science Plan for the Long-Term Site Productivity Research Program
Forest Service, Pacific Northwest Research Station,
Bernard T Bormann
Program Leader, Basic
Susan N. Little
Program Leader, Applied
C. W. Philpot
Station Director, PNW
This document is the initial science plan of the PNW Station Long-term Site Productivity (LTSP) Research Program. This plan also seeks to integrate the basic and applied components of the PNW LTSP Research Program. Background, justification, goals, and administrative structure of the combined Program are presented in more detail in the Program Charter. A more detailed applied research plan will follow later this year to address how management tools for assessing and ameliorating productivity losses will be developed.
LTSP is one of several important new research initiatives in the Pacific Northwest Research Station. In some sense, all of these initiatives seek to better understand ecosystem sustainability. Among the overlapping initiatives are Global Climate Change, New Perspectives in Forestry, Forest Health, Consortium for Social Values in Forestry, Biodiversity, and Cumulative Watershed Effects. The Station also plans to expand basic research on ecological processes and land-water interactions.
The LTSP Program seeks to fill two niches in this research environment: (a) to increase our ability to evaluate the effects of current and future stand management practices and ecological processes and (b) to use the perspective of sustained ecosystem productivity to foster integrated research. A primary focus on integration in the LTSP Program results from slow progress in previous site productivity research because of, we believe, ineffective integration. To achieve these goals, we propose to:
• Develop an approach where direction and design of research will follow from a conceptual model, not from current or envisioned management practices, not from existing models, and not from processes out-of-context;
• Develop a conceptual model that, in its simplest form, says that all major productivity drivers must be evaluated simultaneously even if this means assessing some factors at a less detailed level;
• Apply new predictive models that are compatible with this conceptual model and that can be tested in process studies and in long term experiments;
• Support predictive modeling, retrospective studies, and short- and long- term experiments that can be used to continually re-evaluate and modify our conceptual model; and
• Incorporate perspectives from other ongoing research initiatives, where possible, in experimental designs and conceptual and predictive models.
The ultimate desired outcome is to increase managers' confidence in predicting the consequences of major decisions and to increase public confidence that "best practices" are being used on the land.
Public concern over management policies on federal forest land reflects in part our narrowness of focus in Forestry. Forestry research and management have traditionally concentrated on the production or protection of one product or amenity in a limited geographic area and time scale. A broader demand on National Forests has emerged that calls for a change in research and management. The overall need was recognized in the Multiple-use Sustained-yield (MUSY) Act of 1960 with its goal of achieving and maintaining a high level of production for various renewable resources "without impairment of the productivity of the land". Other federal legislation, including the NFMA (1976) and NEPA (1969), builds on this sustainability concept.
Whether current management strategies have succeeded in meeting these objectives has been called into question. To attain the original goals of the MUSY Act, the LTSP Program has evolved new ways of organizing and conducting research.
SCOPE AND FOCUS OF THE BASIC RESEARCH PROGRAM
This Program first and foremost seeks to identify critical linkages between physical, chemical, and ecological processes operating in all forested ecosystems. Once identified, the key linkages will be quantified under a range of conditions. Predictive models will be employed to assess selected management systems. The overall validity of the predictive models, their underlying assumptions, and the effects of various management practices will be evaluated across a range of conditions and over a long period of time.
The idea of naturalness and normal stability in ecosystems are assumptions being questioned. We have learned that productivity can fluctuate greatly in relatively undisturbed systems due to changes in flora, fauna, and soils. We also recognize that few ecosystems are in equilibrium with present climate, and that no system within the earth's atmosphere is outside the influence of human activities. The question arises as to whether or not the currently observed rates of production can be sustained under any management scheme? Can they be substantially increased? The answers lie in understanding how a multitude of changes might alter the state and function of future forest ecosystems.
In searching for common properties of all ecosystems, we start with vegetation, the foundation of all food chains from microbial to human. Ultimately, plant production is limited by the amount of solar radiation absorbed throughout the growing season. How effectively the radiation is captured through photosynthesis and then transformed into biomass determines the plant, animal, microbial, and detrital composition of the ecosystem. A tangible index of reduced productive capacity is a pronounced reduction in photosynthetically-active radiation (PAR) actually absorbed by vegetation throughout the growing season.
Even in death, plant products are important because they may become residues that store and release water, carbon, and nutrients. All ecosystems contain animals and microbes that speed the cycling of minerals, transform organic matter, and alter plant species composition. Animals and microbes may play important roles in soil fertility and speeding or retarding soil development (e.g., nutrient cycling by detrital feeders, N2-fixers,and denitrifiers; soil mixing by earthworms; increased weathering by microbes).
Change is constant in all ecosystems, but is most dramatic following episodic disturbances such as harvesting, fire, or windthrow. It appears that many species within the ecosystem are well adapted to disturbances that have been part of their historical norm. But we must address what happens when the spatial pattern, magnitude, or frequency of disturbance is significantly altered. Changes in disturbance regime, for example, could result in exclusion of early or late successional species (plants, animals, & microbes), net loss of organic matter and nutrients, and increased incidence of insect pests or disease. Conversely, many forests appear to decline if not periodically disturbed. How often and how extensive must disturbance be to assure recycling and renewal? Quantifying the extent that organisms are adapted to a variety of disturbances also is an important task.
Finally, and importantly, we must evaluate the long-term social and economic consequences of various management options. This is a difficult challenge because management objectives and constraints are likely to change as the supply of and demand for forest products and values change. Whether economic and social returns can be maintained or increased depends in no small measure on improved understanding of forest ecosystems.
Admittedly, some products and values, such as endangered species or aesthetic qualities, may be difficult to relate well to established measures of biological productivity. These must be considered in the broader Programs such as New Perspectives in Forestry and the Consortium for Social Values in Forestry. New Perspectives and LTSP will be closely integrated by selecting common research sites, exchanging ideas, and collective modeling.
LTSP Program approach
The Program seeks to improve our ability to predict site-specific LTSP effects under changing management, environment, and biotic composition. To achieve this, we propose an integrated research approach (Figure 1). Direction and design of research will follow from the conceptual model---not from current or envisioned management practices, existing models, or concepts of processes taken out-of-context. The Program will sponsor research and develop models to better understand ecosystem function. We will continually search for simplification and generality as new methods and insights emerge. Both conceptual and predictive models will be tested in the near-term and over extensive periods.
Figure 1. Information flow in the PNW Station LTSP Program.
Most short- and long- term experimentation will occur on six to eight "Integrated Research Sites" distributed widely on National Forests in Oregon, Washington, and Alaska. These sites will be chosen to be representative of "general" forest land; land not given a single-use designation by the Forest (wilderness, riparian, spotted owl habitat areas, pine martin, viewsheds, etc..). These are lands the Forest Service expects to be managing for multiple-use over the next 50 years. Research will be tied across sites through research design and consistent methodology (minimum measurements, documentation, data and sample storage, and quality control). We are building a strong partnership with land managers, especially the National Forest System and the Bureau of Land Management, to facilitate installation of sites and eventual application of research results.
We have designed the Integrated Research Sites to allow small-scale process-level research to be linked with measurement of stand-level responses. We seek to increase integration by (1) having a common conceptual model that integrates a wide variety of biological disciplines; (2) having much of the work done on common sites with a common design; (3) supporting scientists committed to integration; and (4) developing close links with other related programs.
Our conceptual model strives to: (1) forge an integrated approach; (2) further develop the concept of sustainability; (3) guide formation of predictive models; (4) identify important research areas; and (5) help link with other research programs and models.
In its simplest form, our conceptual model is that long-term site productivity is the product of changes in the complex interaction between the biotic assemblage and abiotic environmental factors (Fig. 2). Activity of the biotic assemblage is ultimately controlled by its aggregate genetic composition (within and between species). Support for this model rests on the observation that living systems modify their environment, and thus, to a large extent, affect their own production and production of future assemblages.
Figure 2. The LTSP conceptual model: mechanisms of change in biotic-environment interactions (potential mechanisms are listed in Table 1; environmental variables and biotic fluxes are listed in Appendix 2)
Mechanisms of change will be explored in retrospective studies and short- and long-term experiments. We place initial emphasis on management-driven mechanisms (e.g., changes in species composition, initial changes in environment) as well as intrinsic ecological mechanisms (e.g., succession, soil development, senescence, ...).
Stand-level measures of physiology of forest ecosystems will be used to explore constraints on the rates of basic processes. We also seek a small set of measures that encompass the net effect of the many interactive ecosystem functions (Appendix 2). For example, animals and microbes make up a critical part of the biota and their physiological status may be as important to assess as that of vegetation (e.g., CO2 flux from the soil is greatly affected by roots, microbes, and animals through processes such as soil mixing, spore dispersal, and decomposition).
Management and ecological mechanisms that alter the biotic-environment complex are the primary driving force for short- and long- term changes in productivity. It follows implicitly (1) that specific management practices can sustain production in some environments for some assemblages but not in others; (2) that long-term site productivity can be altered by manipulating the biota, and; (3) that interpretations and predictions apply over a restricted range where the biota and environment are well specified.
Foresters have traditionally sought to index site productivity using the height growth patterns of dominant crop trees. A new vision of site productivity is needed because of increasing concern of the sustainability of entire ecosystems, greater emphasis on non-crop-tree products and values, and the potential for large changes in climate and management practices. As the LTSP Program develops, we expect to continually refine our definitions of productivity.
Our definition of forest productivity encompasses the view that the forest can provide a wide variety of benefits to society. Thus, forest productivity is the rate of production of specific products (e.g., timber, recreation, clean water, fisheries, wildlife...) and resource values (e.g., aesthetically pleasing landscapes, biodiversity, healthy wildlife populations, wilderness,...). Developing a single measure or index of forest productivity based on a specific product or resource value has obvious limitations, especially with shifting management objectives.
We propose to use actual ecosystem productivity, the measured rate of accumulation of organic matter in the ecosystem, as an integrative index of forest productivity. We also extend this concept to the redistribution of organic matter into (1) a wide range of specific products, (2) living plants, animals, and microbes, and (3) detrital pools (heartwood, standing dead trees, large woody debris, and various forms of litter and humus in soil horizons). The change in the rate of accumulation of organic matter over multiple rotations or generations, is the ultimate means of evaluating changes in long-term ecosystem productivity.
We recognize that individual measures of ecosystem productivity are insufficient by themselves to assess "sustainability" of managed or unmanaged ecosystems. Even trends in ecosystem productivity may not be sufficient to address some aspects of sustainability. Additional indicators of sustainability will be sought by the Program.
We define potential ecosystem productivity to be a theoretical maximum ecosystem productivity based on optimum rates of biologically controlled fluxes and specified environmental variables. The difference between actual and potential ecosystem productivity gives us insight into the relative limitations of local biota and, conversely, in other situations the relative limitations of the environment. This difference may also represent an investment in the productivity of subsequent biotic assemblages in anticipation of unknown future conditions (e.g., genetic and structural diversity and process redundancies related to past ecosystem history).
The primary output of LTSP models will be future ecosystem productivity. Models are needed to predict future productivity of ecosystems because of the complex interaction of mechanisms, biota, and environment over long time periods.
Models to predict future productivity
Modeling future productivity is a challenging, yet critical task. Most current predictive models suffer from inadequate information and untested assumptions. It is also often difficult to understand embedded assumptions in or confirm predictions from these models. We propose an alternative modeling approach based on further refinement of our conceptual model to predict long-term changes in ecosystem productivity and distribution of organic matter and imply effects on production of specific products and resource values (Fig. 3).
▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓LTSP predictive models▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
▓ ┌─────────────────────────────────────────┐ ▓
▓INPUT │Initial site-specific biotic/environment │ ▓
▓ │ conditions; management objectives │ ▓
▓ └──────────────────┬──────────────────────┘ ▓
▓ ┌──────────────────v──────────────────────┐ ▓
▓MECH │ Imposed or projected mechanisms of │<──┐ ▓
▓models │ change in biotic-environment complex │<─┐│ construc- ▓
▓ └──────────────────┬──────────────────────┘<┐││ tion ▓
▓ ┌──────────────────v──────────────────────┬─┘││ and ▓
▓BXE │ Biotic-Environment interactions model │<─│┤ testing ▓
▓models └──────────────────┬──────────────────────┘<┐││ ▓
▓ ┌──────────────────V──────────────────────┐ │││ ▓
▓OUTPUT │ Change in ecosystem productivity, C ├─┘││ ▓
▓ │ distribution implications for specific ├──┘│ ▓
▓ │ product production and resource values │ │ ▓
▓ └──────────────────┬──────────────────────┘ │ ▓
│Other non-LTSP models (Programs): │ │
│landscape-level disturbance models, C-channelling │ │
│models (New Perspectives); global C balance │ │
│(Climate Change); social implications (Social ├─┘
│Consortium); defining forest health (Forest Health│
│Program); evaluating functional biodiversity │
│(Biodiversity Team); Soil porosity-organic matter │
│interactions (USFS National long-term soil │
│productivity study) │
Figure 3. Initial ideas on LTSP predictive models and their relation to other models.
Initially, we propose to model the effects of sets of management practices and ecological processes as mechanisms that change the biotic-environment complex. Mechanism-induced changes in the biotic-environment complex would be detected by measuring biotic and environment variables that affect key processes (Appendix 2). By evaluating these relationships over a broad range of practices, biotic assemblages, and environments, we expect to develop relationships that are generally applicable throughout the region.
To allow extrapolation across regions, quantitative functions of models must have mechanistic plausibility and be easily verified. We accept the basic premise that it is easier to measure large changes in small quantities (e.g., the rate of a process) rather than small changes in large quantities (e.g., changes in pool size of carbon or nitrogen). The initial biotic-environment interaction model focuses on the flux and storage of carbon products controlled by linkage to a small set of all-encompassing variables that describe net function of the ecosystem.
Mechanisms that could bring about changes in the biotic-environment complex are quite numerous (Table 1). A model of all of these mechanisms and their interactions would seem to attempt to explain nearly all forest biology. This appears to be beyond our abilities at this time.
Initial focus and links to other programs and models
The LTSP Program appears best adapted to studying the biotic-environment complex and a limited set of mechanisms. We propose to study mechanisms that have a high potential for long-term effects, that have important stand-level components, and that can be altered by management practice or intrinsic ecological processes (e.g., succession, soil development, climate change, stand development, plant-animal-microbe interactions).
The LTSP Program investigations will be largely limited to stand and sub-stand spatial scales for three reasons: (1) we believe that we need to explore a wide range of treatments that would not be possible in larger scale experiments; (2) areas with uniform soil large enough for replicated long-term experiments may not be available at larger than stand-levels; and (3) integration of processes and ecosystem responses will be most efficient at the stand level due to existing measurement techniques and logistics.
Possible linkages with other research efforts can be best demonstrated as an exchange of information (Fig. 3). For example, General Circulation modelers acting through the PNW Global Climate Change Program could identify a range of likely shifts in climate variables to feed into LTSP biotic-environment, mechanism, and potential productivity models. Conversely, the LTSP Program and other PNW Programs will be able to provide information on changes in C capture and distribution that could be used to feed into or test climate models.
Given the complicated effects of management and changing environments on the biotic-environment complex, any outside efforts to explain mechanisms of change at any spatial or temporal scale will be eagerly followed. Such work will be especially valuable if it can suggest hypotheses that can be tested in stand-level experiments. Existing ecological process models could be evaluated with the biotic-environment interactions model.
We suggest the desirability of evaluating both upland and riparian sites because: (1) we would then be better able to tie in with land-water interface research, and evaluate specific products such as fisheries; (2) processes rates and mechanisms of change may be very different; and (3) riparian-upland interactions may greatly affect important mechanisms of change. Most of our National Forest System and Bureau of Land Management partners, however, want Integrated Research Sites to be on upland sites. We will explore the possibility of associated studies in riparian areas adjacent to selected upland sites.
Four main areas of research are now envisioned: (1) further development of conceptual and predictive models; (2) short-term experiments; (3) retrospective studies; and (4) long-term experiments. Most short- and long-term experiments will be established on Integrated Research Sites. Retrospective research will be carried out within broad geographic limits.
Conceptual and predictive model development
Further development is needed before the conceptual model can serve to direct research and shape predictive models. We will form a modeling team to pursue model definition and development during fiscal year 1991 (Table 2). After the conceptual/predictive models take form, we expect considerable effort will be required to develop cost-effective and accurate sampling techniques. Some computer simulation models are already available to predict water and nutrient, PAR, and gross primary productivity. New techniques and synthesis of existing ideas and technology will be needed to better measure belowground biotic activity, determine nutrient supplying potential of soil horizons, and gauge potential rooting depth. Emphasis will be given to evaluating spatial patterns and variability. The LTSP Program will seek to test methodology in conjunction with other ongoing programs supported by NASA, NSF (LTER), and EPA.
The primary role for short-term (<10 yr), small-scale (<0.1 ha) experiments will be to construct and initially test models developed by the modeling team. A major purpose of short-term experiments is to measure actual ecosystem productivity and C distribution and relate this to predictor variables. To induce differences in ecosystem productivity and C distribution in short-term experiments, treatments will have to be extreme, or soils will have to be homogenized to overcome natural variability.
Short-term experiments will take place on all of the widely dispersed Integrated Research Sites. For example, biotic composition could be altered by excluding large herbivores or by shifting the composition of plant, microbe, or less mobile animal populations. The environment might be altered, for example, by redistributing soil organic matter, varying large woody debris, or burning slash. We can even envision the possibility of carrying out common-soil or bioassay experiments across Integrated Research Sites. Assessing changes in the rates of key processes and establishing the biotic-environment interactions will improve our understanding of ecosystem function.
A second role for short-term experiments is to test major constituents of the treatments in long-term experiments such as role of individual plant species and the exclusion of large herbivores.
In many existing long-term studies, treatments established with single-discipline objectives have resulted in large ecosystem changes. We have the opportunity to re-evaluate treatments as changes in the biotic-environment complex. Examples of studies include species trials, herbicide experiments, growth and yield studies, animal exclosures, tree genetic trials, and slashburning studies.
Existing managed stands and natural disturbances may allow us to make comparisons of ecosystems with different mechanisms of change in the biotic-environment complex. Examples of these opportunities include past management activities, primary and secondary succession chronosequences, wildfire, and windthrows.
We need new methods to reconstruct disturbance history, and previous biotic composition and environments. For example, concentrations of nutrients and various isotopes in tree rings may give insights into changes in the biotic-environment complex. Detailed stem sectioning may reveal frequency of windstorms, or some types of insect attacks. Palynology might be used to evaluate a wide variety of longer-term changes. These methods are needed in retrospective studies and to establish baseline information in long-term experiments.
Retrospective studies will provide information that will be both useful by itself and useful in predictive models. For this reason, the Program will initiate some stand-alone retrospective projects in FY 1991. A retrospective study team (Sollins, Waring, Oliver, Tiedemann), formed in FY 1990, is developing guidelines for this research.
The conceptual model serves as a framework for designing site-specific treatments to be installed in long-term (100 year+), large scale (15-30 acre; Fig. 4) experiments at Integrated Research Sites. A set of treatments has been designed by the PNW LTSP Integrated Research Site team (Appendix 3) in conjunction with the development of this plan. Two series of long-term experiments will be carried out to look at the influence of: (I) different assemblages of biota and (II) manipulating the initial environmental conditions on subsequent productivity . In both cases, we will begin with existing, relatively even-aged, and uniform stands developed following natural disturbances. This approach minimizes the influence of previous management practices including planting, site preparation, and harvest removals and the influence of cumulative legacies in old-growth stands.
In the series I experiment, we evaluate the general idea that the biotic assemblage has a large long-term, sustained impact on its environment and thus greatly affects its own productivity and that of subsequent assemblages. We also recognize that one of the principal effects of most current management is to greatly shorten early and late successional stages, relative to natural successional patterns. For these reasons, we have decided to vary biota by manipulating successional patterns in four contrasting ways (Table 3). Specific hypotheses are being developed in the Integrated Research Site plan.
Series II treatments center around the idea that detritus pools are one of the more dynamic aspects of the environment and that changes in detritus are likely to affect subsequent biotic assemblages (Table 4). The cumulative effects of previous biotic assemblages and management activities such as harvesting and burning are expected to alter detritus pools such as standing dead vegetation, large woody debris, litter, and organic matter in soil horizons. The distribution, quality, and amount of detritus is closely tied to the biotic-environmental complex (e.g., nutrient cycling, soil structure, rooting depth, secondary producers,...). The treatments are designed to look at the extremes of removal and addition of key detrital components hypothesized to control subsequent productivity.
General research guidelines
Guidelines are needed to ensure that research activities meet the LTSP Program objectives. Of primary importance is the connection with our conceptual model by assessing mechanisms of change as well as the biotic-environment complex. We will invest in cooperative studies to link with other research programs as a means to obtain the broadest possible understanding.
It is the policy of the Program to support competitive funding where it is responsive to Program needs and not burdensome to the program and supported scientists. Competitive funds will be available in clearly defined research areas (retrospective studies and short-term experiments). Preliminary proposals (<5-pages) will be requested. A committee will choose two promising proposals in each research area and return them to the author(s) for completion of a more detailed proposal. One of the two proposals will be assured funding. This policy also means that some exploratory studies and modeling efforts, deemed of key importance, will not be funded competitively. Ongoing and planned studies of this type are: (1) further development of the conceptual and predictive models and, (2) the Existing Studies Project to develop guidelines for retrospective research.