nable development requires that current actions be prohibited if they lead to the average person in the future enjoying less well-being. To use the jargon, sustainable development is a development path along which per capita well-being is non-declining. The question occupying many of the world's politicians is how sustainable development can be achieved. One general response is that an answer lies in how society manages its portfolio of wealth. The emphasis is on the simple observation that the degree to which future generations can enjoy development depends on how much wealth they inherit from the past. In other words, how we--as the current generation--manage our wealth now, may have a significant bearing on prospects for future generations. What does this wealth or capital consist of? Traditionally, it was thought to be, for example, physical infrastructure, but the real progress of the past 10 to 15 years has been to clearly establish the case that it also includes human resources (such as education) and natural capital (such as energy resources, clean air and forests).

Duck on water The Tufted Duck and the Shoveler are varieties of duck that can be found at Kew Gardens in London. Such Botanical Gardens provide a well balanced environment for these birds.

Moorhen on the ground Moorhen are commonly found around lakes and ponds. Their numbers in the UK have fluctuated but since 1972, they have shown moderate decline.

Cleaning Coot A coot cleaning itself on the banks of a pond in Kew Gardens. Coots and moorhen are superficially quite similar, and can be found in the same kind of habitats.

So the question of whether we are developing sustainably becomes one of how we are managing this wealth over time. For example, if we pass on less wealth than we inherited then we risk making future generations worse off than we are. Furthermore, depletion of natural resources and the accumulation of environmental liabilities (such as those associated with the climate change problem) are ways in which we might pass on less wealth. So how does biodiversity fit into this story? Clearly, biological resources can be thought of as one component of natural capital, and current rapid rates of (likely) species extinction can be thought of as undesirable in that we would be better off if greater effort were made to conserve biodiversity. Whether or not this also means that future generations would be worse off than we are now is as yet an unanswered question, although many suspect that this is the case.

LSE

Two baby coots preening themselves at the pond edge. In the UK there are comparatively good data on trends in populations of farmland and woodland bird species.

Concern about what is happening to biodiversity is an integral part of the UK government's Sustainable Development Strategy. One element of this strategy is the measurement and monitoring of 15 headline indicators of sustainability. These indicators are intended to encapsulate the most important elements of the current sustainable development debate (at least as far as policy-makers in the UK have interpreted it). Some of these indicators, such as annual growth in Gross Domestic Product (GDP) or the health status of the (human) population, are well known. Others are more novel, including the indicator being used to characterise the state of UK biodiversity. One problem frequently encountered is that, while there are typically data on the number of species at a single point in time--species counts--what is needed to say something useful are data on changes in the number of species (or changes in the number of individuals in the population of a given species). In other words, the relevant indicator of sustainability is the change in diversity, not the amount of diversity.

There are exceptions. In the UK there are comparatively good data on trends in populations of farmland and woodland bird species. Indeed, it is this indicator that is used in the UK headline indicator set. One effect of the inclusion of this indicator has been to draw attention to the long-term decline in populations of farmland and woodland birds, in particular, and to adverse changes in the state of UK biodiversity more generally. For example, the headline indicator shows that in the past 25 years, populations of farmland birds have declined by 50 percent. A further recent innovation is the publication of headline indicators for the regions of England. Interestingly, these data appear to show that a significant proportion of these losses in farmland and woodland diversity have occurred in the south-east, the south-west and the east of England.

	Thinking Point
	How can indicators of sustainable development be integrated into an overall assessment of the economy?

While all of this information is very interesting, from the point of improving our future prospects the important question is how such indicators can be used to inform policy. This is a challenge to which policy-makers are beginning to rise, although there is still much to learn. In the case of the United Kingdom, the headline indicator on bird populations has been used to determine a recent formal government commitment to the long-term goal of reversing the decline in the number of farmland birds by 2020. However, the implementation of some of the policies needed to fulfil this goal presents considerable political challenges.