Table

Listing of Ecosystem Services

Purification of air and water

Mitigation of floods and droughts

Detoxification and decomposition of wastes

Generation and renewal of soil and soil fertility

Pollination of crops and natural vegetation

Control of the vast majority of potential agricultural pests

Dispersal of seeds and translocation of nutrients

Maintenance of biodiversity, from which humanity has derived key elements of its agricultural, medicinal, and industrial enterprise

Protection from the sun's harmful ultraviolet rays

Partial stabilization of climate

Moderation of temperature extremes and the force of winds and waves Support of diverse human cultures

Providing of aesthetic beauty and intellectual stimulation that lift the human spirit

Source: Adapted from Daily, G. C. (ed.). 1997. Nature's Services. Island Press, Washington, DC.

approach is an overestimate because it implicitly includes values beyond what society is normally prepared to acknowledge. Other applications of the life-support calculation, all of which happen to involve coastal wetlands, are given by Lugo and Brinson (1979), Faber and Costanza (1987), and Costanza et al. (1989).

Probably for various reasons attention has turned in a different direction, and there has been no recent application of the life-support approach to ecosystem valuation. The discussion by ecological economists has evolved to focus on what are termed ecosystem services (Daily, 1997; Daily et al., 1997, 2000; Dakers, 2002; Ehrlich and Mooney, 1983; van Wilgen et al., 1996; Westman, 1977), which essentially constitute life-support functions (Table 8.6). The approach is to identify individual services that ecosystems provide to society and to estimate their value based on methods that are more consistent with classical economics, such as the "willingness-to-pay" approach. A fundamental difference between life-support and ecosystem services revolves around using one number as a measure of value (i.e., ecosystem metabolism) or breaking down a number of individual measures of value (various ecosystem services). The most extensive calculation of ecosystem services is given by Costanza et al. (1997b) who estimated a biosphere value of $16 to 54 trillion (1012) per year with an average of $33 trillion per year for global ecosystem services, which is greater than the global gross national product of strictly economic flows at $18 trillion per year.

These approaches are very relevant to ecological engineering, which involves the construction of new ecosystems to solve problems. These new ecosystems will contribute life-support values and ecosystem services to society beyond their intended purposes. Thus, each new constructed ecosystem, such as a treatment wetland or even a microcosm, adds to the life-support capacity of the environment. Some feasibility studies in ecological engineering are being undertaken to account for this kind of value and the interest can only be expected to grow in the future.

A related valuation approach is to calculate the value of an ecosystem as the cost required to replace it. This is also very relevant to ecological engineering in regard to restoration ecology and associated fields, which seek the least expensive method of ecosystem creation.

Natural Capital, Sustainability, and Carrying Capacity

Ecological economics includes many other ideas that relate to ecological engineering. One example is the concept of natural capital, which is analogous to human capital traditionally considered by economists (Prugh et al., 1995). In a sense, natural capital is the structure of the biosphere's economy from which ecosystem services flow. The concept is described below by Costanza et al. (1997a):

Thinking of the natural environment as "natural capital" is in some ways unsatisfactory, but useful within limits. We may define capital broadly as a stock of something that yields a flow of useful goods or services. Traditionally capital was defined as produced means of production, which we call here human-made capital, as distinct from natural capital which, though not made by man, is nevertheless functionally a stock that yields a flow of useful goods and services. We can distinguish renewable from nonrenewable natural capital, and marketed from nonmarketed natural capital, giving four cross-categories. Pricing natural capital, especially nonmarketable natural capital, is so far an intractable problem, ... All that need be recognized for the argument at hand is that natural capital consists of physical stocks that are complementary to human-made capital.

Although this concept has been developed by ecological economists, Wes Jackson, an environmentalist and agroecologist, introduced the term ecological capital in his proposed revision of modern agriculture (Jackson, 1980). Jackson elaborated his conception in terms of topsoil, with concern for erosion. Figure 8.5 illustrates the data he provides as a simple mass balance analogous to a bank account. The storage of topsoil represents natural or ecological capital, which is produced slowly by biogeochemical processes and soil management procedures but drained relatively quickly by agricultural erosion. Jackson's proposed switch to perennial plant species for crop production, along with other techniques such as no-till cultivation, reduces erosion and allows for greater accumulations of natural capital (in terms of topsoil storage) by agricultural systems. Thus, Jackson presaged the ecological economics concept of natural capital with his metaphor about the value of topsoil.

The natural capital concept has led to a macroeconomics perspective for ecological economics. Developments include the incorporation of natural resources into national-scale accounting (Repetto et al., 1989, 1999) and alternative indices such as the index of sustainable economic welfare (Costanza et al., 1997a; Daly and Cobb, 1989) that provide different perspectives from traditional measures, like gross national product.

FIGURE 8.5 Energy circuit diagram of the system used by Jackson (1980) to discuss the concept of "ecological capital," shown by the storage of topsoil on a farm. Flows are in units of tons/acre/year and the storage is in units of tons/acre, assuming a 4-in. topsoil layer. These values are typical of U.S. agriculture.

Agricultural Erosion

FIGURE 8.5 Energy circuit diagram of the system used by Jackson (1980) to discuss the concept of "ecological capital," shown by the storage of topsoil on a farm. Flows are in units of tons/acre/year and the storage is in units of tons/acre, assuming a 4-in. topsoil layer. These values are typical of U.S. agriculture.

Another important topic in ecological economics is the creation of new kinds of economies that are sustainable over long time periods. Ecological engineering can help society move towards sustainability by reducing costs and by utilizing natural, renewable energy sources. The concept of sustainable development covers many adaptations of society for long-term survival, of which ecological engineering is one of several recent advancements. In this larger context, ecological engineering can play an important role for society as a whole. Two definitions of sustainable development are given below:

1. To live on renewable income and to not deplete natural capital

2. To provide for the needs of the present generation without sacrificing the ability of future generations to meet their needs

A significant contribution from ecological economics has been to differentiate between aspects of growth and development in thinking about sustainable development of an economy (Costanza and Daly, 1992). As noted by Costanza et al. (1997a),

Improvement in human welfare can come about by pushing more matter-energy through the economy, or by squeezing more human want satisfaction out of each unit of matter-energy that passes through. These two processes are so different in their effect on the environment that we must stop conflating them. Better to refer to throughput increase as growth, and efficiency increase as development. Growth is destructive of natural capital and beyond some point will cost us more than it is worth — that is, sacrificed natural capital will be worth more than the extra man-made capital whose production necessitated the sacrifice. At this point growth has become anti-economic, impoverishing rather that enriching. Development, or qualitative improvement, is not at the expense of natural capital. There are clear economic limits to growth, but not to development.

The great challenge of sustainability is a kind of social engineering. Ecological economists not only must help design new systems of resource use but also must find ways to change people's attitudes so that they can change from consumptive lifestyles to sustainable lifestyles. This is a major challenge and the long-term fate of global civilization may depend on its outcome.

One approach to sustainability is to establish the carrying capacity of a system for humans. Carrying capacity is the maximum number of individuals of a population that can be stably maintained in a given environment. It is an important ecological concept that has developed from both mathematical population biology and wildlife management. In mathematical population biology, carrying capacity is a constant (K) developed for the logistic growth equation (see Chapters 3 and 7) that represents the equilibrium population size. It is an asymptote that a population grows up toward when starting from low initial conditions. The mathematical concept was first used by Pierre Verhulst in the early 1800s, but it was "rediscovered" in the early 1900s by Raymond Pearl who incorporated it into modern population biology (Kingsland, 1985). In wildlife management, carrying capacity was defined as the "maximum density of wild game which a particular range is capable of carrying" (Leopold, 1933). It is usually related to the amount of food, water, and cover available to the animals. While this basic definition is quite simple and straightforward, the concept has been used in different ways (Edwards and Fowle, 1955). If a carrying capacity for humans could be established, then the limits to sustainability could be known. This is a critical and controversial subject (Cohen, 1995; Daly, 1995; Hardin, 1986; H. T. Odum, 1976; Sagoff, 1995). One of the latest developments along this line of thought is ecological footprint analysis which attempts to calculate the land and water areas required to support human communities (Wackernagel and Rees, 1996; Wackernagel et al., 1999).

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