A sustainable activity or use is one which, in practice as well as principle, can continue forever. It can be argued that sustainability is essentially a homocentric concept, since the touchstone of moral value remains the effect that actions will have upon the quality or continuance of human life. The idea of sustainable development is ambiguous in that it can be given a technocentric slant, in which environmental conservation criteria are traded-off against economic development criteria, or a more radical, ecocentric spin, which emphasises the constraints on human activity that must be accepted if biospheric systems are to be protected against further life threatening deterioration. The Brundtland Report is inclined to regard species and ecosystems as resources for humans rather than things which have intrinsic value. However, it recognises that the quality of human life can only be guaranteed if it does not put excessive demands upon the carrying capacity of the supporting ecosystems. Following Callicott and Mumford, we may prefer the term ‘ecological sustainability’ to the term ‘sustainable development’. The latter is often taken to imply (or at least condone) continued economic growth, whereas the former encourages a vision of steady-state economic development in which human wants are met through greater efficiency rather than an increased consumption of resources.
Following Brundtland, the principles of sustainability received further definition in Conserving the World’s Biological Diversity. Of particular interest is the set of ethical principles suggested by the authors of this document, which represent an attempt to get beyond ‘resourcist’ thinking. They are based upon the idea of interdependence: ‘humanity is part of nature, and humans are subject to the same immutable ecological laws as all other species on the planet’, from which it follows that sustainability must be ‘the basic principle of all social and economic development. Personal and social values should be chosen to accentuate the richness of flora, fauna and human experience.’ So far these principles could be construed as homocentric, as could the report’s insistence that the well-being of future generations is a social responsibility of the present generation. However, the document also embraces Naess’s principle of biocentric egalitarianism when it states, ‘All species have an inherent right to exist. The ecological processes that support the integrity of the biosphere and its diverse species, landscapes and habitats are to be maintained.’
The report’s attempt to balance the ecocentric with the homocentric is valiant. It attempts to draw a parallel between conserving species diversity and encouraging diversity in ethnic and cultural outlooks towards nature. In doing so, it inevitably ducks some of the difficult, maybe even intractable, conflicts that are sure to arise when the effects of particular cultures or lifestyles are examined closely. Nevertheless, its overall thrust is surely right; it acknowledges ecological limits within which human society must work, but emphasises that these are not limits to human endeavour; ‘instead, they give direction and guidance as to how human affairs can sustain environmental stability and diversity’. If Norton’s convergence hypothesis is right, the steps taken to implement such a policy of sustainable development should also meet most of the concerns of the deep ecologists. What the landscape architectural profession requires, at this stage in its development, is a revised system of values which places sustainability alongside the more traditional interests in aesthetics and utility, together with credible visions of how these three value areas may be combined in realisable landscapes.