Author: Dr. D. Kgathi, Sustainable Resource Manager, National Institute of Development Research and Documentation, University of Botswana. Gaborone, Private Bag 0022, Botswana

Sustainable development and sustainability are common notions in development literature. Their meanings are debated by scholars across a wide range of disciplines, and have become standard topics for scholarly debates. The World Commission on Environment and Development (1987) defines sustainable development as development that ‘meets the needs of the present without compromising the ability of future generations to meet their own needs’. In other words sustainable development means that the well being of the people should at least be increasing over-time. This concept is clearly broader than the concept of sustainable economic growth which means that real per capita GNP is increasing over-time, and is sustainable, and does not mean that the well-being of people is necessarily increasing over-time (Pearce et al, 1990). For sustainable development to take place it is necessary that "the exploitation of resources, the direction of investments, the orientation of technological development, and institutional change are all in harmony" (World Commission on Environment and Development, 1987).

Sustainable development is concerned about inter-generational equity, and should not be confused with "optimal development" which is concerned with maximising the future well being of individuals, regardless of whether sustainability is achieved or not (Pearce et al, 1994). It therefore requires, par excellence, that the future generations should not inherit the level of welfare less than that of the present generations. In order for the welfare of future generations to be sustainable, it is also important to ensure that the present generations do not become impoverished so that there should be some wealth for the future generations to inherit (Turner, 1993).

Sustainability is concerned about the extent to which the stocks of capital (in a broader sense) are enduring or lasting. It is not only concerned about the conservation of the environment, but also about questions of economic efficiency and equity. As Becker et al (1990) put it, "sustainability refers to the viability of socially shaped relationships between society and nature over long periods of time". The notion of sustainability is based on two fundamental principles known as "quantity and quality sustainability" (Pearce et al 1994). The former requires that the quantity of natural resources should not decline over-time as this may reduce their total supply. It requires that natural resources should not be used at a rate which exceeds their rate of replenishment. The latter principle of sustainability requires that the quality of natural resources should not decline over-time as this may reduce their value (Pearce et al, 1994).

There are two concepts of sustainability known as "weak sustainability" and "strong sustainability" Pearce et al, 1994). The former approach is not concerned about the form in which the stocks of capital (man made, natural and human) are passed to future generations. As long as future generations obtain stocks of capital not less than those of the present generation, the conditions of sustainable development are satisfied even if this is done at the expense of drawing down the stocks of natural capital (Gowdy, 1999). A number of scholars have criticised this notion, particularly the assumption that natural capital is substitutable, and can be expressed in monetary terms (Gowdy, 1999).

The "strong sustainability" approach is not only concerned about keeping the aggregate stocks of capital constant, but it also requires that the stocks of natural capital (ecological assets) should not decrease over-time (Pearce et al, 1994). This is mainly because natural capital is associated with ecological assets, which are non-substitutable, and very essential for the welfare and survival of human beings. These assets are often referred to as "critical natural capital". Examples of "critical natural capital" include biological diversity, ozone layer, and carbon cycle (Pearce et al, 1994). This suggests that environmental problems such as global warming, ozone layer depletion, and land degradation will tend to deplete "critical natural capital". This notion is, however, criticised for its failure to address the conflict that arises between social, economic, and environmental sustainability (Gowdy, 1999).

The three concepts mentioned above also define sustainability in another context. Environmental sustainability is defined as "a process of maintaining or improving the integrity of the life support system of the earth" (Holdren et al, 1998). The maintenance and improvement of the life support system of the earth is a necessary condition for welfare of the present and future generations. Economic sustainability, on the other hand, is the maintenance of the stocks of capital or assets in order to produce a non-declining set of benefits (Munasinge, 1995). Simply stated, this is a situation whereby an investment produces non-declining or constant benefits over-time or leads to "constant stream of consumption" over-time (Munasinghe, 1995).

Social sustainability as the name suggests is concerned about the "conservation of social and cultural diversity" (Munasinghe, 1995:31). It is about the preservation of indigenous knowledge on sustainable development, strengthening of institutions that manage natural resources, and more importantly, intragenerational and intergenerational equity (Munasinge, 1995; Mc Neely, 1997). What this means is that the issues of equity, gender equality, and democracy are central to the notion of social sustainability. Also, social sustainability cannot be achieved without environmental sustainability. As Sachs (1999) puts it " there is no social development ethics without environmental wisdom, and conversely, no environmental wisdom without social development ethics".

In the natural sciences, sustainability is sometimes defined in the context of resilience, which is "the ability of an ecosystem to maintain its structure and patterns of behaviour in the face of external disturbance" (Pearce et al 1989). In the agricultural sciences, sustainability so defined refers to the ability of the system to maintain production when faced with stress or shock. Stress is a predictable disturbance on agricultural production caused by such factors as soil erosion, waterlogging, salinity, and indebtedness (Pearce et al; Conway and Barbier, 19900. Shock refers to unpredictable factors such as severe drought, increase in agricultural inputs, and damage of crops by animals and pests (Conway and Barbier, 1990 and Pearce et al, 1989). An agricultural ecosystem is a man-made simplified ecosystem which has replaced a relatively more complex natural biological communities (Ethrlich et al 1973). In managed and natural ecosystems, the resilience will vary, depending on whether "the external disturbance is sudden a shock or a cumulative, continuous stress" (Pearce et al, 1989). It is important for agricultural systems to maintain their resilience, as the failure to do so may render them vulnerable to other shocks (Markandya, 1993).

     If you have entered this site from UNEP.NET or SCOPE, then feel free to use the link below to view the full site.