Common ground

The fundamental message of Garrett Hardin's essay 'The Tragedy of the Commons' [1], recently re-visited in these pages by Peter Kareiva [2], is unassailable. If resources are available to all without restraint, they will be over-exploited. That is a simple tenet of population biology, encapsulated in theories of competitive interaction between individuals, and is an explanation for the well-known phenomenon of logistic population growth and of concepts such as that of equilibrium population density. More surprising, perhaps, is the limited extent of our ability to recognise situations where we are exploiting a common resource, and to act appropriately. I want here to draw attention to some commons that are being damaged and on whose maintenance we depend for our sustainability as a species. If a resource is to be maintained under exploitation, there must be some mechanism limiting the demands placed upon it. In a natural ecosystem, there may be a top-down control, with a predator reducing the population of a prey species below the level at which it can damage its resource base, and reducing competition among individuals. In a human population, we seek to replace such controls — which are ethically unacceptable in civilised societies — by forms of societal regulation, ranging from private ownership to public laws. In order to be able to regulate the exploitation of a resource, however, we need to be able to do two other things first: recognise the existence of a common resource, and measure its capacity and the demands being placed on it, so that we can decide which resources need regulation. Without those actions, we have no means of applying regulation effectively. The common land of a mediaeval English parish, from which we get the metaphor, was not generally seriously over-exploited, partly because the population was regulated by external factors and partly because there were strong systems of regulation in place. Two miles from where I write is a small and exceptionally diverse nature reserve called Askham Bog. It is a mire, with fenland and other plant communities developed on deep peat in a small valley created by melting ice 15,000 years ago. From the Roman period to the early modern, the bog was a major source of peat, which was cut for fuel by the villagers of the neighbouring parishes of Dringhouses and Acomb [3]. The bye-laws of the Manor of Dringhouses declared in 1637 that " no tenant …