It can be really difficult to say if a particular activity is sustainable or not. The definition of sustainable development as provided by Gro Brundtland's Commission on Environment and Development involves maintaining benefits for future generations. That is very general and conceptual. So how does one know it when one sees it?

The answer, I believe, lies in tying it to a particular piece of landscape with some ecological cohesion. An example would be South Florida - stretching from the Kissimee River north of Lake Okeechobee down through the great sweep of the Everglades and including Florida Bay, the Keys and the reefs beyond. Its unity relates to a sheet flow of freshwater from north to south.

Enough has been done to South Florida's hydrology that today only a quarter to a half of normal freshwater flow reaches Florida Bay in any given year. The consequences are adverse affects on biological diversity including the fauna and flora of the Everglades Park, the waters of Florida Bay and even shrimp fishery. Today a massive effort is underway in ecosystem management and ecological restoration to reverse the negative trends.

Ecosystem management has twin, related goals, namely to conserve characteristic biodiversity and maintain ecosystem processes. The first, one might think of as managing the ecosystem so the species list of the natural (restored) South Florida Ecosystem would be the same a hundred or a thousand years from now as it should be today. The second would include the sheet flow of water and other natural flows and cycles of nutrients.

All environmental problems end up affecting biological diversity (e.g. pollution reduces the number and affects the kind of species). Consequently, biodiversity integrates all other environmental problems. So to maintain the characteristic species list, it is necessary to consider all factors intrinsic and extrinsic to the geographic unit.

Basically any set of human activities occurring within the ecosystem that does not interfere with maintaining characteristic biodiversity and ecosystem function is acceptable. This provides a lot of flexibility for human aspiration if the unit of landscape is large enough and not too heavily impacted already.

The social and economic aspects of sustainability must of course be part of this. If they are not dealt with in their own right, they will begin to affect biodiversity and ecosystem process. A first step is recognizing ecosystem values that currently are treated as free goods. An example would be paying landowners in a watershed for the water their lands provide.

Obviously this sets limits on just how much agriculture can occur within one of these large units of landscape, and pesticide use and fertilizer use can be matters of real concern.

It is instructive to consider the effects of the Green Revolution, which did so much to increase agricultural production around the world by intensifying agriculture (increasing the yield per acre). Genetics of major crop species played a major role (as did genes from wild relatives) but so did fertilizer and pesticide use. These latter are often regarded as negative consequences of the Green Revolution. They certainly did affect biodiversity and ecosystems.

At the same time a hugely important benefit of the Green Revolution is often overlooked: the millions of acres of natural habitat that would have been destroyed to create agricultural land if more land had been used because of lower yields per acre. A lot of natural areas and biodiversity survive because of this. A similar benefit for nature stems from the implosion of rural populations into cities in most parts of the developing world. As a consequence, those concerned about the future of nature have a vested interest in better quality of life in those cities so there is not a reverse trend back to the countryside.

Looking ahead from today's 6 billion population to billions more, clearly the world's agricultural effort will have to provide a larger harvest. Ideally this should be relatively intensive in its use of land, and biotechnology and genetic engineering can, I believe, make important contributions to that.

Yet any technology is neutral; it can be used for good or for ill. Inevitably there will be surprises. Soil biodiversity is part of sustainable ecosystem management too and fundamental to generation of soil fertility. So the impact of fertilizers and herbicides and their interactions have to be better understood. A complex research agenda is needed to determine both the better ways to use this new capability and ways we should eschew.

Genetic engineering has come in a rush, providing a great new power to manipulate living systems for human benefit. I believe the potential is enormous. But so are the challenges deriving from technology that is mysterious and to some fearful, and from a world in which agriculture operations from an industrial scale to poor farmers eking out an existence must all be addressed. Unless they are, sustainability will be naught but a dream. If they are, it will contribute to a much better future for ourselves and life on Earth.

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