces the erosive power of flowing water. Perry and others (1989) provide discussions on the role of organic matter in forest productivity in general, and Jurgenson and others (1990) discuss organic-matter issues pertinent to the forests of the Inland Northwest.

Research in the last 20 years on management effects on organic matter has concentrated on two main areas: comparing bole-only and bole-and-crown harvesting; and evaluating the effect of site preparation, primarily fire, on surface organic matter pools (S.U.N.Y. 1979; Ballard and Gessel 1983; Perry and others 1989; Gessel and others 1990; Walstad and others 1990). Both areas of research were motivated primarily by a concern for nutrient capital. Methods typically compared nutrient capital in pre-treatment sites with that removed during the management activity. Long-term effects have been predicted by comparing management losses to natural inputs of nutrients and through models of nutrient cycling (Kimmins and Sollins 1990). Ecological research on contributions of individual species to litter, decomposition, and below-ground processes have also been conducted, but seldom on the same sites as the harvesting research. Direct evidence of long-term impacts from intensive harvesting is weak, primarily due to the lack of long-term, controlled experiments (see Powers and others 1990 for synopsis of multi-generational studies and Dyck and Cole 1990 for a discussion of research needs).

Harvesting and site preparation are the major ways by which forest management practices may influence site organic matter. Current National Forest plans have standards and guidelines for retention of large woody debris and protection of forest floor. The intent of these standards is to protect long-term productivity. Economic trends have altered how harvests are conducted, with more reliance on whole-tree yarding and more complete utilization of individual trees than in the past. The question now is not whether to whole-tree or bole-only harvest, but how much material is to be left on site either as felled trees, or as specified pieces of residue classified by length, diameter or quality. Research is needed to compare organic matter inputs to the forest floor (and subsequently to the soil) as a result of harvesting in even-aged and uneven-aged settings. This research will be most fruitful if combined with studies of the different contributions of species groups to forest floor and soil through annual litterfall and turnover between harvests.

Objectives

The research discussed in this plan has two primary objectives:

A. To examine how potential and realized productivity are affected by the pathway along which succession is directed by management practices. All sites are capable of supporting a variety of forest conditions at any point in a seral sequence. These forest conditions can be described in terms of the species present, their vertical and horizontal distribution and abundance, amount of non-living organic matter, microclimate regimes, general state of health, as well as in terms of relative position of that site to others across the landscape. This research is designed to examine how conditions produced by directing the aboveground plant component of an ecosystem to a particular successional state or "sere" can affect subsequent ecosystem development and productivity. Forest conditions can be altered by management practices that affect composition by removal of species, addition of species, conversion of organic matter to different forms, and change soil physical and chemical properties. This research will focus on three distinct strategies for directing or arresting succession towards forest conditions that may have distinct differences in ecosystem production. These treatments include: (1) incorporating an abundance of early seral species into even-aged management of conifer crop species; (2) directing site resources exclusively to mid-successional conifer crop species to the exclusion of other seral stages; and (3) emphasizing late-seral species and forest structure along with the management of the crop species (fig. 1). A fourth treatment will be an unmanipulated stand, left untended throughout the duration. The crop species will be consistent across treatments within a site, but will not necessarily be consistent across sites.

B. To examine how altering the amount of periodic inputs of organic matter to the forest floor can influence long-term ecosystem productivity. The importance of organic matter will be examined by directly manipulating aboveground organic matter, primarily through the cutting and removal or retention of whole plants. Treatments will be defined as proportion of aboveground biomass to be left in a felled condition after each harvest. Hence, the stand-scale treatments will address the aspects of managing quantity of organic matter (fig. 2). Small-scale studies on these sites will look at issues of quality of organic matter, particularly as it relates to decomposition rates of different sized material, contributions of individual species to annual litterfall and soil-organic-matter quality.

Figure 2. The generalized experimental design for the LTEP integrated research sites. Note that the unmanaged control treatments is not shown, the Olympic Peninsula site has a mid organic matter treatment as well, and that the Oregon Coast Range site includes 10 to 30 residual trees per acre on early and mid treatments.

Hypotheses

The hypotheses listed below represent the central issues to be addressed by the research team through the implementation of this research plan. The primary null hypotheses target four broad categories: net primary productivity, biodiversity, soil organic matter, and soil physical properties. Within each category, alternative hypotheses are proposed, some of which include underlying mechanisms. Some of these hypotheses are stated in a testable form and will be directly addressed by the design. In other cases, small-scale manipulative studies will be needed to test proposed hypotheses, particularly the more mechanistic ones. Hypotheses will be tested within and between sites. Ideally, the ultimate test of most hypotheses concerning long-term ecosystem productivity would be an on-site bioassay of crop production after 200 years of subjecting each site to its array of treatments. In the meantime, the hypotheses will tested from periodic assessments of net and cumulative production, gross primary productivity, biodiversity, and soil attributes. We will be inviting other scientists to explore related hypotheses as an ongoing process, and will allocate space within the units to do so.

Net primary productivity

We will focus on three aspects of net primary productivity (Npp):

C. Annual Npp (Npp yr^-1)—the Npp accumulated over a year. This can be a measured accumulation for one year, or an average derived from total accumulation over a measurement period divided by the years in that period.

D. Cumulative Npp (SNpp)—the Npp accumulated from the initiation of the experiment to some reference point in time; and

E. The function of annual Npp over time.

For both annual and cumulative Npp indices, we will chose mid-rotation as our primary reference point in time. Mid-rotation is site-specific and defined as the halfway point through the rotation length, as determined by local foresters at the time of treatment prescription. However, we will continually monitor Npp and explore treatment differences throughout the experiment.

Null Hypothesis I: Net primary production (Npp yr^-1 and SNpp) at mid-rotation and the shape of the Npp yr^-1 function over time will be the same for all treatments—for all species compositions and OM manipulations—and will not differ from that of the unmanipulated stand.

Alternatives:

1. Within an organic matter treatment, there will be differences in Npp between the different seral treatments. These differences in Npp yr^-1 and SNpp should be evident by mid-rotation.

2. Although annual Npp at mid-rotation will be the same between all treatments, the cumulative Npp will differ: the early seral treatment will have the highest SNpp, and the natural stand will have the lowest SNpp.

3. Year of attainment of maximum Npp yr^-1 will differ between treatments: the natural stand will begin at its maximum Npp yr^-1; the late seral treatment will achieve its maximum Npp yr^-1 by mid-rotation of the first introduced cohort; the mid-seral treatment will achieve its maximum Npp yr^-1 at the end of the first rotation; and the early seral treatment will continue to increase its Npp yr^-1 throughout the second rotation.

4. Organic matter treatments will alter Npp yr^-1, SNpp, and the Npp yr^-1function.

Null Hypothesis II: The proportional allocation of production between ecosystem components is the same for all treatments.

Alternatives:

1. There will be differences between treatments in the proportion of total Npp allocated to bolewood of the crop species. For a given organic matter treatment, this effect is expected to be measurable at the end of the first rotation. The mid-seral treatment is expected to have the greatest proportion of Npp devoted to bolewood, followed by the late seral treatment, then the early seral treatment. The natural stand is expected to have the smallest proportion of Npp allocated to bolewood at the end of the first rotation. These trends should continue through the second rotation. We expect that the early seral treatment will devote a larger portion of Npp to reproduction and annual litterfall. The natural stand will be approaching a relatively stable level of bolewood, and will be devoting a greater proportion of Npp to annual litterfall than the other treatments. The late seral treatment will fall between the mid-seral treatment and the natural stand.

2. Differences between the organic matter treatments in proportional allocation of Npp may not be expressed until the second rotation. Differences in proportional allocation of Npp are expected to be due primarily to differences in decomposition and nutrient uptake.

3. The proportion of Npp devoted to heterotrophic respiration (R_h/Npp) will be higher in treatments with more species diversity due to enhanced diversity of litter quality and associated microbial populations, and greater allocation of resources to reproduction than to structure.

4. The proportion of Npp devoted to autotrophic respiration (R_a/Npp) is expected to be higher in systems stressed by availability of water or nutrients or by pests and pathogens. Which treatments are more stressed than others will differ between sites.

5. The ratio of new heterotrophic respiration to old heterotrophic respiration (R_h-new/ R_h-old) is expected to be the same between the early- and mid-seral treatments, but greater in the late seral treatment and in the natural stand.

6. It is likely that species composition and OM treatments will interact to influence Npp yr^-1, SNpp, allocation of Npp components, and the function of Npp over time. Each plant species present will have a unique effect on the physical and chemical environment, which will influence the diversity of microbial populations present, OM conversions, and subsequent Npp. In addition, OM treatments are likely to influence the presence and abundance of species colonizing the units by creating differential substrate microenvironments for germination. Persistence, dominance, and production by the species present may also be affected by OM levels through differences in nutrient cycling and soil temperature and moisture regimes, and potential herbivore habitat.

Biodiversity

Biodiversity in the context of this plan refers to the diversity of species present within a treated plot.

Null Hypothesis I: There will be no differences in aboveground and below-ground species composition between treatments.

Alternatives:

1. Seral treatments, by definition, impose differences in aboveground plant species. We expect that there will be differences between seral treatments in the kind and abundance of insect, mammalian, and bird species utilizing the treatment units. These differences will be apparent within the first 10 years after initial entry, and are expected to decrease late in the first rotation, but increase during the second rotation. The causes of these differences will be changes in the diversity of potential habitat and food supply.

2. Low OM treatments will reduce diversity of belowground species. This effect is expected to be measurable within 10 years after first entry because of differences in soil surface temperature, quality of forest floor and inputs to the soil organic matter.

3. The abundance and diversity of rodent populations will increase with increasing surface organic matter because of increasing diversity of habitat.

4. Organic matter treatments will influence the plant biodiversity by creating different patterns in substrate and environment for germination.

Interactions between biodiversity and Npp

Null Hypothesis I: Changes in biodiversity of plant species composition will not result in changes in Npp amongst treatments.

Alternatives:

1. Increased plant species diversity will result in higher annual and cumulative Npp. Increased plant species diversity will result in greater utilization of site resources through divergent patterns between species in resource partitioning. It will also enhance Npp by increasing the diversity of soil microbial species that will improve utilization of belowground resources. In the more diverse treatments, SNpp will increase with time most rapidly and early in the rotation, and plateau sooner than the less diverse treatments.

2. More diverse treatments will have higher Npp yr^-1 and SNpp because they are more resilient to perturbations such as disease and insect outbreaks, and climate change.

Soil organic matter

Null Hypothesis I: The amount and distribution of soil organic matter will not differ between treatments.

Alternatives:

1. The organic matter manipulations will influence soil organic matter. The amount of soil organic matter will be greater in those treatments having greater retention of aboveground OM.

2. Species composition will alter soil organic matter. The amount of soil organic matter will be greater in the late seral treatments and the natural stands because of greater large woody debris and uninterrupted litterfall contributed by late seral species.

Null Hypothesis II: The chemical and structural composition of soil organic matter will not differ between treatments.

Alternative:

1. Early seral species will contribute greater amounts of leaf litter to the soil organic matter pool, while later seral species may contribute greater amounts of large woody debris. Decomposition and incorporation of surface OM into the soil profile will be influenced by the effects of different species and forest floor on soil temperature and moisture, and by their associated microbial species.

Null Hypothesis III: Soil development (depth and quality of individual horizons) will not differ between treatments.

Alternatives:

1. Species composition will influence soil development through effects on the microclimate and evaporative demand. Species composition will also affect soil development through their differential biological activity: leaf litter and woody debris fall; root growth and below-ground OM input; root exudation, nutrient uptake and ion exchange; plant species-specific microbial associations and their influence on the biochemistry of the soil.

2. Organic matter treatment will influence the soil development by creating different initial SOM inputs. OM treatments are expected to interact with species composition treatments to influence soil development. Plant and microbial species will interact to influence both each other and their environment, thus affecting the soil profile development.

Soil physical properties

Null Hypothesis I: The mean and variance of soil bulk density (and porosity, water holding capacity, aeration) will not differ between treatments after initial entry and at subsequent measurements through the second rotation.

Alternatives:

1. The change in quality of OM inputs, amounts, and SOM distribution between treatments will alter soil physical properties directly and through change in the activity of soil microbes. For the early seral treatment, soil bulk density will decrease over the first rotation due to increased SOM and quality of litter. Soil bulk density will increase in the mid-seral treatment during the first rotation because of a decline in SOM.

2. In areas disturbed by treatment, there will be treatment differences in the rates of recovery of soil bulk density and porosity, due to differences in amounts and quality of organic matter inputs to the soil and subsequent effects on soil biology.

Methods

Integrated Research Site Locations

A network of five stand-alone experimental, integrated research sites will be established in Washington and Oregon (fig. 3). These sites are representative of the soils and forest types most likely to remain under management in the Pacific Northwest for resource outputs, including timber. Individual sites are described in Table 1. These sites are large enough to accommodate four replications of 7 to ten treatments applied at the stand-scale (8 ha).

Figure 3. Integrated research sites

Philosophy of Approach

No single research design can efficiently provide for research needs pertinent to all forest productivity questions. This research plan describes an approach to investigating questions tangible at the stand-scale (2 hectares) and smaller. The design described here will permit the quantifying and comparing measures of resources tangible at larger scales but will not allow direct comparisons of populations that have larger home ranges. Opportunistic use of natural events, such as insect outbreaks and wildfire, may provide some insights for landscape-scale questions.
Table 1. Description of LTEP integrated research sites (updated 4-2-2000)

Coastal Siskiyou
Location	Pistol River drainage, west and south of Gold Beach, Oregon
Manager	Chetco Ranger District, Siskiyou National Forest
Soils	Sedimentary rock parent material
Species	Douglas-fir, tanoak, and knobcone pine
Elev./topog.	800 to 1100 m; undissected slopes
Age	80 to 100 years old
Past History	Stand replacement following hot wildfires, few surviving residuals
Pathogens	Little evidence of pathogens
Oregon Cascades
Location	Isolation Block, south of Vida and HJ Andrews Experimental Forest
Manager	Blue River District, Willamette National Forest
Soils	Volcanic gravelly loam/loam, relatively homogeneous
Species	Douglas-fir, hemlock, red cedar with alder/maple in draws
Elev./topog.	About 700 m; undissected slopes
Age	About 80 years old
Past History	Stand replacement following hot wildfires with variable survival of residuals
Pathogens	Little evidence of pathogens
Oregon Coast Range
Location	North and east of Hebo, Oregon
Manager	Hebo Ranger District, Siuslaw National Forest (North Coast AMA)
Soils	Tyee sandstone and basalt, highly eroded following fire
Species	Douglas-fir with scattered Sitka spruce and red alder
Elev./topog.	About 400 m; gentle slopes for the Coast Range
Age	About 70 years old
Past History	Early plantation (possibly off-site stock) following a series of hot fires
Pathogens	Little root rot, wind-snaps, possible history of Swiss needlecast
Washington Cascades
Location	East of Mt. Rainier
Manager	Naches Ranger District, Wenatchee National Forest
Soils	Volcanic parent materials
Species	Douglas-fir with mixed conifers
Elev./topog.	About 1000 m; gentle terrain
Age	Uncertain
Past History	Hot wildfire
Pathogens	Little evidence of pathogens
Olympic Peninsula
Location	Near Sappho, Washington
Manager	Washington Department of Natural Resources
Soils	Outwash till with thick forest floor
Species	Douglas-fir, hemlock, and spruce with scattered hardwoods
Elev./topog.	100 m; large outwash deposits along the Sol Duc River
Age	About 70 years
Past History	Railroad logged; blowdown prevalent from previous stand
Pathogens	Mistletoe, some rot pockets

No single measure of production is adequate to assess forest productivity. A suite of measures and indices will be followed on these sites over time. Particular attention will be given to measures of primary production (plants) and the soils supporting that production. Assessments of quality and temporal and spatial distribution will be a part of all measures of production.

The following features are expected to facilitate integration of research results and activities:

· Research will guide as well as be guided by, the development of conceptual models which provide a common framework and language;

· Treatment prescriptions will be written in the context of local productivity concepts developed by interdisciplinary teams;

· Small-scale, manipulative research on key processes and interactions will be conducted within the context of the stand-scale treatments;

· Consistent methods for describing and analyzing ecosystem components and processes will be encouraged;

· Quality assurance will be an integral part of the program (QA plan to be appended); and

· Data will be accessible through a common database.

Overview of Experimental Design

A split-plot design will be used for each integrated research site. Seral treatments will be applied to whole plots, and organic matter treatments will be applied to subplots. Whole plot treatments will be assigned in a randomized complete block design, generally with four blocks per site. This design is chosen primarily to minimize buffer areas by locating similar seral treatments on adjacent subplots. Other advantages include increased sensitivity to differences in organic matter treatments (expected to be smaller in magnitude than differences between seral treatments), and reduced number of timber sales required to impose treatments (which should result in greater economy and ease of execution of treatments).

Individual seral treatments will be applied on at least 18 or 24 ha areas, including 50-m buffers (fig. 4). These areas with common seral treatments will be divided into two or three subplots for application of organic-matter treatments. Within subplots, 2-ha mensuration plots will be established for monitoring stand-level effects (fig. 5). Destructive sampling other than soil sampling will not be permitted in the mensuration plots. Separate destructive sampling zones for trees and other ecosystem components will be delineated from the onset, and dedicated to sampling at prescribed time intervals to allow opportunities for future scientists. Other areas will be reserved for small-plot investigations of varying duration. We anticipate space limitations on some of our sites and may not be able to provide space for small-scale investigations on all blocks. At least one complete replication per research site will have such space reserved.

All foot and wheel traffic on plots will be confined to designated trails in order to protect the long-term integrity of the site. As much as possible, common transects and plots will be used to assess and sample the various ecosystem components and processes. Measurement crews will cover as many aspects as possible in one visit in order to reduce traffic impacts. There will be opportunities during treatment application (harvest) to remove whole shrubs and trees for more thorough stem, biomass, and chemical analyses. Within the destructive sampling zones, priority will be given to investigations that add to inference from mensuration plot. The majority of small-scale plots will be reserved for future generations of scientists in order to provide some incentive for continued scientific support of these sites.