with system management objectives.

T.W.HOEKSTRA, T.F.H.Allen, J.KAY, J.A.TAINTER

INTRODUCTION

Sustainability has become a widely used term that begs clarification of the question, sustainability relative to what? For the purposes of this paper we use the term to describe social and ecological systems. Sustainability is a system condition, a relative term that describes a relative condition. Fortunately, the concept can be tangibly described using system attributes of structure or process. For the purposes of this paper, then, we define sustainability of ecological and social systems on the basis of their structures and processes. Kinds of social (i.e., communities) and ecological (i.e. landscapes) systems are a basic organizing principle. The intent here is to present a brief background of how we view sustainability of social and ecological systems, and how to use criteria and indicators to judge whether the systems are either sustaining or not. There is no middle ground (Allen and Hoekstra, 1994).

We approach the subject of sustainability from a hierarchical theoretical perspective. The principles of hierarchy theory allow us to manage the complexity of the social and ecological systems we are interested in. As participants and observers in many social and ecological systems ( Allen, et al., 1984; Hoekstra, et al., 1991), we need to identify time and space scale of the systems to objectively evaluate sustainability. Structures and processes that compose each kind of ecological and social system are fundamental system properties. By definition they are the criteria and indicators that describe the kinds of systems. System structures and processes are therefore the measured variables for determining sustainability.

An additional principle of hierarchy theory specifies that, in understanding systems, it is necessary to consider the next larger system as the context and the next smallest system as being influenced by the system of interest. Therefore, when we describe a social or ecological system about which sustainability is of particular interest, the context and content of associated systems are also important. Allen and Starr (1982) devised working principles for observing complexity of ecological systems based on their work in the social sciences. Allen et al. (1984) and Allen and Hoekstra (1990) provided further principles for handling complexity. Allen and Hoekstra (1992) described guidelines for stratification of observations by kind of ecological system as separate from the scale of ecological systems. Tainter's (1988) thorough exposition of the basis for collapse of historic civilizations has important implications to the sustainability of our current civilization(s).

Sustainability of ecological and social systems is not only a matter to be evaluated within a hierarchy of the same system, but also between kinds of systems. The means by which those interactions are described involve the same structure and function attributes that occur within a system, except the focus is on variables the interacting systems have in common. An explanation for systems therefore needs to also acknowledge that there are structures and processes that provide for interaction between ecological and social systems. For example, organism structure of both plants and animals is identifiable in several ecological systems, and therefore is a frequent structure for observing interacting ecological systems. Humans are the archetype organism for understanding of the interaction between social and ecological systems. Processes within social systems are almost exclusively human processes. For example, both families and communities are highly interactive with various ecological systems.

A full determination of sustainability not only involves a description of current conditions of system structure and function, but also a measure of change over time and space in the condition of structural and functional variables. The observation of importance is oriented toward the future, not the past. Systems evolve over time and space, and the evaluation of change is focused on whether the system will continue to be sustainable or not. Whether the system was sustainable or not in the past is of little value for evaluating the current situation, or to provide guidance for the what the future of a system should be.

CRITERIA AND INDICATORS FOR SUSTAINABILITY

Social and ecological systems have numerous structures and processes that could be used to determine the likelihood of sustainability. In fact, any structure or process has the potential to be a key determinant as to whether a system is sustainable. An exhaustive treatment of all structures and processes is beyond the scope of this paper and probably unnecessary for any determination of sustainability. Therefore, we identified those structures and processes we believe have major implications for determining sustainability of ecological and social systems. In addition to key criteria and indicators for a system, we have described a management objective for that system which would be the context for the criteria and indicators. The remainder of this paper is organized to present first the ecological criteria and indicators, then social criteria and indicators, and finally those that describe social and ecological system interactions.

ECOLOGICAL CRITERIA AND INDICATORS

During the last 100 years, we have slowly established subdisciplines to the general body of ecological knowledge. Early in this period, we differentiated animal and plant ecology, and later added the subdisciplines of community, ecosystem, landscape, and population ecology. These subdisciplines represent substantial bodies of literature and knowledge of ecology, often with their own professional societies, both of which are valuable in assisting managers with sustainable management efforts. The knowledge and understanding associated with these subdisciplines are an important basis for our description for kinds of ecological systems. Ecology as a whole is a complex subject, and it was only through application of hierarchy theory (Allen and Starr, 1982; Allen and Hoekstra, 1992) that we were able to find a tractable means of establishing a framework for considering social and ecological sustainability. The discussion that follows is a brief description of the application of that framework for managing the complex concept of sustainability.

Population Systems

Population systems include both plants and animals. Management should focus on viability of populations that are threatened, endangered, sensitive, exotic, or excessive. Such populations are not sustainable or not contributing to sustainability of other systems. They require different management objectives than viable populations. Populations not in the above categories are more probably viable, and only need to be monitored. The essential criteria and indicators available for management activity to accomplish the objective can be described as follows:

• Structure

1. Density
1. Age class
2. Sex ratio
3. Distribution of populations within meta populations

• Process

1. Reproductive rate

2. Mortality rate

3. Immigration rate

4. Emigration rate

Organism Systems

Organisms also describe both plant and animal systems. Management should focus on maintaining the vigor of the individual through a normal life span, enabling it to perform all the normal functions of individuals in its age, sex, and caste class. Individuals at the periphery of the species distribution are subjected to relatively greater environmental stress than individuals at the center of the distribution and may not be capable of full normal functioning. Organisms in these peripheral situations may require modified management objectives. The essential criteria and indicators to assess whether management objectives are being met can be described as follows:

• Structure

1. Genetic code (i.e. cloning, hybridization, etc.)
1. Hard and soft tissue alteration

• Process

1. Reproduction physiology
1. Other physiological process for metabolism/catabolism
2. Environmental conditioning

Ecosystem

Ecosystems are very different ecological systems from population and organism kinds of systems. In ecosystems, organisms need be identified only as stores of matter and as energy processors. Populations need not be identified in ecosystems. Different kinds of organisms often have similar roles (types of function) in ecosystems and therefore the species involved are only marginally of interest. Organisms and ecosystems, as kinds of systems, have a high degree of interaction in terms of both structure and function. The objective of management is to degrade energy and maintain nutrients to fuel/facilitate the degradation process. The objective can also be stated as making the fullest use of energy available through the bio-geo-physical processes. Ecosystems can be generalized as cycles where energy is stored in structures upon which processes operate to degrade that energy when it moves to the next structure(s) in the cycle. The essential structures of an ecosystem are organisms, soil, air, and water. The physical and chemical processes in nutrient and hydrologic cycles, and the physiological processes in biological organisms, are examples of ecosystem processes that degrade and build ecosystem structures. Examples of metrics for measuring ecosystem processes include surface temperature, water chemistry, sediment loads, and water yield from systems. The essential criteria and indicators available for assessing management activity to accomplish its objective can be described as follows:

• Structure

1. Collections of organisms
1. Soil
2. Water

• Processes

1. Chemical (mass balance)
1. Physical (rate at which available energy is being used)

Landscape Systems

Landscapes are again a very different kind of system from ecosystems, populations, and organisms. Because landscapes are geographic, their structure and process components are expressed in geographic outcomes; landscape areas and their boundaries are key structural components. Ecosystems, communities, and populations frequently have boundaries that are coincident with landscapes, which is not surprising since some of the landscape processes are interactions of the same processes of other ecological systems. Many significant landscape processes in the present world are the result of the activities of one organism, man. We observe landscapes as the size, shape, and distribution of relatively homogeneous geographic areas. Landscape hierarchies occur as a result of our reductionist attempts to refine the homogeneity of landscapes. However, landscapes always contain some heterogeneous attributes, regardless of scale. The objective of management is to achieve a shifting steady state mosaic of geographic units that positively accommodates the sustainability requirements of ecosystem, population, and community interactions. For example, landscape management objectives should accommodate all seral stages of a plant community with the different species populations associated with those seral stages. The essential criteria and indicators available to assess management activity to accomplish the objective can be described as follows:

• Structure

1. Size of the landscape
1. Shape of the landscape
2. Distribution of similar landscapes

• Processes

1. Organism processes, i.e. change agents that alter the homogeneity of landscape types such as bison altering prairie plant composition by wallowing, man by implementing land use changes, etc.
1. Population processes, i.e. regeneration, mortality, and emigration altering the species composition of communities.
2. Ecosystem processes, i.e. hydrogeomorphic processes that alter stream and associated terrestrial boundaries.
3. Community processes, i.e. fires that alter species composition and seral stages changing the homogeneity of landscapes.

Community Systems

Community systems are the result of individual organisms interacting with each other in time and space. Organism interactions are usually well defined by community processes such as competition, predation, parasitism, mutualism, etc. These processes are the unique domain of community ecology. In addition, organism/organism interactions in communities are also in part the result of regeneration activities of the species, a population process also. Finally, organism interactions in conjunction with disturbances such as fire can alter the competitive balance between organisms and have landscapes consequences.

Community processes establish dependency networks between organisms, and between species, that go beyond simple interactions between individual organisms or species. Thus species belong to species groups within a community. Seral stages are one example of such groupings. The objective of management is to maintain the functional presence of organisms and species -- and groups of organisms and species -- that occur in a community.

• Structures

1. Organisms
1. Species

• Processes

1. Competition
1. Predation
2. Mutualism
3. Commensalism
4. Parasitism

Biome Systems

Biomes are represented by plant and animal life forms in response to the geo-physical environment (climate and soils). Generally recognized biomes are named by the dominant vegetation lifeform: coniferous, deciduous, tall grass, etc. Biomes tend to elicit pictures of large- scale landscapes in our minds. In addition, ecological systems of smaller scale -- referred to as community disclimaxes, such as frost pockets -- can also be considered to meet the definition of biomes. The point here is that ecological systems such as biomes are also multiscaled. The objective of management is to maintain the life form interactions with their environment.

• Structure

1. Kinds of lifeforms

• Processes

1. Organism physiological processes (key)
1. Community processes (secondary)
2. Population processes (secondary)
3. Ecosystem processes (secondary).

SOCIAL CRITERIA AND INDICATORS

The differentiation between social and ecological criteria is the result of the unique role man has in the material world. The simplest explanation is that man is nothing more than another organism/species that exists in the natural world. However, two significant attributes of man require us to look beyond that simple explanation. First, the entire explanation of the biosphere we live in is based on man's unique perception and value system. Other organisms might describe a very different picture. Thus we must be cautious about representing our perception as more than just that.

The second attribute of man's role is associated with our intentional appropriation of the biosphere and all it contains for our benefit. What we consider to be our benefit has evolved with our level of knowledge and our welfare. Early on it was purely a simple matter of survival, like all other organisms. More recently, we have acknowledged the value of other organisms and their long-term existence along with man. It is the latter value that in some measure brings us to the consideration of sustainability. Social values therefore include both those that describe man as a participating organism/species in other ecological systems, and those that describe how we value the biosphere with all its ecological systems upon which we exist.

Determination of social sustainability depends upon the kind of social system. Kinds of social systems range from individuals, families, and communities to national and global systems. The focus of this paper is on smaller, commodity-dependent community systems and their associated families and individuals. Although these smaller communities are the focus of the criteria and indicators that follow, we also need to recognize the upper-level context that communities exist within. We also need to explicitly describe the temporal and spatial scale associated with any determination of sustainability for these community systems. Sustainability of social systems, like ecological systems, involves both structure and process considerations. The management objective is to facilitate/assure that small, commodity-dependent communities continue to exist in a desirable state of social and economic well being.

Criteria and indicators of sustainability assess the structure and process components of this social system. These indicators focus on the well being of small communities that depend upon producing and/or processing commodities such as forest or agricultural products. These communities are vulnerable to changing social values from larger social systems (i.e. state, nation). Medium-sized and large communities are less dependent upon commodity production because of additional income and employment by manufacturing, retailing, and service sectors of the social system. Social system structures and processes interact between communities at different scales, and thereby become the means for understanding and describing the hierarchical relationship.

• Structure indicators

1. Is the rank-size distribution of communities within the ecological system management unit changing in a direction unfavorable to smaller sized communities?
1. Is the distribution of monetary incomes in the area of the ecological system management unit becoming more or less equitable?
2. Is the population age distribution among smaller communities within the forest management unit stable, becoming older, or becoming younger?
3. Is the number of locally-owned businesses stable or increasing?
4. Is the number of businesses in smaller communities stable or increasing?
5. Is the level of economic activity among businesses in smaller communities stable or increasing?
6. Is the availability and feasibility of diverse economic pursuits stable or increasing?
7. Is the travel distance to basic goods and services stable or increasing?
8. Are cultural institutions (e.g. theaters, museums, churches) stable or increasing in variety and number across all communities within the ecological system management unit?
9. Is the physical infrastructure of the communities being maintained or extended?
10. Is there a full suite of government services within the area of the ecological system management unit?
11. Does local government have a land-use planning mechanism that helps to ensure community stability?
12. Does the local land-use planning mechanism operate cooperatively with the ecological system management planning mechanism?
13. Do non-government organizations provide a stable or expanding suite of services to the population of the ecological system management unit?

• Process indicators

1. Are family monetary incomes within the ecological system management unit stable or increasing?
1. Is access to capitol investment funds within the ecological system management unit stable or increasing?
2. Is the net capitol monetary inflow stable or increasing?
3. Is the proportion of children choosing to remain in smaller communities stable or increasing?
4. Are people's expectations of their communities' future being met?
5. Is access to vital forest resources stable or increasing (within the ecological systems capacity)?
6. Are human subsidies from outside the ecological system management unit decreasing (e.g. redistribution of wealth by federal and state governments)?
7. Is the ratio of property value to local income stable?
8. Is the ratio of state and federal income tax to local tax stable?
9. Is the community sense of social/cultural identity stable or at a desired level?
10. Is consensual dispute resolution (in e.g. ecological system management) stable or increasing?
11. Is the external institutional context of the ecological system management unit responsive to local needs?
12. Is there an increasing flow of information between local communities and their context beyond the ecological system management unit?

SOCIAL AND ECOLOGICAL SYSTEM INTERACTION INDICATORS

Social and ecological system criteria and indicators are also indicators of sustainable management. These are processes that describe those human organism/species interactions with ecological systems where man purposefully influences his environment to improve his various forms of welfare. The objectives for management are several and focused on maintaining the balance between meeting man's needs and the environment's needs for ecological sustainability. The principles of sustainable management objectives include the following:

1. Manage for the system rather than for outputs,
1. Manage systems by providing their context,
2. Employ natural subsidies whenever possible,
3. Employ positive feedbacks whenever possible.

Social and ecological system interaction criteria and indicators include the following:

1. Is the contribution from the ecological system management unit to regional, national, and global indicators of social and ecological sustainability stable or increasing? (Think globally and act locally).
1. Is the use of vegetation, fauna, soil, and water resources at a level that is sustainable over the long-term without degrading productive capacity of the ecological systems?
2. Are there effective education and/or information transfer programs to inform people within the area of the ecological system management unit about the sustainable productive capacities of the ecological systems, and about the management actions necessary to secure sustainable production?
3. Is the availability of ecological systems for amenity uses stable or increasing?
4. What portion of economic activity in small communities originates from the ecological system management unit lands?
5. Do people within the area of the ecological system management unit have stable access to resources for basic needs such as fuel, subsistence foods, religious rites, and medicinal plants?
6. Is the range of ecological system management unit activities and uses constrained by the values and preferences of local communities?
7. To what extent do local communities participate in deciding the management direction of the ecological system management unit?
8. To what extent is the ecological system management unit dependent upon local communities for labor and expertise?

CONCLUSIONS

Management for sustainable ecological and social systems is sufficiently complex that it is inadequately conceived of or applied as a whole. Two approaches have been used to deal with the complexity. One uses indicators as a means of generalizing complex conditions. We present an alternative for handling complexity by using a framework of social and ecological systems with their unique and shared structural and process components. This framework allows choices about which kinds of social and ecological systems (and their interactions) should be included in any determination of sustainability, while retaining the detail about those systems to explicitly understand the consequences of management activities. Criteria and indicators are geared to specific structures, processes and interactions. Generalized indices, by contrast, are more difficult to interpret and evaluate. Finally, this paper describes a first approximation of these ideas that will surely evolve as additional ideas and application of these ideas are tested.

REFERENCES